path: root/slib.texi

\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename slib.info
@settitle SLIB
@setchapternewpage on
@c Choices for setchapternewpage are {on,off,odd}.
@paragraphindent 2
@c %**end of header

@iftex
@finalout
@c DL: lose the egregious vertical whitespace, esp. around examples
@c but paras in @defun-like things don't have parindent
@parskip 4pt plus 1pt
@end iftex

@ifinfo
This file documents SLIB, the portable Scheme library.

Copyright (C) 1993 Todd R. Eigenschink
Copyright (C) 1993, 1994, 1995 Aubrey Jaffer

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the author.
@end ifinfo

@titlepage
@title SLIB
@subtitle The Portable Scheme Library
@subtitle Version 2a3
@subtitle June 1995
@author by Todd R. Eigenschink, Dave Love, and Aubrey Jaffer

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1993, 1994, 1995 Todd R. Eigenschink and Aubrey Jaffer

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation approved
by the author.
@end titlepage





@node Top, Overview, (dir), (dir)

@ifinfo
This file documents SLIB, the portable Scheme library.

@heading Good Engineering is 1% inspiration and 99% documentation.

Herein lies the good part.  Many thanks to Todd Eigenschink
<eigenstr@@CS.Rose-Hulman.Edu> (who thanks Dave Love <D.Love@@dl.ac.uk>)
for creating @file{slib.texi}.  I have learned much from their example.

Aubrey Jaffer
jaffer@@ai.mit.edu
@end ifinfo


@menu
* Overview::                    What is SLIB?

* Data Structures::             Various data structures.
* Macros::                      Extensions to Scheme syntax.
* Numerics::                    
* Procedures::                  Miscellaneous utility procedures.
* Standards Support::           Support for Scheme Standards.
* Session Support::             Debugging, Pathnames, Require, etc.

* Optional SLIB Packages::      
* Procedure and Macro Index::   
* Variable Index::              
@end menu


@node Overview, Data Structures, Top, Top
@chapter Overview

SLIB is a portable Scheme library meant to provide compatibility and
utility functions for all standard Scheme implementations, and fixes
several implementations which are non-conforming.  SLIB conforms to
@cite{Revised^4 Report on the Algorithmic Language Scheme} and the IEEE
P1178 specification.  SLIB supports Unix and similar systems, VMS, and
MS-DOS.@refill

For a summary of what each file contains, see the file @file{README}.
For a list of the features that have changed since the last SLIB
release, see the file @file{ANNOUNCE}.  For a list of the features that
have changed over time, see the file @file{ChangeLog}.

The maintainer can be reached as @samp{jaffer@@ai.mit.edu}.

@menu
* Installation::                How to install SLIB on your system.
* Porting::                     SLIB to new platforms
* Coding Standards::            How to write modules for SLIB.
* Copyrights::                  Intellectual propery issues.
* Manual Conventions::          Conventions used in this manual.
@end menu

@node Installation, Porting, Overview, Overview
@section Installation

Check the manifest in @file{README} to find a configuration file for
your Scheme implementation.  Initialization files for most IEEE P1178
compliant Scheme Implementations are included with this distribution.

If the Scheme implementation supports @code{getenv}, then the value of
the shell environment variable @var{SCHEME_LIBRARY_PATH} will be used
for @code{(library-vicinity)} if it is defined.  Currently, Chez, Elk,
MITScheme, scheme->c, VSCM, and SCM support @code{getenv}.

You should check the definitions of @code{software-type},
@code{scheme-implementation-version},
@iftex
@*
@end iftex
@code{implementation-vicinity},
and @code{library-vicinity} in the initialization file.  There are
comments in the file for how to configure it.

Once this is done you can modify the startup file for your Scheme
implementation to @code{load} this initialization file.  SLIB is then
installed.

Multiple implementations of Scheme can all use the same SLIB directory.
Simply configure each implementation's initialization file as outlined
above.

The SCM implementation does not require any initialization file as SLIB
support is already built in to SCM.  See the documentation with SCM for
installation instructions.

SLIB includes methods to create heap images for the VSCM and Scheme48
implementations.  The instructions for creating a VSCM image are in
comments in @file{vscm.init}.  To make a Scheme48 image, @code{cd} to
the SLIB directory and type @code{make slib48}.  This will also create a
shell script with the name @code{slib48} which will invoke the saved
image.

@node Porting, Coding Standards, Installation, Overview
@section Porting

If there is no initialization file for your Scheme implementation, you
will have to create one.  Your Scheme implementation must be largely
compliant with @cite{IEEE Std 1178-1990} or @cite{Revised^4 Report on
the Algorithmic Language Scheme} to support SLIB.

@file{Template.scm} is an example configuration file.  The comments
inside will direct you on how to customize it to reflect your system.
Give your new initialization file the implementation's name with
@file{.init} appended.  For instance, if you were porting
@code{foo-scheme} then the initialization file might be called
@file{foo.init}.

Your customized version should then be loaded as part of your scheme
implementation's initialization.  It will load @file{require.scm}
(@xref{Require}) from the library; this will allow the use of
@code{provide}, @code{provided?}, and @code{require} along with the
@dfn{vicinity} functions (@code{vicinity} functions are documented in
the section on Require.  @xref{Require}).  The rest of the library will
then be accessible in a system independent fashion.@refill

Please mail new working configuration files to @code{jaffer@@ai.mit.edu}
so that they can be included in the SLIB distribution.@refill

@node Coding Standards, Copyrights, Porting, Overview
@section Coding Standards

All library packages are written in IEEE P1178 Scheme and assume that a
configuration file and @file{require.scm} package have already been
loaded.  Other versions of Scheme can be supported in library packages
as well by using, for example, @code{(provided? 'rev3-report)} or
@code{(require 'rev3-report)} (@xref{Require}).@refill

@file{require.scm} defines @code{*catalog*}, an association list of
module names and filenames.  When a new package is added to the library,
an entry should be added to @file{require.scm}.  Local packages can also
be added to @code{*catalog*} and even shadow entries already in the
table.@refill

The module name and @samp{:} should prefix each symbol defined in the
package.  Definitions for external use should then be exported by having
@code{(define foo module-name:foo)}.@refill

Submitted code should not duplicate routines which are already in SLIB
files.  Use @code{require} to force those features to be supported in
your package.  Care should be taken that there are no circularities in
the @code{require}s and @code{load}s between the library
packages.@refill

Documentation should be provided in Emacs Texinfo format if possible,
But documentation must be provided.

Your package will be released sooner with SLIB if you send me a file
which tests your code.  Please run this test @emph{before} you send me
the code!

@subheading Modifications

Please document your changes.  A line or two for @file{ChangeLog} is
sufficient for simple fixes or extensions.  Look at the format of
@file{ChangeLog} to see what information is desired.  Please send me
@code{diff} files from the latest SLIB distribution (remember to send
@code{diff}s of @file{slib.texi} and @file{ChangeLog}).  This makes for
less email traffic and makes it easier for me to integrate when more
than one person is changing a file (this happens a lot with
@file{slib.texi} and @samp{*.init} files).

If someone else wrote a package you want to significantly modify, please
try to contact the author, who may be working on a new version.  This
will insure against wasting effort on obsolete versions.

Please @emph{do not} reformat the source code with your favorite
beautifier, make 10 fixes, and send me the resulting source code.  I do
not have the time to fish through 10000 diffs to find your 10 real fixes.

@node Copyrights, Manual Conventions, Coding Standards, Overview
@section Copyrights

This section has instructions for SLIB authors regarding copyrights.

Each package in SLIB must either be in the public domain, or come with a
statement of terms permitting users to copy, redistribute and modify it.
The comments at the beginning of @file{require.scm} and
@file{macwork.scm} illustrate copyright and appropriate terms.

If your code or changes amount to less than about 10 lines, you do not
need to add your copyright or send a disclaimer.

@subheading Putting code into the Public Domain

In order to put code in the public domain you should sign a copyright
disclaimer and send it to the SLIB maintainer.  Contact
jaffer@@ai.mit.edu for the address to mail the disclaimer to.

@quotation
I, @var{name}, hereby affirm that I have placed the software package
@var{name} in the public domain.

I affirm that I am the sole author and sole copyright holder for the
software package, that I have the right to place this software package
in the public domain, and that I will do nothing to undermine this
status in the future.

@flushright
                                        @var{signature and date}
@end flushright
@end quotation

This wording assumes that you are the sole author.  If you are not the
sole author, the wording needs to be different.  If you don't want to be
bothered with sending a letter every time you release or modify a
module, make your letter say that it also applies to your future
revisions of that module.

Make sure no employer has any claim to the copyright on the work you are
submitting.  If there is any doubt, create a copyright disclaimer and
have your employer sign it.  Mail the signed disclaimer to the SLIB
maintainer.  Contact jaffer@@ai.mit.edu for the address to mail the
disclaimer to.  An example disclaimer follows.

@subheading Explicit copying terms

@noindent
If you submit more than about 10 lines of code which you are not placing
into the Public Domain (by sending me a disclaimer) you need to:

@itemize @bullet
@item
Arrange that your name appears in a copyright line for the appropriate
year.   Multiple copyright lines are acceptable.
@item
With your copyright line, specify any terms you require to be different
from those already in the file.
@item
Make sure no employer has any claim to the copyright on the work you are
submitting.  If there is any doubt, create a copyright disclaimer and
have your employer sign it.  Mail the signed disclaim to the SLIB
maintainer.  Contact jaffer@@ai.mit.edu for the address to mail the
disclaimer to.
@end itemize

@subheading Example: Company Copyright Disclaimer

This disclaimer should be signed by a vice president or general manager
of the company.  If you can't get at them, anyone else authorized to
license out software produced there will do.  Here is a sample wording:

@quotation
@var{employer} Corporation hereby disclaims all copyright
interest in the program @var{program} written by @var{name}.

@var{employer} Corporation affirms that it has no other intellectual
property interest that would undermine this release, and will do nothing
to undermine it in the future.

@flushleft
@var{signature and date},
@var{name}, @var{title}, @var{employer} Corporation
@end flushleft
@end quotation

@node Manual Conventions,  , Copyrights, Overview
@section Manual Conventions

Things that are labeled as Functions are called for their return values.
Things that are labeled as Procedures are called primarily for their
side effects.

All examples throughout this text were produced using the @code{scm}
Scheme implementation.

At the beginning of each section, there is a line that looks something
like

@code{(require 'feature)}.

@noindent
This means that, in order to use @code{feature}, you must include the
line @code{(require 'feature)} somewhere in your code prior to the use
of that feature.  @code{require} will make sure that the feature is
loaded.@refill





@node Data Structures, Macros, Overview, Top
@chapter Data Structures



@menu
* Arrays::                      'array
* Array Mapping::               'array-for-each
* Association Lists::           'alist
* Collections::                 'collect
* Dynamic Data Type::           'dynamic
* Hash Tables::                 'hash-table
* Hashing::                     'hash, 'sierpinski, 'soundex
* Chapter Ordering::            'chapter-order
* Object::                      'object
* Parameter lists::             'parameters
* Priority Queues::             'priority-queue
* Queues::                      'queue
* Records::                     'record
* Base Table::                  
* Relational Database::         'relational-database
* Weight-Balanced Trees::       'wt-tree
* Structures::                  'struct, 'structure
@end menu




@node Arrays, Array Mapping, Data Structures, Data Structures
@section Arrays

@code{(require 'array)}

@defun array? obj
Returns @code{#t} if the @var{obj} is an array, and @code{#f} if not.
@end defun

@defun make-array initial-value bound1 bound2 @dots{}
Creates and returns an array that has as many dimensins as there are
@var{bound}s and fills it with @var{initial-value}.@refill
@end defun

When constructing an array, @var{bound} is either an inclusive range of
indices expressed as a two element list, or an upper bound expressed as
a single integer.  So@refill
@lisp
(make-array 'foo 3 3) @equiv{} (make-array 'foo '(0 2) '(0 2))
@end lisp

@defun make-shared-array array mapper bound1 bound2 @dots{}
@code{make-shared-array} can be used to create shared subarrays of other
arrays.  The @var{mapper} is a function that translates coordinates in
the new array into coordinates in the old array.  A @var{mapper} must be
linear, and its range must stay within the bounds of the old array, but
it can be otherwise arbitrary.  A simple example:@refill
@lisp
(define fred (make-array #f 8 8))
(define freds-diagonal
  (make-shared-array fred (lambda (i) (list i i)) 8))
(array-set! freds-diagonal 'foo 3)
(array-ref fred 3 3)
   @result{} FOO
(define freds-center
  (make-shared-array fred (lambda (i j) (list (+ 3 i) (+ 3 j)))
                     2 2))
(array-ref freds-center 0 0)
   @result{} FOO
@end lisp
@end defun

@defun array-rank obj
Returns the number of dimensions of @var{obj}.  If @var{obj} is not an
array, 0 is returned.
@end defun

@defun array-shape array
@code{array-shape} returns a list of inclusive bounds.  So:
@lisp
(array-shape (make-array 'foo 3 5))
   @result{} ((0 2) (0 4))
@end lisp
@end defun

@defun array-dimensions array
@code{array-dimensions} is similar to @code{array-shape} but replaces
elements with a 0 minimum with one greater than the maximum. So:
@lisp
(array-dimensions (make-array 'foo 3 5))
   @result{} (3 5)
@end lisp
@end defun

@deffn Procedure array-in-bounds? array index1 index2 @dots{}
Returns @code{#t} if its arguments would be acceptable to
@code{array-ref}.
@end deffn

@defun array-ref array index1 index2 @dots{}
Returns the element at the @code{(@var{index1}, @var{index2})} element
in @var{array}.@refill
@end defun

@deffn Procedure array-set! array new-value index1 index2 @dots{}
@end deffn

@defun array-1d-ref array index
@defunx array-2d-ref array index index
@defunx array-3d-ref array index index index
@end defun

@deffn Procedure array-1d-set! array new-value index
@deffnx Procedure array-2d-set! array new-value index index
@deffnx Procedure array-3d-set! array new-value index index index
@end deffn

The functions are just fast versions of @code{array-ref} and
@code{array-set!} that take a fixed number of arguments, and perform no
bounds checking.@refill

If you comment out the bounds checking code, this is about as efficient
as you could ask for without help from the compiler.

An exercise left to the reader: implement the rest of APL.



@node Array Mapping, Association Lists, Arrays, Data Structures
@section Array Mapping

@code{(require 'array-for-each)}

@defun array-map! array0 proc array1 @dots{}
@var{array1}, @dots{} must have the same number of dimensions as
@var{array0} and have a range for each index which includes the range
for the corresponding index in @var{array0}.  @var{proc} is applied to
each tuple of elements of @var{array1} @dots{} and the result is stored
as the corresponding element in @var{array0}.  The value returned is
unspecified.  The order of application is unspecified.
@end defun

@defun array-for-each @var{proc} @var{array0} @dots{}
@var{proc} is applied to each tuple of elements of @var{array0} @dots{}
in row-major order.  The value returned is unspecified.
@end defun

@defun array-indexes @var{array}
Returns an array of lists of indexes for @var{array} such that, if
@var{li} is a list of indexes for which @var{array} is defined, (equal?
@var{li} (apply array-ref (array-indexes @var{array}) @var{li})).
@end defun

@defun array-copy! source destination
Copies every element from vector or array @var{source} to the
corresponding element of @var{destination}.  @var{destination} must have
the same rank as @var{source}, and be at least as large in each
dimension.  The order of copying is unspecified.
@end defun


@node Association Lists, Collections, Array Mapping, Data Structures
@section Association Lists

@code{(require 'alist)}

Alist functions provide utilities for treating a list of key-value pairs
as an associative database.  These functions take an equality predicate,
@var{pred}, as an argument.  This predicate should be repeatable,
symmetric, and transitive.@refill

Alist functions can be used with a secondary index method such as hash
tables for improved performance.

@defun predicate->asso pred
Returns an @dfn{association function} (like @code{assq}, @code{assv}, or
@code{assoc}) corresponding to @var{pred}.  The returned function
returns a key-value pair whose key is @code{pred}-equal to its first
argument or @code{#f} if no key in the alist is @var{pred}-equal to the
first argument.@refill
@end defun

@defun alist-inquirer pred
Returns a procedure of 2 arguments, @var{alist} and @var{key}, which
returns the value associated with @var{key} in @var{alist} or @code{#f} if
@var{key} does not appear in @var{alist}.@refill
@end defun

@defun alist-associator pred
Returns a procedure of 3 arguments, @var{alist}, @var{key}, and
@var{value}, which returns an alist with @var{key} and @var{value}
associated.  Any previous value associated with @var{key} will be
lost.  This returned procedure may or may not have side effects on its
@var{alist} argument.  An example of correct usage is:@refill
@lisp
(define put (alist-associator string-ci=?))
(define alist '())
(set! alist (put alist "Foo" 9))
@end lisp
@end defun

@defun alist-remover pred
Returns a procedure of 2 arguments, @var{alist} and @var{key}, which
returns an alist with an association whose @var{key} is key removed.
This returned procedure may or may not have side effects on its
@var{alist} argument.  An example of correct usage is:@refill
@lisp
(define rem (alist-remover string-ci=?))
(set! alist (rem alist "foo"))
@end lisp
@end defun

@defun alist-map proc alist
Returns a new association list formed by mapping @var{proc} over the
keys and values of @var{alist}.   @var{proc} must be a function of 2
arguments which returns the new value part.
@end defun

@defun alist-for-each proc alist
Applies @var{proc} to each pair of keys and values of @var{alist}.
@var{proc} must be a function of 2 arguments.  The returned value is
unspecified.
@end defun


@node Collections, Dynamic Data Type, Association Lists, Data Structures
@section Collections

@c Much of the documentation in this section was written by Dave Love
@c (d.love@dl.ac.uk) -- don't blame Ken Dickey for its faults.
@c but we can blame him for not writing it!

@code{(require 'collect)}

Routines for managing collections.  Collections are aggregate data
structures supporting iteration over their elements, similar to the
Dylan(TM) language, but with a different interface.  They have
@dfn{elements} indexed by corresponding @dfn{keys}, although the keys
may be implicit (as with lists).@refill

New types of collections may be defined as YASOS objects (@xref{Yasos}).
They must support the following operations:
@itemize @bullet
@item
@code{(collection? @var{self})} (always returns @code{#t});

@item
@code{(size @var{self})} returns the number of elements in the collection;

@item
@code{(print @var{self} @var{port})} is a specialized print operation
for the collection which prints a suitable representation on the given
@var{port} or returns it as a string if @var{port} is @code{#t};@refill

@item
@code{(gen-elts @var{self})} returns a thunk which on successive
invocations yields elements of @var{self} in order or gives an error if
it is invoked more than @code{(size @var{self})} times;@refill

@item
@code{(gen-keys @var{self})} is like @code{gen-elts}, but yields the
collection's keys in order.

@end itemize
They might support specialized @code{for-each-key} and
@code{for-each-elt} operations.@refill

@defun collection? obj
A predicate, true initially of lists, vectors and strings.  New sorts of
collections must answer @code{#t} to @code{collection?}.@refill
@end defun

@deffn Procedure map-elts proc . collections
@deffnx Procedure do-elts proc . collections
@var{proc} is a procedure taking as many arguments as there are
@var{collections} (at least one).  The @var{collections} are iterated
over in their natural order and @var{proc} is applied to the elements
yielded by each iteration in turn.  The order in which the arguments are
supplied corresponds to te order in which the @var{collections} appear.
@code{do-elts} is used when only side-effects of @var{proc} are of
interest and its return value is unspecified.  @code{map-elts} returns a
collection (actually a vector) of the results of the applications of
@var{proc}.@refill

Example:
@lisp
(map-elts + (list 1 2 3) (vector 1 2 3))
   @result{} #(2 4 6)
@end lisp
@end deffn

@deffn Procedure map-keys proc . collections
@deffnx Procedure do-keys proc . collections
These are analogous to @code{map-elts} and @code{do-elts}, but each
iteration is over the @var{collections}' @emph{keys} rather than their
elements.@refill

Example:
@lisp
(map-keys + (list 1 2 3) (vector 1 2 3))
   @result{} #(0 2 4)
@end lisp
@end deffn

@deffn Procedure for-each-key collection proc
@deffnx Procedure for-each-elt collection proc
These are like @code{do-keys} and @code{do-elts} but only for a single
collection; they are potentially more efficient.
@end deffn

@defun reduce proc seed . collections
A generalization of the list-based @code{comlist:reduce-init}
(@xref{Lists as sequences}) to collections which will shadow the
list-based version if @code{(require 'collect)} follows @code{(require
'common-list-functions)} (@xref{Common List Functions}).@refill

Examples:
@lisp
(reduce + 0 (vector 1 2 3))
   @result{} 6
(reduce union '() '((a b c) (b c d) (d a)))
   @result{} (c b d a).
@end lisp
@end defun

@defun any? pred . collections
A generalization of the list-based @code{some} (@xref{Lists as
sequences}) to collections.@refill

Example:
@lisp
(any? odd? (list 2 3 4 5))
   @result{} #t
@end lisp
@end defun

@defun every? pred . collections
A generalization of the list-based @code{every} (@xref{Lists as
sequences}) to collections.@refill

Example:
@lisp
(every? collection? '((1 2) #(1 2)))
   @result{} #t
@end lisp
@end defun

@defun empty? collection
Returns @code{#t} iff there are no elements in @var{collection}.

@code{(empty? @var{collection}) @equiv{} (zero? (size @var{collection}))}
@end defun

@defun size collection
Returns the number of elements in @var{collection}.
@end defun

@defun Setter list-ref
See @xref{Setters} for a definition of @dfn{setter}.  N.B.
@code{(setter list-ref)} doesn't work properly for element 0 of a
list.@refill
@end defun

Here is a sample collection: @code{simple-table} which is also a
@code{table}.@refill
@lisp
(define-predicate TABLE?)
(define-operation (LOOKUP table key failure-object))
(define-operation (ASSOCIATE! table key value)) ;; returns key
(define-operation (REMOVE! table key))          ;; returns value

(define (MAKE-SIMPLE-TABLE)
  (let ( (table (list)) )
    (object
     ;; table behaviors
     ((TABLE? self) #t)
     ((SIZE self) (size table))
     ((PRINT self port) (format port "#<SIMPLE-TABLE>"))
     ((LOOKUP self key failure-object)
      (cond
       ((assq key table) => cdr)
       (else failure-object)
       ))
     ((ASSOCIATE! self key value)
      (cond
       ((assq key table)
        => (lambda (bucket) (set-cdr! bucket value) key))
       (else
        (set! table (cons (cons key value) table))
        key)
       ))
     ((REMOVE! self key);; returns old value
      (cond
       ((null? table) (slib:error "TABLE:REMOVE! Key not found: " key))
       ((eq? key (caar table))
        (let ( (value (cdar table)) )
          (set! table (cdr table))
          value)
        )
       (else
        (let loop ( (last table) (this (cdr table)) )
          (cond
           ((null? this)
            (slib:error "TABLE:REMOVE! Key not found: " key))
           ((eq? key (caar this))
            (let ( (value (cdar this)) )
              (set-cdr! last (cdr this))
              value)
            )
           (else
            (loop (cdr last) (cdr this)))
           ) ) )
       ))
     ;; collection behaviors
     ((COLLECTION? self) #t)
     ((GEN-KEYS self) (collect:list-gen-elts (map car table)))
     ((GEN-ELTS self) (collect:list-gen-elts (map cdr table)))
     ((FOR-EACH-KEY self proc)
      (for-each (lambda (bucket) (proc (car bucket))) table)
      )
     ((FOR-EACH-ELT self proc)
      (for-each (lambda (bucket) (proc (cdr bucket))) table)
      )
     ) ) )
@end lisp





@node Dynamic Data Type, Hash Tables, Collections, Data Structures
@section Dynamic Data Type

@code{(require 'dynamic)}

@defun make-dynamic obj
Create and returns a new @dfn{dynamic} whose global value is @var{obj}.
@end defun

@defun dynamic? obj
Returns true if and only if @var{obj} is a dynamic.  No object
satisfying @code{dynamic?} satisfies any of the other standard type
predicates.@refill
@end defun

@defun dynamic-ref dyn
Return the value of the given dynamic in the current dynamic
environment.
@end defun

@deffn Procedure dynamic-set! dyn obj
Change the value of the given dynamic to @var{obj} in the current
dynamic environment.  The returned value is unspecified.@refill
@end deffn

@defun call-with-dynamic-binding dyn obj thunk
Invoke and return the value of the given thunk in a new, nested dynamic
environment in which the given dynamic has been bound to a new location
whose initial contents are the value @var{obj}.  This dynamic
environment has precisely the same extent as the invocation of the thunk
and is thus captured by continuations created within that invocation and
re-established by those continuations when they are invoked.@refill
@end defun

The @code{dynamic-bind} macro is not implemented.




@node Hash Tables, Hashing, Dynamic Data Type, Data Structures
@section Hash Tables

@code{(require 'hash-table)}

@defun predicate->hash pred
Returns a hash function (like @code{hashq}, @code{hashv}, or
@code{hash}) corresponding to the equality predicate @var{pred}.
@var{pred} should be @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
@code{char=?}, @code{char-ci=?}, @code{string=?}, or
@code{string-ci=?}.@refill
@end defun

A hash table is a vector of association lists.

@defun make-hash-table k
Returns a vector of @var{k} empty (association) lists.
@end defun

Hash table functions provide utilities for an associative database.
These functions take an equality predicate, @var{pred}, as an argument.
@var{pred} should be @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
@code{char=?}, @code{char-ci=?}, @code{string=?}, or
@code{string-ci=?}.@refill

@defun predicate->hash-asso pred
Returns a hash association function of 2 arguments, @var{key} and
@var{hashtab}, corresponding to @var{pred}.  The returned function
returns a key-value pair whose key is @var{pred}-equal to its first
argument or @code{#f} if no key in @var{hashtab} is @var{pred}-equal to
the first argument.@refill
@end defun

@defun hash-inquirer pred
Returns a procedure of 3 arguments, @code{hashtab} and @code{key}, which
returns the value associated with @code{key} in @code{hashtab} or
@code{#f} if key does not appear in @code{hashtab}.@refill
@end defun

@defun hash-associator pred
Returns a procedure of 3 arguments, @var{hashtab}, @var{key}, and
@var{value}, which modifies @var{hashtab} so that @var{key} and
@var{value} associated.  Any previous value associated with @var{key}
will be lost.@refill
@end defun

@defun hash-remover pred
Returns a procedure of 2 arguments, @var{hashtab} and @var{key}, which
modifies @var{hashtab} so that the association whose key is @var{key} is
removed.@refill
@end defun

@defun hash-map proc hash-table
Returns a new hash table formed by mapping @var{proc} over the
keys and values of @var{hash-table}.  @var{proc} must be a function of 2
arguments which returns the new value part.
@end defun

@defun hash-for-each proc hash-table
Applies @var{proc} to each pair of keys and values of @var{hash-table}.
@var{proc} must be a function of 2 arguments.  The returned value is
unspecified.
@end defun





@node Hashing, Chapter Ordering, Hash Tables, Data Structures
@section Hashing

@code{(require 'hash)}

These hashing functions are for use in quickly classifying objects.
Hash tables use these functions.

@defun hashq obj k
@defunx hashv obj k
@defunx hash obj k
Returns an exact non-negative integer less than @var{k}.  For each
non-negative integer less than @var{k} there are arguments @var{obj} for
which the hashing functions applied to @var{obj} and @var{k} returns
that integer.@refill

For @code{hashq}, @code{(eq? obj1 obj2)} implies @code{(= (hashq obj1 k)
(hashq obj2))}.@refill

For @code{hashv}, @code{(eqv? obj1 obj2)} implies @code{(= (hashv obj1 k)
(hashv obj2))}.@refill

For @code{hash}, @code{(equal? obj1 obj2)} implies @code{(= (hash obj1 k)
(hash obj2))}.@refill

@code{hash}, @code{hashv}, and @code{hashq} return in time bounded by a
constant.  Notice that items having the same @code{hash} implies the
items have the same @code{hashv} implies the items have the same
@code{hashq}.@refill
@end defun


@code{(require 'sierpinski)}

@defun make-sierpinski-indexer max-coordinate
Returns a procedure (eg hash-function) of 2 numeric arguments which
preserves @emph{nearness} in its mapping from NxN to N.

@var{max-coordinate} is the maximum coordinate (a positive integer) of a
population of points.  The returned procedures is a function that takes
the x and y coordinates of a point, (non-negative integers) and returns
an integer corresponding to the relative position of that point along a
Sierpinski curve.  (You can think of this as computing a (pseudo-)
inverse of the Sierpinski spacefilling curve.)

Example use: Make an indexer (hash-function) for integer points lying in
square of integer grid points [0,99]x[0,99]:
@example
(define space-key (make-sierpinski-indexer 100))
@end example
Now let's compute the index of some points:
@example
(space-key 24 78)               @result{} 9206
(space-key 23 80)               @result{} 9172
@end example

Note that locations (24, 78) and (23, 80) are near in index and
therefore, because the Sierpinski spacefilling curve is continuous, we
know they must also be near in the plane.  Nearness in the plane does
not, however, necessarily correspond to nearness in index, although it
@emph{tends} to be so.

Example applications:
@table @asis

@item
Sort points by Sierpinski index to get heuristic solution to
@emph{travelling salesman problem}.  For details of performance,
see L. Platzman and J. Bartholdi, "Spacefilling curves and the
Euclidean travelling salesman problem", JACM 36(4):719--737
(October 1989) and references therein.

@item
Use Sierpinski index as key by which to store 2-dimensional data
in a 1-dimensional data structure (such as a table).  Then
locations that are near each other in 2-d space will tend to
be near each other in 1-d data structure; and locations that
are near in 1-d data structure will be near in 2-d space.  This
can significantly speed retrieval from secondary storage because
contiguous regions in the plane will tend to correspond to
contiguous regions in secondary storage.  (This is a standard
technique for managing CAD/CAM or geographic data.)

@end table
@end defun



@code{(require 'soundex)}

@defun soundex name
Computes the @emph{soundex} hash of @var{name}.  Returns a string of an
initial letter and up to three digits between 0 and 6.  Soundex
supposedly has the property that names that sound similar in normal
English pronunciation tend to map to the same key.

Soundex was a classic algorithm used for manual filing of personal
records before the advent of computers.  It performs adequately for
English names but has trouble with other nationalities.

See Knuth, Vol. 3 @cite{Sorting and searching}, pp 391--2

To manage unusual inputs, @code{soundex} omits all non-alphabetic
characters.  Consequently, in this implementation:

@example
(soundex <string of blanks>)    @result{} ""
(soundex "")                    @result{} ""
@end example

Examples from Knuth:

@example
(map soundex '("Euler" "Gauss" "Hilbert" "Knuth"
                       "Lloyd" "Lukasiewicz"))
        @result{} ("E460" "G200" "H416" "K530" "L300" "L222")

(map soundex '("Ellery" "Ghosh" "Heilbronn" "Kant"
                        "Ladd" "Lissajous"))
        @result{} ("E460" "G200" "H416" "K530" "L300" "L222")
@end example

Some cases in which the algorithm fails (Knuth):

@example
(map soundex '("Rogers" "Rodgers"))     @result{} ("R262" "R326")

(map soundex '("Sinclair" "St. Clair")) @result{} ("S524" "S324")

(map soundex '("Tchebysheff" "Chebyshev")) @result{} ("T212" "C121")
@end example
@end defun

@node Chapter Ordering, Object, Hashing, Data Structures
@section Chapter Ordering

@code{(require 'chapter-order)}

The @samp{chap:} functions deal with strings which are ordered like
chapter numbers (or letters) in a book.  Each section of the string
consists of consecutive numeric or consecutive aphabetic characters of
like case.

@defun chap:string<? string1 string2
Returns #t if the first non-matching run of alphabetic upper-case or the
first non-matching run of alphabetic lower-case or the first
non-matching run of numeric characters of @var{string1} is
@code{string<?} than the corresponding non-matching run of characters of
@var{string2}.

@example
(chap:string<? "a.9" "a.10")                    @result{} #t
(chap:string<? "4c" "4aa")                      @result{} #t
(chap:string<? "Revised^@{3.99@}" "Revised^@{4@}")  @result{} #t
@end example

@defunx chap:string>? string1 string2
@defunx chap:string<=? string1 string2
@defunx chap:string>=? string1 string2
Implement the corresponding chapter-order predicates.
@end defun

@defun chap:next-string string
Returns the next string in the @emph{chapter order}.  If @var{string}
has no alphabetic or numeric characters,
@code{(string-append @var{string} "0")} is returnd.  The argument to
chap:next-string will always be @code{chap:string<?} than the result.

@example
(chap:next-string "a.9")                @result{} "a.10"
(chap:next-string "4c")                 @result{} "4d"
(chap:next-string "4z")                 @result{} "4aa"
(chap:next-string "Revised^@{4@}")        @result{} "Revised^@{5@}"

@end example
@end defun

@node Object, Parameter lists, Chapter Ordering, Data Structures
@section Macroless Object System

@code{(require 'object)}

This is the Macroless Object System written by Wade Humeniuk
(whumeniu@@datap.ca).  Conceptual Tributes: @ref{Yasos}, MacScheme's
%object, CLOS, Lack of R4RS macros.

@subsection Concepts
@table @asis

@item OBJECT
An object is an ordered association-list (by @code{eq?}) of methods
(procedures).  Methods can be added (@code{make-method!}), deleted
(@code{unmake-method!}) and retrieved (@code{get-method}).  Objects may
inherit methods from other objects.  The object binds to the environment
it was created in, allowing closures to be used to hide private
procedures and data.

@item GENERIC-METHOD
A generic-method associates (in terms of @code{eq?}) object's method.
This allows scheme function style to be used for objects.  The calling
scheme for using a generic method is @code{(generic-method object param1
param2 ...)}.

@item METHOD
A method is a procedure that exists in the object.  To use a method
get-method must be called to look-up the method.  Generic methods
implement the get-method functionality.  Methods may be added to an
object associated with any scheme obj in terms of eq?

@item GENERIC-PREDICATE
A generic method that returns a boolean value for any scheme obj.

@item PREDICATE
A object's method asscociated with a generic-predicate. Returns
@code{#t}.
@end table

@subsection Procedures

@defun make-object ancestor @dots{}
Returns an object.  Current object implementation is a tagged vector.
@var{ancestor}s are optional and must be objects in terms of object?.
@var{ancestor}s methods are included in the object.  Multiple
@var{ancestor}s might associate the same generic-method with a method.
In this case the method of the @var{ancestor} first appearing in the
list is the one returned by @code{get-method}.
@end defun

@defun object? obj
Returns boolean value whether @var{obj} was created by make-object.
@end defun

@defun make-generic-method exception-procedure
Returns a procedure which be associated with an object's methods.  If
@var{exception-procedure} is specified then it is used to process
non-objects.
@end defun

@defun make-generic-predicate
Returns a boolean procedure for any scheme object.
@end defun

@defun make-method! object generic-method method
Associates @var{method} to the @var{generic-method} in the object.  The
@var{method} overrides any previous association with the
@var{generic-method} within the object.  Using @code{unmake-method!}
will restore the object's previous association with the
@var{generic-method}.  @var{method} must be a procedure.
@end defun

@defun make-predicate! object generic-preciate
Makes a predicate method associated with the @var{generic-predicate}.
@end defun

@defun unmake-method! object generic-method
Removes an object's association with a @var{generic-method} .
@end defun

@defun get-method object generic-method
Returns the object's method associated (if any) with the
@var{generic-method}.  If no associated method exists an error is
flagged.
@end defun

@subsection Examples

@example
(require 'object)

(define instantiate (make-generic-method))

(define (make-instance-object . ancestors)
  (define self (apply make-object
                      (map (lambda (obj) (instantiate obj)) ancestors)))
  (make-method! self instantiate (lambda (self) self))
  self)

(define who (make-generic-method))
(define imigrate! (make-generic-method))
(define emigrate! (make-generic-method))
(define describe (make-generic-method))
(define name (make-generic-method))
(define address (make-generic-method))
(define members (make-generic-method))

(define society
  (let ()
    (define self (make-instance-object))
    (define population '())
    (make-method! self imigrate!
                  (lambda (new-person)
                    (if (not (eq? new-person self))
                        (set! population (cons new-person population)))))
    (make-method! self emigrate!
                  (lambda (person)
                    (if (not (eq? person self))
                        (set! population
                              (comlist:remove-if (lambda (member)
                                                   (eq? member person))
                                                 population)))))
    (make-method! self describe
                  (lambda (self)
                    (map (lambda (person) (describe person)) population)))
    (make-method! self who
                  (lambda (self) (map (lambda (person) (name person))
                                      population)))
    (make-method! self members (lambda (self) population))
    self))

(define (make-person %name %address)
  (define self (make-instance-object society))
  (make-method! self name (lambda (self) %name))
  (make-method! self address (lambda (self) %address))
  (make-method! self who (lambda (self) (name self)))
  (make-method! self instantiate
                (lambda (self)
                  (make-person (string-append (name self) "-son-of")
                               %address)))
  (make-method! self describe
                (lambda (self) (list (name self) (address self))))
  (imigrate! self)
  self)
@end example

@subsubsection Inverter Documentation
Inheritance:
@lisp
        <inverter>::(<number> <description>)
@end lisp
Generic-methods
@lisp
        <inverter>::value      @result{} <number>::value
        <inverter>::set-value! @result{} <number>::set-value!
        <inverter>::describe   @result{} <description>::describe
        <inverter>::help
        <inverter>::invert
        <inverter>::inverter?
@end lisp

@subsubsection Number Documention
Inheritance
@lisp
        <number>::()
@end lisp
Slots
@lisp
        <number>::<x>
@end lisp
Generic Methods
@lisp
        <number>::value
        <number>::set-value!
@end lisp

@subsubsection Inverter code
@example
(require 'object)

(define value (make-generic-method (lambda (val) val)))
(define set-value! (make-generic-method))
(define invert (make-generic-method
                (lambda (val)
                  (if (number? val)
                      (/ 1 val)
                      (error "Method not supported:" val)))))
(define noop (make-generic-method))
(define inverter? (make-generic-predicate))
(define describe (make-generic-method))
(define help (make-generic-method))

(define (make-number x)
  (define self (make-object))
  (make-method! self value (lambda (this) x))
  (make-method! self set-value!
                (lambda (this new-value) (set! x new-value)))
  self)

(define (make-description str)
  (define self (make-object))
  (make-method! self describe (lambda (this) str))
  (make-method! self help (lambda (this) "Help not available"))
  self)

(define (make-inverter)
  (define self (make-object
                (make-number 1)
                (make-description "A number which can be inverted")))
  (define <value> (get-method self value))
  (make-method! self invert (lambda (self) (/ 1 (<value> self))))
  (make-predicate! self inverter?)
  (unmake-method! self help)
  (make-method! self help
                (lambda (self)
                  (display "Inverter Methods:") (newline)
                  (display "  (value inverter) ==> n") (newline)))
  self)

;;;; Try it out

(define invert! (make-generic-method))

(define x (make-inverter))

(make-method! x invert! (lambda () (set-value! x (/ 1 (value x)))))

(value x)                       @result{} 1
(set-value! x 33)               @result{} undefined
(invert! x)                     @result{} undefined
(value x)                       @result{} 1/33

(unmake-method! x invert!)      @result{} undefined

(invert! x)                     @error{}  ERROR: Method not supported: x
@end example

@node Parameter lists, Priority Queues, Object, Data Structures
@section Parameter lists

@code{(require 'parameters)}

@noindent
Arguments to procedures in scheme are distinguished from each other by
their position in the procedure call.  This can be confusing when a
procedure takes many arguments, many of which are not often used.

@noindent
A @dfn{parameter-list} is a way of passing named information to a
procedure.  Procedures are also defined to set unused parameters to
default values, check parameters, and combine parameter lists.

@noindent
A @var{parameter} has the form @code{(@r{parameter-name} @r{value1}
@dots{})}.  This format allows for more than one value per
parameter-name.

@noindent
A @var{parameter-list} is a list of @var{parameter}s, each with a
different @var{parameter-name}.

@deffn Function make-parameter-list parameter-names
Returns an empty parameter-list with slots for @var{parameter-names}.
@end deffn

@deffn Function parameter-list-ref parameter-list parameter-name
@var{parameter-name} must name a valid slot of @var{parameter-list}.
@code{parameter-list-ref} returns the value of parameter
@var{parameter-name} of @var{parameter-list}.
@end deffn

@deffn Procedure adjoin-parameters! parameter-list parameter1 @dots{}
Returns @var{parameter-list} with @var{parameter1} @dots{} merged in.
@end deffn

@deffn Procedure parameter-list-expand expanders parameter-list
@var{expanders} is a list of procedures whose order matches the order of
the @var{parameter-name}s in the call to @code{make-parameter-list}
which created @var{parameter-list}.  For each non-false element of
@var{expanders} that procedure is mapped over the corresponding
parameter value and the returned parameter lists are merged into
@var{parameter-list}.

This process is repeated until @var{parameter-list} stops growing.  The
value returned from @code{parameter-list-expand} is unspecified.
@end deffn

@deffn Function fill-empty-parameters defaults parameter-list
@var{defaults} is a list of lists whose order matches the order of the
@var{parameter-name}s in the call to @code{make-parameter-list} which
created @var{parameter-list}.  @code{fill-empty-parameters} returns a
new parameter-list with each empty parameter filled with the
corresponding @var{default}.
@end deffn

@deffn Function check-parameters checks parameter-list
@var{checks} is a list of procedures whose order matches the order of
the @var{parameter-name}s in the call to @code{make-parameter-list}
which created @var{parameter-list}.

@code{check-parameters} returns @var{parameter-list} if each @var{check}
of the corresponding @var{parameter-list} returns non-false.  If some
@var{check} returns @code{#f} an error is signaled.
@end deffn

@noindent
In the following procedures @var{arities} is a list of symbols.  The
elements of @code{arities} can be:

@table @code
@item single
Requires a single parameter.
@item optional
A single parameter or no parameter is acceptable.
@item boolean
A single boolean parameter or zero parameters is acceptable.
@item nary
Any number of parameters are acceptable.
@item nary1
One or more of parameters are acceptable.
@end table

@deffn Function parameter-list->arglist positions arities types parameter-list
Returns @var{parameter-list} converted to an argument list.  Parameters
of @var{arity} type @code{single} and @code{boolean} are converted to
the single value associated with them.  The other @var{arity} types are
converted to lists of the value(s) of type @var{types}.

@var{positions} is a list of positive integers whose order matches the
order of the @var{parameter-name}s in the call to
@code{make-parameter-list} which created @var{parameter-list}.  The
integers specify in which argument position the corresponding parameter
should appear.
@end deffn

@deffn Function getopt->parameter-list argc argv optnames arities types aliases
Returns @var{argv} converted to a parameter-list.  @var{optnames} are
the parameter-names.  @var{aliases} is a list of lists of strings and
elements of @var{optnames}.  Each of these strings which have length of
1 will be treated as a single @key{-} option by @code{getopt}.  Longer
strings will be treated as long-named options (@pxref{Getopt, getopt--}).
@end deffn

@deffn Function getopt->arglist argc argv optnames positions arities types defaults checks aliases
Like @code{getopt->parameter-list}, but converts @var{argv} to an
argument-list as specified by @var{optnames}, @var{positions},
@var{arities}, @var{types}, @var{defaults}, @var{checks}, and
@var{aliases}.
@end deffn

These @code{getopt} functions can be used with SLIB relational
databases.  For an example, @xref{Database Utilities,
make-command-server}.

@node Priority Queues, Queues, Parameter lists, Data Structures
@section Priority Queues

@code{(require 'priority-queue)}

@defun make-heap pred<?
Returns a binary heap suitable which can be used for priority queue
operations.
@end defun

@defun heap-length heap
Returns the number of elements in @var{heap}.@refill
@end defun

@deffn Procedure heap-insert! heap item
Inserts @var{item} into @var{heap}.  @var{item} can be inserted multiple
times.  The value returned is unspecified.@refill
@end deffn

@defun heap-extract-max! heap
Returns the item which is larger than all others according to the
@var{pred<?} argument to @code{make-heap}.  If there are no items in
@var{heap}, an error is signaled.@refill
@end defun

The algorithm for priority queues was taken from @cite{Introduction to
Algorithms} by T. Cormen, C. Leiserson, R. Rivest.  1989 MIT Press.



@node Queues, Records, Priority Queues, Data Structures
@section Queues

@code{(require 'queue)}

A @dfn{queue} is a list where elements can be added to both the front
and rear, and removed from the front (i.e., they are what are often
called @dfn{dequeues}).  A queue may also be used like a stack.@refill

@defun make-queue
Returns a new, empty queue.
@end defun

@defun queue? obj
Returns @code{#t} if @var{obj} is a queue.
@end defun

@defun queue-empty? q
Returns @code{#t} if the queue @var{q} is empty.
@end defun

@deffn Procedure queue-push! q datum
Adds @var{datum} to the front of queue @var{q}.
@end deffn

@deffn Procedure enquque! q datum
Adds @var{datum} to the rear of queue @var{q}.
@end deffn

All of the following functions raise an error if the queue @var{q} is
empty.@refill

@defun queue-front q
Returns the datum at the front of the queue @var{q}.
@end defun

@defun queue-rear q
Returns the datum at the rear of the queue @var{q}.
@end defun

@deffn Prcoedure queue-pop! q
@deffnx Procedure dequeue! q
Both of these procedures remove and return the datum at the front of the
queue.  @code{queue-pop!} is used to suggest that the queue is being
used like a stack.@refill
@end deffn





@node Records, Base Table, Queues, Data Structures
@section Records

@code{(require 'record)}

The Record package provides a facility for user to define their own
record data types.

@defun make-record-type type-name field-names
Returns a @dfn{record-type descriptor}, a value representing a new data
type disjoint from all others.  The @var{type-name} argument must be a
string, but is only used for debugging purposes (such as the printed
representation of a record of the new type).  The @var{field-names}
argument is a list of symbols naming the @dfn{fields} of a record of the
new type.  It is an error if the list contains any duplicates.  It is
unspecified how record-type descriptors are represented.@refill
@end defun

@c @defun make-record-sub-type type-name field-names rtd
@c Returns a @dfn{record-type descriptor}, a value representing a new data
@c type, disjoint from all others.  The @var{type-name} argument must be a
@c string.  The @var{field-names} argument is a list of symbols naming the
@c additional @dfn{fields} to be appended to @var{field-names} of
@c @var{rtd}.  It is an error if the combinded list contains any
@c duplicates.@refill
@c
@c Record-modifiers and record-accessors for @var{rtd} work for the new
@c record-sub-type as well.  But record-modifiers and record-accessors for
@c the new record-sub-type will not neccessarily work for @var{rtd}.@refill
@c @end defun

@defun record-constructor rtd [field-names]
Returns a procedure for constructing new members of the type represented
by @var{rtd}.  The returned procedure accepts exactly as many arguments
as there are symbols in the given list, @var{field-names}; these are
used, in order, as the initial values of those fields in a new record,
which is returned by the constructor procedure.  The values of any
fields not named in that list are unspecified.  The @var{field-names}
argument defaults to the list of field names in the call to
@code{make-record-type} that created the type represented by @var{rtd};
if the @var{field-names} argument is provided, it is an error if it
contains any duplicates or any symbols not in the default list.@refill
@end defun

@defun record-predicate rtd
Returns a procedure for testing membership in the type represented by
@var{rtd}.  The returned procedure accepts exactly one argument and
returns a true value if the argument is a member of the indicated record
type; it returns a false value otherwise.@refill
@end defun

@c @defun record-sub-predicate rtd
@c Returns a procedure for testing membership in the type represented by
@c @var{rtd} or its parents.  The returned procedure accepts exactly one
@c argument and returns a true value if the argument is a member of the
@c indicated record type or its parents; it returns a false value
@c otherwise.@refill
@c @end defun

@defun record-accessor rtd field-name
Returns a procedure for reading the value of a particular field of a
member of the type represented by @var{rtd}.  The returned procedure
accepts exactly one argument which must be a record of the appropriate
type; it returns the current value of the field named by the symbol
@var{field-name} in that record.  The symbol @var{field-name} must be a
member of the list of field-names in the call to @code{make-record-type}
that created the type represented by @var{rtd}.@refill
@end defun


@defun record-modifier rtd field-name
Returns a procedure for writing the value of a particular field of a
member of the type represented by @var{rtd}.  The returned procedure
accepts exactly two arguments: first, a record of the appropriate type,
and second, an arbitrary Scheme value; it modifies the field named by
the symbol @var{field-name} in that record to contain the given value.
The returned value of the modifier procedure is unspecified.  The symbol
@var{field-name} must be a member of the list of field-names in the call
to @code{make-record-type} that created the type represented by
@var{rtd}.@refill
@end defun

@defun record? obj
Returns a true value if @var{obj} is a record of any type and a false
value otherwise.  Note that @code{record?} may be true of any Scheme
value; of course, if it returns true for some particular value, then
@code{record-type-descriptor} is applicable to that value and returns an
appropriate descriptor.@refill
@end defun

@defun record-type-descriptor record
Returns a record-type descriptor representing the type of the given
record.  That is, for example, if the returned descriptor were passed to
@code{record-predicate}, the resulting predicate would return a true
value when passed the given record.  Note that it is not necessarily the
case that the returned descriptor is the one that was passed to
@code{record-constructor} in the call that created the constructor
procedure that created the given record.@refill
@end defun

@defun record-type-name rtd
Returns the type-name associated with the type represented by rtd.  The
returned value is @code{eqv?} to the @var{type-name} argument given in
the call to @code{make-record-type} that created the type represented by
@var{rtd}.@refill
@end defun

@defun record-type-field-names rtd
Returns a list of the symbols naming the fields in members of the type
represented by @var{rtd}.  The returned value is @code{equal?} to the
field-names argument given in the call to @code{make-record-type} that
created the type represented by @var{rtd}.@refill
@end defun



@node Base Table, Relational Database, Records, Data Structures
@section Base Table

A base table implementation using Scheme association lists is available
as the value of the identifier @code{alist-table} after doing:

@example
(require 'alist-table)
@end example


Association list base tables are suitable for small databases and
support all Scheme types when temporary and readable/writeable Scheme
types when saved.  I hope support for other base table implementations
will be added in the future.

This rest of this section documents the interface for a base table
implementation from which the @ref{Relational Database} package
constructs a Relational system.  It will be of interest primarily to
those wishing to port or write new base-table implementations.

All of these functions are accessed through a single procedure by
calling that procedure with the symbol name of the operation.  A
procedure will be returned if that operation is supported and @code{#f}
otherwise.  For example:

@example
@group
(require 'alist-table)
(define open-base (alist-table 'make-base))
make-base       @result{} *a procedure*
(define foo (alist-table 'foo))
foo             @result{} #f
@end group
@end example

@defun make-base filename key-dimension column-types
Returns a new, open, low-level database (collection of tables)
associated with @var{filename}.  This returned database has an empty
table associated with @var{catalog-id}.  The positive integer
@var{key-dimension} is the number of keys composed to make a
@var{primary-key} for the catalog table.  The list of symbols
@var{column-types} describes the types of each column for that table.
If the database cannot be created as specified, @code{#f} is returned.

Calling the @code{close-base} method on this database and possibly other
operations will cause @var{filename} to be written to.  If
@var{filename} is @code{#f} a temporary, non-disk based database will be
created if such can be supported by the base table implelentation.
@end defun

@defun open-base filename mutable
Returns an open low-level database associated with @var{filename}.  If
@var{mutable?} is @code{#t}, this database will have methods capable of
effecting change to the database.  If @var{mutable?} is @code{#f}, only
methods for inquiring the database will be available.  If the database
cannot be opened as specified @code{#f} is returned.

Calling the @code{close-base} (and possibly other) method on a
@var{mutable?}  database will cause @var{filename} to be written to.
@end defun

@defun write-base lldb filename
Causes the low-level database @var{lldb} to be written to
@var{filename}.  If the write is successful, also causes @var{lldb} to
henceforth be associated with @var{filename}.  Calling the
@code{close-database} (and possibly other) method on @var{lldb} may
cause @var{filename} to be written to.  If @var{filename} is @code{#f}
this database will be changed to a temporary, non-disk based database if
such can be supported by the underlying base table implelentation.  If
the operations completed successfully, @code{#t} is returned.
Otherwise, @code{#f} is returned.
@end defun

@defun sync-base lldb
Causes the file associated with the low-level database @var{lldb} to be
updated to reflect its current state.  If the associated filename is
@code{#f}, no action is taken and @code{#f} is returned.  If this
operation completes successfully, @code{#t} is returned.  Otherwise,
@code{#f} is returned.
@end defun

@defun close-base lldb
Causes the low-level database @var{lldb} to be written to its associated
file (if any).  If the write is successful, subsequent operations to
@var{lldb} will signal an error.  If the operations complete
successfully, @code{#t} is returned.  Otherwise, @code{#f} is returned.
@end defun

@defun make-table lldb key-dimension column-types
Returns the @var{base-id} for a new base table, otherwise returns
@code{#f}.  The base table can then be opened using @code{(open-table
@var{lldb} @var{base-id})}.  The positive integer @var{key-dimension} is
the number of keys composed to make a @var{primary-key} for this table.
The list of symbols @var{column-types} describes the types of each
column.
@end defun

@defvr Constant catalog-id
A constant @var{base-id} suitable for passing as a parameter to
@code{open-table}.  @var{catalog-id} will be used as the base table for
the system catalog.
@end defvr

@defun open-table lldb base-id key-dimension column-types
Returns a @var{handle} for an existing base table in the low-level
database @var{lldb} if that table exists and can be opened in the mode
indicated by @var{mutable?}, otherwise returns @code{#f}.

As with @code{make-table}, the positive integer @var{key-dimension} is
the number of keys composed to make a @var{primary-key} for this table.
The list of symbols @var{column-types} describes the types of each
column.
@end defun

@defun kill-table lldb base-id key-dimension column-types
Returns @code{#t} if the base table associated with @var{base-id} was
removed from the low level database @var{lldb}, and @code{#f} otherwise.
@end defun

@defun make-keyifier-1 type
Returns a procedure which accepts a single argument which must be of
type @var{type}.  This returned procedure returns an object suitable for
being a @var{key} argument in the functions whose descriptions follow.

Any 2 arguments of the supported type passed to the returned function
which are not @code{equal?} must result in returned values which are not
@code{equal?}.
@end defun

@defun make-list-keyifier key-dimension types
The list of symbols @var{types} must have at least @var{key-dimension}
elements.  Returns a procedure which accepts a list of length
@var{key-dimension} and whose types must corresopond to the types named
by @var{types}.  This returned procedure combines the elements of its
list argument into an object suitable for being a @var{key} argument in
the functions whose descriptions follow.

Any 2 lists of supported types (which must at least include symbols and
non-negative integers) passed to the returned function which are not
@code{equal?} must result in returned values which are not
@code{equal?}.
@end defun

@defun make-key-extractor key-dimension types column-number
Returns a procedure which accepts objects produced by application of the
result of @code{(make-list-keyifier @var{key-dimension} @var{types})}.
This procedure returns a @var{key} which is @code{equal?} to the
@var{column-number}th element of the list which was passed to create
@var{combined-key}.  The list @var{types} must have at least
@var{key-dimension} elements.
@end defun

@defun make-key->list key-dimension types
Returns a procedure which accepts objects produced by application of the
result of @code{(make-list-keyifier @var{key-dimension} @var{types})}.
This procedure returns a list of @var{key}s which are elementwise
@code{equal?} to the list which was passed to create @var{combined-key}.
@end defun

@noindent
In the following functions, the @var{key} argument can always be assumed
to be the value returned by a call to a @emph{keyify} routine.

@defun for-each-key handle procedure
Calls @var{procedure} once with each @var{key} in the table opened in
@var{handle} in an unspecified order.  An unspecified value is returned.
@end defun

@defun map-key handle procedure
Returns a list of the values returned by calling @var{procedure} once
with each @var{key} in the table opened in @var{handle} in an
unspecified order.
@end defun

@defun ordered-for-each-key handle procedure
Calls @var{procedure} once with each @var{key} in the table opened in
@var{handle} in the natural order for the types of the primary key
fields of that table.  An unspecified value is returned.
@end defun

@defun present? handle key
Returns a non-@code{#f} value if there is a row associated with
@var{key} in the table opened in @var{handle} and @code{#f} otherwise.
@end defun

@defun delete handle key
Removes the row associated with @var{key} from the table opened in
@var{handle}.  An unspecified value is returned.
@end defun

@defun make-getter key-dimension types
Returns a procedure which takes arguments @var{handle} and @var{key}.
This procedure returns a list of the non-primary values of the relation
(in the base table opened in @var{handle}) whose primary key is
@var{key} if it exists, and @code{#f} otherwise.
@end defun

@defun make-putter key-dimension types
Returns a procedure which takes arguments @var{handle} and @var{key} and
@var{value-list}.  This procedure associates the primary key @var{key}
with the values in @var{value-list} (in the base table opened in
@var{handle}) and returns an unspecified value.
@end defun

@defun supported-type? symbol
Returns @code{#t} if @var{symbol} names a type allowed as a column value
by the implementation, and @code{#f} otherwise.  At a minimum, an
implementation must support the types @code{integer}, @code{symbol},
@code{string}, @code{boolean}, and @code{base-id}.
@end defun

@defun supported-key-type? symbol
Returns @code{#t} if @var{symbol} names a type allowed as a key value by
the implementation, and @code{#f} otherwise.  At a minimum, an
implementation must support the types @code{integer}, and @code{symbol}.
@end defun

@table @code
@item integer
Scheme exact integer.
@item symbol
Scheme symbol.
@item boolean
@code{#t} or @code{#f}.
@item base-id
Objects suitable for passing as the @var{base-id} parameter to
@code{open-table}.  The value of @var{catalog-id} must be an acceptable
@code{base-id}.
@end table

@node Relational Database, Weight-Balanced Trees, Base Table, Data Structures
@section Relational Database

@code{(require 'relational-database)}

This package implements a database system inspired by the Relational
Model (@cite{E. F. Codd, A Relational Model of Data for Large Shared
Data Banks}).  An SLIB relational database implementation can be created
from any @ref{Base Table} implementation.

@menu
* Motivations::                 Database Manifesto
* Creating and Opening Relational Databases::  
* Relational Database Operations::  
* Table Operations::            
* Catalog Representation::      
* Unresolved Issues::           
* Database Utilities::          'database-utilities
@end menu

@node Motivations, Creating and Opening Relational Databases, Relational Database, Relational Database
@subsection Motivations

Most nontrivial programs contain databases: Makefiles, configure
scripts, file backup, calendars, editors, source revision control, CAD
systems, display managers, menu GUIs, games, parsers, debuggers,
profilers, and even error reporting are all rife with databases.  Coding
databases is such a common activity in programming that many may not be
aware of how often they do it.

A database often starts as a dispatch in a program.  The author, perhaps
because of the need to make the dispatch configurable, the need for
correlating dispatch in other routines, or because of changes or growth,
devises a data structure to contain the information, a routine for
interpreting that data structure, and perhaps routines for augmenting
and modifying the stored data.  The dispatch must be converted into this
form and tested.

The programmer may need to devise an interactive program for enabling
easy examination and modification of the information contained in this
database.  Often, in an attempt to foster modularity and avoid delays in
release, intermediate file formats for the database information are
devised.  It often turns out that users prefer modifying these
intermediate files with a text editor to using the interactive program
in order to do operations (such as global changes) not forseen by the
program's author.

In order to address this need, the concientous software engineer may
even provide a scripting language to allow users to make repetitive
database changes.  Users will grumble that they need to read a large
manual and learn yet another programming language (even if it
@emph{almost} has language "xyz" syntax) in order to do simple
configuration.

All of these facilities need to be designed, coded, debugged,
documented, and supported; often causing what was very simple in concept
to become a major developement project.

This view of databases just outlined is somewhat the reverse of the view
of the originators of the @dfn{Relational Model} of database
abstraction.  The relational model was devised to unify and allow
interoperation of large multi-user databases running on diverse
platforms.  A fairly general purpose "Comprehensive Language" for
database manipulations is mandated (but not specified) as part of the
relational model for databases.

One aspect of the Relational Model of some importance is that the
"Comprehensive Language" must be expressible in some form which can be
stored in the database.  This frees the programmer from having to make
programs data-driven in order to use a database.

This package includes as one of its basic supported types Scheme
@dfn{expression}s.  This type allows expressions as defined by the
Scheme standards to be stored in the database.  Using @code{slib:eval}
retrieved expressions can be evaluated (in the top-level environment).
Scheme's @code{lambda} facilitates closure of environments, modularity,
etc. so that procedures (which could not be stored directly most
databases) can still be effectively retrieved.  Since @code{slib:eval}
evaluates expressions in the top-level environment, built-in and user
defined procedures can be easily accessed by name.

This package's purpose is to standardize (through a common interface)
database creation and usage in Scheme programs.  The relational model's
provision for inclusion of language expressions as data as well as the
description (in tables, of course) of all of its tables assures that
relational databases are powerful enough to assume the roles currently
played by thousands of ad-hoc routines and data formats.

@noindent
Such standardization to a relational-like model brings many benefits:

@itemize @bullet
@item
Tables, fields, domains, and types can be dealt with by name in
programs.
@item
The underlying database implementation can be changed (for
performance or other reasons) by changing a single line of code.
@item
The formats of tables can be easily extended or changed without
altering code.
@item
Consistency checks are specified as part of the table descriptions.
Changes in checks need only occur in one place.
@item
All the configuration information which the developer wishes to group
together is easily grouped, without needing to change programs aware of
only some of these tables.
@item
Generalized report generators, interactive entry programs, and other
database utilities can be part of a shared library.  The burden of
adding configurability to a program is greatly reduced.
@item
Scheme is the "comprehensive language" for these databases.  Scripting
for configuration no longer needs to be in a separate language with
additional documentation.
@item
Scheme's latent types mesh well with the strict typing and logical
requirements of the relational model.
@item
Portable formats allow easy interchange of data.  The included table
descriptions help prevent misinterpretation of format.
@end itemize

@node Creating and Opening Relational Databases, Relational Database Operations, Motivations, Relational Database
@subsection Creating and Opening Relational Databases

@defun make-relational-system base-table-implementation

Returns a procedure implementing a relational database using the
@var{base-table-implementation}.

All of the operations of a base table implementation are accessed
through a procedure defined by @code{require}ing that implementation.
Similarly, all of the operations of the relational database
implementation are accessed through the procedure returned by
@code{make-relational-system}.  For instance, a new relational database
could be created from the procedure returned by
@code{make-relational-system} by:

@example
(require 'alist-table)
(define relational-alist-system
        (make-relational-system alist-table))
(define create-alist-database
        (relational-alist-system 'create-database))
(define my-database
        (create-alist-database "mydata.db"))
@end example
@end defun

@noindent
What follows are the descriptions of the methods available from
relational system returned by a call to @code{make-relational-system}.

@defun create-database filename

Returns an open, nearly empty relational database associated with
@var{filename}.  The only tables defined are the system catalog and
domain table.  Calling the @code{close-database} method on this database
and possibly other operations will cause @var{filename} to be written
to.  If @var{filename} is @code{#f} a temporary, non-disk based database
will be created if such can be supported by the underlying base table
implelentation.  If the database cannot be created as specified
@code{#f} is returned.  For the fields and layout of descriptor tables,
@xref{Catalog Representation}
@end defun

@defun open-database filename mutable?

Returns an open relational database associated with @var{filename}.  If
@var{mutable?} is @code{#t}, this database will have methods capable of
effecting change to the database.  If @var{mutable?} is @code{#f}, only
methods for inquiring the database will be available.  Calling the
@code{close-database} (and possibly other) method on a @var{mutable?}
database will cause @var{filename} to be written to.  If the database
cannot be opened as specified @code{#f} is returned.
@end defun

@node Relational Database Operations, Table Operations, Creating and Opening Relational Databases, Relational Database
@subsection Relational Database Operations

@noindent
These are the descriptions of the methods available from an open
relational database.  A method is retrieved from a database by calling
the database with the symbol name of the operation.  For example:

@example
(define my-database
        (create-alist-database "mydata.db"))
(define telephone-table-desc
        ((my-database 'create-table) 'telephone-table-desc))
@end example

@defun close-database
Causes the relational database to be written to its associated file (if
any).  If the write is successful, subsequent operations to this
database will signal an error.  If the operations completed
successfully, @code{#t} is returned.  Otherwise, @code{#f} is returned.
@end defun

@defun write-database filename
Causes the relational database to be written to @var{filename}.  If the
write is successful, also causes the database to henceforth be
associated with @var{filename}.  Calling the @code{close-database} (and
possibly other) method on this database will cause @var{filename} to be
written to.  If @var{filename} is @code{#f} this database will be
changed to a temporary, non-disk based database if such can be supported
by the underlying base table implelentation.  If the operations
completed successfully, @code{#t} is returned.  Otherwise, @code{#f} is
returned.
@end defun

@defun table-exists? table-name
Returns @code{#t} if @var{table-name} exists in the system catalog,
otherwise returns @code{#f}.
@end defun

@defun open-table table-name mutable?
Returns a @dfn{methods} procedure for an existing relational table in
this database if it exists and can be opened in the mode indicated by
@var{mutable?}, otherwise returns @code{#f}.
@end defun

@noindent
These methods will be present only in databases which are
@var{mutable?}.

@defun delete-table table-name
Removes and returns the @var{table-name} row from the system catalog if
the table or view associated with @var{table-name} gets removed from the
database, and @code{#f} otherwise.
@end defun

@defun create-table table-desc-name
Returns a methods procedure for a new (open) relational table for
describing the columns of a new base table in this database, otherwise
returns @code{#f}.  For the fields and layout of descriptor tables,
@xref{Catalog Representation}.

@defunx create-table table-name table-desc-name
Returns a methods procedure for a new (open) relational table with
columns as described by @var{table-desc-name}, otherwise returns
@code{#f}.
@end defun

@defun create-view ??
@defunx project-table ??
@defunx restrict-table ??
@defunx cart-prod-tables ??
Not yet implemented.
@end defun

@node Table Operations, Catalog Representation, Relational Database Operations, Relational Database
@subsection Table Operations

@noindent
These are the descriptions of the methods available from an open
relational table.  A method is retrieved from a table by calling
the table with the symbol name of the operation.  For example:

@example
@group
(define telephone-table-desc
        ((my-database 'create-table) 'telephone-table-desc))
(require 'common-list-functions)
(define ndrp (telephone-table-desc 'row:insert))
(ndrp '(1 #t name #f string))
(ndrp '(2 #f telephone
          (lambda (d)
            (and (string? d) (> (string-length d) 2)
                 (every
                  (lambda (c)
                    (memv c '(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9
                                  #\+ #\( #\  #\) #\-)))
                  (string->list d))))
          string))
@end group
@end example

@noindent
Operations on a single column of a table are retrieved by giving the
column name as the second argument to the methods procedure.  For
example:

@example
(define column-ids ((telephone-table-desc 'get* 'column-number)))
@end example

@noindent
Some operations described below require primary key arguments.  Primary
keys arguments are denoted @var{key1} @var{key2} @dots{}.  It is an
error to call an operation for a table which takes primary key arguments
with the wrong number of primary keys for that table.

@noindent
The term @dfn{row} used below refers to a Scheme list of values (one for
each column) in the order specified in the descriptor (table) for this
table.  Missing values appear as @code{#f}.  Primary keys may not
be missing.

@defun get key1 key2 @dots{}
Returns the value for the specified column of the row associated with
primary keys @var{key1}, @var{key2} @dots{} if it exists, or @code{#f}
otherwise.

@defunx get*
Returns a list of the values for the specified column for all rows in
this table.

@defunx row:retrieve key1 key2 @dots{}
Returns the row associated with primary keys @var{key1}, @var{key2}
@dots{} if it exists, or @code{#f} otherwise.

@defunx row:retrieve*
Returns a list of all rows in this table.
@end defun

@defun row:remove key1 key2 @dots{}
Removes and returns the row associated with primary keys @var{key1},
@var{key2} @dots{} if it exists, or @code{#f} otherwise.

@defunx row:remove*
Removes and returns a list of all rows in this table.
@end defun

@defun row:delete key1 key2 @dots{}
Deletes the row associated with primary keys @var{key1}, @var{key2}
@dots{} if it exists.  The value returned is unspecified.

@defunx row:delete*
Deletes all rows in this table.  The value returned is unspecified.  The
descriptor table and catalog entry for this table are not affected.
@end defun

@defun row:update row
Adds the row, @var{row}, to this table.  If a row for the primary key(s)
specified by @var{row} already exists in this table, it will be
overwritten.  The value returned is unspecified.

@defunx row:update* rows
Adds each row in the list @var{rows}, to this table.  If a row for the
primary key specified by an element of @var{rows} already exists in this
table, it will be overwritten.  The value returned is unspecified.
@end defun

@defun row:insert row
Adds the row @var{row} to this table.  If a row for the primary key(s)
specified by @var{row} already exists in this table an error is
signaled.  The value returned is unspecified.

@defunx row:insert* rows
Adds each row in the list @var{rows}, to this table.  If a row for the
primary key specified by an element of @var{rows} already exists in this
table, an error is signaled.  The value returned is unspecified.
@end defun

@defun for-each-row proc
Calls @var{proc} with each @var{row} in this table in the natural
ordering for the primary key types.  @emph{Real} relational programmers
would use some least-upper-bound join for every row to get them in
order; But we don't have joins yet.
@end defun

@defun close-table
Subsequent operations to this table will signal an error.
@end defun

@defvr Constant column-names
@defvrx Constant column-foreigns
@defvrx Constant column-domains
@defvrx Constant column-types
Return a list of the column names, foreign-key table names, domain
names, or type names respectively for this table.  These 4 methods are
different from the others in that the list is returned, rather than a
procedure to obtain the list.

@defvrx Constant primary-limit
Returns the number of primary keys fields in the relations in this
table.
@end defvr

@node Catalog Representation, Unresolved Issues, Table Operations, Relational Database
@subsection Catalog Representation

@noindent
Each database (in an implementation) has a @dfn{system catalog} which
describes all the user accessible tables in that database (including
itself).

@noindent
The system catalog base table has the following fields.  @code{PRI}
indicates a primary key for that table.

@example
@group
PRI table-name
    column-limit            the highest column number
    coltab-name             descriptor table name
    bastab-id               data base table identifier
    user-integrity-rule
    view-procedure          A scheme thunk which, when called,
                            produces a handle for the view.  coltab
                            and bastab are specified if and only if
                            view-procedure is not.
@end group
@end example

@noindent
Descriptors for base tables (not views) are tables (pointed to by
system catalog).  Descriptor (base) tables have the fields:

@example
@group
PRI column-number           sequential integers from 1
    primary-key?            boolean TRUE for primary key components
    column-name
    column-integrity-rule
    domain-name
@end group
@end example

@noindent
A @dfn{primary key} is any column marked as @code{primary-key?} in the
corresponding descriptor table.  All the @code{primary-key?} columns
must have lower column numbers than any non-@code{primary-key?} columns.
Every table must have at least one primary key.  Primary keys must be
sufficient to distinguish all rows from each other in the table.  All of
the system defined tables have a single primary key.

@noindent
This package currently supports tables having from 1 to 4 primary keys
if there are non-primary columns, and any (natural) number if @emph{all}
columns are primary keys.  If you need more than 4 primary keys, I would
like to hear what you are doing!

@noindent
A @dfn{domain} is a category describing the allowable values to occur in
a column.  It is described by a (base) table with the fields:

@example
@group
PRI domain-name
    foreign-table
    domain-integrity-rule
    type-id
    type-param
@end group
@end example

@noindent
The @dfn{type-id} field value is a symbol.  This symbol may be used by
the underlying base table implementation in storing that field.

@noindent
If the @code{foreign-table} field is non-@code{#f} then that field names
a table from the catalog.  The values for that domain must match a
primary key of the table referenced by the @var{type-param} (or
@code{#f}, if allowed).  This package currently does not support
composite foreign-keys.

@noindent
The types for which support is planned are:
@example
@group
    atom
    symbol
    string                  [<length>]
    number                  [<base>]
    money                   <currency>
    date-time
    boolean

    foreign-key             <table-name>
    expression
    virtual                 <expression>
@end group
@end example

@node Unresolved Issues, Database Utilities, Catalog Representation, Relational Database
@subsection Unresolved Issues

Although @file{rdms.scm} is not large I found it very difficult to write
(six rewrites).  I am not aware of any other examples of a generalized
relational system (although there is little new in CS).  I left out
several aspects of the Relational model in order to simplify the job.
The major features lacking (which might be addressed portably) are
views, transaction boundaries, and protection.

Protection needs a model for specifying priveledges.  Given how
operations are accessed from handles it should not be difficult to
restrict table accesses to those allowed for that user.

The system catalog has a field called @code{view-procedure}.  This
should allow a purely functional implementation of views.  This will
work but is unsatisfying for views resulting from a @dfn{select}ion
(subset of rows); for whole table operations it will not be possible to
reduce the number of keys scanned over when the selection is specified
only by an opaque procedure.

Transaction boundaries present the most intriguing area.  Transaction
boundaries are actually a feature of the "Comprehensive Language" of the
Relational database and not of the database.  Scheme would seem to
provide the opportunity for an extremely clean semantics for transaction
boundaries since the builtin procedures with side effects are small in
number and easily identified.

These side-effect builtin procedures might all be portably redefined to
versions which properly handled transactions.  Compiled library routines
would need to be recompiled as well.  Many system extensions
(delete-file, system, etc.) would also need to be redefined.

@noindent
There are 2 scope issues that must be resolved for multiprocess
transaction boundaries:

@table @asis
@item Process scope
The actions captured by a transaction should be only for the process
which invoked the start of transaction.  Although standard Scheme does
not provide process primitives as such, @code{dynamic-wind} would
provide a workable hook into process switching for many implementations.
@item Shared utilities with state
Some shared utilities have state which should @emph{not} be part of a
transaction.  An example would be calling a pseudo-random number
generator.  If the success of a transaction depended on the
pseudo-random number and failed, the state of the generator would be set
back.  Subsequent calls would keep returning the same number and keep
failing.

Pseudo-random number generators are not reentrant and so would require
locks in order to operate properly in a multiprocess environment.  Are
all examples of utilities whose state should not part of transactions
also non-reentrant?  If so, perhaps suspending transaction capture for
the duration of locks would fix it.
@end table

@node Database Utilities,  , Unresolved Issues, Relational Database
@subsection Database Utilities

@code{(require 'database-utilities)}

@noindent
This enhancement wraps a utility layer on @code{relational-database}
which provides:
@itemize @bullet
@item
Automatic loading of the appropriate base-table package when opening a
database.
@item
Automatic execution of initialization commands stored in database.
@item
Transparent execution of database commands stored in @code{*commands*}
table in database.
@end itemize

@noindent
Also included are utilities which provide:
@itemize @bullet
@item
Data definition from Scheme lists and
@item
Report generation
@end itemize
@noindent
for any SLIB relational database.

@defun create-database filename base-table-type
Returns an open, nearly empty enhanced (with @code{*commands*} table)
relational database (with base-table type @var{base-table-type})
associated with @var{filename}.
@end defun

@defun open-database filename
@defunx open-database filename base-table-type
Returns an open enchanced relational database associated with
@var{filename}.  The database will be opened with base-table type
@var{base-table-type}) if supplied.  If @var{base-table-type} is not
supplied, @code{open-database} will attempt to deduce the correct
base-table-type.  If the database can not be opened or if it lacks the
@code{*commands*} table, @code{#f} is returned.

@defunx open-database! filename
@defunx open-database! filename base-table-type
Returns @emph{mutable} open enchanced relational database @dots{}
@end defun

@noindent
The table @code{*commands*} in an @dfn{enhanced} relational-database has
the fields (with domains):
@example
@group
PRI name        symbol
    parameters  parameter-list
    procedure   expression
    documentation string
@end group
@end example

The @code{parameters} field is a foreign key (domain
@code{parameter-list}) of the @code{*catalog-data*} table and should
have the value of a table described by @code{*parameter-columns*}.  This
@code{parameter-list} table describes the arguments suitable for passing
to the associated command.  The intent of this table is to be of a form
such that different user-interfaces (for instance, pull-down menus or
plain-text queries) can operate from the same table.  A
@code{parameter-list} table has the following fields:
@example
@group
PRI index       uint
    name        symbol
    arity       parameter-arity
    domain      domain
    default     expression
    documentation string
@end group
@end example

The @code{arity} field can take the values:

@table @code
@item single
Requires a single parameter of the specified domain.
@item optional
A single parameter of the specified domain or zero parameters is
acceptable.
@item boolean
A single boolean parameter or zero parameters (in which case @code{#f}
is substituted) is acceptable.
@item nary
Any number of parameters of the specified domain are acceptable.  The
argument passed to the command function is always a list of the
parameters.
@item nary1
One or more of parameters of the specified domain are acceptable.  The
argument passed to the command function is always a list of the
parameters.
@end table

The @code{domain} field specifies the domain which a parameter or
parameters in the @code{index}th field must satisfy.

The @code{default} field is an expression whose value is either
@code{#f} or a procedure of no arguments which returns a parameter or
parameter list as appropriate.  If the expression's value is @code{#f}
then no default is appropriate for this parameter.  Note that since the
@code{default} procedure is called every time a default parameter is
needed for this column, @dfn{sticky} defaults can be implemented using
shared state with the domain-integrity-rule.

@subsubheading Invoking Commands

When an enhanced relational-database is called with a symbol which
matches a @var{name} in the @code{*commands*} table, the associated
procedure expression is evaluated and applied to the enhanced
relational-database.  A procedure should then be returned which the user
can invoke on (optional) arguments.

The command @code{*initialize*} is special.  If present in the
@code{*commands*} table, @code{open-database} or @code{open-database!}
will return the value of the @code{*initialize*} command.  Notice that
arbitrary code can be run when the @code{*initialize*} procedure is
automatically applied to the enhanced relational-database.

Note also that if you wish to shadow or hide from the user
relational-database methods described in @ref{Relational Database
Operations}, this can be done by a dispatch in the closure returned by
the @code{*initialize*} expression rather than by entries in the
@code{*commands*} table if it is desired that the underlying methods
remain accessible to code in the @code{*commands*} table.

@defun make-command-server rdb table-name
Returns a procedure of 2 arguments, a (symbol) command and a call-back
procedure.  When this returned procedure is called, it looks up
@var{command} in table @var{table-name} and calls the call-back
procedure with arguments:
@table @var
@item command
The @var{command}
@item command-value
The result of evaluating the expression in the @var{procedure} field of
@var{table-name} and calling it with @var{rdb}.
@item parameter-name
A list of the @dfn{official} name of each parameter.  Corresponds to the
@code{name} field of the @var{command}'s parameter-table.
@item positions
A list of the positive integer index of each parameter.  Corresponds to
the @code{index} field of the @var{command}'s parameter-table.
@item arities
A list of the arities of each parameter.  Corresponds to the
@code{arity} field of the @var{command}'s parameter-table.  For a
description of @code{arity} see table above.
@item defaults
A list of the defaults for each parameter.  Corresponds to
the @code{defaults} field of the @var{command}'s parameter-table.
@item domain-integrity-rules
A list of procedures (one for each parameter) which tests whether a
value for a parameter is acceptable for that parameter.  The procedure
should be called with each datum in the list for @code{nary} arity
parameters.
@item aliases
A list of lists of @code{(@r{alias} @r{parameter-name})}.  There can be
more than one alias per @var{parameter-name}.
@end table
@end defun

For information about parameters, @xref{Parameter lists}.  Here is an
example of setting up a command with arguments and parsing those
arguments from a @code{getopt} style argument list (@pxref{Getopt}).

@example
(require 'database-utilities)
(require 'parameters)
(require 'getopt)

(define my-rdb (create-database #f 'alist-table))

(define-tables my-rdb
  '(foo-params
    *parameter-columns*
    *parameter-columns*
    ((1 first-argument single string "hithere" "first argument")
     (2 flag boolean boolean #f "a flag")))
  '(foo-pnames
    ((name string))
    ((parameter-index uint))
    (("l" 1)
     ("a" 2)))
  '(my-commands
    ((name symbol))
    ((parameters parameter-list)
     (parameter-names parameter-name-translation)
     (procedure expression)
     (documentation string))
    ((foo
      foo-params
      foo-pnames
      (lambda (rdb) (lambda (foo aflag) (print foo aflag)))
      "test command arguments"))))

(define (dbutil:serve-command-line rdb command-table
                                   command argc argv)
  (set! argv (if (vector? argv) (vector->list argv) argv))
  ((make-command-server rdb command-table)
   command
   (lambda (comname comval options positions
                    arities types defaults dirs aliases)
     (apply comval (getopt->arglist argc argv options positions
                                    arities types defaults dirs aliases)))))

(define (test)
  (set! *optind* 1)
  (dbutil:serve-command-line
   my-rdb 'my-commands 'foo 4 '("dummy" "-l" "foo" "-a")))
(test)
@print{}
"foo" #t
@end example

Some commands are defined in all extended relational-databases.  The are
called just like @ref{Relational Database Operations}.

@defun add-domain domain-row
Adds @var{domain-row} to the @dfn{domains} table if there is no row in
the domains table associated with key @code{(car @var{domain-row})} and
returns @code{#t}.  Otherwise returns @code{#f}.

For the fields and layout of the domain table, @xref{Catalog
Representation}
@end defun

@defun delete-domain domain-name
Removes and returns the @var{domain-name} row from the @dfn{domains}
table.
@end defun

@defun domain-checker domain
Returns a procedure to check an argument for conformance to domain
@var{domain}.
@end defun

@subheading Defining Tables

@deffn Procedure define-tables rdb spec-0 @dots{}
Adds tables as specified in @var{spec-0} @dots{} to the open
relational-database @var{rdb}.  Each @var{spec} has the form:

@lisp
(@r{<name>} @r{<descriptor-name>} @r{<descriptor-name>} @r{<rows>})
@end lisp
or
@lisp
(@r{<name>} @r{<primary-key-fields>} @r{<other-fields>} @r{<rows>})
@end lisp

where @r{<name>} is the table name, @r{<descriptor-name>} is the symbol
name of a descriptor table, @r{<primary-key-fields>} and
@r{<other-fields>} describe the primary keys and other fields
respectively, and @r{<rows>} is a list of data rows to be added to the
table.

@r{<primary-key-fields>} and @r{<other-fields>} are lists of field
descriptors of the form:

@lisp
(@r{<column-name>} @r{<domain>})
@end lisp
or
@lisp
(@r{<column-name>} @r{<domain>} @r{<column-integrity-rule>})
@end lisp

where @r{<column-name>} is the column name, @r{<domain>} is the domain
of the column, and @r{<column-integrity-rule>} is an expression whose
value is a procedure of one argument (and returns non-@code{#f} to
signal an error).

If @r{<domain>} is not a defined domain name and it matches the name of
this table or an already defined (in one of @var{spec-0} @dots{}) single
key field table, a foriegn-key domain will be created for it.
@end deffn


@deffn Procedure create-report rdb destination report-name table
@deffnx Procedure create-report rdb destination report-name
The symbol @var{report-name} must be primary key in the table named
@code{*reports*} in the relational database @var{rdb}.
@var{destination} is a port, string, or symbol.  If @var{destination} is
a:

@table @asis
@item port
The table is created as ascii text and written to that port.
@item string
The table is created as ascii text and written to the file named by
@var{destination}.
@item symbol
@var{destination} is the primary key for a row in the table named *printers*.
@end table

Each row in the table *reports* has the fields:

@table @asis
@item name
The report name.
@item default-table
The table to report on if none is specified.
@item header, footer
A @code{format} string.  At the beginning and end of each page
respectively, @code{format} is called with this string and the (list of)
column-names of this table.
@item reporter
A @code{format} string.  For each row in the table, @code{format} is
called with this string and the row.
@item minimum-break
The minimum number of lines into which the report lines for a row can be
broken.  Use @code{0} if a row's lines should not be broken over page
boundaries.
@end table

Each row in the table *printers* has the fields:

@table @asis
@item name
The printer name.
@item print-procedure
The procedure to call to actually print.
@end table

The report is prepared as follows:

@itemize
@item
@code{Format} (@pxref{Format}) is called with the @code{header} field
and the (list of) @code{column-names} of the table.
@item
@code{Format} is called with the @code{reporter} field and (on
successive calls) each record in the natural order for the table.  A
count is kept of the number of newlines output by format.  When the
number of newlines to be output exceeds the number of lines per page,
the set of lines will be broken if there are more than
@code{minimum-break} left on this page and the number of lines for this
row is larger or equal to twice @code{minimum-break}.
@item
@code{Format} is called with the @code{footer} field and the (list of)
@code{column-names} of the table.  The footer field should not output a
newline.
@item
A new page is output.
@item
This entire process repeats until all the rows are output.
@end itemize
@end deffn

@noindent
The following example shows a new database with the name of
@file{foo.db} being created with tables describing processor families
and processor/os/compiler combinations.

@noindent
The database command @code{define-tables} is defined to call
@code{define-tables} with its arguments.  The database is also
configured to print @samp{Welcome} when the database is opened.  The
database is then closed and reopened.

@example
(require 'database-utilities)
(define my-rdb (create-database "foo.db" 'alist-table))

(define-tables my-rdb
  '(*commands*
    ((name symbol))
    ((parameters parameter-list)
     (procedure expression)
     (documentation string))
    ((define-tables
      no-parameters
      no-parameter-names
      (lambda (rdb) (lambda specs (apply define-tables rdb specs)))
      "Create or Augment tables from list of specs")
     (*initialize*
      no-parameters
      no-parameter-names
      (lambda (rdb) (display "Welcome") (newline) rdb)
      "Print Welcome"))))

((my-rdb 'define-tables)
 '(processor-family
   ((family    atom))
   ((also-ran  processor-family))
   ((m68000           #f)
    (m68030           m68000)
    (i386             8086)
    (8086             #f)
    (powerpc          #f)))

 '(platform
   ((name      symbol))
   ((processor processor-family)
    (os        symbol)
    (compiler  symbol))
   ((aix              powerpc aix     -)
    (amiga-dice-c     m68000  amiga   dice-c)
    (amiga-aztec      m68000  amiga   aztec)
    (amiga-sas/c-5.10 m68000  amiga   sas/c)
    (atari-st-gcc     m68000  atari   gcc)
    (atari-st-turbo-c m68000  atari   turbo-c)
    (borland-c-3.1    8086    ms-dos  borland-c)
    (djgpp            i386    ms-dos  gcc)
    (linux            i386    linux   gcc)
    (microsoft-c      8086    ms-dos  microsoft-c)
    (os/2-emx         i386    os/2    gcc)
    (turbo-c-2        8086    ms-dos  turbo-c)
    (watcom-9.0       i386    ms-dos  watcom))))

((my-rdb 'close-database))

(set! my-rdb (open-database "foo.db" 'alist-table))
@print{}
Welcome
@end example

@node Weight-Balanced Trees, Structures, Relational Database, Data Structures
@section Weight-Balanced Trees

@code{(require 'wt-tree)}

@cindex trees, balanced binary
@cindex balanced binary trees
@cindex binary trees
@cindex weight-balanced binary trees
Balanced binary trees are a useful data structure for maintaining large
sets of ordered objects or sets of associations whose keys are ordered.
MIT Scheme has an comprehensive implementation of weight-balanced binary
trees which has several advantages over the other data structures for
large aggregates:

@itemize @bullet
@item
In addition to the usual element-level operations like insertion,
deletion and lookup, there is a full complement of collection-level
operations, like set intersection, set union and subset test, all of
which are implemented with good orders of growth in time and space.
This makes weight balanced trees ideal for rapid prototyping of
functionally derived specifications.

@item
An element in a tree may be indexed by its position under the ordering
of the keys, and the ordinal position of an element may be determined,
both with reasonable efficiency.

@item
Operations to find and remove minimum element make weight balanced trees
simple to use for priority queues.

@item
The implementation is @emph{functional} rather than @emph{imperative}.
This means that operations like `inserting' an association in a tree do
not destroy the old tree, in much the same way that @code{(+ 1 x)}
modifies neither the constant 1 nor the value bound to @code{x}.  The
trees are referentially transparent thus the programmer need not worry
about copying the trees.  Referential transparency allows space
efficiency to be achieved by sharing subtrees.

@end itemize

These features make weight-balanced trees suitable for a wide range of
applications, especially those that
require large numbers of sets or discrete maps.  Applications that have
a few global databases and/or concentrate on element-level operations like
insertion and lookup are probably better off using hash-tables or
red-black trees.

The @emph{size} of a tree is the number of associations that it
contains.  Weight balanced binary trees are balanced to keep the sizes
of the subtrees of each node within a constant factor of each other.
This ensures logarithmic times for single-path operations (like lookup
and insertion).  A weight balanced tree takes space that is proportional
to the number of associations in the tree.  For the current
implementation, the constant of proportionality is six words per
association.

@cindex binary trees, as sets
@cindex binary trees, as discrete maps
@cindex sets, using binary trees
@cindex discrete maps, using binary trees
Weight balanced trees can be used as an implementation for either
discrete sets or discrete maps (associations).  Sets are implemented by
ignoring the datum that is associated with the key.  Under this scheme
if an associations exists in the tree this indicates that the key of the
association is a member of the set.  Typically a value such as
@code{()}, @code{#t} or @code{#f} is associated with the key.

Many operations can be viewed as computing a result that, depending on
whether the tree arguments are thought of as sets or maps, is known by
two different names.
An example is @code{wt-tree/member?}, which, when
regarding the tree argument as a set, computes the set membership operation, but,
when regarding the tree as a discrete map, @code{wt-tree/member?} is the
predicate testing if the map is defined at an element in its domain.
Most names in this package have been chosen based on interpreting the
trees as sets, hence the name @code{wt-tree/member?} rather than
@code{wt-tree/defined-at?}.


@cindex run-time-loadable option
@cindex option, run-time-loadable
The weight balanced tree implementation is a run-time-loadable option.
To use weight balanced trees, execute

@example
(load-option 'wt-tree)
@end example
@findex load-option

@noindent
once before calling any of the procedures defined here.


@menu
* Construction of Weight-Balanced Trees::  
* Basic Operations on Weight-Balanced Trees::  
* Advanced Operations on Weight-Balanced Trees::  
* Indexing Operations on Weight-Balanced Trees::  
@end menu

@node Construction of Weight-Balanced Trees, Basic Operations on Weight-Balanced Trees, Weight-Balanced Trees, Weight-Balanced Trees
@subsection Construction of Weight-Balanced Trees

Binary trees require there to be a total order on the keys used to
arrange the elements in the tree.  Weight balanced trees are organized
by @emph{types}, where the type is an object encapsulating the ordering
relation.  Creating a tree is a two-stage process.  First a tree type
must be created from the predicate which gives the ordering.  The tree type
is then used for making trees, either empty or singleton trees or trees
from other aggregate structures like association lists.  Once created, a
tree `knows' its type and the type is used to test compatibility between
trees in operations taking two trees.  Usually a small number of tree
types are created at the beginning of a program and used many times
throughout the program's execution.

@deffn {procedure+} make-wt-tree-type key<?
This procedure creates and returns a new tree type based on the ordering
predicate @var{key<?}.
@var{Key<?} must be a total ordering, having the property that for all
key values @code{a}, @code{b} and @code{c}:

@example
(key<? a a)                         @result{} #f
(and (key<? a b) (key<? b a))       @result{} #f
(if (and (key<? a b) (key<? b c))
    (key<? a c)
    #t)                             @result{} #t
@end example

@noindent
Two key values are assumed to be equal if neither is less than the other
by @var{key<?}.

Each call to @code{make-wt-tree-type} returns a distinct value, and
trees are only compatible if their tree types are @code{eq?}.
A consequence is 
that trees that are intended to be used in binary tree operations must all be
created with a tree type originating from the same call to
@code{make-wt-tree-type}.
@end deffn

@defvr {variable+} number-wt-type
A standard tree type for trees with numeric keys.  @code{Number-wt-type}
could have been defined by

@example
(define number-wt-type (make-wt-tree-type  <))
@end example
@end defvr

@defvr {variable+} string-wt-type
A standard tree type for trees with string keys.  @code{String-wt-type}
could have been defined by

@example
(define string-wt-type (make-wt-tree-type  string<?))
@end example
@end defvr



@deffn {procedure+} make-wt-tree wt-tree-type
This procedure creates and returns a newly allocated weight balanced
tree.  The tree is empty, i.e. it contains no associations.
@var{Wt-tree-type} is a weight balanced tree type obtained by calling
@code{make-wt-tree-type}; the returned tree has this type.
@end deffn

@deffn {procedure+} singleton-wt-tree wt-tree-type key datum
This procedure creates and returns a newly allocated weight balanced
tree.  The tree contains a single association, that of @var{datum} with
@var{key}.  @var{Wt-tree-type} is a weight balanced tree type obtained
by calling @code{make-wt-tree-type}; the returned tree has this type.
@end deffn

@deffn {procedure+} alist->wt-tree tree-type alist
Returns a newly allocated weight-balanced tree that contains the same
associations as @var{alist}.  This procedure is equivalent to:

@example
(lambda (type alist)
  (let ((tree (make-wt-tree type)))
    (for-each (lambda (association)
                (wt-tree/add! tree
                              (car association)
                              (cdr association)))
              alist)
    tree))
@end example
@end deffn



@node Basic Operations on Weight-Balanced Trees, Advanced Operations on Weight-Balanced Trees, Construction of Weight-Balanced Trees, Weight-Balanced Trees
@subsection Basic Operations on Weight-Balanced Trees

This section describes the basic tree operations on weight balanced
trees.  These operations are the usual tree operations for insertion,
deletion and lookup, some predicates and a procedure for determining the
number of associations in a tree.

@deffn {procedure+} wt-tree? object
Returns @code{#t} if @var{object} is a weight-balanced tree, otherwise
returns @code{#f}.
@end deffn

@deffn {procedure+} wt-tree/empty? wt-tree
Returns @code{#t} if @var{wt-tree} contains no associations, otherwise
returns @code{#f}.
@end deffn

@deffn {procedure+} wt-tree/size wt-tree
Returns the number of associations in @var{wt-tree}, an exact
non-negative integer.  This operation takes constant time.
@end deffn


@deffn {procedure+} wt-tree/add wt-tree key datum
Returns a new tree containing all the associations in @var{wt-tree} and
the association of @var{datum} with @var{key}.  If @var{wt-tree} already
had an association for @var{key}, the new association overrides the old.
The average and worst-case times required by this operation are
proportional to the logarithm of the number of associations in
@var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/add! wt-tree key datum
Associates @var{datum} with @var{key} in @var{wt-tree} and returns an
unspecified value.  If @var{wt-tree} already has an association for
@var{key}, that association is replaced.  The average and worst-case
times required by this operation are proportional to the logarithm of
the number of associations in @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/member? key wt-tree
Returns @code{#t} if @var{wt-tree} contains an association for
@var{key}, otherwise returns @code{#f}.  The average and worst-case
times required by this operation are proportional to the logarithm of
the number of associations in @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/lookup wt-tree key default
Returns the datum associated with @var{key} in @var{wt-tree}.  If
@var{wt-tree} doesn't contain an association for @var{key},
@var{default} is returned.  The average and worst-case times required by
this operation are proportional to the logarithm of the number of
associations in @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/delete wt-tree key
Returns a new tree containing all the associations in @var{wt-tree},
except that if @var{wt-tree} contains an association for @var{key}, it
is removed from the result.  The average and worst-case times required
by this operation are proportional to the logarithm of the number of
associations in @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/delete! wt-tree key
If @var{wt-tree} contains an association for @var{key} the association
is removed.  Returns an unspecified value.  The average and worst-case
times required by this operation are proportional to the logarithm of
the number of associations in @var{wt-tree}.
@end deffn


@node Advanced Operations on Weight-Balanced Trees, Indexing Operations on Weight-Balanced Trees, Basic Operations on Weight-Balanced Trees, Weight-Balanced Trees
@subsection Advanced Operations on Weight-Balanced Trees

In the following the @emph{size} of a tree is the number of associations
that the tree contains, and a @emph{smaller} tree contains fewer
associations.

@deffn {procedure+} wt-tree/split< wt-tree bound
Returns a new tree containing all and only the associations in
@var{wt-tree} which have a key that is less than @var{bound} in the
ordering relation of the tree type of @var{wt-tree}.  The average and
worst-case times required by this operation are proportional to the
logarithm of the size of @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/split> wt-tree bound
Returns a new tree containing all and only the associations in
@var{wt-tree} which have a key that is greater than @var{bound} in the
ordering relation of the tree type of @var{wt-tree}.  The average and
worst-case times required by this operation are proportional to the
logarithm of size of @var{wt-tree}.
@end deffn

@deffn {procedure+} wt-tree/union wt-tree-1 wt-tree-2
Returns a new tree containing all the associations from both trees.
This operation is asymmetric: when both trees have an association for
the same key, the returned tree associates the datum from @var{wt-tree-2}
with the key.  Thus if the trees are viewed as discrete maps then
@code{wt-tree/union} computes the map override of @var{wt-tree-1} by
@var{wt-tree-2}.  If the trees are viewed as sets the result is the set
union of the arguments.
The worst-case time required by this operation
is proportional to the sum of the sizes of both trees.
If the minimum key of one tree is greater than the maximum key of
the other tree then the time required is at worst proportional to
the logarithm of the size of the larger tree.
@end deffn

@deffn {procedure+} wt-tree/intersection wt-tree-1 wt-tree-2
Returns a new tree containing all and only those associations from
@var{wt-tree-1} which have keys appearing as the key of an association
in @var{wt-tree-2}.  Thus the associated data in the result are those
from @var{wt-tree-1}.  If the trees are being used as sets the result is
the set intersection of the arguments.  As a discrete map operation,
@code{wt-tree/intersection} computes the domain restriction of
@var{wt-tree-1} to (the domain of) @var{wt-tree-2}.
The time required by this operation is never worse that proportional to
the sum of the sizes of the trees.
@end deffn

@deffn {procedure+} wt-tree/difference wt-tree-1 wt-tree-2
Returns a new tree containing all and only those associations from
@var{wt-tree-1} which have keys that @emph{do not} appear as the key of
an association in @var{wt-tree-2}.  If the trees are viewed as sets the
result is the asymmetric set difference of the arguments.  As a discrete
map operation, it computes the domain restriction of @var{wt-tree-1} to
the complement of (the domain of) @var{wt-tree-2}.
The time required by this operation is never worse that proportional to
the sum of the sizes of the trees.
@end deffn


@deffn {procedure+} wt-tree/subset? wt-tree-1 wt-tree-2
Returns @code{#t} iff the key of each association in @var{wt-tree-1} is
the key of some association in @var{wt-tree-2}, otherwise returns @code{#f}.
Viewed as a set operation, @code{wt-tree/subset?} is the improper subset
predicate.
A proper subset predicate can be constructed:

@example
(define (proper-subset? s1 s2)
  (and (wt-tree/subset? s1 s2)
       (< (wt-tree/size s1) (wt-tree/size s2))))
@end example

As a discrete map operation, @code{wt-tree/subset?} is the subset
test on the domain(s) of the map(s).  In the worst-case the time
required by this operation is proportional to the size of
@var{wt-tree-1}.
@end deffn


@deffn {procedure+} wt-tree/set-equal? wt-tree-1 wt-tree-2
Returns @code{#t} iff for every association in @var{wt-tree-1} there is
an association in @var{wt-tree-2} that has the same key, and @emph{vice
versa}.

Viewing the arguments as sets @code{wt-tree/set-equal?} is the set
equality predicate.  As a map operation it determines if two maps are
defined on the same domain.

This procedure is equivalent to

@example
(lambda (wt-tree-1 wt-tree-2)
  (and (wt-tree/subset? wt-tree-1 wt-tree-2
       (wt-tree/subset? wt-tree-2 wt-tree-1)))
@end example

In the worst-case the time required by this operation is proportional to
the size of the smaller tree.
@end deffn


@deffn {procedure+} wt-tree/fold combiner initial wt-tree
This procedure reduces @var{wt-tree} by combining all the associations,
using an reverse in-order traversal, so the associations are visited in
reverse order.  @var{Combiner} is a procedure of three arguments: a key,
a datum and the accumulated result so far.  Provided @var{combiner}
takes time bounded by a constant, @code{wt-tree/fold} takes time
proportional to the size of @var{wt-tree}.

A sorted association list can be derived simply:

@example
(wt-tree/fold  (lambda (key datum list)
                 (cons (cons key datum) list))
               '()
               @var{wt-tree}))
@end example

The data in the associations can be summed like this:

@example
(wt-tree/fold  (lambda (key datum sum) (+ sum datum))
               0
               @var{wt-tree})
@end example
@end deffn

@deffn {procedure+} wt-tree/for-each action wt-tree
This procedure traverses the tree in-order, applying @var{action} to
each association.
The associations are processed in increasing order of their keys.
@var{Action} is a procedure of two arguments which take the key and
datum respectively of the association.
Provided @var{action} takes time bounded by a constant,
@code{wt-tree/for-each} takes time proportional to in the size of
@var{wt-tree}.
The example prints the tree:

@example
(wt-tree/for-each (lambda (key value)
                    (display (list key value)))
                  @var{wt-tree}))
@end example
@end deffn


@node Indexing Operations on Weight-Balanced Trees,  , Advanced Operations on Weight-Balanced Trees, Weight-Balanced Trees
@subsection Indexing Operations on Weight-Balanced Trees

Weight balanced trees support operations that view the tree as sorted
sequence of associations.  Elements of the sequence can be accessed by
position, and the position of an element in the sequence can be
determined, both in logarthmic time.

@deffn {procedure+} wt-tree/index wt-tree index
@deffnx {procedure+} wt-tree/index-datum wt-tree index
@deffnx {procedure+} wt-tree/index-pair wt-tree index
Returns the 0-based @var{index}th association of @var{wt-tree} in the
sorted sequence under the tree's ordering relation on the keys.
@code{wt-tree/index} returns the @var{index}th key,
@code{wt-tree/index-datum} returns the datum associated with the
@var{index}th key and @code{wt-tree/index-pair} returns a new pair
@code{(@var{key} . @var{datum})} which is the @code{cons} of the @var{index}th
key and its datum.  The average and worst-case times required by this
operation are proportional to the logarithm of the number of
associations in the tree.

These operations signal an error if the tree is empty, if
@var{index}@code{<0}, or if @var{index} is greater than or equal to the
number of associations in the tree.

Indexing can be used to find the median and maximum keys in the tree as
follows:

@example
median:   (wt-tree/index @var{wt-tree} (quotient (wt-tree/size @var{wt-tree}) 2))

maximum:  (wt-tree/index @var{wt-tree} (-1+ (wt-tree/size @var{wt-tree})))
@end example
@end deffn

@deffn {procedure+} wt-tree/rank wt-tree key
Determines the 0-based position of @var{key} in the sorted sequence of
the keys under the tree's ordering relation, or @code{#f} if the tree
has no association with for @var{key}.  This procedure returns either an
exact non-negative integer or @code{#f}.  The average and worst-case
times required by this operation are proportional to the logarithm of
the number of associations in the tree.
@end deffn

@deffn {procedure+} wt-tree/min wt-tree
@deffnx {procedure+} wt-tree/min-datum wt-tree
@deffnx {procedure+} wt-tree/min-pair wt-tree
Returns the association of @var{wt-tree} that has the least key under the tree's ordering relation.
@code{wt-tree/min} returns the least key,
@code{wt-tree/min-datum} returns the datum associated with the
least key and @code{wt-tree/min-pair} returns a new pair
@code{(key . datum)} which is the @code{cons} of the minimum key and its datum.
The average and worst-case times required by this operation are
proportional to the logarithm of the number of associations in the tree.

These operations signal an error if the tree is empty.
They could be written
@example
(define (wt-tree/min tree)        (wt-tree/index tree 0))
(define (wt-tree/min-datum tree)  (wt-tree/index-datum tree 0))
(define (wt-tree/min-pair tree)   (wt-tree/index-pair tree 0))
@end example
@end deffn

@deffn {procedure+} wt-tree/delete-min wt-tree
Returns a new tree containing all of the associations in @var{wt-tree}
except the association with the least key under the @var{wt-tree}'s
ordering relation.  An error is signalled if the tree is empty.  The
average and worst-case times required by this operation are proportional
to the logarithm of the number of associations in the tree.  This
operation is equivalent to

@example
(wt-tree/delete @var{wt-tree} (wt-tree/min @var{wt-tree}))
@end example
@end deffn


@deffn {procedure+} wt-tree/delete-min! wt-tree
Removes the association with the least key under the @var{wt-tree}'s
ordering relation.  An error is signalled if the tree is empty.  The
average and worst-case times required by this operation are proportional
to the logarithm of the number of associations in the tree.  This
operation is equivalent to

@example
(wt-tree/delete! @var{wt-tree} (wt-tree/min @var{wt-tree}))
@end example
@end deffn



@node Structures,  , Weight-Balanced Trees, Data Structures
@section Structures

@code{(require 'struct)} (uses defmacros)

@code{defmacro}s which implement @dfn{records} from the book
@cite{Essentials of Programming Languages} by Daniel P. Friedman, M.
Wand and C.T. Haynes.  Copyright 1992 Jeff Alexander, Shinnder Lee, and
Lewis Patterson@refill

Matthew McDonald <mafm@@cs.uwa.edu.au> added field setters.

@defmac define-record tag (var1 var2 @dots{})
Defines several functions pertaining to record-name @var{tag}:

@defun make-@var{tag} var1 var2 @dots{}
@end defun
@defun @var{tag}? obj
@end defun
@defun @var{tag}->var1 obj
@end defun
@defun @var{tag}->var2 obj
@end defun
@dots{}
@defun set-@var{@var{tag}}-var1! obj val
@end defun
@defun set-@var{@var{tag}}-var2! obj val
@end defun
@dots{}

Here is an example of its use.

@example
(define-record term (operator left right))
@result{} #<unspecified>
(define foo (make-term 'plus  1 2))
@result{} foo
(term-left foo)
@result{} 1
(set-term-left! foo 2345)
@result{} #<unspecified>
(term-left foo)
@result{} 2345
@end example
@end defmac

@defmac variant-case exp (tag (var1 var2 @dots{}) body) @dots{}
executes the following for the matching clause:

@example
((lambda (@var{var1} @var{var} @dots{}) @var{body})
   (@var{tag->var1} @var{exp})
   (@var{tag->var2} @var{exp}) @dots{})
@end example
@end defmac

@node Macros, Numerics, Data Structures, Top
@chapter Macros
@menu
* Defmacro::                    Supported by all implementations

* R4RS Macros::                 'macro
* Macro by Example::            'macro-by-example
* Macros That Work::            'macros-that-work
* Syntactic Closures::          'syntactic-closures
* Syntax-Case Macros::          'syntax-case

Syntax extensions (macros) included with SLIB.  Also @xref{Structures}.

* Fluid-Let::                   'fluid-let
* Yasos::                       'yasos, 'oop, 'collect
@end menu


@node Defmacro, R4RS Macros, Macros, Macros
@section Defmacro

Defmacros are supported by all implementations.
@c See also @code{gentemp}, in @ref{Macros}.

@defun gentemp
Returns a new (interned) symbol each time it is called.  The symbol
names are implementation-dependent
@lisp
(gentemp) @result{} scm:G0
(gentemp) @result{} scm:G1
@end lisp
@end defun

@defun defmacro:eval e
Returns the @code{slib:eval} of expanding all defmacros in scheme
expression @var{e}.
@end defun

@defun defmacro:load filename
@var{filename} should be a string.  If filename names an existing file,
the @code{defmacro:load} procedure reads Scheme source code expressions
and definitions from the file and evaluates them sequentially.  These
source code expressions and definitions may contain defmacro
definitions.  The @code{macro:load} procedure does not affect the values
returned by @code{current-input-port} and
@code{current-output-port}.@refill
@end defun

@defun defmacro? sym
Returns @code{#t} if @var{sym} has been defined by @code{defmacro},
@code{#f} otherwise.
@end defun

@defun macroexpand-1 form
@defunx macroexpand form
If @var{form} is a macro call, @code{macroexpand-1} will expand the
macro call once and return it.  A @var{form} is considered to be a macro
call only if it is a cons whose @code{car} is a symbol for which a
@code{defmacr} has been defined.

@code{macroexpand} is similar to @code{macroexpand-1}, but repeatedly
expands @var{form} until it is no longer a macro call.
@end defun

@defmac defmacro name lambda-list form @dots{}
When encountered by @code{defmacro:eval}, @code{defmacro:macroexpand*},
or @code{defmacro:load} defines a new macro which will henceforth be
expanded when encountered by @code{defmacro:eval},
@code{defmacro:macroexpand*}, or @code{defmacro:load}.
@end defmac

@subsection Defmacroexpand
@code{(require 'defmacroexpand)}

@defun defmacro:expand* e
Returns the result of expanding all defmacros in scheme expression
@var{e}.
@end defun

@node R4RS Macros, Macro by Example, Defmacro, Macros
@section R4RS Macros

@code{(require 'macro)} is the appropriate call if you want R4RS
high-level macros but don't care about the low level implementation.  If
an SLIB R4RS macro implementation is already loaded it will be used.
Otherwise, one of the R4RS macros implemetations is loaded.

The SLIB R4RS macro implementations support the following uniform
interface:

@defun macro:expand sexpression
Takes an R4RS expression, macro-expands it, and returns the result of
the macro expansion.
@end defun

@defun macro:eval sexpression
Takes an R4RS expression, macro-expands it, evals the result of the
macro expansion, and returns the result of the evaluation.
@end defun

@deffn Procedure macro:load filename
@var{filename} should be a string.  If filename names an existing file,
the @code{macro:load} procedure reads Scheme source code expressions and
definitions from the file and evaluates them sequentially.  These source
code expressions and definitions may contain macro definitions.  The
@code{macro:load} procedure does not affect the values returned by
@code{current-input-port} and @code{current-output-port}.@refill
@end deffn

@node  Macro by Example, Macros That Work, R4RS Macros, Macros
@section Macro by Example

@code{(require 'macro-by-example)}

A vanilla implementation of @cite{Macro by Example} (Eugene Kohlbecker,
R4RS) by Dorai Sitaram, (dorai@@cs.rice.edu) using @code{defmacro}.

@itemize @bullet

@item
generating hygienic global @code{define-syntax} Macro-by-Example macros
@strong{cheaply}.

@item
can define macros which use @code{...}.

@item
needn't worry about a lexical variable in a macro definition
clashing with a variable from the macro use context

@item
don't suffer the overhead of redefining the repl if @code{defmacro}
natively supported (most implementations)

@end itemize
@subsection Caveat
These macros are not referentially transparent (@pxref{Macros, , ,r4rs,
Revised(4) Scheme}).  Lexically scoped macros (i.e., @code{let-syntax}
and @code{letrec-syntax}) are not supported.  In any case, the problem
of referential transparency gains poignancy only when @code{let-syntax}
and @code{letrec-syntax} are used.  So you will not be courting
large-scale disaster unless you're using system-function names as local
variables with unintuitive bindings that the macro can't use.  However,
if you must have the full @cite{r4rs} macro functionality, look to the
more featureful (but also more expensive) versions of syntax-rules
available in slib @ref{Macros That Work}, @ref{Syntactic Closures}, and
@ref{Syntax-Case Macros}.

@defmac define-syntax keyword transformer-spec
The @var{keyword} is an identifier, and the @var{transformer-spec}
should be an instance of @code{syntax-rules}.

The top-level syntactic environment is extended by binding the
@var{keyword} to the specified transformer.

@example
(define-syntax let*
  (syntax-rules ()
    ((let* () body1 body2 ...)
     (let () body1 body2 ...))
    ((let* ((name1 val1) (name2 val2) ...)
       body1 body2 ...)
     (let ((name1 val1))
       (let* (( name2 val2) ...)
         body1 body2 ...)))))
@end example
@end defmac

@defmac syntax-rules literals syntax-rule @dots{}
@var{literals} is a list of identifiers, and each @var{syntax-rule}
should be of the form

@code{(@var{pattern} @var{template})}

where the @var{pattern} and  @var{template} are as in the grammar above.

An instance of @code{syntax-rules} produces a new macro transformer by
specifying a sequence of hygienic rewrite rules.  A use of a macro whose
keyword is associated with a transformer specified by
@code{syntax-rules} is matched against the patterns contained in the
@var{syntax-rule}s, beginning with the leftmost @var{syntax-rule}.
When a match is found, the macro use is trancribed hygienically
according to the template.

Each pattern begins with the keyword for the macro.  This keyword is not
involved in the matching and is not considered a pattern variable or
literal identifier.
@end defmac

@node Macros That Work, Syntactic Closures, Macro by Example, Macros
@section Macros That Work

@code{(require 'macros-that-work)}

@cite{Macros That Work} differs from the other R4RS macro
implementations in that it does not expand derived expression types to
primitive expression types.

@defun macro:expand expression
@defunx macwork:expand expression
Takes an R4RS expression, macro-expands it, and returns the result of
the macro expansion.
@end defun

@defun macro:eval expression
@defunx macwork:eval expression
@code{macro:eval} returns the value of @var{expression} in the current
top level environment.  @var{expression} can contain macro definitions.
Side effects of @var{expression} will affect the top level
environment.@refill
@end defun

@deffn Procedure macro:load filename
@deffnx Procedure macwork:load filename
@var{filename} should be a string.  If filename names an existing file,
the @code{macro:load} procedure reads Scheme source code expressions and
definitions from the file and evaluates them sequentially.  These source
code expressions and definitions may contain macro definitions.  The
@code{macro:load} procedure does not affect the values returned by
@code{current-input-port} and @code{current-output-port}.@refill
@end deffn

References:

The @cite{Revised^4 Report on the Algorithmic Language Scheme} Clinger
and Rees [editors].  To appear in LISP Pointers.  Also available as a
technical report from the University of Oregon, MIT AI Lab, and
Cornell.@refill

@center Macros That Work.  Clinger and Rees.  POPL '91.

The supported syntax differs from the R4RS in that vectors are allowed
as patterns and as templates and are not allowed as pattern or template
data.

@example
transformer spec  @expansion{}  (syntax-rules literals rules)

rules  @expansion{}  ()
         |  (rule . rules)

rule  @expansion{}  (pattern template)

pattern  @expansion{}  pattern_var      ; a symbol not in literals
           |  symbol           ; a symbol in literals
           |  ()
           |  (pattern . pattern)
           |  (ellipsis_pattern)
           |  #(pattern*)                     ; extends R4RS
           |  #(pattern* ellipsis_pattern)    ; extends R4RS
           |  pattern_datum

template  @expansion{}  pattern_var
            |  symbol
            |  ()
            |  (template2 . template2)
            |  #(template*)                   ; extends R4RS
            |  pattern_datum

template2  @expansion{}  template
             |  ellipsis_template

pattern_datum  @expansion{}  string                    ; no vector
                 |  character
                 |  boolean
                 |  number

ellipsis_pattern  @expansion{} pattern ...

ellipsis_template  @expansion{}  template ...

pattern_var  @expansion{}  symbol   ; not in literals

literals  @expansion{}  ()
            |  (symbol . literals)
@end example

@subsection Definitions

@table @asis

@item Scope of an ellipsis
Within a pattern or template, the scope of an ellipsis (@code{...}) is
the pattern or template that appears to its left.

@item Rank of a pattern variable
The rank of a pattern variable is the number of ellipses within whose
scope it appears in the pattern.

@item Rank of a subtemplate
The rank of a subtemplate is the number of ellipses within whose scope
it appears in the template.

@item Template rank of an occurrence of a pattern variable
The template rank of an occurrence of a pattern variable within a
template is the rank of that occurrence, viewed as a subtemplate.

@item Variables bound by a pattern
The variables bound by a pattern are the pattern variables that appear
within it.

@item Referenced variables of a subtemplate
The referenced variables of a subtemplate are the pattern variables that
appear within it.

@item Variables opened by an ellipsis template
The variables opened by an ellipsis template are the referenced pattern
variables whose rank is greater than the rank of the ellipsis template.

@end table

@subsection Restrictions

No pattern variable appears more than once within a pattern.

For every occurrence of a pattern variable within a template, the
template rank of the occurrence must be greater than or equal to the
pattern variable's rank.

Every ellipsis template must open at least one variable.

For every ellipsis template, the variables opened by an ellipsis
template must all be bound to sequences of the same length.

The compiled form of a @var{rule} is

@example
rule  @expansion{}  (pattern template inserted)

pattern  @expansion{}  pattern_var
           |  symbol
           |  ()
           |  (pattern . pattern)
           |  ellipsis_pattern
           |  #(pattern)
           |  pattern_datum

template  @expansion{}  pattern_var
            |  symbol
            |  ()
            |  (template2 . template2)
            |  #(pattern)
            |  pattern_datum

template2  @expansion{}  template
             |  ellipsis_template

pattern_datum  @expansion{}  string
                 |  character
                 |  boolean
                 |  number

pattern_var  @expansion{}  #(V symbol rank)

ellipsis_pattern  @expansion{}  #(E pattern pattern_vars)

ellipsis_template  @expansion{}  #(E template pattern_vars)

inserted  @expansion{}  ()
            |  (symbol . inserted)

pattern_vars  @expansion{}  ()
                |  (pattern_var . pattern_vars)

rank  @expansion{}  exact non-negative integer
@end example

where V and E are unforgeable values.

The pattern variables associated with an ellipsis pattern are the
variables bound by the pattern, and the pattern variables associated
with an ellipsis template are the variables opened by the ellipsis
template.

If the template contains a big chunk that contains no pattern variables
or inserted identifiers, then the big chunk will be copied
unnecessarily.  That shouldn't matter very often.





@node Syntactic Closures, Syntax-Case Macros, Macros That Work, Macros
@section Syntactic Closures

@code{(require 'syntactic-closures)}

@defun macro:expand expression
@defunx synclo:expand expression
Returns scheme code with the macros and derived expression types of
@var{expression} expanded to primitive expression types.@refill
@end defun

@defun macro:eval expression
@defunx synclo:eval expression
@code{macro:eval} returns the value of @var{expression} in the current
top level environment.  @var{expression} can contain macro definitions.
Side effects of @var{expression} will affect the top level
environment.@refill
@end defun

@deffn Procedure macro:load filename
@deffnx Procedure synclo:load filename
@var{filename} should be a string.  If filename names an existing file,
the @code{macro:load} procedure reads Scheme source code expressions and
definitions from the file and evaluates them sequentially.  These
source code expressions and definitions may contain macro definitions.
The @code{macro:load} procedure does not affect the values returned by
@code{current-input-port} and @code{current-output-port}.@refill
@end deffn

@subsection Syntactic Closure Macro Facility

@center A Syntactic Closures Macro Facility
@center by Chris Hanson
@center 9 November 1991

This document describes @dfn{syntactic closures}, a low-level macro
facility for the Scheme programming language.  The facility is an
alternative to the low-level macro facility described in the
@cite{Revised^4 Report on Scheme.} This document is an addendum to that
report.

The syntactic closures facility extends the BNF rule for
@var{transformer spec} to allow a new keyword that introduces a
low-level macro transformer:@refill
@example
@var{transformer spec} := (transformer @var{expression})
@end example

Additionally, the following procedures are added:
@lisp
make-syntactic-closure
capture-syntactic-environment
identifier?
identifier=?
@end lisp

The description of the facility is divided into three parts.  The first
part defines basic terminology.  The second part describes how macro
transformers are defined.  The third part describes the use of
@dfn{identifiers}, which extend the syntactic closure mechanism to be
compatible with @code{syntax-rules}.@refill

@subsubsection Terminology

This section defines the concepts and data types used by the syntactic
closures facility.

@itemize

@item @dfn{Forms} are the syntactic entities out of which programs are
recursively constructed.  A form is any expression, any definition, any
syntactic keyword, or any syntactic closure.  The variable name that
appears in a @code{set!} special form is also a form.  Examples of
forms:@refill
@lisp
17
#t
car
(+ x 4)
(lambda (x) x)
(define pi 3.14159)
if
define
@end lisp

@item An @dfn{alias} is an alternate name for a given symbol.  It can
appear anywhere in a form that the symbol could be used, and when quoted
it is replaced by the symbol; however, it does not satisfy the predicate
@code{symbol?}.  Macro transformers rarely distinguish symbols from
aliases, referring to both as identifiers.@refill

@item A @dfn{syntactic} environment maps identifiers to their
meanings.  More precisely, it determines whether an identifier is a
syntactic keyword or a variable.  If it is a keyword, the meaning is an
interpretation for the form in which that keyword appears.  If it is a
variable, the meaning identifies which binding of that variable is
referenced.  In short, syntactic environments contain all of the
contextual information necessary for interpreting the meaning of a
particular form.@refill

@item A @dfn{syntactic closure} consists of a form, a syntactic
environment, and a list of identifiers.  All identifiers in the form
take their meaning from the syntactic environment, except those in the
given list.  The identifiers in the list are to have their meanings
determined later.  A syntactic closure may be used in any context in
which its form could have been used.  Since a syntactic closure is also
a form, it may not be used in contexts where a form would be illegal.
For example, a form may not appear as a clause in the cond special form.
A syntactic closure appearing in a quoted structure is replaced by its
form.@refill

@end itemize

@subsubsection Transformer Definition

This section describes the @code{transformer} special form and the
procedures @code{make-syntactic-closure} and
@code{capture-syntactic-environment}.@refill

@deffn Syntax transformer expression

Syntax: It is an error if this syntax occurs except as a
@var{transformer spec}.@refill

Semantics: The @var{expression} is evaluated in the standard transformer
environment to yield a macro transformer as described below.  This macro
transformer is bound to a macro keyword by the special form in which the
@code{transformer} expression appears (for example,
@code{let-syntax}).@refill

A @dfn{macro transformer} is a procedure that takes two arguments, a
form and a syntactic environment, and returns a new form.  The first
argument, the @dfn{input form}, is the form in which the macro keyword
occurred.  The second argument, the @dfn{usage environment}, is the
syntactic environment in which the input form occurred.  The result of
the transformer, the @dfn{output form}, is automatically closed in the
@dfn{transformer environment}, which is the syntactic environment in
which the @code{transformer} expression occurred.@refill

For example, here is a definition of a push macro using
@code{syntax-rules}:@refill
@lisp
(define-syntax  push
  (syntax-rules ()
    ((push item list)
     (set! list (cons item list)))))
@end lisp

Here is an equivalent definition using @code{transformer}:
@lisp
(define-syntax push
  (transformer
   (lambda (exp env)
     (let ((item
            (make-syntactic-closure env '() (cadr exp)))
           (list
            (make-syntactic-closure env '() (caddr exp))))
       `(set! ,list (cons ,item ,list))))))
@end lisp

In this example, the identifiers @code{set!} and @code{cons} are closed
in the transformer environment, and thus will not be affected by the
meanings of those identifiers in the usage environment
@code{env}.@refill

Some macros may be non-hygienic by design.  For example, the following
defines a loop macro that implicitly binds @code{exit} to an escape
procedure.  The binding of @code{exit} is intended to capture free
references to @code{exit} in the body of the loop, so @code{exit} must
be left free when the body is closed:@refill
@lisp
(define-syntax loop
  (transformer
   (lambda (exp env)
     (let ((body (cdr exp)))
       `(call-with-current-continuation
         (lambda (exit)
           (let f ()
             ,@@(map (lambda  (exp)
                       (make-syntactic-closure env '(exit)
                                               exp))
                     body)
             (f))))))))
@end lisp

To assign meanings to the identifiers in a form, use
@code{make-syntactic-closure} to close the form in a syntactic
environment.@refill
@end deffn

@defun make-syntactic-closure environment free-names form

@var{environment} must be a syntactic environment, @var{free-names} must
be a list of identifiers, and @var{form} must be a form.
@code{make-syntactic-closure} constructs and returns a syntactic closure
of @var{form} in @var{environment}, which can be used anywhere that
@var{form} could have been used.  All the identifiers used in
@var{form}, except those explicitly excepted by @var{free-names}, obtain
their meanings from @var{environment}.@refill

Here is an example where @var{free-names} is something other than the
empty list.  It is instructive to compare the use of @var{free-names} in
this example with its use in the @code{loop} example above: the examples
are similar except for the source of the identifier being left
free.@refill
@lisp
(define-syntax let1
  (transformer
   (lambda (exp env)
     (let ((id (cadr exp))
           (init (caddr exp))
           (exp (cadddr exp)))
       `((lambda (,id)
           ,(make-syntactic-closure env (list id) exp))
         ,(make-syntactic-closure env '() init))))))
@end lisp

@code{let1} is a simplified version of @code{let} that only binds a
single identifier, and whose body consists of a single expression.  When
the body expression is syntactically closed in its original syntactic
environment, the identifier that is to be bound by @code{let1} must be
left free, so that it can be properly captured by the @code{lambda} in
the output form.@refill

To obtain a syntactic environment other than the usage environment, use
@code{capture-syntactic-environment}.@refill
@end defun

@defun capture-syntactic-environment procedure

@code{capture-syntactic-environment} returns a form that will, when
transformed, call @var{procedure} on the current syntactic environment.
@var{procedure} should compute and return a new form to be transformed,
in that same syntactic environment, in place of the form.@refill

An example will make this clear.  Suppose we wanted to define a simple
@code{loop-until} keyword equivalent to@refill
@lisp
(define-syntax loop-until
  (syntax-rules ()
    ((loop-until id init test return step)
     (letrec ((loop
               (lambda (id)
                 (if test return (loop step)))))
       (loop init)))))
@end lisp

The following attempt at defining @code{loop-until} has a subtle bug:
@lisp
(define-syntax loop-until
  (transformer
   (lambda (exp env)
     (let ((id (cadr exp))
           (init (caddr exp))
           (test (cadddr exp))
           (return (cadddr (cdr exp)))
           (step (cadddr (cddr exp)))
           (close
            (lambda (exp free)
              (make-syntactic-closure env free exp))))
       `(letrec ((loop
                  (lambda (,id)
                    (if ,(close test (list id))
                        ,(close return (list id))
                        (loop ,(close step (list id)))))))
          (loop ,(close init '())))))))
@end lisp

This definition appears to take all of the proper precautions to prevent
unintended captures.  It carefully closes the subexpressions in their
original syntactic environment and it leaves the @code{id} identifier
free in the @code{test}, @code{return}, and @code{step} expressions, so
that it will be captured by the binding introduced by the @code{lambda}
expression.  Unfortunately it uses the identifiers @code{if} and
@code{loop} within that @code{lambda} expression, so if the user of
@code{loop-until} just happens to use, say, @code{if} for the
identifier, it will be inadvertently captured.@refill

The syntactic environment that @code{if} and @code{loop} want to be
exposed to is the one just outside the @code{lambda} expression: before
the user's identifier is added to the syntactic environment, but after
the identifier loop has been added.
@code{capture-syntactic-environment} captures exactly that environment
as follows:@refill
@lisp
(define-syntax loop-until
  (transformer
   (lambda (exp env)
     (let ((id (cadr exp))
           (init (caddr exp))
           (test (cadddr exp))
           (return (cadddr (cdr exp)))
           (step (cadddr (cddr exp)))
           (close
            (lambda (exp free)
              (make-syntactic-closure env free exp))))
       `(letrec ((loop
                  ,(capture-syntactic-environment
                    (lambda (env)
                      `(lambda (,id)
                         (,(make-syntactic-closure env '() `if)
                          ,(close test (list id))
                          ,(close return (list id))
                          (,(make-syntactic-closure env '()
                                                    `loop)
                           ,(close step (list id)))))))))
          (loop ,(close init '())))))))
@end lisp

In this case, having captured the desired syntactic environment, it is
convenient to construct syntactic closures of the identifiers @code{if}
and the @code{loop} and use them in the body of the
@code{lambda}.@refill

A common use of @code{capture-syntactic-environment} is to get the
transformer environment of a macro transformer:@refill
@lisp
(transformer
 (lambda (exp env)
   (capture-syntactic-environment
    (lambda (transformer-env)
      ...))))
@end lisp
@end defun

@subsubsection Identifiers

This section describes the procedures that create and manipulate
identifiers.  Previous syntactic closure proposals did not have an
identifier data type -- they just used symbols.  The identifier data
type extends the syntactic closures facility to be compatible with the
high-level @code{syntax-rules} facility.@refill

As discussed earlier, an identifier is either a symbol or an
@dfn{alias}.  An alias is implemented as a syntactic closure whose
@dfn{form} is an identifier:@refill
@lisp
(make-syntactic-closure env '() 'a)
   @result{} an @dfn{alias}
@end lisp

Aliases are implemented as syntactic closures because they behave just
like syntactic closures most of the time.  The difference is that an
alias may be bound to a new value (for example by @code{lambda} or
@code{let-syntax}); other syntactic closures may not be used this way.
If an alias is bound, then within the scope of that binding it is looked
up in the syntactic environment just like any other identifier.@refill

Aliases are used in the implementation of the high-level facility
@code{syntax-rules}.  A macro transformer created by @code{syntax-rules}
uses a template to generate its output form, substituting subforms of
the input form into the template.  In a syntactic closures
implementation, all of the symbols in the template are replaced by
aliases closed in the transformer environment, while the output form
itself is closed in the usage environment.  This guarantees that the
macro transformation is hygienic, without requiring the transformer to
know the syntactic roles of the substituted input subforms.

@defun identifier?  object
Returns @code{#t} if @var{object} is an identifier, otherwise returns
@code{#f}.  Examples:@refill
@lisp
(identifier? 'a)
   @result{} #t
(identifier? (make-syntactic-closure env '() 'a))
   @result{} #t
(identifier? "a")
   @result{} #f
(identifier? #\a)
   @result{} #f
(identifier? 97)
   @result{} #f
(identifier? #f)
   @result{} #f
(identifier? '(a))
   @result{} #f
(identifier? '#(a))
   @result{} #f
@end lisp

The predicate @code{eq?} is used to determine if two identifers are
``the same''.  Thus @code{eq?} can be used to compare identifiers
exactly as it would be used to compare symbols.  Often, though, it is
useful to know whether two identifiers ``mean the same thing''.  For
example, the @code{cond} macro uses the symbol @code{else} to identify
the final clause in the conditional.  A macro transformer for
@code{cond} cannot just look for the symbol @code{else}, because the
@code{cond} form might be the output of another macro transformer that
replaced the symbol @code{else} with an alias.  Instead the transformer
must look for an identifier that ``means the same thing'' in the usage
environment as the symbol @code{else} means in the transformer
environment.@refill
@end defun

@defun identifier=? environment1 identifier1 environment2 identifier2
@var{environment1} and @var{environment2} must be syntactic
environments, and @var{identifier1} and @var{identifier2} must be
identifiers.  @code{identifier=?} returns @code{#t} if the meaning of
@var{identifier1} in @var{environment1} is the same as that of
@var{identifier2} in @var{environment2}, otherwise it returns @code{#f}.
Examples:@refill

@lisp
(let-syntax
    ((foo
      (transformer
       (lambda (form env)
         (capture-syntactic-environment
          (lambda (transformer-env)
            (identifier=? transformer-env 'x env 'x)))))))
  (list (foo)
        (let ((x 3))
          (foo))))
   @result{} (#t #f)
@end lisp

@lisp
(let-syntax ((bar foo))
  (let-syntax
      ((foo
        (transformer
         (lambda (form env)
           (capture-syntactic-environment
            (lambda (transformer-env)
              (identifier=? transformer-env 'foo
                            env (cadr form))))))))
    (list (foo foo)
          (foobar))))
   @result{} (#f #t)
@end lisp
@end defun

@subsubsection Acknowledgements

The syntactic closures facility was invented by Alan Bawden and Jonathan
Rees.  The use of aliases to implement @code{syntax-rules} was invented
by Alan Bawden (who prefers to call them @dfn{synthetic names}).  Much
of this proposal is derived from an earlier proposal by Alan
Bawden.@refill





@node Syntax-Case Macros, Fluid-Let, Syntactic Closures, Macros
@section Syntax-Case Macros

@code{(require 'syntax-case)}

@defun macro:expand expression
@defunx syncase:expand expression
Returns scheme code with the macros and derived expression types of
@var{expression} expanded to primitive expression types.@refill
@end defun

@defun macro:eval expression
@defunx syncase:eval expression
@code{macro:eval} returns the value of @var{expression} in the current
top level environment.  @var{expression} can contain macro definitions.
Side effects of @var{expression} will affect the top level
environment.@refill
@end defun

@deffn Procedure macro:load filename
@deffnx Procedure syncase:load filename
@var{filename} should be a string.  If filename names an existing file,
the @code{macro:load} procedure reads Scheme source code expressions and
definitions from the file and evaluates them sequentially.  These
source code expressions and definitions may contain macro definitions.
The @code{macro:load} procedure does not affect the values returned by
@code{current-input-port} and @code{current-output-port}.@refill
@end deffn

This is version 2.1 of @code{syntax-case}, the low-level macro facility
proposed and implemented by Robert Hieb and R. Kent Dybvig.

This version is further adapted by Harald Hanche-Olsen
<hanche@@imf.unit.no> to make it compatible with, and easily usable
with, SLIB.  Mainly, these adaptations consisted of:

@itemize @bullet
@item
Removing white space from @file{expand.pp} to save space in the
distribution.  This file is not meant for human readers anyway@dots{}

@item
Removed a couple of Chez scheme dependencies.

@item
Renamed global variables used to minimize the possibility of name
conflicts.

@item
Adding an SLIB-specific initialization file.

@item
Removing a couple extra files, most notably the documentation (but see
below).
@end itemize

If you wish, you can see exactly what changes were done by reading the
shell script in the file @file{syncase.sh}.

The two PostScript files were omitted in order to not burden the SLIB
distribution with them.  If you do intend to use @code{syntax-case},
however, you should get these files and print them out on a PostScript
printer.  They are available with the original @code{syntax-case}
distribution by anonymous FTP in
@file{cs.indiana.edu:/pub/scheme/syntax-case}.@refill

In order to use syntax-case from an interactive top level, execute:
@lisp
(require 'syntax-case)
(require 'repl)
(repl:top-level macro:eval)
@end lisp
See the section Repl (@xref{Repl}) for more information.

To check operation of syntax-case get
@file{cs.indiana.edu:/pub/scheme/syntax-case}, and type
@lisp
(require 'syntax-case)
(syncase:sanity-check)
@end lisp

Beware that @code{syntax-case} takes a long time to load -- about 20s on
a SPARCstation SLC (with SCM) and about 90s on a Macintosh SE/30 (with
Gambit).

@subsection Notes

All R4RS syntactic forms are defined, including @code{delay}.  Along
with @code{delay} are simple definitions for @code{make-promise} (into
which @code{delay} expressions expand) and @code{force}.@refill

@code{syntax-rules} and @code{with-syntax} (described in @cite{TR356})
are defined.@refill

@code{syntax-case} is actually defined as a macro that expands into
calls to the procedure @code{syntax-dispatch} and the core form
@code{syntax-lambda}; do not redefine these names.@refill

Several other top-level bindings not documented in TR356 are created:
@itemize
@item the ``hooks'' in @file{hooks.ss}
@item the @code{build-} procedures in @file{output.ss}
@item @code{expand-syntax} (the expander)
@end itemize

The syntax of define has been extended to allow @code{(define @var{id})},
which assigns @var{id} to some unspecified value.@refill

We have attempted to maintain R4RS compatibility where possible.  The
incompatibilities should be confined to @file{hooks.ss}.  Please let us
know if there is some incompatibility that is not flagged as such.@refill

Send bug reports, comments, suggestions, and questions to Kent Dybvig
(dyb@@iuvax.cs.indiana.edu).

@subsection Note from maintainer

Included with the @code{syntax-case} files was @file{structure.scm}
which defines a macro @code{define-structure}.  There is no
documentation for this macro and it is not used by any code in SLIB.

@node Fluid-Let, Yasos, Syntax-Case Macros, Macros
@section Fluid-Let

@code{(require 'fluid-let)}

@deffn Syntax fluid-let @code{(@var{bindings} @dots{})} @var{forms}@dots{}
@end deffn
@lisp
(fluid-let ((@var{variable} @var{init}) @dots{})
   @var{expression} @var{expression} @dots{})
@end lisp

The @var{init}s are evaluated in the current environment (in some
unspecified order), the current values of the @var{variable}s are saved,
the results are assigned to the @var{variable}s, the @var{expression}s
are evaluated sequentially in the current environment, the
@var{variable}s are restored to their original values, and the value of
the last @var{expression} is returned.@refill

The syntax of this special form is similar to that of @code{let}, but
@code{fluid-let} temporarily rebinds existing @var{variable}s.  Unlike
@code{let}, @code{fluid-let} creates no new bindings; instead it
@emph{assigns} the values of each @var{init} to the binding (determined
by the rules of lexical scoping) of its corresponding
@var{variable}.@refill


@node Yasos,  , Fluid-Let, Macros
@section Yasos

@c Much of the documentation in this section was written by Dave Love
@c (d.love@dl.ac.uk) -- don't blame Ken Dickey for its faults.
@c but we can blame him for not writing it!

@code{(require 'oop)} or @code{(require 'yasos)}

`Yet Another Scheme Object System' is a simple object system for Scheme
based on the paper by Norman Adams and Jonathan Rees: @cite{Object
Oriented Programming in Scheme}, Proceedings of the 1988 ACM Conference
on LISP and Functional Programming, July 1988 [ACM #552880].@refill

Another reference is:

Ken Dickey.
@ifset html
<A HREF="ftp://ftp.cs.indiana.edu/pub/scheme-repository/doc/pubs/swob.txt">
@end ifset
Scheming with Objects
@ifset html
</A>
@end ifset
@cite{AI Expert} Volume 7, Number 10 (October 1992), pp. 24-33.

@menu
* Yasos terms::                 Definitions and disclaimer.
* Yasos interface::             The Yasos macros and procedures.
* Setters::                     Dylan-like setters in Yasos.
* Yasos examples::              Usage of Yasos and setters.
@end menu

@node Yasos terms, Yasos interface, Yasos, Yasos
@subsection Terms

@table @asis
@item @dfn{Object}
Any Scheme data object.

@item @dfn{Instance}
An instance of the OO system; an @dfn{object}.

@item @dfn{Operation}
A @var{method}.
@end table

@table @emph
@item Notes:
The object system supports multiple inheritance.  An instance can
inherit from 0 or more ancestors.  In the case of multiple inherited
operations with the same identity, the operation used is that from the
first ancestor which contains it (in the ancestor @code{let}).  An
operation may be applied to any Scheme data object---not just instances.
As code which creates instances is just code, there are no @dfn{classes}
and no meta-@var{anything}.  Method dispatch is by a procedure call a la
CLOS rather than by @code{send} syntax a la Smalltalk.@refill

@item Disclaimer:
There are a number of optimizations which can be made.  This
implementation is expository (although performance should be quite
reasonable).  See the L&FP paper for some suggestions.@refill
@end table





@node Yasos interface, Setters, Yasos terms, Yasos
@subsection Interface

@deffn Syntax define-operation @code{(}opname self arg @dots{}@code{)} @var{default-body}
Defines a default behavior for data objects which don't handle the
operation @var{opname}.  The default default behavior (for an empty
@var{default-body}) is to generate an error.@refill
@end deffn

@deffn Syntax define-predicate opname?
Defines a predicate @var{opname?}, usually used for determining the
@dfn{type} of an object, such that @code{(@var{opname?} @var{object})}
returns @code{#t} if @var{object} has an operation @var{opname?} and
@code{#f} otherwise.@refill
@end deffn

@deffn Syntax object @code{((@var{name} @var{self} @var{arg} @dots{}) @var{body})} @dots{}
Returns an object (an instance of the object system) with operations.
Invoking @code{(@var{name} @var{object} @var{arg} @dots{}} executes the
@var{body} of the @var{object} with @var{self} bound to @var{object} and
with argument(s) @var{arg}@dots{}.@refill
@end deffn

@deffn Syntax object-with-ancestors @code{((}ancestor1 init1@code{)} @dots{}@code{)} operation @dots{}
A @code{let}-like form of @code{object} for multiple inheritance.  It
returns an object inheriting the behaviour of @var{ancestor1} etc.  An
operation will be invoked in an ancestor if the object itself does not
provide such a method.  In the case of multiple inherited operations
with the same identity, the operation used is the one found in the first
ancestor in the ancestor list.
@end deffn

@deffn Syntax operate-as component operation self arg @dots{}
Used in an operation definition (of @var{self}) to invoke the
@var{operation} in an ancestor @var{component} but maintain the object's
identity.  Also known as ``send-to-super''.@refill
@end deffn

@deffn Procedure print obj port
A default @code{print} operation is provided which is just @code{(format
@var{port} @var{obj})} (@xref{Format}) for non-instances and prints
@var{obj} preceded by @samp{#<INSTANCE>} for instances.
@end deffn

@defun size obj
The default method returns the number of elements in @var{obj} if it is
a vector, string or list, @code{2} for a pair, @code{1} for a character
and by default id an error otherwise.  Objects such as collections
(@xref{Collections}) may override the default in an obvious way.@refill
@end defun





@node Setters, Yasos examples, Yasos interface, Yasos
@subsection Setters

@dfn{Setters} implement @dfn{generalized locations} for objects
associated with some sort of mutable state.  A @dfn{getter} operation
retrieves a value from a generalized location and the corresponding
setter operation stores a value into the location.  Only the getter is
named -- the setter is specified by a procedure call as below.  (Dylan
uses special syntax.)  Typically, but not necessarily, getters are
access operations to extract values from Yasos objects (@xref{Yasos}).
Several setters are predefined, corresponding to getters @code{car},
@code{cdr}, @code{string-ref} and @code{vector-ref} e.g., @code{(setter
car)} is equivalent to @code{set-car!}.

This implementation of setters is similar to that in Dylan(TM)
(@cite{Dylan: An object-oriented dynamic language}, Apple Computer
Eastern Research and Technology).  Common LISP provides similar
facilities through @code{setf}.

@defun setter getter
Returns the setter for the procedure @var{getter}.  E.g., since
@code{string-ref} is the getter corresponding to a setter which is
actually @code{string-set!}:
@example
(define foo "foo")
((setter string-ref) foo 0 #\F) ; set element 0 of foo
foo @result{} "Foo"
@end example
@end defun

@deffn Syntax set place new-value
If @var{place} is a variable name, @code{set} is equivalent to
@code{set!}.  Otherwise, @var{place} must have the form of a procedure
call, where the procedure name refers to a getter and the call indicates
an accessible generalized location, i.e., the call would return a value.
The return value of @code{set} is usually unspecified unless used with a
setter whose definition guarantees to return a useful value.
@example
(set (string-ref foo 2) #\O)  ; generalized location with getter
foo @result{} "FoO"
(set foo "foo")               ; like set!
foo @result{} "foo"
@end example
@end deffn

@deffn Procedure add-setter getter setter
Add procedures @var{getter} and @var{setter} to the (inaccessible) list
of valid setter/getter pairs.  @var{setter} implements the store
operation corresponding to the @var{getter} access operation for the
relevant state.  The return value is unspecified.
@end deffn

@deffn Procedure remove-setter-for getter
Removes the setter corresponding to the specified @var{getter} from the
list of valid setters.  The return value is unspecified.
@end deffn

@deffn Syntax define-access-operation getter-name
Shorthand for a Yasos @code{define-operation} defining an operation
@var{getter-name} that objects may support to return the value of some
mutable state.  The default operation is to signal an error.  The return
value is unspecified.
@end deffn





@node Yasos examples,  , Setters, Yasos
@subsection Examples

@lisp
(define-operation (print obj port)
  (format port
          (if (instance? obj) "#<instance>" "~s")
          obj))

(define-operation (SIZE obj)
  (cond
   ((vector? obj) (vector-length obj))
   ((list?   obj) (length obj))
   ((pair?   obj) 2)
   ((string? obj) (string-length obj))
   ((char?   obj) 1)
   (else
    (error "Operation not supported: size" obj))))

(define-predicate cell?)
(define-operation (fetch obj))
(define-operation (store! obj newValue))

(define (make-cell value)
  (object
   ((cell? self) #t)
   ((fetch self) value)
   ((store! self newValue)
    (set! value newValue)
    newValue)
   ((size self) 1)
   ((print self port)
    (format port "#<Cell: ~s>" (fetch self)))))

(define-operation (discard obj value)
  (format #t "Discarding ~s~%" value))

(define (make-filtered-cell value filter)
  (object-with-ancestors ((cell (make-cell value)))
                         ((store! self newValue)
                          (if (filter newValue)
                              (store! cell newValue)
                              (discard self newValue)))))

(define-predicate array?)
(define-operation (array-ref array index))
(define-operation (array-set! array index value))

(define (make-array num-slots)
  (let ((anArray (make-vector num-slots)))
    (object
     ((array? self) #t)
     ((size self) num-slots)
     ((array-ref self index)           (vector-ref  anArray index))
     ((array-set! self index newValue) (vector-set! anArray index newValue))
     ((print self port) (format port "#<Array ~s>" (size self))))))

(define-operation (position obj))
(define-operation (discarded-value obj))

(define (make-cell-with-history value filter size)
  (let ((pos 0) (most-recent-discard #f))
    (object-with-ancestors
     ((cell (make-filtered-call value filter))
      (sequence (make-array size)))
     ((array? self) #f)
     ((position self) pos)
     ((store! self newValue)
      (operate-as cell store! self newValue)
      (array-set! self pos newValue)
      (set! pos (+ pos 1)))
     ((discard self value)
      (set! most-recent-discard value))
     ((discarded-value self) most-recent-discard)
     ((print self port)
      (format port "#<Cell-with-history ~s>" (fetch self))))))

(define-access-operation fetch)
(add-setter fetch store!)
(define foo (make-cell 1))
(print foo #f)
@result{} "#<Cell: 1>"
(set (fetch foo) 2)
@result{}
(print foo #f)
@result{} "#<Cell: 2>"
(fetch foo)
@result{} 2
@end lisp

@node Numerics, Procedures, Macros, Top
@chapter Numerics

@menu
* Bit-Twiddling::               'logical
* Modular Arithmetic::          'modular
* Prime Testing and Generation::  'primes
* Prime Factorization::         'factor
* Random Numbers::              'random
* Cyclic Checksum::             'make-crc
* Plotting::                    'charplot
* Root Finding::                
@end menu


@node Bit-Twiddling, Modular Arithmetic, Numerics, Numerics
@section Bit-Twiddling

@code{(require 'logical)}

The bit-twiddling functions are made available through the use of the
@code{logical} package.  @code{logical} is loaded by inserting
@code{(require 'logical)} before the code that uses these
functions.@refill

@defun logand n1 n1
Returns the integer which is the bit-wise AND of the two integer
arguments.

Example:
@lisp
(number->string (logand #b1100 #b1010) 2)
   @result{} "1000"
@end lisp
@end defun

@defun logior n1 n2
Returns the integer which is the bit-wise OR of the two integer
arguments.

Example:
@lisp
(number->string (logior #b1100 #b1010) 2)
   @result{} "1110"
@end lisp
@end defun

@defun logxor n1 n2
Returns the integer which is the bit-wise XOR of the two integer
arguments.

Example:
@lisp
(number->string (logxor #b1100 #b1010) 2)
   @result{} "110"
@end lisp
@end defun

@defun lognot n
Returns the integer which is the 2s-complement of the integer argument.

Example:
@lisp
(number->string (lognot #b10000000) 2)
   @result{} "-10000001"
(number->string (lognot #b0) 2)
   @result{} "-1"
@end lisp
@end defun

@defun logtest j k
@example
(logtest j k) @equiv{} (not (zero? (logand j k)))

(logtest #b0100 #b1011) @result{} #f
(logtest #b0100 #b0111) @result{} #t
@end example
@end defun

@defun logbit? index j
@example
(logbit? index j) @equiv{} (logtest (integer-expt 2 index) j)

(logbit? 0 #b1101) @result{} #t
(logbit? 1 #b1101) @result{} #f
(logbit? 2 #b1101) @result{} #t
(logbit? 3 #b1101) @result{} #t
(logbit? 4 #b1101) @result{} #f
@end example
@end defun

@defun ash int count
Returns an integer equivalent to
@code{(inexact->exact (floor (* @var{int} (expt 2 @var{count}))))}.@refill

Example:
@lisp
(number->string (ash #b1 3) 2)
   @result{} "1000"
(number->string (ash #b1010 -1) 2)
   @result{} "101"
@end lisp
@end defun

@defun logcount n
Returns the number of bits in integer @var{n}.  If integer is positive,
the 1-bits in its binary representation are counted.  If negative, the
0-bits in its two's-complement binary representation are counted.  If 0,
0 is returned.

Example:
@lisp
(logcount #b10101010)
   @result{} 4
(logcount 0)
   @result{} 0
(logcount -2)
   @result{} 1
@end lisp
@end defun

@defun integer-length n
Returns the number of bits neccessary to represent @var{n}.

Example:
@lisp
(integer-length #b10101010)
   @result{} 8
(integer-length 0)
   @result{} 0
(integer-length #b1111)
   @result{} 4
@end lisp
@end defun

@defun integer-expt n k
Returns @var{n} raised to the non-negative integer exponent @var{k}.

Example:
@lisp
(integer-expt 2 5)
   @result{} 32
(integer-expt -3 3)
   @result{} -27
@end lisp
@end defun

@defun bit-extract n start end
Returns the integer composed of the @var{start} (inclusive) through
@var{end} (exclusive) bits of @var{n}.  The @var{start}th bit becomes
the 0-th bit in the result.@refill

Example:
@lisp
(number->string (bit-extract #b1101101010 0 4) 2)
   @result{} "1010"
(number->string (bit-extract #b1101101010 4 9) 2)
   @result{} "10110"
@end lisp
@end defun


@node Modular Arithmetic, Prime Testing and Generation, Bit-Twiddling, Numerics
@section Modular Arithmetic

@code{(require 'modular)}

@defun extended-euclid n1 n2
Returns a list of 3 integers @code{(d x y)} such that d = gcd(@var{n1},
@var{n2}) = @var{n1} * x + @var{n2} * y.@refill
@end defun

@defun symmetric:modulus n
Returns @code{(quotient (+ -1 n) -2)} for positive odd integer @var{n}.
@end defun

@defun modulus->integer modulus
Returns the non-negative integer characteristic of the ring formed when
@var{modulus} is used with @code{modular:} procedures.
@end defun

@defun modular:normalize modulus n
Returns the integer @code{(modulo @var{n} (modulus->integer
@var{modulus}))} in the representation specified by @var{modulus}.
@end defun

@noindent
The rest of these functions assume normalized arguments; That is, the
arguments are constrained by the following table:

@noindent
For all of these functions, if the first argument (@var{modulus}) is:
@table @code
@item positive?
Work as before.  The result is between 0 and @var{modulus}.

@item zero?
The arguments are treated as integers.  An integer is returned.

@item negative?
The arguments and result are treated as members of the integers modulo
@code{(+ 1 (* -2 @var{modulus}))}, but with @dfn{symmetric}
representation; i.e. @code{(<= (- @var{modulus}) @var{n}
@var{modulus})}.
@end table

@noindent
If all the arguments are fixnums the computation will use only fixnums.

@defun modular:invertable? modulus k
Returns @code{#t} if there exists an integer n such that @var{k} * n
@equiv{} 1 mod @var{modulus}, and @code{#f} otherwise.
@end defun

@defun modular:invert modulus k2
Returns an integer n such that 1 = (n * @var{k2}) mod @var{modulus}.  If
@var{k2} has no inverse mod @var{modulus} an error is signaled.
@end defun

@defun modular:negate modulus k2
Returns (@minus{}@var{k2}) mod @var{modulus}.
@end defun

@defun modular:+ modulus k2 k3
Returns (@var{k2} + @var{k3}) mod @var{modulus}.
@end defun

@defun modular:@minus{} modulus k2 k3
Returns (@var{k2} @minus{} @var{k3}) mod @var{modulus}.
@end defun

@defun modular:* modulus k2 k3
Returns (@var{k2} * @var{k3}) mod @var{modulus}.

The Scheme code for @code{modular:*} with negative @var{modulus} is not
completed for fixnum-only implementations.
@end defun

@defun modular:expt modulus k2 k3
Returns (@var{k2} ^ @var{k3}) mod @var{modulus}.
@end defun


@node Prime Testing and Generation, Prime Factorization, Modular Arithmetic, Numerics
@section Prime Testing and Generation

@code{(require 'primes)}

This package tests and generates prime numbers.  The strategy used is
as follows:

@itemize
@item
First, use trial division by small primes (primes less than 1000) to
quickly weed out composites with small factors.  As a side benefit, this
makes the test precise for numbers up to one million.
@item
Second, apply the Miller-Rabin primality test to detect (with high
probability) any remaining composites.
@end itemize

The Miller-Rabin test is a Monte-Carlo test---in other words, it's fast
and it gets the right answer with high probability.  For a candidate
that @emph{is} prime, the Miller-Rabin test is certain to report
"prime"; it will never report "composite".  However, for a candidate
that is composite, there is a (small) probability that the Miller-Rabin
test will erroneously report "prime".  This probability can be made
arbitarily small by adjusting the number of iterations of the
Miller-Rabin test.

@defun probably-prime? candidate
@defunx probably-prime? candidate iter
Returns @code{#t} if @code{candidate} is probably prime.  The optional
parameter @code{iter} controls the number of iterations of the
Miller-Rabin test.  The probability of a composite candidate being
mistaken for a prime is at most @code{(1/4)^iter}.  The default value of
@code{iter} is 15, which makes the probability less than 1 in 10^9.

@end defun

@defun primes< start count
@defunx primes< start count iter
@defunx primes> start count
@defunx primes> start count iter
Returns a list of the first @code{count} odd probable primes less (more)
than or equal to @code{start}.  The optional parameter @code{iter}
controls the number of iterations of the Miller-Rabin test for each
candidate.  The probability of a composite candidate being mistaken for
a prime is at most @code{(1/4)^iter}.  The default value of @code{iter}
is 15, which makes the probability less than 1 in 10^9.

@end defun

@menu
* The Miller-Rabin Test::       How the Miller-Rabin test works
@end menu

@node The Miller-Rabin Test,  , Prime Testing and Generation, Prime Testing and Generation
@subsection Theory

Rabin and Miller's result can be summarized as follows.  Let @code{p}
(the candidate prime) be any odd integer greater than 2.  Let @code{b}
(the "base") be an integer in the range @code{2 ... p-1}.  There is a
fairly simple Boolean function---call it @code{C}, for
"Composite"---with the following properties:
@itemize

@item
If @code{p} is prime, @code{C(p, b)} is false for all @code{b} in the range
@code{2 ... p-1}.

@item
If @code{p} is composite, @code{C(p, b)} is false for at most 1/4 of all
@code{b} in the range @code{ 2 ... p-1}.  (If the test fails for base
@code{b}, @code{p} is called a @emph{strong pseudo-prime to base
@code{b}}.)

@end itemize
For details of @code{C}, and why it fails for at most 1/4 of the
potential bases, please consult a book on number theory or cryptography
such as "A Course in Number Theory and Cryptography" by Neal Koblitz,
published by Springer-Verlag 1994.

There is nothing probablistic about this result.  It's true for all
@code{p}.  If we had time to test @code{(1/4)p + 1} different bases, we
could definitively determine the primality of @code{p}.  For large
candidates, that would take much too long---much longer than the simple
approach of dividing by all numbers up to @code{sqrt(p)}.  This is
where probability enters the picture.

Suppose we have some candidate prime @code{p}.  Pick a random integer
@code{b} in the range @code{2 ... p-1}.  Compute @code{C(p,b)}.  If
@code{p} is prime, the result will certainly be false.  If @code{p} is
composite, the probability is at most 1/4 that the result will be false
(demonstrating that @code{p} is a strong pseudoprime to base @code{b}).
The test can be repeated with other random bases.  If @code{p} is prime,
each test is certain to return false.  If @code{p} is composite, the
probability of @code{C(p,b)} returning false is at most 1/4 for each
test.  Since the @code{b} are chosen at random, the tests outcomes are
independent. So if @code{p} is composite and the test is repeated, say,
15 times, the probability of it returning false all fifteen times is at
most (1/4)^15, or about 10^-9.  If the test is repeated 30 times, the
probability of failure drops to at most 8.3e-25.

Rabin and Miller's result holds for @emph{all} candidates @code{p}.
However, if the candidate @code{p} is picked at random, the probability
of the Miller-Rabin test failing is much less than the computed bound.
This is because, for @emph{most} composite numbers, the fraction of
bases that cause the test to fail is much less than 1/4.  For example,
if you pick a random odd number less than 1000 and apply the
Miller-Rabin test with only 3 random bases, the computed failure bound
is (1/4)^3, or about 1.6e-2.  However, the actual probability of failure
is much less---about 7.2e-5.  If you accidentally pick 703 to test for
primality, the probability of failure is (161/703)^3, or about 1.2e-2,
which is almost as high as the computed bound.  This is because 703 is a
strong pseudoprime to 161 bases.  But if you pick at random there is
only a small chance of picking 703, and no other number less than 1000
has that high a percentage of pseudoprime bases.

The Miller-Rabin test is sometimes used in a slightly different fashion,
where it can, at least in principle, cause problems.  The weaker version
uses small prime bases instead of random bases.  If you are picking
candidates at random and testing for primality, this works well since
very few composites are strong pseudo-primes to small prime bases.  (For
example, there is only one composite less than 2.5e10 that is a strong
pseudo-prime to the bases 2, 3, 5, and 7.)  The problem with this
approach is that once a candidate has been picked, the test is
deterministic.  This distinction is subtle, but real.  With the
randomized test, for @emph{any} candidate you pick---even if your
candidate-picking procedure is strongly biased towards troublesome
numbers, the test will work with high probability.  With the
deterministic version, for any particular candidate, the test will
either work (with probability 1), or fail (with probability 1).  It
won't fail for very many candidates, but that won't be much consolation
if your candidate-picking procedure is somehow biased toward troublesome
numbers.


@node Prime Factorization, Random Numbers, Prime Testing and Generation, Numerics
@section Prime Factorization

@code{(require 'factor)}


@defun factor k
Returns a list of the prime factors of @var{k}.  The order of the
factors is unspecified.  In order to obtain a sorted list do
@code{(sort! (factor k) <)}.@refill
@end defun

@emph{Note:} The rest of these procedures implement the Solovay-Strassen
primality test.  This test has been superseeded by the faster
@xref{Prime Testing and Generation, probably-prime?}.  However these are
left here as they take up little space and may be of use to an
implementation without bignums.

See Robert Solovay and Volker Strassen, @cite{A Fast Monte-Carlo Test
for Primality}, SIAM Journal on Computing, 1977, pp 84-85.

@defun jacobi-symbol p q
Returns the value (+1, @minus{}1, or 0) of the Jacobi-Symbol of exact
non-negative integer @var{p} and exact positive odd integer
@var{q}.@refill
@end defun

@defun prime? p
Returns @code{#f} if @var{p} is composite; @code{#t} if @var{p} is
prime.  There is a slight chance @code{(expt 2 (- prime:trials))} that a
composite will return @code{#t}.@refill
@end defun

@defun prime:trials
Is the maxinum number of iterations of Solovay-Strassen that will be
done to test a number for primality.
@end defun



@node Random Numbers, Cyclic Checksum, Prime Factorization, Numerics
@section Random Numbers

@code{(require 'random)}


@deffn Procedure random n
@deffnx Procedure random n state
Accepts a positive integer or real @var{n} and returns a number of the
same type between zero (inclusive) and @var{n} (exclusive).  The values
returned have a uniform distribution.@refill

The optional argument @var{state} must be of the type produced by
@code{(make-random-state)}.  It defaults to the value of the variable
@code{*random-state*}.  This object is used to maintain the state of the
pseudo-random-number generator and is altered as a side effect of the
@code{random} operation.@refill
@end deffn

@defvar *random-state*
Holds a data structure that encodes the internal state of the
random-number generator that @code{random} uses by default.  The nature
of this data structure is implementation-dependent.  It may be printed
out and successfully read back in, but may or may not function correctly
as a random-number state object in another implementation.@refill
@end defvar

@deffn Procedure make-random-state
@deffnx Procedure make-random-state state
Returns a new object of type suitable for use as the value of the
variable @code{*random-state*} and as a second argument to
@code{random}.  If argument @var{state} is given, a copy of it is
returned.  Otherwise a copy of @code{*random-state*} is returned.@refill
@end deffn

If inexact numbers are support by the Scheme implementation,
@file{randinex.scm} will be loaded as well.  @file{randinex.scm}
contains procedures for generating inexact distributions.@refill

@deffn Procedure random:uniform state
Returns an uniformly distributed inexact real random number in the
range between 0 and 1.
@end deffn

@deffn Procedure random:solid-sphere! vect
@deffnx Procedure random:solid-sphere! vect state
Fills @var{vect} with inexact real random numbers the sum of whose
squares is less than 1.0.  Thinking of @var{vect} as coordinates in
space of dimension @var{n} = @code{(vector-length @var{vect})}, the
coordinates are uniformly distributed within the unit @var{n}-shere.
The sum of the squares of the numbers is returned.@refill
@end deffn

@deffn Procedure random:hollow-sphere! vect
@deffnx Procedure random:hollow-sphere! vect state
Fills @var{vect} with inexact real random numbers the sum of whose
squares is equal to 1.0.  Thinking of @var{vect} as coordinates in space
of dimension n = @code{(vector-length @var{vect})}, the coordinates are
uniformly distributed over the surface of the unit n-shere.@refill
@end deffn

@deffn Procedure random:normal
@deffnx Procedure random:normal state
Returns an inexact real in a normal distribution with mean 0 and
standard deviation 1.  For a normal distribution with mean @var{m} and
standard deviation @var{d} use @code{(+ @var{m} (* @var{d}
(random:normal)))}.@refill
@end deffn

@deffn Procedure random:normal-vector! vect
@deffnx Procedure random:normal-vector! vect state
Fills @var{vect} with inexact real random numbers which are independent
and standard normally distributed (i.e., with mean 0 and variance 1).
@end deffn

@deffn Procedure random:exp
@deffnx Procedure random:exp state
Returns an inexact real in an exponential distribution with mean 1.  For
an exponential distribution with mean @var{u} use (* @var{u}
(random:exp)).@refill
@end deffn


@node Cyclic Checksum, Plotting, Random Numbers, Numerics
@section Cyclic Checksum

@code{(require 'make-crc)}

@defun make-port-crc
@defunx make-port-crc degree
@defunx make-port-crc degree generator
Returns an expression for a procedure of one argument, a port.  This
procedure reads characters from the port until the end of file and
returns the integer checksum of the bytes read.

The integer @var{degree}, if given, specifies the degree of the
polynomial being computed -- which is also the number of bits computed
in the checksums.  The default value is 32.

The integer @var{generator} specifies the polynomial being computed.
The power of 2 generating each 1 bit is the exponent of a term of the
polynomial.  The bit at position @var{degree} is implicit and should not
be part of @var{generator}.  This allows systems with numbers limited to
32 bits to calculate 32 bit checksums.  The default value of
@var{generator} when @var{degree} is 32 (its default) is:

@example
(make-port-crc 32 #b00000100110000010001110110110111)
@end example

Creates a procedure to calculate the P1003.2/D11.2 (POSIX.2) 32-bit
checksum from the polynomial:

@example
     32    26    23    22    16    12    11
  ( x   + x   + x   + x   + x   + x   + x   +

      10    8    7    5    4    2    1
     x   + x  + x  + x  + x  + x  + x  + 1 )  mod 2
@end example
@end defun

@example
(require 'make-crc)
(define crc32 (slib:eval (make-port-crc)))
(define (file-check-sum file) (call-with-input-file file crc32))
(file-check-sum (in-vicinity (library-vicinity) "ratize.scm"))

@result{} 3553047446
@end example

@node Plotting, Root Finding, Cyclic Checksum, Numerics
@section Plotting on Character Devices

@code{(require 'charplot)}

The plotting procedure is made available through the use of the
@code{charplot} package.  @code{charplot} is loaded by inserting
@code{(require 'charplot)} before the code that uses this
procedure.@refill

@defvar charplot:height
The number of rows to make the plot vertically.
@end defvar

@defvar charplot:width
The number of columns to make the plot horizontally.
@end defvar

@deffn Procedure plot! coords x-label y-label
@var{coords} is a list of pairs of x and y coordinates.  @var{x-label}
and @var{y-label} are strings with which to label the x and y
axes.@refill

Example:
@example
(require 'charplot)
(set! charplot:height 19)
(set! charplot:width 45)

(define (make-points n)
  (if (zero? n)
      '()
      (cons (cons (/ n 6) (sin (/ n 6))) (make-points (1- n)))))

(plot! (make-points 37) "x" "Sin(x)")
@print{}
@group
  Sin(x)   ______________________________________________
      1.25|-                                             |
          |                                              |
         1|-       ****                                  |
          |      **    **                                |
  750.0e-3|-    *        *                               |
          |    *          *                              |
  500.0e-3|-  *            *                             |
          |  *                                           |
  250.0e-3|-                *                            |
          | *                *                           |
         0|-------------------*--------------------------|
          |                                     *        |
 -250.0e-3|-                   *               *         |
          |                     *             *          |
 -500.0e-3|-                     *                       |
          |                       *          *           |
 -750.0e-3|-                       *        *            |
          |                         **    **             |
        -1|-                          ****               |
          |____________:_____._____:_____._____:_________|
        x              2           4      
@end group
@end example
@end deffn


@node Root Finding,  , Plotting, Numerics
@section Root Finding

@code{(require 'root)}

@defun newtown:find-integer-root f df/dx x0
Given integer valued procedure @var{f}, its derivative (with respect to
its argument) @var{df/dx}, and initial integer value @var{x0} for which
@var{df/dx}(@var{x0}) is non-zero, returns an integer @var{x} for which
@var{f}(@var{x}) is closer to zero than either of the integers adjacent
to @var{x}; or returns @code{#f} if such an integer can't be found.

To find the closest integer to a given integers square root:

@example
(define (integer-sqrt y)
  (newton:find-integer-root
   (lambda (x) (- (* x x) y))
   (lambda (x) (* 2 x))
   (ash 1 (quotient (integer-length y) 2))))

(integer-sqrt 15) @result{} 4
@end example
@end defun

@defun integer-sqrt y
Given a non-negative integer @var{y}, returns the rounded square-root of
@var{y}.
@end defun

@defun newton:find-root f df/dx x0 prec
Given real valued procedures @var{f}, @var{df/dx} of one (real)
argument, initial real value @var{x0} for which @var{df/dx}(@var{x0}) is
non-zero, and positive real number @var{prec}, returns a real @var{x}
for which @code{abs}(@var{f}(@var{x})) is less than @var{prec}; or
returns @code{#f} if such a real can't be found.

If @code{prec} is instead a negative integer, @code{newton:find-root}
returns the result of -@var{prec} iterations.
@end defun

@noindent
H. J. Orchard, @cite{The Laguerre Method for Finding the Zeros of
Polynomials}, IEEE Transactions on Circuits and Systems, Vol. 36,
No. 11, November 1989, pp 1377-1381.

@quotation
There are 2 errors in Orchard's Table II.  Line k=2 for starting
value of 1000+j0 should have Z_k of 1.0475 + j4.1036 and line k=2
for starting value of 0+j1000 should have Z_k of 1.0988 + j4.0833.
@end quotation


@defun laguerre:find-root f df/dz ddf/dz^2 z0 prec
Given complex valued procedure @var{f} of one (complex) argument, its
derivative (with respect to its argument) @var{df/dx}, its second
derivative @var{ddf/dz^2}, initial complex value @var{z0}, and positive
real number @var{prec}, returns a complex number @var{z} for which
@code{magnitude}(@var{f}(@var{z})) is less than @var{prec}; or returns
@code{#f} if such a number can't be found.

If @code{prec} is instead a negative integer, @code{laguerre:find-root}
returns the result of -@var{prec} iterations.
@end defun

@defun laguerre:find-polynomial-root deg f df/dz ddf/dz^2 z0 prec
Given polynomial procedure @var{f} of integer degree @var{deg} of one
argument, its derivative (with respect to its argument) @var{df/dx}, its
second derivative @var{ddf/dz^2}, initial complex value @var{z0}, and
positive real number @var{prec}, returns a complex number @var{z} for
which @code{magnitude}(@var{f}(@var{z})) is less than @var{prec}; or
returns @code{#f} if such a number can't be found.

If @code{prec} is instead a negative integer,
@code{laguerre:find-polynomial-root} returns the result of -@var{prec}
iterations.
@end defun


@node Procedures, Standards Support, Numerics, Top
@chapter Procedures

Anything that doesn't fall neatly into any of the other categories winds
up here.

@menu
* Batch::                       'batch
* Common List Functions::       'common-list-functions
* Format::                      'format
* Generic-Write::               'generic-write
* Line I/O::                    'line-i/o
* Multi-Processing::            'process
* Object-To-String::            'object->string
* Pretty-Print::                'pretty-print, 'pprint-file
* Sorting::                     'sort
* Topological Sort::            
* Standard Formatted I/O::      'printf, 'scanf
* String-Case::                 'string-case
* String Ports::                'string-port
* String Search::               
* Tektronix Graphics Support::  
* Tree Operations::             'tree
@end menu

@node Batch, Common List Functions, Procedures, Procedures
@section Batch

@code{(require 'batch)}

@noindent
The batch procedures provide a way to write and execute portable scripts
for a variety of operating systems.  Each @code{batch:} procedure takes
as its first argument a parameter-list (@pxref{Parameter lists}).  This
parameter-list argument @var{parms} contains named associations.  Batch
currently uses 2 of these:

@table @code
@item batch-port
The port on which to write lines of the batch file.
@item batch-dialect
The syntax of batch file to generate.  Currently supported are:
@itemize @bullet
@item
unix
@item
dos
@item
vms
@item
system
@item
*unknown*
@end itemize
@end table

@noindent
@file{batch.scm} uses 2 enhanced relational tables (@pxref{Database
Utilities}) to store information linking the names of
@code{operating-system}s to @code{batch-dialect}es.

@defun batch:initialize! database
Defines @code{operating-system} and @code{batch-dialect} tables and adds
the domain @code{operating-system} to the enhanced relational database
@var{database}.
@end defun

@defvar batch:platform
Is batch's best guess as to which operating-system it is running under.
@code{batch:platform} is set to @code{(software-type)}
(@pxref{Configuration}) unless @code{(software-type)} is @code{unix},
in which case finer distinctions are made.
@end defvar

@defun batch:call-with-output-script parms file proc
@var{proc} should be a procedure of one argument.  If @var{file} is an
output-port, @code{batch:call-with-output-script} writes an appropriate
header to @var{file} and then calls @var{proc} with @var{file} as the
only argument.  If @var{file} is a string,
@code{batch:call-with-output-script} opens a output-file of name
@var{file}, writes an appropriate header to @var{file}, and then calls
@var{proc} with the newly opened port as the only argument.  Otherwise,
@code{batch:call-with-output-script} acts as if it was called with the
result of @code{(current-output-port)} as its third argument.
@end defun

@defun batch:apply-chop-to-fit proc arg1 arg2 @dots{} list
The procedure @var{proc} must accept at least one argument and return
@code{#t} if successful, @code{#f} if not.
@code{batch:apply-chop-to-fit} calls @var{proc} with @var{arg1},
@var{arg2}, @dots{}, and @var{chunk}, where @var{chunk} is a subset of
@var{list}.  @code{batch:apply-chop-to-fit} tries @var{proc} with
successively smaller subsets of @var{list} until either @var{proc}
returns non-false, or the @var{chunk}s become empty.
@end defun

@noindent
The rest of the @code{batch:} procedures write (or execute if
@code{batch-dialect} is @code{system}) commands to the batch port which
has been added to @var{parms} or @code{(copy-tree @var{parms})} by the
code:

@example
(adjoin-parameters! @var{parms} (list 'batch-port @var{port}))
@end example

@defun batch:system parms string1 string2 @dots{}
Calls @code{batch:try-system} (below) with arguments, but signals an
error if @code{batch:try-system} returns @code{#f}.
@end defun

@noindent
These functions return a non-false value if the command was successfully
translated into the batch dialect and @code{#f} if not.  In the case of
the @code{system} dialect, the value is non-false if the operation
suceeded.

@defun batch:try-system parms string1 string2 @dots{}
Writes a command to the @code{batch-port} in @var{parms} which executes
the program named @var{string1} with arguments @var{string2} @dots{}.
@end defun

@defun batch:run-script parms string1 string2 @dots{}
Writes a command to the @code{batch-port} in @var{parms} which executes
the batch script named @var{string1} with arguments @var{string2}
@dots{}.

@emph{Note:} @code{batch:run-script} and @code{batch:try-system} are not the
same for some operating systems (VMS).
@end defun

@defun batch:comment parms line1 @dots{}
Writes comment lines @var{line1} @dots{} to the @code{batch-port} in
@var{parms}.
@end defun

@defun batch:lines->file parms file line1 @dots{}
Writes commands to the @code{batch-port} in @var{parms} which create a
file named @var{file} with contents @var{line1} @dots{}.
@end defun

@defun batch:delete-file parms file
Writes a command to the @code{batch-port} in @var{parms} which deletes
the file named @var{file}.
@end defun

@defun batch:rename-file parms old-name new-name
Writes a command to the @code{batch-port} in @var{parms} which renames
the file @var{old-name} to @var{new-name}.
@end defun

@noindent
In addition, batch provides some small utilities very useful for writing
scripts:

@defun replace-suffix str old new
Returns a new string similar to @code{str} but with the suffix string
@var{old} removed and the suffix string @var{new} appended.  If the end
of @var{str} does not match @var{old}, an error is signaled.
@end defun

@defun string-join joiner string1 @dots{}
Returns a new string consisting of all the strings @var{string1} @dots{}
in order appended together with the string @var{joiner} between each
adjacent pair.
@end defun

@defun must-be-first list1 list2
Returns a new list consisting of the elements of @var{list2} ordered so
that if some elements of @var{list1} are @code{equal?} to elements of
@var{list2}, then those elements will appear first and in the order of
@var{list1}.
@end defun

@defun must-be-last list1 list2
Returns a new list consisting of the elements of @var{list1} ordered so
that if some elements of @var{list2} are @code{equal?} to elements of
@var{list1}, then those elements will appear last and in the order of
@var{list2}.
@end defun

@defun os->batch-dialect osname
Returns its best guess for the @code{batch-dialect} to be used for the
operating-system named @var{osname}.  @code{os->batch-dialect} uses the
tables added to @var{database} by @code{batch:initialize!}.
@end defun

@noindent
Here is an example of the use of most of batch's procedures:

@example
(require 'database-utilities)
(require 'parameters)
(require 'batch)

(define batch (create-database #f 'alist-table))
(batch:initialize! batch)

(define my-parameters
  (list (list 'batch-dialect (os->batch-dialect batch:platform))
        (list 'platform batch:platform)
        (list 'batch-port (current-output-port)))) ;gets filled in later

(batch:call-with-output-script
 my-parameters
 "my-batch"
 (lambda (batch-port)
   (adjoin-parameters! my-parameters (list 'batch-port batch-port))
   (and
    (batch:comment my-parameters
                   "================ Write file with C program.")
    (batch:rename-file my-parameters "hello.c" "hello.c~")
    (batch:lines->file my-parameters "hello.c"
                       "#include <stdio.h>"
                       "int main(int argc, char **argv)"
                       "@{"
                       "  printf(\"hello world\\n\");"
                       "  return 0;"
                       "@}" )
    (batch:system my-parameters "cc" "-c" "hello.c")
    (batch:system my-parameters "cc" "-o" "hello"
                  (replace-suffix "hello.c" ".c" ".o"))
    (batch:system my-parameters "hello")
    (batch:delete-file my-parameters "hello")
    (batch:delete-file my-parameters "hello.c")
    (batch:delete-file my-parameters "hello.o")
    (batch:delete-file my-parameters "my-batch")
    )))
@end example

@noindent
Produces the file @file{my-batch}:

@example
#!/bin/sh
# "my-batch" build script created Sat Jun 10 21:20:37 1995
# ================ Write file with C program.
mv -f hello.c hello.c~
rm -f hello.c
echo '#include <stdio.h>'>>hello.c
echo 'int main(int argc, char **argv)'>>hello.c
echo '@{'>>hello.c
echo '  printf("hello world\n");'>>hello.c
echo '  return 0;'>>hello.c
echo '@}'>>hello.c
cc -c hello.c
cc -o hello hello.o
hello
rm -f hello
rm -f hello.c
rm -f hello.o
rm -f my-batch
@end example

@noindent
When run, @file{my-batch} prints:

@example
bash$ my-batch
mv: hello.c: No such file or directory
hello world
@end example


@node Common List Functions, Format, Batch, Procedures
@section Common List Functions

@code{(require 'common-list-functions)}

The procedures below follow the Common LISP equivalents apart from
optional arguments in some cases.

@menu
* List construction::           
* Lists as sets::               
* Lists as sequences::          
* Destructive list operations::  
* Non-List functions::          
@end menu


@node List construction, Lists as sets, Common List Functions, Common List Functions
@subsection List construction

@defun make-list k . init
@code{make-list} creates and returns a list of @var{k} elements.  If
@var{init} is included, all elements in the list are initialized to
@var{init}.@refill

Example:
@lisp
(make-list 3)
   @result{} (#<unspecified> #<unspecified> #<unspecified>)
(make-list 5 'foo)
   @result{} (foo foo foo foo foo)
@end lisp
@end defun


@defun list* x . y
Works like @code{list} except that the cdr of the last pair is the last
argument unless there is only one argument, when the result is just that
argument.  Sometimes called @code{cons*}.  E.g.:@refill
@lisp
(list* 1)
   @result{} 1
(list* 1 2 3)
   @result{} (1 2 . 3)
(list* 1 2 '(3 4))
   @result{} (1 2 3 4)
(list* @var{args} '())
   @equiv{} (list @var{args})
@end lisp
@end defun

@defun copy-list lst
@code{copy-list} makes a copy of @var{lst} using new pairs and returns
it. Only the top level of the list is copied, i.e., pairs forming
elements of the copied list remain @code{eq?} to the corresponding
elements of the original; the copy is, however, not @code{eq?} to the
original, but is @code{equal?} to it.@refill

Example:
@lisp
(copy-list '(foo foo foo))
   @result{} (foo foo foo)
(define q '(foo bar baz bang))
(define p q)
(eq? p q)
   @result{} #t
(define r (copy-list q))
(eq? q r)
   @result{} #f
(equal? q r)
   @result{} #t
(define bar '(bar))
(eq? bar (car (copy-list (list bar 'foo))))
@result{} #t
   @end lisp
@end defun






@node Lists as sets, Lists as sequences, List construction, Common List Functions
@subsection Lists as sets

@code{eq?} is used to test for membership by all the procedures below
which treat lists as sets.@refill

@defun adjoin e l
@code{adjoin} returns the adjoint of the element @var{e} and the list
@var{l}.  That is, if @var{e} is in @var{l}, @code{adjoin} returns
@var{l}, otherwise, it returns @code{(cons @var{e} @var{l})}.@refill

Example:
@lisp
(adjoin 'baz '(bar baz bang))
   @result{} (bar baz bang)
(adjoin 'foo '(bar baz bang))
   @result{} (foo bar baz bang)
@end lisp
@end defun

@defun union l1 l2
@code{union} returns the combination of @var{l1} and @var{l2}.
Duplicates between @var{l1} and @var{l2} are culled.  Duplicates within
@var{l1} or within @var{l2} may or may not be removed.@refill

Example:
@lisp
(union '(1 2 3 4) '(5 6 7 8))
   @result{} (4 3 2 1 5 6 7 8)
(union '(1 2 3 4) '(3 4 5 6))
   @result{} (2 1 3 4 5 6)
@end lisp
@end defun

@defun intersection l1 l2
@code{intersection} returns all elements that are in both @var{l1} and
@var{l2}.@refill

Example:
@lisp
(intersection '(1 2 3 4) '(3 4 5 6))
   @result{} (3 4)
(intersection '(1 2 3 4) '(5 6 7 8))
   @result{} ()
@end lisp
@end defun

@defun set-difference l1 l2
@code{set-difference} returns the union of all elements that are in
@var{l1} but not in @var{l2}.@refill

Example:
@lisp
(set-difference '(1 2 3 4) '(3 4 5 6))
   @result{} (1 2)
(set-difference '(1 2 3 4) '(1 2 3 4 5 6))
   @result{} ()
@end lisp
@end defun

@defun member-if pred lst
@code{member-if} returns @var{lst} if @code{(@var{pred} @var{element})}
is @code{#t} for any @var{element} in @var{lst}.  Returns @code{#f} if
@var{pred} does not apply to any @var{element} in @var{lst}.@refill

Example:
@lisp
(member-if vector? '(1 2 3 4))
   @result{} #f
(member-if number? '(1 2 3 4))
   @result{} (1 2 3 4)
@end lisp
@end defun

@defun some pred lst . more-lsts
@var{pred} is a boolean function of as many arguments as there are list
arguments to @code{some} i.e., @var{lst} plus any optional arguments.
@var{pred} is applied to successive elements of the list arguments in
order.  @code{some} returns @code{#t} as soon as one of these
applications returns @code{#t}, and is @code{#f} if none returns
@code{#t}.  All the lists should have the same length.@refill


Example:
@lisp
(some odd? '(1 2 3 4))
   @result{} #t

(some odd? '(2 4 6 8))
   @result{} #f

(some > '(2 3) '(1 4))
   @result{} #f
@end lisp
@end defun

@defun every pred lst . more-lsts
@code{every} is analogous to @code{some} except it returns @code{#t} if
every application of @var{pred} is @code{#t} and @code{#f}
otherwise.@refill

Example:
@lisp
(every even? '(1 2 3 4))
   @result{} #f

(every even? '(2 4 6 8))
   @result{} #t

(every > '(2 3) '(1 4))
   @result{} #f
@end lisp
@end defun

@defun notany pred . lst
@code{notany} is analogous to @code{some} but returns @code{#t} if no
application of @var{pred} returns @code{#t} or @code{#f} as soon as any
one does.@refill
@end defun

@defun notevery pred . lst
@code{notevery} is analogous to @code{some} but returns @code{#t} as soon
as an application of @var{pred} returns @code{#f}, and @code{#f}
otherwise.@refill

Example:
@lisp
(notevery even? '(1 2 3 4))
   @result{} #t

(notevery even? '(2 4 6 8))
   @result{} #f
@end lisp
@end defun

@defun find-if pred lst
@code{find-if} searches for the first @var{element} in @var{lst} such
that @code{(@var{pred} @var{element})} returns @code{#t}.  If it finds
any such @var{element} in @var{lst}, @var{element} is returned.
Otherwise, @code{#f} is returned.@refill

Example:
@lisp
(find-if number? '(foo 1 bar 2))
   @result{} 1

(find-if number? '(foo bar baz bang))
   @result{} #f

(find-if symbol? '(1 2 foo bar))
   @result{} foo
@end lisp
@end defun

@defun remove elt lst
@code{remove} removes all occurrences of @var{elt} from @var{lst} using
@code{eqv?} to test for equality and returns everything that's left.
N.B.: other implementations (Chez, Scheme->C and T, at least) use
@code{equal?} as the equality test.@refill

Example:
@lisp
(remove 1 '(1 2 1 3 1 4 1 5))
   @result{} (2 3 4 5)

(remove 'foo '(bar baz bang))
   @result{} (bar baz bang)
@end lisp
@end defun

@defun remove-if pred lst
@code{remove-if} removes all @var{element}s from @var{lst} where
@code{(@var{pred} @var{element})} is @code{#t} and returns everything
that's left.@refill

Example:
@lisp
(remove-if number? '(1 2 3 4))
   @result{} ()

(remove-if even? '(1 2 3 4 5 6 7 8))
   @result{} (1 3 5 7)
@end lisp
@end defun

@defun remove-if-not pred lst
@code{remove-if-not} removes all @var{element}s from @var{lst} for which
@code{(@var{pred} @var{element})} is @code{#f} and returns everything that's
left.@refill

Example:
@lisp
(remove-if-not number? '(foo bar baz))
   @result{} ()
(remove-if-not odd? '(1 2 3 4 5 6 7 8))
   @result{} (1 3 5 7)
@end lisp
@end defun

@defun has-duplicates? lst
returns @code{#t} if 2 members of @var{lst} are @code{equal?}, @code{#f}
otherwise.
Example:
@lisp
(has-duplicates? '(1 2 3 4))
   @result{} #f

(has-duplicates? '(2 4 3 4))
   @result{} #t
@end lisp
@end defun


@node Lists as sequences, Destructive list operations, Lists as sets, Common List Functions
@subsection Lists as sequences

@defun position obj lst
@code{position} returns the 0-based position of @var{obj} in @var{lst},
or @code{#f} if @var{obj} does not occur in @var{lst}.@refill

Example:
@lisp
(position 'foo '(foo bar baz bang))
   @result{} 0
(position 'baz '(foo bar baz bang))
   @result{} 2
(position 'oops '(foo bar baz bang))
   @result{} #f
@end lisp
@end defun

@defun reduce p lst
@code{reduce} combines all the elements of a sequence using a binary
operation (the combination is left-associative).  For example, using
@code{+}, one can add up all the elements.  @code{reduce} allows you to
apply a function which accepts only two arguments to more than 2
objects.  Functional programmers usually refer to this as @dfn{foldl}.
@code{collect:reduce} (@xref{Collections}) provides a version of
@code{collect} generalized to collections.@refill

Example:
@lisp
(reduce + '(1 2 3 4))
   @result{} 10
(define (bad-sum . l) (reduce + l))
(bad-sum 1 2 3 4)
   @equiv{} (reduce + (1 2 3 4))
   @equiv{} (+ (+ (+ 1 2) 3) 4)
@result{} 10
(bad-sum)
   @equiv{} (reduce + ())
   @result{} ()
(reduce string-append '("hello" "cruel" "world"))
   @equiv{} (string-append (string-append "hello" "cruel") "world")
   @result{} "hellocruelworld"
(reduce anything '())
   @result{} ()
(reduce anything '(x))
   @result{} x
@end lisp

What follows is a rather non-standard implementation of @code{reverse}
in terms of @code{reduce} and a combinator elsewhere called
@dfn{C}.@refill

@lisp
;;; Contributed by Jussi Piitulainen (jpiitula@@ling.helsinki.fi)

(define commute
  (lambda (f)
    (lambda (x y)
      (f y x))))

(define reverse
  (lambda (args)
    (reduce-init (commute cons) args)))
@end lisp
@end defun

@defun reduce-init p init lst
@code{reduce-init} is the same as reduce, except that it implicitly
inserts @var{init} at the start of the list.  @code{reduce-init} is
preferred if you want to handle the null list, the one-element, and
lists with two or more elements consistently.  It is common to use the
operator's idempotent as the initializer.  Functional programmers
usually call this @dfn{foldl}.@refill

Example:
@lisp
(define (sum . l) (reduce-init + 0 l))
(sum 1 2 3 4)
   @equiv{} (reduce-init + 0 (1 2 3 4))
   @equiv{} (+ (+ (+ (+ 0 1) 2) 3) 4)
   @result{} 10
(sum)
   @equiv{} (reduce-init + 0 '())
   @result{} 0

(reduce-init string-append "@@" '("hello" "cruel" "world"))
@equiv{}
(string-append (string-append (string-append "@@" "hello")
                               "cruel")
               "world")
@result{} "@@hellocruelworld"
@end lisp

Given a differentiation of 2 arguments, @code{diff}, the following will
differentiate by any number of variables.
@lisp
(define (diff* exp . vars)
  (reduce-init diff exp vars))
@end lisp

Example:
@lisp
;;; Real-world example:  Insertion sort using reduce-init.

(define (insert l item)
  (if (null? l)
      (list item)
      (if (< (car l) item)
          (cons (car l) (insert (cdr l) item))
          (cons item l))))
(define (insertion-sort l) (reduce-init insert '() l))

(insertion-sort '(3 1 4 1 5)
   @equiv{} (reduce-init insert () (3 1 4 1 5))
   @equiv{} (insert (insert (insert (insert (insert () 3) 1) 4) 1) 5)
   @equiv{} (insert (insert (insert (insert (3)) 1) 4) 1) 5)
   @equiv{} (insert (insert (insert (1 3) 4) 1) 5)
   @equiv{} (insert (insert (1 3 4) 1) 5)
   @equiv{} (insert (1 1 3 4) 5)
   @result{} (1 1 3 4 5)
   @end lisp
@end defun

@defun butlast lst n
@code{butlast} returns all but the last @var{n} elements of
@var{lst}.@refill

Example:
@lisp
(butlast '(1 2 3 4) 3)
   @result{} (1)
(butlast '(1 2 3 4) 4)
   @result{} ()
@end lisp
@end defun

@defun nthcdr n lst
@code{nthcdr} takes @var{n} @code{cdr}s of @var{lst} and returns the
result.  Thus @code{(nthcdr 3 @var{lst})} @equiv{} @code{(cdddr
@var{lst})}

Example:
@lisp
(nthcdr 2 '(1 2 3 4))
   @result{} (3 4)
(nthcdr 0 '(1 2 3 4))
   @result{} (1 2 3 4)
@end lisp
@end defun

@defun last lst n
@code{last} returns the last @var{n} elements of @var{lst}.  @var{n}
must be a non-negative integer.

Example:
@lisp
(last '(foo bar baz bang) 2)
   @result{} (baz bang)
(last '(1 2 3) 0)
   @result{} 0
@end lisp
@end defun






@node Destructive list operations, Non-List functions, Lists as sequences, Common List Functions
@subsection Destructive list operations

These procedures may mutate the list they operate on, but any such
mutation is undefined.

@deffn Procedure nconc args
@code{nconc} destructively concatenates its arguments.  (Compare this
with @code{append}, which copies arguments rather than destroying them.)
Sometimes called @code{append!} (@xref{Rev2 Procedures}).@refill

Example:  You want to find the subsets of a set.  Here's the obvious way:

@lisp
(define (subsets set)
  (if (null? set)
      '(())
      (append (mapcar (lambda (sub) (cons (car set) sub))
                      (subsets (cdr set)))
              (subsets (cdr set)))))
@end lisp
But that does way more consing than you need.  Instead, you could
replace the @code{append} with @code{nconc}, since you don't have any
need for all the intermediate results.@refill

Example:
@lisp
(define x '(a b c))
(define y '(d e f))
(nconc x y)
   @result{} (a b c d e f)
x
   @result{} (a b c d e f)
@end lisp

@code{nconc} is the same as @code{append!} in @file{sc2.scm}.
@end deffn

@deffn Procedure nreverse lst
@code{nreverse} reverses the order of elements in @var{lst} by mutating
@code{cdr}s of the list.  Sometimes called @code{reverse!}.@refill

Example:
@lisp
(define foo '(a b c))
(nreverse foo)
   @result{} (c b a)
foo
   @result{} (a)
@end lisp

Some people have been confused about how to use @code{nreverse},
thinking that it doesn't return a value.  It needs to be pointed out
that@refill
@lisp
(set! lst (nreverse lst))
@end lisp
@noindent
is the proper usage, not
@lisp
(nreverse lst)
@end lisp
The example should suffice to show why this is the case.
@end deffn

@deffn Procedure delete elt lst
@deffnx Procedure delete-if pred lst
@deffnx Procedure delete-if-not pred lst
Destructive versions of @code{remove} @code{remove-if}, and
@code{remove-if-not}.@refill

Example:
@lisp
(define lst '(foo bar baz bang))
(delete 'foo lst)
   @result{} (bar baz bang)
lst
   @result{} (foo bar baz bang)

(define lst '(1 2 3 4 5 6 7 8 9))
(delete-if odd? lst)
   @result{} (2 4 6 8)
lst
   @result{} (1 2 4 6 8)
@end lisp

Some people have been confused about how to use @code{delete},
@code{delete-if}, and @code{delete-if}, thinking that they dont' return
a value.  It needs to be pointed out that@refill
@lisp
(set! lst (delete el lst))
@end lisp
@noindent
is the proper usage, not
@lisp
(delete el lst)
@end lisp
The examples should suffice to show why this is the case.
@end deffn



@node Non-List functions,  , Destructive list operations, Common List Functions
@subsection Non-List functions

@defun and? . args
@code{and?} checks to see if all its arguments are true.  If they are,
@code{and?} returns @code{#t}, otherwise, @code{#f}.  (In contrast to
@code{and}, this is a function, so all arguments are always evaluated
and in an unspecified order.)@refill

Example:
@lisp
(and? 1 2 3)
   @result{} #t
(and #f 1 2)
   @result{} #f
@end lisp
@end defun

@defun or? . args
@code{or?} checks to see if any of its arguments are true.  If any is
true, @code{or?} returns @code{#t}, and @code{#f} otherwise.  (To
@code{or} as @code{and?} is to @code{and}.)@refill

Example:
@lisp
(or? 1 2 #f)
   @result{} #t
(or? #f #f #f)
   @result{} #f
@end lisp
@end defun

@defun atom? object
Returns @code{#t} if @var{object} is not a pair and @code{#f} if it is
pair.  (Called @code{atom} in Common LISP.)
@lisp
(atom? 1)
   @result{} #t
(atom? '(1 2))
   @result{} #f
(atom? #(1 2))   ; dubious!
   @result{} #t
@end lisp
@end defun

@defun type-of object
Returns a symbol name for the type of @var{object}.
@end defun

@defun coerce object result-type
Converts and returns @var{object} of type @code{char}, @code{number},
@code{string}, @code{symbol}, @code{list}, or @code{vector} to
@var{result-type} (which must be one of these symbols).
@end defun

@node Format, Generic-Write, Common List Functions, Procedures
@section Format

@code{(require 'format)}

@menu
* Format Interface::            
* Format Specification::        
@end menu

@node Format Interface, Format Specification, Format, Format
@subsection Format Interface

@defun format destination format-string . arguments
An almost complete implementation of Common LISP format description
according to the CL reference book @cite{Common LISP} from Guy L.
Steele, Digital Press.  Backward compatible to most of the available
Scheme format implementations.

Returns @code{#t}, @code{#f} or a string; has side effect of printing
according to @var{format-string}.  If @var{destination} is @code{#t},
the output is to the current output port and @code{#t} is returned.  If
@var{destination} is @code{#f}, a formatted string is returned as the
result of the call.  NEW: If @var{destination} is a string,
@var{destination} is regarded as the format string; @var{format-string} is
then the first argument and the output is returned as a string. If
@var{destination} is a number, the output is to the current error port
if available by the implementation. Otherwise @var{destination} must be
an output port and @code{#t} is returned.@refill

@var{format-string} must be a string.  In case of a formatting error
format returns @code{#f} and prints a message on the current output or
error port.  Characters are output as if the string were output by the
@code{display} function with the exception of those prefixed by a tilde
(~).  For a detailed description of the @var{format-string} syntax
please consult a Common LISP format reference manual.  For a test suite
to verify this format implementation load @file{formatst.scm}. Please
send bug reports to @code{lutzeb@@cs.tu-berlin.de}.

Note: @code{format} is not reentrant, i.e. only one @code{format}-call
may be executed at a time.

@end defun

@node Format Specification,  , Format Interface, Format
@subsection Format Specification (Format version 3.0)

Please consult a Common LISP format reference manual for a detailed
description of the format string syntax.  For a demonstration of the
implemented directives see @file{formatst.scm}.@refill

This implementation supports directive parameters and modifiers
(@code{:} and @code{@@} characters). Multiple parameters must be
separated by a comma (@code{,}).  Parameters can be numerical parameters
(positive or negative), character parameters (prefixed by a quote
character (@code{'}), variable parameters (@code{v}), number of rest
arguments parameter (@code{#}), empty and default parameters.  Directive
characters are case independent. The general form of a directive
is:@refill

@noindent
@var{directive} ::= ~@{@var{directive-parameter},@}[:][@@]@var{directive-character}

@noindent
@var{directive-parameter} ::= [ [-|+]@{0-9@}+ | '@var{character} | v | # ]


@subsubsection Implemented CL Format Control Directives

Documentation syntax: Uppercase characters represent the corresponding
control directive characters. Lowercase characters represent control
directive parameter descriptions.

@table @asis
@item @code{~A}
Any (print as @code{display} does).
@table @asis
@item @code{~@@A}
left pad.
@item @code{~@var{mincol},@var{colinc},@var{minpad},@var{padchar}A}
full padding.
@end table
@item @code{~S}
S-expression (print as @code{write} does).
@table @asis
@item @code{~@@S}
left pad.
@item @code{~@var{mincol},@var{colinc},@var{minpad},@var{padchar}S}
full padding.
@end table
@item @code{~D}
Decimal.
@table @asis
@item @code{~@@D}
print number sign always.
@item @code{~:D}
print comma separated.
@item @code{~@var{mincol},@var{padchar},@var{commachar}D}
padding.
@end table
@item @code{~X}
Hexadecimal.
@table @asis
@item @code{~@@X}
print number sign always.
@item @code{~:X}
print comma separated.
@item @code{~@var{mincol},@var{padchar},@var{commachar}X}
padding.
@end table
@item @code{~O}
Octal.
@table @asis
@item @code{~@@O}
print number sign always.
@item @code{~:O}
print comma separated.
@item @code{~@var{mincol},@var{padchar},@var{commachar}O}
padding.
@end table
@item @code{~B}
Binary.
@table @asis
@item @code{~@@B}
print number sign always.
@item @code{~:B}
print comma separated.
@item @code{~@var{mincol},@var{padchar},@var{commachar}B}
padding.
@end table
@item @code{~@var{n}R}
Radix @var{n}.
@table @asis
@item @code{~@var{n},@var{mincol},@var{padchar},@var{commachar}R}
padding.
@end table
@item @code{~@@R}
print a number as a Roman numeral.
@item @code{~:R}
print a number as an ordinal English number.
@item @code{~:@@R}
print a number as a cardinal English number.
@item @code{~P}
Plural.
@table @asis
@item @code{~@@P}
prints @code{y} and @code{ies}.
@item @code{~:P}
as @code{~P but jumps 1 argument backward.}
@item @code{~:@@P}
as @code{~@@P but jumps 1 argument backward.}
@end table
@item @code{~C}
Character.
@table @asis
@item @code{~@@C}
prints a character as the reader can understand it (i.e. @code{#\} prefixing).
@item @code{~:C}
prints a character as emacs does (eg. @code{^C} for ASCII 03).
@end table
@item @code{~F}
Fixed-format floating-point (prints a flonum like @var{mmm.nnn}).
@table @asis
@item @code{~@var{width},@var{digits},@var{scale},@var{overflowchar},@var{padchar}F}
@item @code{~@@F}
If the number is positive a plus sign is printed.
@end table
@item @code{~E}
Exponential floating-point (prints a flonum like @var{mmm.nnn@code{E}ee}).
@table @asis
@item @code{~@var{width},@var{digits},@var{exponentdigits},@var{scale},@var{overflowchar},@var{padchar},@var{exponentchar}E}
@item @code{~@@E}
If the number is positive a plus sign is printed.
@end table
@item @code{~G}
General floating-point (prints a flonum either fixed or exponential).
@table @asis
@item @code{~@var{width},@var{digits},@var{exponentdigits},@var{scale},@var{overflowchar},@var{padchar},@var{exponentchar}G}
@item @code{~@@G}
If the number is positive a plus sign is printed.
@end table
@item @code{~$}
Dollars floating-point (prints a flonum in fixed with signs separated).
@table @asis
@item @code{~@var{digits},@var{scale},@var{width},@var{padchar}$}
@item @code{~@@$}
If the number is positive a plus sign is printed.
@item @code{~:@@$}
A sign is always printed and appears before the padding.
@item @code{~:$}
The sign appears before the padding.
@end table
@item @code{~%}
Newline.
@table @asis
@item @code{~@var{n}%}
print @var{n} newlines.
@end table
@item @code{~&}
print newline if not at the beginning of the output line.
@table @asis
@item @code{~@var{n}&}
prints @code{~&} and then @var{n-1} newlines.
@end table
@item @code{~|}
Page Separator.
@table @asis
@item @code{~@var{n}|}
print @var{n} page separators.
@end table
@item @code{~~}
Tilde.
@table @asis
@item @code{~@var{n}~}
print @var{n} tildes.
@end table
@item @code{~}<newline>
Continuation Line.
@table @asis
@item @code{~:}<newline>
newline is ignored, white space left.
@item @code{~@@}<newline>
newline is left, white space ignored.
@end table
@item @code{~T}
Tabulation.
@table @asis
@item @code{~@@T}
relative tabulation.
@item @code{~@var{colnum,colinc}T}
full tabulation.
@end table
@item @code{~?}
Indirection (expects indirect arguments as a list).
@table @asis
@item @code{~@@?}
extracts indirect arguments from format arguments.
@end table
@item @code{~(@var{str}~)}
Case conversion (converts by @code{string-downcase}).
@table @asis
@item @code{~:(@var{str}~)}
converts by @code{string-capitalize}.
@item @code{~@@(@var{str}~)}
converts by @code{string-capitalize-first}.
@item @code{~:@@(@var{str}~)}
converts by @code{string-upcase}.
@end table
@item @code{~*}
Argument Jumping (jumps 1 argument forward).
@table @asis
@item @code{~@var{n}*}
jumps @var{n} arguments forward.
@item @code{~:*}
jumps 1 argument backward.
@item @code{~@var{n}:*}
jumps @var{n} arguments backward.
@item @code{~@@*}
jumps to the 0th argument.
@item @code{~@var{n}@@*}
jumps to the @var{n}th argument (beginning from 0)
@end table
@item @code{~[@var{str0}~;@var{str1}~;...~;@var{strn}~]}
Conditional Expression (numerical clause conditional).
@table @asis
@item @code{~@var{n}[}
take argument from @var{n}.
@item @code{~@@[}
true test conditional.
@item @code{~:[}
if-else-then conditional.
@item @code{~;}
clause separator.
@item @code{~:;}
default clause follows.
@end table
@item @code{~@{@var{str}~@}}
Iteration (args come from the next argument (a list)).
@table @asis
@item @code{~@var{n}@{}
at most @var{n} iterations.
@item @code{~:@{}
args from next arg (a list of lists).
@item @code{~@@@{}
args from the rest of arguments.
@item @code{~:@@@{}
args from the rest args (lists).
@end table
@item @code{~^}
Up and out.
@table @asis
@item @code{~@var{n}^}
aborts if @var{n} = 0
@item @code{~@var{n},@var{m}^}
aborts if @var{n} = @var{m}
@item @code{~@var{n},@var{m},@var{k}^}
aborts if @var{n} <= @var{m} <= @var{k}
@end table
@end table


@subsubsection Not Implemented CL Format Control Directives

@table @asis
@item @code{~:A}
print @code{#f} as an empty list (see below).
@item @code{~:S}
print @code{#f} as an empty list (see below).
@item @code{~<~>}
Justification.
@item @code{~:^}
(sorry I don't understand its semantics completely)
@end table


@subsubsection Extended, Replaced and Additional Control Directives

@table @asis
@item @code{~@var{mincol},@var{padchar},@var{commachar},@var{commawidth}D}
@item @code{~@var{mincol},@var{padchar},@var{commachar},@var{commawidth}X}
@item @code{~@var{mincol},@var{padchar},@var{commachar},@var{commawidth}O}
@item @code{~@var{mincol},@var{padchar},@var{commachar},@var{commawidth}B}
@item @code{~@var{n},@var{mincol},@var{padchar},@var{commachar},@var{commawidth}R}
@var{commawidth} is the number of characters between two comma characters.
@end table

@table @asis
@item @code{~I}
print a R4RS complex number as @code{~F~@@Fi} with passed parameters for
@code{~F}.
@item @code{~Y}
Pretty print formatting of an argument for scheme code lists.
@item @code{~K}
Same as @code{~?.}
@item @code{~!}
Flushes the output if format @var{destination} is a port.
@item @code{~_}
Print a @code{#\space} character
@table @asis
@item @code{~@var{n}_}
print @var{n} @code{#\space} characters.
@end table
@item @code{~/}
Print a @code{#\tab} character
@table @asis
@item @code{~@var{n}/}
print @var{n} @code{#\tab} characters.
@end table
@item @code{~@var{n}C}
Takes @var{n} as an integer representation for a character. No arguments
are consumed. @var{n} is converted to a character by
@code{integer->char}.  @var{n} must be a positive decimal number.@refill
@item @code{~:S}
Print out readproof.  Prints out internal objects represented as
@code{#<...>} as strings @code{"#<...>"} so that the format output can always
be processed by @code{read}.
@refill
@item @code{~:A}
Print out readproof.  Prints out internal objects represented as
@code{#<...>} as strings @code{"#<...>"} so that the format output can always
be processed by @code{read}.
@item @code{~Q}
Prints information and a copyright notice on the format implementation.
@table @asis
@item @code{~:Q}
prints format version.
@end table
@refill
@item @code{~F, ~E, ~G, ~$}
may also print number strings, i.e. passing a number as a string and
format it accordingly.
@end table

@subsubsection Configuration Variables

Format has some configuration variables at the beginning of
@file{format.scm} to suit the systems and users needs. There should be
no modification necessary for the configuration that comes with SLIB.
If modification is desired the variable should be set after the format
code is loaded. Format detects automatically if the running scheme
system implements floating point numbers and complex numbers.

@table @asis

@item @var{format:symbol-case-conv}
Symbols are converted by @code{symbol->string} so the case type of the
printed symbols is implementation dependent.
@code{format:symbol-case-conv} is a one arg closure which is either
@code{#f} (no conversion), @code{string-upcase}, @code{string-downcase}
or @code{string-capitalize}. (default @code{#f})

@item @var{format:iobj-case-conv}
As @var{format:symbol-case-conv} but applies for the representation of
implementation internal objects. (default @code{#f})

@item @var{format:expch}
The character prefixing the exponent value in @code{~E} printing. (default
@code{#\E})

@end table

@subsubsection Compatibility With Other Format Implementations

@table @asis
@item SLIB format 2.x:
See @file{format.doc}.

@item SLIB format 1.4:
Downward compatible except for padding support and @code{~A}, @code{~S},
@code{~P}, @code{~X} uppercase printing.  SLIB format 1.4 uses C-style
@code{printf} padding support which is completely replaced by the CL
@code{format} padding style.

@item MIT C-Scheme 7.1:
Downward compatible except for @code{~}, which is not documented
(ignores all characters inside the format string up to a newline
character).  (7.1 implements @code{~a}, @code{~s},
~@var{newline}, @code{~~}, @code{~%}, numerical and variable
parameters and @code{:/@@} modifiers in the CL sense).@refill

@item Elk 1.5/2.0:
Downward compatible except for @code{~A} and @code{~S} which print in
uppercase.  (Elk implements @code{~a}, @code{~s}, @code{~~}, and
@code{~%} (no directive parameters or modifiers)).@refill

@item Scheme->C 01nov91:
Downward compatible except for an optional destination parameter: S2C
accepts a format call without a destination which returns a formatted
string. This is equivalent to a #f destination in S2C. (S2C implements
@code{~a}, @code{~s}, @code{~c}, @code{~%}, and @code{~~} (no directive
parameters or modifiers)).@refill

@end table

This implementation of format is solely useful in the SLIB context
because it requires other components provided by SLIB.@refill


@node Generic-Write, Line I/O, Format, Procedures
@section Generic-Write

@code{(require 'generic-write)}

@code{generic-write} is a procedure that transforms a Scheme data value
(or Scheme program expression) into its textual representation and
prints it.  The interface to the procedure is sufficiently general to
easily implement other useful formatting procedures such as pretty
printing, output to a string and truncated output.@refill

@deffn Procedure generic-write obj display? width output
@table @var
@item obj
Scheme data value to transform.
@item display?
Boolean, controls whether characters and strings are quoted.
@item width
Extended boolean, selects format:
@table @asis
@item #f
single line format
@item integer > 0
pretty-print (value = max nb of chars per line)
@end table
@item output
Procedure of 1 argument of string type, called repeatedly with
successive substrings of the textual representation.  This procedure can
return @code{#f} to stop the transformation.
@end table

The value returned by @code{generic-write} is undefined.

Examples:
@lisp
(write obj) @equiv{} (generic-write obj #f #f @var{display-string})
(display obj) @equiv{} (generic-write obj #t #f @var{display-string})
@end lisp
@noindent
where
@lisp
@var{display-string} @equiv{}
(lambda (s) (for-each write-char (string->list s)) #t)
@end lisp
@end deffn





@node Line I/O, Multi-Processing, Generic-Write, Procedures
@section Line I/O

@code{(require 'line-i/o)}

@defun read-line
@defunx read-line port
Returns a string of the characters up to, but not including a newline or
end of file, updating @var{port} to point to the character following the
newline.  If no characters are available, an end of file object is
returned.  @var{port} may be omitted, in which case it defaults to the
value returned by @code{current-input-port}.@refill
@end defun

@defun read-line! string
@defunx read-line! string port
Fills @var{string} with characters up to, but not including a newline or
end of file, updating the port to point to the last character read or
following the newline if it was read.  If no characters are available,
an end of file object is returned.  If a newline or end of file was
found, the number of characters read is returned.  Otherwise, @code{#f}
is returned.  @var{port} may be omitted, in which case it defaults to
the value returned by @code{current-input-port}.@refill
@end defun

@defun write-line string
@defunx write-line string port
Writes @var{string} followed by a newline to the given port and returns
an unspecified value.  Port may be omited, in which case it defaults to
the value returned by @code{current-input-port}.@refill
@end defun




@node Multi-Processing, Object-To-String, Line I/O, Procedures
@section Multi-Processing

@code{(require 'process)}

@deffn Procedure add-process! proc
Adds proc, which must be a procedure (or continuation) capable of
accepting accepting one argument, to the @code{process:queue}.  The
value returned is unspecified.  The argument to @var{proc} should be
ignored.  If @var{proc} returns, the process is killed.@refill
@end deffn

@deffn Procedure process:schedule!
Saves the current process on @code{process:queue} and runs the next
process from @code{process:queue}.  The value returned is
unspecified.@refill
@end deffn


@deffn Procedure kill-process!
Kills the current process and runs the next process from
@code{process:queue}.  If there are no more processes on
@code{process:queue}, @code{(slib:exit)} is called (@xref{System}).
@end deffn





@node Object-To-String, Pretty-Print, Multi-Processing, Procedures
@section Object-To-String

@code{(require 'object->string)}

@defun object->string obj
Returns the textual representation of @var{obj} as a string.
@end defun




@node Pretty-Print, Sorting, Object-To-String, Procedures
@section Pretty-Print

@code{(require 'pretty-print)}

@deffn Procedure pretty-print obj
@deffnx Procedure pretty-print obj port

@code{pretty-print}s @var{obj} on @var{port}.  If @var{port} is not
specified, @code{current-output-port} is used.

Example:
@example
@group
(pretty-print '((1 2 3 4 5) (6 7 8 9 10) (11 12 13 14 15)
                (16 17 18 19 20) (21 22 23 24 25)))
   @print{} ((1 2 3 4 5)
   @print{}  (6 7 8 9 10)
   @print{}  (11 12 13 14 15)
   @print{}  (16 17 18 19 20)
   @print{}  (21 22 23 24 25))
@end group
@end example
@end deffn


@code{(require 'pprint-file)}

@deffn Procedure pprint-file infile
@deffnx Procedure pprint-file infile outfile
Pretty-prints all the code in @var{infile}.  If @var{outfile} is
specified, the output goes to @var{outfile}, otherwise it goes to
@code{(current-output-port)}.@refill
@end deffn

@defun pprint-filter-file infile proc outfile
@defunx pprint-filter-file infile proc
@var{infile} is a port or a string naming an existing file.  Scheme
source code expressions and definitions are read from the port (or file)
and @var{proc} is applied to them sequentially.

@var{outfile} is a port or a string.  If no @var{outfile} is specified
then @code{current-output-port} is assumed.  These expanded expressions
are then @code{pretty-print}ed to this port.

Whitepsace and comments (introduced by @code{;}) which are not part of
scheme expressions are reproduced in the output.  This procedure does
not affect the values returned by @code{current-input-port} and
@code{current-output-port}.@refill
@end defun

@code{pprint-filter-file} can be used to pre-compile macro-expansion and
thus can reduce loading time.  The following will write into
@file{exp-code.scm} the result of expanding all defmacros in
@file{code.scm}.
@lisp
(require 'pprint-file)
(require 'defmacroexpand)
(defmacro:load "my-macros.scm")
(pprint-filter-file "code.scm" defmacro:expand* "exp-code.scm")
@end lisp


@node Sorting, Topological Sort, Pretty-Print, Procedures
@section Sorting

@code{(require 'sort)}

Many Scheme systems provide some kind of sorting functions.  They do
not, however, always provide the @emph{same} sorting functions, and
those that I have had the opportunity to test provided inefficient ones
(a common blunder is to use quicksort which does not perform well).

Because @code{sort} and @code{sort!} are not in the standard, there is
very little agreement about what these functions look like.  For
example, Dybvig says that Chez Scheme provides
@lisp
(merge predicate list1 list2)
(merge! predicate list1 list2)
(sort predicate list)
(sort! predicate list)
@end lisp
@noindent
while MIT Scheme 7.1, following Common LISP, offers unstable
@lisp
(sort list predicate)
@end lisp
@noindent
TI PC Scheme offers
@lisp
(sort! list/vector predicate?)
@end lisp
@noindent
and Elk offers
@lisp
(sort list/vector predicate?)
(sort! list/vector predicate?)
@end lisp

Here is a comprehensive catalogue of the variations I have found.

@enumerate
@item
Both @code{sort} and @code{sort!} may be provided.
@item
@code{sort} may be provided without @code{sort!}.
@item
@code{sort!} may be provided without @code{sort}.
@item
Neither may be provided.
@item
The sequence argument may be either a list or a vector.
@item
The sequence argument may only be a list.
@item
The sequence argument may only be a vector.
@item
The comparison function may be expected to behave like @code{<}.
@item
The comparison function may be expected to behave like @code{<=}.
@item
The interface may be @code{(sort predicate? sequence)}.
@item
The interface may be @code{(sort sequence predicate?)}.
@item
The interface may be @code{(sort sequence &optional (predicate? <))}.
@item
The sort may be stable.
@item
The sort may be unstable.
@end enumerate

All of this variation really does not help anybody.  A nice simple merge
sort is both stable and fast (quite a lot faster than @emph{quick} sort).

I am providing this source code with no restrictions at all on its use
(but please retain D.H.D.Warren's credit for the original idea).  You
may have to rename some of these functions in order to use them in a
system which already provides incompatible or inferior sorts.  For each
of the functions, only the top-level define needs to be edited to do
that.

I could have given these functions names which would not clash with any
Scheme that I know of, but I would like to encourage implementors to
converge on a single interface, and this may serve as a hint.  The
argument order for all functions has been chosen to be as close to
Common LISP as made sense, in order to avoid NIH-itis.

Each of the five functions has a required @emph{last} parameter which is
a comparison function.  A comparison function @code{f} is a function of
2 arguments which acts like @code{<}.  For example,@refill

@lisp
(not (f x x))
(and (f x y) (f y z)) @equiv{} (f x z)
@end lisp

The standard functions @code{<}, @code{>}, @code{char<?}, @code{char>?},
@code{char-ci<?}, @code{char-ci>?}, @code{string<?}, @code{string>?},
@code{string-ci<?}, and @code{string-ci>?} are suitable for use as
comparison functions.  Think of @code{(less? x y)} as saying when
@code{x} must @emph{not} precede @code{y}.@refill

@defun sorted? sequence less?
Returns @code{#t} when the sequence argument is in non-decreasing order
according to @var{less?} (that is, there is no adjacent pair @code{@dots{} x
y @dots{}} for which @code{(less? y x)}).@refill

Returns @code{#f} when the sequence contains at least one out-of-order
pair.  It is an error if the sequence is neither a list nor a vector.
@end defun

@defun merge list1 list2 less?
This merges two lists, producing a completely new list as result.  I
gave serious consideration to producing a Common-LISP-compatible
version.  However, Common LISP's @code{sort} is our @code{sort!} (well,
in fact Common LISP's @code{stable-sort} is our @code{sort!}, merge sort
is @emph{fast} as well as stable!) so adapting CL code to Scheme takes a
bit of work anyway.  I did, however, appeal to CL to determine the
@emph{order} of the arguments.
@end defun

@deffn Procedure merge! list1 list2 less?
Merges two lists, re-using the pairs of @var{list1} and @var{list2} to
build the result.  If the code is compiled, and @var{less?} constructs
no new pairs, no pairs at all will be allocated.  The first pair of the
result will be either the first pair of @var{list1} or the first pair of
@var{list2}, but you can't predict which.

The code of @code{merge} and @code{merge!} could have been quite a bit
simpler, but they have been coded to reduce the amount of work done per
iteration.  (For example, we only have one @code{null?} test per
iteration.)@refill
@end deffn

@defun sort sequence less?
Accepts either a list or a vector, and returns a new sequence which is
sorted.  The new sequence is the same type as the input.  Always
@code{(sorted? (sort sequence less?) less?)}.  The original sequence is
not altered in any way.  The new sequence shares its @emph{elements}
with the old one; no elements are copied.@refill
@end defun

@deffn Procedure sort! sequence less?
Returns its sorted result in the original boxes.  If the original
sequence is a list, no new storage is allocated at all.  If the original
sequence is a vector, the sorted elements are put back in the same
vector.

Some people have been confused about how to use @code{sort!}, thinking
that it doesn't return a value.  It needs to be pointed out that
@lisp
(set! slist (sort! slist <))
@end lisp
@noindent
is the proper usage, not
@lisp
(sort! slist <)
@end lisp
@end deffn

Note that these functions do @emph{not} accept a CL-style @samp{:key}
argument.  A simple device for obtaining the same expressiveness is to
define@refill
@lisp
(define (keyed less? key)
  (lambda (x y) (less? (key x) (key y))))
@end lisp
@noindent
and then, when you would have written
@lisp
(sort a-sequence #'my-less :key #'my-key)
@end lisp
@noindent
in Common LISP, just write
@lisp
(sort! a-sequence (keyed my-less? my-key))
@end lisp
@noindent
in Scheme.

@node Topological Sort, Standard Formatted I/O, Sorting, Procedures
@section Topological Sort

@code{(require 'topological-sort)} or @code{(require 'tsort)}

@noindent
The algorithm is inspired by Cormen, Leiserson and Rivest (1990)
@cite{Introduction to Algorithms}, chapter 23.

@defun tsort dag pred
@defunx topological-sort dag pred
where
@table @var
@item dag
is a list of sublists.  The car of each sublist is a vertex.  The cdr is
the adjacency list of that vertex, i.e. a list of all vertices to which
there exists an edge from the car vertex.
@item pred
is one of @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
@code{char=?}, @code{char-ci=?}, @code{string=?}, or @code{string-ci=?}.
@end table

Sort the directed acyclic graph @var{dag} so that for every edge from
vertex @var{u} to @var{v}, @var{u} will come before @var{v} in the
resulting list of vertices.

Time complexity: O (|V| + |E|)

Example (from Cormen):
@quotation
Prof. Bumstead topologically sorts his clothing when getting
dressed.  The first argument to `tsort' describes which
garments he needs to put on before others.  (For example,
Prof Bumstead needs to put on his shirt before he puts on his
tie or his belt.)  `tsort' gives the correct order of dressing:
@end quotation

@example
(require 'tsort)
(tsort '((shirt tie belt)
         (tie jacket)
         (belt jacket)
         (watch)
         (pants shoes belt)
         (undershorts pants shoes)
         (socks shoes))
       eq?)
@result{}
(socks undershorts pants shoes watch shirt belt tie jacket)
@end example
@end defun

@node Standard Formatted I/O, String-Case, Topological Sort, Procedures
@section Standard Formatted I/O

@menu
* Standard Formatted Output::   
* Standard Formatted Input::    
@end menu

@subsection stdio

@code{(require 'stdio)}

@code{require}s @code{printf} and @code{scanf} and additionally defines
the symbols:

@defvar stdin
Defined to be @code{(current-input-port)}.
@end defvar
@defvar stdout
Defined to be @code{(current-output-port)}.
@end defvar
@defvar stderr
Defined to be @code{(current-error-port)}.
@end defvar


@node Standard Formatted Output, Standard Formatted Input, Standard Formatted I/O, Standard Formatted I/O
@subsection Standard Formatted Output

@code{(require 'printf)}

@deffn Procedure printf format arg1 @dots{}
@deffnx Procedure fprintf port format arg1 @dots{}
@deffnx Procedure sprintf str format arg1 @dots{}

Each function converts, formats, and outputs its @var{arg1} @dots{}
arguments according to the control string @var{format} argument and
returns the number of characters output.

@code{printf} sends its output to the port @code{(current-output-port)}.
@code{fprintf} sends its output to the port @var{port}.  @code{sprintf}
@code{string-set!}s locations of the non-constant string argument
@var{str} to the output characters.

@quotation
@emph{Note:} sprintf should be changed to a macro so a @code{substring}
expression could be used for the @var{str} argument.
@end quotation

The string @var{format} contains plain characters which are copied to
the output stream, and conversion specifications, each of which results
in fetching zero or more of the arguments @var{arg1} @dots{}.  The
results are undefined if there are an insufficient number of arguments
for the format.  If @var{format} is exhausted while some of the
@var{arg1} @dots{} arguments remain unused, the excess @var{arg1}
@dots{} arguments are ignored.

The conversion specifications in a format string have the form:

@example
% @r{[} @var{flags} @r{]} @r{[} @var{width} @r{]} @r{[} . @var{precision} @r{]} @r{[} @var{type} @r{]} @var{conversion}
@end example

An output conversion specifications consist of an initial @samp{%}
character followed in sequence by:

@itemize @bullet
@item 
Zero or more @dfn{flag characters} that modify the normal behavior of
the conversion specification.

@table @asis
@item @samp{-}
Left-justify the result in the field.  Normally the result is
right-justified.

@item @samp{+}
For the signed @samp{%d} and @samp{%i} conversions and all inexact
conversions, prefix a plus sign if the value is positive.

@item @samp{ }
For the signed @samp{%d} and @samp{%i} conversions, if the result
doesn't start with a plus or minus sign, prefix it with a space
character instead.  Since the @samp{+} flag ensures that the result
includes a sign, this flag is ignored if both are specified.

@item @samp{#}
For inexact conversions, @samp{#} specifies that the result should
always include a decimal point, even if no digits follow it.  For the
@samp{%g} and @samp{%G} conversions, this also forces trailing zeros
after the decimal point to be printed where they would otherwise be
elided.

For the @samp{%o} conversion, force the leading digit to be @samp{0}, as
if by increasing the precision.  For @samp{%x} or @samp{%X}, prefix a
leading @samp{0x} or @samp{0X} (respectively) to the result.  This
doesn't do anything useful for the @samp{%d}, @samp{%i}, or @samp{%u}
conversions.  Using this flag produces output which can be parsed by the
@code{scanf} functions with the @samp{%i} conversion (@pxref{Standard
Formatted Input}).


@item @samp{0}
Pad the field with zeros instead of spaces.  The zeros are placed after
any indication of sign or base.  This flag is ignored if the @samp{-}
flag is also specified, or if a precision is specified for an exact
converson.
@end table

@item 
An optional decimal integer specifying the @dfn{minimum field width}.
If the normal conversion produces fewer characters than this, the field
is padded (with spaces or zeros per the @samp{0} flag) to the specified
width.  This is a @emph{minimum} width; if the normal conversion
produces more characters than this, the field is @emph{not} truncated.
@cindex minimum field width (@code{printf})

Alternatively, if the field width is @samp{*}, the next argument in the
argument list (before the actual value to be printed) is used as the
field width.  The width value must be an integer.  If the value is
negative it is as though the @samp{-} flag is set (see above) and the
absolute value is used as the field width.

@item 
An optional @dfn{precision} to specify the number of digits to be
written for numeric conversions and the maximum field width for string
conversions.  The precision is specified by a period (@samp{.}) followed
optionally by a decimal integer (which defaults to zero if omitted).
@cindex precision (@code{printf})

Alternatively, if the precision is @samp{.*}, the next argument in the
argument list (before the actual value to be printed) is used as the
precision.  The value must be an integer, and is ignored if negative.
If you specify @samp{*} for both the field width and precision, the
field width argument precedes the precision argument.  The @samp{.*}
precision is an enhancement.  C library versions may not accept this
syntax.

For the @samp{%f}, @samp{%e}, and @samp{%E} conversions, the precision
specifies how many digits follow the decimal-point character.  The
default precision is @code{6}.  If the precision is explicitly @code{0},
the decimal point character is suppressed.

For the @samp{%g} and @samp{%G} conversions, the precision specifies how
many significant digits to print.  Significant digits are the first
digit before the decimal point, and all the digits after it.  If the
precision is @code{0} or not specified for @samp{%g} or @samp{%G}, it is
treated like a value of @code{1}.  If the value being printed cannot be
expressed accurately in the specified number of digits, the value is
rounded to the nearest number that fits.

For exact conversions, if a precision is supplied it specifies the
minimum number of digits to appear; leading zeros are produced if
necessary.  If a precision is not supplied, the number is printed with
as many digits as necessary.  Converting an exact @samp{0} with an
explicit precision of zero produces no characters.

@item
An optional one of @samp{l}, @samp{h} or @samp{L}, which is ignored for
numeric conversions.  It is an error to specify these modifiers for
non-numeric conversions.

@item
A character that specifies the conversion to be applied.
@end itemize

@subsubsection Exact Conversions

@table @asis
@item @samp{d}, @samp{i}
Print an integer as a signed decimal number.  @samp{%d} and @samp{%i}
are synonymous for output, but are different when used with @code{scanf}
for input (@pxref{Standard Formatted Input}).

@item @samp{o}
Print an integer as an unsigned octal number.

@item @samp{u}
Print an integer as an unsigned decimal number.

@item @samp{x}, @samp{X}
Print an integer as an unsigned hexadecimal number.  @samp{%x} prints
using the digits @samp{0123456789abcdef}.  @samp{%X} prints using the
digits @samp{0123456789ABCDEF}.
@end table

@subsubsection Inexact Conversions
@emph{Note:} Inexact conversions are not supported yet.

@table @asis
@item @samp{f}
Print a floating-point number in fixed-point notation.

@item @samp{e}, @samp{E}
Print a floating-point number in exponential notation.  @samp{%e} prints
@samp{e} between mantissa and exponont.  @samp{%E} prints @samp{E}
between mantissa and exponont.

@item @samp{g}, @samp{G}
Print a floating-point number in either normal or exponential notation,
whichever is more appropriate for its magnitude.  @samp{%g} prints
@samp{e} between mantissa and exponont.  @samp{%G} prints @samp{E}
between mantissa and exponont.
@end table

@subsubsection Other Conversions
@table @asis
@item @samp{c}
Print a single character.  The @samp{-} flag is the only one which can
be specified.  It is an error to specify a precision.

@item @samp{s}
Print a string.  The @samp{-} flag is the only one which can be
specified.  A precision specifies the maximum number of characters to
output; otherwise all characters in the string are output.

@item @samp{a}, @samp{A}
Print a scheme expression.  The @samp{-} flag left-justifies the output.
The @samp{#} flag specifies that strings and characters should be quoted
as by @code{write} (which can be read using @code{read}); otherwise,
output is as @code{display} prints.  A precision specifies the maximum
number of characters to output; otherwise as many characters as needed
are output.

@emph{Note:} @samp{%a} and @samp{%A} are SLIB extensions.

@c @item @samp{p}
@c Print the value of a pointer.

@c @item @samp{n}
@c Get the number of characters printed so far.  @xref{Other Output Conversions}.
@c Note that this conversion specification never produces any output.

@c @item @samp{m}
@c Print the string corresponding to the value of @code{errno}.
@c (This is a GNU extension.)
@c @xref{Other Output Conversions}.

@item @samp{%}
Print a literal @samp{%} character.  No argument is consumed.  It is an
error to specifiy flags, field width, precision, or type modifiers with
@samp{%%}.
@end table
@end deffn


@node Standard Formatted Input,  , Standard Formatted Output, Standard Formatted I/O
@subsection Standard Formatted Input

@code{(require 'scanf)}

@deffn Function scanf-read-list format
@deffnx Function scanf-read-list format port
@deffnx Function scanf-read-list format string
@end deffn

@defmac scanf format arg1 @dots{}
@defmacx fscanf port format arg1 @dots{}
@defmacx sscanf str format arg1 @dots{}

Each function reads characters, interpreting them according to the
control string @var{format} argument.

@code{scanf-read-list} returns a list of the items specified as far as
the input matches @var{format}.  @code{scanf}, @code{fscanf}, and
@code{sscanf} return the number of items successfully matched and
stored.  @code{scanf}, @code{fscanf}, and @code{sscanf} also set the
location corresponding to @var{arg1} @dots{} using the methods:

@table @asis
@item symbol
@code{set!}
@item car expression
@code{set-car!}
@item cdr expression
@code{set-cdr!}
@item vector-ref expression
@code{vector-set!}
@item substring expression
@code{substring-move-left!}
@end table

The argument to a @code{substring} expression in @var{arg1} @dots{} must
be a non-constant string.  Characters will be stored starting at the
position specified by the second argument to @code{substring}.  The
number of characters stored will be limited by either the position
specified by the third argument to @code{substring} or the length of the
matched string, whichever is less.

The control string, @var{format}, contains conversion specifications and
other characters used to direct interpretation of input sequences.  The
control string contains:

@itemize @bullet
@item White-space characters (blanks, tabs, newlines, or formfeeds)
that cause input to be read (and discarded) up to the next
non-white-space character.

@item An ordinary character (not @samp{%}) that must match the next
character of the input stream.

@item Conversion specifications, consisting of the character @samp{%}, an
optional assignment suppressing character @samp{*}, an optional
numerical maximum-field width, an optional @samp{l}, @samp{h} or
@samp{L} which is ignored, and a conversion code.

@c @item The conversion specification can alternatively be prefixed by
@c the character sequence @samp{%n$} instead of the character @samp{%},
@c where @var{n} is a decimal integer in the range.  The @samp{%n$}
@c construction indicates that the value of the next input field should be
@c placed in the @var{n}th place in the return list, rather than to the next
@c unused one.  The two forms of introducing a conversion specification,
@c @samp{%} and @samp{%n$}, must not be mixed within a single format string
@c with the following exception: Skip fields (see below) can be designated
@c as @samp{%*} or @samp{%n$*}.  In the latter case, @var{n} is ignored.

@end itemize

Unless the specification contains the @samp{n} conversion character
(described below), a conversion specification directs the conversion of
the next input field.  The result of a conversion specification is
returned in the position of the corresponding argument points, unless
@samp{*} indicates assignment suppression.  Assignment suppression
provides a way to describe an input field to be skipped.  An input field
is defined as a string of characters; it extends to the next
inappropriate character or until the field width, if specified, is
exhausted.

@quotation
@emph{Note:} This specification of format strings differs from the
@cite{ANSI C} and @cite{POSIX} specifications.  In SLIB, white space
before an input field is not skipped unless white space appears before
the conversion specification in the format string.  In order to write
format strings which work identically with @cite{ANSI C} and SLIB,
prepend whitespace to all conversion specifications except @samp{[} and
@samp{c}.
@end quotation

The conversion code indicates the interpretation of the input field; For
a suppressed field, no value is returned.  The following conversion
codes are legal:

@table @asis

@item @samp{%}
A single % is expected in the input at this point; no value is returned.

@item @samp{d}, @samp{D}
A decimal integer is expected.

@item @samp{u}, @samp{U}
An unsigned decimal integer is expected.

@item @samp{o}, @samp{O}
An octal integer is expected.

@item @samp{x}, @samp{X}
A hexadecimal integer is expected.

@item @samp{i}
An integer is expected.  Returns the value of the next input item,
interpreted according to C conventions; a leading @samp{0} implies
octal, a leading @samp{0x} implies hexadecimal; otherwise, decimal is
assumed.

@item @samp{n}
Returns the total number of bytes (including white space) read by
@code{scanf}.  No input is consumed by @code{%n}.

@item @samp{f}, @samp{F}, @samp{e}, @samp{E}, @samp{g}, @samp{G}
A floating-point number is expected.  The input format for
floating-point numbers is an optionally signed string of digits,
possibly containing a radix character @samp{.}, followed by an optional
exponent field consisting of an @samp{E} or an @samp{e}, followed by an
optional @samp{+}, @samp{-}, or space, followed by an integer.

@item @samp{c}, @samp{C}
@var{Width} characters are expected.  The normal skip-over-white-space
is suppressed in this case; to read the next non-space character, use
@samp{%1s}.  If a field width is given, a string is returned; up to the
indicated number of characters is read.

@item @samp{s}, @samp{S}
A character string is expected The input field is terminated by a
white-space character.  @code{scanf} cannot read a null string.

@item @samp{[}
Indicates string data and the normal skip-over-leading-white-space is
suppressed.  The left bracket is followed by a set of characters, called
the scanset, and a right bracket; the input field is the maximal
sequence of input characters consisting entirely of characters in the
scanset.  @samp{^}, when it appears as the first character in the
scanset, serves as a complement operator and redefines the scanset as
the set of all characters not contained in the remainder of the scanset
string.  Construction of the scanset follows certain conventions.  A
range of characters may be represented by the construct first-last,
enabling @samp{[0123456789]} to be expressed @samp{[0-9]}.  Using this
convention, first must be lexically less than or equal to last;
otherwise, the dash stands for itself.  The dash also stands for itself
when it is the first or the last character in the scanset.  To include
the right square bracket as an element of the scanset, it must appear as
the first character (possibly preceded by a @samp{^}) of the scanset, in
which case it will not be interpreted syntactically as the closing
bracket.  At least one character must match for this conversion to
succeed.
@end table

The @code{scanf} functions terminate their conversions at end-of-file,
at the end of the control string, or when an input character conflicts
with the control string.  In the latter case, the offending character is
left unread in the input stream.
@end defmac

@node String-Case, String Ports, Standard Formatted I/O, Procedures
@section String-Case

@code{(require 'string-case)}

@deffn Procedure string-upcase str
@deffnx Procedure string-downcase str
@deffnx Procedure string-capitalize str
The obvious string conversion routines.  These are non-destructive.
@end deffn

@defun string-upcase! str
@defunx string-downcase! str
@defunx string-captialize! str
The destructive versions of the functions above.
@end defun





@node String Ports, String Search, String-Case, Procedures
@section String Ports

@code{(require 'string-port)}

@deffn Procedure call-with-output-string proc
@var{proc} must be a procedure of one argument.  This procedure calls
@var{proc} with one argument: a (newly created) output port.  When the
function returns, the string composed of the characters written into the
port is returned.@refill
@end deffn

@deffn Procedure call-with-input-string string proc
@var{proc} must be a procedure of one argument.  This procedure calls
@var{proc} with one argument: an (newly created) input port from which
@var{string}'s contents may be read.  When @var{proc} returns, the port
is closed and the value yielded by the procedure @var{proc} is
returned.@refill
@end deffn


@node String Search, Tektronix Graphics Support, String Ports, Procedures
@section String Search

@code{(require 'string-search)}

@deffn Procedure string-index string char
Returns the index of the first occurence of @var{char} within
@var{string}, or @code{#f} if the @var{string} does not contain a
character @var{char}.
@end deffn

@deffn procedure substring? pattern string
Searches @var{string} to see if some substring of @var{string} is equal
to @var{pattern}.  @code{substring?} returns the index of the first
character of the first substring of @var{string} that is equal to
@var{pattern}; or @code{#f} if @var{string} does not contain
@var{pattern}.

@example
(substring? "rat" "pirate") @result{}  2
(substring? "rat" "outrage") @result{}  #f
(substring? "" any-string) @result{}  0
@end example
@end deffn

@deffn Procedure find-string-from-port? str in-port max-no-chars
@deffnx Procedure find-string-from-port? str in-port
Looks for a string @var{str} within the first @var{max-no-chars} chars
of the input port @var{in-port}.  @var{max-no-chars} may be omitted: in
that case, the search span is limited by the end of the input stream.
When the @var{str} is found, the function returns the number of
characters it has read from the port, and the port is set to read the
first char after that (that is, after the @var{str}) The function
returns @code{#f} when the @var{str} isn't found.

@code{find-string-from-port?} reads the port @emph{strictly}
sequentially, and does not perform any buffering.  So
@code{find-string-from-port?} can be used even if the @var{in-port} is
open to a pipe or other communication channel.
@end deffn


@node Tektronix Graphics Support, Tree Operations, String Search, Procedures
@section Tektronix Graphics Support

@emph{Note:} The Tektronix graphics support files need more work, and
are not complete.

@subsection Tektronix 4000 Series Graphics

The Tektronix 4000 series graphics protocol gives the user a 1024 by
1024 square drawing area.  The origin is in the lower left corner of the
screen.  Increasing y is up and increasing x is to the right.

The graphics control codes are sent over the current-output-port and can
be mixed with regular text and ANSI or other terminal control sequences.

@deffn Procedure tek40:init
@end deffn

@deffn Procedure tek40:graphics
@end deffn

@deffn Procedure tek40:text
@end deffn

@deffn Procedure tek40:linetype linetype
@end deffn

@deffn Procedure tek40:move x y
@end deffn

@deffn Procedure tek40:draw x y
@end deffn

@deffn Procedure tek40:put-text x y str
@end deffn

@deffn Procedure tek40:reset
@end deffn


@subsection Tektronix 4100 Series Graphics

The graphics control codes are sent over the current-output-port and can
be mixed with regular text and ANSI or other terminal control sequences.

@deffn Procedure tek41:init
@end deffn

@deffn Procedure tek41:reset
@end deffn

@deffn Procedure tek41:graphics
@end deffn

@deffn Procedure tek41:move x y
@end deffn

@deffn Procedure tek41:draw x y
@end deffn

@deffn Procedure tek41:point x y number
@end deffn

@deffn Procedure tek41:encode-x-y x y
@end deffn

@deffn Procedure tek41:encode-int number
@end deffn



@node Tree Operations,  , Tektronix Graphics Support, Procedures
@section Tree operations

@code{(require 'tree)}

These are operations that treat lists a representations of trees.

@defun subst new old tree
@defunx substq new old tree
@defunx substv new old tree
@code{subst} makes a copy of @var{tree}, substituting @var{new} for
every subtree or leaf of @var{tree} which is @code{equal?} to @var{old}
and returns a modified tree.  The original @var{tree} is unchanged, but
may share parts with the result.@refill

@code{substq} and @code{substv} are similar, but test against @var{old}
using @code{eq?} and @code{eqv?} respectively.@refill

Examples:
@lisp
(substq 'tempest 'hurricane '(shakespeare wrote (the hurricane)))
   @result{} (shakespeare wrote (the tempest))
(substq 'foo '() '(shakespeare wrote (twelfth night)))
   @result{} (shakespeare wrote (twelfth night . foo) . foo)
(subst '(a . cons) '(old . pair)
       '((old . spice) ((old . shoes) old . pair) (old . pair)))
   @result{} ((old . spice) ((old . shoes) a . cons) (a . cons))
@end lisp
@end defun

@defun copy-tree tree
Makes a copy of the nested list structure @var{tree} using new pairs and
returns it.  All levels are copied, so that none of the pairs in the
tree are @code{eq?} to the original ones -- only the leaves are.@refill

Example:
@lisp
(define bar '(bar))
(copy-tree (list bar 'foo))
   @result{} ((bar) foo)
(eq? bar (car (copy-tree (list bar 'foo))))
   @result{} #f
@end lisp
@end defun





@node Standards Support, Session Support, Procedures, Top
@chapter Standards Support



@menu
* With-File::                   'with-file
* Transcripts::                 'transcript
* Rev2 Procedures::             'rev2-procedures
* Rev4 Optional Procedures::    'rev4-optional-procedures
* Multi-argument / and -::      'multiarg/and-
* Multi-argument Apply::        'multiarg-apply
* Rationalize::                 'rationalize
* Promises::                    'promise
* Dynamic-Wind::                'dynamic-wind
* Values::                      'values
* Time::                        'time
* CLTime::                      'common-lisp-time
@end menu

@node With-File, Transcripts, Standards Support, Standards Support
@section With-File

@code{(require 'with-file)}

@defun with-input-from-file file thunk
@defunx with-output-to-file file thunk
Description found in R4RS.
@end defun

@node Transcripts, Rev2 Procedures, With-File, Standards Support
@section Transcripts

@code{(require 'transcript)}

@defun transcript-on filename
@defunx transcript-off filename
Redefines @code{read-char}, @code{read}, @code{write-char},
@code{write}, @code{display}, and @code{newline}.@refill
@end defun





@node Rev2 Procedures, Rev4 Optional Procedures, Transcripts, Standards Support
@section Rev2 Procedures

@code{(require 'rev2-procedures)}

The procedures below were specified in the @cite{Revised^2 Report on
Scheme}.  @strong{N.B.}: The symbols @code{1+} and @code{-1+} are not
@cite{R4RS} syntax.  Scheme->C, for instance, barfs on this
module.@refill

@deffn Procedure substring-move-left! string1 start1 end1 string2 start2
@deffnx Procedure substring-move-right! string1 start1 end1 string2 start2
@var{string1} and @var{string2} must be a strings, and @var{start1},
@var{start2} and @var{end1} must be exact integers satisfying@refill

@display
0 <= @var{start1} <= @var{end1} <= (string-length @var{string1})
0 <= @var{start2} <= @var{end1} - @var{start1} + @var{start2} <= (string-length @var{string2})
@end display

@code{substring-move-left!} and @code{substring-move-right!} store
characters of @var{string1} beginning with index @var{start1}
(inclusive) and ending with index @var{end1} (exclusive) into
@var{string2} beginning with index @var{start2} (inclusive).@refill

@code{substring-move-left!} stores characters in time order of
increasing indices.  @code{substring-move-right!} stores characters in
time order of increasing indeces.@refill
@end deffn

@deffn Procedure substring-fill! string start end char
Fills the elements @var{start}--@var{end} of @var{string} with the
character @var{char}.@refill
@end deffn

@defun string-null? str
@equiv{} @code{(= 0 (string-length @var{str}))}
@end defun

@deffn Procedure append! . pairs
Destructively appends its arguments.  Equivalent to @code{nconc}.
@end deffn

@defun 1+ n
Adds 1 to @var{n}.
@end defun

@defun -1+ n
Subtracts 1 from @var{n}.
@end defun

@defun <?
@defunx <=?
@defunx =?
@defunx >?
@defunx >=?
These are equivalent to the procedures of the same name but without the
trailing @samp{?}.
@end defun



@node Rev4 Optional Procedures, Multi-argument / and -, Rev2 Procedures, Standards Support
@section Rev4 Optional Procedures

@code{(require 'rev4-optional-procedures)}

For the specification of these optional procedures,
@xref{Standard procedures, , ,r4rs, Revised(4) Scheme}.

@defun list-tail l p
@end defun

@defun string->list s
@end defun

@defun list->string l
@end defun

@defun string-copy
@end defun

@deffn Procedure string-fill! s obj
@end deffn

@defun list->vector l
@end defun

@defun vector->list s
@end defun

@deffn Procedure vector-fill! s obj
@end deffn





@node Multi-argument / and -, Multi-argument Apply, Rev4 Optional Procedures, Standards Support
@section Multi-argument / and -

@code{(require 'mutliarg/and-)}

For the specification of these optional forms, @xref{Numerical
operations, , ,r4rs, Revised(4) Scheme}.  The @code{two-arg:}* forms are
only defined if the implementation does not support the many-argument
forms.@refill

@defun two-arg:/ n1 n2
The original two-argument version of @code{/}.
@end defun

@defun / divident . divisors
@end defun

@defun two-arg:- n1 n2
The original two-argument version of @code{-}.
@end defun

@defun - minuend . subtrahends
@end defun





@node Multi-argument Apply, Rationalize, Multi-argument / and -, Standards Support
@section Multi-argument Apply

@code{(require 'multiarg-apply)}

@noindent
For the specification of this optional form,
@xref{Control features, , ,r4rs, Revised(4) Scheme}.

@defun two-arg:apply proc l
The implementation's native @code{apply}.  Only defined for
implementations which don't support the many-argument version.
@end defun

@defun apply proc . args
@end defun





@node Rationalize, Promises, Multi-argument Apply, Standards Support
@section Rationalize

@code{(require 'rationalize)}

The procedure rationalize is interesting because most programming
languages do not provide anything analogous to it.  For simplicity, we
present an algorithm which computes the correct result for exact
arguments (provided the implementation supports exact rational numbers
of unlimited precision), and produces a reasonable answer for inexact
arguments when inexact arithmetic is implemented using floating-point.
We thank Alan Bawden for contributing this algorithm.

@defun rationalize x e
@end defun





@node Promises, Dynamic-Wind, Rationalize, Standards Support
@section Promises

@code{(require 'promise)}

@defun make-promise proc
@end defun

Change occurrences of @code{(delay @var{expression})} to
@code{(make-promise (lambda () @var{expression}))} and @code{(define
force promise:force)} to implement promises if your implementation
doesn't support them
(@pxref{Control features, , ,r4rs, Revised(4) Scheme}).




@node Dynamic-Wind, Values, Promises, Standards Support
@section Dynamic-Wind

@code{(require 'dynamic-wind)}

This facility is a generalization of Common LISP @code{unwind-protect},
designed to take into account the fact that continuations produced by
@code{call-with-current-continuation} may be reentered.@refill

@deffn Procedure dynamic-wind thunk1 thunk2 thunk3
The arguments @var{thunk1}, @var{thunk2}, and @var{thunk3} must all be
procedures of no arguments (thunks).@refill

@code{dynamic-wind} calls @var{thunk1}, @var{thunk2}, and then
@var{thunk3}.  The value returned by @var{thunk2} is returned as the
result of @code{dynamic-wind}.  @var{thunk3} is also called just before
control leaves the dynamic context of @var{thunk2} by calling a
continuation created outside that context.  Furthermore, @var{thunk1} is
called before reentering the dynamic context of @var{thunk2} by calling
a continuation created inside that context.  (Control is inside the
context of @var{thunk2} if @var{thunk2} is on the current return stack).

@strong{Warning:} There is no provision for dealing with errors or
interrupts.  If an error or interrupt occurs while using
@code{dynamic-wind}, the dynamic environment will be that in effect at
the time of the error or interrupt.@refill
@end deffn




@node Values, Time, Dynamic-Wind, Standards Support
@section Values

@code{(require 'values)}

@defun values obj @dots{}
@code{values} takes any number of arguments, and passes (returns) them
to its continuation.@refill
@end defun


@defun call-with-values thunk proc
@var{thunk} must be a procedure of no arguments, and @var{proc} must be
a procedure.  @code{call-with-values} calls @var{thunk} with a
continuation that, when passed some values, calls @var{proc} with those
values as arguments.@refill

Except for continuations created by the @code{call-with-values}
procedure, all continuations take exactly one value, as now; the effect
of passing no value or more than one value to continuations that were
not created by the @code{call-with-values} procedure is
unspecified.@refill
@end defun

@node Time, CLTime, Values, Standards Support
@section Time

The procedures @code{current-time}, @code{difftime}, and
@code{offset-time} are supported by all implementations (SLIB provides
them if feature @code{('current-time)} is missing.  @code{current-time}
returns a @dfn{calendar time} (caltime) which can be a number or other
type.

@defun current-time
Returns the time since 00:00:00 GMT, January 1, 1970, measured in
seconds.  Note that the reference time is different from the reference
time for @code{get-universal-time} in @ref{CLTime}.  On implementations
which cannot support actual times, @code{current-time} will increment a
counter and return its value when called.
@end defun

@defun difftime caltime1 caltime0
Returns the difference (number of seconds) between twe calendar times:
@var{caltime1} - @var{caltime0}.  @var{caltime0} can also be a number.
@end defun

@defun offset-time caltime offset
Returns the calendar time of @var{caltime} offset by @var{offset} number
of seconds @code{(+ caltime offset)}.
@end defun

@example
(require 'posix-time)
@end example

These procedures are intended to be compatible with Posix time
conversion functions.

@defvar *timezone*
contains the difference, in seconds, between UTC and local standard time
(for example, in the U.S.  Eastern time zone (EST), timezone is
5*60*60).  @code{*timezone*} is initialized by @code{tzset}.
@end defvar

@defun tzset
initializes the @var{*timezone*} variable from the TZ environment
variable.  This function is automatically called by the other time
conversion functions that depend on the time zone.
@end defun

@defun gmtime caltime
converts the calendar time @var{caltime} to a vector of integers
representing the time expressed as Coordinated Universal Time (UTC).

@defunx localtime caltime
converts the calendar time @var{caltime} to a vector of integers expressed
relative to the user's time zone.  @code{localtime} sets the variable
@var{*timezone*} with the difference between Coordinated Universal Time
(UTC) and local standard time in seconds by calling @code{tzset}.
The elements of the returned vector are as follows:

@enumerate 0
@item
 seconds (0 - 61)
@item
 minutes (0 - 59)
@item
 hours since midnight
@item
 day of month
@item
 month (0 - 11).  Note difference from @code{decode-universal-time}.
@item
 year (A.D.)
@item
 day of week (0 - 6)
@item
 day of year (0 - 365)
@item
 1 for daylight savings, 0 for regular time
@end enumerate
@end defun

@defun mktime univtime
Converts a vector of integers in Coordinated Universal Time (UTC) format
to calendar time (caltime) format.
@end defun

@defun asctime univtime
Converts the vector of integers @var{caltime} in Coordinated
Universal Time (UTC) format into a string of the form
@code{"Wed Jun 30 21:49:08 1993"}.
@end defun

@defun ctime caltime
Equivalent to @code{(time:asctime (time:localtime @var{caltime}))}.
@end defun

@node CLTime,  , Time, Standards Support
@section CLTime

@defun get-decoded-time
Equivalent to @code{(decode-universal-time (get-universal-time))}.
@end defun

@defun get-universal-time
Returns the current time as @dfn{Universal Time}, number of seconds
since 00:00:00 Jan 1, 1900 GMT.  Note that the reference time is
different from @code{current-time}.
@end defun

@defun decode-universal-time univtime
Converts @var{univtime} to @dfn{Decoded Time} format.
Nine values are returned:
@enumerate 0
@item
 seconds (0 - 61)
@item
 minutes (0 - 59)
@item
 hours since midnight
@item
 day of month
@item
 month (1 - 12).  Note difference from @code{gmtime} and @code{localtime}.
@item
 year (A.D.)
@item
 day of week (0 - 6)
@item
 #t for daylight savings, #f otherwise
@item
 hours west of GMT (-24 - +24)
@end enumerate

Notice that the values returned by @code{decode-universal-time} do not
match the arguments to @code{encode-universal-time}.
@end defun

@defun encode-universal-time second minute hour date month year
@defunx encode-universal-time second minute hour date month year time-zone
Converts the arguments in Decoded Time format to Universal Time format.
If @var{time-zone} is not specified, the returned time is adjusted for
daylight saving time.  Otherwise, no adjustment is performed.

Notice that the values returned by @code{decode-universal-time} do not
match the arguments to @code{encode-universal-time}.
@end defun


@node Session Support, Optional SLIB Packages, Standards Support, Top
@chapter Session Support

@menu
* Repl::                        Macros at top-level
* Quick Print::                 Loop-safe Output
* Debug::                       To err is human ...
* Breakpoints::                 Pause execution
* Trace::                       'trace
* Getopt::                      Command Line option parsing
* Command Line::                A command line reader for Scheme shells
* System Interface::            'system and 'getenv

Certain features are so simple, system-dependent, or widely subcribed
that they are supported by all implementations as part of the
@samp{*.init} files.

The features described in the following sections are provided by all
implementations.

* Require::                     Module Management
* Vicinity::                    Pathname Management
* Configuration::               Characteristics of Scheme Implementation
* Input/Output::                Things not provided by the Scheme specs.
* Legacy::                      
* System::                      LOADing, EVALing, ERRORing, and EXITing
@end menu



@node Repl, Quick Print, Session Support, Session Support
@section Repl

@code{(require 'repl)}

Here is a read-eval-print-loop which, given an eval, evaluates forms.

@deffn Procedure repl:top-level repl:eval
@code{read}s, @code{repl:eval}s and @code{write}s expressions from
@code{(current-input-port)} to @code{(current-output-port)} until an
end-of-file is encountered.  @code{load}, @code{slib:eval},
@code{slib:error}, and @code{repl:quit} dynamically bound during
@code{repl:top-level}.@refill
@end deffn

@deffn Procedure repl:quit
Exits from the invocation of @code{repl:top-level}.
@end deffn

The @code{repl:} procedures establish, as much as is possible to do
portably, a top level environment supporting macros.
@code{repl:top-level} uses @code{dynamic-wind} to catch error conditions
and interrupts.  If your implementation supports this you are all set.

Otherwise, if there is some way your implementation can catch error
conditions and interrupts, then have them call @code{slib:error}.  It
will display its arguments and reenter @code{repl:top-level}.
@code{slib:error} dynamically bound by @code{repl:top-level}.@refill

To have your top level loop always use macros, add any interrupt
catching lines and the following lines to your Scheme init file:
@lisp
(require 'macro)
(require 'repl)
(repl:top-level macro:eval)
@end lisp

@node Quick Print, Debug, Repl, Session Support
@section Quick Print

@code{(require 'qp)}

@noindent
When displaying error messages and warnings, it is paramount that the
output generated for circular lists and large data structures be
limited.  This section supplies a procedure to do this.  It could be
much improved.

@quotation
Notice that the neccessity for truncating output eliminates
Common-Lisp's @xref{Format} from consideration; even when variables
@code{*print-level*} and @code{*print-level*} are set, huge strings and
bit-vectors are @emph{not} limited.
@end quotation

@deffn Procedure qp arg1 @dots{}
@deffnx Procedure qpn arg1 @dots{}
@deffnx Procedure qpr arg1 @dots{}
@code{qp} writes its arguments, separated by spaces, to
@code{(current-output-port)}.  @code{qp} compresses printing by
substituting @samp{...} for substructure it does not have sufficient
room to print.  @code{qpn} is like @code{qp} but outputs a newline
before returning.  @code{qpr} is like @code{qpn} except that it returns
its last argument.@refill
@end deffn

@defvar *qp-width*
@code{*qp-width*} is the largest number of characters that @code{qp}
should use.@refill
@end defvar

@node Debug, Breakpoints, Quick Print, Session Support
@section Debug

@code{(require 'debug)}

@noindent
Requiring @code{debug} automatically requires @code{trace} and
@code{break}.

@noindent
An application with its own datatypes may want to substitute its own
printer for @code{qp}.  This example shows how to do this:

@example
(define qpn (lambda args) @dots{})
(provide 'qp)
(require 'debug)
@end example

@deffn Procedure trace-all file
Traces (@pxref{Trace}) all procedures @code{define}d at top-level in
file @file{file}.
@end deffn

@deffn Procedure break-all file
Breakpoints (@pxref{Breakpoints}) all procedures @code{define}d at
top-level in file @file{file}.
@end deffn

@node Breakpoints, Trace, Debug, Session Support
@section Breakpoints

@code{(require 'break)}

@defun init-debug
If your Scheme implementation does not support @code{break} or
@code{abort}, a message will appear when you @code{(require 'break)} or
@code{(require 'debug)} telling you to type @code{(init-debug)}.  This
is in order to establish a top-level continuation.  Typing
@code{(init-debug)} at top level sets up a continuation for
@code{break}.
@end defun

@defun breakpoint arg1 @dots{}
Returns from the top level continuation and pushes the continuation from
which it was called on a continuation stack.
@end defun

@defun continue
Pops the topmost continuation off of the continuation stack and returns
an unspecified value to it.
@defunx continue arg1 @dots{}
Pops the topmost continuation off of the continuation stack and returns
@var{arg1} @dots{} to it.
@end defun

@defmac break proc1 @dots{}
Redefines the top-level named procedures given as arguments so that
@code{breakpoint} is called before calling @var{proc1} @dots{}.
@defmacx break
With no arguments, makes sure that all the currently broken identifiers
are broken (even if those identifiers have been redefined) and returns a
list of the broken identifiers.
@end defmac

@defmac unbreak proc1 @dots{}
Turns breakpoints off for its arguments.
@defmacx unbreak
With no arguments, unbreaks all currently broken identifiers and returns
a list of these formerly broken identifiers.
@end defmac

The following routines are the procedures which actually do the tracing
when this module is supplied by SLIB, rather than natively.  If
defmacros are not natively supported by your implementation, these might
be more convenient to use.

@defun breakf proc
@defunx breakf proc name
@defunx debug:breakf proc
@defunx debug:breakf proc name
To break, type
@lisp
(set! @var{symbol} (breakf @var{symbol}))
@end lisp
@noindent
or
@lisp
(set! @var{symbol} (breakf @var{symbol} '@var{symbol}))
@end lisp
@noindent
or
@lisp
(define @var{symbol} (breakf @var{function}))
@end lisp
@noindent
or
@lisp
(define @var{symbol} (breakf @var{function} '@var{symbol}))
@end lisp
@end defun

@defun unbreakf proc
@defunx debug:unbreakf proc
To unbreak, type
@lisp
(set! @var{symbol} (unbreakf @var{symbol}))
@end lisp
@end defun

@node Trace, Getopt, Breakpoints, Session Support
@section Tracing

@code{(require 'trace)}

@defmac trace proc1 @dots{}
Traces the top-level named procedures given as arguments.
@defmacx trace
With no arguments, makes sure that all the currently traced identifiers
are traced (even if those identifiers have been redefined) and returns a
list of the traced identifiers.
@end defmac

@defmac untrace proc1 @dots{}
Turns tracing off for its arguments.
@defmacx untrace
With no arguments, untraces all currently traced identifiers and returns
a list of these formerly traced identifiers.
@end defmac

The following routines are the procedures which actually do the tracing
when this module is supplied by SLIB, rather than natively.  If
defmacros are not natively supported by your implementation, these might
be more convenient to use.

@defun tracef proc
@defunx tracef proc name
@defunx debug:tracef proc
@defunx debug:tracef proc name
To trace, type
@lisp
(set! @var{symbol} (tracef @var{symbol}))
@end lisp
@noindent
or
@lisp
(set! @var{symbol} (tracef @var{symbol} '@var{symbol}))
@end lisp
@noindent
or
@lisp
(define @var{symbol} (tracef @var{function}))
@end lisp
@noindent
or
@lisp
(define @var{symbol} (tracef @var{function} '@var{symbol}))
@end lisp
@end defun

@defun untracef proc
@defunx debug:untracef proc
To untrace, type
@lisp
(set! @var{symbol} (untracef @var{symbol}))
@end lisp
@end defun


@node Getopt, Command Line, Trace, Session Support
@section Getopt

@code{(require 'getopt)}

This routine implements Posix command line argument parsing.  Notice
that returning values through global variables means that @code{getopt}
is @emph{not} reentrant.

@defvar *optind*
Is the index of the current element of the command line.  It is
initially one.  In order to parse a new command line or reparse an old
one, @var{*opting*} must be reset.
@end defvar

@defvar *optarg*
Is set by getopt to the (string) option-argument of the current option.
@end defvar

@deffn Procedure getopt argc argv optstring
Returns the next option letter in @var{argv} (starting from
@code{(vector-ref argv *optind*)}) that matches a letter in
@var{optstring}.  @var{argv} is a vector or list of strings, the 0th of
which getopt usually ignores. @var{argc} is the argument count, usually
the length of @var{argv}.  @var{optstring} is a string of recognized
option characters; if a character is followed by a colon, the option
takes an argument which may be immediately following it in the string or
in the next element of @var{argv}.

@var{*optind*} is the index of the next element of the @var{argv} vector
to be processed.  It is initialized to 1 by @file{getopt.scm}, and
@code{getopt} updates it when it finishes with each element of
@var{argv}.

@code{getopt} returns the next option character from @var{argv} that
matches a character in @var{optstring}, if there is one that matches.
If the option takes an argument, @code{getopt} sets the variable
@var{*optarg*} to the option-argument as follows:

@itemize @bullet
@item
If the option was the last character in the string pointed to by an
element of @var{argv}, then @var{*optarg*} contains the next element of
@var{argv}, and @var{*optind*} is incremented by 2.  If the resulting
value of @var{*optind*} is greater than or equal to @var{argc}, this
indicates a missing option argument, and @code{getopt} returns an error
indication.

@item
Otherwise, @var{*optarg*} is set to the string following the option
character in that element of @var{argv}, and @var{*optind*} is
incremented by 1.
@end itemize

If, when @code{getopt} is called, the string @code{(vector-ref argv
*optind*)} either does not begin with the character @code{#\-} or is
just @code{"-"}, @code{getopt} returns @code{#f} without changing
@var{*optind*}.  If @code{(vector-ref argv *optind*)} is the string
@code{"--"}, @code{getopt} returns @code{#f} after incrementing
@var{*optind*}.

If @code{getopt} encounters an option character that is not contained in
@var{optstring}, it returns the question-mark @code{#\?} character.  If
it detects a missing option argument, it returns the colon character
@code{#\:} if the first character of @var{optstring} was a colon, or a
question-mark character otherwise.  In either case, @code{getopt} sets
the variable @var{getopt:opt} to the option character that caused the
error.

The special option @code{"--"} can be used to delimit the end of the
options; @code{#f} is returned, and @code{"--"} is skipped.

RETURN VALUE

@code{getopt} returns the next option character specified on the command
line.  A colon @code{#\:} is returned if @code{getopt} detects a missing argument
and the first character of @var{optstring} was a colon @code{#\:}.

A question-mark @code{#\?} is returned if @code{getopt} encounters an option
character not in @var{optstring} or detects a missing argument and the first
character of @var{optstring} was not a colon @code{#\:}.

Otherwise, @code{getopt} returns @code{#f} when all command line options have been
parsed.

Example:
@lisp
#! /usr/local/bin/scm
;;;This code is SCM specific.
(define argv (program-arguments))
(require 'getopt)

(define opts ":a:b:cd")
(let loop ((opt (getopt (length argv) argv opts)))
  (case opt
    ((#\a) (print "option a: " *optarg*))
    ((#\b) (print "option b: " *optarg*))
    ((#\c) (print "option c"))
    ((#\d) (print "option d"))
    ((#\?) (print "error" getopt:opt))
    ((#\:) (print "missing arg" getopt:opt))
    ((#f) (if (< *optind* (length argv))
              (print "argv[" *optind* "]="
                     (list-ref argv *optind*)))
          (set! *optind* (+ *optind* 1))))
  (if (< *optind* (length argv))
      (loop (getopt (length argv) argv opts))))

(slib:exit)
@end lisp
@end deffn

@section Getopt--

@defun getopt-- argc argv optstring
The procedure @code{getopt--} is an extended version of @code{getopt}
which parses @dfn{long option names} of the form
@samp{--hold-the-onions} and @samp{--verbosity-level=extreme}.  
@w{@code{Getopt--}} behaves as @code{getopt} except for non-empty
options beginning with @samp{--}.

Options beginning with @samp{--} are returned as strings rather than
characters.  If a value is assigned (using @samp{=}) to a long option,
@code{*optarg*} is set to the value.  The @samp{=} and value are
not returned as part of the option string.

No information is passed to @code{getopt--} concerning which long
options should be accepted or whether such options can take arguments.
If a long option did not have an argument, @code{*optarg} will be set to
@code{#f}.  The caller is responsible for detecting and reporting
errors.

@example
(define opts ":-:b:")
(define argc 5)
(define argv '("foo" "-b9" "--f1" "--2=" "--g3=35234.342" "--"))
(define *optind* 1)
(define *optarg* #f)
(require 'qp)
(do ((i 5 (+ -1 i)))
    ((zero? i))
  (define opt (getopt-- argc argv opts))
  (print *optind* opt *optarg*)))
@print{}
2 #\b "9" 
3 "f1" #f 
4 "2" "" 
5 "g3" "35234.342" 
5 #f "35234.342" 
@end example
@end defun

@node Command Line, System Interface, Getopt, Session Support
@section Command Line

@code{(require 'read-command)}

@defun read-command port
@defunx read-command
@code{read-command} converts a @dfn{command line} into a list of strings
suitable for parsing by @code{getopt}.  The syntax of command lines
supported resembles that of popular @dfn{shell}s.  @code{read-command}
updates @var{port} to point to the first character past the command
delimiter.

If an end of file is encountered in the input before any characters are
found that can begin an object or comment, then an end of file object is
returned.

The @var{port} argument may be omitted, in which case it defaults to the
value returned by @code{current-input-port}.

The fields into which the command line is split are delimited by
whitespace as defined by @code{char-whitespace?}.  The end of a command
is delimited by end-of-file or unescaped semicolon (@key{;}) or
@key{newline}.  Any character can be literally included in a field by
escaping it with a backslach (@key{\}).

The initial character and types of fields recognized are:
@table @asis
@item @samp{\}
The next character has is taken literally and not interpreted as a field
delimiter.  If @key{\} is the last character before a @key{newline},
that @key{newline} is just ignored.  Processing continues from the
characters after the @key{newline} as though the backslash and
@key{newline} were not there.
@item @samp{"}
The characters up to the next unescaped @key{"} are taken literally,
according to [R4RS] rules for literal strings (@pxref{Strings, , ,r4rs,
Revised(4) Scheme}).
@item @samp{(}, @samp{%'}
One scheme expression is @code{read} starting with this character.  The
@code{read} expression is evaluated, converted to a string
(using @code{display}), and replaces the expression in the returned
field.
@item @samp{;}
Semicolon delimits a command.  Using semicolons more than one command
can appear on a line.  Escaped semicolons and semicolons inside strings
do not delimit commands.
@end table

@noindent
The comment field differs from the previous fields in that it must be
the first character of a command or appear after whitespace in order to
be recognized.  @key{#} can be part of fields if these conditions are
not met.  For instance, @code{ab#c} is just the field ab#c.

@table @samp
@item #
Introduces a comment.  The comment continues to the end of the line on
which the semicolon appears.  Comments are treated as whitespace by
@code{read-dommand-line} and backslashes before @key{newline}s in
comments are also ignored.
@end table
@end defun

@node System Interface, Require, Command Line, Session Support
@section System Interface

If @code{(provided? 'getenv)}:

@defun getenv name
Looks up @var{name}, a string, in the program environment.  If @var{name} is
found a string of its value is returned.  Otherwise, @code{#f} is returned.
@end defun

If @code{(provided? 'system)}:

@defun system command-string
Executes the @var{command-string} on the computer and returns the
integer status code.
@end defun


@node Require, Vicinity, System Interface, Session Support
@section Require

These variables and procedures are provided by all implementations.

@defvar *features*
Is a list of symbols denoting features supported in this implementation.
@end defvar

@defvar *modules*
Is a list of pathnames denoting files which have been loaded.
@end defvar

@defvar *catalog*
Is an association list of features (symbols) and pathnames which will
supply those features.  The pathname can be either a string or a pair.
If pathname is a pair then the first element should be a macro feature
symbol, @code{source}, or @code{compiled}.  The cdr of the pathname
should be either a string or a list.
@end defvar

In the following three functions if @var{feature} is not a symbol it is
assumed to be a pathname.@refill

@defun provided? feature
Returns @code{#t} if @var{feature} is a member of @code{*features*} or
@code{*modules*} or if @var{feature} is supported by a file already
loaded and @code{#f} otherwise.@refill
@end defun

@deffn Procedure require feature
If @code{(not (provided? @var{feature}))} it is loaded if @var{feature}
is a pathname or if @code{(assq @var{feature} *catalog*)}.  Otherwise an
error is signaled.@refill
@end deffn

@deffn Procedure provide feature
Assures that @var{feature} is contained in @code{*features*} if
@var{feature} is a symbol and @code{*modules*} otherwise.@refill
@end deffn

@defun require:feature->path feature
Returns @code{#t} if @var{feature} is a member of @code{*features*} or
@code{*modules*} or if @var{feature} is supported by a file already
loaded.  Returns a path if one was found in @code{*catalog*} under the
feature name, and @code{#f} otherwise.  The path can either be a string
suitable as an argument to load or a pair as described above for
*catalog*.
@end defun

Below is a list of features that are automatically determined by
@code{require}.  For each item, @code{(provided? '@var{feature})} will
return @code{#t} if that feature is available, and @code{#f} if
not.@refill

@itemize @bullet
@item
'inexact
@item
'rational
@item
'real
@item
'complex
@item
'bignum
@end itemize





@node Vicinity, Configuration, Require, Session Support
@section Vicinity

A vicinity is a descriptor for a place in the file system.  Vicinities
hide from the programmer the concepts of host, volume, directory, and
version.  Vicinities express only the concept of a file environment
where a file name can be resolved to a file in a system independent
manner.  Vicinities can even be used on @dfn{flat} file systems (which
have no directory structure) by having the vicinity express constraints
on the file name.  On most systems a vicinity would be a string.  All of
these procedures are file system dependent.

These procedures are provided by all implementations.

@defun make-vicinity filename
Returns the vicinity of @var{filename} for use by @code{in-vicinity}.
@end defun

@defun program-vicinity
Returns the vicinity of the currently loading Scheme code.  For an
interpreter this would be the directory containing source code.  For a
compiled system (with multiple files) this would be the directory where
the object or executable files are.  If no file is currently loading it
the result is undefined.  @strong{Warning:} @code{program-vicinity} can
return incorrectl values if your program escapes back into a
@code{load}.@refill
@end defun

@defun library-vicinity
Returns the vicinity of the shared Scheme library.
@end defun

@defun implementation-vicinity
Returns the vicinity of the underlying Scheme implementation.  This
vicinity will likely contain startup code and messages and a compiler.
@end defun

@defun user-vicinity
Returns the vicinity of the current directory of the user.  On most
systems this is @file{""} (the empty string).
@end defun

@c @defun scheme-file-suffix
@c Returns the default filename suffix for scheme source files.  On most
@c systems this is @samp{.scm}.@refill
@c @end defun

@defun in-vicinity vicinity filename
Returns a filename suitable for use by @code{slib:load},
@code{slib:load-source}, @code{slib:load-compiled},
@code{open-input-file}, @code{open-output-file}, etc.  The returned
filename is @var{filename} in @var{vicinity}.  @code{in-vicinity} should
allow @var{filename} to override @var{vicinity} when @var{filename} is
an absolute pathname and @var{vicinity} is equal to the value of
@code{(user-vicinity)}.  The behavior of @code{in-vicinity} when
@var{filename} is absolute and @var{vicinity} is not equal to the value
of @code{(user-vicinity)} is unspecified.  For most systems
@code{in-vicinity} can be @code{string-append}.@refill
@end defun

@defun sub-vicinity vicinity name
Returns the vicinity of @var{vicinity} restricted to @var{name}.  This
is used for large systems where names of files in subsystems could
conflict.  On systems with directory structure @code{sub-vicinity} will
return a pathname of the subdirectory @var{name} of
@var{vicinity}.@refill
@end defun



@node Configuration, Input/Output, Vicinity, Session Support
@section Configuration

These constants and procedures describe characteristics of the Scheme
and underlying operating system.  They are provided by all
implementations.

@defvr Constant char-code-limit
An integer 1 larger that the largest value which can be returned by
@code{char->integer}.@refill
@end defvr

@defvr Constant most-positive-fixnum
The immediate integer closest to positive infinity.
@end defvr

@defvr Constant slib:tab
The tab character.
@end defvr

@defvr Constant slib:form-feed
The form-feed character.
@end defvr

@defun software-type
Returns a symbol denoting the generic operating system type.  For
instance, @code{unix}, @code{vms}, @code{macos}, @code{amiga}, or
@code{ms-dos}.
@end defun

@defun slib:report-version
Displays the versions of SLIB and the underlying Scheme implementation
and the name of the operating system.  An unspecified value is returned.

@example
(slib:report-version) @result{} slib "2a3" on scm "4e1" on unix 
@end example
@end defun

@defun slib:report
Displays the information of @code{(slib:report-version)} followed by
almost all the information neccessary for submitting a problem report.
An unspecified value is returned.

@defunx slib:report #t
provides a more verbose listing.

@defunx slib:report filename
Writes the report to file @file{filename}.

@example
(slib:report)
@result{}
slib "2a3" on scm "4e1" on unix 
(implementation-vicinity) is "/usr/local/src/scm/" 
(library-vicinity) is "/usr/local/lib/slib/" 
(scheme-file-suffix) is ".scm" 
implementation *features* : 
        bignum complex real rational
        inexact vicinity ed getenv
        tmpnam system abort transcript
        with-file ieee-p1178 rev4-report rev4-optional-procedures
        hash object-hash delay eval
        dynamic-wind multiarg-apply multiarg/and- logical
        defmacro string-port source array-for-each
        array full-continuation char-ready? line-i/o
        i/o-extensions pipe
implementation *catalog* : 
        (rev4-optional-procedures . "/usr/local/lib/slib/sc4opt")
        ... 
@end example
@end defun

@node Input/Output, Legacy, Configuration, Session Support
@section Input/Output

These procedures are provided by all implementations.

@deffn Procedure file-exists? filename
Returns @code{#t} if the specified file exists.  Otherwise, returns
@code{#f}.  If the underlying implementation does not support this
feature then @code{#f} is always returned.
@end deffn

@deffn Procedure delete-file filename
Deletes the file specified by @var{filename}.  If @var{filename} can not
be deleted, @code{#f} is returned.  Otherwise, @code{#t} is
returned.@refill
@end deffn

@deffn Procedure tmpnam
Returns a pathname for a file which will likely not be used by any other
process.  Successive calls to @code{(tmpnam)} will return different
pathnames.@refill
@end deffn

@deffn Procedure current-error-port
Returns the current port to which diagnostic and error output is
directed.
@end deffn

@deffn Procedure force-output
@deffnx Procedure force-output port
Forces any pending output on @var{port} to be delivered to the output
device and returns an unspecified value.  The @var{port} argument may be
omitted, in which case it defaults to the value returned by
@code{(current-output-port)}.@refill
@end deffn

@deffn Procedure output-port-width
@deffnx Procedure output-port-width port

Returns the width of @var{port}, which defaults to
@code{(current-output-port)} if absent.  If the width cannot be
determined 79 is returned.@refill
@end deffn

@deffn Procedure output-port-height
@deffnx Procedure output-port-height port

Returns the height of @var{port}, which defaults to
@code{(current-output-port)} if absent.  If the height cannot be
determined 24 is returned.@refill
@end deffn

@node Legacy, System, Input/Output, Session Support
@section Legacy

@defun identity x
@var{identity} returns its argument.

Example:
@lisp
(identity 3)
   @result{} 3
(identity '(foo bar))
   @result{} (foo bar)
(map identity @var{lst})
   @equiv{} (copy-list @var{lst})
@end lisp
@end defun

These were present in Scheme until R4RS (@pxref{Notes, , Language
changes ,r4rs, Revised(4) Scheme}).

@defvr Constant t
Derfined as @code{#t}.
@end defvr

@defvr Constant nil
Defined as @code{#f}.
@end defvr

@defun last-pair l
Returns the last pair in the list @var{l}.  Example:
@lisp
(last-pair (cons 1 2))
   @result{} (1 . 2)
(last-pair '(1 2))
   @result{} (2)
    @equiv{} (cons 2 '())
@end lisp
@end defun

@node  System,  , Legacy, Session Support
@section System

These procedures are provided by all implementations.

@deffn Procedure slib:load-source name
Loads a file of Scheme source code from @var{name} with the default
filename extension used in SLIB.  For instance if the filename extension
used in SLIB is @file{.scm} then @code{(slib:load-source "foo")} will
load from file @file{foo.scm}.
@end deffn

@deffn Procedure slib:load-compiled name
On implementations which support separtely loadable compiled modules,
loads a file of compiled code from @var{name} with the implementation's
filename extension for compiled code appended.
@end deffn

@deffn Procedure slib:load name
Loads a file of Scheme source or compiled code from @var{name} with the
appropriate suffixes appended.  If both source and compiled code are
present with the appropriate names then the implementation will load
just one.  It is up to the implementation to choose which one will be
loaded.

If an implementation does not support compiled code then
@code{slib:load} will be identical to @code{slib:load-source}.
@end deffn

@deffn Procedure slib:eval obj
@code{eval} returns the value of @var{obj} evaluated in the current top
level environment.@refill
@end deffn

@deffn Procedure slib:eval-load filename eval
@var{filename} should be a string.  If filename names an existing file,
the Scheme source code expressions and definitions are read from the
file and @var{eval} called with them sequentially.  The
@code{slib:eval-load} procedure does not affect the values returned by
@code{current-input-port} and @code{current-output-port}.@refill
@end deffn

@deffn Procedure slib:error arg1 arg2 @dots{}
Outputs an error message containing the arguments, aborts evaluation of
the current form and responds in a system dependent way to the error.
Typical responses are to abort the program or to enter a read-eval-print
loop.@refill
@end deffn

@deffn Procedure slib:exit n
@deffnx Procedure slib:exit
Exits from the Scheme session returning status @var{n} to the system.
If @var{n} is omitted or @code{#t}, a success status is returned to the
system (if possible).  If @var{n} is @code{#f} a failure is returned to
the system (if possible).  If @var{n} is an integer, then @var{n} is
returned to the system (if possible).  If the Scheme session cannot exit
an unspecified value is returned from @code{slib:exit}.
@end deffn


@node Optional SLIB Packages, Procedure and Macro Index, Session Support, Top
@chapter Optional SLIB Packages

Several Scheme packages have been written using SLIB.  There are several
reasons why a package might not be included in the SLIB distribution:
@itemize @bullet
@item
Because it requires special hardware or software which is not universal.
@item
Because it is large and of limited interest to most Scheme users.
@item
Because it has copying terms different enough from the other SLIB
packages that its inclusion would cause confusion.
@item
Because it is an application program, rather than a library module.
@item
Because I have been too busy to integrate it.
@end itemize

Once an optional package is installed (and an entry added to
@code{*catalog*}, the @code{require} mechanism allows it to be called up
and used as easily as any other SLIB package.  Some optional packages
(for which @code{*catalog*} already has entries) available from SLIB
sites are:

@table @asis
@item SLIB-PSD is a portable debugger for Scheme (requires emacs editor).
@lisp
ftp-swiss.ai.mit.edu:pub/scm/slib-psd1-3.tar.gz
prep.ai.mit.edu:pub/gnu/jacal/slib-psd1-3.tar.gz
ftp.maths.tcd.ie:pub/bosullvn/jacal/slib-psd1-3.tar.gz
ftp.cs.indiana.edu:/pub/scheme-repository/utl/slib-psd1-3.tar.gz
@end lisp

With PSD, you can run a Scheme program in an Emacs buffer, set
breakpoints, single step evaluation and access and modify the program's
variables. It works by instrumenting the original source code, so it
should run with any R4RS compliant Scheme. It has been tested with SCM,
Elk 1.5, and the sci interpreter in the Scheme->C system, but should
work with other Schemes with a minimal amount of porting, if at
all. Includes documentation and user's manual.  Written by Pertti
Kellom\"aki, pk@@cs.tut.fi.  The Lisp Pointers article describing PSD
(Lisp Pointers VI(1):15-23, January-March 1993) is available as
@lisp
http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html
@end lisp
@item SLIB-SCHELOG is an embedding of Prolog in Scheme.
@lisp
ftp-swiss.ai.mit.edu:pub/scm/slib-schelog.tar.gz
prep.ai.mit.edu:pub/gnu/jacal/slib-schelog.tar.gz
ftp.maths.tcd.ie:pub/bosullvn/jacal/slib-schelog.tar.gz
ftp.cs.indiana.edu:/pub/scheme-repository/utl/slib-schelog.tar.gz
@end lisp
@end table

@node Procedure and Macro Index, Variable Index, Optional SLIB Packages, Top
@unnumbered Procedure and Macro Index

This is an alphabetical list of all the procedures and macros in SLIB.

@printindex fn

@node Variable Index,  , Procedure and Macro Index, Top
@unnumbered Variable Index

This is an alphabetical list of all the global variables in SLIB.

@printindex vr

@contents
@bye