path: root/slib.info-6

This is Info file slib.info, produced by Makeinfo-1.64 from the input
file slib.texi.

  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.

  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.


File: slib.info,  Node: Sorting,  Next: Topological Sort,  Prev: Pretty-Print,  Up: Procedures

Sorting
=======

  `(require 'sort)'

  Many Scheme systems provide some kind of sorting functions.  They do
not, however, always provide the *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 `sort' and `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
     (merge predicate list1 list2)
     (merge! predicate list1 list2)
     (sort predicate list)
     (sort! predicate list)

while MIT Scheme 7.1, following Common LISP, offers unstable
     (sort list predicate)

TI PC Scheme offers
     (sort! list/vector predicate?)

and Elk offers
     (sort list/vector predicate?)
     (sort! list/vector predicate?)

  Here is a comprehensive catalogue of the variations I have found.

  1. Both `sort' and `sort!' may be provided.

  2. `sort' may be provided without `sort!'.

  3. `sort!' may be provided without `sort'.

  4. Neither may be provided.

  5. The sequence argument may be either a list or a vector.

  6. The sequence argument may only be a list.

  7. The sequence argument may only be a vector.

  8. The comparison function may be expected to behave like `<'.

  9. The comparison function may be expected to behave like `<='.

 10. The interface may be `(sort predicate? sequence)'.

 11. The interface may be `(sort sequence predicate?)'.

 12. The interface may be `(sort sequence &optional (predicate? <))'.

 13. The sort may be stable.

 14. The sort may be unstable.

  All of this variation really does not help anybody.  A nice simple
merge sort is both stable and fast (quite a lot faster than *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 *last* parameter which is a
comparison function.  A comparison function `f' is a function of 2
arguments which acts like `<'.  For example,

     (not (f x x))
     (and (f x y) (f y z)) == (f x z)

  The standard functions `<', `>', `char<?', `char>?', `char-ci<?',
`char-ci>?', `string<?', `string>?', `string-ci<?', and `string-ci>?'
are suitable for use as comparison functions.  Think of `(less? x y)'
as saying when `x' must *not* precede `y'.

 - Function: sorted? SEQUENCE LESS?
     Returns `#t' when the sequence argument is in non-decreasing order
     according to LESS? (that is, there is no adjacent pair `... x y
     ...' for which `(less? y x)').

     Returns `#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.

 - Function: 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 `sort' is our `sort!' (well, in
     fact Common LISP's `stable-sort' is our `sort!', merge sort is
     *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
     *order* of the arguments.

 - Procedure: merge! LIST1 LIST2 LESS?
     Merges two lists, re-using the pairs of LIST1 and LIST2 to build
     the result.  If the code is compiled, and 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 LIST1 or the first pair of
     LIST2, but you can't predict which.

     The code of `merge' and `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 `null?' test
     per iteration.)

 - Function: 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 `(sorted? (sort sequence less?) less?)'.  The original
     sequence is not altered in any way.  The new sequence shares its
     *elements* with the old one; no elements are copied.

 - 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 `sort!', thinking
     that it doesn't return a value.  It needs to be pointed out that
          (set! slist (sort! slist <))

     is the proper usage, not
          (sort! slist <)

  Note that these functions do *not* accept a CL-style `:key' argument.
A simple device for obtaining the same expressiveness is to define
     (define (keyed less? key)
       (lambda (x y) (less? (key x) (key y))))

and then, when you would have written
     (sort a-sequence #'my-less :key #'my-key)

in Common LISP, just write
     (sort! a-sequence (keyed my-less? my-key))

in Scheme.


File: slib.info,  Node: Topological Sort,  Next: Standard Formatted I/O,  Prev: Sorting,  Up: Procedures

Topological Sort
================

  `(require 'topological-sort)' or `(require 'tsort)'

The algorithm is inspired by Cormen, Leiserson and Rivest (1990)
`Introduction to Algorithms', chapter 23.

 - Function: tsort DAG PRED
 - Function: topological-sort DAG PRED
     where
    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.

    PRED
          is one of `eq?', `eqv?', `equal?', `=', `char=?',
          `char-ci=?', `string=?', or `string-ci=?'.

     Sort the directed acyclic graph DAG so that for every edge from
     vertex U to V, U will come before V in the resulting list of
     vertices.

     Time complexity: O (|V| + |E|)

     Example (from Cormen):
          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:

          (require 'tsort)
          (tsort '((shirt tie belt)
                   (tie jacket)
                   (belt jacket)
                   (watch)
                   (pants shoes belt)
                   (undershorts pants shoes)
                   (socks shoes))
                 eq?)
          =>
          (socks undershorts pants shoes watch shirt belt tie jacket)


File: slib.info,  Node: Standard Formatted I/O,  Next: String-Case,  Prev: Topological Sort,  Up: Procedures

Standard Formatted I/O
======================

* Menu:

* Standard Formatted Output::
* Standard Formatted Input::

stdio
-----

  `(require 'stdio)'

  `require's `printf' and `scanf' and additionally defines the symbols:

 - Variable: stdin
     Defined to be `(current-input-port)'.

 - Variable: stdout
     Defined to be `(current-output-port)'.

 - Variable: stderr
     Defined to be `(current-error-port)'.


File: slib.info,  Node: Standard Formatted Output,  Next: Standard Formatted Input,  Prev: Standard Formatted I/O,  Up: Standard Formatted I/O

Standard Formatted Output
-------------------------

  `(require 'printf)'

 - Procedure: printf FORMAT ARG1 ...
 - Procedure: fprintf PORT FORMAT ARG1 ...
 - Procedure: sprintf STR FORMAT ARG1 ...
     Each function converts, formats, and outputs its ARG1 ...
     arguments according to the control string FORMAT argument and
     returns the number of characters output.

     `printf' sends its output to the port `(current-output-port)'.
     `fprintf' sends its output to the port PORT.  `sprintf'
     `string-set!'s locations of the non-constant string argument STR
     to the output characters.

          *Note:* sprintf should be changed to a macro so a `substring'
          expression could be used for the STR argument.

     The string 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 ARG1 ....  The
     results are undefined if there are an insufficient number of
     arguments for the format.  If FORMAT is exhausted while some of the
     ARG1 ... arguments remain unused, the excess ARG1 ... arguments
     are ignored.

     The conversion specifications in a format string have the form:

          % [ FLAGS ] [ WIDTH ] [ . PRECISION ] [ TYPE ] CONVERSION

     An output conversion specifications consist of an initial `%'
     character followed in sequence by:

        * Zero or more "flag characters" that modify the normal
          behavior of the conversion specification.

         `-'
               Left-justify the result in the field.  Normally the
               result is right-justified.

         `+'
               For the signed `%d' and `%i' conversions and all inexact
               conversions, prefix a plus sign if the value is positive.

         ` '
               For the signed `%d' and `%i' conversions, if the result
               doesn't start with a plus or minus sign, prefix it with
               a space character instead.  Since the `+' flag ensures
               that the result includes a sign, this flag is ignored if
               both are specified.

         `#'
               For inexact conversions, `#' specifies that the result
               should always include a decimal point, even if no digits
               follow it.  For the `%g' and `%G' conversions, this also
               forces trailing zeros after the decimal point to be
               printed where they would otherwise be elided.

               For the `%o' conversion, force the leading digit to be
               `0', as if by increasing the precision.  For `%x' or
               `%X', prefix a leading `0x' or `0X' (respectively) to
               the result.  This doesn't do anything useful for the
               `%d', `%i', or `%u' conversions.  Using this flag
               produces output which can be parsed by the `scanf'
               functions with the `%i' conversion (*note Standard
               Formatted Input::.).

         `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 `-' flag is also specified, or if
               a precision is specified for an exact converson.

        * An optional decimal integer specifying the "minimum field
          width".  If the normal conversion produces fewer characters
          than this, the field is padded (with spaces or zeros per the
          `0' flag) to the specified width.  This is a *minimum* width;
          if the normal conversion produces more characters than this,
          the field is *not* truncated.

          Alternatively, if the field width is `*', 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 `-'
          flag is set (see above) and the absolute value is used as the
          field width.

        * An optional "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 (`.') followed optionally by a decimal integer (which
          defaults to zero if omitted).

          Alternatively, if the precision is `.*', 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 `*' for both the field
          width and precision, the field width argument precedes the
          precision argument.  The `.*' precision is an enhancement.  C
          library versions may not accept this syntax.

          For the `%f', `%e', and `%E' conversions, the precision
          specifies how many digits follow the decimal-point character.
          The default precision is `6'.  If the precision is
          explicitly `0', the decimal point character is suppressed.

          For the `%g' and `%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 `0' or not specified for `%g'
          or `%G', it is treated like a value of `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 `0' with an explicit
          precision of zero produces no characters.

        * An optional one of `l', `h' or `L', which is ignored for
          numeric conversions.  It is an error to specify these
          modifiers for non-numeric conversions.

        * A character that specifies the conversion to be applied.

Exact Conversions
.................

    `d', `i'
          Print an integer as a signed decimal number.  `%d' and `%i'
          are synonymous for output, but are different when used with
          `scanf' for input (*note Standard Formatted Input::.).

    `o'
          Print an integer as an unsigned octal number.

    `u'
          Print an integer as an unsigned decimal number.

    `x', `X'
          Print an integer as an unsigned hexadecimal number.  `%x'
          prints using the digits `0123456789abcdef'.  `%X' prints
          using the digits `0123456789ABCDEF'.

Inexact Conversions
...................

     *Note:* Inexact conversions are not supported yet.

    `f'
          Print a floating-point number in fixed-point notation.

    `e', `E'
          Print a floating-point number in exponential notation.  `%e'
          prints `e' between mantissa and exponont.  `%E' prints `E'
          between mantissa and exponont.

    `g', `G'
          Print a floating-point number in either normal or exponential
          notation, whichever is more appropriate for its magnitude.
          `%g' prints `e' between mantissa and exponont.  `%G' prints
          `E' between mantissa and exponont.

Other Conversions
.................

    `c'
          Print a single character.  The `-' flag is the only one which
          can be specified.  It is an error to specify a precision.

    `s'
          Print a string.  The `-' 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.

    `a', `A'
          Print a scheme expression.  The `-' flag left-justifies the
          output.  The `#' flag specifies that strings and characters
          should be quoted as by `write' (which can be read using
          `read'); otherwise, output is as `display' prints.  A
          precision specifies the maximum number of characters to
          output; otherwise as many characters as needed are output.

          *Note:* `%a' and `%A' are SLIB extensions.

    `%'
          Print a literal `%' character.  No argument is consumed.  It
          is an error to specifiy flags, field width, precision, or
          type modifiers with `%%'.


File: slib.info,  Node: Standard Formatted Input,  Prev: Standard Formatted Output,  Up: Standard Formatted I/O

Standard Formatted Input
------------------------

  `(require 'scanf)'

 - Function: scanf-read-list FORMAT
 - Function: scanf-read-list FORMAT PORT
 - Function: scanf-read-list FORMAT STRING

 - Macro: scanf FORMAT ARG1 ...
 - Macro: fscanf PORT FORMAT ARG1 ...
 - Macro: sscanf STR FORMAT ARG1 ...
     Each function reads characters, interpreting them according to the
     control string FORMAT argument.

     `scanf-read-list' returns a list of the items specified as far as
     the input matches FORMAT.  `scanf', `fscanf', and `sscanf' return
     the number of items successfully matched and stored.  `scanf',
     `fscanf', and `sscanf' also set the location corresponding to ARG1
     ... using the methods:

    symbol
          `set!'

    car expression
          `set-car!'

    cdr expression
          `set-cdr!'

    vector-ref expression
          `vector-set!'

    substring expression
          `substring-move-left!'

     The argument to a `substring' expression in ARG1 ... must be a
     non-constant string.  Characters will be stored starting at the
     position specified by the second argument to `substring'.  The
     number of characters stored will be limited by either the position
     specified by the third argument to `substring' or the length of the
     matched string, whichever is less.

     The control string, FORMAT, contains conversion specifications and
     other characters used to direct interpretation of input sequences.
     The control string contains:

        * White-space characters (blanks, tabs, newlines, or formfeeds)
          that cause input to be read (and discarded) up to the next
          non-white-space character.

        * An ordinary character (not `%') that must match the next
          character of the input stream.

        * Conversion specifications, consisting of the character `%', an
          optional assignment suppressing character `*', an optional
          numerical maximum-field width, an optional `l', `h' or `L'
          which is ignored, and a conversion code.

     Unless the specification contains the `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 `*' 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.

          *Note:* This specification of format strings differs from the
          `ANSI C' and `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 `ANSI C' and SLIB, prepend whitespace to all
          conversion specifications except `[' and `c'.

     The conversion code indicates the interpretation of the input
     field; For a suppressed field, no value is returned.  The
     following conversion codes are legal:

    `%'
          A single % is expected in the input at this point; no value
          is returned.

    `d', `D'
          A decimal integer is expected.

    `u', `U'
          An unsigned decimal integer is expected.

    `o', `O'
          An octal integer is expected.

    `x', `X'
          A hexadecimal integer is expected.

    `i'
          An integer is expected.  Returns the value of the next input
          item, interpreted according to C conventions; a leading `0'
          implies octal, a leading `0x' implies hexadecimal; otherwise,
          decimal is assumed.

    `n'
          Returns the total number of bytes (including white space)
          read by `scanf'.  No input is consumed by `%n'.

    `f', `F', `e', `E', `g', `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 `.', followed
          by an optional exponent field consisting of an `E' or an `e',
          followed by an optional `+', `-', or space, followed by an
          integer.

    `c', `C'
          WIDTH characters are expected.  The normal
          skip-over-white-space is suppressed in this case; to read the
          next non-space character, use `%1s'.  If a field width is
          given, a string is returned; up to the indicated number of
          characters is read.

    `s', `S'
          A character string is expected The input field is terminated
          by a white-space character.  `scanf' cannot read a null
          string.

    `['
          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.  `^', 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 `[0123456789]' to be expressed `[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 `^') 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.

     The `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.


File: slib.info,  Node: String-Case,  Next: String Ports,  Prev: Standard Formatted I/O,  Up: Procedures

String-Case
===========

  `(require 'string-case)'

 - Procedure: string-upcase STR
 - Procedure: string-downcase STR
 - Procedure: string-capitalize STR
     The obvious string conversion routines.  These are non-destructive.

 - Function: string-upcase! STR
 - Function: string-downcase! STR
 - Function: string-captialize! STR
     The destructive versions of the functions above.


File: slib.info,  Node: String Ports,  Next: String Search,  Prev: String-Case,  Up: Procedures

String Ports
============

  `(require 'string-port)'

 - Procedure: call-with-output-string PROC
     PROC must be a procedure of one argument.  This procedure calls
     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.

 - Procedure: call-with-input-string STRING PROC
     PROC must be a procedure of one argument.  This procedure calls
     PROC with one argument: an (newly created) input port from which
     STRING's contents may be read.  When PROC returns, the port is
     closed and the value yielded by the procedure PROC is returned.


File: slib.info,  Node: String Search,  Next: Tektronix Graphics Support,  Prev: String Ports,  Up: Procedures

String Search
=============

  `(require 'string-search)'

 - Procedure: string-index STRING CHAR
     Returns the index of the first occurence of CHAR within STRING, or
     `#f' if the STRING does not contain a character CHAR.

 - procedure: substring? PATTERN STRING
     Searches STRING to see if some substring of STRING is equal to
     PATTERN.  `substring?' returns the index of the first character of
     the first substring of STRING that is equal to PATTERN; or `#f' if
     STRING does not contain PATTERN.

          (substring? "rat" "pirate") =>  2
          (substring? "rat" "outrage") =>  #f
          (substring? "" any-string) =>  0

 - Procedure: find-string-from-port? STR IN-PORT MAX-NO-CHARS
 - Procedure: find-string-from-port? STR IN-PORT
     Looks for a string STR within the first MAX-NO-CHARS chars of the
     input port IN-PORT.  MAX-NO-CHARS may be omitted: in that case,
     the search span is limited by the end of the input stream.  When
     the 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 STR) The function returns `#f' when
     the STR isn't found.

     `find-string-from-port?' reads the port *strictly* sequentially,
     and does not perform any buffering.  So `find-string-from-port?'
     can be used even if the IN-PORT is open to a pipe or other
     communication channel.


File: slib.info,  Node: Tektronix Graphics Support,  Next: Tree Operations,  Prev: String Search,  Up: Procedures

Tektronix Graphics Support
==========================

  *Note:* The Tektronix graphics support files need more work, and are
not complete.

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.

 - Procedure: tek40:init

 - Procedure: tek40:graphics

 - Procedure: tek40:text

 - Procedure: tek40:linetype LINETYPE

 - Procedure: tek40:move X Y

 - Procedure: tek40:draw X Y

 - Procedure: tek40:put-text X Y STR

 - Procedure: tek40:reset

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.

 - Procedure: tek41:init

 - Procedure: tek41:reset

 - Procedure: tek41:graphics

 - Procedure: tek41:move X Y

 - Procedure: tek41:draw X Y

 - Procedure: tek41:point X Y NUMBER

 - Procedure: tek41:encode-x-y X Y

 - Procedure: tek41:encode-int NUMBER


File: slib.info,  Node: Tree Operations,  Prev: Tektronix Graphics Support,  Up: Procedures

Tree operations
===============

  `(require 'tree)'

  These are operations that treat lists a representations of trees.

 - Function: subst NEW OLD TREE
 - Function: substq NEW OLD TREE
 - Function: substv NEW OLD TREE
     `subst' makes a copy of TREE, substituting NEW for every subtree
     or leaf of TREE which is `equal?' to OLD and returns a modified
     tree.  The original TREE is unchanged, but may share parts with
     the result.

     `substq' and `substv' are similar, but test against OLD using
     `eq?' and `eqv?' respectively.

     Examples:
          (substq 'tempest 'hurricane '(shakespeare wrote (the hurricane)))
             => (shakespeare wrote (the tempest))
          (substq 'foo '() '(shakespeare wrote (twelfth night)))
             => (shakespeare wrote (twelfth night . foo) . foo)
          (subst '(a . cons) '(old . pair)
                 '((old . spice) ((old . shoes) old . pair) (old . pair)))
             => ((old . spice) ((old . shoes) a . cons) (a . cons))

 - Function: copy-tree TREE
     Makes a copy of the nested list structure TREE using new pairs and
     returns it.  All levels are copied, so that none of the pairs in
     the tree are `eq?' to the original ones - only the leaves are.

     Example:
          (define bar '(bar))
          (copy-tree (list bar 'foo))
             => ((bar) foo)
          (eq? bar (car (copy-tree (list bar 'foo))))
             => #f


File: slib.info,  Node: Standards Support,  Next: Session Support,  Prev: Procedures,  Up: Top

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


File: slib.info,  Node: With-File,  Next: Transcripts,  Prev: Standards Support,  Up: Standards Support

With-File
=========

  `(require 'with-file)'

 - Function: with-input-from-file FILE THUNK
 - Function: with-output-to-file FILE THUNK
     Description found in R4RS.


File: slib.info,  Node: Transcripts,  Next: Rev2 Procedures,  Prev: With-File,  Up: Standards Support

Transcripts
===========

  `(require 'transcript)'

 - Function: transcript-on FILENAME
 - Function: transcript-off FILENAME
     Redefines `read-char', `read', `write-char', `write', `display',
     and `newline'.


File: slib.info,  Node: Rev2 Procedures,  Next: Rev4 Optional Procedures,  Prev: Transcripts,  Up: Standards Support

Rev2 Procedures
===============

  `(require 'rev2-procedures)'

  The procedures below were specified in the `Revised^2 Report on
Scheme'.  *N.B.*: The symbols `1+' and `-1+' are not `R4RS' syntax.
Scheme->C, for instance, barfs on this module.

 - Procedure: substring-move-left! STRING1 START1 END1 STRING2 START2
 - Procedure: substring-move-right! STRING1 START1 END1 STRING2 START2
     STRING1 and STRING2 must be a strings, and START1, START2 and END1
     must be exact integers satisfying

          0 <= START1 <= END1 <= (string-length STRING1)
          0 <= START2 <= END1 - START1 + START2 <= (string-length STRING2)

     `substring-move-left!' and `substring-move-right!' store
     characters of STRING1 beginning with index START1 (inclusive) and
     ending with index END1 (exclusive) into STRING2 beginning with
     index START2 (inclusive).

     `substring-move-left!' stores characters in time order of
     increasing indices.  `substring-move-right!' stores characters in
     time order of increasing indeces.

 - Procedure: substring-fill! STRING START END CHAR
     Fills the elements START-END of STRING with the character CHAR.

 - Function: string-null? STR
     == `(= 0 (string-length STR))'

 - Procedure: append! . PAIRS
     Destructively appends its arguments.  Equivalent to `nconc'.

 - Function: 1+ N
     Adds 1 to N.

 - Function: -1+ N
     Subtracts 1 from N.

 - Function: <?
 - Function: <=?
 - Function: =?
 - Function: >?
 - Function: >=?
     These are equivalent to the procedures of the same name but
     without the trailing `?'.


File: slib.info,  Node: Rev4 Optional Procedures,  Next: Multi-argument / and -,  Prev: Rev2 Procedures,  Up: Standards Support

Rev4 Optional Procedures
========================

  `(require 'rev4-optional-procedures)'

  For the specification of these optional procedures, *Note Standard
procedures: (r4rs)Standard procedures.

 - Function: list-tail L P

 - Function: string->list S

 - Function: list->string L

 - Function: string-copy

 - Procedure: string-fill! S OBJ

 - Function: list->vector L

 - Function: vector->list S

 - Procedure: vector-fill! S OBJ


File: slib.info,  Node: Multi-argument / and -,  Next: Multi-argument Apply,  Prev: Rev4 Optional Procedures,  Up: Standards Support

Multi-argument / and -
======================

  `(require 'mutliarg/and-)'

  For the specification of these optional forms, *Note Numerical
operations: (r4rs)Numerical operations.  The `two-arg:'* forms are only
defined if the implementation does not support the many-argument forms.

 - Function: two-arg:/ N1 N2
     The original two-argument version of `/'.

 - Function: / DIVIDENT . DIVISORS

 - Function: two-arg:- N1 N2
     The original two-argument version of `-'.

 - Function: - MINUEND . SUBTRAHENDS


File: slib.info,  Node: Multi-argument Apply,  Next: Rationalize,  Prev: Multi-argument / and -,  Up: Standards Support

Multi-argument Apply
====================

  `(require 'multiarg-apply)'

For the specification of this optional form, *Note Control features:
(r4rs)Control features.

 - Function: two-arg:apply PROC L
     The implementation's native `apply'.  Only defined for
     implementations which don't support the many-argument version.

 - Function: apply PROC . ARGS


File: slib.info,  Node: Rationalize,  Next: Promises,  Prev: Multi-argument Apply,  Up: Standards Support

Rationalize
===========

  `(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.

 - Function: rationalize X E


File: slib.info,  Node: Promises,  Next: Dynamic-Wind,  Prev: Rationalize,  Up: Standards Support

Promises
========

  `(require 'promise)'

 - Function: make-promise PROC

  Change occurrences of `(delay EXPRESSION)' to `(make-promise (lambda
() EXPRESSION))' and `(define force promise:force)' to implement
promises if your implementation doesn't support them (*note Control
features: (r4rs)Control features.).


File: slib.info,  Node: Dynamic-Wind,  Next: Values,  Prev: Promises,  Up: Standards Support

Dynamic-Wind
============

  `(require 'dynamic-wind)'

  This facility is a generalization of Common LISP `unwind-protect',
designed to take into account the fact that continuations produced by
`call-with-current-continuation' may be reentered.

 - Procedure: dynamic-wind THUNK1 THUNK2 THUNK3
     The arguments THUNK1, THUNK2, and THUNK3 must all be procedures of
     no arguments (thunks).

     `dynamic-wind' calls THUNK1, THUNK2, and then THUNK3.  The value
     returned by THUNK2 is returned as the result of `dynamic-wind'.
     THUNK3 is also called just before control leaves the dynamic
     context of THUNK2 by calling a continuation created outside that
     context.  Furthermore, THUNK1 is called before reentering the
     dynamic context of THUNK2 by calling a continuation created inside
     that context.  (Control is inside the context of THUNK2 if THUNK2
     is on the current return stack).

     *Warning:* There is no provision for dealing with errors or
     interrupts.  If an error or interrupt occurs while using
     `dynamic-wind', the dynamic environment will be that in effect at
     the time of the error or interrupt.


File: slib.info,  Node: Values,  Next: Time,  Prev: Dynamic-Wind,  Up: Standards Support

Values
======

  `(require 'values)'

 - Function: values OBJ ...
     `values' takes any number of arguments, and passes (returns) them
     to its continuation.

 - Function: call-with-values THUNK PROC
     THUNK must be a procedure of no arguments, and PROC must be a
     procedure.  `call-with-values' calls THUNK with a continuation
     that, when passed some values, calls PROC with those values as
     arguments.

     Except for continuations created by the `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 `call-with-values' procedure is
     unspecified.


File: slib.info,  Node: Time,  Next: CLTime,  Prev: Values,  Up: Standards Support

Time
====

  The procedures `current-time', `difftime', and `offset-time' are
supported by all implementations (SLIB provides them if feature
`('current-time)' is missing.  `current-time' returns a "calendar time"
(caltime) which can be a number or other type.

 - Function: 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 `get-universal-time' in *Note CLTime::.  On
     implementations which cannot support actual times, `current-time'
     will increment a counter and return its value when called.

 - Function: difftime CALTIME1 CALTIME0
     Returns the difference (number of seconds) between twe calendar
     times: CALTIME1 - CALTIME0.  CALTIME0 can also be a number.

 - Function: offset-time CALTIME OFFSET
     Returns the calendar time of CALTIME offset by OFFSET number of
     seconds `(+ caltime offset)'.

     (require 'posix-time)

  These procedures are intended to be compatible with Posix time
conversion functions.

 - Variable: *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).  `*timezone*' is initialized by `tzset'.

 - Function: tzset
     initializes the *TIMEZONE* variable from the TZ environment
     variable.  This function is automatically called by the other time
     conversion functions that depend on the time zone.

 - Function: gmtime CALTIME
     converts the calendar time CALTIME to a vector of integers
     representing the time expressed as Coordinated Universal Time
     (UTC).

 - Function: localtime CALTIME
     converts the calendar time CALTIME to a vector of integers
     expressed relative to the user's time zone.  `localtime' sets the
     variable *TIMEZONE* with the difference between Coordinated
     Universal Time (UTC) and local standard time in seconds by calling
     `tzset'.  The elements of the returned vector are as follows:

       0.  seconds (0 - 61)

       1.  minutes (0 - 59)

       2.  hours since midnight

       3.  day of month

       4.  month (0 - 11).  Note difference from
          `decode-universal-time'.

       5.  year (A.D.)

       6.  day of week (0 - 6)

       7.  day of year (0 - 365)

       8.  1 for daylight savings, 0 for regular time

 - Function: mktime UNIVTIME
     Converts a vector of integers in Coordinated Universal Time (UTC)
     format to calendar time (caltime) format.

 - Function: asctime UNIVTIME
     Converts the vector of integers CALTIME in Coordinated Universal
     Time (UTC) format into a string of the form `"Wed Jun 30 21:49:08
     1993"'.

 - Function: ctime CALTIME
     Equivalent to `(time:asctime (time:localtime CALTIME))'.


File: slib.info,  Node: CLTime,  Prev: Time,  Up: Standards Support

CLTime
======

 - Function: get-decoded-time
     Equivalent to `(decode-universal-time (get-universal-time))'.

 - Function: get-universal-time
     Returns the current time as "Universal Time", number of seconds
     since 00:00:00 Jan 1, 1900 GMT.  Note that the reference time is
     different from `current-time'.

 - Function: decode-universal-time UNIVTIME
     Converts UNIVTIME to "Decoded Time" format.  Nine values are
     returned:
       0.  seconds (0 - 61)

       1.  minutes (0 - 59)

       2.  hours since midnight

       3.  day of month

       4.  month (1 - 12).  Note difference from `gmtime' and
          `localtime'.

       5.  year (A.D.)

       6.  day of week (0 - 6)

       7.  #t for daylight savings, #f otherwise

       8.  hours west of GMT (-24 - +24)

     Notice that the values returned by `decode-universal-time' do not
     match the arguments to `encode-universal-time'.

 - Function: encode-universal-time SECOND MINUTE HOUR DATE MONTH YEAR
 - Function: encode-universal-time SECOND MINUTE HOUR DATE MONTH YEAR
          TIME-ZONE
     Converts the arguments in Decoded Time format to Universal Time
     format.  If 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 `decode-universal-time' do not
     match the arguments to `encode-universal-time'.


File: slib.info,  Node: Session Support,  Next: Optional SLIB Packages,  Prev: Standards Support,  Up: Top

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
`*.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


File: slib.info,  Node: Repl,  Next: Quick Print,  Prev: Session Support,  Up: Session Support

Repl
====

  `(require 'repl)'

  Here is a read-eval-print-loop which, given an eval, evaluates forms.

 - Procedure: repl:top-level REPL:EVAL
     `read's, `repl:eval's and `write's expressions from
     `(current-input-port)' to `(current-output-port)' until an
     end-of-file is encountered.  `load', `slib:eval', `slib:error',
     and `repl:quit' dynamically bound during `repl:top-level'.

 - Procedure: repl:quit
     Exits from the invocation of `repl:top-level'.

  The `repl:' procedures establish, as much as is possible to do
portably, a top level environment supporting macros.  `repl:top-level'
uses `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 `slib:error'.  It will
display its arguments and reenter `repl:top-level'.  `slib:error'
dynamically bound by `repl:top-level'.

  To have your top level loop always use macros, add any interrupt
catching lines and the following lines to your Scheme init file:
     (require 'macro)
     (require 'repl)
     (repl:top-level macro:eval)


File: slib.info,  Node: Quick Print,  Next: Debug,  Prev: Repl,  Up: Session Support

Quick Print
===========

  `(require 'qp)'

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.

     Notice that the neccessity for truncating output eliminates
     Common-Lisp's *Note Format:: from consideration; even when
     variables `*print-level*' and `*print-level*' are set, huge
     strings and bit-vectors are *not* limited.

 - Procedure: qp ARG1 ...
 - Procedure: qpn ARG1 ...
 - Procedure: qpr ARG1 ...
     `qp' writes its arguments, separated by spaces, to
     `(current-output-port)'.  `qp' compresses printing by substituting
     `...' for substructure it does not have sufficient room to print.
     `qpn' is like `qp' but outputs a newline before returning.  `qpr'
     is like `qpn' except that it returns its last argument.

 - Variable: *qp-width*
     `*qp-width*' is the largest number of characters that `qp' should
     use.


File: slib.info,  Node: Debug,  Next: Breakpoints,  Prev: Quick Print,  Up: Session Support

Debug
=====

  `(require 'debug)'

Requiring `debug' automatically requires `trace' and `break'.

An application with its own datatypes may want to substitute its own
printer for `qp'.  This example shows how to do this:

     (define qpn (lambda args) ...)
     (provide 'qp)
     (require 'debug)

 - Procedure: trace-all FILE
     Traces (*note Trace::.) all procedures `define'd at top-level in
     file `file'.

 - Procedure: break-all FILE
     Breakpoints (*note Breakpoints::.) all procedures `define'd at
     top-level in file `file'.


File: slib.info,  Node: Breakpoints,  Next: Trace,  Prev: Debug,  Up: Session Support

Breakpoints
===========

  `(require 'break)'

 - Function: init-debug
     If your Scheme implementation does not support `break' or `abort',
     a message will appear when you `(require 'break)' or `(require
     'debug)' telling you to type `(init-debug)'.  This is in order to
     establish a top-level continuation.  Typing `(init-debug)' at top
     level sets up a continuation for `break'.

 - Function: breakpoint ARG1 ...
     Returns from the top level continuation and pushes the
     continuation from which it was called on a continuation stack.

 - Function: continue
     Pops the topmost continuation off of the continuation stack and
     returns an unspecified value to it.

 - Function: continue ARG1 ...
     Pops the topmost continuation off of the continuation stack and
     returns ARG1 ... to it.

 - Macro: break PROC1 ...
     Redefines the top-level named procedures given as arguments so that
     `breakpoint' is called before calling PROC1 ....

 - Macro: 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.

 - Macro: unbreak PROC1 ...
     Turns breakpoints off for its arguments.

 - Macro: unbreak
     With no arguments, unbreaks all currently broken identifiers and
     returns a list of these formerly broken identifiers.

  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.

 - Function: breakf PROC
 - Function: breakf PROC NAME
 - Function: debug:breakf PROC
 - Function: debug:breakf PROC NAME
     To break, type
          (set! SYMBOL (breakf SYMBOL))

     or
          (set! SYMBOL (breakf SYMBOL 'SYMBOL))

     or
          (define SYMBOL (breakf FUNCTION))

     or
          (define SYMBOL (breakf FUNCTION 'SYMBOL))

 - Function: unbreakf PROC
 - Function: debug:unbreakf PROC
     To unbreak, type
          (set! SYMBOL (unbreakf SYMBOL))


File: slib.info,  Node: Trace,  Next: Getopt,  Prev: Breakpoints,  Up: Session Support

Tracing
=======

  `(require 'trace)'

 - Macro: trace PROC1 ...
     Traces the top-level named procedures given as arguments.

 - Macro: 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.

 - Macro: untrace PROC1 ...
     Turns tracing off for its arguments.

 - Macro: untrace
     With no arguments, untraces all currently traced identifiers and
     returns a list of these formerly traced identifiers.

  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.

 - Function: tracef PROC
 - Function: tracef PROC NAME
 - Function: debug:tracef PROC
 - Function: debug:tracef PROC NAME
     To trace, type
          (set! SYMBOL (tracef SYMBOL))

     or
          (set! SYMBOL (tracef SYMBOL 'SYMBOL))

     or
          (define SYMBOL (tracef FUNCTION))

     or
          (define SYMBOL (tracef FUNCTION 'SYMBOL))

 - Function: untracef PROC
 - Function: debug:untracef PROC
     To untrace, type
          (set! SYMBOL (untracef SYMBOL))