path: root/FAQ

FAQ (Frequently Asked Questions and answers) for SLIB Scheme Library (slib2a6).
Written by Aubrey Jaffer (jaffer@ai.mit.edu).

		INTRODUCTION AND GENERAL INFORMATION

[]	What is SLIB?

SLIB is a portable scheme library meant to provide compatibiliy and
utility functions for all standard scheme implementations.

[]	What is Scheme?

Scheme is a programming language in the Lisp family.

[]	Which implementations has SLIB been ported to?

SLIB is currently supported by Chez, ELK 2.1, GAMBIT, MacScheme,
MITScheme, scheme->C, Scheme48, T3.1, SCM and VSCM

[]	How can I get SLIB?

SLIB is available via ftp from:
 ftp-swiss.ai.mit.edu:pub/scm/slib2a6.tar.gz
 prep.ai.mit.edu:pub/gnu/jacal/slib2a6.tar.gz
 ftp.maths.tcd.ie:pub/bosullvn/jacal/slib2a6.tar.gz
 ftp.cs.indiana.edu:/pub/scheme-repository/imp/slib2a6.tar.gz

SLIB is also included with SCM floppy disks.

[]	How do I install SLIB?

Read the INSTALLATION INSTRUCTIONS in "slib/README".

[]	What are slib.texi and slib.info?

"slib.texi" is the `texinfo' format documentation for SLIB.
"slib.info" is produced from "slib.texi" by either Gnu Emacs or the
program `makeinfo'.  "slib.info" can be viewed using either Gnu Emacs
or `info' or a text editor.

Programs for printing and viewing TexInfo documentation (which SLIB
has) come with GNU Emacs or can be obtained via ftp from:
prep.ai.mit.edu:pub/gnu/texinfo-3.1.tar.gz

[]	How often is SLIB released?

SLIB was released 9 times in 1993.

[]	What is the latest version?

The version as of this writing is slib2a6.

[]	What version am I using?

The Version is in the first line of the files slib/FAQ, slib/ANNOUNCE,
and slib/README.  If you have Scheme and SLIB running, type
(slib:report-version)

		SLIB INSTALLATION PROBLEMS

[]	When I load an SLIB initialization file for my Scheme
	implementation, I get ERROR: Couldn't find "require.scm"

Did you remember to set either the environment variable
SCHEME_LIBRARY_PATH or the library-vicinity in your initialization
file to the correct location?  Make sure if you set only the
environment variable SCHEME_LIBRARY_PATH that your implementation
supports getenv.

[]	When I load an SLIB initialization file for my Scheme
	implementation, I get ERROR: Couldn't find
	"/usr/local/lib/slibrequire.scm"

Notice that it is looking for "slibrequire.scm" rather than
"slib/require.scm".  You need to put a trailing slash on either the
environment variable SCHEME_LIBRARY_PATH or in the library-vicinity in
your initialization file.

[]	SLIB used to work, but now I get ERROR: Couldn't find
	"slib/require.scm".  What happened?

You changed directories and now the relative pathname
"slib/require.scm" no longer refers to the same directory.  The
environment variable SCHEME_LIBRARY_PATH and library-vicinity in your
initialization file should be absolute pathnames.

[]	When I type (require 'macro) I get "ERROR: unbound variable:
	require".

You need to arrange to have your Scheme implementation load the
appropriate SLIB initialization file ("foo.init") before using SLIB.
If your implementation loads an initialization file on startup, you
can have it load the SLIB initialization file automatically.  For
example (load "/usr/local/lib/slib/foo.init").

[]	Why do I get a string-ref (or other) error when I try to load
	or use SLIB.

Check that the version of the Scheme implementation you are using
matches the version for which the SLIB initialization file was
written.  There are some notes in the SLIB initialization files about
earlier versions.  You may need to get a more recent version of your
Scheme implementation.

		USING SLIB PROCEDURES

[]	I installed SLIB.  When I type (random 5) I get "ERROR:
	unbound variable:  random".  Doesn't SLIB have a `random'
	function?

Before you can use most SLIB functions, the associated module needs to
be loaded.  You do this by typing the line that appears at the top of
the page in slib.info (or slib.texi) where the function is documented.
In the case of random, the line is (require 'random).

[]	Why doesn't SLIB just load all the functions so I don't have
	to type require statements?

SLIB currently has more than 1 Megabyte of Scheme source code.  Many
scheme implementations take unacceptably long to load 1 Megabyte of
source; some implementations cannot allocate enough storage.  If you
use a package often, you can put the require statement in your Scheme
initialization file.  Consult the manual for your Scheme
implementation to find out the initialization file's name.

`Autoloads' will work with many Scheme implementations.  You could put
the following in your initialization file:
 (define (random . args) (require 'random) (apply random args))

I find that I only type require statements at top level when
debugging.  I put require statements in my Scheme files so that the
appropriate modules are loaded automatically.

[]	Why does SLIB have PRINTF when it already has the more
	powerful (CommonLisp) FORMAT?

CommonLisp FORMAT does not support essential features which PRINTF
does.  For instance, how do you format a signed 0 extended number?

  (format t "~8,'0,X~%" -3)	==>	000000-3

But printf gets it right:

  (printf "%08x\n" -3)		==>	-0000003

How can one trunctate a non-numeric field using FORMAT?  This feature
is essential for printing reports.  The first 20 letters of a name is
sufficient to identify it.  But if that name doesn't get trucated to
the desired length it can displace other fields off the page.  Once
again, printf gets it right:

  (printf "%.20s\n" "the quick brown fox jumped over the lazy dog")
				==>	the quick brown fox 

FORMAT also lacks directives for formatting date and time.  printf
does not handle these directly, but a related function strftime does.

[]	Why doesn't SLIB:ERROR call FORMAT?

Format does not provide a method to truncate fields.  When an error
message contains non-terminating or large expressions, the essential
information of the message may be lost in the ensuing deluge.

FORMAT as currently written in SLIB is not reentrant.  Until this is
fixed exception handlers and errors which might occur while using
FORMAT cannot use it.

		MACROS

[]	Why are there so many macro implementations in SLIB?

The R4RS committee specified only the high level pattern language in
the Revised^4 Report on Scheme and left to the free marketplace of
ideas the details of the low-level facility.  Each macro package has a
different low-level facility.  The low-level facilities are sometimes
needed because the high level pattern language is insufficiently
powerful to accomplish tasks macros are often written to do.

[]	Why are there both R4RS macros and Common-Lisp style defmacros
	in SLIB?

Most current Scheme implementations predate the adoption of the R4RS
macro specification.  It turns out that all of the implementations
can support defmacro natively.

[]	I did (LOAD "slib/yasos.scm").  The error I get is "variable
	define-syntax is undefined".

The way to load the struct macro package is (REQUIRE 'YASOS).

[]	I did (REQUIRE 'YASOS).  Now when I type (DEFINE-PREDICATE
	CELL?)  The error I get is "variable define-predicate is
	undefined".

If like most implementations, your Scheme does not natively support
R4RS macros you will need to install a macro-capable read-eval-print
loop.  This is done by:
 (require 'macro)	;already done if you did (require 'yasos)
 (require 'repl)
 (repl:top-level macro:eval)

This is also true for Schemes which don't support DEFMACRO.  The lines
in this case are:
 (require 'repl)
 (repl:top-level defmacro:eval)

[]	I always use R4RS macros.  How can I avoid having to type
	require statements every time I start Scheme?

As is explained in the Repl entry in slib.info (or slib.texi):

 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)