### 7.7 Extra-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:

- Because it requires special hardware or software which is not universal.
- Because it is large and of limited interest to most Scheme users.
- Because it has copying terms different enough from the other SLIB packages that its inclusion would cause confusion.
- Because it is an application program, rather than a library module.
- Because I have been too busy to integrate it.

Once an optional package is installed (and an entry added to `*catalog*`), the `require` mechanism allows it to be called up and used as easily as any other SLIB package. Some optional packages (for which `*catalog*` already has entries) available from SLIB sites are:

SLIB-PSD ¶

  is a portable debugger for Scheme (requires emacs editor).
  http://groups.csail.mit.edu/mac/ftpdir/scm/slib-psd1-3.tar.gz
  ftp://ftp.cs.indiana.edu/pub/scheme-repository/utl/slib-psd1-3.tar.gz

  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 Kellomäki, the Lisp Pointers article describing PSD (Lisp Pointers VI(1):15-23, January-March 1993) is available at
  http://www.cs.tut.fi/staff/pk/scheme/psd/article/article.html

SCHELOG ¶

  is an embedding of Prolog in Scheme.
  http://www.ccs.neu.edu/~dorai/schelog/schelog.html

JFILTER ¶

  is a Scheme program which converts text among the JIS, EUC, and Shift-JIS Japanese character sets.
  http://www.math.u-toyama.ac.jp/~iwao/Scheme/Jfilter