-*- outline -*-

* Overview

This directory includes an example program for extending Guile with a
new (and even useful) data type, putting it into a shared library, so it 
can be called from an unmodified guile interpreter. Further, the shared 
library defines a new guile module.


* Build Instructions

To build the example, simply type

  make libbox-module

in this directory.


* The Box Data Type

A box is simply an object for storing one other object in.  It can be
used for passing parameters by reference, for example.  You simply
store an object into a box, pass it to another procedure which can
store a new object into it and thus return a value via the box.


** Usage

Box objects are created with `make-box', set with `box-set!' and
examined with `box-ref'.  Note that these procedures are placed in a
module called (box-module) and can thus only be accessed after using
this module.  See the following example session for usage details.


** The Module (box-module)

Extend your LD_LIBRARY_PATH variable (or equivalent) to include . and
.libs and make sure that your current working directory is the one
this file is contained in.

$ guile
guile> (use-modules (box-module))
guile> (define b (make-box))
guile> b
#<box #f>
guile> (box-set! b '(list of values))
guile> b
#<box (list of values)>
guile> (box-ref b)
(list of values)
guile> (quit)
$


** The Module (box-mixed)

The following example uses the module (box-mixed), also included in
this directory.  It uses the shared library libbox-module like the
module (box-module) above, but does not export the procedures from
that module.  It only implements some procedures for dealing with box
objects.

$ guile
guile> (use-modules (box-mixed))
guile> (define bl  (make-box-list 1 2 3)) 
guile> bl
(#<box 1> #<box 2> #<box 3>)
guile> (box-map 1+ bl)
(#<box 2> #<box 3> #<box 4>)
guile> (quit)
$

If you like this example so much that you want to have it available
for normal usage, install the dynamic libraries in the .libs directory
to the directory $(prefix)/lib and the scheme file `box-module.scm' in
a directory in your GUILE_LOAD_PATH.