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-*- outline -*-
* Overview
This directory includes an example program for extending Guile with a
new (and even useful) data type.
The `box' program created by this example is nearly identical to the
one produced in directory ../box, with one (important) difference: The
interpreter in this directory will place all defined primitive
procedures in a module called (box-module). That means that this
module must be used before the primitives can be accessed.
* Build Instructions
To build the example, simply type
make box
in this directory.
The resulting `box' program is a Guile interpreter which has one
additional data type called `box'.
* 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:
** Example Session
$ ./box
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)
$
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