guile/examples/box/README

							       -*- outline -*-

* Overview

This directory includes an example program for extending Guile with a
new (and even useful) data type.


* 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'.  See the following example session for usage
details:


** Example Session

$ ./box
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)
$