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[lilypond.git] / guile18 / examples / box-module / README

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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)
+$