Data::Variant
-------------

This module implements Variant datatypes for perl. This is something
akin to the Haskell/O'Caml datatypes. The module also offers pattern
matching against the variant constructors.

For more information see for instance:
http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?algebraic+data+type

A typical example:

    use Data::Variant;
    use vars qw(&Empty &Leaf &Node);

    register_variant("Tree","Empty","Leaf <INT>","Node Tree Tree");
    my $tree = Node((Node ((Leaf 3), (Leaf 4))), Leaf 5);

    sub printTree {
	my $tree = shift;
	my ($data, $left, $right);

	print "Data $data\n" 
	    if (match $tree,"Leaf", $data);
	printTree($left), printTree($right) 
	    if (match $tree,"Node",$left,$right);
    }

There is a bigger example included as lambda.pl.

NOTE: If you are used to Haskell, these variants will behave slightly
different. The documentation spells out the differences in detail.

Please report errors or ideas to the author, but you might want to take
a look at the TODO list first.


Copyright (c) 2004 Viktor Leijon (leijon@ludd.ltu.se) All rights
reserved.  This program is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.