Name
    Math::Cartesian::Product - Generate the cartesian product of zero or
    more lists.

Synopsis
     use Math::Cartesian::Product;

     cartesian {say "@_"} [qw(a b c)], [1..2];

     #  a 1
     #  a 2
     #  b 1
     #  b 2
     #  c 1
     #  c 2

Description
    Generate the cartesian product of zero or more lists.

    Given two lists, say: [a,b] and [1,2,3], the cartesian product is the
    set of all possible ordered pairs:

     (a,1), (a,2), (a,3), (b,1), (b,2), (b,3)

    which select their first element from all the possibilities listed in
    the first list, and select their second element from all the
    possibilities in the second list.

    The idea can be generalized to any number of lists. In particular, the
    cartesian product of zero lists is the empty set, as is the cartesian
    product of any set of lists which contain a list with no elements.

    "cartesian()" takes the following parameters:

    1. A block of code to process each selection of list elements.

    2. zero or more lists.

    "cartesian()" returns an array of references to all the pairs (more
    generally n-tuples) produced, each pair being held as an array.

    "cartesian()" croaks if you try to form the cartesian product of
    something other than a list of things.

    The cartesian product of lists A,B,C is associative, that is:

      (A X B) X C = A X (B X C)

    "cartesian()" respects associativity by allowing you to include a
    cartesian product produced by an earlier call to "cartesian()" in the
    set of lists whose cartesian product is to be formed.

      my $a = [qw(a b)];
      my $b = [cartesian {} $a, $a;
      ok 16 == cartesian {} $b, $b;

      # a a a a
      # a a a b       
      # a a b a 
      # ...

    "cartesian()" is easy to use and fast. It is written in 100% Pure Perl.

Export
    The "cartesian()" function is exported.

Installation
    Standard Module::Build process for building and installing modules:

      perl Build.PL
      ./Build
      ./Build test
      ./Build install

    Or, if you're on a platform (like DOS or Windows) that doesn't require
    the "./" notation, you can do this:

      perl Build.PL
      Build
      Build test
      Build install

Author
    PhilipRBrenan@handybackup.com

    http://www.handybackup.com

See Also
Copyright
    Copyright (c) 2009 Philip R Brenan.

    This module is free software. It may be used, redistributed and/or
    modified under the same terms as Perl itself.

