Perl algorithm to iterate through subsets of a list.

"Subsets" in this context refers to lists with elements taken
from the original list, and in the same order as the elements in the
original list.  After creating the object, subsequent calls to next()
will return the next such list in lexicographic order (where the alphabet
is the original list).

WWW: http://search.cpan.org/dist/Algorithm-ChooseSubsets/