Programming challenge: wildcard exclusion in cartesian products

[wkehowski at cox.net]

Flame war? Absolutely not. My reason is to learn. There are many sites
dedicated to reasonably objective comparisons between languages. Here
are two examples:

http://www.smallscript.org/Language%20Comparison%20Chart.asp
http://www.jvoegele.com/software/langcomp.html

The wildcard exclusion problem is interesting enough to have many
distinct, elegant solutions in as many languages. It would be
interesting to see if they converge to roughly the same solution or if
there are essential differences. And your code is a crash course in
Haskell! Tossing aside the 'flame war' inquiry your code response is my
only goal. I hope many others find the problem and responses as
fascinating as I do.