[Haskell-cafe] Patch combinators

[Emil Axelsson]

Hi all!

Based on ideas by Koen Claessen, I have made a small module for what 
might be called patch combinators:

   http://hpaste.org/56501

Examples are found as comments.

Before I push this to Hackage, I just wanted to check if there is any 
package that already provides this sort of functionality.

(We're planning to use this module for expressing compile-time 
constraints on Feldspar functions.)

Thanks for any feedback!

/ Emil