Simon PJ and I are implementing view patterns, a way of pattern matching against abstract datatypes, in GHC. Our design is described here:
http://hackage.haskell.org/trac/ghc/wiki/ViewPatterns
If you have any comments or suggestions about this design, we'd love to hear them. You can respond to this list (and we can take it to haskell-cafe if the thread gets long) or, if you prefer, directly to me.
I find the => operator excessive. GHC Haskell seems to be growing too rapidly syntax wise in my opinion. The important features of code are correctness, maintainability and readibility (IMHO), and I think => is working against these. => uses up more syntax. Buys very little. Equivalent to "-> Just _ " or "-> Just x " as far as I can see. I would prefer to type the extra 6 characters rather than having the hidden Maybe. It is also one more thing to learn. One more confusing type error when you mix them up. Rene.