Am Montag, 9. März 2009 17:30 schrieb Peter Verswyvelen: > In Haskell, a data constructor can be used partially applied: > data Pair a b = P a b > > f = P 1 > > however, I cannot do "partial pattern matching", e.g > > firstCoord (P x) = x > > does not work. > > I guess a very important reason must exist why this is the case?
For one, the type. If x :: a, then P x :: b -> Pair a b, so we'd have firstCoord :: (b -> Pair a b) -> a But you can pattern-match only on constructors of the appropriate type. P is not a constructor of (b -> Pair a b) (function types don't have constructors), so you can't match on a partially applied constructor. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe