Yes of course, P x is a function, and you can't pattern match against
functions, I knew that. How silly of me, I could have guessed that myself.
On Mon, Mar 9, 2009 at 5:43 PM, Daniel Fischer
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.