On 11-jan-2007, at 16:30, Marco Túlio Gontijo e Silva wrote:
Em Qui, 2007-01-11 às 16:14 +0100, minh thu escreveu:
you might want invistigate "heterogeneous lists" : in your case, it's "heterogeneous typle".
But aren't tuples always heterogeneous?
Yes, and precisely therein lies the problem. There is no way for the compiler to infer that in tupleMap f (a, b) = (f a, f b) the type of f should be polymorphic. If you want it to be, explicitly require it to be so: tupleMap :: (forall a b . a -> b) -> (b,c) -> (d,e) tupleMap f (a,b) = (f a, f b) However, this will still not allow you to write tupleMap show ("string",3) as you require f to be fully polymorphic, and not constrained by any context. With regards, Arthur. -- /\ / | arthurvl@cs.uu.nl | Work like you don't need the money /__\ / | A friend is someone with whom | Love like you have never been hurt / \/__ | you can dare to be yourself | Dance like there's nobody watching