11 Jan
2007
11 Jan
'07
3:42 p.m.
Udo Stenzel wrote:
Marco T?lio Gontijo e Silva wrote:
is there a way to defined something as a map to use in tuples? I tried this:
mapTuple f (a, b) = (f a, f b)
But the type inferred to it is not as generic as I wanted:
mapTuple :: (t -> t1) -> (t, t) -> (t1, t1)
What you seem to want to do is impossible. Just want type would you want to assign to mapTuple? I bet you can't even express that in natural language, no wonder it's impossible in Haskell.
Maybe some of the type experts could pipe up, but couldn't you express that as an intersection type? mapTuple :: ((a -> b) ^ (c -> d)) -> (a,c) -> (b,d) http://www.cs.cmu.edu/~rwh/theses/pierce.pdf Greg Buchholz