Dne 28.5.2013 10:54, Dominique Devriese napsal(a):
Hi all,
I often find myself needing the following definitions:
mapPair :: (a -> b) -> (c -> d) -> (a,c) -> (b,d) mapPair f g (x,y) = (f x, g y)
mapFst :: (a -> b) -> (a,c) -> (b,c) mapFst f = mapPair f id
mapSnd :: (b -> c) -> (a,b) -> (a,c) mapSnd = mapPair id
But they seem missing from the prelude and Hoogle or Hayoo only turn up versions of them in packages like scion or fgl. Has anyone else felt the need for these functions? Am I missing some generalisation of them perhaps? Apart from Arrows, there is also package "bifunctors" that defines this functionality for (,), Either and a few others: http://hackage.haskell.org/packages/archive/bifunctors/3.2.0.1/doc/html/Data...
Petr Pudlak