Re: Data.Tuple impoverished

On Fri, Jun 15, 2012 at 11:25:56AM +0100, Herbert Valerio Riedel wrote:

Ivan Lazar Miljenovic writes:

...

...

 mapPair :: (a -> c, b -> d) -> (a, b) -> (c, d)  mapFst :: (a -> c) -> (a, b) -> (c, b)  mapSnd :: (b -> c) -> (a, b) -> (a, c)

I believe these are covered by Control.Arrow...

I'm not sure those are really equivalent, as the ones from "Data.Tuple.HT" use lazy pattern matching, e.g.:

mapPair ~(f,g) ~(x,y) = (f x, g y)

mapFst f ~(a,b) = (f a, b)

mapSnd f ~(a,b) = (a, f b)

From Control.Arrow:

instance Arrow (->) where arr f = f first f = f *** id second f = id *** f (***) f g ~(x,y) = (f x, g y)