On Tue, May 28, 2013 at 10:54 AM, Dominique Devriese <
[email protected]> wrote:
> 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)
>
That's Control.Arrow.(***), e.g.:
ghci> (+3) *** (*5) $ (20,30)
(23,150)
>
> mapFst :: (a -> b) -> (a,c) -> (b,c)
> mapFst f = mapPair f id
>
> mapSnd :: (b -> c) -> (a,b) -> (a,c)
> mapSnd = mapPair id
>
That's Control.Arrow.{first, second}:
ghci> first (+10) (1,1)
(11,1)
ghci> second (+10) (1,1)
(1,11)
G
--
Gregory Collins <[email protected]>
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