Re: [Haskell-cafe] How to understand the fmap here ?

Hello z_axis, Tuesday, May 5, 2009, 1:27:16 PM, you wrote:

floatLocation :: Window -> X (ScreenId, W.RationalRect)

rr <- snd `fmap` floatLocation w

class Functor f where fmap :: (a -> b) -> f a -> f b

looks ok. X===f, fmap executes floatLocation w :: X (ScreenId, W.RationalRect) === f a and then applies snd :: (ScreenId, W.RationalRect) -> W.RationalRect === a->b to result, so that entire (snd `fmap` floatLocation w) has type X W.RationalRect === f b -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com