#4189: Add (<.>) operator (generalizing (.) to Functor)

1 Aug 2010


      The proposal is to add (<.>) function to Data.Functor/Control.Applicative:
(<.>) :: (b -> c) -> (a -> f b) -> a -> f c
f <.> g = fmap f . g -- (<.>) = (.) . fmap

In intend it is related to <$> in the same way as (.) is related to $:
(a . b . c) d = a $ b $ c $ d
(a <.> b <.> c) d = a <$> b <$> c <$> d

a is not specialized to f a to allow such chaining:
const 1 <.> print <=< (read :: String -> Int) <.> readFile
  :: (Num t) => FilePath -> IO t

Discussion deadline: 31th August 2010

#4189: Add (<.>) operator (generalizing (.) to Functor)

Maciej Marcin Piechotka