Specializing "Handle" functions

specialize-handle.hs

{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}

data Handle = Handle

generic1 :: Handle -> Char -> Bool -> IO ()
generic1 = undefined

generic2 :: Handle -> String -> Char -> Bool -> IO ()
generic2 = undefined

--------------------------------------------------------------------------------
-- Method 1: the "haskell" way

specialized1 :: Handle -> Bool -> IO ()
specialized1 = generic1 .< 'a'

specialized2 :: Handle -> Bool -> IO ()
specialized2 = generic2 .< "Hello" .< 'b'

(.<) :: (a -> b -> c) -> b -> (a -> c)
(.<) = flip

--------------------------------------------------------------------------------
-- Method 2: the "I promise to always put a top level signature on it" way

specialized1' :: Handle -> Bool -> IO ()
specialized1' = specialize generic1 'a'

specialized2' :: Handle -> Bool -> IO ()
specialized2' = specialize generic2 "Hello" 'b'

class Specialize f g where
    specialize :: f -> g

instance Specialize (a -> b) (a -> b) where
    specialize = id

instance Specialize (a -> c) f => Specialize (a -> b -> c) (b -> f) where
    specialize f = \b -> specialize (\a -> f a b)