wtf.hs

{-# LANGUAGE MultiParamTypeClasses
  , FlexibleInstances
  , TypeFamilies
  , OverlappingInstances
  , IncoherentInstances #-}
class WTF a b e where
    ($$) :: [a] -> e -> [b]
infixl 5 $$

instance (a ~ c, b ~ d) => WTF a b (c -> d) where
    ($$) = flip map

instance (a ~ b, b ~ c) => WTF a b c where
    xs $$ x = xs ++ [x]
    
--  [] $$ 1 $$ 2 $$ 3 $$ (+10) --> [11,12,13]
-- [] $$ (+1) $$ (+2) $$ (+3) --> []