CanMap

Main.hs

{-# LANGUAGE OverlappingInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}

module Main where
import Prelude hiding (map)
import qualified Data.Text as T
import qualified Data.Vector.Unboxed as U
import Data.Char as C
import Control.Monad (Functor)

class CanMap ca cb a b | ca -> a, cb -> b, cb a -> ca, ca b -> cb where
  map :: (a -> b) -> ca -> cb

instance CanMap T.Text T.Text Char Char where
  map = T.map

instance Functor f => CanMap (f a) (f b) a b where
  map = fmap

instance (U.Unbox a, U.Unbox b) => CanMap (U.Vector a) (U.Vector b) a b where
  map = U.map

main = do
  let l = [1,2,3] :: [Int]
  let m = Just 5
  let t = (T.pack "Hello")
      v = U.fromList [1,2,3]
  print $ map (*2) l
  print $ map (*2) m
  print $ map C.toUpper t
  print $ map (fromIntegral :: Int -> Double) v 
  return ()