{-# LANGUAGE ScopedTypeVariables #-}
module ProxyExample where

------------------------

import Data.Proxy
import Prelude

-------------------------

-- This will not compile:
-- showread :: String -> String
-- showread = show . read
-- ScopedTypeVariables: otherwise refering a is not possible
--
-- showread (Proxy :: Proxy Int) "3"
--   "3"
-- showread (Proxy :: Proxy Bool) "'fail'"
--   **exception**


showread :: forall a. (Show a, Read a) => Proxy a -> String -> String
showread _ = (show :: a -> String) . read