{-# LANGUAGE DeriveGeneric, ScopedTypeVariables #-}

module Main where

import GHC.Generics (Generic)

import Test.QuickCheck

import Test.QuickCheck.Function

data D a = C1 a | C2 deriving (Eq, Show, Read, Generic)

instance Arbitrary a => Arbitrary (D a)

instance CoArbitrary a => CoArbitrary (D a)

instance (Show a, Read a) => Function (D a) where

  function = functionShow

main :: IO ()

main = quickCheck $ \(Fun _ f) ->

  f (C1 (2::Int)) `elem` [0, 1 :: Int]