flip-check.hs

{-# LANGUAGE FlexibleInstances #-}

import Test.QuickCheck
import Test.QuickCheck.Checkers
import Test.QuickCheck.Classes

newtype Flip f a b = Flip (f b a) deriving (Eq, Show)

instance (Arbitrary a, Arbitrary b, Arbitrary (f b a)) => Arbitrary (Flip f a b) where
    arbitrary = do
        f <- arbitrary
        return $ Flip f

newtype K a b = K a deriving (Eq, Show)

instance (Arbitrary a) => Arbitrary (K a b) where
    arbitrary = do
        a <- arbitrary
        return $ K a

instance Functor (Flip K a) where
  fmap f (Flip (K a)) = Flip (K (f a))

instance (Eq (f a b)) => EqProp (Flip f b a) where (=-=) = eq

main = do
  let trigger :: Flip K String (String, String, String)
      trigger = undefined
  quickBatch $ functor trigger