Using the ClassLaws lib for a trivial example

eq_laws.hs

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE EmptyDataDecls #-}

module Main where

import Test.ClassLaws

data EqLaw1 a

class Eq a => EqLaws a where
    eqLaw1 :: Law (EqLaw1 a)
    eqLaw1 (x, y) = (x == y) =.= not (x /= y)

type instance LawArgs (EqLaw1 a) = (a, a)
type instance LawBody (EqLaw1 a) = Bool

-- Not entirely sure why this is needed.
type instance Param Bool = Bool

instance TestEqual Int where
    testEqual l _ = testEq (==) l

instance TestEqual Bool where
    testEqual l _ = testEq (==) l

instance (EqLaws a, TestEqual a) => LawTest (EqLaw1 a) where
    lawtest _ = testEqual . eqLaw1

instance EqLaws Int
instance EqLaws Bool
instance EqLaws a => EqLaws [a]

main :: IO ()
main = do
    quickLawCheck (undefined :: EqLaw1 Int)
    quickLawCheck (undefined :: EqLaw1 Bool)