[Haskell-cafe] Testing polymorphic properties with QuickCheck

[Tom Ellis]

On Thu, Feb 19, 2015 at 07:41:25AM +1100, Stuart Hungerford wrote:
> prop_left_add_id :: (Eq a, Monoid a) => a -> Bool
> prop_left_add_id x = zero |+| x == x
> 
> monoid_suite :: TestTree
> monoid_suite = testGroup "monoid" [
>   testProperty "left additive identity (Integer)"
>     (prop_left_add_id :: Integer -> Bool),
> 
>   testProperty "left additive identity (Rational)"
>     (prop_left_add_id :: Rational -> Bool),
> 
>   testProperty "left additive identity ((Integer, Integer))"
>     (prop_left_add_id :: (Integer, Integer) -> Bool),
>   -- ...]

I'm not quite sure what you're asking specifically, but maybe this will
help:

{-# LANGUAGE ScopedTypeVariables #-}

monoid_suite :: forall m. (Eq m, Monoid m) => String -> Proxy m -> TestTree
monoid_suite typename _ = testGroup "monoid" [
   testProperty ("left additive identity (" ++ typename ++ ")")
     (prop_left_add_id :: m -> Bool),

   ... <other general monoid properties here>
   ]

monoid_suite_integer :: TestTree
monoid_suite_integer = monoid_suite "Integer" (Proxy :: Integer)

monoid_suite_rational :: TestTree
monoid_suite_rational = monoid_suite "Rational" (Proxy :: Rational)

monoid_suite_pair :: TestTree
monoid_suite_pair = monoid_suite "(Integer, Integer)" (Proxy :: (Integer, Integer))