Hedgehog.Function

{-# language DeriveGeneric #-}
{-# language TypeApplications #-}

import Hedgehog
import Hedgehog.Function

data A = ...
  deriving (Generic, ...)

instance Arg A
instance Vary A

genB :: MonadGen m => m B
genB = ...

prop_test :: Property
prop_test =
  property $ do
    f <- forAllFn $ fn @A genB
    ...

{-# language RankNTypes #-}
{-# language ScopedTypeVariables, TypeApplications #-}

import Hedgehog
import Hedgehog.Function
import qualified Hedgehog.Gen as Gen
import qualified Hedgehog.Range as Range

map_compose
  :: forall f a b c
   . ( Functor f
     , Show (f a)
     , Show a, Arg a, Vary a
     , Show b, Arg b, Vary b
     , Show c
     , Eq (f c)
     , Show (f c)
     )
  => (forall x. Gen x -> Gen (f x))
  -> Gen a
  -> Gen b
  -> Gen c
  -> Property
map_compose genF genA genB genC =
  property $ do
    g <- forAllFn $ fn @a genB
    f <- forAllFn $ fn @b genC
    xs <- forAll $ genF genA
    fmap (f . g) xs === fmap f (fmap g xs)

prop_map_list :: Property
prop_map_list =
  map_compose
    (Gen.list (Range.constant 0 100))
    Gen.bool
    Gen.bool
    Gen.bool