-- | Utilities for testing partial semigroups using the @hedgehog@ property
-- testing library.
module Test.PartialSemigroup.Hedgehog
  ( assoc,
  )
where

import Data.PartialSemigroup (PartialSemigroup (..))
import Hedgehog (Gen, Property, forAll, property, (===))

-- | The partial semigroup associativity axiom:
--
-- For all @x@, @y@, @z@: If @x '<>?' y = 'Just' xy@ and @y '<>?' z = 'Just' yz@,
-- then @x '<>?' yz = xy '<>?' z@.
assoc :: (PartialSemigroup a, Eq a, Show a) => Gen a -> Property
assoc gen = property $ do
  x <- forAll gen
  y <- forAll gen
  z <- forAll gen

  sequence_ $
    do
      xy <- x <>? y
      yz <- y <>? z

      return (x <>? yz === xy <>? z)