law.pony

use "ponytest"
use "ponycheck"
use ".."

interface val _TestSemigroupAssociativity[T] is UnitTest

  fun semigroup(): Semigroup[T]

  fun t(): String

  fun name(): String => "laws/associative/" + t()

  fun gen(): Generator[(T, T, T)] val

  fun is_associative(h: TestHelper)? =>
    let sg = semigroup()
    Ponycheck.for_all[(T, T, T)](gen(), h)(
     {(args, ph) =>
       (let x, let y, let z) = args
       // can't find definition of 'T'
       ph.assert_eq[T](
         sg.combine(sg.combine(x, y), z),
         sg.combine(x, sg.combine(y, z))
       )
     })?