How to create a value of the Haskell hedgehog type `Gen a`?

Question

I'm trying to write a property based test that is verifying congruence of equality.

To do that I need to be able to run it by providing 2 values of the type Gen a:

fun_cong_equality
:: forall m a
. (Monad m, Arg a, Vary a, Eq a, Show a)
=> Gen a
-> Gen a
-> PropertyT m ()
fun_cong_equality genA genB = do
a <- forAll genA
b <- forAll genB
f <- forAllFn $ fn @a genA
f a === f b

prop_fun_cong_equality :: Property
prop_fun_cong_equality =
property $
    fun_cong_equality $ -- TODO need to pass 2 `Gen a` values as arguments

My question is: how do I create values of type Gen a?

Note: the property based test is not finished, it still need to filter for generated values that are equal.

Answer 1

What I needed was a value of a type that has instances of the typeclasses Vary, Arg, Eq and Show.

Int happens to meet that criteria.

A solution is to use:

fun_cong_equality (Gen.int (Range.linear 1 100)) (Gen.int (Range.linear 1 100))