Hello! Basically I want to express couple of types/specs. Type parametricity is working for types:

@type functor(a) :: functor(a)
@type either(a, b) :: {:error, a} | {:ok, b}

But is not working for specs. This will not compile for some reason:

@spec fmap((a -> b), functor(a)) :: functor(b)

I don’t want to define a and b. I want them to be generic - just some type a, and some type b which might be not equal to type a.

Another question is how to do shrinking and negation on type level, for example:

@type thunk ???
@type not_a_function ???
@type curried :: (term -> curried | thunk | not_a_function)
@spec curry(function) :: curried | thunk

where thunk is a function of arity equal to zero, and not_a_function is any type except function.

Thanks for your attention.