Kind of Kind

[horta]

Bug report

What's wrong

I would like to do

from __future__ import annotations

from typing import TypeVar
from returns.primitives.hkt import Kind1, Kind2

class Alphabet:
    pass

_A = TypeVar("_A", bound=Alphabet)

class State(Kind1["State", _A]):
    pass

_S = TypeVar("_S", bound=State)

class Step(Kind2["Step", _A, _S]):
    def foo(self, step: Step[_A, Kind1[_S, _A]]): # mypy error
        del step
        del self
        pass

Such that the step parameter of Step.foo has the type-hint Step[_A, _S[_A]].

System information

• python version: Python 3.9.1
• returns version: master:1fec2a8a79175da5afa39695e3ccc177c8c73ab7
• mypy version: mypy 0.800

[horta]

I have just tried

Was that supposed to work?

[sobolevn]

Nested kinds are not supported at the moment 😢

[horta]

I figured. This is an improvement then but I wonder if it is worth the work.

[sobolevn]

I have some use-cases when this would be a good thing to have. It really depends on how much time / effort / hacks are required to make it work.