Function "bind" on Result adt doesn't typecheck about adt HOT 4 OPEN

from adt import adt, Case
from typing import Callable, Generic, TypeVar

A = TypeVar("A")
B = TypeVar("B")
E = TypeVar("E")

@adt
class Result(Generic[E, A]):
    OK: Case[A]
    ERR: Case[E]

    def bind(self, f: Callable[[A], Result[E, B]]) -> Result[E, B]:
        ok: Callable[[A], Result[E, B]] = f
        err: Callable[[E], Result[E, B]] = Result.ERR
        return self.match(ok=f, err=err)

from dataclasses import dataclass
from typing import Generic, TypeVar, Callable, cast, Union, Mapping

E = TypeVar("E")
A = TypeVar("A")
B = TypeVar("B")
Fun = Callable[[A], B]

class Result(Generic[E, A]):
    @staticmethod
    def OK(value: A) -> 'Result[E, A]':
        return Result(True, value)

    @staticmethod
    def ERR(value: E) -> 'Result[E, A]':
        return Result(False, value)

    def __init__(self, ok: bool, value: Union[E, A]):
        self.ok = ok
        self.value = value

    def __repr__(self):
        return f"OK {repr(self.value)}" if self.ok else f"ERR {repr(self.value)}"

    def __str__(self):
        return repr(self)

    def match(self, ok: Fun[A, B], err: Fun[E, B]) -> B:
        return ok(cast(A, self.value)) if self.ok else err(cast(E, self.value))

    def bind(self, f: Fun[A, 'Result[E, B]']) -> 'Result[E, B]':
        return self.match(ok=f, err=Result.ERR)

@dataclass
class User:
    id: int
    name: str

USERS: Mapping[int, User] = {
    0: User(id=0, name="root")
}

def parse_user_id(s: str) -> Result[str, int]:
    try:
        return Result.OK(int(s))
    except ValueError as e:
        return Result.ERR(e.args[0])

def get_user(id: int) -> Result[str, User]:
    if id not in USERS:
        return Result.ERR('User not found')
    else:
        return Result.OK(USERS[id])

def get_user_from_str(s: str) -> Result[str, User]:
    return parse_user_id(s).bind(get_user)

print(get_user_from_str("foo")) # ERR "invalid literal for int() with base 10: 'foo'"
print(get_user_from_str("10"))  # ERR 'User not found'
print(get_user_from_str("0"))   # OK User(id=0, name='root')