Pyre doesn't seem to understand universal quantification about pyre-check

[kinto0]

Hi! As far as I know, TypeVars must be present in the function's parameters. To work around this, you could use a similar strategy as decorator factories from our documentation for this error. I did it here

[vthemelis]

@kinto0 thank you ver much! Indeed, I should have seen this earlier.

With some modification, it looks like I can type check car and cdr as well:

Pyre playground here

Something that may be of interest is that I need to write car like:

def car(cons: MyCallableProtocol[T, U]) -> T:
    cont: Callable[[T, U], T] = lambda x, _: x
    return cons(cont)

rather than

def car(cons: MyCallableProtocol[T, U]) -> T:
    return cons(lambda x, _: x)

to get full type safety. Without this change, changing the return type of car from T to something else doesn't elicit a type error.

In other words, it doesn't seem like pyre can infer the type of the lambda correctly.

Thanks a lot for the help!