Support (un)curry up to 20 arguments

[MangelMaxime]

#3514

@dbrattli Can you please have a look at the fable-library-py/Util.py.

I don't understand why Pylance generates errors when the function as more that 10 arguments.

I tried to check for syntax errors, but could not find any.

[dbrattli]

@MangelMaxime the thing here is that Python is a bit different with typing than e.g. F#. A generic type argument in Python must be used more than one time in a function signature to make sense (which makes sense for F# as well when you think about it). So, if a function has e.g a type _T11 that is used only once, you can just as well replace it with Any.

So, for the outer function signature you can see that the type arguments make sense because it locks the type of the input arguments to the output arguments. But for the inner functions e.g:

def f2(a1: _T1, a2: _T2, a3: _T3, a4: _T4, a5: _T5) -> _TResult:
        return f(a1)(a2)(a3)(a4)(a5)

You can see that the type arguments are all different. Thus, they do not provide any additional value. No input is locked to any output. They do not inherit the outer type arguments, so they are not locked to the outer function declaration either. E.g a function like:

def id(value: _T1) -> _T2:
   return value

is no different than

def id(value: Any) -> Any:
   return value

Thus, the inner functions should be written like this instead to avoid the type errors you see:

def f2(a1: Any, a2: Any, a3: Any, a4: Any, a5: Any) -> Any:
        return f(a1)(a2)(a3)(a4)(a5)

[MangelMaxime]

Thanks for the explanation but why does it work for uncurry2 to uncurry10?

And doesn't anymore starting from uncurry11?

If I understand correctly the function below should have the errors too on f2 definition but that's not the case.

def uncurry2(
    f: Callable[[_T1], Callable[[_T2], _TResult]]
) -> Callable[[_T1, _T2], _TResult]:
    def f2(a1: _T1, a2: _T2) -> _TResult:
        return f(a1)(a2)

    _curried[f2] = f
    return f2

Another interrogation is why would the error only be on _T11, _T12, _T13, etc. and not all the types starting from _T1 ?

CleanShot.2023-10-20.at.14.39.40.mp4

Replacing _TX with Any for uncurry11 and plus, makes the error goes away. If you are fine with that I can make the change.

[dbrattli]

Yes, it's fine. We have no clue about whatTX is and it doesn't really matter. It's just important that the signature of the outer function locks input types to output types.