Consider adding `to_iterable` converter

[sobolevn]

After #244 we now have .from_iterable constructor on every container.

We should also add to_iterable(container: Container[Sequence[T]]) -> Iterable[Container[T]]: (where Container is just an alias, we should support types for all existing containers).
So, this will allow us to construct and deconstruct values easily.

[sobolevn]

I am really tired for now. Let's move it to the next release.

[thepabloaguilar]

We have a problem with HKT here, it can't convert Sequence[Kind1[_ContainerKind, _FirstType]] to Sequence[Container[_FirstType]]!

@kinded
def to_iterable(
    container: KindN[
        _ContainerKind, Sequence[_FirstType], _SecondType, _ThirdType
    ]
) -> Sequence[KindN[_ContainerKind, _FirstType, _SecondType, _ThirdType]]:
    ...

mypy output:

returns/converters.py:97: error: Value of type variable "_FunctionType" of "kinded" cannot be "Callable[[KindN[_ContainerKind, Sequence[_FirstType], _SecondType, _ThirdType]], Sequence[KindN[_ContainerKind, _FirstType, _SecondType, _ThirdType]]]"

Do you want to open an issue for this?

[sobolevn]

Ok, I see. @kinded forces us to have KindN as a return type. I think, that this is a correct behaviour. Not a bug.

Any ideas on how to support it?

[thepabloaguilar]

I don't have any ideas 😞

[sobolevn]

Ok, we should change how @kinded works in the future.
Because we can and will have cases when we need wrapped expressions like List[KindN[...].
Today I have tried to write Maybe[KindN[...]], but I was not able to do that. That's sad.

But, to fully support this, we need python/mypy#9001 to be released.

[thepabloaguilar]

I'm excited waiting for the next mypy release, should be fixed at least three issues here hahaha