Support default arguments in functions

[croyzor]

Just like in python! This may give us a useful hack to do some faux overloading, seems like a win

[qubitserfed]

I'm seconding this, as the lack of this feature resulted in quite a bit of duplicate code in my iceberg code implementation.

[CQargi]

Default values would be really useful. Please consider this again.
Also, being able to use named arguments (instead of purely positional) would make the code more readable.

[mark-koch]

Agreed that would be useful.

One question is how to deal with higher-order function values:

def foo(x: int): ...

def bar(x: int): ...

def baz(y: int): ...

def faz(x: int, y: int = 10): ...

def main(b: bool):
    f = foo if b else bar
    f(x=42)  # Allow kwarg here?
    g = foo if b else baz  # Do these unify if the argument names are different?
    h = foo if b else faz  # What about these?

An easy solution would be to say "no, yes, no" to the above and just allow kwargs and omitting defaults when calling function directly. Would this be too restrictive?