function argument shadowing

[nolta]

This should probably generate a warning:

julia> f(x,x) = 2x

julia> f(1,3)
6

[johnmyleswhite]

Personally, I think that should be fatal error. So wacky.

[StefanKarpinski]

Although I basically agree, there is one possibly far-reaching consequence of this: we might need to make _ special the way it is in Ruby. The reasoning is that currently _ can be a normal variable and you can binding multiply for things you don't care about like so:

_, x, _ = f()

But if we start warning about shadowed assignments like this, does that become illegal? Anyway, since we allow just omitting argument names, maybe having it be an error just in function signatures is ok.

[JeffBezanson]

Multiple assignment is actually sequential, so that just rebinds _. Function arguments are the only instance of "simultaneous" assignments. Talk about details! Anyway this might as well be an error.