More consistent function types

[rudkx (Mark Lacey)]

@MutatingFunk

However, from what I gather, the alternative suggestion is to aim for a different kind of symmetry, which could be defined as so:

Definitely not all of these things.

Let's look at each example specifically.

@MutatingFunk

'(T) -> U where T == ()' ↔ '(()) -> U' ↔ '() -> U' (zero element sugar)

This is the only thing proposed. Effectively redefine ( ) -> U to be synonymous with (()) -> U.

@MutatingFunk

'(T) -> U where T == (A)' ↔ '((A)) -> U'

We don't have single element tuples as a result of the syntactic ambiguity. We could have unambiguous single-element labeled tuples, but do not as mentioned here.

So no, this doesn't happen and this proposal doesn't change that in any way.

@MutatingFunk

'(T) -> U where T == (A, B)'

This happens today, and is completely legitimate. You can infer T to be a single argument, of tuple type. However that does not imply:

@MutatingFunk

'(T) -> U where T == (A, B)' ↔ '(A, B) -> U' (multiple parameters)

Which is splatting.