Typed variadic arguments

[tiansivive]

Add a variadic param type, inspired by Typescript's rest params

Possible syntax:

fn: Int -> ...String -> Bool



> fn 1!         -- FnApp <fn> [TLit 1, TVariadic []]
> fn 1 "hello"! -- FnApp <fn> [TLit 1, TVariadic [TLit "hello"]]

Edge cases:

fn: ...String -> String -> Int


> fn "hello"!         -- FnApp <fn> [ TVariadic [], TLit "hello"]
> fn "hello" "world"! -- FnApp <fn> [ TVariadic [TLit "hello"], TLit "world"]

[tiansivive]

Considering allowing syntax for non-curried arguments in order to facilitate this feature.
Could also be valuable for language ergonomics

Proposed syntax could be

add: Int, Int -> Int

For a variadic version one could do:

add: Int, Int* -> Int

Here we're using regex syntax that should be familiar to most to indicate 0 or more.
This might need some restrictions because we don't want null/undefined problems.

A curried version could then be:

add: (Int ->)* Int -> Int

This means applying add with n params will always result in another function. However, it's unclear if this is helpful at all because one can simply be

add: Int* -> Int -> Int

Which would be much simpler to understand.
Currying is also problematic because you can end up with Infinite types. Imagine:

fn: Int -> (Int ->)* Int

This could be interpreted that no matter how many args you apply to fn, you always get back a function.