Shorthand notation for erased arguments

[raffopazzo]

Introducing all function arguments required by later dependent-types can get verbose.

func choose(
  0 u64_t n,
  0 scope_t a,
  0 typename t,
    bool_t which,
    ref_t(array_t(t, n), a) p,
    ref_t(array_t(t, n), a) q
) -> ref_t(array_t(t, n), a);

It might be handy to have a shorthand notation to introduce erased arguments, something like this.

func choose(bool_t which, ref_t(array_t(@t, @n), @a) p, ref_t(array_t(t, n), a) q) -> ref_t(array_t(t, n), a);

This will require clarifying the rules of where each @x goes in the desugared argument list and in which order they are processed.