Relative scoping for hierarchical ADT arguments

Language Design
115

There are also multi-level enums to consider:
(They are not an accepted SIP yet, but it’s hard to argue either proposal is so important that breaking the other is irrelevant, see forum, SIP)

enum Animal:
  case enum Mammal:
    case Dog, Cat
  case enum Bird:
    case Sparrow, Pinguin

def foo(x: Animal) = ???

foo(Animal.Mammal.Dog) // Allowed
foo(Mammal.Dog) // Allowed ?
foo(Dog) // Allowed ?

This can be somewhat solved with .. (but it’s very ugly):

enum Animal:
  case enum Mammal:
    case Dog, Cat
  case enum Bird:
    case Sparrow, Pinguin

def foo(x: Animal) = ???

foo(Animal.Mammal.Dog) // Allowed
foo(..Mammal.Dog) // Allowed
foo(....Dog) // Allowed ?
// or the following, but it makes less sense
foo(..Dog) // Allowed ?

Maybe # is superior in this regard:

enum Animal:
  case enum Mammal:
    case Dog, Cat
  case enum Bird:
    case Sparrow, Pinguin

def foo(x: Animal) = ???

foo(Animal.Mammal.Dog) // Allowed
foo(#Mammal.Dog) // Allowed
foo(##Dog) // Allowed ?
// or the more sensible
foo(#.Mammal.Dog) // Allowed
foo(#.#.Dog) // Allowed ?