Constant Value Types

[sezna]

Literals should be allowed as types, and they will be subtypes, processed via the Satisfies constraint, of their parent types. For example,

type Foo = '"this" | '"that"; -- the ' denotes that it is a type, and not a value.

Then, fn foo(foo in 'Foo) could only ever accept "this" or "that". But fn foo(foo in 'string) could accept a 'Foo, or any other string.

This is more ergonomic than having to define an enum with to_str() and from_str() like Rust, and is one of the more valuable features from the Typescript type system that I enjoy.