Type system

[Quaqqer]

The saft language should be a typed language. Typing could be added incrementally.

• Type annotations. Declarations and functions should be annotated. Functions should contain annotations for parameters as well as the return value. If the return type is omitted the function returns nil.
• Types. The types of values that can be represented are currently nil, numbers, functions, vectors (of types), and strings. Types should be defined by items, not just keywords. This allows for type aliasing for instance, with type x = int;. Currently Saft has no good way of defining items in a prelude-esque way, so this would be a starting step.
• The method for inference and checking in Saft is not yet decided. Currently I am considering some kind of Hindley Milner type system, or a bidirectional type system. Right now I am leaning more towards bidirectional type checking, it seems fun.