Function Annotations

[BobVarioa]

Motivations:

• Right now, there isn't really any way to give information to the compiler about various aspects of a method. I ran into this more specifically in Memory improvements + Type analysis #56 with the return type of the Date constructor, a return type based on new.target, not exactly a union type but moreso a type that requires a condition to be true.
• This is but one example though, for instance, we use hacks like $get to denote accessors for length or size, this could remedy that.

This could likely be implemented in various ways, but I imagine the following:

@Constructor("Date")
@Returns<string>
function Date() {
  // ...
}

or

@Accessor("size")
@Inline 
@Pure 
function __Set_prototype_size() {
  // ...
}

I would imagine that some of these will become less necessary with time, for example when objects are introduced, but something like @Inline or @Pure could be really helpful hints to the compiler