> Now... I don't really know what I am talking about - but is this in fact
> a special case of something bigger, something similar to hygienic macros
> or whatever it is called? (Slate, Scheme etc) I mean, some way of
> manipulating the AST of the code itself (which is my very shallow
> understanding of what that is)?

That is precisely right. It is easy to see how one would generalize the 
behavior to something like, e.g.,:

    "Tell the variable var how to retrieve and store its value"
    &var toGet: [self instVarAt: 1]
    &var toSet: [:newValue| self instVarAt: 1 put: newValue].

Accessing variables is then conceptually equivalent to:

    &var value. "read value of variable"
    &var value: newValue. "write value of variable"

With the compiler merely inlining the definitions of the accessors.

Cheers,
  - Andreas