Re: AST observations

> Anyway, it seemed like a clear delegation to me

Right, but I expected the walker to pass itself, rather than giving
the visitor a new method.  I would be quite happy if the object was
assigned, rather than a bound method:

        visitor.walker = self

A bit more conventional, but you won't need to pass the walker to
every visit method.

> So I figured, I'd just use an assignment and explain it in the doc
> string.

That's fine.  I don't see a need for accessors.

-Eric