rtype not set

I just got this diagnostic from NQP, and boy, is that not a helpful error message. Of course, since it's in PAST->POST compilation, there's no line number or token output.

FWIW, the problem was that I was doing this:

self.declarator := '' ~ $name;

when, as anyone can plainly see, I should have been doing this:

self.declarator('' ~ $name);

because .declarator is a method, not an attribute. D'oh.

I've seen this error once before, and I didn't remember what caused it. I hope that next time I'll remember it, or that The All-Knowing Oz will be able to remind me.

Parrot Multi-Subs and Inheritance

One of the things I've added to Slam (the Close compiler) is support for declaring multi-subs. In another language, these would be called "overloaded methods" or "overloaded functions," but in Close, it's all about the underlying hardware, and that means MultiSubs.

Before I write too much, let me make this clear: Parrot is not the same as Perl6, or Python, or whatever your favorite language is. And so, the way Parrot (and Close) handle things like object dispatch -- the "Object Meta-model," as it is called -- is different from the way other languages handle these things. This is one of those times where the difference matters. (And specifically, the stuff I write below about inheritance isn't true for Perl6. You have been warned.)

Top versus Bottom

Last time, I posted on multiple inheritance, and on "class"-ifying the Slam code in general. Sadly, that is a "rat-hole" that I've gone down, and other than "still working on it" there hasn't been much to post. :-(

So I thought I'd dig out this little gem of a topic that I've had sitting in reserve: the difference between top-down and bottom-up parsing, and what it means to you.