More Rakudo ng hacking

Originally published on 7 November 2009 by Jonathan Worthington.

I’ve spent most of my waking hours today (and a bit of yesterday) starting to build things out on top of the metamodel foundations in Rakudo’s ng branch. It’s feeling much cleaner that what we had before, and I’ve not found anywhere yet where it’s feeling like I’m having to stick magic into the actions that is specific to a certain type of package. In fact, compared to before, the package_def action method is really quite compact and clean. The whole process of constructing a class (or role or grammar) is just a series of method calls on the metaclass.

Here’s a list of things that I’ve got done since the last blog post.

• Got classes inheriting from Any again by default, which took me on a detour into getting the add_parent method of the metaclass working. We can’t quite do inheritance again yet though - that needs traits to be completed too.
• Added handling of the grammar package declarator back in. Now the “inherit from Grammar by default and not Any” stuff is just done by us having a metaclass for grammars - GrammarHOW - that subclasses the metaclass for classes - ClassHOW. It simply overrides the compose method (what we call when we’re finished defining a package) and checks if there are any explicit parents, and if not adds Grammar as a parent, then delegates up to the superclass to do the rest of the work.
• Got us parsing trait modifiers and building AST for them. We have protoregexes now, so I could make it just pretty much just like STD. There were also some tweaks to synchronize with. Much of it was just brining code in from the existing actions and re-organizing it a bit.
• One I had those in place, I got attribute accessor generation done. I had wanted traits so I could straight away add the is rw variant too. Again, the accessor method is added thorugh the metaclass, and this time it got a proper signature (I suspect there was probably a bug in the previous implementation to be found - maybe even a ticket - over this).
• In doing the above, I realized that I needed to sort out handling of the invocant. Before, we were having Parrot handle it for us, which meant it was handled out of band with respect to the signature binder. In ng we just handle it like any other parameter, apart from we also make it available through self (or only make it available through self if the invocant is not specifically requested). This fixes the “can’t put where clauses on the invocant” issue that came up a while back - now (in theory at least - didn’t test it) you’ll be able to write a bunch of multis that dispatch based on constraints on the invocant.
• I started preparing to put roles - parametric ones too - back in place, again built around the metamodel approach. I’m hoping things get cleaner again as a result of that.
• Helped Patrick with working out why compilation is so painfully slow. I timed all of the stages, and it turns out - at least on my box - that we’re spending about 10/11ths of the time in the very final stage, turning POST (a tree representing the Parrot opcodes) to PIR. Since that just walks a tree and builds up a string, that’s all rather strange. pmichaud++ is investigating.

Basically, my aim is to get us able to start bringing the Raku setting back as soon as possible. Today Patrick did the infrastructural work for that, which was a great start. I was close to us having inheritance working by writing a trait modifier in there, but then realized that while lexical subs now work great (like, way cleaner than in master), package ones don’t. Fail. Ah well, it’s 3am and I need sleep. Thanks to Vienna.pm for sponsoring this chunk of work.