KindaPerl6 Common Lisp status update

A lot of work has been done on the KindaPerl6 Common Lisp backend for KindaPerl6 since I last 89wrote about it. Variables, subs, lexicals, closures, basic datatypes (int, str, num, hash, array, ..), control structures (if, for, while, ..) are working. We're missing user-defined classes & methods, some internal methods (sort, map, grep, ...), junctions, pairs, gather and probably some other things. Aankhen++ has been doing most of the work with the occasional contribution from myself.

Things sped up a bit recently after fax++ wrote a meta-object model (MOP) for us based on CLOS. The one in the Perl 5 backend does not use the Perl 5 object system (implements its own @ISA and so on) but so far it looks like we can build the Perl 6 MOP on top of CLOS which is more flexible.

A method in the MOP uses the same calling convention regardless of whether it's internal to the compiler or compiled from a user defined class. An example of an internal method using the new calling convention is the dispatch method that implements the .elems method for hashes:

(defmethod kp6-dispatch ((invocant kp6-Hash) interpreter (method (eql :elems)) &rest parameters)
  "Returns the number of elements in the hash"
  (declare (ignore parameters interpreter))
  (make-instance 'kp6-Int
     :value (hash-table-count (slot-value invocant 'value))))

In the case of %hash.elems this would be called as:

(kp6-dispatch (lookup-lexical-variable (kp6-generate-variable "%" "hash")) |Main| :elems)

The object system is used for pretty much everything. For example the .Str method is used to get the string representation of an object, .Int for its integer form, .true to check whether it wants to be true (used in all boolean contexts) etc. Not everything has been moved to the new system internally. Helping with that would be an easy beginner task.

Speaking of beginner tasks there's a lot more of them. And since we have MOP now implementing things is often just a matter of seeing how the Perl 5 backend does things and filling in the gaps in the Lisp backend.

We have some bugs like my @a; @a[123] = 456; which causes an error currently since the underlying CL array isn't extended properly. As well as a lot of things like substr() which are easy to implement but simply aren't at the moment.

So if you're interested in hacking a Perl 6 compiler in Perl 6 and Common Lisp head over to #perl6 and poke us for a commit bit.

Comments

[Richard Freytag]

Fascinating project. This is the shortest path that gives Perl the power of LISP. I hope you keep the updates coming!