youjinbou / pil Goto Github PK

This is a small implementation of prolog.
The License is GPL2 with Ocaml linking exception (same as the Ocaml source code).

At this point the language has only a few primitives implemented:

true/0, false/0, listing/0, halt/0, ground/1, var/1, asserta/1, assertz/1, consult/1, =/2,
is/2, arithmetic and comparison operators for integers, and the mandatory conjunction and
disjunction operators.


I started writing this project after I realized that it might be possible to implement
prolog without a goal stack (which is the usually the choosen design) using continuation 
passing style programming. I wrote several parsers using this style in the past, and
also an Earley parser (which you'll find on github as well). You may see that the later
basically follows a principle similar to prolog, but with breadth first search rather
than depth first.

So there are two branches provided, "master" which hosts the CPS based implementation, and
"stack-based", whose name is quite explicit. Actually, it turned out more involved to
write the stack based version, once I had the CPS one basically working (which feels much
more natural, and whose code looks quite less convoluted).

There are probably still bugs lingering in the code - if you find any just let me know -
and it hasn't been written with speed in mind, so don't try comparing it with any other 
implementation yet (well, if you can manage to find code which only relies on the few 
primitives supported here).