Glacial Grammar Engine -- a Perl 6 grammar engine written in Perl 6
Latest commit d6a018c Dec 10, 2015 @masak Merge pull request #4 from zoffixznet/fix-failures
Fix some failures


== Glacial Grammar Engine -- like PGE, but slower

Ok, so there was some guy called Patrick who implemented a thing called
PGE, right? It was a grammar engine written in PIR, the assembly language of
Parrot. PGE was the first thing in the known universe that could parse Perl 6
regexes. It was then plugged into PCT, a toolkit for building HLL (Higher-Level
Language) compilers for Parrot. Rakudo, a Perl 6 compiler, was built on
top of PCT.

In short, a whole lot of abstractions, and in the bottom of it all, driving
the parser, sat PGE. Humming along, it did all the daily parsing we now
take, more or less, for granted.

Patrick was once caught saying that given the little time he had spent
optimizing PGE, he was surprised it wasn't actually much slower.  What he
might not have guessed was that this off-hand statement could be read as a
challenge: PGE surprisingly not slow enough? We know a number of ways to
fix that...

GGE, the Glacial Grammar Engine, is a faithful port of PGE from PIR to Perl
6. It tries to be implementation-independent, and it also attempts (though
perhaps not too convincingly) to be a drop-in replacement for PGE. Most
importantly, besides being written in Perl 6 rather than PIR, it brings one new
essential feature to the table: it's slower. Much slower... but still quite
cool. Hence the name.

The "though perhaps not too convincingly" reservation to GGE attempting to
be a drop-in replacement for PGE stems from the fact that now that regular
expressions _are_ in fact available in the Perl 6 language (through PGE
in the case of the old-generation Rakudo, or nqp-rx in the case of the
new-generation Rakudo), it's sometimes too tempting not to use them. Of
course, it would be a fun challenge in itself to restrict the writing of
GGE to a strict subset of Perl 6 -- one not using any regexes at all,
directly or indirectly -- but that is not the kind of fun optimized for in
this case. Future teams of developers are welcome to optimize for that kind
of fun, should they wish. The instances of conscious transgressions in GGE are
listed in docs/REGEXES_IN_GGE.

For an overview of the status of the project, see STATUS. For an overview
of the cool things that could be built with the project as a dependency,
see docs/COOLTHINGS.

== License

Code coming from the Parrot repository is Artistic License 2.0. See