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Glacial Grammar Engine -- a Perl 6 grammar engine written in Perl 6

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README
== 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, sits PGE. Humming along, it does 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 (albeit not too hard) 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. Hence the name.

The "albeit not too hard" reservation to the implementation-independence
stems from the fact that some PIR tricks used by PGE are unavailable in
Perl 6. When faced with a choice of (a) giving up, and (b) cheating by
introducing some PIR-dependent workaround, the latter road will be chosen.
That said, implementation-independence stands as a goal whenever possible,
just as with all honest Perl 6 code.

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),
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.

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 COOLTHINGS.

== License

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