Pugs-Rule: Grammar support.

[Audrey Tang]

Today I added two more rules in the default grammar, in addition to <p6rule>: rule p6namedrule     { rule \s+ ([\w|<'::'>]+) \s* \{ <p6rule> \} ;? \s* } rule p6grammar     { ^ grammar \s+ ([\w|<'::'>]+); \s* <p6namedrule>* $ } With this, the PILN grammar is now successfully parsed with its Syntax.grammar file.  To support that, tewk and I have implement various contructs: Enumerated character classes: <[abc]> Complemented character classes: <-[abc]> Literals: <'abc'> Begin/End anchors: ^ $ ^^ $$ Partial parse of <p6rule> so it stops at the closing brace when used as part of <p6grammar>. In addition to that, I've written a simple tree trasforming function for <p6grammar>, which takes a Match object and turns it into compiled rule expressions.  Instead of using TGE-style separate set of attribute grammars as decribed in the Parrot compiler tools plan, I'm associating each rules with consumers, using e.g. SYB Generics to handle post-subrule-parsing production. However, that scheme means we needed to perform multiple redundant traversals.  I'd much rather something like this, with a :{} rule trait and a conjectural @<p6namedrule> to mean @$<p6namedrule>: rule p6namedrule   :{ ($1 => $<p6rule>) }    { rule \s+ ([\w|<'::'>]+) \s* \{ <p6rule> \} ;? \s* } rule p6grammar   :{ Grammar.new(name => $1, rules => hash(@<p6namedrule>) }    { ^ grammar \s+ ([\w|<'::'>]+); \s* <p6namedrule>* $ } Some discussion on #perl6 ensued; luqui and I bounced some ideas about embedding attribute grammars into the rule declarations, and promptly went into tangents such as the evilness of keeping $! as global -- $!, $/ and $_ really should all be environmental -- expect some p6l threads about them in the near future... (http://pugs.blogs.com/pugs/2006/01/grammar_support.html )

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