R3: A Ruby native parsing framework ported from Perl6 Rules.
Introduction:
R3 is a Ruby native implementation of Perl6's Rule engine specification. Perl6 Rules is a good compiler tool set for dynamic languages due to it heavy use of regular expressions and language native constructs such as classes, objects, strings, streams etc. R3 is envisioned as a possible new language feature to Ruby, not merely an add-on library or external compiler tool set such as lex and yaxx, or Antlr.
Power and Rational of Rules:
Perl6 Rules are the basis for many features in Perl6 and can be the basis of corresponding features in other dynamic languages. LISP style macros for dynamic languages can be defined in rules. Dynamically syntax can be implemented using rules. In other words the ability to change the syntax of the language on the fly. Support for first class Domain Specific Languages and corresponding syntax can be implemented using rules. Rules can be used to parse any type of stream: strings, IO streams, network protocol streams.
Proposed work:
* Implement sub rules and nested match objects to support parsing.
* Implement sufficient backtracking support to parse Ruby syntax.
* Implement a Ruby Grammar defined using R3 rules syntax.
* Implement a Grammar/Rules DSL approach where a Grammar is a class
and Rules are methods in the class.
* Implement inline use of rules as an alternative for Ruby Regexs.
Delimitations:
* The features of Perl6 rules are extensive, R3 will initially only
support a minimum subset in an attempt to parse Ruby syntax.
* R3, initially being a port or translation of Perl6 ideas, will
utilize much of the Perl6 syntax for rules. This is a benefit, as
work commences, since much of the syntax come from regular
expressions, which is widely shared across languages.
* Although not it final potential, R3 will be initially implemented as
Background:
The Perl6 Regex/Rules engine interests me and I think it is a powerful way to build parsers. In order to better understand how it works, I originally tried to help implement rules in Haskell. Recently, I attempted to port PGE, another Perl6 Rules implementation to Ruby and later to Perl5. PGE is written in PIR which is parrot assembly(Perl5 data types, with assembly syntax). Getting from labels and jumps to Perl5 was doable since Perl5 has gotos. Ruby was a little harder. Gotos had to be emulated using blocks and exceptions. Each of theses attempts ended in abandonment, but with each try, I became more familiar with the design and syntax of rules.
My latest attempt(R3) has been to port Pugs::Compiler::Rules to Ruby and I'm finally getting some traction. The control structure of Pugs::Compiler::Rules, continuation passing style(CPS), is easily implemented in Ruby using Procs. As a result, this port has been much more straight forward than previous attempts.
R3 mirrors the architecture of Pugs::Compiler::Rules.
* Match.rb => Regex/Rules matches returned by rules, which are
chained together to form rudimentary parse trees.
* RuntimeRule.rb => Runtime regex primitives needed to implement rules.
* GrammarRule.rb => Grammar of Rules expressed using primitives from
RuntimeRule.rb.
* RuleCompiler.rb => uses the Grammar in GrammarRule.rb to parse
rules into rule parse trees.
* RubyEmitter.rb => Takes a rule parse tree from RuleCompiler and
emits ruby code to parse the grammar specified by rules.
R3 is just now beginning to parse the Perl6 Rule syntax. All of the modules above except the RubyEmitter.rb module have primitive functionality. Work on the RubyEmitter has not yet begun. R3 is is currently hosted in a private SVN repository. See tewk.com/r3.tgz <http://tewk.com/r3.tgz>.
Perl6 Rules Reference Implementations
* PGE Parrot Grammar Engine (Written in PIR, uses coroutines for
continued parsing)
* https://svn.perl.org/parrot/trunk/compilers/pge
# Pugs Rules Engine (Written in Haskell)
* http://svn.openfoundry.org/pugs/src/Text/Parser
# Pugs::Compiler::Rules (Written in Perl5, generates Perl5 code, uses continuation passing style to backtrack)
* http://svn.openfoundry.org/pugs/misc/pX/Common/Pugs-Compiler-Rule
# My Previous Attempts
* http://svn.openfoundry.org/pugs/misc/pX/tewk
See also:
* http://search.cpan.org/~ltoetsch/parrot-0.4.3/compilers/pge/README.pod
* http://dev.perl.org/perl6/doc/design/syn/S05.html
* http://dev.perl.org/perl6/doc/design/apo/A05.html
* http://dev.perl.org/perl6/doc/design/exe/E05.html
Last I checked, it was faster and