From: Phrogz <phrogz@...>
Date: 2008-01-28T14:54:56+09:00
Subject: Re: Treetop parser (or PEG in general?) questions

An additional Treetop question that has me stumped:

I have a simple grammar as listed at the end of this post. In the
following code, why can I not get the 'to_xml' method to flow through
the 'inline_atom' rule, to use the to_xml of the underlying wrrd and
numz classes? Why does inline_atom not provide the #wrrd and #numz
SyntaxNode methods inside the handlers for inline_atom? How can I
rewrite inline_atom to allow the flow through?


require 'rubygems'
require 'treetop'

Treetop.load "t1.treetop"
@parser = T1Parser.new
@root = @parser.parse( "Hi 123\n\n" )
p @root
#=>SyntaxNode+Paragraph1+Paragraph0 offset=0, "Hi 123\n
\n" (inline_content,to_xml):
#=>  SyntaxNode+InlineContent2+InlineContent1 offset=0, "Hi
123" (all_items,to_xml,items,last_item):
#=>    SyntaxNode offset=0, "Hi ":
#=>      SyntaxNode+InlineContent0 offset=0, "Hi " (wspace,item):
#=>        SyntaxNode+InlineAtom1+Wrrd0 offset=0, "Hi" (to_xml):
#=>          SyntaxNode offset=0, "H"
#=>          SyntaxNode offset=1, "i"
#=>        SyntaxNode offset=2, " ":
#=>          SyntaxNode offset=2, " "
#=>    SyntaxNode+InlineAtom0+Numz0 offset=3, "123" (to_xml):
#=>      SyntaxNode offset=3, "1"
#=>      SyntaxNode offset=4, "2"
#=>      SyntaxNode offset=5, "3"
#=>  SyntaxNode offset=6, "\n\n"

p @root.to_xml
#=> NameError: undefined local variable or method 'wrrd' for
#<Treetop::Runtime::SyntaxNode:0x5c7808>


-_- t1.treetop -_-

grammar T1
  rule paragraph
    inline_content "\n\n" {
      def to_xml
        "<p>#{inline_content.to_xml}</p>\n"
      end
    }
  end

  rule inline_content
    items:( item:inline_atom wspace )* last_item:inline_atom {
      def to_xml
        all_items.map{ |atom| atom.to_xml }.join( ' ' )
      end
      def all_items
        all = []
        all << first_item if methods.include?( 'first_item' )
        all.concat items.elements.map{ |el| el.item }
        all << last_item if methods.include?( 'last_item' )
        all
      end
    }
  end

  rule inline_atom
    numz {
      def to_xml
        numz.to_xml
      end
    }
    /
    wrrd {
      def to_xml
        wrrd.to_xml
      end
    }
  end

  rule wrrd
    [A-Za-z]+ {
      def to_xml
        "<word>#{text_value}</word>"
      end
    }
  end

  rule numz
    ([1-9]+ / '0') {
      def to_xml
        "<i>#{text_value}</i>"
      end
    }
  end

  rule wspace
    [ \t]+
  end

end