CODEWITHSUNDEEP
rubyparsingtreetop
pingu
pingu

Reputation: 8827

How do I process a treetop parse tree?

I have written a parser using treetop which successfully produces a parse tree, part of which is reproduced below.

SyntaxNode offset=4043, "   ":
  SyntaxNode offset=4043, " "
  SyntaxNode offset=4044, " "
  SyntaxNode offset=4045, " "
StringLiteral+StringLiteral1 offset=4046, "\"MS Sans Serif\"":
  SyntaxNode offset=4046, "\""
  SyntaxNode offset=4047, "MS Sans Serif":
    SyntaxNode+StringLiteral0 offset=4047, "M":
      SyntaxNode offset=4047, ""
      SyntaxNode offset=4047, "M"
    SyntaxNode+StringLiteral0 offset=4048, "S":
      SyntaxNode offset=4048, ""
      SyntaxNode offset=4048, "S"
    SyntaxNode+StringLiteral0 offset=4049, " ":
      SyntaxNode offset=4049, ""
      SyntaxNode offset=4049, " "
    SyntaxNode+StringLiteral0 offset=4050, "S":
      SyntaxNode offset=4050, ""
      SyntaxNode offset=4050, "S"
    SyntaxNode+StringLiteral0 offset=4051, "a":
      SyntaxNode offset=4051, ""
      SyntaxNode offset=4051, "a"
    SyntaxNode+StringLiteral0 offset=4052, "n":
      SyntaxNode offset=4052, ""
      SyntaxNode offset=4052, "n"
    SyntaxNode+StringLiteral0 offset=4053, "s":
      SyntaxNode offset=4053, ""
      SyntaxNode offset=4053, "s"
    SyntaxNode+StringLiteral0 offset=4054, " ":
      SyntaxNode offset=4054, ""
      SyntaxNode offset=4054, " "
    SyntaxNode+StringLiteral0 offset=4055, "S":
      SyntaxNode offset=4055, ""
      SyntaxNode offset=4055, "S"
    SyntaxNode+StringLiteral0 offset=4056, "e":
      SyntaxNode offset=4056, ""
      SyntaxNode offset=4056, "e"
    SyntaxNode+StringLiteral0 offset=4057, "r":
      SyntaxNode offset=4057, ""
      SyntaxNode offset=4057, "r"
    SyntaxNode+StringLiteral0 offset=4058, "i":
      SyntaxNode offset=4058, ""
      SyntaxNode offset=4058, "i"
    SyntaxNode+StringLiteral0 offset=4059, "f":
      SyntaxNode offset=4059, ""
      SyntaxNode offset=4059, "f"
  SyntaxNode offset=4060, "\""

Now that I have this tree, I don't know how to filter it so that I only process specific nodes that match a specific rule.

I am wanting to replace string literals with an identifier, that references the string in a string file.

cool_parser.treetop

rule string_literal
  '"' (!'"' . / '""')* '"'
end

require 'treetop'

# Load the grammar
Treetop.load 'cool'

class Parser

  # Create the parser
  @@parser = CoolParser.new

  def self.parse(data)

    # Pass the data over to the parser instance
    tree = @@parser.parse(data)

    if(tree.nil?)
      raise Exception, "Parse error at offset: #{@@parser.index}"
    end

    return tree
  end

end

tree = Parser.parse(File.open("myfile.txt").read)

puts tree.inspect

Upvotes: 0

Views: 242

Answers (1)

Josh Voigts
Josh Voigts

Reputation: 4132

I'm not sure what you mean by "replace with an identifier"? But, here's an example of returning the value of the string nodes as an array.

cool_parser.treetop

   rule start
      (not_string_literal / string_literal)*
      {
         def value
            elements.map {|e| e.value }.compact
         end
      }
   end

   rule string_literal
      '"' (!'"' . / '""')* '"'
      {
         def value
            text_value
         end
      }
   end

   rule not_string_literal
      !string_literal .
      {
         def value
         end
      }
   end

Then access the parsed object's newly added value method:

tree = Parser.parse(File.open("myfile.txt").read)

puts tree.value.inspect

# => ["\"strings\"", "\"sentences\""]

Upvotes: 1

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