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Contents
# Load the builder class
require_relative '../../../lib/rley/syntax/grammar_builder'
require_relative '../../../lib/rley/parser/token'
module AmbiguousGrammarHelper
# Factory method. Creates a grammar builder for a basic ambiguous
# expression grammar.
# (based on an example from Fisher and LeBlanc: "Crafting a Compiler")
def grammar_builder()
builder = Rley::Syntax::GrammarBuilder.new
builder.add_terminals('+', 'id')
builder.add_production('S' => 'E')
builder.add_production('E' => %w(E + E))
builder.add_production('E' => 'id')
builder
end
# Basic tokenizing method
def tokenize(aText, aGrammar)
tokens = aText.scan(/\S+/).map do |lexeme|
case lexeme
when '+'
terminal = aGrammar.name2symbol[lexeme]
when /^[_a-zA-Z][_a-zA-Z0-9]*$/
terminal = aGrammar.name2symbol['id']
else
msg = "Unknown input text '#{lexeme}'"
raise StandardError, msg
end
Rley::Parser::Token.new(lexeme, terminal)
end
return tokens
end
end # module
Version data entries
7 entries across 7 versions & 1 rubygems