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# Load the builder class
require_relative '../../../lib/rley/syntax/grammar_builder'
require_relative '../../../lib/rley/tokens/token'
# Utility class.
class GrammarPBHelper
# Factory method. Creates a grammar for a basic arithmetic
# expression based on example found in paper of
# K. Pingali and G. Bilardi:
# "A Graphical Model for Context-Free Grammar Parsing"
def grammar()
@grammar ||= begin
builder = Rley::Syntax::GrammarBuilder.new do
t_int = Rley::Syntax::Literal.new('int', /[-+]?\d+/)
t_plus = Rley::Syntax::VerbatimSymbol.new('+')
t_lparen = Rley::Syntax::VerbatimSymbol.new('(')
t_rparen = Rley::Syntax::VerbatimSymbol.new(')')
add_terminals(t_int, t_plus, t_lparen, t_rparen)
rule 'S' => 'E'
rule 'E' => 'int'
rule 'E' => %w[( E + E )]
rule 'E' => %w[E + E]
end
builder.grammar
end
end
# Basic expression tokenizer
def tokenize(aText)
tokens = aText.scan(/\S+/).map do |lexeme|
case lexeme
when '+', '(', ')'
terminal = @grammar.name2symbol[lexeme]
when /^[-+]?\d+$/
terminal = @grammar.name2symbol['int']
else
msg = "Unknown input text '#{lexeme}'"
raise StandardError, msg
end
Rley::Tokens::Token.new(lexeme, terminal)
end
return tokens
end
end # module
# End of file
Version data entries
8 entries across 8 versions & 1 rubygems