Sha256: 2f46adff86d6f59a3f4b454af430a491b1244786801f53521b18496243f55238
Contents?: true
Size: 1.26 KB
Versions: 10
Compression:
Stored size: 1.26 KB
Contents
# frozen_string_literal: true
# Load the builder class
require_relative '../../../lib/rley/syntax/base_grammar_builder'
require_relative '../../../lib/rley/lexical/token'
module GrammarBExprHelper
# Factory method. Creates a grammar builder for a basic arithmetic
# expression grammar.
# (based on the article about Earley's algorithm in Wikipedia)
def grammar_expr_builder
Rley::Syntax::BaseGrammarBuilder.new do
add_terminals('+', '*', 'integer')
rule 'P' => 'S'
rule 'S' => 'S + M'
rule 'S' => 'M'
rule 'M' => 'M * T'
rule 'M' => 'T'
rule 'T' => 'integer'
end
end
# Basic expression tokenizer
def expr_tokenizer(aText)
scanner = StringScanner.new(aText)
tokens = []
loop do
scanner.skip(/\s+/)
curr_pos = scanner.pos
lexeme = scanner.scan(/\S+/)
break unless lexeme
case lexeme
when '+', '*'
terminal = lexeme
when /^[-+]?\d+$/
terminal = 'integer'
else
msg = "Unknown input text '#{lexeme}'"
raise StandardError, msg
end
pos = Rley::Lexical::Position.new(1, curr_pos + 1)
tokens << Rley::Lexical::Token.new(lexeme, terminal, pos)
end
return tokens
end
end # module
# End of file
Version data entries
10 entries across 10 versions & 1 rubygems