x.rb

class Parser
rule
  string
    | a_or_cs abb
    | abb         
    ;
  a_or_cs
    : a_or_cs a_or_c
    | a_or_c
    ;
  a_or_c : 'a' | 'c' ;
  abb    : 'a' 'b' 'b' { puts "I found abb!" };
end

---- inner

def next_token
  @q.shift
end

def parse(text)
  @q = text.chars.map { |c| [c, c] }

  do_parse
end

---- footer
parser = Parser.new

# raises Racc::ParseError on failed match
parser.parse(ARGV[0])