title: Help me find an appropriate ruby/python parser generator
body: <p>The first parser generator I've worked with was Parse::RecDescent, and the guides/tutorials available for it were great, but the most useful feature it has was it's debugging tools, specifically the <b>tracing</b> capabilities ( activated by setting $RD_TRACE to 1 ). I am looking for a parser generator that can help you debug it's rules.</p>
  
  <p>The thing is, it has to be written in python or in ruby, and have a verbose mode/trace mode or very helpful debugging techniques.</p>
  
  <p>Does anyone know such a parser generator ?</p>
  
  <p>EDIT: when I said debugging, I wasn't referring to debugging python or ruby. I was referring to debugging the parser generator, see what it's doing at every step, see every char it's reading, rules it's trying to match. Hope you get the point.</p>
  
  <p><b>BOUNTY EDIT: to win the bounty, please show a parser generator framework, and illustrate some of it's debugging features. I repeat, I'm not interested in pdb, but in parser's debugging framework. Also, please don't mention treetop. I'm not interested in it.</b></p>