public Symbol parse()

in util/src/main/java/java_cup/runtime/lr_parser.java [525:626]
57 lines of code
8 McCabe index (conditional complexity)

  public Symbol parse() throws java.lang.Exception
    {
      /* the current action code */
      int act;

      /* the Symbol/stack element returned by a reduce */
      Symbol lhs_sym = null;

      /* information about production being reduced with */
      short handle_size, lhs_sym_num;

      /* set up direct reference to tables to drive the parser */

      production_tab = production_table();
      action_tab     = action_table();
      reduce_tab     = reduce_table();

      /* initialize the action encapsulation object */
      init_actions();

      /* do user initialization */
      user_init();

      /* get the first token */
      cur_token = scan(); 

      /* push dummy Symbol with start state to get us underway */
      stack.removeAllElements();
      stack.push(new Symbol(0, start_state()));
      tos = 0;

      /* continue until we are told to stop */
      for (_done_parsing = false; !_done_parsing; )
	{
	  /* Check current token for freshness. */
	  if (cur_token.used_by_parser)
	    throw new Error("Symbol recycling detected (fix your scanner).");

	  /* current state is always on the top of the stack */

	  /* look up action out of the current state with the current input */
	  act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);

	  /* decode the action -- > 0 encodes shift */
	  if (act > 0)
	    {
	      /* shift to the encoded state by pushing it on the stack */
	      cur_token.parse_state = act-1;
	      cur_token.used_by_parser = true;
	      stack.push(cur_token);
	      tos++;

	      /* advance to the next Symbol */
	      cur_token = scan();
	    }
	  /* if its less than zero, then it encodes a reduce action */
	  else if (act < 0)
	    {
	      /* perform the action for the reduce */
	      lhs_sym = do_action((-act)-1, this, stack, tos);

	      /* look up information about the production */
	      lhs_sym_num = production_tab[(-act)-1][0];
	      handle_size = production_tab[(-act)-1][1];

	      /* pop the handle off the stack */
	      for (int i = 0; i < handle_size; i++)
		{
		  stack.pop();
		  tos--;
		}
	      
	      /* look up the state to go to from the one popped back to */
	      act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);

	      /* shift to that state */
	      lhs_sym.parse_state = act;
	      lhs_sym.used_by_parser = true;
	      stack.push(lhs_sym);
	      tos++;
	    }
	  /* finally if the entry is zero, we have an error */
	  else if (act == 0)
	    {
	      /* call user syntax error reporting routine */
	      syntax_error(cur_token);

	      /* try to error recover */
	      if (!error_recovery(false))
		{
		  /* if that fails give up with a fatal syntax error */
		  unrecovered_syntax_error(cur_token);

		  /* just in case that wasn't fatal enough, end parse */
		  done_parsing();
		} else {
		  lhs_sym = (Symbol)stack.peek();
		}
	    }
	}
      return lhs_sym;
    }