use Parse::RecDescent;

$RD_HINT++;
$RD_WARN++;

my $grammar = q{
  Start: Expression(s) /\Z/

  Expression: 
    LineNum Print    
    {                
      $thisparser->{_lines}->{$item[1]} = $item[1].' PRINT "'.$item[2].'"';
    }
    | LineNum Goto  
    {               
      $text = $item[1] . " GOTO " . $item[2] . $text;
      foreach ( sort { $b <=> $a } grep { $_ >= $item[2] } keys %{$thisparser->{_lines}} ) {
        $text = $thisparser->{_lines}->{$_} . $text;
      }                                             
    }
    | <error>

  Print: /print/i /\"/ /[\s\w]+/ /\"/  
  {
      print "$item[3]\n";
      $item[3];          
  }
  Goto: /goto/i LineNum
  {
      $item[2];
               
      # print "Seen a goto line $item[2]\n";
      # How do I seek back to line $item[2] of
      # the input?                            
  }
  LineNum: /\d+/
};

my $parser = new Parse::RecDescent($grammar);

undef $/;
my $text = <DATA>;

$parser->Start($text);

__END__
10 print "hello"
20 print "this"
30 print "is"
40 print "a"
50 print "test"
60 print "goodbye"
70 goto 30