PPRepeatingParser is indeed how the 'plus' method is implemented for example. The problem is that, by specifying #letter asParser I accept any kind of letter, thus #letter asParser plus accepts any number of any kind of letters. The problem is that I need to accept only multiple occurrences of the same letter :) I could do something like: $a asParser plus / $b asParser plus / ... but that's not really nice code :) Anyway, thanks for the help! On Feb 3, 2011, at 1:38 PM, Fabrizio Perin wrote: