This is a bug in your parser, causing a direct recursion with "optional star". Also this is a bug in Pharo causing direct recursion to hang the image. #optional is a parser that always succeeds. #star is an parser that parsers 0 or more times eagerly. Thus #star loops forever. Thus, you should remove the #optional parser in your grammar, #star alone already makes the receiver optional. Lukas On 7 August 2011 18:08, Sean P. DeNigris <sean(a)clipperadams.com> wrote: -- Lukas Renggli www.lukas-renggli.ch