1> "aaaa" 1> "bbbb" 1> . "aaaabbbb" consecutive strings are concatenated by parser, without ++ operator, while 2> 'aaaa' 2> 'bbbb' 2> . * 2: syntax error before: bbbb atoms are not. Maybe not very homogeneous... By the way, I do not really see the need to include \n in atoms... Regards