Whenever there is a spac after an open parenthesis, one gets a TK error. For instance, try and type the following definition: (defvar xxx   '(   abc       x y z )) Leave a space between the open parenthesis and abc. The Tk message is:  Index 0 out of bounds for (SIMPLE-ARRAY CHARACTER(0)), should be nonnegative and <0. I guess the problem has to do with the token coloring algorithm.