Andy> It seems if you let bind a constant string, e.g: Andy> (let ((mystr "\n")) ...) Andy> and then attach an extent to it, if you run this code the extents will Andy> *accumulate* rather than replace each other. Semantically when I let bind a Andy> constant string I would expect it to be extent free... C89 improved on K&R C by segfaulting if you tried to modify a literal string constant. In the same spirit, we should make literal lisp strings lisp-readonly, so that attempts to modify the literal string generates a lisp error. If you are going to use a modified string temporarily, do (let ((mystr (copy-sequence "\n"))) Martin Many academic folks and language implementors like making it difficult for the user to modify any objects after initialization.