The following two forms seem to more or less do the right thing, AFAIK, under lispworks to support SLIME (un)tracing. (defun tracedp (symbol) (member symbol (trace) :test #'eq)) (defslimefun toggle-trace-fdefinition (fname-string) (let ((fname (from-string fname-string))) (print `(got ,fname-string and ,fname)) (cond ((tracedp fname) (compiler::ensure-untrace-1 (list fname)) (format nil "~S is now untraced." fname)) (t (compiler::ensure-trace-1 (list fname)) (format nil "~S is now traced." fname)))))