Hi! I wonder if you are still willing to be bugged about these things..... Anyway, if yes, here is a question: `letf', as implemented by cl-macs, is suboptimal. It always works like this (roughly): `(let ((oldval VAR)) (unwind-protect (progn (setf VAR VALUE) ,＠body) (setf VAR oldval))) While this works generally, for some defsetfs it is pretty wasteful. For instance, it would be nice if: (letf (((current-buffer) somebuffer)) ...) were transformed to: (save-current-buffer (set-buffer somebuffer) ...) instead of the usual unwind-protect drill. It would be a win because save-current-buffer is a subr in (X)Emacs 20. The same applies to other cases, where it is a matter of correctness rather than efficiency. For example, `specifier-instance' has `set-specifier' as its setf method. This means that this: (letf (((specifier-instance SPECIFIER VALUE DOMAIN))) ... code ...) doesn't work as expected, because it expands to: `(let ((oldval (specifier-instance SPECIFIER DOMAIN))) (unwind-protect (progn (set-specifier SPECIFIER VALUE DOMAIN) ,＠body) (set-specifier SPECIFIER OLDVAL DOMAIN))) However, the second `set-specifier' is incorrect, because it adds a new specification to DOMAIN instead of removing the temporary one. This `letf' should actually expand to: (with-specifier-instance SPECIFIER VALUE DOMAIN ... code ...) because with-specifier-instance knows how to handle this correctly. So, is there a way to detach `letf' from `setf'? How does Common Lisp handle this? -- Hrvoje Niksic <hniksic(a)srce.hr&gt; | Student at FER Zagreb, Croatia --------------------------------+-------------------------------- Old numerical analysts never die, they just get disarrayed.