Looks good! Much cleaner/better.
-Robert
On Sun, Feb 24, 2013 at 6:30 AM, James M. Lawrence llmjjmll@gmail.com wrote:
On Sat, Feb 23, 2013 at 4:09 AM, Robert Smith quad@symbo1ics.com wrote:
(defun delete-from-plist (plist &rest keys) "Delete all keys and pairs indicated by KEYS from the plist PLIST." (labels ((assert-proper-plist (x) (assert x () "Expected a proper plist, got ~S" plist)) (bad-key-p (key) (member key keys :test #'eq)) (find-first () "Find the first cons in PLIST to keep." (loop :for the-cons :on plist :by #'cddr :unless (prog1 (bad-key-p (car the-cons)) (assert-proper-plist (cdr the-cons))) :do (return the-cons) :finally (return nil)))) (declare (inline assert-proper-plist bad-key-p find-first)) ;; Find the first good key and delete any bad key-value pairs ;; between it and the start. (let ((first (find-first))) (unless (eq first plist) (setf (cddr plist) first))
;; At this point, we know FIRST points to the first key ;; which exists, or NIL. (loop :with last-good := first ; Keep the last good key :for the-cons :on (cddr first) :by #'cddr :do (progn (assert-proper-plist (cdr the-cons)) (if (bad-key-p (car the-cons)) (setf (cddr last-good) (cddr the-cons)) (setf last-good the-cons))) :finally (return first)))))Using two loops seems awkward to me. How about one?
(defun delete-from-plist (plist &rest keys) (loop with head = plist with tail = nil for (key . rest) on plist by #'cddr do (assert rest () "Expected a proper plist, got ~S" plist) (if (member key keys :test #'eq) (let ((next (cdr rest))) (if tail (setf (cdr tail) next) (setf head next))) (setf tail rest)) finally (return head)))
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