Changeset 265

Timestamp:

Jan 11, 2004, 11:30:46 PM (21 years ago)

Author:

Gary Byers

Message:

BUTLAST, NBUTLAST handle dotted lists again.

File:

• trunk/ccl/lib/lists.lisp (modified) (3 diffs)

trunk/ccl/lib/lists.lisp

@@ -156 +156 @@
 
 
+(defun alt-list-length (l)
+  "Detect (and complain about) cirucular lists; allow any atom to
+terminate the list"
+  (do* ((n 0 (1+ n))
+        (fast l)
+        (slow l))
+       ((atom fast) (if fast (the fixnum (1+ n)) n))
+    (declare (fixnum n))
+    (setq fast (cdr fast))
+    (if (logbitp 0 n)
+      (if (eq (setq slow (cdr slow)) fast)
+        (%err-disp $XIMPROPERLIST l)))))
+
 (defun butlast (list &optional (n 1 n-p))
   "Returns a new list the same as List without the N last elements."
@@ -164 +177 @@
                (not (typep n 'unsigned-byte))))
     (report-bad-arg n 'unsigned-byte))
-  (let* ((length (length list)))
+  (let* ((length (alt-list-length list)))
     (declare (fixnum length))           ;guaranteed
     (when (< n length)
@@ -184 +197 @@
                (not (typep n 'unsigned-byte))))
     (report-bad-arg n 'unsigned-byte))
-  (let* ((length (length list)))
+  (let* ((length (alt-list-length list)))
     (declare (fixnum length))           ;guaranteed
     (when (< n length)