X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcode%2Fearly-extensions.lisp;h=81b6f7b046a5bf0285d767fee01697d73b18640e;hb=174feb792c8082846666e1218c58d5b0ab3b85b0;hp=c5cf3b2e13735afa11d0d7818b9b412949f5472c;hpb=f6f238261f95e8ffff2870ed3ac6fc00ddf09ef2;p=sbcl.git

diff --git a/src/code/early-extensions.lisp b/src/code/early-extensions.lisp
index c5cf3b2..81b6f7b 100644
--- a/src/code/early-extensions.lisp
+++ b/src/code/early-extensions.lisp
@@ -288,7 +288,12 @@
   ;; just define ASSQ explicitly in terms of more primitive
   ;; operations:
   (dolist (pair alist)
-    (when (and pair (eq (car pair) item))
+    ;; though it may look more natural to write this as 
+    ;;   (AND PAIR (EQ (CAR PAIR) ITEM))
+    ;; the temptation to do so should be resisted, as pointed out by PFD
+    ;; sbcl-devel 2003-08-16, as NIL elements are rare in association
+    ;; lists.  -- CSR, 2003-08-16
+    (when (and (eq (car pair) item) (not (null pair)))
       (return pair))))
 
 ;;; like (DELETE .. :TEST #'EQ):
@@ -1092,6 +1097,33 @@ which can be found at <http://sbcl.sourceforge.net/>.~:@>"
                (let ((it ,test)) (declare (ignorable it)),@body)
                (acond ,@rest))))))
 
+;;; (binding* ({(name initial-value [flag])}*) body)
+;;; FLAG may be NIL or :EXIT-IF-NULL
+;;;
+;;; This form unites LET*, MULTIPLE-VALUE-BIND and AWHEN.
+(defmacro binding* ((&rest bindings) &body body)
+  (let ((bindings (reverse bindings)))
+    (loop with form = `(progn ,@body)
+          for binding in bindings
+          do (destructuring-bind (names initial-value &optional flag)
+                 binding
+               (multiple-value-bind (names declarations)
+                   (etypecase names
+                     (null
+                      (let ((name (gensym)))
+                        (values (list name) `((declare (ignorable ,name))))))
+                     (symbol
+                      (values (list names) nil))
+                     (list
+                      (values names nil)))
+                 (setq form `(multiple-value-bind ,names
+                                 ,initial-value
+                               ,@declarations
+                               ,(ecase flag
+                                       ((nil) form)
+                                       ((:exit-if-null)
+                                        `(when ,(first names) ,form)))))))
+          finally (return form))))
 
 ;;; Delayed evaluation
 (defmacro delay (form)