(defpackage #:collect
(:use #:common-lisp #:mdw.base)
- (:export #:collecting #:with-collection #:collect))
+ (:export #:collecting #:with-collection #:collect #:collect-tail))
(in-package collect)
(eval-when (:compile-toplevel :load-toplevel)
(defvar *collecting-anon-list-name* (gensym)
"The default name for anonymous `collecting' lists.")
(defun make-collector ()
- (let ((c (cons nil nil)))
- (cons c c))))
+ (let ((head (cons nil nil)))
+ (setf (car head) head))))
+
(defmacro collecting (vars &body body)
"Collect items into lists. The VARS are a list of collection variables --
-their values are unspecified, except that they may be passed to `collect' and
-`collect-tail' If VARS is empty then *collecting-anon-list-name* is used.
-VARS may be an atom instead of a singleton list. The form produces multiple
-values, one for each list constructed."
+ their values are unspecified, except that they may be passed to `collect'
+ and `collect-tail' If VARS is empty then *collecting-anon-list-name* is
+ used. VARS may be an atom instead of a singleton list. The form produces
+ multiple values, one for each list constructed."
(cond ((null vars) (setf vars (list *collecting-anon-list-name*)))
((atom vars) (setf vars (list vars))))
`(let ,(mapcar (lambda (v) `(,v (make-collector))) vars)
,@body
- (values ,@(mapcar (lambda (v) `(cdar ,v)) vars))))
+ (values ,@(mapcar (lambda (v) `(the list (cdr ,v))) vars))))
+
(defmacro with-collection (vars collection &body body)
"Collect items into lists VARS according to the form COLLECTION; then
-evaluate BODY with VARS bound to those lists."
+ evaluate BODY with VARS bound to those lists."
`(multiple-value-bind
- ,(listify vars)
+ ,(listify vars)
(collecting ,vars ,collection)
,@body))
+
(defmacro collect (x &optional (name *collecting-anon-list-name*))
"Add item X to the `collecting' list NAME (or *collecting-anon-list-name*
-by default)."
- (with-gensyms tmp
- `(let ((,tmp (cons ,x nil)))
- (setf (cddr ,name) ,tmp)
- (setf (cdr ,name) ,tmp))))
+ by default)."
+ (with-gensyms new
+ `(let ((,new (cons ,x nil)))
+ (setf (cdar ,name) ,new)
+ (setf (car ,name) ,new))))
+
(defmacro collect-tail (x &optional (name *collecting-anon-list-name*))
"Make item X be the tail of `collecting' list NAME (or
-*collecting-anon-list-name* by default). It is an error to continue trying
-to add stuff to the list."
+ *collecting-anon-list-name* by default). It is an error to continue
+ trying to add stuff to the list."
`(progn
- (setf (cddr ,name) ,x)
- (setf (cdr ,name) nil)))
+ (setf (cdar ,name) ,x)
+ (setf (car ,name) nil)))
;;;----- That's all, folks --------------------------------------------------