X-Git-Url: https://git.distorted.org.uk/~mdw/lisp/blobdiff_plain/bf0a8c394bdf34895ad53771665f70c3b80e272e..fe0f07ea19b36ce1abc1ec305d0203323cbf2316:/collect.lisp

diff --git a/collect.lisp b/collect.lisp
index 813707e..359780c 100644
--- a/collect.lisp
+++ b/collect.lisp
@@ -25,46 +25,65 @@
 
 (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)))
+
+(defmacro collect-append (list &optional (name *collecting-anon-list-name*))
+  "Append LIST to the tail of `collecting' list NAME.  This obviously
+   involves copying LIST."
+  (with-gensyms item
+    `(dolist (,item ,list)
+       (collect ,item ,name))))
+
+(defmacro collect-nconc (list &optional (name *collecting-anon-list-name*))
+  "Attach LIST to the tail of `collecting' list NAME.  This will involve
+   destroying LIST if anything else gets collected afterwards."
+  (let*/gensyms list
+    `(when ,list
+       (setf (cdar ,name) ,list)
+       (setf (car ,name) (last ,list)))))
 
 ;;;----- That's all, folks --------------------------------------------------