X-Git-Url: https://git.distorted.org.uk/~mdw/lisp/blobdiff_plain/0ff9df03bb54ba792cefa551face51748ae34259..fe0f07ea19b36ce1abc1ec305d0203323cbf2316:/collect.lisp

diff --git a/collect.lisp b/collect.lisp
index 28986e0..359780c 100644
--- a/collect.lisp
+++ b/collect.lisp
@@ -32,8 +32,8 @@
   (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 --
@@ -45,7 +45,7 @@
 	((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
@@ -58,17 +58,32 @@
 (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))))
+  (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."
   `(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 --------------------------------------------------