mop: Handy function for making modified copies of instances.

[lisp] / mdw-base.lisp

diff --git a/mdw-base.lisp b/mdw-base.lisp
index 0b68b8d..59ea692 100644 (file)
--- a/mdw-base.lisp
+++ b/mdw-base.lisp
@@ -30,7 +30,7 @@
   (:use #:common-lisp)
   (:export #:compile-time-defun
           #:show
-          #:stringify #:listify #:fix-pair #:pairify #:parse-body
+          #:stringify #:mappend #:listify #:fix-pair #:pairify #:parse-body
           #:whitespace-char-p
           #:slot-uninitialized
           #:nlet #:while #:case2 #:ecase2
@@ -69,6 +69,12 @@
     (t (with-output-to-string (s)
         (princ str s)))))
 
+(defun mappend (function list &rest more-lists)
+  "Apply FUNCTION to corresponding elements of LIST and MORE-LISTS, yielding
+   a list.  Return the concatenation of all the resulting lists.  Like
+   mapcan, but nondestructive."
+  (apply #'append (apply #'mapcar function list more-lists)))
+
 (compile-time-defun listify (x)
   "If X is a (possibly empty) list, return X; otherwise return (list X)."
   (if (listp x) x (list x)))