From: Kevin M. Rosenberg <kevin@rosenberg.net>
Date: Mon, 22 Mar 2010 19:35:00 +0000 (-0600)
Subject: optimize flatten function
X-Git-Tag: v1.101~1
X-Git-Url: http://git.kpe.io/?p=kmrcl.git;a=commitdiff_plain;h=94c161e4a288d874d8d763b768312e1004a888ec

optimize flatten function
---

diff --git a/lists.lisp b/lists.lisp
index 5cd193c..eaa3f9d 100644
--- a/lists.lisp
+++ b/lists.lisp
@@ -73,11 +73,14 @@
             it
             nil)))))
 
-(defun flatten (lis)
-  (cond ((atom lis) lis)
-        ((listp (car lis))
-         (append (flatten (car lis)) (flatten (cdr lis))))
-        (t (append (list (car lis)) (flatten (cdr lis))))))
+(defun flatten (tree)
+  (let ((result '()))
+    (labels ((scan (item)
+               (if (listp item)
+                 (map nil #'scan item)
+                 (push item result))))
+      (scan tree))
+    (nreverse result)))
 
 ;;; Keyword functions