bug#25826: 26.0.50; cl-mapc and cl-mapl do needless consing

[Tino Calancha]

npostavs@users.sourceforge.net writes:

> Tino Calancha <tino.calancha@gmail.com> writes:
>
>> Current implementation of cl-mapc (cl-mapl) uses `cl-mapcar'
>> (`cl-maplist') when input contains > 1 sequence.  Thus,
>> they cons the values and just discard then at the end.
>>
>> Following patch adds a defvar which acts as a flag for consing
>> the values.  The flag is bind to nil in the case of `cl-mapc' and
>> `cl-mapl'.
>
> Is it possible to do this via a parameter instead?  Using a global
> variable seems like asking for trouble in case of nested calls or
> similar.
How about the following updated patch?

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>From 917e290e9101426b492becd814f2f570d1fc9802 Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Wed, 22 Feb 2017 12:06:04 +0900
Subject: [PATCH] Prevent for consing in cl-mapc and cl-mapl

* lisp/emacs-lisp/cl-extra.el (cl--mapcar-many): Add optional arg ACC;
If non-nil, accumulate values in the result (Bug#25826).
(cl-mapc): Do computations inside function instead of call cl-map.
(cl-mapl): Do computations inside function instead of call cl-maplist.
* lisp/emacs-lisp/cl-lib.el (mapcar): Add autoload cookie.
Call cl--mapcar-many with non-nil 3rd argument.
---
 lisp/emacs-lisp/cl-extra.el | 38 ++++++++++++++++++++++++++------------
 lisp/emacs-lisp/cl-lib.el   |  5 +++--
 2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/lisp/emacs-lisp/cl-extra.el b/lisp/emacs-lisp/cl-extra.el
index edd14b816f..8cba913710 100644
--- a/lisp/emacs-lisp/cl-extra.el
+++ b/lisp/emacs-lisp/cl-extra.el
@@ -89,7 +89,7 @@ cl-equalp
 ;;; Control structures.
 
 ;;;###autoload
-(defun cl--mapcar-many (cl-func cl-seqs)
+(defun cl--mapcar-many (cl-func cl-seqs &optional acc)
   (if (cdr (cdr cl-seqs))
       (let* ((cl-res nil)
             (cl-n (apply 'min (mapcar 'length cl-seqs)))
@@ -106,20 +106,23 @@ cl--mapcar-many
                          (setcar cl-p1 (cdr (car cl-p1))))
                      (aref (car cl-p1) cl-i)))
            (setq cl-p1 (cdr cl-p1) cl-p2 (cdr cl-p2)))
-         (push (apply cl-func cl-args) cl-res)
+         (if acc
+             (push (apply cl-func cl-args) cl-res)
+           (apply cl-func cl-args))
          (setq cl-i (1+ cl-i)))
-       (nreverse cl-res))
+       (and acc (nreverse cl-res)))
     (let ((cl-res nil)
          (cl-x (car cl-seqs))
          (cl-y (nth 1 cl-seqs)))
       (let ((cl-n (min (length cl-x) (length cl-y)))
            (cl-i -1))
        (while (< (setq cl-i (1+ cl-i)) cl-n)
-         (push (funcall cl-func
-                         (if (consp cl-x) (pop cl-x) (aref cl-x cl-i))
-                         (if (consp cl-y) (pop cl-y) (aref cl-y cl-i)))
-                cl-res)))
-      (nreverse cl-res))))
+         (let ((val (funcall cl-func
+                             (if (consp cl-x) (pop cl-x) (aref cl-x cl-i))
+                             (if (consp cl-y) (pop cl-y) (aref cl-y cl-i)))))
+           (when acc
+             (push val cl-res)))))
+       (and acc (nreverse cl-res)))))
 
 ;;;###autoload
 (defun cl-map (cl-type cl-func cl-seq &rest cl-rest)
@@ -142,7 +145,7 @@ cl-maplist
        (while (not (memq nil cl-args))
          (push (apply cl-func cl-args) cl-res)
          (setq cl-p cl-args)
-         (while cl-p (setcar cl-p (cdr (pop cl-p)) )))
+         (while cl-p (setcar cl-p (cdr (pop cl-p)))))
        (nreverse cl-res))
     (let ((cl-res nil))
       (while cl-list
@@ -155,8 +158,14 @@ cl-mapc
   "Like `cl-mapcar', but does not accumulate values returned by the function.
 \n(fn FUNCTION SEQUENCE...)"
   (if cl-rest
-      (progn (apply 'cl-map nil cl-func cl-seq cl-rest)
-            cl-seq)
+      (if (or (cdr cl-rest) (nlistp cl-seq) (nlistp (car cl-rest)))
+          (progn
+            (cl--mapcar-many cl-func (cons cl-seq cl-rest))
+            cl-seq)
+        (let ((cl-x cl-seq) (cl-y (car cl-rest)))
+          (while (and cl-x cl-y)
+            (funcall cl-func (pop cl-x) (pop cl-y)))
+          cl-seq))
     (mapc cl-func cl-seq)))
 
 ;;;###autoload
@@ -164,7 +173,12 @@ cl-mapl
   "Like `cl-maplist', but does not accumulate values returned by the function.
 \n(fn FUNCTION LIST...)"
   (if cl-rest
-      (apply 'cl-maplist cl-func cl-list cl-rest)
+      (let ((cl-args (cons cl-list (copy-sequence cl-rest)))
+           cl-p)
+       (while (not (memq nil cl-args))
+          (apply cl-func cl-args)
+         (setq cl-p cl-args)
+         (while cl-p (setcar cl-p (cdr (pop cl-p))))))
     (let ((cl-p cl-list))
       (while cl-p (funcall cl-func cl-p) (setq cl-p (cdr cl-p)))))
   cl-list)
diff --git a/lisp/emacs-lisp/cl-lib.el b/lisp/emacs-lisp/cl-lib.el
index 5aa8f1bf65..8c4455a3da 100644
--- a/lisp/emacs-lisp/cl-lib.el
+++ b/lisp/emacs-lisp/cl-lib.el
@@ -347,8 +347,9 @@ cl-float-negative-epsilon
 
 (cl--defalias 'cl-copy-seq 'copy-sequence)
 
-(declare-function cl--mapcar-many "cl-extra" (cl-func cl-seqs))
+(declare-function cl--mapcar-many "cl-extra" (cl-func cl-seqs &optional acc))
 
+;;;###autoload
 (defun cl-mapcar (cl-func cl-x &rest cl-rest)
   "Apply FUNCTION to each element of SEQ, and make a list of the results.
 If there are several SEQs, FUNCTION is called with that many arguments,
@@ -358,7 +359,7 @@ cl-mapcar
 \n(fn FUNCTION SEQ...)"
   (if cl-rest
       (if (or (cdr cl-rest) (nlistp cl-x) (nlistp (car cl-rest)))
-         (cl--mapcar-many cl-func (cons cl-x cl-rest))
+         (cl--mapcar-many cl-func (cons cl-x cl-rest) 'accumulate)
        (let ((cl-res nil) (cl-y (car cl-rest)))
          (while (and cl-x cl-y)
            (push (funcall cl-func (pop cl-x) (pop cl-y)) cl-res))
-- 
2.11.0

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In GNU Emacs 26.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.7)
 of 2017-02-22
Repository revision: fb997d30af28da4712ca64876feddbd07db20e13