From: David Kastrup <dak@gnu.org>
Date: Sat, 14 Sep 2013 09:09:18 +0000 (+0200)
Subject: Issue 3552: Don't modify lists returned by markup list functions in interpret-markup... 
X-Git-Tag: release/2.17.27-1~34
X-Git-Url: https://git.donarmstrong.com/?a=commitdiff_plain;h=1dc774fbea585861dd3c958f8ae1efa95e5165fe;p=lilypond.git

Issue 3552: Don't modify lists returned by markup list functions in interpret-markup-list

This requires either
a) copying any list manually
b) interpreting markup lists right-to-left
c) more complicated and/or non-O(n) algorithms

This patch chooses b).  Modifying the lists is not really appropriate
since the lists may be created by user-written markup commands and any
problems resulting from not expecting modifications of the return
value might be quite hard to debug.
---

diff --git a/scm/markup.scm b/scm/markup.scm
index 69a6ad13ff..64a1139738 100644
--- a/scm/markup.scm
+++ b/scm/markup.scm
@@ -48,16 +48,13 @@ Example:
 (define-public interpret-markup ly:text-interface::interpret-markup)
 
 (define-public (interpret-markup-list layout props markup-list)
-  ;; This relies on the markup list returned by a markup list command
-  ;; to be modifiable
-  (reverse!
-   (fold
-    (lambda (m prev)
-      (if (markup-command-list? m)
-          (reverse! (apply (car m) layout props (cdr m)) prev)
-          (cons (interpret-markup layout props m) prev)))
-    '()
-    markup-list)))
+  (fold-right
+   (lambda (m prev)
+     (if (markup-command-list? m)
+         (append (apply (car m) layout props (cdr m)) prev)
+         (cons (interpret-markup layout props m) prev)))
+   '()
+   markup-list))
 
 (define-public (prepend-alist-chain key val chain)
   (cons (acons key val (car chain)) (cdr chain)))