Fix composition of markup lists containing markup command list calls

scm/markup.scm

 ;;;; This file is part of LilyPond, the GNU music typesetter.
 ;;;;
 ;;;; Copyright (C) 2003--2012 Han-Wen Nienhuys <hanwen@xs4all.nl>
 ;;;;
 ;;;; LilyPond is free software: you can redistribute it and/or modify
 ;;;; it under the terms of the GNU General Public License as published by
 ;;;; the Free Software Foundation, either version 3 of the License, or
 ;;;; (at your option) any later version.
 ;;;;
 ;;;; LilyPond is distributed in the hope that it will be useful,
@@ skipping 30 matching lines @@
 (define (markup-join markups sep)
   "Return line-markup of MARKUPS, joining them with markup SEP"
   (if (pair? markups)
       (make-line-markup (list-insert-separator markups sep))
       empty-markup))
 
 
 (define-public interpret-markup ly:text-interface::interpret-markup)
 
 (define-public (interpret-markup-list layout props markup-list)
-  (let ((stencils (list)))
-    (for-each (lambda (m)
-                (set! stencils
-                      (if (markup-command-list? m)
-                          (append! (reverse! (apply (car m) layout props (cdr m)))
-                                   stencils)
-                          (cons (interpret-markup layout props m) stencils))))
-              markup-list)
-    (reverse! stencils)))
+  ;; 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)))
 
 (define-public (prepend-alist-chain key val chain)
   (cons (acons key val (car chain)) (cdr chain)))
 
 (define-public (stack-stencil-line space stencils)
   "Adjoin a list of STENCILS along the X axis, leaving SPACE between the
    end of each stencil and the reference point of the following stencil."
   (if (and (pair? stencils)
            (ly:stencil? (car stencils)))
 
@@ skipping 73 matching lines @@
       (markup->string (ly:modules-lookup scopes var) (cons mod scopes))))
 
    ;; ignore all other markup functions
    ((markup-function? (car m)) "")
 
    ;; handle markup lists
    ((list? m)
     (string-join (map (lambda (mm) (markup->string mm scopes)) m) " "))
 
    (else "ERROR, unable to extract string from markup"))))