Add for-some-music and fold-some-music

diff --git a/scm/music-functions.scm b/scm/music-functions.scm
index 84424584105f1cfd882b07cf55e3e069b29cb706..84055ed9addd552432c11ecba6afec558ef5a98f 100644 (file)
--- a/scm/music-functions.scm
+++ b/scm/music-functions.scm
@@ -1640,21 +1640,41 @@ and only recurse if this returns @code{#f}."
                    (map loop arts)))
          music))))
 
+(define-public (for-some-music stop? music)
+  "Walk through @var{music}, process all elements calling @var{stop?}
+and only recurse if this returns @code{#f}."
+  (let loop ((music music))
+    (if (not (stop? music))
+       (let ((elt (ly:music-property music 'element)))
+         (if (ly:music? elt)
+             (loop elt))
+         (for-each loop (ly:music-property music 'elements))
+         (for-each loop (ly:music-property music 'articulations))))))
+
+(define-public (fold-some-music pred? proc init music)
+  "This works recursively on music like @code{fold} does on a list,
+calling @samp{(@var{pred?} music)} on every music element.  If
+@code{#f} is returned for an element, it is processed recursively
+with the same initial value of @samp{previous}, otherwise
+@samp{(@var{proc} music previous)} replaces @samp{previous}
+and no recursion happens.
+The top @var{music} is processed using @var{init} for @samp{previous}."
+  (let loop ((music music) (previous init))
+    (if (pred? music)
+       (proc music previous)
+       (fold loop
+             (fold loop
+                   (let ((elt (ly:music-property music 'element)))
+                     (if (null? elt)
+                         previous
+                         (loop elt previous)))
+                   (ly:music-property music 'elements))
+             (ly:music-property music 'articulations)))))
+
 (define-public (extract-music music pred?)
   "Return a flat list of all music matching @var{pred?} inside of
 @var{music}, not recursing into matches themselves."
-  (reverse!
-   (let loop ((music music) (res '()))
-     (if (pred? music)
-        (cons music res)
-        (fold loop
-              (fold loop
-                    (let ((elt (ly:music-property music 'element)))
-                      (if (null? elt)
-                          res
-                          (loop elt res)))
-                    (ly:music-property music 'elements))
-              (ly:music-property music 'articulations))))))
+  (reverse! (fold-some-music pred? cons '() music)))
 
 (define-public (extract-named-music music music-name)
   "Return a flat list of all music named @var{music-name} (either a