Allows slurs to break at barlines.

ly/music-functions-init.ly

 %%%% -*- Mode: Scheme -*-
 
 %%%% This file is part of LilyPond, the GNU music typesetter.
 %%%%
 %%%% Copyright (C) 2003--2012 Han-Wen Nienhuys <hanwen@xs4all.nl>
 %%%%                          Jan Nieuwenhuizen <janneke@gnu.org>
 %%%%
 %%%% 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
@@ skipping 402 matching lines @@
 post-event, the @code{\\footnote} command itself needs to be attached
 to the preceding note or rest as a post-event with @code{-}.")
    (let ((mus (make-music
                'FootnoteEvent
                'X-offset (car offset)
                'Y-offset (cdr offset)
                'automatically-numbered (not mark)
                'text (or mark (make-null-markup))
                'footnote-text footnote)))
      #{ \tweak footnote-music #mus #item #}))
+
+free =
+#(define-music-function (parser location music) (ly:music?)
+  (_i "@var{event} should start a free spanner.")
+  (let ((name (ly:music-property music 'name)))
+    (cond
+      ((eq? name 'SlurEvent)
+       (make-music 'BreakSlurEvent
+                   'span-direction (ly:music-property music 'span-direction)
+                   'direction (ly:music-property music 'direction)
+                   'spanner-id (ly:music-property music 'spanner-id)))
+      ((eq? name 'PhrasingSlurEvent)
+       (make-music 'BreakPhrasingSlurEvent
+                   'span-direction (ly:music-property music 'span-direction)
+                   'direction (ly:music-property music 'direction)
+                   'spanner-id (ly:music-property music 'spanner-id)))
+      (else
+        (begin
+          (ly:music-warning music (_ "not a breakable event"))
+        music)))))
 
 grace =
 #(def-grace-function startGraceMusic stopGraceMusic
    (_i "Insert @var{music} as grace notes."))
 
 grobdescriptions =
 #(define-scheme-function (parser location descriptions) (list?)
    (_i "Create a context modification from @var{descriptions}, a list
 in the format of @code{all-grob-descriptions}.")
    (ly:make-context-mod
@@ skipping 1068 matching lines @@
 Use this if you want to have a scheme expression evaluated
 because of its side-effects, but its value ignored."))
 
 withMusicProperty =
 #(define-music-function (parser location sym val music)
    (symbol? scheme? ly:music?)
    (_i "Set @var{sym} to @var{val} in @var{music}.")
 
    (set! (ly:music-property music sym) val)
    music)