+(define-public (event-chord-reduce music)
+ "Reduces event chords in @var{music} to their first note event,
+retaining only the chord articulations. Returns the modified music."
+ (map-some-music
+ (lambda (m)
+ (and (music-is-of-type? m 'event-chord)
+ (let*-values (((notes arts) (partition
+ (lambda (mus)
+ (music-is-of-type? mus 'rhythmic-event))
+ (ly:music-property m 'elements)))
+ ((dur) (ly:music-property m 'duration))
+ ((full-arts) (append arts
+ (ly:music-property m 'articulations)))
+ ((first-note) (and (pair? notes) (car notes))))
+ (cond (first-note
+ (set! (ly:music-property first-note 'articulations)
+ full-arts)
+ first-note)
+ ((ly:duration? dur)
+ ;; A repeat chord. Produce an unpitched note.
+ (make-music 'NoteEvent
+ 'duration dur
+ 'articulations full-arts))
+ (else
+ (ly:music-error m (_ "Missing duration"))
+ (make-music 'NoteEvent
+ 'duration (ly:make-duration 2 0 0)
+ 'articulations full-arts))))))
+ music))
+
+
+(defmacro-public make-relative (variables reference music)
+ "The list of pitch or music variables in @var{variables} is used as
+a sequence for creating relativable music from @var{music}.
+
+When the constructed music is used outside of @code{\\relative}, it
+just reflects plugging in the @var{variables} into @var{music}.
+
+The action inside of @code{\\relative}, however, is determined by
+first relativizing the surrogate @var{reference} with the variables
+plugged in and then using the variables relativized as a side effect
+of relativizing @var{reference} for evaluating @var{music}.
+
+Since pitches don't have the object identity required for tracing the
+effect of the reference call, they are replaced @emph{only} for the
+purpose of evaluating @var{reference} with simple pitched note events.
+
+The surrogate @var{reference} expression has to be written with that
+in mind. In addition, it must @emph{not} contain @emph{copies} of
+music that is supposed to be relativized but rather the
+@emph{originals}. This @emph{includes} the pitch expressions. As a
+rule, inside of @code{#@{@dots{}#@}} variables must @emph{only} be
+introduced using @code{#}, never via the copying construct @code{$}.
+The reference expression will usually just be a sequential or chord
+expression naming all variables in sequence, implying that following
+music will be relativized according to the resulting pitch of the last
+or first variable, respectively.
+
+Since the usual purpose is to create more complex music from general
+arguments and since music expression parts must not occur more than
+once, one @emph{does} generally need to use copying operators in the
+@emph{replacement} expression @var{music} when using an argument more
+than once there. Using an argument more than once in @var{reference},
+in contrast, does not make sense.
+
+There is another fine point to mind: @var{music} must @emph{only}
+contain freshly constructed elements or copied constructs. This will
+be the case anyway for regular LilyPond code inside of
+@code{#@{@dots{}#@}}, but any other elements (apart from the
+@var{variables} themselves which are already copied) must be created
+or copied as well.
+
+The reason is that it is usually permitted to change music in-place as
+long as one does a @var{ly:music-deep-copy} on it, and such a copy of
+the whole resulting expression will @emph{not} be able to copy
+variables/values inside of closures where the information for
+relativization is being stored.
+"
projects / lilypond.git / blobdiff