Issue 4296: Let \displayLilyMusic print even repeated durations

\displayLilyMusic { c4 c c c } now produces { c4 c4 c4 c4 } in order to
better match the content of the music rather than the shortest possible
input representation.

7 files changed, 127 insertions, 133 deletions

diff --git a/Documentation/changes.tely b/Documentation/changes.tely
index a90f386485..46675428be 100644
--- a/Documentation/changes.tely
+++ b/Documentation/changes.tely
@@ -518,6 +518,15 @@ examples where this makes for readable input:
 @end lilypond
 
 @item
+@code{\displayLilyMusic} and its underlying Scheme functions no
+longer omit redundant note durations.  This makes it easier to
+reliably recognize and format standalone durations in expressions
+like
+@example
+@{ c4 d4 8 @}
+@end example
+
+@item
 Beaming exceptions can now be constructed using the
 @code{\beamExceptions} scheme function.  One can now write
 
diff --git a/Documentation/extending/scheme-tutorial.itely b/Documentation/extending/scheme-tutorial.itely
index fc2eba1c6d..a399570dec 100644
--- a/Documentation/extending/scheme-tutorial.itely
+++ b/Documentation/extending/scheme-tutorial.itely
@@ -1264,7 +1264,7 @@ The note pitch can be changed by setting this @code{'pitch} property,
        (ly:make-pitch 0 1 0)) ;; set the pitch to d'.
 \displayLilyMusic \someNote
 ===>
-d'
+d'4
 @end example
 
 
diff --git a/Documentation/notation/input.itely b/Documentation/notation/input.itely
index 8cede953f0..ad827e0e36 100644
--- a/Documentation/notation/input.itely
+++ b/Documentation/notation/input.itely
@@ -3413,7 +3413,7 @@ line.  For example,
 will display
 
 @example
-@{ a,4 cis e fis g @}
+@{ a,4 cis4 e4 fis4 g4 @}
 @end example
 
 By default, LilyPond will print these messages to the console
diff --git a/input/regression/display-lily-tests.ly b/input/regression/display-lily-tests.ly
index b14fa52090..cbbebd6539 100644
--- a/input/regression/display-lily-tests.ly
+++ b/input/regression/display-lily-tests.ly
@@ -48,24 +48,24 @@ stderr of this run."
 }
 
 %% Sequential music
-\test ##[ { { a b } { c d } } #]		% SequentialMusic
-\test ##[ << { a b } { c d } >> #]		% SimultaneousMusic
-\test ##[ << { a b } \\ { c d } >> #]		% VoiceSeparator
+\test ##[ { { a4 b4 } { c4 d4 } } #]		% SequentialMusic
+\test ##[ << { a4 b4 } { c4 d4 } >> #]		% SimultaneousMusic
+\test ##[ << { a4 b4 } \\ { c4 d4 } >> #]	% VoiceSeparator
 
 %% Chords and Notes
-\test ##[ { ceses ces c cis cisis } #]		% NoteEvent
-\test ##[ { deses des d dis disis } #]
-\test ##[ { eeses ees e eis eisis } #]
-\test ##[ { feses fes f fis fisis } #]
-\test ##[ { geses ges g gis gisis } #]
-\test ##[ { aeses aes a ais aisis } #]
-\test ##[ { beses bes b bis bisis } #]
-\test ##[ { c,, d' } #]
-\test ##[ { c' d'=' } #]
-\test ##[ { c! c? } #]
+\test ##[ { ceses4 ces4 c4 cis4 cisis4 } #]	% NoteEvent
+\test ##[ { deses4 des4 d4 dis4 disis4 } #]
+\test ##[ { eeses4 ees4 e4 eis4 eisis4 } #]
+\test ##[ { feses4 fes4 f4 fis4 fisis4 } #]
+\test ##[ { geses4 ges4 g4 gis4 gisis4 } #]
+\test ##[ { aeses4 aes4 a4 ais4 aisis4 } #]
+\test ##[ { beses4 bes4 b4 bis4 bisis4 } #]
+\test ##[ { c,,4 d'4 } #]
+\test ##[ { c'4 d'='4 } #]
+\test ##[ { c!4 c?4 } #]
 \test ##[ r1.*4/3 #]		% RestEvent
 \test ##[ c1\rest #]		% RestEvent
-\test ##[ s2..*3/4 #]			% SkipEvent
+\test ##[ s2..*3/4 #]		% SkipEvent
 \test ##[ R1.*2/3 #]		% MultiMeasureRestMusicGroup, MultiMeasureRestEvent
 \test ##[ \skip 2.*3/4 #]		% SkipMusic
 \test ##[ < c\1 e\3 >4.*3/4-. #]	% EventChord, NoteEvent, StringNumberEvent, ArticulationEvent
@@ -73,22 +73,22 @@ stderr of this run."
 \test ##[ { < c e g c' >4 q8-. } #] % RepeatedChord
 
 %% tags
-\test ##[ { \tag #'foo { c4 d } } #]
-\test ##[ c-\tag #'foo -\tag #'baz -^-. #]
+\test ##[ { \tag #'foo { c4 d4 } } #]
+\test ##[ c4-\tag #'foo -\tag #'baz -^-. #]
 
 %% Graces
 \test ##[ { \grace c8 d2 } #]				% GraceMusic
 \test ##[ { \appoggiatura c8 d2 } #]
 \test ##[ { \acciaccatura c8 d2 } #]
-\test ##[ { c1 \afterGrace { b,16 c } d2 } #]
+\test ##[ { c1 \afterGrace { b,16 c16 } d2 } #]
 
 %% Clusters
-\test ##[ { \makeClusters { c4 g } } #]			% ClusterNoteEvent
+\test ##[ { \makeClusters { c4 g4 } } #]		% ClusterNoteEvent
 
 %% Figured bass
-\test ##[ \figures { < 6 > } #]				% BassFigureEvent
-\test ##[ \figuremode { < 1-- 3- > < 2+ 4++ > < _! 7! > } #]
-\test ##[ \figuremode { < [6 > < 5] > } #]
+\test ##[ \figures { < 6 >4 } #]			% BassFigureEvent
+\test ##[ \figuremode { < 1-- 3- >4 < 2+ 4++ >4 < _! 7! >4 } #]
+\test ##[ \figuremode { < [6 >4 < 5] >4 } #]
 
 %% Lyrics
 \test ##[ \lyrics { a b } #]
@@ -96,53 +96,53 @@ stderr of this run."
 \test ##[ \lyricmode { a __ b } #] 		% ExtenderEvent
 \test ##[ \lyricmode { "a " } #] 			% LyricEvent
 \test ##[ \lyricsto "foo" { bla bla  } #]		% LyricCombineMusic
-\test ##[ { { c d }
+\test ##[ { { c4 d4 }
   \addlyrics { bla bla  } } #]
 
 %% Drums
-\test ##[ \drums { hihat } #]
+\test ##[ \drums { hihat4 } #]
 \test ##[ \drummode { hihat4.*3/4 } #]
 
 %% Expressive marks
 \test ##[ c4 ~ #]			 		% TieEvent
-\test ##[ c\noBeam #] 					% BeamForbidEvent
-\test ##[ c\1 #] 					% StringNumberEvent
-\test ##[ { c:8 c:1 } #]				% TremoloEvent
-\test ##[ { c-^ c^^ c_^ } #]				% ArticulationEvent
-\test ##[ { c-+ c^+ c_+ } #]
-\test ##[ { c-- c^- c_- } #]
-\test ##[ { c-! c^! c_! } #]
-\test ##[ { c-> c^> c_> } #]
-\test ##[ { c-. c^. c_. } #]
-\test ##[ { c-_ c^_ c__ } #]
-\test ##[ { c\trill c^\trill c_\trill } #]
-\test ##[ { c-1 c^2 c_3 } #]				% FingerEvent
-\test ##[ { c-"foo" c^"foo" c_"foo" } #]		% TextScriptEvent
-\test ##[ { R1*4-"foo" R^"foo" R_"foo" } #]		% MultiMeasureTextEvent
-\test ##[ { < c\harmonic >4 < c e\harmonic > } #] 	% HarmonicEvent
-\test ##[ { c\glissando c^\glissando c_\glissando } #]	% GlissandoEvent
-\test ##[ { c\arpeggio c^\arpeggio c_\arpeggio } #] 	% ArpeggioEvent
-\test ##[ { c\p c^\ff c_\sfz } #] 			% AbsoluteDynamicEvent
-\test ##[ { c[ c] c^[ c^] c_[ c_] } #] 			% BeamEvent
-\test ##[ { c( c) c^( c^) c_( c_) } #] 			% SlurEvent
-\test ##[ { c\< c\! c^\< c^\! c_\< c_\! } #]		% CrescendoEvent
-\test ##[ { c\> c\! c^\> c^\! c_\> c_\! } #]		% DecrescendoEvent
-\test ##[ { c\episemInitium c\episemFinis } #]		% EpisemaEvent
-\test ##[ { c\( c\) c^\( c^\) c_\( c_\) } #]		% PhrasingSlurEvent
-\test ##[ { c\sustainOn c\sustainOff } #]		% SustainEvent
-\test ##[ { c\sostenutoOn c\sostenutoOff } #]		% SostenutoEvent
+\test ##[ c4\noBeam #] 					% BeamForbidEvent
+\test ##[ c4\1 #] 					% StringNumberEvent
+\test ##[ { c4:8 c4:1 } #]				% TremoloEvent
+\test ##[ { c4-^ c4^^ c4_^ } #]				% ArticulationEvent
+\test ##[ { c4-+ c4^+ c4_+ } #]
+\test ##[ { c4-- c4^- c4_- } #]
+\test ##[ { c4-! c4^! c4_! } #]
+\test ##[ { c4-> c4^> c4_> } #]
+\test ##[ { c4-. c4^. c4_. } #]
+\test ##[ { c4-_ c4^_ c4__ } #]
+\test ##[ { c4\trill c4^\trill c4_\trill } #]
+\test ##[ { c4-1 c4^2 c4_3 } #]				% FingerEvent
+\test ##[ { c4-"foo" c4^"foo" c4_"foo" } #]		% TextScriptEvent
+\test ##[ { R1*4-"foo" R1*4^"foo" R1*4_"foo" } #]	% MultiMeasureTextEvent
+\test ##[ { < c\harmonic >4 < c e\harmonic >4 } #] 	% HarmonicEvent
+\test ##[ { c4\glissando c4^\glissando c4_\glissando } #]	% GlissandoEvent
+\test ##[ { c4\arpeggio c4^\arpeggio c4_\arpeggio } #] 	% ArpeggioEvent
+\test ##[ { c4\p c4^\ff c4_\sfz } #] 			% AbsoluteDynamicEvent
+\test ##[ { c4[ c4] c4^[ c4^] c4_[ c4_] } #] 		% BeamEvent
+\test ##[ { c4( c4) c4^( c4^) c4_( c4_) } #] 		% SlurEvent
+\test ##[ { c4\< c4\! c4^\< c4^\! c4_\< c4_\! } #]	% CrescendoEvent
+\test ##[ { c4\> c4\! c4^\> c4^\! c4_\> c4_\! } #]	% DecrescendoEvent
+\test ##[ { c4\episemInitium c4\episemFinis } #]	% EpisemaEvent
+\test ##[ { c4\( c4\) c4^\( c4^\) c4_\( c4_\) } #]	% PhrasingSlurEvent
+\test ##[ { c4\sustainOn c4\sustainOff } #]		% SustainEvent
+\test ##[ { c4\sostenutoOn c4\sostenutoOff } #]		% SostenutoEvent
 \test ##[ \melisma #]
 \test ##[ \melismaEnd #]
-\test ##[ { c\startTextSpan c\stopTextSpan } #]		% TextSpanEvent
-\test ##[ { c\startTrillSpan c\stopTrillSpan } #]	% TrillSpanEvent
-\test ##[ { c \startStaff c \stopStaff } #]		% StaffSpanEvent
-\test ##[ { c\startGroup c\stopGroup c^\startGroup c^\stopGroup c_\startGroup c_\stopGroup } #]    % NoteGroupingEvent
-\test ##[ { c\unaCorda c\treCorde } #]			% UnaCordaEvent
+\test ##[ { c4\startTextSpan c4\stopTextSpan } #]	% TextSpanEvent
+\test ##[ { c4\startTrillSpan c4\stopTrillSpan } #]	% TrillSpanEvent
+\test ##[ { c4 \startStaff c4 \stopStaff } #]		% StaffSpanEvent
+\test ##[ { c4\startGroup c4\stopGroup c4^\startGroup c4^\stopGroup c4_\startGroup c4_\stopGroup } #]    % NoteGroupingEvent
+\test ##[ { c4\unaCorda c4\treCorde } #]		% UnaCordaEvent
 \test ##[ \breathe #]
-\test ##[ { c \[ c \] } #]			% LigatureEvent
+\test ##[ { c4 \[ c4 \] } #]				% LigatureEvent
 \test ##[ \~ #]						% PesOrFlexaEvent
-\test ##[ c\bendAfter #3 #]    % BendAfterEvent
-\test ##[ c\rightHandFinger #1 #]    % StrokeFingerEvent
+\test ##[ c4\bendAfter #3 #]				% BendAfterEvent
+\test ##[ c4\rightHandFinger #1 #]			% StrokeFingerEvent
 
 \test ##[ \break #]
 \test ##[ \noBreak #]
@@ -176,41 +176,41 @@ stderr of this run."
 \test ##[ \bar "|." #]
 
 %% staff switches
-\test ##[ \autochange { c d } #]			% AutoChangeMusic
-\test ##[ { \change Staff = "up" { c d } } #]		% ContextChange
+\test ##[ \autochange { c4 d4 } #]			% AutoChangeMusic
+\test ##[ { \change Staff = "up" { c4 d4 } } #]		% ContextChange
 
 %% Tuplets
-\test ##[ \tuplet 3/2 { c8 d e } #]				% TimeScaledMusic
-\test ##[ \tuplet 6/4 { c16 d e f g a } #]
-\test ##[ \tuplet 3/2 { c4 d e \tuplet 5/2 { f4 e d2 d4 } c4 } #]
-\test ##[ \tuplet 3/2 2 { c4 d e \tuplet 5/2 2 { f4 e d2 d4 } c4 } #]
+\test ##[ \tuplet 3/2 { c8 d8 e8 } #]				% TimeScaledMusic
+\test ##[ \tuplet 6/4 { c16 d16 e16 f16 g16 a16 } #]
+\test ##[ \tuplet 3/2 { c4 d4 e4 \tuplet 5/2 { f4 e4 d2 d4 } c4 } #]
+\test ##[ \tuplet 3/2 2 { c4 d4 e4 \tuplet 5/2 2 { f4 e4 d2 d4 } c4 } #]
 
 %% pure rhythm
 \test ##[ { 4 4 8 \tuplet 3/2 { 8[ 16] } 16 } #]
 
 %% \relative and \tranpose
-\test #"NOT A BUG" ##[ \relative c' { c b } #]	% RelativeOctaveMusic
-\test #"NOT A BUG" ##[ \transpose c d { c d } #]	% TransposedMusic
+\test #"NOT A BUG" ##[ \relative c' { c4 b4 } #]	% RelativeOctaveMusic
+\test #"NOT A BUG" ##[ \transpose c d { c4 d4 } #]	% TransposedMusic
 
 %% Repeats
-\test ##[ \repeat volta 2 { c d } #]		% VoltaRepeatedMusic
-\test ##[ \repeat unfold 2 { c d } #]			% UnfoldedRepeatedMusic
-\test ##[ \repeat percent 2 { c d } #]			% PercentRepeatedMusic
-\test ##[ \repeat tremolo 4 { c16 d } #]		% TremoloRepeatedMusic
-\test ##[ \repeat tremolo 7 { c''32 b' } #]
-\test ##[ \repeat tremolo 15 { c''16 b' } #]
-\test ##[ \repeat volta 2 { c4 d } \alternative { { c d } { e f } } #]    % 
+\test ##[ \repeat volta 2 { c4 d4 } #]			% VoltaRepeatedMusic
+\test ##[ \repeat unfold 2 { c4 d4 } #]			% UnfoldedRepeatedMusic
+\test ##[ \repeat percent 2 { c4 d4 } #]		% PercentRepeatedMusic
+\test ##[ \repeat tremolo 4 { c16 d16 } #]		% TremoloRepeatedMusic
+\test ##[ \repeat tremolo 7 { c''32 b'32 } #]
+\test ##[ \repeat tremolo 15 { c''16 b'16 } #]
+\test ##[ \repeat volta 2 { c4 d4 } \alternative { { c4 d4 } { e4 f4 } } #]    % 
 
 %% Context creation
-\test ##[ \new Staff { c d } #]				% ContextSpeccedMusic
-\test ##[ \new Staff = "up" { c d } #]				% ContextSpeccedMusic
-\test ##[ \context Staff { c d } #]
-\test ##[ \context Staff = "up" { c d } #]
+\test ##[ \new Staff { c4 d4 } #]			% ContextSpeccedMusic
+\test ##[ \new Staff = "up" { c4 d4 } #]		% ContextSpeccedMusic
+\test ##[ \context Staff { c4 d4 } #]
+\test ##[ \context Staff = "up" { c4 d4 } #]
 \test ##[
 \new Staff \with {
   \consists "Timing_engraver"
   \remove "Clef_engraver"
-} { c d } #]
+} { c4 d4 } #]
 %% Context properties
 \test ##[ \once \set Score . skipBars = ##t #]		% PropertySet
 \test ##[ \set autoBeaming = ##f #]
@@ -236,22 +236,22 @@ stderr of this run."
 \test ##[ \partial 4*2/3 #]
 
 %% \partcombine
-\test ##[ \partcombine { c e }
-{ d f } #]						% PartCombineMusic UnrelativableMusic
+\test ##[ \partcombine { c4 e4 }
+{ d4 f4 } #]						% PartCombineMusic UnrelativableMusic
 
 %% Cue notes
-\test ##[ \cueDuring #"foo" #1 { c d } #]
-\test ##[ \quoteDuring #"foo" { c d } #]
+\test ##[ \cueDuring #"foo" #1 { c4 d4 } #]
+\test ##[ \quoteDuring #"foo" { c4 d4 } #]
 
 %% \ottava
 \test ##[ \ottava #1 #]    % OttavaMusic
 
 %% \tweak
-\test ##[ < \tweak duration-log #2 c > #]
-\test ##[ < c \tweak transparent ##t e > #]
-\test ##[ < \tweak color #'(1.0 0.0 0.0) \tweak duration-log #2 c > #]
-\test ##[ c-\tweak font-size #3 -> #]
-\test ##[ < \tweak Accidental.color #'(1.0 0.0 0.0) cis eis g > #]
+\test ##[ < \tweak duration-log #2 c >4 #]
+\test ##[ < c \tweak transparent ##t e >4 #]
+\test ##[ < \tweak color #'(1.0 0.0 0.0) \tweak duration-log #2 c >4 #]
+\test ##[ c4-\tweak font-size #3 -> #]
+\test ##[ < \tweak Accidental.color #'(1.0 0.0 0.0) cis eis g >4 #]
 
 %% end test.
 
diff --git a/scm/define-music-display-methods.scm b/scm/define-music-display-methods.scm
index 845b514f44..ca532c5029 100644
--- a/scm/define-music-display-methods.scm
+++ b/scm/define-music-display-methods.scm
@@ -105,15 +105,13 @@ expression."
 ;;;
 ;;; durations
 ;;;
-(define*-public (duration->lily-string ly-duration #:key (prev-duration (*previous-duration*))
-                                       (force-duration (*force-duration*))
-                                       (time-scale (*time-scale*))
-                                       remember)
-  (if remember (*previous-duration* ly-duration))
+(define*-public (duration->lily-string ly-duration #:key
+                                       (force-duration #f)
+                                       (time-scale (*time-scale*)))
   (let ((log2    (ly:duration-log ly-duration))
         (dots    (ly:duration-dot-count ly-duration))
         (scale (ly:duration-scale ly-duration)))
-    (if (or force-duration (not prev-duration) (not (equal? ly-duration prev-duration)))
+    (if (or force-duration (not (*omit-duration*)))
         (string-append (case log2
                          ((-1) "\\breve")
                          ((-2) "\\longa")
@@ -429,14 +427,15 @@ Otherwise, return #f."
                ;; '<' (notepitch | drumpitch)* '>" duration post_events
                (let ((duration (duration->lily-string (ly:music-property
                                                        (car chord-elements)
-                                                       'duration)
-                                                      #:remember #t)))
+                                                       'duration))))
                  ;; Format duration first so that it does not appear on
                  ;; chord elements
                  (format #f "< ~{~a ~}>~a~:{~:[-~;~]~a~^ ~}"
-                         (map-in-order (lambda (music)
-                                         (music->lily-string music parser))
-                                       chord-elements)
+                         (parameterize ((*omit-duration* #t))
+                                       (map-in-order
+                                        (lambda (music)
+                                          (music->lily-string music parser))
+                                        chord-elements))
                          duration
                          (map-in-order (lambda (music)
                                          (list
@@ -444,8 +443,7 @@ Otherwise, return #f."
                                           (music->lily-string music parser)))
                                        other-elements))))
               ((ly:duration? chord-repeat)
-               (let ((duration (duration->lily-string chord-repeat
-                                                      #:remember #t)))
+               (let ((duration (duration->lily-string chord-repeat)))
                  (format #f "q~a~:{~:[-~;~]~a~^ ~}"
                          duration
                          (map-in-order (lambda (music)
@@ -467,8 +465,7 @@ Otherwise, return #f."
 
 (define-display-method MultiMeasureRestMusic (mmrest parser)
   (format #f "R~a~{~a~^ ~}"
-          (duration->lily-string (ly:music-property mmrest 'duration)
-                                 #:remember #t)
+          (duration->lily-string (ly:music-property mmrest 'duration))
           (map-in-order (lambda (music)
                           (music->lily-string music parser))
                         (ly:music-property mmrest 'articulations))))
@@ -504,8 +501,7 @@ Otherwise, return #f."
                                         (make-string (1- (* -1 octave-check)) #\,))
                                        (else "")))
                 ""))
-          (duration->lily-string (ly:music-property event 'duration)
-                                 #:remember #t)
+          (duration->lily-string (ly:music-property event 'duration))
           (if ((make-music-type-predicate 'RestEvent) event)
               "\\rest" "")
           (map-in-order (lambda (event)
@@ -519,19 +515,15 @@ Otherwise, return #f."
          (simple-note->lily-string note parser))
         ((not (null? (ly:music-property note 'drum-type))) ;; drum
          (format #f "~a~a~{~a~}" (ly:music-property note 'drum-type)
-                 (duration->lily-string (ly:music-property note 'duration)
-                                        #:remember #t)
+                 (duration->lily-string (ly:music-property note 'duration))
                  (map-in-order (lambda (event)
                                  (music->lily-string event parser))
                                (ly:music-property note 'articulations))))
         (else
          ;; pure duration
-         ;; FIXME: { c4 c4 4 4 } must not be output as { c4 c 4 4 }
-         ;; quite tricky to do.  Do it when outputting sequences?
          (format #f "~a~{~a~}"
                  (duration->lily-string (ly:music-property note 'duration)
-                                        #:force-duration #t
-                                        #:remember #t)
+                                        #:force-duration #t)
                  (map-in-order (lambda (event)
                                  (music->lily-string event parser))
                                (ly:music-property note 'articulations))))))
@@ -543,20 +535,17 @@ Otherwise, return #f."
   (if (not (null? (ly:music-property rest 'pitch)))
       (simple-note->lily-string rest parser)
       (format #f "r~a~{~a~}"
-              (duration->lily-string (ly:music-property rest 'duration)
-                                     #:remember #t)
+              (duration->lily-string (ly:music-property rest 'duration))
               (map-in-order (lambda (event)
                               (music->lily-string event parser))
                             (ly:music-property rest 'articulations)))))
 
 (define-display-method MultiMeasureRestEvent (rest parser)
-  (string-append "R" (duration->lily-string (ly:music-property rest 'duration)
-                                            #:remember #t)))
+  (string-append "R" (duration->lily-string (ly:music-property rest 'duration))))
 
 (define-display-method SkipEvent (rest parser)
   (format #f "s~a~{~a~}"
-          (duration->lily-string (ly:music-property rest 'duration)
-                                 #:remember #t)
+          (duration->lily-string (ly:music-property rest 'duration))
           (map-in-order (lambda (event)
                           (music->lily-string event parser))
                         (ly:music-property rest 'articulations))))
@@ -631,7 +620,7 @@ Otherwise, return #f."
             (if (null? bracket-stop) "" "]"))))
 
 (define-display-method LyricEvent (lyric parser)
-  (format "~a~{~a~^ ~}"
+  (format #f "~a~{~a~^ ~}"
           (let ((text (ly:music-property lyric 'text)))
             (if (or (string? text)
                     (eqv? (first text) simple-markup))
@@ -674,7 +663,6 @@ Otherwise, return #f."
           (and span (duration->lily-string span #:force-duration #t)))
          (scale (/ num den))
          (time-scale (*time-scale*)))
-    (*previous-duration* #f)
     (let ((result
            (parameterize ((*force-line-break* #f)
                           (*time-scale* (* time-scale scale)))
@@ -683,7 +671,6 @@ Otherwise, return #f."
                                  num
                                  formatted-span
                                  (music->lily-string (ly:music-property times 'element) parser)))))
-      (*previous-duration* #f)
       result)))
 
 (define-display-method RelativeOctaveMusic (m parser)
@@ -1104,7 +1091,8 @@ Otherwise, return #f."
 (define-display-method LyricCombineMusic (expr parser)
   (format #f "\\lyricsto ~s ~a"
           (ly:music-property expr 'associated-context)
-          (parameterize ((*explicit-mode* #f))
+          (parameterize ((*explicit-mode* #f)
+                         (*omit-duration* #t))
                         (music->lily-string (ly:music-property expr 'element) parser))))
 
 ;; \addlyrics
@@ -1124,7 +1112,8 @@ Otherwise, return #f."
                         (format #f "~a~a \\addlyrics ~a"
                                 (music->lily-string ?note-sequence parser)
                                 (new-line->lily-string)
-                                (parameterize ((*explicit-mode* #f))
+                                (parameterize ((*explicit-mode* #f)
+                                               (*omit-duration* #t))
                                               (music->lily-string ?lyric-sequence parser)))
                         #f)))
 
diff --git a/scm/display-lily.scm b/scm/display-lily.scm
index 6d38fff784..8d8645b36b 100644
--- a/scm/display-lily.scm
+++ b/scm/display-lily.scm
@@ -11,10 +11,10 @@
 ;;; Display methods are stored in the `display-methods' property of each music
 ;;; type.
 ;;;
-;;; - `music->lily-string' return a string describing a music expression using
-;;; LilyPond notation. The special variables *indent*, *previous-duration*,
-;;; and *force-duration* influence the indentation level and the display of
-;;; music durations.
+;;; - `music->lily-string' return a string describing a music
+;;; expression using LilyPond notation. The special variables *indent*
+;;; and *omit-duration* influence the indentation level and the
+;;; display of music durations.
 ;;;
 ;;; - `with-music-match' can be used to destructure a music expression, extracting
 ;;; some interesting music properties.
@@ -282,11 +282,8 @@ inside body."
 ;;; indentation
 (define-public *indent* (make-parameter 0))
 
-;;; set to #t to force duration printing
-(define-public *force-duration* (make-parameter #f))
-
-;;; last duration found
-(define-public *previous-duration* (make-parameter (ly:make-duration 2)))
+;;; set to #t to omit duration printing
+(define-public *omit-duration* (make-parameter #f))
 
 ;;; Set to #t to force a line break with some kinds of expressions (eg sequential music)
 (define *force-line-break* (make-parameter #t))
diff --git a/scm/music-functions.scm b/scm/music-functions.scm
index 1b679a7228..611879ae8b 100644
--- a/scm/music-functions.scm
+++ b/scm/music-functions.scm
@@ -234,8 +234,7 @@ which often can be read back in order to generate an equivalent expression."
   "Display the music expression using LilyPond syntax"
   (memoize-clef-names supported-clefs)
   (parameterize ((*indent* 0)
-                 (*previous-duration* (ly:make-duration 2))
-                 (*force-duration* force-duration))
+                 (*omit-duration* #f))
                 (display (music->lily-string expr parser) port)
                 (newline port)))