Re: \displayLilyMusic

[Nicolas Sceaux]

Han-Wen Nienhuys <address@hidden> writes:

> Nicolas Sceaux wrote:
>> I have an nearly complete implementation of a \displayLilyMusic
>> command.
>> \displayLilyMusic \new Voice {   \clef alto   \time 3/4   \key g
>> \minor   c'2. |
>>   \once \override TextScript #'padding = #2
>>   d'2 e'4^\markup { \bold { hello \italic world ! } }
>> }
>> ==>
>> \new Voice {
>>   \clef "alto"
>>   \time 3/4
>>   \key g \minor
>>    c'2. |
>>   \once \override TextScript #'padding = #2
>>   d'2 e'4^\markup \line { \bold "hello" \bold \italic "world" \bold
>> "!"}  }
>> \displayLilyMusic \transpose c' a { <c e> <d f> }
>> ==>
>> { < a, cis > < b, d > }
>> Should there be such a command inside the LilyPond distribution?
>
> it would be wonderful to have it. My only reservation is
> maintainability. How sensitive is this to breakage when we change the
> music implementation (property names, etc?)

This is indeed a major concern. Of course, the print method for a
music type will stop working if the relevant property names are changed.
Here is an example of such a method:

(define-primary-print-method TimeScaledMusic (times)
  (parameterize ((*force-line-break* #f)
                 (*time-factor-numerator* (ly:music-property times 'numerator))
                 (*time-factor-denominator* (ly:music-property times 
'denominator)))
     (format #f "\\times ~a/~a ~a" 
             (*time-factor-numerator*)
             (*time-factor-denominator*)
             (print-lily-music (ly:music-property times 'element)))))

in this case, if numerator and denominator names change, it will print
something like:
  \times ()/() { ... }
Or if it is the element property that changes, it will print:
  \times 3/4 %{ expecting a music expression: () %}

If a print method is not implemented for some music type:
  %{ Print method not implemented for music type StrangeEvent %}

When I have finished implementing methods for the remaining music
types, I'll send here the code. (I've just seen some improvements to
do also).
;;BusyPlayingEvent
;;ClusterNoteEvent
;;FoldedRepeatedMusic
;;LyricCombineMusic
;;MelismaPlayingEvent
;;MultiMeasureTextEvent
;;NewLyricCombineMusic
;;NoteGroupingEvent
;;OutputPropertySetMusic
;;PartCombineMusic
;;PesOrFlexaEvent
;;QuoteMusic
;;ScriptEvent
;;SoloOneEvent
;;SoloTwoEvent
;;StartPlayingEvent
;;UnaCordaEvent
;;UnisonoEvent
;;UnrelativableMusic
;;UntransposableMusic

A music pattern matcher was defined for recognizing some more complex
expressions, eg: 

(add-print-method ContextSpeccedMusic (expr)
  "If `expr' is a bar, return \"\\bar ...\".
Otherwise, return #f."
  (with-music-match (expr (music
                           'ContextSpeccedMusic
                           element (music
                                    'ContextSpeccedMusic
                                    context-type 'Timing
                                    element (music
                                             'PropertySet
                                             value ?bar-type
                                             symbol 'whichBar))))
     (format #f "\\bar \"~a\"~a" ?bar-type (print-lily-new-line))))

Here, if the implementation of bars changes somewhat, the default
methods for contexts and property sets will be called.
  \context Score \set Timing . whichBar = #"||"

nicolas