Re: "compound music expression" to "music" expression"

[Gianmaria Lari]

Thank you David for your help.

I made some tests with \displayMusic and I have seen the situation :)

Thank you Aaron for the detailed explanation and also for the other code!

I will continue to use your \extract code but I keep also the new one for the future :)

Have a nice w/e.

Ciao, g

On Sat, 24 Apr 2021 at 11:40, Aaron Hill <lilypond@hillvisions.com> wrote:

On 2021-04-23 11:32 pm, David Kastrup wrote:
> Gianmaria Lari <gianmarialari@gmail.com> writes:
>
>> Thank you Aaron and Jean, your code works!
>>
>> But I have some trivial questions.
>> If I write:
>>
>> \displayLilyMusic \chordmode {c}
>>
>>
>> I get:
>>
>> { < c' e' g' >4 }
>>
>>
>> It looks a good "compound music _expression_".
>
> Try \displayMusic rather than \displayLilyMusic for more details.

In case David's hint was not sufficient, there is an additional layer of
complexity when using \chordmode.  Unfortunately, that layer is not
visible when using \displayLilyMusic, and this is where the confusion
arises.

\chordmode produces UnrelativableMusic that contains SequentialMusic and
then EventChords of NoteEvents.

Jean's first-element assumes that the music argument has a property
called elements and resolves to the first value within the collection. 
UnrelativableMusic only has an element property, so first-element gets
stuck.  Here is a modified version of first-element that does not:

%%%%
#(define (first-element music)
   (or (ly:music-property music 'element #f)
       (first (ly:music-property music 'elements))))

% This works, but you get a SequentialMusic.
{ #(first-element #{ \chordmode {c} #}) }

% This grabs the EventChord from the SequentialMusic.
{ #(first-element (first-element #{ \chordmode {c} #})) }
%%%%

My \extract uses the built-in extract-typed-music procedure to do the
heavy lifting, including the logic necessary to traverse nested music
expressions with both element and elements properties.


-- Aaron Hill