Re: How to get all Voice-Contexts?

[Thomas Morley]

2015-11-27 23:45 GMT+01:00 David Kastrup <address@hidden>:
> Thomas Morley <address@hidden> writes:
>
>> Hi,
>>
>> for some engraver I need to look at all Voices, comparing them in some 
>> regard.
>>
>> If I put the engraver in every Voice, then every Voice is processed,
>> yes, but I can't find a method to compare them.
>> So I thought the way might be to put the engraver in Score, get the
>> Voices and do nasty things ...
>>
>> Though, I can't find a method to select all Voices.
>>
>> Consider this tiny and boiled down example:
>>
>> %%%%%%%%%%%%%%%
>> \version "2.19.32"
>>
>> get-Voices =
>> \context Score \applyContext #(lambda (ctx) (display ctx))
>>
>> \score {
>>     \new Staff
>>     <<
>>       \new Voice = "1" { \get-Voices c''1 }
>>       \new Voice = "2" { e'1 }
>>     >>
>> }
>> %%%%%%%%%%%%%%%%
>>
>> How to get all Voices looking down from Score?
>
> You could have an engraver listen for AnnounceNewContext and
> RemoveContext events and keep tally of the Voice contexts among them in
> a hash table or something like that.
>
> --
> David Kastrup

As a first step, this leads to:

\version "2.19.32"

#(define (my-engraver ctx)
  (let ((voices '()))
     `(
       (listeners
        ;; TODO: don't forget `RemoveContext'
        (AnnounceNewContext
          .
          ,(lambda (engraver event)
            (let ((context (ly:event-property event 'context)))
             (if (eq? (ly:context-name context) 'Voice)
                 (set! voices (cons context voices)))
             (write-me "voices " voices)
             )))))))

\score {
  \new Staff
  <<
    \new Voice = "1" { c''1 }
    \new Voice = "2" { e'1 }
  >>
  \layout {
    \context {
      \Score
      \consists #my-engraver
    }
  }
}


Promising. Thanks a lot!

Btw, AnnounceNewContext and RemoveContex are not listed in the IR, I
had to git grep them. Intended or over-sight?


Thanks,
  Harm