Re: key-change-event listener in 2.20

[Aaron Hill]

On 2020-09-03 5:03 am, Maurits Lamers wrote:
> Hi all,
>
> I finally figured out what goes wrong here. The issue is that I get
> the key signature and the last key signature from the context in the
> following way:
>
> (ly:context-property (ly:translator-context engraver) 'keySignature))
> (ly:context-property (ly:translator-context engraver) 
> 'lastKeySignature))
>
> which works in 2.14 up to 2.18. In 2.20 these properties seem to have
> been renamed to keyAlterations and lastKeyAlterations (according to
> http://lilypond.org/doc/v2.20/Documentation/internals/key_005fengraver)
> What would be the best way to support both 2.18 and 2.20? Is there a
> better / more reliable method of getting this information?

You could check to see which symbol exists as a translator property:

;;;;
(define (translator-property? symbol)
  (memq symbol all-translation-properties))

;; ...

(ly:context-property
  (ly:translator-context engraver)
  (car (filter translator-property? '(keyAlterations keySignature)))
  '())
;;;;


-- Aaron Hill