Re: shiftDurations and tempo

[Jean Abou Samra]

Le 27/06/2022 à 20:10, Simon Albrecht a écrit :
> Hello everyone,
>
> I’m trying to encode a piece such that I can switch whether or not 
> durations will be shifted (note values halved/doubled). Unfortunately 
> \tempo isn’t affected by \shiftDurations (that would be a sensible 
> feature request, right?),

Go open an issue.


> so I tried this:
> %%%%%%%%%%%%%%%%%%%%%%%%%%%
> \version "2.23.9"
>
> durationShiftOne = #-1
> {
>   \tempo #(ly:make-duration (+ 3 durationShiftOne)) = 152
>   \shiftDurations \durationShiftOne #0 { 8 }
> }
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>
> but unfortunately Lily won’t accept that Scheme expression instead of 
> the normal duration.
>
> Can I make that work some other way?
>
> Should the parser be able to take that Scheme expression there?


\version "2.23.9"

durationShiftOne = #-1
{
  \tempo $(ly:make-duration (+ 3 durationShiftOne)) = 152
  \shiftDurations \durationShiftOne #0 { 8 }
}


You just need to use $ instead of #. See these pages about the difference:

https://lilypond.org/doc/v2.23/Documentation/extending/lilypond-scheme-syntax.html
https://extending-lilypond.readthedocs.io/en/latest/lily-and-scheme.html#hash-vs-dollar

The problem is that \tempo has multiple syntaxes (\tempo <markup>,
\tempo <duration> = <bpm> and \tempo <markup> <duration> = <bpm>),
which makes it impossible to accept # here because early evaluation
is needed to disambiguate, I think. I'm no expert of the parser
though.

Best,
Jean