shiftDurations and tempo

[Simon Albrecht]

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?), 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?

Best, Simon