Re: Setting lytics to alternative endings

[Jean Abou Samra]

> Le 16 déc. 2022 à 15:25, Kieren MacMillan <kieren@kierenmacmillan.info> a 
> écrit :
> 
> In a certain way, the unfolded example is inconsistent, right? Shouldn’t it 
> be something like […]
> 
> Otherwise, you have an example with music that has a \repeat command and 
> lyrics that don’t…


This doc example is not a problem in the slightest. I think I was not clear 
explaining what is OK and what is not. The golden rule is: *if a bit of music 
is repeated, in the actual performance by the player, it should be enclosed in 
a \repeat block, otherwise it shouldn’t*.

The example is just fine in this regard.

Now, it turns out that repeat bar lines and volta brackets are not good at 
expressing repeats that are different across staves. Try to imagine two staves 
in parallel, of which only one has repeat bar lines. That would be just crazy. 
Therefore, as a *corollary*, it does not make sense to use \repeat volta in one 
staff or music expression while another staff or music expression in parallel 
does not use \repeat volta. The same goes for \repeat segno. Because of 
technical details of how \repeat volta works currently, it happens that

<<
  \new Staff \repeat volta 2 { c'1 }
  \new Staff { c'1 }
>>

prints a repeat bar line on both staves, but the semantic meaning of that music 
is that the upper staff plays for two measures while the lower staff plays for 
one measure only, and LilyPond could equally choose to print a normal bar line 
in the lower staff. The input just makes no sense.

On the other hand, for \repeat unfold and \repeat percent, using the command in 
one staff but not others makes sense and is useful, common and fully supported.

If this causes cognitive dissonance, keep in mind the principle: through 
\repeat commands, the lily music describes the *performance*, not the notation.

Indeed, you would not expect

<<
  \new Staff \repeat unfold 2 { c'1 }
  \new Staff { c'1 }
>>

to make the note in the lower staff repeated twice. From this point of view, 
\repeat volta is no different.

Best,
Jean