Re: \bar "||" and \repeat around a line break

[Jim Long]

On Thu, Jan 17, 2013 at 09:52:14PM -0500, Ralph Palmer wrote:
> >
> > Consider a composition of the form
> >
> > A B A C A D A E
> >
> > The composer requires that each section begin on a new line of
> > the page; and end with a double barline, except the final
> > section:
> >
> > A = { ... \bar "||" \break }
> > ...
> > E = { ... \bar "|." }
> >
> > Sections B and D begin with a volta repeat, but sections C and E
> > do not:
> >
> > A = { ... \bar "||" \break }
> > B = { \repeat volta 2 { ... } ... \bar "||" \break }
> > C = { ... \bar "||" \break }
> > D = { \repeat volta 2 { ... } ... \bar "||" \break }
> > E = { ... \bar "|." }
> 
> Okay, but how does Lilypond know that you are starting a new section

Not relevant.  Lilypond only knows that the source file said:

\bar "||" \break

Keep in mind here that, as I understand Johan's request, we're
specifically talking about double bar lines at the end of a
staff.  I've never seen nor used a double bar in the middle of a
staff adjacent to an open repeat, nor in the middle of a staff
adjacent to a closing repeat, so I can't comment on those use
cases.  Someone who has a clear idea of how those should look can
chime in if they want to.  I'm referring to the specific case
where the composer explicitly calls out a double barline at the
explicit end of a line.

> that you want a double bar before some repeats, but possibly not others

There is no confusion at all.  The source file tells Lilypond
exactly where the double bars should be.  Lilypond knows that at
several places, the source code says:

\bar "||" \break

As I understood Johan's suggestion, Lilypond should interpret
that to mean, 'put a double barline at this point in the layout,
break the line and continue engraving sequential music (if any)
on the next line.'  I think he wants that behaviour regardless of
what music comes next, or indeed whether any music comes next at
all.  Just Do It.  Spit out the double-bar line, break the line,
and continue.  I can't say whether that's programmaticly feasible
in Lilypond's internals, but I think the *intent* of the syntax
is pretty clear.

I just wanted to increment the tally on Johan's feature request.