Re: pageBreak outside a score?

[Valentin Petzel]

Hello Eric,

that is understandable. For some context:

when you put \pageBreak at toplevel (or bookpart level) it is first just a 
music stream made up of a single event. Now, when Lilypond encounters toplevel 
music objects it usually defaults to truning it into a score, using the scheme 
procedure (scorify-music music). But there is some additional logic, which is 
done by the scheme procedure (collect-music-aux score-handler music) (where 
score-handler is a function that handles the created score). This procedure 
has a special path for single event music of type page-marker (which something 
like \pageBreak falls under as can be seen in \displayMusic \pageBreak).

Basically instead of a score it creates a Page_marker object, which you can 
see if you do

{ c }
\pageBreak
{ c }
#(display toplevel-scores)

Now, of course in markup this does not work, as first a markup will not take 
music, and very importantly markup will not include any page layout events of 
any sort. It would be possible to do something like

(collect-music-aux add-score #{ \pageBreak #})

in a markup, scheme or void function, but this would cause some trouble in 
when exactly this is evaluated. Usually we’d expect something like this to to 
be placed positionally where the markup is. Let’s say we use a scheme 
function:

pagebreak =
#(define-void-function () ()
   (collect-music-aux add-score #{ \pageBreak #}))

This is evaluated at the time the expression is parsed (more or less). So 
doing

\markup "a"
\markup "b"
\markup{ \pagebreak }
\markup "c"

will behave as intended, but

\markup "a"
test = \markup { \pagebreak }
\markup "b"
\test
\markup "c"

will not. If we use a markup function like this

#(define-markup-command (pagebreak layout props) ()
   (collect-music-aux add-score #{ \pageBreak #})
   empty-stencil)

the command is only evaluated when interpreting that markup, at which point 
all scores have been added (so we do not get any effect):

\markup "a"
\markup "b"
\markup { \pagebreak }
\markup "c"

So you see there is currently no real way of any kind for getting page layout 
commands into a markup. Of course this can be limiting if you want to do 
complex formatting of markups and markuplists, but Lilypond is a music 
engraving software, not a typesetting or text layouting software. Lilypond’s 
handling of text is quite primitive, as this is not the main focus of 
development.

Cheers,
Valentin

Am Freitag, 5. Mai 2023, 01:34:56 CEST schrieb Eric Benson:
> Well then, sorry for bothering you all! I don't know how I confused myself
> so badly, but I'm just glad to be out of that hole! I think I tried to put
> the \pageBreak inside the \markup, which definitely does not work.
> 
> On Thu, May 4, 2023 at 4:24 PM Kieren MacMillan
> <kieren@kierenmacmillan.info>
> wrote:
> > Hi Eric,
> > 
> > > Oh! I think this is new behavior.
> > 
> > I don’t think so…?
> > I’ve been using this for many years.  :)
> > 
> > Cheers,
> > Kieren.
> > ______________________________________________
> > 
> > My work day may look different than your work day. Please do not feel
> > obligated to read or respond to this email outside of your normal working
> > hours.

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