Re: displayLilyMusic and scheme-engraver

[Jan-Peter Voigt]

Hi David,

Am 05.02.2017 um 16:19 schrieb David Kastrup:
> David Kastrup <address@hidden> writes:
>
> > Jan-Peter Voigt <address@hidden> writes:
> >
> > > Hi folks,
> > >
> > > I just stumbled over a bug with \displayLilyMusic and
> > > scheme-engravers. The following fails in recent devel:
> > >
> > > %%%
> > >
> > > \version "2.19.55"
> > >
> > > \displayLilyMusic \new Staff \with {
> > >   \consists #(lambda (context)
> > >                (make-engraver))
> > > } \relative { bes'4 a c b }
> > >
> > > %%%
> > >
> > > ERROR: In procedure symbol->string:
> > > ERROR: Wrong type argument in position 1 (expecting symbol):
> > > #<procedure #f (context)>
> > >
> > > %%%
> > >
> > > Until 2.19.53 or 54 this didn't crash, but the output was not a
> > > serialization of the context-mod (\with), so I assume, someone is
> > > working on it :-)
> > >
> > > I will have a look into the internals after lunch.
> >
> > I think you are understating the problem.  \displayLilyMusic has nothing
> > to do with it.
yes, I do :-)
> > This is a "how did this ever pass testing" kind of case [checking the
> > regtests].
> >
> > The regtests don't use \with at all but only layout redefinitions.
> >
> > This is a showstopper in case anybody was thinking of rolling a
> > developer release right now.
>
> Ok, no it isn't a showstopper.  The problem here is that (make-engraver)
> returns an empty list, and an empty list is not accepted right now as an
> engraver.  The moment you actually have anything that deserves the name
> "engraver", it works.
>
> Arguably, this wants fixing but it is sort of a "meh" example.

Thank you very much!
So I have empty engravers creeping around ... that is easy to fix!

Best
Jan-Peter