Re: displayLilyMusic and scheme-engraver

[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.
>
> 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.

How do people even think of those things?

-- 
David Kastrup