Re: Guile library function availability

[Jean Abou Samra]

Le 24/05/2021 à 19:21, Lukas-Fabian Moser a écrit :
> Hi,
>
> during my experiments with TextSpanners I stumbled upon the following:
>
> \version "2.22"
>
> \layout {
>   \override NoteHead.after-line-breaking =
>   #(lambda (grob) (pretty-print "I explode."))
> }
>
> {
>   a4
> }
>
> explodes because pretty-print isn't available (the same happens for 
> functions like "last" etc.)
>
> In contrast, the following works:
>
> \version "2.22"
>
> {
>   \override NoteHead.after-line-breaking =
>   #(lambda (grob) (pretty-print "I work just fine."))
>
>   a4
> }
>
> What's the reason for the different availability of scheme library 
> functions between working in \layout {} vs. in music?

I never understood the whole thing fully (and it is at the heart of the 
problem that led to disabling LilyPond on WikiMedia), but output 
definitions have their own scope, which is implemented as a Guile 
module. pretty-print is defined by another Guile module, (ice-9 
pretty-print), which is generally available in LilyPond code because it 
is loaded upon initialization of LilyPond (see init.ly). last is in 
(srfi srfi-1), which is also loaded by default.

If you want these functions in a \layout, you have to load the 
corresponding module by hand:

\layout {
  #(use-modules (ice-9 pretty-print))
  \override NoteHead.after-line-breaking =
  #(lambda (grob) (pretty-print "I explode."))
}

{
  a4
}

Don't ask me why this works then:

#(define myVar 5)

\layout {
  #(display myVar)
}

It would seem that assignments work a bit differently from loading 
modules, but I'm not looking at the code right now.

Hope that helps,
Jean