Re: Guile library function availability

[Lukas-Fabian Moser]

Hi Jean,

> 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
> }

Thanks much for the explanation and the pointers to workarounds!

That's the kind of pitfall that lets you start doubting your sanity: You 
create and test a scheme \override, and when it finally works, you copy 
it into a general-purpose definition of a new context ... and it stops 
working (with the strange error message that "last" is an unknown 
variable). :-)

At least now I understand why I sometimes see (car (last-pair 
some-list)) in examples where I'd usually expect (last some-list).

Lukas