Guile library function availability

[Lukas-Fabian Moser]

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?

Lukas