Re: Lilypond Substitution Function

[Jean Abou Samra]

Le 27/02/2021 à 02:16, Ken Ledeen a écrit :

> I am struggling to understand the restrictions on substitution functions.
>
> For example:
>
> 1) can a function include "\score { ...}"  or can it only be invoked 
> INSIDE a \score?
>
> 2) is it possible to include \header { ...}  inside a substitution 
> function?  It fails when I try, but I don't understand why.
>
> I assume I am missing some basic concepts regarding their use.
>
> Thanks!


Hello,

Music functions must return music objects; \score blocks are not music 
but general containers that enclose music as well as other objects such 
as \header and \layout blocks.

However, replacing define-music-function with define-scheme-function, 
you can define more versatile functions that are allowed to return any 
kind of object for interpretation. For example:

\version "2.23.1"

failingFunction =
#(define-music-function () ()
   #{
     \score {
       \header {
         piece = "Piece A"
       }
       { c' }
     }
   #})

% \failingFunction

succeedingFunction =
#(define-scheme-function () ()
   #{
     \score {
       \header {
         piece = "Piece B"
       }
       { c' }
     }
   #})

\succeedingFunction


Hope that helps,
Jean