Re: Override a StaffSymbol property outside \new Staff { ... } context

[Aaron Hill]

On 2020-01-15 6:41 pm, Paolo Prete wrote:
Sorry Aaron, I was not precise in my question.
I need to override a property of StaffSymbol, for every staff, outside 
any
music expression/block context. Probably I'm not using the right words 
even
now.
But what I need is a sort of a "global" variable which is set for any 
staff
without having to put it into some music expression (like \layout 
{\context
{...}} , or \new Staff \with { ... } etc.).
This is why I asked if is there a Scheme solution

To my knowledge, there is nothing more "global" than the top-level 
\layout.  (The same goes for \header, \paper, and \midi.)

If you are insistent on using Scheme, I believe the following is 
functionally equivalent:

%%%%
\version "2.19.83"

% LilyPond:
%   \layout { \context { \Staff \override StaffSymbol.color = #red } }
% Scheme:
#(ly:output-def-set-variable! $defaultlayout 'Staff
    (ly:context-def-modify
      (ly:output-def-lookup $defaultlayout 'Staff)
      #{ \with { \override StaffSymbol.color = #red } #}))

<< \new Staff { b'4 } \new Staff { b'4 } >>
%%%%

Note that I still use LilyPond syntax to define the context-mod (i.e. 
\with block), but even that could be completely done in Scheme:

%%%%
\version "2.19.83"

#(ly:output-def-set-variable! $defaultlayout 'Staff
    (ly:context-def-modify
      (ly:output-def-lookup $defaultlayout 'Staff)
      ; LilyPond:
      ;   #{ \with { \override StaffSymbol.color = #red } #}
      ; Scheme:
      (ly:make-context-mod
        `((assign StaffSymbol ,(ly:make-grob-properties
             `((color . ,red))))))))

<< \new Staff { b'4 } \new Staff { b'4 } >>
%%%%

However, why jump through such Scheme hoops when LilyPond syntax is more 
direct?


-- Aaron Hill