Coloring grobs and notational elements using a sophisticated music function

Some scholarly or ‘urtext’ editions use grey color to indicate editorial additions. I find this very elegant, so I wrote a function to easily use this in a score. Instead of writing \override [Context.]Grob.color = #grey …some music… \revert [Context.]Grob.color, it allows to simply write \ed [Context.]Grob [#color] { …some music } (or omit the {}, if it’s only for one note or rest). Note that in v2.18 there is a shortcoming here: a single rest or multi measure rest will need to be enclosed in braces. This doesn’t hold anymore with v2.19, at the least since 2.19.8.

The color may be optionally specified to use another than the default color (defined as editorsColor).

In order to conveniently address more complex notational elements (and to save typing with long grob names), the function also permits using shortcuts such as \ed Note { …some music } . Some are predefined, but others may be easily added.

\version "2.24.0"

%{
 With version 2.18.x, \ed Rest and \ed Mmr need the music
expression to be enclosed into {}. From 2.19.x on (tested for .8),
this is not required anymore.
%}

editorsColor = #grey
ed =
#(define-music-function (grob col mus)
   (symbol-list-or-symbol? (color? editorsColor) ly:music?)
   ;; for abbreviations, we need a symbol instead of a one-element list
   (let ((grob (if (= 1 (length grob)) (car grob) grob)))
     (case
      grob
      ;; define abbreviations
      ;; which call the function recursively with a value
      ;; leading into the (else) clause
      ;; (or to _another_ abbreviation)
      ;; be careful to avoid infinite recursion :-)
      ;; – abbreviation names must not be actual grob names
      ;; (at least if they’re used in the corresponding
      ;; clause) or recursion will be infinite also
      ;; It is recommended to use singular forms only
      ;; for abbreviations.
      ((Caut) #{ \ed Staff.AccidentalCautionary #})
      ((LedgerLine) #{ % barline is workaround to issue 3949
        \once\hide Staff.BarLine \bar "|"
        \stopStaff
        \ed Staff.LedgerLineSpanner {
          \startStaff
          $mus
          \stopStaff
        }
        \once\hide Staff.BarLine \bar "|"
        \startStaff #})
      ((Mmr) #{ \ed MultiMeasureRest $mus #})
      ((Note) #{ \ed Staff.Accidental
                 \ed Beam
                 \ed Dots
                 \ed Flag
                 \ed LedgerLine
                 \ed NoteHead
                 \ed Rest
                 \ed Stem $mus #})
      ((Pitch) #{ \ed NoteHead $mus #})
      ((Suggest) #{ \ed Staff.AccidentalSuggestion #})
      ((StemWithFlag) #{ \ed Stem \ed Flag $mus #})
      ((Tuplet) #{ \ed TupletNumber \ed TupletBracket $mus #})
      ;; ‘normal’ case
      (else
       #{
         \override $grob . color = #col
         $mus
         \revert $grob . color
       #}))))

%%%%%%%%%%%%%%%%%%%%%%%%%% EXAMPLE %%%%%%%%%%%%%%%%%%%%%%%%%%

\relative {
  \ed Note { c'8 d16. e32 fis g a16 r bes }
  \ed Script e,2\trill
  \ed Mmr { R1 } % brackets not required anymore in v.2.19.x
}