Re: Autochange with Staves named other than "up" and "down"

[Aaron Hill]

On 2020-12-19 3:14 pm, Pine, Zachary V wrote:
> Hello Community,
>
> I'm writing a piano piece across three staves. Sometimes I would like
> to use autochange to engrave material on the top two staves, other
> times across the bottom two. I know autochange works by default on
> staves named "up" and "down".
>
> Is there any way to override the names of the staves autochange looks
> for? Perhaps there is another solution I'm not seeing other than
> manually inputting \change Staff everytime.

Here is one approach, although I cannot be certain it covers all edge 
cases:

%%%%
\version "2.20.0"

#(define (symbol-pair? arg)
  (and (pair? arg) (symbol? (car arg)) (symbol? (cdr arg))))
#(define (symbol-pair-list? arg)
  (and (list? arg) (every symbol-pair? arg)))

replaceContextChanges =
#(define-music-function
  (replacements music)
  (symbol-pair-list? ly:music?)
  (define (proc music)
   (if (music-is-of-type? music 'context-specification)
    (ly:music-set-property! music 'context-id
     (let* ((id (ly:music-property music 'context-id))
            (sym (string->symbol id)))
      (if (eq? "" id) id ; Sometimes context-id is an empty string.
       (symbol->string (ly:assoc-get sym replacements sym))))))
   (if (music-is-of-type? music 'auto-change-instruction)
    (ly:music-set-property! music 'context-change-list
     (map (lambda (p) (let ((mom (car p)) (sym (cdr p)))
           (cons mom (ly:assoc-get sym replacements sym))))
      (ly:music-property music 'context-change-list))))
   music)
  #{ \musicMap #proc #music #})

<< \new Staff = upper { \clef treble s1*3 }
   \new Staff = middle { \clef alto s1*3 }
   \new Staff = lower { \clef bass
    \replaceContextChanges #'((down . lower) (up . middle))
    \autochange { a4 b d' e' }
    \replaceContextChanges #'((down . middle) (up . upper))
    \autochange { a4 b d' e' }
    \replaceContextChanges #'((down . upper) (up . lower))
    \autochange { a4 b d' e' }
   } >>
%%%%


-- Aaron Hill

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