Re: "smart" transposition of key signatures

[Kieren MacMillan]

Hi David,

One small improvement could [possibly?] be made: allowing for the extraction of 
the keys into a variable separate from the notes.
As you can see in the attached snippet, that doesn't work as expected.

*THAT* solution will definitely be worth both a snippet and some euros.

Thanks again,
Kieren.
_________________________

smartkey =
#(define-music-function (parser location pitch scale music)
  (ly:pitch? list? ly:music?)
  (let ((key #{ \key $pitch #scale #}))
    (make-music 'SequentialMusic
                 'elements (list key music)
                 'elements-callback
                 (lambda (m)
                   (let* ((elts (ly:music-property m 'elements))
                          (key (car elts))
                          (sh (fold (lambda (elt total) (+ (cdr elt) total))
                                    0
                                    (ly:music-property key 'pitch-alist))))
                     (cond ((< sh -3)
                            (map (lambda (m)
                                   (ly:music-transpose m #{ bis #}))
                                 elts))
                           ((> sh 3)
                            (map (lambda (m)
                                   (ly:music-transpose m #{ deses' #}))
                                 elts))
                           (else elts)))))))

global = {
  \key c \minor s1
  \key cis \major s1
  \key es \minor s1
}

smartglobal = {
  \smartkey c \minor s1
  \smartkey cis \major s1
  \smartkey es \minor s1
}

notes = \relative c' {
  c4 es g <c, es g>
  cis eis gis <cis, eis gis>
  es ges bes <es, ges bes>
}

music = << \global \notes >>
smartmusic = << \smartglobal \notes >>

<<
 \new Staff \music
 \new Staff \transpose c g \music
 \new Staff \transpose c es \music
 \new Staff \transpose c fis \music
>>

<<
 \new Staff \smartmusic
 \new Staff \transpose c g \smartmusic
 \new Staff \transpose c es \smartmusic
 \new Staff \transpose c fis \smartmusic
>>