Re: "smart" transposition of key signatures

[Kieren MacMillan]

Hi David,

You are worth your weight in gold, to me personally and to the whole Lilypond 
community.  =)

For everyone to see how great this is, I've modified your snippet slightly:
1. I've added \relative notes.
2. I've added a NON-SMART version of your SMART score.

> You owe me a snippet submission or its monetary equivalent.

ABSOLUTELY — the snippet for sure, and possibly some money as well.

I truly believe this needs to be in the regular distro.
I will work on a patch (with the slightly better function name \smartkey, 
unless someone else has an even better suggestion).

Many thanks,
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)))))))

music =
\relative c' {
\key c \minor { c es g <c, es g> }
\key cis \major { cis eis gis <cis, eis gis> }
\key es \minor { es ges bes <es, ges bes> }
}

smartmusic =
\relative c' {
\smartkey c\minor { c es g <c, es g> }
\smartkey cis\major { cis eis gis <cis, eis gis> }
\smartkey es\minor { es ges bes <es, ges bes> }
}

<<
 \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
>>