Several thoughts for implementing accordion standard bass support

[David Kastrup]

Hi,

I am currently wrestling with accordion standard bass support.
Basically, there are single bass buttons and chord buttons, and in the
simplest mode, single basses are written in the -2 octave, and chord
notes are wrapped/inversed to the -1 octave.

When writing stuff, single basses are written with upper case letters,
chords with lower case letters.

Buttons may be combined.

So a typical pattern may look like

StdbassEngraver = #`((listeners
                       (note-event .
                        ,(lambda (engraver event)
                          (let* ((pitch (ly:event-property event 'pitch)))
                           (ly:event-set-property! event 'pitch
                            (ly:make-pitch
                             (if (> (ly:pitch-octave pitch) -1) -1 -2)
                             (ly:pitch-notename pitch)
                             (ly:pitch-alteration pitch))))))))
\layout {
  \context {
    \Voice
    \consists \StdbassEngraver
}}

{ \clef "bass"
 \chordmode { c,4:1 c g,:1 c b,:1 g:7^5 g,:1 g:7^5 c,1*0:1 c1 }
}

Now I don't like the input syntax: being able to overlay stuff just with
*0 is a crutch, things like c/c, just don't work (apparently, octave
indicators for the bass note are not really heeded sensibly).

In addition, things like holding a bass button while changing chord
buttons need additional voices, and chordmode does not permit them.

So one thing I would like would be << ... >> support in chord mode.  Are
there technical necessities for not permitting this?

What about octave indicators?  Shouldn't c/c, be <c c' e' g'> rather
than <c e' g'>?  Why doesn't even c:5.1/c have a 1 in the chord?

Hints, comments?

-- 
David Kastrup