banter-style from chord-names-jazz.ly broken, 'case'-problem

[Thomas Morley]

Hi.

I started to rewrite chord-namings and stumbled over a problem in
chord-generic-names.ly

/Documentation/included/chord-names-jazz.ly with uncommented
Banter-style is broken.
At least since 2.12.3

The problem is in 'step->markup-plusminus'

Here you see the old code commented and a possible patch inserted:

  (define (step->markup-plusminus pitch)
    (make-line-markup
     (list
      (make-simple-markup (number->string (step-nr pitch)))
      (make-simple-markup
       ;(case (step-alteration pitch)
       ;  ((DOUBLE-FLAT) "--")
       ;  ((FLAT) "-")
       ;  ((NATURAL) "")
       ;  ((SHARP) "+")
       ;  ((DOUBLE-SHARP) "++"))
       (case (step-alteration pitch)
         ((-1) "--")
         ((-1/2) "-")
         ((0) "")
         ((1/2) "+")
         ((1) "++"))
       ))))

case uses eqv? to compare. (guile-manual)
(step-alteration pitch) returns: -1 or -1/2 or 0 or 1/2 or 1
(display (eqv? -1/2 FLAT), etc returns #t

Thus I've no clue why the old code fails.
Any hint?

Cheers,
  Harm