[Denemo-devel] Scheme question

[Andreas Schneider]

Trying to write an input filter for my master keyboard, I use the angry
delete as template and, as a first step, want to display the incoming
midi events. This is what I have:

;;; Master keyboard filter
(let ((midi 0)
      (command 0)
      (bank 0)
      (note 0)
      (velocity 0)
      (loop 0))
     (d-InputFilterNames (_ "Master Keyboard MIDI Filter"))
     (d-SetMidiCapture #t)
     (set! loop  (lambda ()
                (begin          
                  (set! midi (d-GetMidi))
                  (set! velocity (bit-extract midi 16 24))
                  (set! command (bit-extract midi 0 4))
                  (set! bank (bit-extract midi 4 8))
                  (display "command " command ", bank " bank ", velocity " 
velocity)
                  (if (= command 0)
                      (display "Filter stopping")
                      (loop)))))
     (loop))
(d-SetMidiCapture #f)

It gives the error
(#f Wrong number of arguments to ~A (#<procedure display (_ #:optional
_)>) #f)
What do I do wrong?

Thanks

Andreas