predicate pitch-or-music? - getting rid of ##{ #} ?

[Thomas Morley]

Hi,

I tried to create a function which should accept a pitch _or_ music.
So I defined a pitch-or-music? predicate:

#(define (pitch-or-music? x)
  (or (ly:pitch? x) (ly:music? x)))

Calling the function, I have to use ##{ ... #} for music _and_ for a
single pitch.
Calling the function for a single pitch doesn't work, if ##{ #} are
omitted, but it'll work if the predicate would be ly:pitch?
I don't understand this behaviour.

To demonstrate it, I created the following simplified function:

\version "2.16.0"

#(define (pitch-or-music? x)
  (or (ly:pitch? x) (ly:music? x)))

dummyFunction =
#(define-music-function (parser location pitch-or-music color mus)
          (pitch-or-music? list? ly:music?)
          ;; (ly:pitch? list? ly:music?)
(newline)(display "pitch? ")(write (ly:pitch? pitch-or-music))
(newline)(display "music? ")(write (ly:music? Pitch-or-music))

;; some dummy-commands:
(if (ly:pitch? pitch-or-music)
   #{
           \override NoteHead #'color = $(car color)
           $mus
   #}
   #{
           \override NoteHead #'color = $(cadr color)
           $mus
   #}))

\relative c' {
        \dummyFunction
        c                 % works only, if the predicate is ly:pitch?
        %##{ c #}  % works
        %##{ c d e #}  % works
        #`(,red ,green)
        c1
}


Is there any possibility to get rid of ##{ #}, when calling the
function with a single pitch, but to keep the possibility to call it
with some music?



Regards,
  Harm