music function cannot have four arguments

[Graham Percival]

2.9.18; the below music function works fine with three variables, but 
adding "four" produces the output below.  I'm guessing this is a parser 
issue?


----
beamingThree = #(define-music-function
  (parser location one two three four)
  (string? string? string? string?)
#{
  \mark \markup {
    \tiny {
    \override #'(baseline-skip . 1)
    \override #'(word-space . 0.4)
    \override #'(font-family . number)
    \line {
      \column { $one "8" } \lower #0.5 "+"
      \column { $two "8" } \lower #0.5 "+"
      \column { $three "8" }
  } } }
#})
{
  c1
  \beamingThree #"3" #"3" #"2" #"4"
  c1
}
----


programming error: can't find signature for music function
continuing, cross fingers
Backtrace:
In unknown file:
   ?:  0* [lilypond-main ("bug.ly")]
   ?:  1* (letrec ((no-files-handler #)) (if (ly:get-option #) 
(gui-main files)) ...)
In 
/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:
 399:  2  (let* ((failed #)) (if (pair? failed) (begin # #) (begin # #)))
 399:  3* [lilypond-all ("bug.ly")]
 425:  4  (let* ((failed #) (handler #)) (for-each (lambda # # # ...) 
files) failed)
 429:  5* [for-each #<procedure #f (x)> ("bug.ly")]
In unknown file:
   ?:  6* [#<procedure #f (x)> "bug.ly"]
In 
/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:
 431:  7* [lilypond-file #<procedure #f (key failed-file)> "bug.ly"]
 440:  8  [catch ly-file-failed #<procedure #f {()}> #<procedure #f (x 
. args)>]
In unknown file:
   ?:  9* [#<procedure #f {()}>]
In 
/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:
 441: 10* [ly:parse-file "bug.ly"]
In unknown file:
   ?: 11* [type-check-list # # #]
   ?: 12* (letrec ((recursion-helper #)) (recursion-helper signature 
arguments 1))
In 
/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:
 205: 13  [recursion-helper # # 1]
    ...
 202: 14  (and (helper # # count) (recursion-helper # # #))
 202: 15* [helper #<primitive-procedure string?> ...
 202: 16* [car {()}]

/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:202:38: 
In procedure car in expression (car arguments):
/Users/gperciva/Apps/LilyPond.app/Contents/Resources/bin/../share/lilypond/current/scm/lily.scm:202:38: 
Wrong type (expecting pair): ()