\parenthesize and optional arguments

[Marc Hohl]

Hi list,

my scheme-fu is a bit rusty, so I tried to get a new start
by enhancing the parenthesize function defined in
ly/music-functions-init.ly with the code to be found in

http://lsr.di.unimi.it/LSR/Snippet?id=902

Here is what I have so far:

\version "2.19.20"

parenthesize =
#(define-music-function (dir arg) ((number? 0) ly:music?)
   (_i "Tag @var{arg} to be parenthesized. @arg{dir} is optional and may be
   set to @code{#LEFT} or @code{#RIGHT} for left/right parentheses only.")

   (display dir)
   (case dir
         ((-1) #{ \once\override ParenthesesItem.stencils = #(lambda (grob)
                                   (let ((par-list 
(parentheses-item::calc-parenthesis-stencils grob)))
                                        (list (car par-list) 
point-stencil ))) #})
         ((1) #{ \once \override ParenthesesItem.stencils = #(lambda (grob)
                                   (let ((par-list 
(parentheses-item::calc-parenthesis-stencils grob)))
                                        (list point-stencil (cadr 
par-list)))) #}) )

   (if (memq 'event-chord (ly:music-property arg 'types))
       ;; arg is an EventChord -> set the parenthesize property
       ;; on all child notes and rests
       (for-each
        (lambda (ev)
          (if (or (memq 'note-event (ly:music-property ev 'types))
                  (memq 'rest-event (ly:music-property ev 'types)))
              (set! (ly:music-property ev 'parenthesize) #t)))
        (ly:music-property arg 'elements))
       ;; No chord, simply set property for this expression:
       (set! (ly:music-property arg 'parenthesize) #t))

   arg)

{ \parenthesize c \parenthesize #LEFT d \parenthesize #RIGHT e}


It seems as if the \override does not have any effect, though,
but I don't understand why.

Any pointers in the right direction are highly appreciated!

Thanks,

Marc