\version "2.11.43" 
\header { title="Redefining parenthesize for rests, single notes, chords" }

parenthesize =
#(define-music-function (parser loc arg) (ly:music?)
   (_i "Tag @var{arg} to be parenthesized.")
   (if (memq 'event-chord (ly:music-property arg 'types)) 
     ; arg is an EventChord -> set the parenthesize property on all child notes and rests
     (map 
       (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)


\relative c'' {
  % parentheses on single notes (with articulations), inside chord and articulation
  \parenthesize c \parenthesize c-. <\parenthesize c> c-\parenthesize-. |
  % parenthesized rests and whole chords
  \parenthesize <c e g>4-> \parenthesize r \parenthesize r2^"rest" |
  % parenthesizing other music expressions does nothing
  \parenthesize {c4 c-. <c e g> r} 
}