Apply event function *within* music-function

[Urs Liska]

Hi all,

I'm trying to apply event functions to music passed into a music function like that:

\version "2.19.57"

test =
#(define-music-function (mus)(ly:music?)
   #{
     #mus \startGroup
   #})

{
  \test c' d' e' f' \stopGroup
}

(of course this is not what I ultimately want to achieve, but the nucleus from which I'll be able to continue on my own).

This fails with "error: syntax error, unexpected EVENT_IDENTIFIER". I think it is because the #mus _expression_ is somehow already complete (differently from when used in regular input) and I have to somehow *apply* the \startGroup event function to the #mus argument.

From \displayMusic I can see that it is added as a NoteGroupingEvent to the note's articulations, but I'd like to ask if there's a more straightforward way to attach the event to the music than rebuilding the music _expression_ in Scheme.
OTOH I will want to do that for the first *and last* element in a music _expression_ (in order to apply the start and stop command to a sequence of notes), so I may *have* to extract the Scheme representation anyway?

TIA
Urs

-- 
address@hidden
https://openlilylib.org
http://lilypondblog.org