Using \startTextSpan and \stopTextSpan in separate music functions

[Abraham Lee]

All,

Going off the of the thread here: 

http://lists.gnu.org/archive/html/lilypond-user/2016-09/msg00374.html

and some personal email exchanges, I tried out a few things (found a working solution, though not ideal) and ran into something curious. I'd like to do something like the following, but it doesn't seem to work:

%%%%%%%%%

\version "2.19.36"

myStartTextSpan = #(define-music-function (mus) (ly:music?)

#{

  \once \override TextSpanner.bound-details.left.text = "rit."

  $mus \startTextSpan

#})

myStopTextSpan = #(define-music-function (mus) (ly:music?)

#{

  $mus \stopTextSpan

  <>^\markup \italic "a tempo"

#})

\relative c' {

  \myStartTextSpan b'1 

  c1

  \myStopTextSpan e,1 

  g1

}

%%%%%%%%%

This results in "unexpected EVENT_IDENTIFIER" errors at both

  $mus \startTextSpan

and

  $mus \stopTextSpan

When I put everything into a single _expression_ without using music functions, it works as expected:

%%%%%%%%%

\version "2.19.36"

\relative c' {

  \override TextSpanner.bound-details.left.text = "rit."

  b'1\startTextSpan 

  c1

  e,1\stopTextSpan

  <>^\markup \italic "a tempo"

  g1

}

%%%%%%%%%

This is just a simple example. The real use-case has numerous other \override statements that should occur prior to \startTextSpan, but the general idea is the same.

Anyone know what's going on here?

Best,

Abraham