Re: How to return markup conditionally?

[Valentin Petzel]

Hello Trevor,

instead of trying to use a callback on bound-details.left.text you can use the 
before-line-breaking and after-line-breaking hooks to modifiy this property:

%%% BEGIN %%%

\version "2.24"

% no left text set
{
  \once \override TextSpanner.before-line-breaking =
    #(lambda (grob)
       (let* ((bound-details (ly:grob-property grob 'bound-details))
              (left (assoc-get 'left bound-details))
              (left (assoc-set!
                     left
                     'text
                     (if (equal? red (ly:grob-property grob 'color))
                         (markup "foo")
                         (markup "bar"))))
              (bound-details (assoc-set! bound-details 'left left)))
         (ly:grob-set-property! grob 'bound-details bound-details)))
  c'1
  - \tweak color #red
  \startTextSpan
  c'1
  \stopTextSpan
}

%%% END %%%

In your case you want to use after-line-breaking, as you want to work with the 
broken copies.

Then basically what you want to do is:

 - If you want to handle the case of an unbroken spanner differently, use 
(unbroken-spanner? grob) to check if the spanner is not broken
 - Use (unbroken-or-last-broken-spanner? grob) to determine if the grob is the 
last broken sibling.
 - Decide whether your endpoint condition applies (e.g. from (ly:grob-property 
grob 'right-bound-info))
 - If so set bound-info.right.text to bound-info.right.right-broken

Cheers,
Valentin

> 
> The problem I'm wanting to solve has to do with swapping a text spanner's
> right text for its right-broken text, conditionally based on the spanner's
> end position. The problem looks complicated, so I'll introduce it as a
> separate thread.
> 
> Trevor.

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