Re: Changing the car or cdr of a pair

[Malte Meyn]

Am 25.12.2017 um 17:48 schrieb Menu Jacques:
> The edge-height pair can be given a value with:
>
>         \once \override Staff.LigatureBracket.edge-height = #'(0 . +0.7)
>
> but how can I change only one of the members of the pair, leaving the other one 
> as it is?

There are two options: Either use the \offset command (if you want to 
add a number to one of the members) or \override before-line-breaking 
(if you want to replace one of the members without depending on the 
original value). Both options can be seen in the following code (have a 
close look to the exact output for difference).

\version "2.19.80"

{
  % this takes the original values and adds 0 to left and 3 to right
  \once \offset edge-height #'(0 . 3) LigatureBracket
  \[ c'1 d' \]

  % this takes the originale value for left and sets 3 (not 3+original) 
for right
  \once \override LigatureBracket.before-line-breaking =
  #(lambda (grob)
     (let* ((orig-height (ly:grob-property grob 'edge-height))
            (orig-left (car orig-height)))
       (ly:grob-set-property! grob 'edge-height (cons orig-left 3))))
  \[ c'1 d' \]
}