On 01/02/2023 01:23, Ahanu Banerjee wrote:
> Is it possible to have one of the arguments rely on a property of another
> argument?
>
> In my example, I want the default value for "parenColor" to be the same as
> the color of the "parenItem":
>
> \version "2.24"
> \language "english"
> altParen = #(define-music-function
> (parenColor parenSize parenItem)
> ( (color? "black") (number? -4) ly:music?)
> #{
> \tweak Parentheses.font-size #parenSize \tweak Parentheses.color
> #parenColor \parenthesize #parenItem
> #})
> { c \altParen -\tweak color "green" \upbow }Well, the color you want to access isn't a property of parentItem. parenItem is just a bit of music. Rather, it is a property of the grob that will eventually be caused by the music parentItem. So, in the music function, the color is not available. However, what you can do is writing a callback which runs waay later in the process, and can access it. Cf. https://extending-lilypond.readthedocs.io/en/latest/extending/backend.html#understanding-callbacks \version "2.24.0" \language "english" #(define (color-from-host grob) (ly:grob-property (ly:grob-object grob 'sticky-host) 'color)) altParen = #(define-music-function (parenColor parenSize parenItem) ( (color? color-from-host) (number? -4) ly:music?) #{ \tweak Parentheses.font-size #parenSize \tweak Parentheses.color #parenColor \parenthesize #parenItem #}) { c \altParen -\tweak color "green" \upbow } Actually, because this is a common pattern for grobs like parentheses which attach to another grob, there is a shortcut: \version "2.24.0" \language "english" altParen = #(define-music-function (parenColor parenSize parenItem) ( (color? (sticky-grob-interface::inherit-property 'color)) (number? -4) ly:music?) #{ \tweak Parentheses.font-size #parenSize \tweak Parentheses.color #parenColor \parenthesize #parenItem #}) { c \altParen -\tweak color "green" \upbow } Jean
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