Re: equivalent to \once within scheme?

[Alexander Kobel]

On 2010-09-15 10:09, Marc Hohl wrote:
> Hello all,
>
> IIUC, \override grob #'foo = #bar
> is more or less the same as
> (ly:grob-set-property! grob foo bar)
>
> Is there a scheme equivalent for
> \once \override Grob #'foo = #bar ?

Hi, Marc,

if _I_ understand correctly, the (ly:grob-set-property! grob ...) is 
_exactly_ the \once \override ..., since it applies to the specific 
instance of a grob you give as an parameter.  It just depends where you 
call it - which is usually inside some callback set by \override Grob 
#'after-line-breaking or such.  Thus, the (ly:grob-set-property grob 
...) is called for every grob of type Grob.
But if you, say, construct grobs in scheme, and run the function only 
for one of the resulting grobs, or apply it only the second instance of 
a broken spanner (which is divided into two grobs (or even more for a 
three-system-long VoltaBracket, e.g.?) it behaves exactly like a \once 
\override.


HTH,
Alexander