Re: Help for \beamExceptions

[David Kastrup]

Richard Shann <address@hidden> writes:

> On Wed, 2015-09-02 at 20:13 +0200, David Kastrup wrote:
>> 
>> > And there is a comment somewhere about using | to separate
>> something,
>> > I guess bars with the same \time signature (or, indeed different
>> > ones).
>> 
>> No, it's always for exactly one time signature, but at the time it is
>> called, LilyPond has no idea just how long a bar is and can't count it
>> off itself.  So you need to separate rule patterns by |. 
>
> Ah, in that case I need a way of building up the list of beamExceptions,
> so the user can define beaming rules for all the time signature changes
> they use in the score.

There are separate commands for defining time-signature-specific
exceptions rather than the currently active exception list.

>   (make-music
>     'PropertySet
>     'value
>     (list (list (quote end) (list 1/8 5 3))
>           (list (quote end) (list 1/8 4 2)))
>     'symbol
>     'beamExceptions))
>
> Which I guess means that this is not creating a beaming rule specific to
> those time signatures - can I augment the alist returned by
> \beamExceptions to make it into a rule specific to the time signature
> concerned? I guess I would know the answer to this if I could find out
> what the alist holds initially, but my feeble attempt to elicit this via
> \void \displayScheme #beamExceptions
> gave me
>
> #<Music function #<procedure #f (music)>>
>
> which is the "music" function rather than the alist - how come these two
> things appear to have the same name?

Convenience.  Just so that you don't need to remember two names.  As a
context property, 'beamExceptions is just a symbol.  You could probably
use something like

\applyContext #(lambda (c) (write
                             (ly:context-property c 'beamExceptions)))

to dump the current beamExceptions at any place in the score.

-- 
David Kastrup