Re: Help for \beamExceptions

[Richard Shann]

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. My first attempt was this:
8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><
beamExceptions_first =   \beamExceptions { \time 4/4  e'8 f'8[ a'8 b'8  a'8] 
f'8[ e'8 e'8] }
beamExceptions_second =  \beamExceptions { \time 6/8  e'8 f'8[ b'8  a'8] f'8[ 
e'8] }

\layout {
\set beamExceptions = #(append beamExceptions_first beamExceptions_second)
}
8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><8><

but using \displayScheme I see that this results in

(make-music
  'ContextSpeccedMusic
  'context-type
  'Bottom
  'element
  (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?

Richard