Beam setting surprises because of processing order

[Mats Bengtsson]

Hi,

Consider the following three examples. Would you expect them to produce 
the same result or different and in that case, which are the same?

\version "2.13.49"
% First test:
\score{
\relative c' <<
\new Staff {
  \time 2/2
  \set Timing.baseMoment = #(ly:make-moment 1 4)
  c8 d e f g f e d
  }
\new Staff {
  \time 2/2
  c8 d e f g f e d
  }
>>
}
% Second test:
\score{
\relative c' <<
\new Staff {
  \time 2/2
  c8 d e f g f e d
  }
\new Staff {
  \time 2/2
  \set Timing.baseMoment = #(ly:make-moment 1 4)
  c8 d e f g f e d
  }
>>
}
% Third test:
\score{
\relative c' <<
\new Staff {
  \time 2/2
  \set Timing.baseMoment = #(ly:make-moment 1 4)
  c8 d e f g f e d
  }
\new Staff {
  \time 2/2
  \set Timing.baseMoment = #(ly:make-moment 1 4)
  c8 d e f g f e d
  }
>>
}


Trying it in LilyPond, it turns out that the processing order plays a 
trick here. In the first test, the baseMoment setting is done after the 
\time command, so it should be effective, however it turns out that the 
setting is processed before the \time command in the second stave. So, 
the only safe thing is to do all beam related settings in every single 
stave of the score in order to be sure that a \time command in other 
staves doesn't overwrite the settings.
You could argue that it's sufficient to have the \time command in a 
single stave, but since the time signature is typeset in every stave, 
it's very likely that a LilyPond user includes it in all the staves. On 
the other hand, you don't really want to repeat all beam related 
settings all over the place.

Am I the first one to run into this problem? I couldn't find it 
mentioned in the mailing list archives.
Adding a sentence like:
"Note that these settings have to be made in all staves of the score, to 
avoid the risk that the setting is overridden by a \time command in 
another stave."
Hmm, at second thought, this is probably gibberish to most readers. If 
you can find a better formulation, please use that instead.

     /Mats

--
=============================================
        Mats Bengtsson
        Signal Processing
        School of Electrical Engineering
        Royal Institute of Technology (KTH)
        SE-100 44  STOCKHOLM
        Sweden
        Phone: (+46) 8 790 8463                         
        Fax:   (+46) 8 790 7260
        Email: address@hidden
        WWW: http://www.s3.kth.se/~mabe
=============================================