Re: [PATCH]: Allow context modifications to be stored in a variable and inserted into \context or \with

[Mats Bengtsson]

Reinhold Kainhofer wrote:
> Our problems with \RemoveEmptyStaffContext resetting previous context 
> modifications highlights one problem we have: So far, it was not possible to 
> store a bunch of context modifications into a variable and apply them later 
> on. 
>   
Right!
> Another incarnation of this problem is that it is not possible to collect some 
> modifications and use them in a \with block. So far, the contents of the \with 
> block had to be explicitly written out. I had the problem that in a full score 
> I needed several staves to be smaller (since they are optional), but I 
> couldn't use a global definition of the settings (defining my own Staff-
> derived context was also not possible, because in the instrumental part, I 
> need a normal Staff, so all \override Staff.... would break in one or the 
> other case).
>   
No, that's not a problem, as long as you include a
\alias "Staff"
line in the definition of your new context.
> So, here is a patch against current origin/master:
>     http://codereview.appspot.com/475041
>
> It modifies the parser so that context mods can be stored in variables and can 
> be inserted into \with or \context blocks:
>
> -) context modifications lists are stored in a dedicated simple scheme object
>      (C++ class Context_mod)
> -) Changes to the parser:
>   -) context_modifications objects (stored in variables) are now also allowed
>      with \with clauses
>   -) context_modifications objects are also allowed inside \context
>
> -) this allows us to rewrite \RemoveEmptyStaffContext (unfortunately with
>    a little different syntax, since we no longer store \Staff inside the
>    new \RemoveEmptyStaves command) so that it no longer erases previous
>    settings to the Staff context. Now, instead of
>              \context { \RemoveEmptyStaffContext }
>    one can do
>              \context { \Staff \RemoveEmptyStaves }
>    with the same effect and preserve previous changes to the Staff
>    context. (The same applies of course to \DrumStaff, \RhythmicStaff,
>    etc. as well)
>
> -) Adjusted engraver-init.ly and the regtests accordingly; Also added regtest
>    that checks for RESC not discarding previous settings to the Staff context
>   
Without looking at the actual patch, it looks like a very good thing.
The next step would be to somehow also be able to handle music functions 
and/or Scheme functions in \with and \context blocks, so that you could 
do a setting like
\overrideBeamSettings ...
or
#(set-accidental-style ...)
in such a block, so you can better separate layout settings from the 
actual music.
Of course, such a change is probably much more difficult than your 
current patch.

  /Mats