Re: [bounty] context generating function - how to get context def from its name?

[Janek Warchoł]

Hi David & all,

2014-07-25 21:34 GMT+02:00 David Kastrup <address@hidden>:
>
> Janek Warchoł <address@hidden> writes:
>> 2) i didn't manage to get midi stuff done inside the same function as
>> the layout stuff - but i think that i'll be able to solve that if i
>> have a solution to 1).
>
> You basically need to collect just the context definitions and apply
> those (a context definition is applied by looking up its \name and
> overwriting the variable with that name).
>
> Frankly, I am tempted to create something like
> #{
>    \output {
>      \context ...
>      xxx = 3\cm
>    }
> #}
>
> that will either execute a number of assignments or alternatively return
> an anonymous lambda or define-void-function doing the same so that you
> can easily splice it into different output definitions.
>
> Something like that would apparently serve a need.

Ok, i reread what you wrote and now i understand that this is indeed
what i need :)  So if you could write a function like this, i would be
very grateful (and i would happily increase your bounty!).  My own
(_very_ naive) attempt at removing code duplication failed:

\version "2.19.10"

% Create a new xxxStaff and xxxVoice contexts with specified settings,
% derived from specified yyyStaff and yyyVoice contexts.
newInstrument =
#(define-scheme-function
  (parser location name parent-name group-name staff-settings voice-settings)
  (string? string? string? ly:context-mod? ly:context-mod?)
  (let* ((staff-name (string-append name "Staff"))
         (voice-name (string-append name "Voice"))
         (parent-name (if (string=? parent-name "default") "" parent-name))
         (parent-staff-name (string-append parent-name "Staff"))
         (parent-voice-name (string-append parent-name "Voice"))
         (common
          #{
            \context {
              $(module-ref (current-module) (string->symbol group-name))
              \accepts #staff-name
            }
            \context {
              $(module-ref (current-module) (string->symbol parent-staff-name))
              \name #staff-name
              \alias #parent-staff-name
              % is it possible to make it accept Voices of derived instruments?
              \accepts #voice-name
              \defaultchild #voice-name

              #staff-settings
            }
            \context {
              $(module-ref (current-module) (string->symbol parent-voice-name))
              \name #voice-name
              \alias #parent-voice-name

              #voice-settings
            }
          #}))
    (ly:parser-define! parser '$defaultlayout
      #{ \layout #common #})
    (ly:parser-define! parser '$defaultmidi
      #{ \midi #common #})))

thanks again for your help!
Janek