Re: Getting context-definiton, while being in applyContext

[David Kastrup]

Thomas Morley <address@hidden> writes:

> Am So., 18. Nov. 2018 um 19:19 Uhr schrieb David Kastrup <address@hidden>:
>>
>> Thomas Morley <address@hidden> writes:
>>
>> > Hi,
>> >
>> > consider the code below. I'd like to restrict usage to Staff-like
>> > contexts, i.e. Staff, Tab- and DrumStaff, etc would be ok, but
>> > container-contexts like StaffGroup, etc should lead to return '().
>> >
>> > Pseudo-code:
>> >
>> > \new Staff(Group)
>> >   \with {
>> >     \applyContext
>> >      #(lambda (context)
>> >        (if <condition>
>> >            ;; Do something, if we are in a Staff-like context
>> >            ;;   Multiple Bottom-contexts may happen
>> >            (lambda (x) ...)
>> >            ;; Do nothing if we are are in container-contexts like 
>> > ChoirStaff,
>> >            ;; StaffGroup, etc
>> >            '()
>> >        )
>> >   }
>> > { c''1 }
>> >
>> > I thought the <condition> could be "Do I have the Staff_symbol_engraver?"
>> > Though, how to code?
>> >     \applyContext
>> >      #(lambda (context)
>> >        (ly:context-def-lookup context 'consists))
>> > does not work, because 'context' is not a context-definition.
>> >
>> > Any hint how to proceed would be great.
>>
>> Why don't you check whether they have a Staff alias?  Basically if
>> looking up 'Staff returns the context itself.
>
> You mean like below?
>
> foo =
>   \applyContext
>     #(lambda (ctx)
>        (let* ((ctx-name (ly:context-name ctx))
>               (staff-ctx-def (ly:output-find-context-def $defaultlayout 
> 'Staff))
>               (staff-like? (assoc-get ctx-name staff-ctx-def #f)))
>
>        (if staff-like?
>            (format #t "\n\tI'm in a staff-like context: ~a" ctx-name)
>            (format #t "\n\tWrong here in: ~a" ctx-name))))
>
> \score {
>   <<
>     \new StaffGroup R1
>     \new Staff R1
>     \new TabStaff R1
>     \new DrumStaff R1
>     \new ChoirStaff R1
>   >>
>   \layout {
>       \context Staff \foo
>     \context {
>       \StaffGroup
>       \foo
>     }
>     \context {
>       \ChoirStaff
>       \foo
>     }
>   }
> }

No.  Don't refer to the definition at all.  Just do

(eq? ctx (ly:context-find ctx 'Staff))

-- 
David Kastrup