David Kastrup <[email protected]> writes:
> Paul Morris <[email protected]> writes:
>
>> This would really simplify the process of creating custom contexts,
>> especially in the common case of wanting a modified version of an
>> existing context that works everywhere it does.”
>>
>> See full discussion thread here:
>> http://lists.gnu.org/archive/html/lilypond-user/2015-02/msg00684.html
>
> The discussion does not lead to any workable conclusion. In its course,
> there is a proposal of an additional \alias-like command that would
> differ with regard to \alias in that it would declare acceptability.
> That's all very wishy-washy.
>
> I think it would make more sense to have a command that will walk
> through an output definition and make the required changes, like
>
> \accept-like Voice myVoice
> \layout {
> \context {
> \Voice
> \name "myVoice"
> ...
> }
> }
>
> That does not require new internals and is pretty straightforward to
> write as a scheme function taking two symbols and an output definition
> as arguments and returning an output definition.
Here is a proof of concept.
accept-like =
#(define-scheme-function (parser location old new out)
(symbol? symbol? ly:output-def?)
(for-each
(lambda (p)
(let* ((sym (car p))
(def (cdr p))
(acc (ly:context-def-lookup def 'accepts)))
(if (and (memq old acc) (not (memq new acc)))
(ly:output-def-set-variable! out sym
(ly:context-def-modify
def
(ly:make-context-mod
`((accepts ,new))))))))
(ly:output-find-context-def out))
out)
\accept-like Voice my-Voice
\layout {
\context {
\Voice
\name my-Voice
}
}
{
\new my-Voice { c1 }
}
--
David Kastrup
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