2009/8/5 Mark Polesky <markpole...@yahoo.com>:
> Is it possible to write a scheme procedure to test if a given
> context contains a particular engraver? Like...
> (context-has-engraver? context 'Span_arpeggio_engraver)
>From engraver-doc-string:
(if in-which-contexts
(let* ((layout-alist (ly:output-description $defaultlayout))
(context-description-alist (map cdr layout-alist))
(contexts
(apply append
(map
(lambda (x)
(let* ((context (cdr (assoc 'context-name x)))
(group (assq-ref x 'group-type))
(consists (append
(if group
(list group)
'())
(cdr (assoc 'consists x)))))
(if (member name-sym consists)
(list context)
'())))
context-description-alist)))
Unfortunately, this doesn't seem particularly useful, since you need
access to the correct output-def: $defaultlayout won't pick up a
Span_arpeggio_engraver in the Staff context if it's been added using
\with.
Regards,
Neil
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