Thomas Morley-2 wrote
> No.
> It abuses the syntax for an _optional_ argument, with the default ""
Ah, I see. Thanks for the explanation and example. I see that if you don't
use the (predicate? default) form for supplying an optional/default argument
then you get an error: Unbound variable "x"
So I suppose that currently the preferred way to use a new type predicate
combination (when you want one that has not been predefined) would be as
follows.
Cheers,
-Paul
\version "2.18.2"
#(define (markup-or-stencil-or-procedure-or-false? x)
(or
(markup? x)
(ly:stencil? x)
(procedure? x)
(and (boolean? x) (not x))))
substitute =
#(define-music-function (parser location new-stl item)
(markup-or-stencil-or-procedure-or-false?
symbol-list-or-music?)
#{
\tweak stencil
#(if (markup? new-stl)
(lambda (item) (grob-interpret-markup item new-stl))
new-stl)
#item
#})
%%%%%%%%%%%%%%%%%%%%%
{
c'1
\once \substitute \markup "x" Staff.NoteHead
d'1
\once \substitute #(make-circle-stencil 0.5 0.1 #t) Staff.NoteHead
e'1
\once \substitute ##f Staff.NoteHead
g'1
\once \substitute
#(lambda (grob)
;; just an example procedure
(display grob)(newline)
#f)
Staff.NoteHead
a'1
}
--
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