Hi Leah,
On Thu, Apr 30, 2015 at 7:28 PM, Leah Velleman <[email protected]>
wrote:
> To do something like you want, you really would need access to context
>> properties....
>>
>
> Ok — good to know I haven't missed some simple solution.
>
> It seems like there ought to be some way of smuggling information out of
> an \applyContext. But I guess there's a variable scope issue that keeps you
> from doing it straightforwardly:
>
> k = "OOPS"
>
> text = #(define-music-function (parser location music) (ly:music?)
> #{
> \applyContext
>
> #(lambda (context)
> (set! k
> (ly:context-property context 'tonic))
> (display k)
> )
> \transpose #(ly:make-pitch 0 0) #k #music
> #}
> )
> \score {
>
> \new Staff {
> \key a \major
>
> \test { Fa So La fa so }
> }
>
> }
>
> In that code, the (display k) works fine, displaying #<Pitch a>. But then the
> \transpose #(ly:make-pitch 0 0) #k #music gets ahold of the global
> definition of #k rather than the local one and so you end up with a type
> error: expecting pitch, found "OOPS".
>
> So maybe the question is, does Lilypond Scheme have anything like global
> variables?
>
Sure. But even defining the function with a local variable gives the same
results:
test =
#(define-music-function (parser location music) (ly:music?)
(let ((k "ERROR"))
#{
\applyContext
#(lambda (context)
(set! k (ly:context-property context 'tonic))
(display k)
)
\transpose #(ly:make-pitch 0 0) #k #music
#(display k)
#(newline)
#}
))
\score {
\new Staff {
\key a \major
\test { a b cis d e }
}
}
The problem arises because \applyContext is evaluated later than
\transpose. When music functions do their work, contexts have not been
created yet,
The output shows that the original binding of k is in effect when
\transpose is called.
Possibly you could just write a music function that firsts sets the key and
then transposes everything. Here's a sketch:
\version "2.19"
test =
#(define-music-function (parser location pitch music) (ly:pitch? ly:music?)
#{
\key #pitch \major
\transpose #(ly:make-pitch 0 0) #pitch #music
#})
\score {
\new Staff {
\test a { c' d' e' f' g' a' b' c'' }
}
}
David
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