Re: Nesting ly:music-property error

[Michael Ellis]

Right. In the general case, you need to recurse through 'elements and
'element similar to the following:

(define-public (change-pitches music converter)
    ;; Recurse through music, applying converter to pitches.
    ;; The converter function must take a single pitch as its
    ;; argument and return a new pitch.  These are LilyPond
    ;; scheme pitches, e.g. (ly:make-pitch 0 2 0)

    (let ((es (ly:music-property music 'elements))
          (e (ly:music-property music 'element))
          (p (ly:music-property music 'pitch)))

        (cond
            ((ly:pitch? p)
                (ly:music-set-property! music 'pitch (converter p)))

            ((pair? es)
                (map (lambda (x) (change-pitches x converter)) es))

            ((ly:music? e)
                (change-pitches e converter)))))


Cheers,
Mike



On Sat, Jan 29, 2011 at 8:22 PM,  <address@hidden> wrote:
> Thanks
>
> (car ) was the trick I would have been looking for a long time to come up
> with that one.
>
> (car (...))- returns the first member of a list.
>
> I'm assuming that if that member is a function it returns the functions
> result, which is why we get the solution?
>
> Scott
>
>
> -----Original Message-----
> From: Michael Ellis [mailto:address@hidden
> Sent: Saturday, January 29, 2011 07:01 PM
> To: address@hidden
> Cc: address@hidden
> Subject: Re: Nesting ly:music-property error
>
> Sorry, my previous answer was rubbish. The following runs without error and
> prints the pitch object. myN = #(define-music-function (parser location myx
> ) (ly:music?) (display-scheme-music (ly:music-property (car
> (ly:music-property myx 'elements)) 'pitch)) myx) \myN c Cheers, Mike On Sat,
> Jan 29, 2011 at 6:46 PM, Michael Ellis wrote: > Hi Scott, > > I think the
> problem is that the music in your example doesn't have an > 'elements
> property.  You can eliminate the error by changing the third > line in your
> code to > > #(display-scheme-music (ly:music-property $myx 'pitch)) > > but
> what gets displayed is an empty list '().  Probably not what you > want,
> right? > > Some of the more experienced Schemers on the list may be able to
> offer > better help. > > Cheers, > Mike > > > > On Sat, Jan 29, 2011 at 6:28
> PM,   wrote: >> myN = #(define-music-function (parser location myx )
> (ly:music?) >> #{ >> #(display-scheme-music (ly:music-property
> (ly:music-property $myx 'elements) >> 'pitch)) >> #}) >> >>     \myN c >