Re: Any disadvantage to #'tag ?

[Graham Percival]

On 6-Jan-05, at 1:29 PM, Nicolas Sceaux wrote:
> Speaking of \keepWithTag, I usually use a custom version of it,
> that let me write:
>
>   \keepWithTag #'tag1 music
>
> or
>
>   \keepWithTag #'(tag1 tag2 ...) music
>
> or
>
>   \keepWithTag #'() music
>
> (the last one being the same as \removeWithTag)

So your version adds the possibility of a list of tags to use?  That
could be useful -- especially if some people (like me) start
using #'tag for complete instrument parts.

> If one thinks that this is useful, I'll change the definition in
> ly/music-functions-init.ly

Sounds good to me!

Cheers,
- Graham

> #(use-modules (srfi srfi-1))
> #(define* (has-some-member? list1 list2 #:key (test eqv?))
>   "Return a true value iif there exists an element of list1 that also
> belongs to list2 under test."
>   (if (null? list1)
>       #f
>       (or (member (car list1) list2 test)
>           (has-some-member? (cdr list1) list2 #:test test))))
>
> #(define (symbol-or-symbols? x)
>   (or (null? x)
>       (symbol? x)
>       (and (list? x) (every symbol? x))))
>
> keepWithTag = #(def-music-function (parser location tags music) 
> (symbol-or-symbols? ly:music?)
>                 (music-filter (lambda (m)
>                                 (let ((m.tags (ly:music-property m 
> 'tags)))
>                                   (cond ((symbol? tags)
>                                          (or (null? m.tags) (memq tags 
> m.tags)))
>                                         ((null? tags)
>                                          (null? m.tags))
>                                         ((list? tags)
>                                          (or (null? m.tags) 
> (has-some-member? tags m.tags)))
>                                         (else #t))))
>                               music))
>
> nicolas