On Wed, 2015-01-14 at 12:34 +0100, Urs Liska wrote: > Am 14.01.2015 um 12:28 schrieb Richard Shann: > > On Wed, 2015-01-14 at 11:29 +0100, Urs Liska wrote: > >> Am 14.01.2015 um 11:18 schrieb Mattes: > >>> > >>> Am Mittwoch, 14. Januar 2015 09:42 CET, Urs Liska <u...@openlilylib.org> > >>> schrieb: > >>> > >>>> Yes, I made some surprising progress with Scheme recently. I didn't even > >>>> get stuck in the ands and parens in the actual predicate I wrote > >>>> > >>>> #(define (annotation? obj) > >>>> (and > >>>> (and (list? obj) > >>>> (every pair? obj)) > >>>> (and (if (assoc-ref obj "type") #t #f) > >>>> (if (assoc-ref obj "location") #t #f)))) > >>> Proper indentation helps ;-) > >>> But why so contrived? Your code is equivalent to: > >>> > >>> #(define (annotation? obj) > >>> (and > >>> (list? obj) > >>> (every pair? obj) > >>> (if (assoc-ref obj "type") #t #f) > >>> (if (assoc-ref obj "location") #t #f))) > > ... and is this just equivalent to: > > > > #(define (annotation? obj) > > (and > > (list? obj) > > (every pair? obj) > > (assoc-ref obj "type") > > (assoc-ref obj "location"))) > > > > > > ??? > > I don't think so because the result of the function would be the result > of the last expression.
yes, and in Scheme all expressions except #f are true. (That's why #t is used so rarely, because it is just an "empty" symbol, used when you haven't got anything else.) Richard > assoc-ref returns the "value" to the "key", so if passed a valid object > the result of the predicate wouldn't be #t but the content of "location". > That's why I enclosed these checks in if constructs. > > Urs > > > > > Richard > > > > > > > >>> HTH Ralf Mattes > >>> > >>> > >>> > >> Thanks, this is of course better. > >> sorting out nested conditionals has never been my strongest point ;-) > >> > >> Urs > >> > >> _______________________________________________ > >> lilypond-user mailing list > >> lilypond-user@gnu.org > >> https://lists.gnu.org/mailman/listinfo/lilypond-user > > > _______________________________________________ lilypond-user mailing list lilypond-user@gnu.org https://lists.gnu.org/mailman/listinfo/lilypond-user
