Re: Attaching an alist to a grob

[Urs Liska]

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 <address@hidden> 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.
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
> >
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