Re: Attaching an alist to a grob

[Mattes]

Am Mittwoch, 14. Januar 2015 12:34 CET, Urs Liska <address@hidden> schrieb:

>

> >>> #(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.

Richard is right, the if-clauses aren't neccessary. Scheme has the
concept "generalized" booleans, i.e. anything that isn't explicitly
false is considered to be true:

 guile> (if 42 'true 'false)

I was just trying to keep as much of your code as possible ....

 Cheers, RalfD