Re: [SPAM] Re: Validating a Scheme list

[Urs Liska]

Am 15.05.2014 10:26, schrieb David Kastrup:
> Urs Liska <address@hidden> writes:
>
> > Hi all,
> >
> > I am working on a Scheme function and would like to check if I have found the 
> > best solution for a specific subpart. Somehow it looks more complicated than 
> > necessary.
> >
> > The function needs to test if each element of a given list is a (sub)list with 
> > exactly two elements. So
> >
> > '((1 2)(3 4))
> >
> > would return #t while
> >
> > '((5 6)(7 8 9))
> >
> > would return #f.
> >
> > My solution is
> >
> > \version "2.19.6"
> >
> > validate =
> >
> > #(define-scheme-function (parser location lst) (list?)
> >
> >     (if (memv #f (map (lambda sig
>
> Why (lambda sig ... rather than (lambda (sig) ... here and consequently
> (car sig) instead of sig below?

getting lost maybe? ;-)

> >                         (and (list? (car sig))
> >
> >                              (= 2 (length (car sig))))) lst))
> >
> >         (display "invalid")
> >
> >         (display "valid"))
> >
> >     (newline))
>
> (if (every (lambda (sig) (eqv 2 (length+ sig))) lst)
>      (display "valid")
>      (display "invalid"))

Apart from that it's "eqv?" this works perfectly and is (other than 
Orm's solution) simple to incorporate in my actual function.

Thanks
Urs


--