Re: fif function from On Lisp

[weber]

On Mar 4, 11:07 am, weber <hug...@gmail.com> wrote:
> On Mar 4, 10:59 am, weber <hug...@gmail.com> wrote:
>
>
>
> > On Mar 4, 9:53 am, bojohan+n...@dd.chalmers.se (Johan Bockgård) wrote:
>
> > > weber <hug...@gmail.com> writes:
> > > > Hi folks.
> > > > For some reason this function from On Lisp doesn't work:
>
> > > > (defun fif (a b &optional c)
> > > >   '(lambda (x)
> > > >    (if (funcall a x)
> > > >            (funcall b x)
> > > >            (unless (null c) (funcall c x)))))
>
> > > > I should be able to call it like this:
>
> > > > (mapcar (fif 'zerop '1+ 1-) '(0 1 2 3) => (1 0 1 2)
>
> > > > but i'm probably missing something that is differs from Common Lisp to
> > > > Elisp.
>
> > > The code above doesn't work in Common Lisp either, but anyway, Emacs
> > > Lisp doesn't have lexical closures (yet).
>
> > > (info "(elisp) Extent")
>
> > > --
> > > Johan Bockgård
>
> > Hm. Does that snippet really depends on lexical closures?
> > I just need that function to expand to this:
>
> > (mapcar (lambda (x) (if (funcall 'zerop x) (funcall '1+ x) (funcall
> > '1- x)))
> >                 '(0 1 2 3))
>
> > ... maybe I can solve it with a macro then?
>
> > -weber
>
> Ok, i can.
> Tks anyway.
>
> (defmacro fif (a b &optional c)
>   `(lambda (x)
>          (if (funcall ,a x)
>                  (funcall ,b x)
>                  (unless (null ,c) (funcall ,c x)))))
>
> -weber

Just needed to post a correct version:

(defmacro fif (a b &optional c)
  `(lambda (x)
         (if (funcall ,a x)
                 (funcall ,b x)
                 (if (null ,c) x (funcall ,c x)))))

-weber