[heresy-devel] Equality testing.

[Matt Lamari]

(note - has to be read in heresy namespace, i.e. add it to the file)
 
I believe it works correctly with sub-lists too.

Also note - consumes stack - when I get time I'll rewrite it in 
continuation-calling form.  It does not consume stack based on list 
"length"; but on list-of-list depth.  I'll also optimize it better for 
speed (expand out/not use those readpoints and their performance hit).


(defun equal/ (a b)
  (let ((infinite (iterate/ #'identity nil))
        (end (cons nil nil))
        (a-is-list (listp/ a))
        (b-is-list (listp/ b)))
    (cond
     ((and a-is-list b-is-list)
      (let ((a (read-point-built (to-lazy-list a)))
            (b (read-point-built (to-lazy-list b))))
        (unless
            (loop while not (or (read-point-at-end a) (read-point-at-end 
b)) do
                  (unless (equal/ (read-point-value a) (read-point-value b))
                    (return-from nil t))
                  (setq a (read-point-advanced a))
                  (setq b (read-point-advanced b)))
          (not (or (read-point-at-end a) (read-point-at-end b))))))
     ((or a-is-list b-is-list) nil)
     (t (equal a b)))))


Robin Lee Powell wrote:
> * (equal (LIST/ 'B 'A 'Q '(C 1)) (LIST/ 'B 'A 'Q '(C 1)))
> NIL
>
> So, umm, how do I do that?  Convert to a regular list first?
>
> -Robin
>
>