Re: Translating circular Haskell code to lisp

B. Pym wrote:

Pascal Costanza wrote:
 

I don't need a general purpose transformation, just some guidelines to
follow when I see code like this.

 
General guideline: Look for a solution that uses LOOP. ;)
 
(defun diff3 (list)
   (let ((avg (loop for element in list
                    sum element into sum
                    count t into length
                    finally (return (/ sum length)))))
     (loop for element in list
           collect (- element avg))))

 
Gauche Scheme
 
(define (diff3 lst)
  (let ((len 0) (sum 0))
    (dolist (x lst) (inc! len) (inc! sum x))
    (map (cute  - <> (/ sum len)) lst)))
 
(diff3 '(1 2 3 4 5))
  ===>
(-2 -1 0 1 2)

Since it's "cute" instead of "cut", (/ sum len) is done only once.

"Cute is a variation of cut that evaluates expr-or-slots before
creating the procedure."