Re: How to cast an imperative loop into a readable recursive function ?

[Tim Bradshaw <tfb@tfeb.org>]

On 2010-12-03 03:19:43 +0000, Katalin Sinkov said:

> your iterate is again a loop, ie a non-functional construct

Is it?  Consider this form:

(for (i 0 100)
  (print i))

This is iterative, right, I mean obviously.

Except here's the definition of FOR:

(defmacro for ((var min max) &body decls-and-forms)
  (let ((maxn (make-symbol "MAX"))
        (nextn (make-symbol "NEXT-1")))
    `(let ((,maxn ,max))
       (labels ((,nextn (,var)
                  (when (= ,var ,maxn)
                    (return-from ,nextn ,maxn))
                  (let ((,var ,var))
                    ,@decls-and-forms)
                  (,nextn (1+ ,var)))
                (next ()
                  (,nextn (1+ ,var))))
         (,nextn ,min)))))

There seems to be no iteration there, and expanding (and renaming 
gensyms to make it clearer):

(let ((max 100))
  (labels ((next-1 (i)
             (when (= i max) (return-from next-1 max))
             (let ((i i))
			 (print i))
             (next-1 (1+ i)))
           (next () (next-1 (1+ i))))
    (next-1 0)))

No iteration there.