Re: YANQ - When to map, when to iterate, when to recurse? And why CLOS?

Wade Humeniuk wrote:

John Connors wrote:
 

Yet Another Noob Question.

 

What are the characteristics of each implementation?

 

How can I tell which I should be writing in what context...

 

(defun find-indicies (lst tst)
  (let ((li 0))
    (labels ((qpred (a)
               (incf li)
               (if (funcall tst a)
                   (1- li)
                   nil)))
      (remove nil (mapcar #'qpred lst)))))

 

(defun find-indices (lst tst)
  (loop
   for el in lst
   counting t into index
   if (funcall tst el)
   collect index))

 
You are allergic to loop
 
(defun find-indices (list test)
   (loop for element in list
         for index from 1
         when (funcall test element) collect index))

Gauche Scheme

(define (find-indices lst test)
  (filter-map
    (lambda (e i) (and (test e) i))
    lst
    (lrange 1)))

(find-indices '(0 88 409 66 77) odd?)
  ===>
(3 5)