Re: Ex. 3.5 in ACL

Zachary Beane wrote:

   (defun mapcar-pos+ (list)
     (let ((i -1))
       (mapcar #'(lambda (elt) (+ elt (incf i)))

Truly abysmal ignorance or willful stupidity.

The #' is redundant.

 

iteration:
>
(defun pos+ (lst)
   (setf acc NIL)
   (setf i 0)
   (dolist (obj lst)
; i know, instead of append, i could do a cons and reverse afterwards...
     (progn (setf acc (append acc (list (+ obj i))))
       (setf i (+ i 1))))
   acc)

 
I'd prefer LOOP here:
 
   (defun loop-pos+ (list)
     (loop for i from 0
           for elt in list
           collect (+ elt i)))

Gauche Scheme:

(define (pos+ input)
  (@ (i -1)  map x : (+ x (++ i)) input))

(pos+ '(900 800 700 600 500))
  ===>
(900 801 702 603 504)

Given:

(define ++ inc!)

(define-syntax @-aux
  (syntax-rules (:)
    [(_ () goodlets func (vars ...) : expr lst ...)
     (let* goodlets (func (lambda (vars ...) expr) lst ...))]
    [(_ () goodlets func (vars ...) var more ...)
     (@-aux () goodlets func (vars ... var) more ...)]
    [(_ (var val more ...) (goodlets ...) stuff ...)
     (@-aux (more ...) (goodlets ... (var val)) stuff ...)]))

(define-syntax @
  (syntax-rules ()
    [(_ (lets ...) func stuff ...)
     (@-aux (lets ...) () func () stuff ...)]
    [(_ func stuff ...)
     (@ () func stuff ...)]))