is there another way to code such a function/idea?

this is (at the moment) a "theoretically function"... no concret use - l'art pour l'art :-)

thanx for smarter LISP-code-IDEAS!

andré

 

;;; evaluate PROGN (as a reset)

(progn
  (defstruct counter n)
  (defvar cnt)
  (setf cnt (make-counter :n -1))
  (defun read-list-in-steps (alist)
    (nth (setf (counter-n cnt) (1+ (counter-n cnt))) alist)))

;;; evaluate a view times, so one value after the other will be in the output
;;; you have to evaluate the progn-seq before every new start!!!

(read-list-in-steps '(1 2 3 4 5 6))
(read-list-in-steps '(c4 f4 e4 f4 g5))

 

(let ((i -1))
  (defun next (liste) 
    (nth 
     (mod (incf i) (length liste))
     liste)))

;;; (next '(a b c d e f))

SB.

great... that's a smart solution :-) simpler then mine

...i didn't know how to set "-1" outside the FUNCTION without DEFSTRUCT

thanx!!

 

i like it when the program tells me that it has done the job... so i coded a little extension:

(let ((i -1))
  (defun next (liste &key (stop 'nil) (one-cycle 'nil)) 
    (if (equal stop 't)
      (if (< i (1- (length liste)))
        (nth (mod (incf i) (length liste)) liste)
        (if (equal one-cycle 'nil)
          (progn 
            (setf i -1)
            'nil)
          'nil))
      (nth (mod (incf i) (length liste)) liste))))
        

(next '(a b c d e f))
(next '(a b c d e f) :stop t :one-cycle nil) ;; shows a NIL after last value, then starts again
(next '(a b c d e f) :stop t :one-cycle t) ;; shwows only NILs after the last value