Common Lisp LAST function

#1

I’ve found it useful to have a subset of the Common Lisp LAST function. In particular I was interested in doing circular list to implement a port of https://rosettacode.org/wiki/Averages/Simple_moving_average#Common_Lisp to uLisp

(defun sma (qlist)
   (let ((period (length qlist))
         (sum (apply #'+ qlist))
         (qptr qlist))
        (setf (rest (last qlist)) qlist)
        (lambda (val)
             (decf sum (first qptr))
             (incf sum val)
             (setf (first qptr) val)
             (setf qptr (rest qptr))
             (/ sum period))))

(defvar test (sma '(4 4 4 4)))
(test 9)

Since I need it to work with SETF, it required more than just a fn_last()…

If anyone would find it useful:

 object *fn_last (object *args, object *env) {
     (void) env;
     object *list = first(args);
     if (list == NULL) return nil;
     if (atom(list)) error(LAST, PSTR("first argument to last is not a list"), list);
     while (list != NULL && listp(list)) { 
       object *tail = cdr(list);
       if (atom(tail) || tail == NULL)  break;
       list = tail;
     }
    return list;
}

and in object **place()

if (fname == LAST) {
  object *list = eval(second(args), env);
  if (list == NULL) return nil;
  if (atom(list)) error(LAST, PSTR("first argument to last is not a list"), list);
  while (list != NULL && listp(list)) {
    object *tail = cdr(list);
    if (atom(tail) || tail == NULL)  break;
    list = tail;
  }
  return &list;
}

I’m sure this can be much improved (this was my first cut), but I am hoping that a subset implementation of LAST would be a worthwhile addition.