a solution to http://blog.jazzychad.net/2012/08/01/array-iteration-problem.html in chicken scheme.

array.scm

;; blog.jazzychad.net/2012/08/01/array-iteration-problem.html

(use srfi-1)

(: f ((list-of number) number number -> (list-of number)))
(define f 
  (lambda (arr n i) 
    (cond [(< n 0) 
           ;; if we are going right-to-left, reverse the list and use the abs count
           (reverse (f (reverse arr) (abs n) i))] 
          [else 
           ;; else walk the list with a counter j, incrementing any i values 
           (letrec ([n_ne_0? (not (eq? n 0))] 
                    [g 
                     (lambda (arr_ j) 
                       (cond 
                        [(or (null? arr_) (and n_ne_0? (eq? j n))) 
                         ;; return rest of list if null, or n != 0 and j == n 
                         ;; (in which case we want to cease adding, and 
                         ;; j == n is our termination test
                         arr_]
                        [else
                         ;; if the first elt is i, increment it and the counter
                         (let* ([ca (car arr_)] 
                                [p (cond [(eq? ca i) 1] [else 0])])
                           (cons (+ ca p) (g (cdr arr_) (+ j p))))]))]) 
             (g arr 0))])))