(define snlist-recur
  (lambda (flist fatom init)
    (letrec ([helper (lambda (l)
		       (cond [(null? l) init]
			     [(pair? (car l))
			      (flist (helper (car l))
				     (helper (cdr l)))]
			     [else (fatom (car l)
					  (helper (cdr l)))]))])
      helper)))

(define last (snlist-recur (lambda (x y) (if (null? y) x y)) (lambda (x y) (if (null? y) x y)) '()))

(define first (snlist-recur (lambda (x y) (if (null? x) y x)) (lambda (x y) (if (null? x) y x)) '()))

(define matrix-ref
  (lambda (m row col)
    ((snlist-recur (lambda (x y)
		     (if (number? y)
			 (if (= y row)
			     x
			     (+ y 1))
			 y))
		   (lambda (x y)
		     (if (number? y)
			 (if (= y col)
			     x
			     (+ y 1))
			 y))
		   0)
     m)))
(define matrix-ref-2
  (lambda (m row col)
    (let ([currow 0]
	  [curcol 0]
	  [rower #f]
	  [coler #f])
      ((snlist-recur (lambda (x y)
		       (if (= row currow)
			   (set! rower coler)
			   (set! currow (+ currow 1))))
		     (lambda (x y);;; need to use local let
		       (if (= col curcol)
			   (set! coler rower)
			   (set! curcol (+ curcol 1))))

		     0)
       m)
      coler)))