heap resize error

(use posix extras)

;(set-gc-report! 1)

(define x)

(define (iter)
; (set! x '())
 (let loop ((i 0)
            (a '()))
 (when (< i 5000)
;    (set! x (cons (list iter (number->string i) (/ i 0.5) (/ i 0.5) (/ i 0.5) (/ i 0.5) i i i i i) x))
    (loop (add1 i)
          (cons (list iter "aa" i i i i i i i i i i i i i i i i i i i i i) a)
    ))))

(define n 0)
(define tt (current-milliseconds))
(let loop ((t (current-milliseconds))
            (m 0))
  (iter)
  (set! n (add1 n))
  (if (> m 16) (print "max " m))
  (if (< n 1000)
    (loop (current-milliseconds)
          (max (- (current-milliseconds) t))
    )))

(print "time:" (- (current-milliseconds) tt))