The Little Hacker's Room

(define cols 78)
(define rows 39)
(define iter 36)

(define (density n)
  (cond ((= n iter) #\ )
        ((and (>= n 0) (<= n 9)) (integer->char (+ n 48)))
        ((and (>= n 10) (<= n 36)) (integer->char (+ n 35 -10)))
        (else #\.)))

(define (mandelbrot left right bottom top)
  (do ((i 0 (1+ i))) ((>= i rows))
    (do ((j 0 (1+ j))) ((>= j cols))
      (let ((x (+ (* (/ j cols) (- right left)) left))
            (y (+ (* (/ i rows) (- top bottom)) bottom)))
        (write-char (density (let lp ((c (make-rectangular x y))
                                      (z 0+0i)
                                      (k 0))
                               (cond ((or (= k iter) (>= (magnitude z) 2)) k)
                                     (else (lp c (+ (* z z) c) (1+ k )) )) ))) ))
    (newline)))

(mandelbrot -2 2 -2 2)