@(do 
    (defvar x-centre -0.5)
    (defvar y-centre 0.0)
    (defvar width 4.0)
    (defvar i-max 80)
    (defvar j-max 60)
    (defvar n 100)
    (defvar r-max 2.0)
    (defvar file "mandelbrot.pgm")
    (defvar colour-max 255)
    (defvar pixel-size (/ width i-max))
    (defvar x-offset (- x-centre (* 0.5 pixel-size (+ i-max 1))))
    (defvar y-offset (+ y-centre (* 0.5 pixel-size (+ j-max 1))))
 
    ;; complex number library
    (macro-time
      (defmacro cplx (x y) ^(cons ,x ,y))
      (defmacro re (c) ^(car ,c))
      (defmacro im (c) ^(cdr ,c))

      (defsymacro c0 (cplx 0 0)))

    (macro-time 
      (defun with-cplx-expand (specs body)
        (tree-case specs
           (((re im expr) . rest) 
            ^(tree-bind (,re . ,im) ,expr ,(with-cplx-expand rest body)))
           (() (tree-case body
                 ((a b . rest) ^(progn ,a ,b ,*rest))
                 ((a) a)
                 (x (error "with-cplx: invalid body ~s" body))))
           (x (error "with-cplx: bad args ~s" x))))

      (defmacro with-cplx (specs . body)
        (with-cplx-expand specs body)))

    (defun c+ (x y)
      (with-cplx ((a b x) (c d y))
        (cplx (+ a c) (+ b d))))

    (defun c* (x y)
      (with-cplx ((a b x) (c d y))
        (cplx (- (* a c) (* b d)) (+ (* b c) (* a d)))))

    (defun modulus (z)
      (with-cplx ((a b z))
        (sqrt (+ (* a a) (* b b)))))

    ;; Mandelbrot routines
    (defun inside-p (z0 : (z c0) (n n))
      (and (< (modulus z) r-max)
           (or (zerop n)
               (inside-p z0 (c+ (c* z z) z0) (- n 1)))))

    (defun pixel (i j)
      (inside-p
        (cplx (+ x-offset (* pixel-size i))
              (- y-offset (* pixel-size j)))))

    ;; Mandelbrot loop and output
    (each ((j (range 1 j-max)))
      (each ((i (range 1 i-max)))
        (put-char (if (pixel i j) #\* #\space)))
      (put-char #\newline)))