[racket] Challenge: Game of life in 140 chars

Here's a rough draft that has tons of room for improvement:

#lang racket

(define glider
  (string->number "#x\
010000\
001000\
111000\
000000\
000000\
000000\
"))

(define (life s)
  (define (c s n)
    (if (= -1 n)
        0
        (+ (if (bitwise-bit-set? 3080 (arithmetic-shift s (* -4 n)))
               (expt 16 n)
               0)
           (c (modulo s (expt 16 n)) (sub1 n)))))
  (c (* s #x111000181000111/10000000)
     36))


;; helper functions: run (step) repeatedly to watch

(define current glider)

(define (show s)
  (define str1 (format "~x" s))
  (define str (string-append (make-string (- 6 (modulo (string-length
str1) 6)) #\0) str1))
  (for ([i (in-range 0 (string-length str) 6)])
    (displayln (substring str i (+ i 6)))))

(define (step)
  (set! current (life current))
  (show current))