[racket] Challenge: Game of life in 140 chars

On Sun, 19 Feb 2012, SF wrote:

> 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))

Here's my shortening of the life function above:

(define (life s)
   (define (c s n)
     (+ (if (bitwise-bit-set? 3080 (quotient s n))
            n
            0)
        (if (= n 1) 0 (c (modulo s n) (/ n 16)))))
   (c (* s #x111000181000111/10000000)
      (expt 8 48)))

By my count, that packs down to 159 characters.

-- Jeremiah Willcock