How to resolve the algorithm Conway's Game of Life step by step in the Scheme programming language
How to resolve the algorithm Conway's Game of Life step by step in the Scheme programming language
Table of Contents
Problem Statement
The Game of Life is a cellular automaton devised by the British mathematician John Horton Conway in 1970. It is the best-known example of a cellular automaton. Conway's game of life is described here: A cell C is represented by a 1 when alive, or 0 when dead, in an m-by-m (or m×m) square array of cells. We calculate N - the sum of live cells in C's eight-location neighbourhood, then cell C is alive or dead in the next generation based on the following table: Assume cells beyond the boundary are always dead. The "game" is actually a zero-player game, meaning that its evolution is determined by its initial state, needing no input from human players. One interacts with the Game of Life by creating an initial configuration and observing how it evolves.
Although you should test your implementation on more complex examples such as the glider in a larger universe, show the action of the blinker (three adjoining cells in a row all alive), over three generations, in a 3 by 3 grid.
Let's start with the solution:
Step by Step solution about How to resolve the algorithm Conway's Game of Life step by step in the Scheme programming language
Source code in the scheme programming language
;;An R6RS Scheme implementation of Conway's Game of Life --- assumes
;;all cells outside the defined grid are dead
;if n is outside bounds of list, return 0 else value at n
(define (nth n lst)
(cond ((> n (length lst)) 0)
((< n 1) 0)
((= n 1) (car lst))
(else (nth (- n 1) (cdr lst)))))
;return the next state of the supplied universe
(define (next-universe universe)
;value at (x, y)
(define (cell x y)
(if (list? (nth y universe))
(nth x (nth y universe))
0))
;sum of the values of the cells surrounding (x, y)
(define (neighbor-sum x y)
(+ (cell (- x 1) (- y 1))
(cell (- x 1) y)
(cell (- x 1) (+ y 1))
(cell x (- y 1))
(cell x (+ y 1))
(cell (+ x 1) (- y 1))
(cell (+ x 1) y)
(cell (+ x 1) (+ y 1))))
;next state of the cell at (x, y)
(define (next-cell x y)
(let ((cur (cell x y))
(ns (neighbor-sum x y)))
(cond ((and (= cur 1)
(or (< ns 2) (> ns 3)))
0)
((and (= cur 0) (= ns 3))
1)
(else cur))))
;next state of row n
(define (row n out)
(let ((w (length (car universe))))
(if (= (length out) w)
out
(row n
(cons (next-cell (- w (length out)) n)
out)))))
;a range of ints from bot to top
(define (int-range bot top)
(if (> bot top) '()
(cons bot (int-range (+ bot 1) top))))
(map (lambda (n)
(row n '()))
(int-range 1 (length universe))))
;represent the universe as a string
(define (universe->string universe)
(define (prettify row)
(apply string-append
(map (lambda (b)
(if (= b 1) "#" "-"))
row)))
(if (null? universe)
""
(string-append (prettify (car universe))
"\n"
(universe->string (cdr universe)))))
;starting with seed, show reps states of the universe
(define (conway seed reps)
(when (> reps 0)
(display (universe->string seed))
(newline)
(conway (next-universe seed) (- reps 1))))
;; --- Example Universes --- ;;
;blinker in a 3x3 universe
(conway '((0 1 0)
(0 1 0)
(0 1 0)) 5)
;glider in an 8x8 universe
(conway '((0 0 1 0 0 0 0 0)
(0 0 0 1 0 0 0 0)
(0 1 1 1 0 0 0 0)
(0 0 0 0 0 0 0 0)
(0 0 0 0 0 0 0 0)
(0 0 0 0 0 0 0 0)
(0 0 0 0 0 0 0 0)
(0 0 0 0 0 0 0 0)) 30)
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