single commit implementation :O

Conway.hs

@@ -0,0 +1,42 @@
+import Control.Monad
+import Data.Matrix
+
+type Cell = Bool
+
+next :: Cell -> [Cell] -> Cell
+next True cs
+    | neighbors < 2 = False
+    | neighbors == 2 || neighbors == 3 = True
+    | otherwise = False
+    where neighbors = neighborCount cs
+next False cs
+    | neighborCount cs == 3 = True
+    | otherwise = False
+
+neighborCount :: ([Cell] -> Int)
+neighborCount = length . filter id
+
+step :: Matrix Cell -> Matrix Cell
+step world =
+    foldl (\w r -> mapRow (\c cell -> next cell (neighborsOf r c)) r w) world [1..rmax]
+    where rmax = nrows world
+          cmax = ncols world
+          allNeighborCoords r c = [ (r + r', c + c') | r' <- [-1..1], c' <- [-1..1] ]
+          neighborCoordsOf r c = [ coord | coord <- allNeighborCoords r c, (okCoord coord r c) ]
+          neighborsOf r c = map (\(x, y) -> getElem x y world) $ neighborCoordsOf r c
+          okCoord (x, y) r c
+            | x == r && y == c = False
+            | x < 1 || x > rmax = False
+            | y < 1 || y > cmax = False
+            | otherwise = True
+
+convert :: (a -> b) -> Matrix a -> Matrix b
+convert f m = fromList (nrows m) (ncols m) $ map f $ toList m
+
+drawAndStep world = do
+    print $ convert (\x -> if x then '.' else '_') world
+    return $ step world
+
+main = do foldM (\w _ -> drawAndStep w) initialWorld iterations
+    where initialWorld = fromList 9 9 $ cycle [True, True, False, True]
+          iterations = [1..]