chapter11.hs

import Data.Char
import Data.List
import System.IO

size :: Int
size = 3

type Grid = [[Player]]

data Player = O | B | X deriving (Eq, Ord, Show)

next :: Player -> Player
next O = X
next X = O
next B = B

empty :: Grid
empty = replicate size (replicate size B)

full :: Grid -> Bool
full = all (/= B) . concat

turn :: Grid -> Player
turn g = if os <= xs then O else X
    where
        os = length (filter (== O) ps)
        xs = length (filter (== X) ps)
        ps = concat g

wins :: Player -> Grid -> Bool
wins p g = any line (rows ++ cols ++ dias)
    where 
        line = all (== p)
        rows = g
        cols = transpose g
        dias = [diag g, diag (map reverse g)]


diag :: Grid -> [Player]
diag g = [g !! n !! n | n <- [0..size-1]]

won :: Grid -> Bool
won g = wins O g || wins X g

putGrid :: Grid -> IO ()
putGrid = putStrLn . unlines . concat . interleave bar . map showRow
    where bar = [replicate ((size * 4) -1) '-']

showRow :: [Player] -> [String]
showRow = beside . interleave bar . map showPlayer
    where
        beside = foldr1 (zipWith (++))
        bar = replicate 3 "|"

showPlayer :: Player -> [String]
showPlayer O = ["   ", " O ", "   "]
showPlayer B = ["   ", "   ", "   "]
showPlayer X = ["   ", " X ", "   "]

interleave :: a -> [a] -> [a]
interleave x [] = []
interleave x [y] = [y]
interleave x (y:ys) = y : x : interleave x ys


howPlayer O = ["   ", " O ", "   "]