sample.hs

minimaxWithLeastDepth :: Tree Grid -> Tree (Grid, Player, Int)
minimaxWithLeastDepth (Node g [])
    | wins O g = Node (g,O,1) []
    | wins X g = Node (g,X,1) []
    | otherwise = Node (g,B,1) []
minimaxWithLeastDepth (Node g ts)
    | turn g == O = Node (g, minimum ps, minimum cs) ts'
    | turn g == X = Node (g, maximum ps, minimum cs) ts'
        where
            ts' = map minimaxWithLeastDepth ts
            raw = [(p,c) | Node (_,p,c) _ <- ts']
            ps = [p | (p,_) <- raw]
            cs = [c + 1 | (_,c) <- raw]

type GridWDepth = (Grid,Int)

leastDepth :: [GridWDepth] -> GridWDepth
leastDepth [] = ([],0)
leastDepth (x:xs) = checkBranchDepth x xs

checkBranchDepth :: GridWDepth -> [GridWDepth] -> GridWDepth
checkBranchDepth m [] = m
checkBranchDepth m (y:ys) | (snd y) < (snd m) = checkBranchDepth y ys
                          | otherwise = checkBranchDepth m ys

leastDepthBestmove :: Grid -> Player -> Grid
leastDepthBestmove g p = fst $ leastDepth [(g',c) | Node (g',p',c) _ <- ts, p' == best]
            where
                tree = prune depth (gametree g p)
                Node (_,best,_) ts = minimaxWithLeastDepth tree