Hi All, I am new to Haskell and got stuck while experimenting with minimax algorithm (tic-tac-toe game). Just for learning I am trying to avoid external modules and use only the standard Prelude library. Here is the code snippet: type Pos = (Int,Int) -- Players are O (minimizing) and X (maximizing), B is for the draw (blank), I and J are used for -INF and +INF respectively data Player = I | O | B | X | J deriving (Eq, Ord, Show) type Grid = [(Pos,Player)] data Tree a = Node a [Tree a] deriving Show minimax :: Player -> Player -> Tree Grid -> Tree (Grid, Player) minimax _ _ (Node g []) | wins X g = Node (g,X) [] | wins O g = Node (g,O) [] | otherwise = Node (g,B) [] minimax a b (Node g ts) | turn g == X = let ts' = [minimax alpha b t | t <- ts, alpha < b] ps = [p | Node (_,p) _ <- ts'] alpha = maximum (a:ps) in Node (g, alpha) ts' | turn g == O = let ts' = [minimax a beta t | t <- ts, a < beta] ps = [p | Node (_,p) _ <- ts'] beta = minimum (b:ps) in Node (g, beta) ts' The function call is like: minimax I J tree It looks like I got a recursion loop. Could someone advise how to approach the problem? Thank you, Max