Re: [Haskell-beginners] Problem with minimax with alpha beta pruning

Got it. Thank you Kim-Ee! On 22 Dec 2020, 08:28 +0000, Kim-Ee Yeoh , wrote:

Hi Maxim,

The scope of this question falls outside this beginners list, which tends toward questions about haskell syntax (see other active thread).

You will typically find more response on the haskell-cafe list, which you might want to resend your query to.

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On Mon, Dec 21, 2020 at 11:01 PM Maxim Frolov wrote:

...

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

_______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners -- -- Kim-Ee

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