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3. Coursework - Connect 4

13/02/23

Run the Haskell code as ghc -02 connect4.ls

The Board​

rows = 6
cols = 7
win = 4
depth = 6 --search depth

type Board = [Row]
type Row = [Player]

data Player = O  | B | X deriving (Ord, Eq, Show) -- Gives class instances for free

What is deriving?​

class Eq a where 
    (==) :: a -> a -> Bool--infix operator. True if =, false if not
    (/=) :: a -> a -> Bool--Not equal, true if not equal
x /= y = not (x == y)

Class is a collection of related types

What happens when you do deriving eq

instance Eq Player where
    O == O = True
    B == B = True
    X == X = True
    _ == _ = False

Ord - Ordering of values on type. Is dependent on the order you write the constructors. Show - Displays the requested item

Game Trees​

Essence in writing a strong computer player for connect 4. Can have up to a million boards

Strategy (minimax)​

  1. Produce the game tree to specified depth
  2. Label each leaf with winner, or Blank if game not over or draw
  3. Then work up the tree(propagate)
    • If O to play, take min of children. (O<B<X)
    • If X to play, take max of children (O<B<X)
  4. Best move is one with same label as root