[Haskell-beginners] A good data structure for representing a tic-tac-toe board?

[Costello, Roger L.]

Hi Folks,

Currently I am representing a tic-tac-toe board as a string, with 'X' denoting player 1 and 'O' denoting player 2. For example, I represent this 2x2 game board:

     'X' 	|  
-----------------------
  	|   'O'

with this string: "X  O"

The nice thing about that representation is that it is each to identify which cells are filled or empty, and it is easy to mark a cell with an 'X' or 'O'.

The problem with the representation is that it is difficult to determine when a player has won.

Can you recommend a representation that makes it easy to:

1. determine when a player has won
2. identify cells that are filled or empty
3. mark an empty cell 

/Roger