If taking the array approach, I'd recommend using a single array indexed by the (x,y) position of the cell, this way neither direction has a greater implied significance. Diagonals should also be easier.

Aside: Tony Morris wrote a very interesting exercise based on tic-tac-toe and it is available on Hackage: http://hackage.haskell.org/package/TicTacToe

On Tue, Mar 19, 2013 at 3:49 AM, Peter Hall <peter.hall@memorphic.com> wrote:

Start with a data type for the cell values, instead of Char. Then use an Array of Arrays, containing those values.

data Cell = Empty | O | X

type Board = Array Int Cell

Finding winning "rows" and "columns" is easy. Diagonals are slightly more complicated. 

Peter

On 18 March 2013 15:54, Costello, Roger L. <costello@mitre.org> wrote:

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

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