tic-tac-toe (7 languages in 7 Weeks, Scala chapter)

tictactoe.scala

import scala.Console
// Write a game that will take a tic-tac-toe board with X, O, and blank
// characters and detect the winner or whether there is a tie or no
// winner yet. Use classes where appropriate.

// Represent a board with X,O,blank plays.
class Board(positions:String) {
  val winningTuples = List( (0,1,2), (3,4,5), (6,7,8), // L-to-R
                            (0,3,6), (1,4,7), (2,5,8), // T-to-B
                            (0,4,8), (2,4,6))          // Diagonal

  def countWinsFor(p:Char):Int = {
    val possibleWins = winningTuples.map(t => (positions.charAt(t._1), positions.charAt(t._2), positions.charAt(t._3)))
    possibleWins.filter( _ == (p, p, p)).length
  }

  def evalGameState:GameState = {
    val (x, o) = (countWinsFor('X'), countWinsFor('O'))
    (x compareTo o) match {
      case -1 => OWins
      case 1 => XWins
      case 0 => if (x == 0) NoWinner else Tie
    }
  }
}

trait GameState
object XWins extends GameState    { override def toString = "X Wins" }
object OWins extends GameState    { override def toString = "O Wins" }
object Tie extends GameState      { override def toString = "Tie" }
object NoWinner extends GameState { override def toString = "No Winner" }

// Read in 9 characters.  Ignore anything but " ", "X", and "O".

println("Enter a board")

object boardBuffer {
  var buffer = new StringBuffer()
  def accum(c:Char) { buffer.append(c) }

  def board:Option[String] = {
    (buffer.length >= 9) match {
      case true => {
        val b = buffer.substring(0,9)
        buffer = new StringBuffer()
        Some(b)
      }
      case false => None
    }
  }
}

while(true) {
  val r = Console.readLine()
  r match {
    case null => println("(ignoring EOF)")
    case x => x.foreach( c =>
      if (c == ' ' || c == 'X' || c == 'O') {
        boardBuffer.accum(c)
      }
    )
  }
  boardBuffer.board.map(s => println(new Board(s).evalGameState))
}