game.scala

/*
 * This source-code is based on 
 * source-code on http://blog.srinivasan.biz/software/if-you-have-to-learn-just-one-programming-language
 * Using foldLeft often simplifies functional codes.
 */
/*
 * Question: Do you want to play this game?
 * You put down some money and roll a die between 1 and 100
 * Depending on your roll:
 *    1-50: I keep your money.
 *   51-65: You get your money back.
 *   66-75: You get 1.5 times your money
 *   76-99: You get 2 times your money
 *     100: You get 3 times your money
 * Do you want to play?
*/
 
object game { // object is used to define a singleton class

  // alas, type inference doesn't work for function args.
  def play(bet: Double, numPlays: Int) = {
    // parameter values can't be changed
    import java.util.Random // imports can be inside function

    // val is like final in java or const in C
    val r = new Random()
    // type of moneyStart and money need not be specified.
    // However, unlike python or ruby, they are inferred as
    // Double at compile time. Similarly for r and dice.
    val moneyStart = numPlays * bet
    val money = Stream.fill(numPlays)(r.nextInt(100)+1).foldLeft(moneyStart){
      (money, dice) =>
        if(dice <= 50) money - bet
        else if(dice >= 66 && dice <= 75) money + 0.5 * bet
        else if(dice >= 76 && dice <= 99) money + bet
        else if(dice == 100) money + 2 * bet
        else money
    }
    printf("%6.0f$ became %6.0f$ after %6d plays: " +
           "You get %.2f for a dollar\n", moneyStart,
           money, numPlays, (money / moneyStart))
  }
}
 
game.play(1.0, 100000) // Each bet is $1, play 100000 times
game.play(1.5, 5000)
game.play(4.0, 10000)