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  1. import scala.annotation.tailrec
  2.  
  3. trait State {
  4.   def isAcceptState: Boolean
  5. }
  6.  
  7. trait FSM[T <: FSM[T, A, S], -A, +S <: State] { this: T =>
  8.   def state: S
  9.  
  10.   def resume(input: A): T
  11. }
  12.  
  13. object FSM {
  14.   @tailrec
  15.   def resumeUntilAcceptance[T <: FSM[T, A, S], A, S <: State](fsm: T, inputs: Iterator[A]): T = {
  16.   	if (inputs.hasNext) {
  17.       val input = inputs.next
  18.       val newFSM = fsm.resume(input)
  19.       if (newFSM.state.isAcceptState) {
  20.         newFSM
  21.       } else {
  22.         resumeUntilAcceptance[T, A, S](newFSM, inputs)
  23.       }
  24.   	} else {
  25.   	  throw new Exception("not enough inputs")
  26.   	}
  27.   }
  28. }
  29.  
  30. sealed abstract class BattleAlphabet
  31. case object Action extends BattleAlphabet
  32. case object Bonus extends BattleAlphabet
  33.  
  34. sealed abstract class BattleState extends State
  35. case object PlayerTurn extends BattleState { override def isAcceptState = false }
  36. case object EnemyTurn extends BattleState { override def isAcceptState = false }
  37. case object PlayerWon extends BattleState { override def isAcceptState = true }
  38. case object EnemyWon extends BattleState { override def isAcceptState = true }
  39.  
  40. case class Battle(playerHealth: Int,
  41.                   enemyHealth: Int,
  42.                   state: BattleState)
  43.   extends FSM[Battle, BattleAlphabet, BattleState] {
  44.   override def resume(input: BattleAlphabet) = state match {
  45.   	case PlayerTurn =>
  46.   	  input match {
  47.   	    case Action =>
  48.   	      val nextState = if (enemyHealth == 1) PlayerWon else EnemyTurn
  49.   	      copy(enemyHealth = enemyHealth - 1, state = nextState)
  50.   	    case Bonus =>
  51.   	      copy(playerHealth = playerHealth + 1)
  52.   	  }
  53.   	case EnemyTurn => 
  54.   	  input match {
  55.   	    case Action =>
  56.   	      val nextState = if (playerHealth == 1) EnemyWon else PlayerTurn
  57.   	      copy(playerHealth = playerHealth - 1, state = nextState)
  58.   	    case Bonus =>
  59.   	      copy(enemyHealth = enemyHealth + 1)
  60.   	  }
  61.     case PlayerWon => this
  62.     case EnemyWon => this
  63.   }
  64. }
  65.  
  66. object Main extends App {
  67.   val battle = Battle(2, 2, PlayerTurn)
  68.   println(FSM.resumeUntilAcceptance[Battle, BattleAlphabet, BattleState](battle, List(Action, Bonus, Action, Action, Action).iterator))
  69. }
  70.  
Success #stdin #stdout 0.42s 382080KB
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Battle(0,1,EnemyWon)
https://ideone.com/UtECc9
language:
Scala (scala 2.12.8)
created:
9 years ago
visibility:
public

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