问获取“值x不是xyz的成员”

EN

class Pouring(val capacity : Vector[Int] ) {

  type State = Vector[Int]

  val initialState : State = capacity map ( x => 0 )

  // Moves
  trait Move {
    def change( state : State ) : State
  }
  case class Empty( glass: Int )        extends Move {
    def change( state: State ) = state updated( glass, 0 )
  }
  case class Fill( glass: Int )         extends Move {
    def change( state: State ) = state updated( glass, capacity( glass ) )
  }
  case class Pour( from: Int, to: Int ) extends Move {
    def change( state: State ) = {
      val amount = state(from) min (capacity(to) - state(to))
        state.updated( from, state(from) - amount )
             .updated( to,   state(to)   + amount )
    }
  }

  class Path(history: List[Move]) {
    def endState : State = (history foldRight initialState)(_ change _)
    def extend(move: Move) = new Path( move :: history )
    override def toString = (history.reverse mkString " ") + " => " + endState
  }

  val initialPath = new Path(Nil)

  val glasses = capacity.indices

  val moves =
    ( for ( g <- glasses ) yield Empty(g) ) ++
    ( for ( g <- glasses ) yield Fill(g) ) ++
    ( for ( from <- glasses ; to <- glasses if from != to ) yield Pour(from,to) )


  def from( paths: Set[Path] ): Stream[Set[Path]] =
    if ( paths.isEmpty ) Stream.empty
    else {
      val more = for {
        path <- paths
        move <- moves
      } yield path.extend( move )
      paths #:: from( more )
    }

  val pathSets = from(Set(initialPath))

}

object testing {
  val problem = new Pouring(Vector(4, 7))

  problem.initialState // works
  problem.glasses      // works
  problem.moves        // works
  problem.initialPath  // fails
  problem.pathSets     // fails
}