FixedArray.swift

public protocol VectorType {
  typealias Scalar
  var endIndex: Int {get}
  subscript(_: Int) -> Scalar {get set}
  init()
}

public struct EmptyVector<T> : VectorType {
  public init() {}
  typealias Scalar = T
  public let endIndex: Int = 0
  public subscript(idx: Int) -> Scalar {
    get { fatalError("Index out of range") }
    set { fatalError("Index out of range") }
  }
}

public struct Vector<Tail : VectorType> : VectorType, CollectionType {
  typealias Scalar = Tail.Scalar
  private var (scalar, tail): (Scalar, Tail)
  public var startIndex: Int { return 0 }
  public var endIndex: Int { return tail.endIndex + 1 }
  public subscript(idx: Int) -> Scalar {
    get { return idx == 0 ? scalar : tail[idx - 1] }
    set { idx == 0 ? (scalar = newValue) : (tail[idx - 1] = newValue) }
  }
  private init(head: Scalar, tail: Tail = Tail()) {
    scalar = head
    self.tail = tail
  }
  public init() { preconditionFailure() }
}

infix operator ⋮ {
  associativity right
  precedence 1
}


public func ⋮ <T> (lhs: T, rhs: T) -> Vector<Vector<EmptyVector<T>>> {
  return Vector(head: lhs, tail: Vector(head: rhs))
}
public func ⋮ <T, U : VectorType where U.Scalar == T> (lhs: T, rhs: Vector<U>) -> Vector<Vector<U>> {
  return Vector(head: lhs, tail: rhs)
}

let some = 1 ⋮ 2 ⋮ 3 ⋮ 4 // Vector<Vector<Vector<Vector<EmptyVector<Int>>>>>

Array(some) // [1, 2, 3, 4]