 
 	case End(Box<Index>)
 	case Recursive(Box<Index>, Box<Description>)
+	case Argument(Box<Index>, Any -> Description)
 }
 
 


	public func analysis<T>(
		@noescape #ifEnd: Index -> T,
		@noescape ifRecursive: (Index, Description) -> T) -> T {
		switch self {
		case let .End(index):
			return ifEnd(index.value)
		case let .Recursive(index, description):
			return ifRecursive(index.value, description.value)
		}
	}


	var end: Index? {
		return analysis(
			ifEnd: unit,
			ifRecursive: const(nil),
			ifArgument: const(nil))
	}

	var recursive: (Index, Description)? {
		return analysis(
			ifEnd: const(nil),
			ifRecursive: unit,
			ifArgument: const(nil))
	}


