Algebraic data type in Swift.

adt.swift

// cf. https://ja.wikipedia.org/wiki/%E4%BB%A3%E6%95%B0%E7%9A%84%E3%83%87%E3%83%BC%E3%82%BF%E5%9E%8B

enum Node {
    case leaf(Int)
    indirect case branch(Node, Node)
}

func dump(node: Node) {
    func iter(node: Node) {
        switch node {
        case let .leaf(x):
            print(x, terminator: "")
        case let .branch(left, right):
            print("(", terminator: "")
            iter(left)
            print(" . ", terminator: "")
            iter(right)
            print(")", terminator: "")
        }
    }

    iter(node)
    print()
}

dump(.leaf(1))
// 1
dump(.branch(.leaf(1), .leaf(2)))
// (1 . 2)
dump(.branch(.branch(.leaf(1), .leaf(2)), .leaf(3)))
// ((1 . 2) . 3)