Terriermon

var vendingMachine = VendingMachine()
vendingMachine.coinsDeposited = 8
do {
    try buyFavoriteSnack(person: "Alice", vendingMachine: vendingMachine)
    print("Success! Yum.")
} catch VendingMachineError.invalidSelection {
    print("Invalid Selection.")
} catch VendingMachineError.outOfStock {
    print("Out of Stock.")
} catch VendingMachineError.insufficientFunds(let coinsNeeded) {

Terriermon

protocol Validatable { }

extension Int: Validatable { }
extension String: Validatable { }

protocol ValidatorConvertible {
    associatedtype ValidationType
    func validated(_ value: ValidationType) -> Promise<ValidationType>
}