A naive (?) solution to this problem: "Given an Array of Strings, return a String listing them with correct Oxford commas"

OxfordComma.swift

let test = [
    [""],
    ["Hello"],
    ["Hello", "World"],
    ["cat", "apple", "mac", "dog", "mouse", "seahorse"]
]

let oxford: ([String]) -> String = { strings in
    switch strings.count {
    case 1:     return strings[0]
    case 1...:  return strings.dropLast().joined(separator: ", ") + ", and " + strings.last!
    default:    return "no can do cap'n"
    }
}

let output = test.map { oxford($0) }
// [""]
// ["Hello"]
// ["Hello, and World"]
// ["cat, apple, mac, dog, mouse, and seahorse"]