Head and tail for Swift

head_tail.swift

extension Array {
    var match : (head: T, tail: [T])? {
      return (count > 0) ? (self[0],Array(self[1..<count])) : nil
    }
}

func map<A,B>(f: A -> B, arr: [A]) -> [B] {
    if let (head,tail) = arr.match {
        return [f(head)] + map(f, tail)
    } else {
        return []
    }
}