Swift: Find the first element of a Sequence that matches an element of another Sequence

findFirst.swift

extension SequenceType {
    func find(predicate: Generator.Element -> Bool) -> Generator.Element? {
        for x in self {
            if predicate(x) { return x }
        }
        return .None
    }
}

infix operator <|> {}

// Alternative for Optional - return `lhs` if non-nil, otherwise return `rhs`
func <|> <A>(lhs:A?, rhs:A?) -> A? {
    return lhs.map { $0 } ?? rhs
}

// Find the first element in SequenceType argument that matches an element in `self`
extension SequenceType where Generator.Element: Equatable {
    func findFirst<S:SequenceType where S.Generator.Element == Generator.Element>(xs: S) -> Generator.Element? {
        return xs.reduce(.None) { acc, x in
            acc <|> self.find { $0 == x }
        }
    }
}

// examples:
[3,29,9,23].findFirst(20...30) // .Some(23)
[3,29,9,23].findFirst([50, 9, 3]) // .Some(9)
["a","b","c"].findFirst(["x","b"]) // .Some("b")