A few Array extensions

ArrayExtensions.swift

extension Array {
    /*
    'span' takes a predicate and returns a tuple where first element is longest prefix (possibly empty)
    of elements of self that satisfy 'predicate' and second element is the remainder of self:
    
    -- > [1,2,3,4,1,2,3,4].span { $0 < 3 } == ([1,2],[3,4,1,2,3,4])
    -- > [1,2,3].span { $0 < 9 } == ([1,2,3],[])
    -- > [1,2,3].span { $0 < 0 } == ([],[1,2,3])
    */
    
    func span(@noescape predicate: Element -> Bool) -> ([Element], [Element]) {
        return indexOf { !predicate($0) }
            .map { i in (Array(prefixUpTo(i)), Array(suffixFrom(i))) } ?? (self, [])
    }
    
    /*
    'partition' takes a predicate and returns a tuple of Arrays. Elements of first Array
    match the predicate, elements of second Array don't match the predicate
    
    -- > [1,2,3,4,1,2,3,4].partition { $0 < 3 } == ([1,2,1,2],[3,4,3,4])
    -- > [1,2,3].partition { $0 < 9 } == ([1,2,3],[])
    -- > [1,2,3].partition { $0 < 0 } == ([],[1,2,3])
    */
    func partition(@noescape predicate: Element -> Bool) -> ([Element], [Element]) {
        var (l,r) = ([Element](), [Element]())
        for e in self {
            predicate(e) ? l.append(e) : r.append(e)
        }
        return (l,r)
    }
    
    // a quick implementation of 'scan'
    // [1,2,3,4,5].scan(0, combine: +) == [1, 3, 6, 10, 15]
    func scan<T>(var initial: T, combine: (T, Element) -> T) -> [T] {
        var a = [T]()
        for e in self {
            initial = combine(initial, e)
            a.append(initial)
        }
        return a
    }
}