uniques.swift

public struct UniquesGen<G : GeneratorType where G.Element : Hashable> : GeneratorType {
  
  typealias Element = G.Element
  
  private var prevs: Set<Element>
  private var g: G
  
  public mutating func next() -> Element? {
    return g.next().flatMap{n in prevs.contains(n) ? next() : {prevs.insert(n); return n}()}
  }
}

public struct UniquesSeq<S : SequenceType where S.Generator.Element : Hashable> : SequenceType {
  typealias Generator = UniquesGen<S.Generator>
  private let seq: S
  public func generate() -> Generator {
    return UniquesGen(prevs: [], g: seq.generate())
  }
}