AnySequence.swift

public final class AnyGen<Element> : GeneratorType {
  private let nextFunc: () -> Element?
  public final func next() -> Element? { return nextFunc() }
  public init<G : GeneratorType where G.Element == Element>(var _ base: G) {
    nextFunc = {base.next()}
  }
}

public struct AnySeq<Element> : SequenceType {
  private let genFunc: () -> AnyGen<Element>
  public func generate() -> AnyGen<Element> { return genFunc() }
  public init<S : SequenceType where S.Generator.Element == Element>(_ base: S) {
    genFunc = {AnyGen(base.generate())}
  }
}

// Or, using AnyGenerator:

public struct AnySeqG<Element> : SequenceType {
  private let genFunc: () -> AnyGenerator<Element>
  public func generate() -> AnyGenerator<Element> { return genFunc() }
  public init<S : SequenceType where S.Generator.Element == Element>(_ base: S) {
    genFunc = {anyGenerator(base.generate())}
  }
}