anchor.diff:  
     /// Returns a stream that runs the given job each time a value is requested
     /// before requesting the next value from the given stream.  If the given job
  -  /// fails, the returned stream also fails.
  -#if DOC
  -  ///
  -  /// Reference implementation:
  -  ///
  -  ///> let rec beforeEach yJ xs =
  -  ///>   yJ >>. xs >>=* function Nil -> nil
  -  ///>                         | Cons (x, xs) -> cons x (beforeEach yJ xs)
  -#endif
  +  /// fails, the returned stream also fails.  `beforeEach yJ xs` is equivalent
  +  /// to `pullOn (indefinitely yJ) xs`.
     val beforeEach: timeout: Job<_> -> Stream<'x> -> Stream<'x>
   
     /// Given a stream of dates, returns a stream that produces the dates after
  
positive.code:   /// is similar to
    ///
    ///> live |> samplesAfter ticks
  #endif
    val pullOn: ticks: Stream<_> -> Stream<'x> -> Stream<'x>
  
  
negative.code:   val zip: Stream<'x> -> Stream<'y> -> Stream<'x * 'y>
  
    /// `zipWithFun f xs ys` is equivalent to `zip xs ys |> mapFun (fun (x, y) ->
    /// f x y)`.
    val zipWithFun: ('x -> 'y -> 'z) -> Stream<'x> -> Stream<'y> -> Stream<'z>
  
    /// Returns a stream whose elements are computed using the given job and
  