anchor.diff:  //        finally
   //            handler ()
   //
  -//    // 'T * ('T -> M<'U>) -> M<'U> when 'U :> IDisposable
  +//    // 'T * ('T -> M<'U>) -> M<'U> when 'T :> IDisposable
   //    member this.Using (resource : ('T :> System.IDisposable), body : 'T -> ReaderWriterStateFunc<_,_,_,_,_>)
   //        : ReaderWriterStateFunc<'Env, 'Output, 'S1, 'S2, unit> =
   //        try body resource
  
positive.code:             : StatefulChoiceFunc<'State, 'U, 'Error> =
          bind (mapping >> ``return``) m
  
      [<CompiledName("Attempt")>]
      let attempt (generator : unit -> 'T) : StatefulChoiceFunc<'State, 'T, exn> =
          statefulChoice {
  
negative.code: type AsyncMaybeBuilder () =
      // 'T -> M<'T>
      member (*inline*) __.Return value : Async<'T option> =
          async.Return <| Some value
  
      // M<'T> -> M<'T>
      member (*inline*) __.ReturnFrom value : Async<'T option> =
          value
  
      // unit -> M<'T>
      member inline this.Zero () : Async<unit option> =
          this.Return ()
  
      // (unit -> M<'T>) -> M<'T>
      member __.Delay (generator : unit -> Async<'T option>) : Async<'T option> =
          async.Delay generator
  
      // M<'T> -> M<'T> -> M<'T>
      // or
  