anchor.diff:                             "false"
                              "null"]
   
  -let isTracked obj =
  -    let notTrackedNodes = [typeof<BinaryOperatorNodeBase>
  -                           typeof<SetIdentifierNode>]
  -    let objType = obj.GetType()
  -    not <| List.exists (fun (t : Type) -> t.IsAssignableFrom(objType)) notTrackedNodes
  -
   let valueToList parser = parser >>= (Seq.singleton >> Seq.toList >> preturn)
   
   let space = pchar ' '
  
positive.code:         match reply.Status with
          | Ok -> let endPosition = stream.Position
                  let result = reply.Result :> NodeBase
                  if isTracked result then
                      result.StartLocation <- lexemLocation startPosition
                      result.EndLocation <- lexemLocation endPosition
                  reply
          | _  -> reply
  
negative.code: open Lens.SyntaxTree.SyntaxTree.Expressions
  open Lens.SyntaxTree.SyntaxTree.Operators
  open Lens.SyntaxTree.Utils
  
  let isStartTracked obj = 
      typeof<IStartLocationTrackingEntity>.IsAssignableFrom(obj.GetType())
  
  let isEndTracked obj = 
      typeof<IEndLocationTrackingEntity>.IsAssignableFrom(obj.GetType())
  
  let keywords = Set.ofList ["using"
                             "record"
  