anchor.diff:                  |> Array.map 
                       (
                           function 
  -                            Smbl e -> (sprintf "%s%c" lexerErrMsg <| fst e), snd e |> getDocumentRange 
  +                            Smbl (char, position) -> (sprintf "%s %c" lexerErrMsg char), position |> getDocumentRange 
                               | e -> failwithf "Unexpected tokenization result: %A" e
                       )
                   |> Array.iter addLError 
  
positive.code:     let mutable forest: list<Tree<'TokenType> * _> = [] 
      let mutable otherForest : list<OtherTree<'TokenType>> = []
  
      let mutable generationState : TreeGenerationState<'node> = Start
      
      ///creates instance of LexingFinishedArgs
      let prepareToTrigger (graph : ParserInputGraph<'TokenType>) tokenToTreeNode = 
  
negative.code: open YC.FSA.FsaApproximation
  open YC.FSA.GraphBasedFsa
  
  let lexerErrMsg = "Unexpected symbol:"
  let parserErrMsg = "Syntax error. Unexpected token"
  let undefinedVariableErrMsg = "Undefined variable"
  
  type DrawingGraph (vertices : IEnumerable<int>, edges : ResizeArray<TaggedEdge<int, string>>) =
      member this.Vertices = vertices
  