anchor.diff:      inherit System.EventArgs()
       member this.Lang = lang
   
  -type TreeGenerationState<'node> = 
  +(*type TreeGenerationState<'node> = 
       | Start
       | InProgress of 'node * AstNode list
  -    | End of 'node
  +    | End of 'node*)
   
   exception LexerException of string * obj
   
  
positive.code:                 |> Array.map 
                      (
                          function 
                              Smbl e -> (sprintf "%s%c" lexerErrMsg <| fst e), snd e |> getDocumentRange 
                              | e -> failwithf "Unexpected tokenization result: %A" e
                      )
                  |> Array.iter addLError 
  
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
  