anchor.diff:  /// handles keypresses for F# Interactive
   type FSharpFsiEditorCompletion() =
       inherit TextEditorExtension()
  -    //let promptWidth = 3
  -    //let promptStart = "> "
  -    //let promptExt = "- "
       let getCaretLine (editor:TextEditor) =
           let line =
               editor.CaretLine
  
positive.code:     let mutable session = setupSession()
  
      let getCaretLine() =
          editor.CaretLine 
          |> editor.GetLine 
          |> editor.GetLineText
  
      let setCaretLine (s: string) =
          let line = editor.GetLineByOffset editor.CaretOffset
  
negative.code:                     else
                          Task.FromResult false
                  | SpecialKey.BackSpace ->
                      if x.Editor.CaretLine = x.Editor.LineCount && x.Editor.CaretColumn > 1 then
                          base.KeyPress (descriptor)
                      else
  