anchor.diff:  
       override expr.ToString() =
         match expr with
  -      | BinaryOperation (op, lhs, rhs) -> sprintf "%s %s %s" (lhs.ToString()) (string op) (rhs.ToString())
  +      | BinaryOperation (op, lhs, rhs) -> sprintf "%O %O %O" lhs op rhs
         | Number n -> sprintf "%f" n
         | Variable identifier -> sprintf "%s" identifier 
         | Call(fn, args) ->
  
positive.code:         do 
            printf "%s" prompt
            let lines = readLines scanner
            if String.IsNullOrWhiteSpace(lines)
              then runRepl ()
            let result = Parser.run lines
            Parser.showResult result
            runRepl ()
  
negative.code:     | Success(result, _, _) ->
        do
          printfn ""
          printfn "=> %O" result
          printfn ""
      | Failure(message, _, _) ->
        do 
  