anchor.diff:  | Choice1Of2 () -> printfn "checked and executed ok"
   | Choice2Of2 exn -> printfn "execution exception: %s" exn.Message
   
  +
   (**
   Gives:
   
  
positive.code: Evaluating and executing code
  -----------------------------
  
  The F# interactive service exposes two methods that can be used for interaction. The first
  is `EvalExpression` which evaluates an expression and returns its result. The result contains
  the returned value (as `obj`) and the statically inferred type of the value:
  *)
  
negative.code: evaluation a declaration:
  *)
  
  fsiSession.EvalInteraction "let xxx = 1 + 1"
  
  (**
  
  