anchor.diff:    e.Message
   
   let format_md5 bytes =
  -  let sb = 
  -    Array.fold 
  +  let sb =
  +    Array.fold
         (fun (acc:StringBuilder) (by:byte) ->
           acc.Append(by.ToString("x2")))
         (new StringBuilder())
  
positive.code: let write_hints (_: string) (_: hints_db): unit =
    failwith "[record_hints_json]: not implemented"
  
  let read_hints (_: string): option<hints_db> =
    failwith "[record_hints_json]: not implemented"
  
negative.code: type time = System.DateTime
  let now () = System.DateTime.Now
  let time_diff (t1:time) (t2:time) : float * int =
      let ts = t2 - t1 in
      ts.TotalSeconds, int32 ts.TotalMilliseconds
  let record_time f =
      let start = now () in
      let res = f () in
      let _, elapsed = time_diff start (now()) in
      res, elapsed
  let get_file_last_modification_time f = System.IO.File.GetLastWriteTime f
  