anchor.diff:      let ft = f.Type
       let parsePrimitiveField t =
           if t = typeof<DateTime> then
  -            match getDateTimeFormat f with
  -            | None -> parsePrimitiveType t
  -            | Some fmt -> parseDateTime fmt
  +            parseDateTime (getDateTimeFormat f)
           else
               parsePrimitiveType t
       if isPrimitive ft then
  
positive.code:     | true, x -> Some (box x)
      | false, _ -> None
  
  let parseDateTime (fmt: string) =
      let rT = System.Globalization.DateTimeStyles.RoundtripKind
      opt <| fun x -> DateTime.TryParseExact(x, fmt, System.Globalization.CultureInfo.InvariantCulture, rT)
  
  let writeDateTime (fmt: string) =
      fun (x: obj) -> (x :?> DateTime).ToString(fmt)
  
  /// Dict<type, (encode * decode)>
  
negative.code:                 s |> Seq.iteri (fun i c ->
                      writeEscaped b (i + 1 = s.Length) c)
                  b.Flush())))
      d.Add(typeof<DateTime>, (parseDateTime None, writeDateTime None))
      d
  
  let isPrimitive t =
  