I was just doing the usual incantation for an exception type:

    data DatagramException = ...
      deriving stock (Eq,Show)
    instance Exception Datagram

And it suddenly hit me what a shame it was that I cannot put the Exception instance in a deriving clause like the others. It would be more visually pleasing to write:

    data DatagramException = ...
      deriving stock (Eq,Show)
      deriving defaulted (Exception)

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-Andrew Thaddeus Martin