Warning found:
at tests/purs/warning/NewtypeInstance2.purs:15:1 - 15:86 (line 15, column 1 - line 15, column 86)

  The derived newtype instance for
                                 
    Main.MonadWriter w           
                     (MyWriter w)
                                 
  does not include a derived superclass instance for Control.Monad.Monad.


See https://github.com/purescript/documentation/blob/master/errors/MissingNewtypeSuperclassInstance.md for more information,
or to contribute content related to this warning.