Warning found:
at tests/purs/warning/NewtypeInstance4.purs:23:1 - 23:86 (line 23, column 1 - line 23, column 86)

  The derived newtype instance for
                                 
    Main.MonadWriter w           
                     (MyWriter w)
                                 
  implies an superclass instance for Main.MonadTell which could not be verified.


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