Hi, Am Montag, den 21.10.2013, 13:08 -0400 schrieb Richard Eisenberg:
For the curious, you can see the code in my github fork at https://raw.github.com/goldfirere/ghc/master/compiler/typecheck/TcDeriv.lhs (search for `role_errs`). An example of the new error message is in https://github.com/goldfirere/testsuite/blob/master/tests/roles/should_fail/...
you say Roles10.hs:16:12: Can't make a derived instance of ‛C Age’ (even with cunning newtype deriving): it is not type-safe to use GeneralizedNewtypeDeriving on this class; ‛meth’, specialized to type ‛a -> F a’, cannot be converted safely In the newtype declaration for ‛Age’ but shouldn’t that be either Roles10.hs:16:12: Can't make a derived instance of ‛C Age’ (even with cunning newtype deriving): it is not type-safe to use GeneralizedNewtypeDeriving on this class; the type of ‛meth’, ‛a -> F a’, cannot be converted safely In the newtype declaration for ‛Age’ or Roles10.hs:16:12: Can't make a derived instance of ‛C Age’ (even with cunning newtype deriving): it is not type-safe to use GeneralizedNewtypeDeriving on this class; ‛meth’, specialized to type ‛Age -> F Age’, cannot be converted safely In the newtype declaration for ‛Age’ (I’m confused by “specialized to” when the type as printed is not specialized.) Greetings, Joachim -- Joachim Breitner e-Mail: mail@joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata@joachim-breitner.de