I definitely think this should be considered a usage. Ideally, you should always be able to resolve warnings, but there'd be no straightforward way to do so if LHS-only usages cause warnings. Also, It's quite useful to use type variables only on the LHS. Usage example: https://hackage.haskell.org/package/base-4.8.1.0/docs/src/Data.Type.Equality.html#EqStar
-Michael On Thu, Dec 10, 2015 at 6:48 AM, Jan Stolarek <[email protected]> wrote: > An intersting thing came up when implementing warnings for unused type > variables in type family > patterns (#10982 / D1576): > > type family X a b where > X a a = Int > > Should we emit a warning that `a` is unused? It does not appear in the RHS > but it is actually used > because of non-linear pattern. We can fix this by prefixing both > appearances of `a` with an > underscore - this silences the warning and maintains semantics. > Nevertheless, if a variable is > unused it should be perfectly valid to replace it with an underscore - > that is not the case in > this example. Thoughts? > > Janek > > --- > Politechnika Łódzka > Lodz University of Technology > > Treść tej wiadomości zawiera informacje przeznaczone tylko dla adresata. > Jeżeli nie jesteście Państwo jej adresatem, bądź otrzymaliście ją przez > pomyłkę > prosimy o powiadomienie o tym nadawcy oraz trwałe jej usunięcie. > > This email contains information intended solely for the use of the > individual to whom it is addressed. > If you are not the intended recipient or if you have received this message > in error, > please notify the sender and delete it from your system. > _______________________________________________ > ghc-devs mailing list > [email protected] > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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