See https://ghc.haskell.org/trac/ghc/ticket/8745 and https://ghc.haskell.org/trac/ghc/ticket/8827 which discuss this problem at length.
The short answer: It's conceivable that a role-unaware library author would have abstraction expectations that are defeated through the use of `coerce`. I would strongly welcome a proposal for how to make `coerce`, and hence GeneralizedNewtypeDeriving, to be considered Safe for 7.10. Richard On Aug 15, 2014, at 4:04 PM, Wolfgang Jeltsch <g9ks1...@acme.softbase.org> wrote: > Hi, > > I would expect the function > > coerce :: Coercible a b => a -> b > > to be safe in the sense of Safe Haskell. However, the Data.Coerce module > is marked “Unsafe”. The coerce function is also available via GHC.Exts > and GHC.Prim. The former module is marked “Unsafe”, but the latter is > (surprisingly) marked “Safe-Inferred”. > > What are the reasons behind this? > > All the best, > Wolfgang > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
