#9562: Type families + hs-boot files = unsafeCoerce -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: GHC | Blocked By: accepts invalid program | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by adamgundry): Ouch! I conjecture that the following lighter restriction will restore type soundness: a hs-boot file must list all type instance declarations used (transitively) in the typechecking of any definition whose declaration appears in the hs-boot file. (That is, a type instance declaration must be listed if its axiom would appear in the fully-unfolded elaborated Core term corresponding to any declaration in the hs-boot file.) Even if this conjecture is correct, of course, this may be unreasonably hard to implement/explain. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9562#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler