#11282: Injectivity annotation fails in the presence of higher-rank use of constraint family -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Actually, this has nothing to do with injective type families. If I change the code to {{{ meth :: (G a => a) -> () }}} I get an error. That error explains that `a` is untouchable, which makes some small degree of sense, given that `G a` might reduce to an equality constraint. But the original error message is quite unfortunate, because `F` is indeed injective! So this bug is really about the error message, not the rejection. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11282#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler