#9117: Coercible constraint solver misses one -------------------------------------+------------------------------------ Reporter: goldfire | Owner: nomeata Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by goldfire): But doesn't the constraint solver already deal with overlap somehow? For example, if we have `newtype MyMaybe a = Mk (Maybe a)`, and we want `Coercible (MyMaybe Int) (MyMaybe Age)`, there are two ways to get this.... unless there is a role annotation on `MyMaybe`, meaning only the unwrap-coerce-wrap solution is available, or unless the constructor is not available, when only the coerce-directly solution is available. So, if this all works, there has to be some way of dealing with the overlap and a small amount of "search". Is the case in this ticket somehow different/worse? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9117#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler