#8177: Roles for type families -------------------------------------+------------------------------------- Reporter: simonpj | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by goldfire): Roles for data families (associated or not) cannot be inferred, because they are open. But, theoretically, they can be declared and then checked. That is the subject of this ticket. So, it conceivable to give the roles you ask for. But, you don't seem to need those roles, because you seem interested in coercing in and out of the newtype, not among different instantiations of the newtype. This is possible as long as the newtype constructor (`Quantity'`) is in scope. Roles aren't a part of the story, in your case. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8177#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler