#14101: Type synonyms can make roles too conservative -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.4.1 Component: Compiler (Type | Version: 8.2.1 checker) | Resolution: | Keywords: roles Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #8234 | Differential Rev(s): Phab:D3838 Wiki Page: | -------------------------------------+------------------------------------- Comment (by ethercrow): I'm not sure if it belongs to this ticket. I'm trying to make a specialization for leaves in a hashmap when key type is something small, e.g. Int: {{{ data LeafInt v = LI !Int v data LeafPoly k v = LP !k v type family Leaf a where Leaf Int = LeafInt Leaf k = LeafPoly k }}} The hashmap {{{ data HashMap k v = Leaf !Hash !(Leaf k v) ... }}} itself has a type role annotation: {{{ type role HashMap nominal representational }}} I get the error {{{ • Role mismatch on variable v: Annotation says representational but role nominal is required • while checking a role annotation for ‘HashMap’ }}} I tried to express the same using data family and a class with associated type, the result is the same. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14101#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler