#12159: Record-like GADTs with repeated fields (of same type) rejected -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by adamgundry): A few of us discussed this and believe that both cases above can be covered with a single generalisation: for all the constructors that mention the field, require that the field types are the same, then take the anti-unifier of all the result types and check that this includes all the variables mentioned by the common field type. For example: {{{#!hs data S x where S1 :: { f :: Maybe a } -> S ([a], Int) S2 :: { f :: Maybe a } -> S ([a], Bool) f :: S ([a], b) -> Maybe a }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12159#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler