
#8177: Roles for type families -------------------------------------+------------------------------------- Reporter: simonpj | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 7.6.3 Resolution: | Keywords: TypeFamilies 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 glguy): I'd like to share my usecase for wanting this feature Given the following type: {{{#!haskell -- | Family of N-ary operator types. type family Op n a b where Op 'Z a b = b Op ('S n) a b = a -> Op n a b }}} I'd love to be able to {{{#!haskell coerce :: Coercible a b => Op n a c -> Op n b c }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8177#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler