#12564: Type family in type pattern kind -------------------------------------+------------------------------------- Reporter: int-index | Owner: goldfire Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: TypeInType, Resolution: | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: 14119 | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Current error message is a bit better ``` T12564.hs:18:3: error: • Illegal type synonym family application ‘Len @a _1’ in instance: At @a ((':) @a x _1) ('FZ @(Len @a _1)) • In the equations for closed type family ‘At’ In the type family declaration for ‘At’ | 18 | At (x ': _) FZ = x | ^^^^^^^^^^^^^^^^^^ ``` -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12564#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler