#14991: GHC HEAD regression involving TYPEs in type families -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.5 checker) | Keywords: TypeInType, Resolution: | TypeFamilies 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 goldfire): This is conceivably correct behavior. In the last two lines, all we know about the kinds of `a` and `b` is that they are `TYPE r1` and `TYPE r2`. Because you don't have instances to promote/demote `TYPE`, GHC gets stuck. In function type signatures, GHC defaults `RuntimeRep`s to `LiftedRep`. Perhaps it should, also, in type family instances. I don't know why this behavior changed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14991#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler