#14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal -------------------------------------+------------------------------------- Reporter: hvr | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #14236 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Crumbs. comment:15 exposes a completely new bug in float-out. I have a fix validating. The relevant Note is {{{ {- Note [Floating and kind casts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this case x of K (co :: * ~# k) -> let v :: Int |> co v = e in blah Then, even if we are abstracting over Ids, or if e is bottom, we can't float v outside the 'co' binding. Reason: if we did we'd get v' :: forall k. (Int ~# Age) => Int |> co and now 'co' isn't in scope in that type. The underlying reason is that 'co' is a value-level thing and we can't abstract over that in a type. So if v's /type/ mentions 'co' we can't float it out beyond the binding site of 'co'. That's why we have this as_far_as_poss stuff. Usually as_far_as_poss is just tOP_LEVEL; but occasionally a coercion variable (which is an Id) mentioned in type prevents this. Example Trac #14270 comment:15. }}} However this is ''not'' the original bug for this ticket. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14270#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler