#11120: Missing type representations -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: patch Priority: high | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1769 Wiki Page: | -------------------------------------+------------------------------------- Description changed by bgamari: Old description:
When I say
{{{ {-# LANGUAGE DataKinds #-}
module Bug where
import Data.Typeable
foo = typeRep (Proxy :: Proxy '[]) }}}
I get
{{{ GHC error in desugarer lookup in Bug: Can't find interface-file declaration for variable tc'[] Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.11.20151120 for x86_64-apple-darwin): initDs IOEnv failure }}}
And I think there may be more trouble. Below are notes I have written to ghc-devs:
------------------------------
I'm a bit confused by the new handling of `Typeable`.
1. You say (in `Note [Grand plan for Typeable]`) that there is trouble making the `TyCon`/`Module` information for the types in `GHC.Types`. But what precisely goes wrong? I agree that it seems a bit fishy, but I don't actually see the spot where trouble lurks. Did you try this?
2. Even more bizarre would be putting `TyCon`/`Module` info for `GHC.Prim` stuff (I'm thinking about the super-magical `TYPE` from my branch) right in `GHC.Prim`. But still I can't quite articulate what goes wrong. There is no Prim.hi file that would be wonky. And, provided that `GHC.Types` itself doesn't try to solve a `Typeable` constraint, no one would ever notice the weird dependency. I recognize that this means we'd have to build the info somewhere manually in GHC, but I don't think that would be too hard -- and I think easier than the current story around name-mangling just so that you can write the typereps by hand in `Data.Typeable.Internal`. There's also not very many lifted tycons in `GHC.Prim`. I count `TYPE` and `RealWorld`, and that's it.
For what it's worth, a weird dependency from `GHC.Prim` to `GHC.Types` actually works in practice. I put `Levity` in `GHC.Types` but `TYPE :: Levity -> TYPE 'Lifted` in `GHC.Prim`. No one complained.
3. Let's assume that we really can't clean up this mess. It still seems that several `TyCon`s are missing from `Data.Typeable.Internal`. Like promoted nil and cons, and `Nat`, and `Symbol`. At the least, we should put a loud comment in the export list of `GHC.Types` saying that everything defined there must be accompanied by a definition in `Data.Typeable.Internal`.
4. `Data.Typeable.Internal` uses `mkGhcTypesTyCon`, which refers to `GHC.Types`. But this function is used also for things from `GHC.Prim`, like `(->)`. Solving `Typeable (->)` works fine. But I'm sure there's trouble lurking here.
New description: When I say {{{#!hs {-# LANGUAGE DataKinds #-} module Bug where import Data.Typeable foo = typeRep (Proxy :: Proxy '[]) }}} I get {{{ GHC error in desugarer lookup in Bug: Can't find interface-file declaration for variable tc'[] Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.11.20151120 for x86_64-apple-darwin): initDs IOEnv failure }}} And I think there may be more trouble. Below are notes I have written to ghc-devs: ------------------------------ I'm a bit confused by the new handling of `Typeable`. 1. You say (in `Note [Grand plan for Typeable]`) that there is trouble making the `TyCon`/`Module` information for the types in `GHC.Types`. But what precisely goes wrong? I agree that it seems a bit fishy, but I don't actually see the spot where trouble lurks. Did you try this? 2. Even more bizarre would be putting `TyCon`/`Module` info for `GHC.Prim` stuff (I'm thinking about the super-magical `TYPE` from my branch) right in `GHC.Prim`. But still I can't quite articulate what goes wrong. There is no Prim.hi file that would be wonky. And, provided that `GHC.Types` itself doesn't try to solve a `Typeable` constraint, no one would ever notice the weird dependency. I recognize that this means we'd have to build the info somewhere manually in GHC, but I don't think that would be too hard -- and I think easier than the current story around name-mangling just so that you can write the typereps by hand in `Data.Typeable.Internal`. There's also not very many lifted tycons in `GHC.Prim`. I count `TYPE` and `RealWorld`, and that's it. For what it's worth, a weird dependency from `GHC.Prim` to `GHC.Types` actually works in practice. I put `Levity` in `GHC.Types` but `TYPE :: Levity -> TYPE 'Lifted` in `GHC.Prim`. No one complained. 3. Let's assume that we really can't clean up this mess. It still seems that several `TyCon`s are missing from `Data.Typeable.Internal`. Like promoted nil and cons, and `Nat`, and `Symbol`. At the least, we should put a loud comment in the export list of `GHC.Types` saying that everything defined there must be accompanied by a definition in `Data.Typeable.Internal`. 4. `Data.Typeable.Internal` uses `mkGhcTypesTyCon`, which refers to `GHC.Types`. But this function is used also for things from `GHC.Prim`, like `(->)`. Solving `Typeable (->)` works fine. But I'm sure there's trouble lurking here. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11120#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler