Typeable solver regression
This bug is known and fixed in master. Simon and Austin and Iavor are all aware of it. This ticket exists to ensure that the fix doesn't get lost.
This code breaks under the Typeable solver in 7.10.1-rc3 and is fixed in master.
The relevant commit in master is 3a0019e3 : Improve Typeable solver.
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE FlexibleContexts #-}
module Bug where
import Data.Typeable
newtype V n a = V [a]
class Typeable a => C a
instance (Typeable (V n), Typeable a) => C (V n a)
-- Bug.hs:13:10:
-- Could not deduce (Typeable (V n a))
-- arising from the superclasses of an instance declaration
-- from the context (Typeable (V n), Typeable a)
-- bound by the instance declaration at Bug.hs:13:10-50
-- In the instance declaration for ‘C (V n a)’Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.10.1-rc3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | highest |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | diatchki |
| Operating system | |
| Architecture |