panic: Unify.uTys_s: mismatched type lists!
This erroneous program provokes a panic instead of a type error, with GHC 6.8.3, 6.10.4 and 6.12.1. I don't have any recent snapshots to hand to try.
{-# LANGUAGE GADTs #-}
data Id p x y = Id (p x y)
data Sealed p where
Sealed :: p x -> Sealed p
rp :: Bool -> Maybe (w (Id p))
rp _ = Just rp'
where rp' :: Sealed (Id p x)
rp' = undefinedghc: panic! (the 'impossible' happened)
(GHC version 6.12.1 for x86_64-unknown-linux):
Unify.uTys_s: mismatched type lists!Trac metadata
| Trac field | Value |
|---|---|
| Version | 6.8.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
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