Panic "tcTyVarDetails" in GHCi when :forcing a data family instance
I loaded the following code into GHCi:
{-# LANGUAGE GADTs, DataKinds, KindSignatures, TypeFamilies, PolyKinds #-}
data Nat = Zero | Succ Nat
data family Sing (a :: k)
data instance Sing (a :: Nat) where
SZero :: Sing Zero
SSucc :: Sing n -> Sing (Succ n)
Then. I run these commands at the prompt:
*Main> let x = SSucc SZero
*Main> :f x
The response is
ghc: panic! (the 'impossible' happened)
(GHC version 7.7.20121031 for x86_64-apple-darwin):
tcTyVarDetails
<<details unavailable>>
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | GHCi |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |