Panic "tcTyVarDetails" when :forcing a kind-polymorphic data family instance
I have
{-# LANGUAGE TypeFamilies, DataKinds, PolyKinds #-}
data family Sing (a :: k)
data instance Sing (a :: [k]) = SNil
x :: Sing '[]
x = SNil
When I load into GHCi and tried to force x
, this happened:
*Main> :force x
ghc: panic! (the 'impossible' happened)
(GHC version 7.7.20131031 for x86_64-apple-darwin):
tcTyVarDetails k{tv a3Gv} [tv]
This was tested on the build from Oct 31 -- apologies if it has since been fixed. If I make the [k]
in the instance declaration k
, the file compiles fine.
Trac metadata
Trac field | Value |
---|---|
Version | 7.7 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |