GHC panic with DataKinds and TypeOperators
The following program causes a GHC panic:
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE KindSignatures #-}
import GHC.TypeLits
data Proxy (n :: Nat) = Proxy
data Foo a = Foo a
foo :: Foo (Proxy (2 * 2))
foo = Foo _
The error message is:
ghc: panic! (the 'impossible' happened)
(GHC version 8.0.2 for x86_64-unknown-linux):
initTc: unsolved constraints
WC {wc_insol = [W] __aBJ :: t_aBI[tau:1] (CHoleCan: _)}