Probably AllowAmbiguousTypes + UndecidableInstances + TypeInType

ghc.exe: panic! (the 'impossible' happened)

(GHC version 8.0.2 for x86_64-unknown-mingw32):

isInjectiveTyCon sees a TcTyCon KLN

{-# LANGUAGE RankNTypes, GADTs, TypeOperators, PolyKinds, DataKinds, TypeFamilies, AllowAmbiguousTypes, UndecidableInstances, TypeInType #-}

module MCS.Function where

import MCS.Core
--import MCS.Value
import Data.Kind -- necessary for *

type family KLN (n :: k) :: Nat where
    KLN (f :: v -> k) = S (KLN (forall t. f t))
    KLN (f :: *) = Z

type family Reveal (n :: k) (l :: Vect (KLN n) L) :: * where
    Reveal (f :: v -> k) (Cons (Label (t :: v)) l) = Reveal (f t) l
    Reveal (a :: *) Nil = a

The problem *has* to be somewhere in the KLN / Reveal interaction, so I removed everything else for this. Every other weird area is commented out or unused, and the bug vanished when KLN / Reveal was commented out. KLN shouldn't even work. If it could be interaction with the rest of the document, I'll put that back in.

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Windows
Architecture