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Opened by Serge Kosyrev@_deepfireReporter

ghc-8.0.1-rc4: tyConRoles sees a TcTyCon

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UnicodeSyntax #-}

type Constrd a = Num a ⇒ a

data ADT a = ADT (Constrd a) ExistentiallyLost

data ExistentiallyLost = ∀ u. TC u ⇒ ExistentiallyLost u

class u ~ (ATF1 u, ATF2 u) ⇒ TC u where
    type ATF1    u ∷ *
    type ATF2    u ∷ *
    uie_handlers   ∷ ADT Int

-- Loop:
--  - ADT depends on ExistentiallyLost (also the Constrd appendage)
--  - ExistentiallyLost depends on TC
--  - TC depends on ADT

-->

[1 of 1] Compiling Main             ( /home/deepfire/src/ghc-testcases/tyconroles-sees-a-tctycon-tyalias.hs, interpreted )
<- ghc: panic! (the 'impossible' happened)
     (GHC version 8.0.0.20160421 for x86_64-unknown-linux):
   	tyConRoles sees a TcTyCon Constrd

   Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Edited by Serge Kosyrev