type synonym to unboxed tuple causes crash

{-# LANGUAGE UnboxedTuples #-}

module Main where

-- type Null = (# #)

{-# NOINLINE showNull #-}
showNull :: (# #) -> String
showNull (# #) = "(# #)"

{-# NOINLINE showNullPair #-}
showNullPair :: (# (# #), (# #) #) -> String
showNullPair (# n1, n2 #) = "(# " ++ showNull n1 ++ ", " ++ showNull n2 ++ "#)"

main :: IO ()
main = do
    putStrLn (showNullPair (# (# #), (# #) #))

If I use the Null type synonym here instead of (# #), I get:

[1 of 1] Compiling Main             ( empty.hs, empty.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-unknown-linux):
        unboxed tuple PrimRep

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

Tried with: 8.0.1

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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