Unboxed tuples have no type representations
This ticket continues with the long tradition of types missing type representations (see #12082 (closed), #12132 (closed), #11120 (closed)). This time the culprit is unboxed tuples,
$ ghci
GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /home/ben/.ghci
λ> import Data.Typeable
λ> :set -XUnboxedTuples
λ> typeRep (Proxy :: Proxy (#Int, Int#))
ghc: panic! (the 'impossible' happened)
(GHC version 8.0.1 for x86_64-unknown-linux):
tyConRep (#,#)
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
The problem, as usual, is that the tycons are missing from primTyCons
.