ghci-only panic

{-# LANGUAGE TypeFamilies #-}

main = do
        b <- a
        return (+b) -- return b -- is the same
        
a = return undefined

x = ()

*Main> main
ghc: panic! (the 'impossible' happened)
  (GHC version 8.10.3:
	nameModule
  system $dNum_a1LQ
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1179:37 in ghc:Outputable
        pprPanic, called at compiler/basicTypes/Name.hs:251:3 in ghc:Name

*Main> x
ghc: panic! (the 'impossible' happened)
  (GHC version 8.10.3:
	nameModule
  system $dMonad_a20B
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1179:37 in ghc:Outputable
        pprPanic, called at compiler/basicTypes/Name.hs:251:3 in ghc:Name