GHC crashes when encountering arrow syntax

Compiling the following code makes GHC 6.8.20070916 crash:

{-# LANGUAGE Arrows #-}
module ArrowSyntax where
    import Control.Arrow

    arrow :: (Arrow arrow) => arrow () ()
    arrow = proc () -> do returnA -< ()

The message is:

ghc-6.8.0.20070916: panic! (the 'impossible' happened)
  (GHC version 6.8.0.20070916 for i386-unknown-linux):
        initC: srt_lbl

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

I encountered the same behavior with other expressions using arrow syntax, so the arrow syntax really seems to be the cause of this panic.

Edited Mar 09, 2019 by Ross Paterson

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GHC crashes when encountering arrow syntax