panic in arrow code "foo = returnA -< []"

[Ross Paterson]

On Fri, Mar 12, 2004 at 01:30:58PM -0500, Isaac Jones wrote:
> The following malformed code causes a panic in ghc 6.2, and some folks
> on IRC tried it in various CVS snapshots, where it also breaks.
> 
> module Main where
> import Control.Arrow
> 
> foo = returnA -< []

It's not legal to use -< except inside proc, so the bug is that this isn't
being rejected.  Will check.