I was trying to get some template haskell thing to work and was messing around and ran into this bug.

Prelude> let $([d||])
ghc: panic! (the 'impossible' happened)
  (GHC version 7.8.2 for x86_64-unknown-linux):
        cvBindsAndSigs $[splice{v}]([d| |])
 
Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 
Prelude>

The following file:

{-# LANGUAGE TemplateHaskell #-}
let $([d||])
main = do
   return ()

gives the following error message:

test.hs:3:1:
    parse error (possibly incorrect indentation or mismatched brackets)

but doesn't crash. So it seems to be ghci-specific...?

the other oxford brackets work fine (or don't suffer from exactly the same bug, anyway)