If I look at the production for strict_mark in the parser https://github.com/ghc/ghc/blob/master/compiler/parser/Parser.y#L1355 strict_mark :: { Located ([AddAnn],HsBang) } : '!' { sL1 $1 ([],HsUserBang Nothing True) } | '{-# UNPACK' '#-}' { sLL $1 $> ([mo $1,mc $2],HsUserBang (Just True) False) } | '{-# NOUNPACK' '#-}' { sLL $1 $> ([mo $1,mc $2],HsUserBang (Just False) True) } -- ***Correct? | '{-# UNPACK' '#-}' '!' { sLL $1 $> ([mo $1,mc $2],HsUserBang (Just True) True) } | '{-# NOUNPACK' '#-}' '!' { sLL $1 $> ([mo $1,mc $2],HsUserBang (Just False) True) } I would expect the final True or False value to reflect the presence of the '!' mark. But the second line has no '!' but returns True. I suspect this is an error. Alan