Anything that is not Haskell 2010 is *by definition* a language extension. If you want to change the language, that is a discussion for Haskell' not GHC.
I'm not sure this is entirely true. In ghc file compiler/parser/Lexer.x it is stated. -- Pushing a new implicit layout context. If the indentation of the -- next token is not greater than the previous layout context, then -- Haskell 98 says that the new layout context should be empty; that is -- the lexer must generate {}. -- -- We are slightly more lenient than this: when the new context is start ed -- by a 'do', then we allow the new context to be at the same indentation as -- the previous context. This is what the 'strict' argument is for. I think this means that the following is valid in ghc but not in haskell 98/2010. main :: IO () main = do if True then return () else do return () Silvio