[Haskell-cafe] Question: Do block precedence

Dear Haskell-Cafe mailing list people (?) I've been writing parenthesis around do blocks since forever now, but I don't get why they are necessary. I can't seem to come up with a program where they are necessary. Am I missing something or are parenthesis around do blocks nececairy for no reason? Since parsing 'do' blocks as if they have parenthesis around them doesn't seem to break any code, why not do so? when (doBlocksNeedParenthesis) do putStrLn "This code is invalid." when (doBlocksNeedParenthesis) $ do putStrLn "This code is valid." when (doBlocksHaveInvisibleParenthesis) do putStrLn "These are equal v" when (doBlocksHaveInvisibleParenthesis) (do putStrLn "These are equal ^")