[Haskell-cafe] Equivalent of if/then/else for IO Bool?

Is there some sort of equivalent of the if/then/else construct for use in the IO monad? For instance the following can get quite tedious:

do bool <- doesFileExist filename if bool then sth else sth'

Is there a more compact way of writing that? Something akin to:

condM (doesFileExist filename) (sth) (sth')

Or maybe there's a more sensible way of doing the above that I've missed. I seem to use endless alternate conditions sometimes and there's bound to be a better way.