Perhaps you could write _everything_ in monadic style, and then derive the non-monadic version by running it on an "empty" state monad. But then if everything was already monadic you wouldn't need the non-monadic version.. :) ...
Perhaps the "inherent disadvantage" is that functions written in the monadic style must have different types compared with their conceptually similar non-monadic functions..
mapM :: Monad m => (a -> m b) -> [a] -> m [b] map :: (a -> b) -> [a] -> [b]
filter :: (a -> Bool) -> [a] -> [a] filterM :: (Monad m) => (a -> m Bool) -> [a] -> m [a]
foldl :: (a -> b -> a) -> a -> [b] -> a foldM :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m a
Some would say "but they're different functions!", others would say "close enough".
I imagine this would be an absolute pain for library writers. Notice that we get Data.Map.map but no Data.Map.mapM - or perhaps there's some magical lifting combinator that I am not aware of?
Ben.