You could do all that with IO, sure. But the fact that IO happens to be a monad is completely irrelevant to doing that stuff. Monads are important because of

You could do all that with IO, sure. But the fact that IO happens to be a monad is completely irrelevant to doing that stuff. Monads are important because of the abstraction, not specific use cases. If you're thinking in terms of specific use cases, you're already wrong. The monad abstraction lets you abstract out all kinds of control flow operations that apply to types of the right shape. It turns out to be a very general abstraction - it appears in a lot of places. And it turns out to be a sufficiently-powerful abstraction to lift any Turing-complete control flow from functions on simple types to functions on the monadic types. So, the abstraction is general and powerful. Why isn't it used in all languages? Because most languages don't have anything like the bookkeeping mechanisms necessary to make it syntactically lightweight. Haskell, on the other hand, is sufficiently not-terrible to provide enough facility for abstraction to actually take advantage of monads. (All programming languages are terrible. Haskell is just less terrible than most.)