That's allowed in the IO monad, and, really, it's allowed. The idea in Haskell is to have many contexts where side effects are not allowed so that in those con

That's allowed in the IO monad, and, really, it's allowed. The idea in Haskell is to have many contexts where side effects are not allowed so that in those contexts your code must be pure, and pure code is easier to write tests for and reason about.