> As soon as you have side-effects (an IO is a side-effect) you can through your assumptions about "strict conformation to definition" out of the window

You misunderstand what an IO action is. An IO action in Haskell is a value which describes a side effect. For example, an IO Int is a value that describes a side effect which, at runtime will produce a value of type Int inside the IO monad.

The difference is that the IO Int is a value, it’s a constant which describes how to perform something at runtime (also called promises in some languages). It’s like a callback function, which takes a value as an argument that will be available when it’s called (at runtime).