This is beside the point. Haskell have a number of built-in unpure operations like putStrLn. You can use the built-in IO type to execute these unpure operations

This is beside the point. Haskell have a number of built-in unpure operations like putStrLn. You can use the built-in IO type to execute these unpure operations. If you define your own type called IO you can't use it to execute unpure operations.