Isn’t code in Haskell pure by default and you have to use special keywords to have code with side effects?

There's no special keyword, just a "generic" type `IO<T>` defined in standard library which has a similar "tainting" property like `async` function coloring.

Any side effect has to be performed inside `IO<T>` type, which means impure functions need to be marked as `IO<T>` return. And any function that tries to "execute" `IO<T>` side effect has to mark itself as returning `IO<T>` as well.

It's pure even with side effects.

You basically compose a description of the side effects and pass this value representing those to the main handler which is special in that it can execute the side effects.

For the rest of the codebase this is simply an ordinary value you can pass on/store etc.