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Seriously, why? The only compelling argument for monadic effect systems I see is in languages with no easy-to-use and lightweight concurrency, and this is where Go shines. I thinks this is cool and all but I don't think it can ever be justified with this added complexity in Go. I have worked much with Cats Effect in Scala, which is nice but it adds some serious cognitive overhead.

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One of the design aspects is to make a distinction between functions with and without side effects (pure). In a way to tell these apart by looking at the function signature without having to read the function body. The library uses a function signature without an input but with an output for this purpose. Aside from the trivial case of a constant function, such a signature can only mean that the function has side effects.

type IO[A any] func() A

If you consider this a valid approach, then the set of monadic helper functions make it easier to compose these effectful functions with pure functions.

This article https://betterprogramming.pub/investigating-the-i-o-monad-in... contains some more detailed reasoning.

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