[doyougnu]

Agreed. the Haskeller in me screams "You've just implemented the IO monad without language support".

[AndyKelley]

It's not a monad because it doesn't return a description of how to carry out I/O that is performed by a separate system; it does the I/O inside the function before returning. That's a regular old interface, not a monad.

[tome]

> 1. a description of how to carry out I/O that is performed by a separate system

> 2. does the I/O inside the function before returning

How do you distinguish those two things? To put my cards on the table, I believe Haskell does 2, and I think my Haskell effect system Bluefin makes this abundantly clear. (Zig's `Io` seems to correspond to Bluefin's `IOE`.)

There is a persistent myth in the Haskell world (and beyond) that Haskell does 1. In fact I think it's hard to make it a true meaningful statement, but I can probably just about concede it is with a lot of leeway on what it means for I/O to be "performed by a separate system", and even then only in a way that it's also true and meaningful for every other language with a run time system (which is basically all of them).

The need to believe that Haskell does 1 comes from the insistence that Haskell be considered a "pure" language, and the inference that means it doesn't do I/O, and therefore the need that "something else" must do I/O. I just prefer not to call Haskell a "pure" language. Instead I call it "referentially transparent", and the problem vanishes. In Haskell program like

    main :: IO ()
    main = do
       foo
       foo

    foo :: IO ()
    foo = putStrLn "Hello"

I would say that "I/O is done inside `foo` before returning". Simple. No mysteries or contradiction.

https://hackage-content.haskell.org/package/bluefin/docs/Blu...

[endgame]

So it's the reader monad, then? ;-)

[throwawaymaths]

i mean not really? it absolutely does nothing to segregate stateful impurity into a type theoretically stateless token