Thanks for the followup! > In Haskell, the lack of side effects is by the fact IO is provided by the platform. There is no fundamental difference between Haske

Thanks for the followup! > In Haskell, the lack of side effects is by the fact IO is provided by the platform. There is no fundamental difference between Haskell's `getLine` and the DOM's `fetch`, both return a boxed value. In his talk about "effects"[1], Chris Armstrong also talked about making testing easier in Haskell, though I paid less attention to that part, to be honest. `fetch` returns a promise, but calling fetch causes the side effect to occur immediately. I don't know if that's how `getLine` works in Haskell. If I want to test code that calls `fetch` without an HTTP request actually hitting the network, I need to put in a mock `fetch`.[2] Or, if there was another return type that put the side effect in a box that the platform handles later (or not at all, in the case of a test), that seems like a win. [1]: https://www.youtube.com/watch?v=D37dc9EoFus https://www.youtube.com/watch?v=D37dc9EoFus [2]: another option, pointed out on Twitter, is that a promise (either from the fetch or from the test) could be passed in to the code under test. That seems less pleasant but requires no new machinery.