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Hey y'all, I saw that arrow now uses suspend functions to represent side effects, but I haven't found anything about the reasoning. Is it a marker? So if you call an impure suspend function, your function is now impure and thus must be suspended? (edit: marker, not sentinel)

I think you meant “marker” not “sentinel” :+1:

It's maybe also because side effects are usually used for I/O, and `suspend (T) -&gt; V` is isomorphic with `IO`? Not sure though.

Here is a small doc about the reasoning behind it. <https://github.com/arrow-kt/arrow-fx/tree/master/arrow-docs/docs/io>

It will be added to the docs with the next release, when we actually deprecate `IO`.

`suspend` is indeed isomorphic with `IO`, and you can leverage it to achieve the exact same semantics and guarantees as with `IO`. Only `suspend` is native to the Kotlin Compiler,  and thus results in more efficient programs.
With the added benefit that this makes Arrow's functional effect system much more idiomatic in Kotlin.