Comment by littlestymaar

> * It's quite rare for a function to unexpectedly gain a dependency on "doing IO" in general.

I don't know where you got this, but it's definitely not the case, otherwise async would never cause problems either. (Now the problem in both cases is pretty minor, you just need to change the type signature of the call stack, which isn't generally that big, but it's exactly the same situation)

> In practice, most of your codebase will have access to an `Io`, and only leaf functions doing pure computation will not need them.

So it's exactly similar to making all of your functions async by default…