A coroutine is a computation that can `yield`, suspending itself and passing control back up to the caller. It can then be resumed at the caller's leisure.

An function with an effect (in this sense) is a function which can ask a handler to `perform` some effect for it. This suspends the function and passes control to whichever handler is in scope for that call, allowing that handler to resume the function at its leisure.

I suspect that you're misunderstanding what is meant by effect, because despite buzz about them and backend support for them in OCaml 5, they aren't yet implemented with syntax and type-level support in any mainstream languages I'm aware of.