I think I see where the confusion is coming from. A coroutine can be nexted repeatedly. A partial function can only be called once. The coroutine in the example

I think I see where the confusion is coming from. A coroutine can be nexted repeatedly. A partial function can only be called once. The coroutine in the example is just a toy, so it's effectively the same as calling a partial many times in a loop. A more interesting coroutine might encapsulate state that changes across next'ing. Yes, other kinds of functions can change state across calls, too... It turns out many techniques can accomplish the same thing.