One of the biggest reasons for using coroutines in Haskell is when you want to mix them with effects. For example, using lazy streams to do IO can lead to unpre

One of the biggest reasons for using coroutines in Haskell is when you want to mix them with effects. For example, using lazy streams to do IO can lead to unpredictable resource usage so many people use coroutine libraries to do the IO in a more predictable manner (piper / conduits / io-streams / etc). Finally, while lazy streams go a long way, in terms of preventing the inversion of control that you usually need to use coroutines for, there are still some situations where coroutines are useful. For example try writing that consumer/producer example from the blog post he linked using only lazy streams...