The merge function does not seem to run its argument coroutines in parallel

[blamario]

Function

Control.Monad.Coroutine.merge :: forall s m x. (Monad m, Functor s) =>
                                 (forall x. [m x] -> m [x]) -> (forall x. [s x] -> s [x])
                              -> [Coroutine s m x] -> Coroutine s m [x]

appears to work properly, except that its test in the TestCoroutine? module apparently always uses only one CPU core.