Given that you 'forkIO' functions in the IO monad, i.e. impure functions, what do you mean by that? 'forkIO' in Haskell is essentially the same as dispatching a green thread in any other language, e.g. the same as 'go' in Go.
Haskell/GHC's threads are primarily a concurrency construct, not a parallelism one. You 'forkIO' a bunch of impure functions and communicate between them using channels, STM, etc., exactly the same as in other languages. For parallelism in pure functions there are much better tools--par seq, parallel strategies, repa, Data Parallel Haskell, etc.
