I don't really have strong feelings about source file organization, but the way it works in Haskell is that all IO actions have type "IO a", where "a" is the ty

I don't really have strong feelings about source file organization, but the way it works in Haskell is that all IO actions have type "IO a", where "a" is the type of the action's result. To do multithreading, you just do e.g. foo :: IO () -- optional type declaration foo = forever (print "hi") forkIO foo Now Foo will run in its own green thread forever. Very simple. This works with any IO action. You can put it in whatever file you like. For communicating across threads you have many great options like STM. If you like Go-style chans, there are libraries that provide various types of chans.