[m_arnold]

>A good example would be a program that runs fine suddenly now needs a "timeout" on an operation. FP implementations now need to thread the notion of time from somewhere near the top of the implementation the whole way down the chain to the function that needs "time".

A sufficiently complicated FP codebase almost certainly has some form of effects management in place (monad transformers or algebraic effects, for instance), so adding a timeout is as simple as adding the effect to the type signature at the top level and then letting the compiler tell you all the places you need to wire it up. I've done this in many codebases. It's actually a dream, as the type system won't allow you to make a mistake.