When transliterating code from distributed systems papers (uncomfortably imperative) to Haskell, I had an excellent experience with Lenses and the State monad.

When transliterating code from distributed systems papers (uncomfortably imperative) to Haskell, I had an excellent experience with Lenses and the State monad. It allows you to reproduce imperative, mutable code in functional Haskell and without mutability. The semantics are also much more restricted (in a good way) than imperative code in a real imperative language. For example, you have to specify the entire state beforehand, which prevents you from falling for ultimately unproductive temptations like global variables. You can even do for loops if you want. http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Traversable.html#v:for http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Tr... for [1,2,3] $ \i -> do counter += i print i I wrote a bit about the experience here if you're interested. It was on HN a while back. http://yager.io/Distributed/Distributed.html http://yager.io/Distributed/Distributed.html