[kazagistar]

Many of the same effects can be obtained using even non-functional languages in a disciplined way. However, many of the best strategies and patterns for constructing pure, stateless software are enshrined in the Haskell standard libraries.

Once you learn the techniques and programming styles of Haskell, you can certainly apply those ideas elsewhere, but they lose a lot of their power when you (or another developer on the same code base) start "cheating".