Practically anything in Haskell * Monads. Yes - the big scary word that makes increadibly easy parsers, IO, operations on Lists and other things so easy (once you notice common pattern) * Arrows. The same for advanced users ;) * Standard stuff like lambdas etc. * Currying functions * Algebraic data types * Pattern matching And many more. PS. Yes. I am Haskell fanboy if anyone asked.