Rob Napier has been to Monad, to the Functor of Doom. He has seen the map, flattened and lensed. He has folded the infinite, lifted a Maybe, and he would do it all over again. But from what he has seen, from Haskell to Church, we can rely on one truth, which is this: Swift is not a functional programming language. Pushing too hard to make it one fights Swift and breaks Cocoa. However, Swift has absorbed some fantastic lessons from the functional world, and while value types may not quite be the present, they are clearly the future. Rob explores how decades of work in functional languages have influenced Swift, and how you can use those features best while staying true to Swift, playing nice with Cocoa, and embracing Protocol Oriented Programming.