1. Yetanotherpresentationon MONADS MarcinGryszko @mgryszko

2. whyam I doingthis?

3. accordingto Brian Marick… http://www.vimeo.com/20717301

4. Thereisanancient Mayan profecy thatstatesthatsomedayevery single human onearthwillhave done a tutorial aboutmonads and onthatpointthepurpose of theuniversewillhavebeenachieved and allhumanswillascenttoparadise

5. I’ll try to do my bit so thathumanity can reach nirvana

6. origins

7. XVIII century

8. Gottfried 1714 Monadologie

9. eternal indecomposable individual hierarchical and aggregated autonomic and independent can change itself according to some intrinsic laws infinite space, time matter, and motion are phenomenal atom human being soul god – first monad ultimate elements of the universe

10. XX century

11. categorytheory

12. abstractview of mathematical concepts (which are already quite abstract )

13. categories have: objects morphisms or maps or arrows see a relationship with classes, objects and methods?

14. defines monad howitisrelatedtofunctionalprogramming?

15. functionalprogramming

16. what are monads?

17. containers generalized interface for sequential computations pattern for transmitting state using functions without mutation

18. what defines a monad?

19. monadictypeM java.util.List unitoperation value -> monad constructor/factory method [1, 2, 3] (Integer -> List<Integer>) bindoperation monad -> next monad, exposing its internal value for a transformation function any method in Groovy taking a closure as param [1, 2, 3].bind({ x -> [x, x + 1] }) == [1, 2, 2, 3, 3, 4]

20. what does bind? (typically)

21. Take a function and apply it to all values inside the monad Each invocation returns monad M<U> defintermediateMonads = collect { x -> f(x) } Extract U values from all intermediate M<U> monads and assemble the final M<U> monad intermediateMonads.flatten()

22. monadic laws (or when a monad is a monad)

23. 1. identity m.bind { x -> unit(x) } ≡ m transforming to unit doesn’t change a monad

24. 2. unit unit(x).bind(f) ≡ f(x) unit must preserve the value inside the monad

25. 3. associativity m.bind(f).bind(g) ≡ m.bind{ x -> f(x).bind(g) } order of monad composition doesn’t matter

26. monadic zeros (optional, empty monad) []

27. 1. bindingwithzero m.flatMap({ x -> mzero})≡ mzero 2. unit mzero.bind(f) ≡ mzero 3. plus mzero.plus(m) ≡ m m.plus(mzero) ≡ m

28. examples ListAsMonad IO State Result

29. sources https://github.com/dsrkoc/monadologie http://james-iry.blogspot.com/2007/09/monads-are-elephants-part-1.html http://james-iry.blogspot.com/2007/10/monads-are-elephants-part-2.html http://james-iry.blogspot.com/2007/10/monads-are-elephants-part-3.html http://james-iry.blogspot.com/2007/11/monads-are-elephants-part-4.html

30. Thank you!