Adopting FP: the good, the familiar, and the unknown

Transcript

1. Adopting FP: the good, the familiar, and the unknown Colin Jones @trptcolin
2. Adopting FP: the good, the familiar, and the unknown Colin Jones @trptcolin
3. language paradigms functional object-oriented structured logic
4. the good
5. What is functional programming? first-class functions immutability
6. first-class functions def presented_users users = User.where(active: true) users.map {|user| UserPresenter.new(user)} end
7. first-class functions def present_user lambda {|user| UserPresenter.new(user)} end def presented_users users = User.where(active: true) users.map(&present_user) end
8. immutability def get_client_id(params) params[:warehouse][:client_id] end def test_client_id_equality params = {warehouse: {client_id: 42}} client_id_1 = get_client_id(params) client_id_2 = get_client_id(params) assert_equal(client_id_1, client_id_2) end
9. immutability def get_client_id(params) params[:warehouse].delete(:client_id) end def test_client_id_equality params = {warehouse: {client_id: 42}} client_id_1 = get_client_id(params) client_id_2 = get_client_id(params) assert_equal(client_id_1, client_id_2) end
10. immutability (deftest test-client-id-equality (let [params {:warehouse {:client-id 42}} client-id-1 (get-client-id params) client-id-2 (get-client-id params)] (is (= client-id-1 client-id-2))))
11. immutability (defn- get-item-value [item] (* (:price item) (:quantity-available item))) (defn get-total-value [inventory] (->> (:items inventory) (map get-item-value) (reduce +)))
12. immutability (let [params {:warehouse {:client-id 42}} updated (update-in params [:warehouse :client-id] inc)] (println "params:" (pr-str params)) (println "updated:" (pr-str updated))) ;; params: {:warehouse {:client-id 42}} ;; updated: {:warehouse {:client-id 43}} ;; => nil
13. #1 hit benefits safer concurrency / parallelism simplicity / clarity easier testing / modularity useful constraints
14. the familiar
15. "This FP stuff sounds great… for toy examples"
16. How do I structure larger systems in FP?
17. How do I structure larger systems in OO?
18. What tools does OO provide? polymorphism namespacing encapsulation inheritance/composition data containment state change
19. What tools does FP provide? polymorphism namespacing encapsulation inheritance/composition data containment state change
20. What tools does FP provide? polymorphism namespacing encapsulation inheritance/composition data containment state change
21. OO Principles DRY 4 rules of simple design command-query separation SOLID principles package principles code smells refactorings
22. OO FP Software Principles DRY 4 rules of simple design command-query separation SOLID principles package principles code smells refactorings
23. Example: Dependency Inversion Principle A. High level modules should not depend upon low level modules. Both should depend upon abstractions. B. Abstractions should not depend upon details. Details should depend upon abstractions.
24. What is an "abstraction"? interfaces (Java, …) classes w/ only pure virtual methods (C++, …) duck typing (Ruby, …)
25. What is an "abstraction"? duck typing (Erlang, Elixir, …) generic types (Haskell, Elm, F#, …) protocols (Clojure, Swift, Elixir, …) multimethods (Clojure, CLOS, …) typeclasses (Haskell, …) signatures (ML, OCaml, …) behaviours (Erlang, …) functions (we all have these!!!)
26. the unknown
27. Risk
28. Learning curve
29. The virtues of boring tech
30. Mitigating by learning practice reading community teammates/consultants
31. Mitigating with use cases innovation budget developer tools testing breakable toys/katas low-risk applications/services
32. Takeaways
33. Reading "Why Functional Programming Matters" by John Hughes https://www.cs.kent.ac.uk/people/staff/dat/miranda/whyfp90.pdf "What is Functional Programming?" by Kris Jenkins http://blog.jenkster.com/2015/12/what-is-functional-programming.html "Go To Statement Considered Harmful" by Edsger Dijkstra http://homepages.cwi.nl/~storm/teaching/reader/Dijkstra68.pdf "Understanding Clojure's Persistent Vectors" by Jean-Niklas L'Orange http://hypirion.com/musings/understanding-persistent-vector-pt-1 "Clojure Protocols" by Stuart Halloway http://gotocon.com/dl/jaoo-aarhus-2010/slides/StuartHalloway_ClojureProtocolsArenotInterfaces.pdf "Choose Boring Technology" by Dan McKinley http://mcfunley.com/choose-boring-technology
34. Thanks! Colin Jones @trptcolin