Adopting FP: the good, the familiar, and the unknown Colin Jones @trptcolin

Adopting FP: the good, the familiar, and the unknown Colin Jones @trptcolin

language paradigms functional object-oriented structured logic

the good

What is functional programming? first-class functions immutability

first-class functions def presented_users users = User.where(active: true) users.map {|user| UserPresenter.new(user)} end

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

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

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

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))))

immutability (defn- get-item-value [item] (* (:price item) (:quantity-available item))) (defn get-total-value [inventory] (->> (:items inventory) (map get-item-value) (reduce +)))

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

#1 hit benefits safer concurrency / parallelism simplicity / clarity easier testing / modularity useful constraints

the familiar

"This FP stuff sounds great… for toy examples"

How do I structure larger systems in FP?

How do I structure larger systems in OO?

What tools does OO provide? polymorphism namespacing encapsulation inheritance/composition data containment state change

What tools does FP provide? polymorphism namespacing encapsulation inheritance/composition data containment state change

What tools does FP provide? polymorphism namespacing encapsulation inheritance/composition data containment state change

OO Principles DRY 4 rules of simple design command-query separation SOLID principles package principles code smells refactorings

OO FP Software Principles DRY 4 rules of simple design command-query separation SOLID principles package principles code smells refactorings

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.

What is an "abstraction"? interfaces (Java, …) classes w/ only pure virtual methods (C++, …) duck typing (Ruby, …)

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!!!)

the unknown

Risk

Learning curve

The virtues of boring tech

Mitigating by learning practice reading community teammates/consultants

Mitigating with use cases innovation budget developer tools testing breakable toys/katas low-risk applications/services

Takeaways

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

Thanks! Colin Jones @trptcolin