Think functionally f(x) = y Presenters Pavel Struhar - - PowerPoint PPT Presentation

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Think functionally f(x) = y Presenters Pavel Struhar - - PowerPoint PPT Presentation

Oct 01, 2022 314 likes •1.12k views

Think functionally f(x) = y Presenters Pavel Struhar pavel.struhar@accenture.com Twitter: @pavestru Daniel Derevjanik daniel.derevjanik@accenture.com Twitter: @dderevjanik Both from Lightweight Arch. core team Spoiler Everything is a

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Think functionally

f(x) = y

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Presenters

Pavel Struhar pavel.struhar@accenture.com Twitter: @pavestru Daniel Derevjanik daniel.derevjanik@accenture.com Twitter: @dderevjanik Both from Lightweight Arch. core team

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Spoiler

Everything is a function

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A monad is just a monoid in the category of endofunctors.

What's the problem?

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Data and Functions

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Data Flow - Expectations f

INPUT DATA OUTPUT DATA

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Data Flow - Expectations f

INPUT DATA OUTPUT DATA PROCESS DATA

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Data Flow - Expectations f

INPUT DATA OUTPUT DATA

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Simplicity is a key

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Data Flow - Expectations f f f

INPUT DATA

f f

OUTPUT DATA

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Data Flow - Expectations f f f

INPUT DATA

f f

OUTPUT DATA PROCESS DATA

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Data Flow - Expectations f f f

INPUT DATA

f f

OUTPUT DATA

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Simplicity is a key, still...

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Data Flow - Reality

INPUT DATA

class class class method method method method method method

CLASS DATA CLASS DATA CLASS DATA

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Data Flow - Reality - OOP in nutshell

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Simplicity ? Errr….

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What can we achieve ?

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What can we achieve ?

  • one directional dataflow

f

INPUT DATA

f f

OUTPUT DATA

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How can we achieve that ?

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Separation of Data and Functions

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No Hidden Information

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No Side-effects

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Simple is Pure Function

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Pure Function

Function without time, (Always the same output for the same arguments.)

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Pure Function is Timeless

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Pure Function has No side-effects

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Pure Function is Opposite to Class Method

No this keyword

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Why should you care about pure functions ?

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Pure functions advantages

  • Easier to maintain
  • Testability
  • Easy to debug
  • Simply reusable
  • Thread-safe
  • One-directional data-flow
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Time for Demo

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Immutability

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Immutability

default in Functional languages

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Immutability by default in JavaScript?

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ECMAScript 6 introduced let keyword

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ECMAScript 6 introduced let keyword also introduced const

const

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Real life: Code reviews

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Immutable Data Structures FTW

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Immutable building blocks

  • Records
  • Vectors
  • Maps
  • Sets

… build anything you want

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Tree data structure

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We want to change one node

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...or keep it for the history record

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Immutability in Java

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Practices for immutability in Java (make them habits)

  • Mark the class final
  • Mark all the fields private and final
  • Force all the callers to construct an object of the class

directly, i.e. do not use any setter methods

  • Do not change the state of the objects in any methods of the

class

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“Classes should be immutable unless there's a very good reason to make them mutable.... If a class cannot be made immutable, limit its mutability as much as possible.”

  • - Joshua Bloch (taken from the book Effective Java)
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Benefits of immutable objects

  • Thread-safety
  • Easier to parallelize
  • Consistent internal state (in spite of exception)
  • References to immutable objects can be cached

○ Easy to implement UNDO - REDO functionality

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Time for a success story

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Redux.js

  • FLUX-ish library by Dan Abramov

○ Creator of Hot Module Reloading for ReactJS

  • Motivation:

○ We want Hot Module Reloading not only for View Components ○ but also for Business logic inside FLUX stores (like Models in MVC)

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Redux

  • Solution

○ Take state out of Stores ○ Make Store methods immutable / pure functions ○ No classes, just functions - reducers

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Redux

  • Result

○ HMR also for reducers ○ Application keeps state after HMR !!! ○ Time travelling ○ Awesome debugging tools ○ Community excitement - this is how FLUX was supposed to work from the start

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Summary

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What can we improve in our daily programming ?

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Shared mutable state is the root

  • f all evil.

Pete Hunt, ReactJS team @ Facebook

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Avoid mutability

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Don’t use global scoped variables

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Make const not var

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Separate Data from Business logic

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Use Pure functions

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Learning Haskell will help you write better Java(Script) code

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OOP vs FP ?

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Composition over Inheritance

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Topics for future sessions

Functional programming

  • Higher order functions
  • Partial application
  • Currying
  • Closures
  • Functors
  • …
  • Monads?
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Topics for future sessions

Functional Reactive Programming

  • ReactiveX (RxJS, RxJava), …

○ underscore / lodash for streams of events / data

  • Observables
  • Reactive (user) interfaces
  • …
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Topics for future sessions

Clojure ClojureScript Haskell PureScript Ocaml ReasonML Elm

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Happy building