Brown Bag: Learn the things I'm learning

FP -> DDD -> CA

 

 

August 27, 2020
David Horm
Pronouns: he, him, his
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TL;DR

• Ride-the-Duck Tour
• Hermit Wisdom?
  or Crazy Talk?
• Journey with React
• Functional Programming
• Domain Driven Design
• Clean Architecture

Journey

• Baby
• Imposter Syndrome
• Ever-evolving technology
• Don't Stop Believing

React

React

• Functional Components & Hooks
• useEffect() for Side Effects?
• useReducer() and Redux uses Immutable objects?
• useMemo() & Memoized?
• Ah, using concepts from Functional Programming

Arrow Function Syntax

					function addOne(value) {
						return value + 1;
					}

					const addOne = (value) => {
						return value + 1;
					};

					const addOne = (oldValue) => { return oldValue + 1; };

					const addOne = (oldValue) => oldValue + 1;
				

Make Veggie 🥪: OOP Example

					// ['Loaf of Bread', 'Loaf of Bread', 'Slab Bacon', 'Whole Tomato', 'Head of Lettuce']
					// => 'The sandwich has: slice of Bread, sliced Tomato, Lettuce leaf, slice of Bread'
					const makeVeggieSandwich = (ingredients: string[]): string => {
						let sandwichIngredients = [];
						for (let i = 0; i < ingredients.length; i++) {
							if (isVeggieType(ingredients[i])) {
								const slicedIngredient = getSlicedIngredient(ingredients[i]);
								sandwichIngredients.push(slicedIngredient);
							}
						}

						sortIngredients(sandwichIngredients);

						let sandwich = 'The sandwich has: ';
						for (let j = 0; j < sandwichIngredients.length; j++) {
							sandwich += `${sandwichIngredients[j].value}, `;
						}
						return sandwich;
					};
				

Make Veggie 🥪: FP Example

					// ['Loaf of Bread', 'Loaf of Bread', 'Slab Bacon', 'Whole Tomato', 'Head of Lettuce']
					// => 'The sandwich has: slice of Bread, sliced Tomato, Lettuce leaf, slice of Bread'
					const makeVeggieSandwich = (ingredients: string[]): string => {
						const sandwich = ingredients
							.filter(isVeggieType)
							.map(getSlicedIngredient)
							.sort(sortIngredients)
							.reduce(
								(sandwich, ingredient) => `${sandwich}, ${ingredient.value}`,
								'The sandwich has: '
							);
						
						return sandwich;
					};
				

Same Input => Same Output

					let word = 'World';
					doSomething(word);
					console.log(`Hello ${word}`); // 'Hello World'?
				

Same Input => Same Output

					let word = 'World';
					const doSomething = (word) => {
						a(word); b(word); c(word); d(word); e(word); f(word);
					};
					doSomething(word);
					console.log(`Hello ${word}`); // 'Hello F-Word'?!
				

Same Input => Same Output

					// impure
					let minimum = 21;
					const checkAge = (age) => age >= minimum;

					// pure
					const checkAge = (age) => {
						const minimum = 21;
						return age >= minimum;
					};

					// pure with currying
					const checkAge = (age) => (minimum) => age >= minimum;
					const isOfAge = checkAge(36)(18);
				

OOP Error Handling

					// 1 => "Luke Skywalker"
					const getCharacterName = (id: number): string => {
						fetch(`https://swapi.dev/api/people/${id}/`)
						.then((response) => { 
							if (!response.ok) {
								throw new Error('HTTP error')
							}

							response.json()
							.then((character) => {
								if (!character) {
									throw new Error('no character object');
								}
	
								if (!character.name) {
									throw new Error('No name property');
								}
	
								return character.name;
							});
						})
						.catch((error) => {
							throw new Error(`Fetch Error: ${error}`);
						});
					};
				

FP Error Handling

FP: Additional Resources

• 📖 Mostly adequate guide to FP – Brian Lonsdorf
• Why Isn't Functional Programming the Norm? – Richard Feldman
• GOTO 2018 • Functional Programming in 40 Minutes • Russ Olsen
• Functional Design Patterns - Scott Wlaschin

Domain Driven Design

					module CardGame =
						type Suit = Club | Diamond | Spade | Heart
						type Rank = Two | Three | Four | Five | ...
						type Card = Suit * Rank
						type Hand = Card list
						type Deck = Card list

						type Deal = Deck -> (Deck * Card)
				

Domain Driven Design

					module CardGame =
						type Suit = Club | Diamond | Spade | Heart
						type Rank = Two | Three | Four | Five | ...
						type Card = Suit * Rank
						type Hand = Card list
						type Deck = Card list

						type ShuffledDeck = Card list
						type Shuffle = Deck -> ShuffledDeck
						type Deal = ShuffledDeck -> (ShuffledDeck * Card)
				

Domain Driven Design

					type Contact = {
						FirstName: string
						MiddleInitial: string
						LastName: string

						EmailAddress: string
						IsEmailVerified: bool
					}
				

Domain Driven Design

					type PersonName = {
						FirstName: String50
						MiddleInitial: String1 option
						LastName: String50
					}

					type EmailContactInfo = {
						EmailAddress: EmailAddress
						IsEmailVerified: bool
					}

					type Contact = {
						Name: PersonName
						Email: EmailContactInfo
					}
				

Domain Driven Design

					type PersonName = {
						FirstName: String50
						MiddleInitial: String1 option
						LastName: String50
					}

					type VerifiedEmail = VerifiedEmail of EmailAddress

					type VerificationService = (EmailAddress * VerificationHash) -> VerifiedEmail

					type EmailContactInfo = 
						| Unverified of EmailAddress
						| Verified of VerifiedEmail
					
					type Contact = {
						Name: PersonName
						Email: EmailContactInfo
					}
				

DDD: Additional Resources

• 📖 Domain-Driven Design by Eric Evans
• Scott Wlaschin - Talk Session: Domain Modeling Made Functional
• Domain Driven Design: The Good Parts - Jimmy Bogard
• GOTO 2018 • 50.000 Orange Stickies Later • Alberto Brandolini

Clean Architecture Influences

• Ports & Adapters (a.k.a. Hexagonal Architecture) by Alistair Cockburn
• Onion Architecture by Jeffrey Palermo
• Screaming Architecture by "Uncle Bob" Martin
• BCE (Boundary, Control, Entity) architecture by Ivar Jacobson
• DCI (Data, Context, Interaction) architecture by James Coplien, & Trygve Reenskaug