dewey92

fillNames :: String -> String -> String -> String
fillNames firstN middleN lastN = firstN ++ middleN ++ lastN

a :: String -> String -> String
a = fillNames "Jihad"

b :: String
b = a " Dzikri" " Waspada"
b == "Jihad Dzikri Waspada" -- True

dewey92

type Tree<A> = Leaf<A> | Branch<A>;
type Leaf<A> = { _f: 'tree', kind: 'leaf', value: A };
type Branch<A> = { _f: 'tree', kind: 'branch', left: Tree<A>, right: Tree<A> };

function mapTree<A, B>(map: (val: A) => B, tree: Tree<A>): Tree<B> {
  switch (tree.kind) {
    case 'leaf':
      return leaf(map(tree.value));
    case 'branch':
      return branch(

dewey92

export interface TimeSlot {
  deliveryId: number;
  from: string;
  to: string;
}

export interface DeliveryTimeResponse {
  date: string;
  slots: {
    DayTime: TimeSlot;

dewey92

/* Enum */
enum Status {
  Initial,
  Fetching,
  Done,
  Error
}

interface ProductStore {
  products: ProductModel[];

dewey92

/* Intersection type */
interface Goku {
  withKamehameha: boolean;
}
interface Bejita {
  sayKakarot: boolean;
}
type Gogeta = Goku & Bejita;

const gogeta: Gogeta = {

dewey92

const getFinalPrice = (product: ProductModel) =>
  product.price + product.tax;

const getProductById = (products: ProductModel[], id: number) =>
  products.find(product => product.id === id);

const product = getProductById(productList, 1);
const finalPrice = getFinalPrice(product); // <- ERROR
// Argument of type 'ProductModel | undefined' is not assignable to parameter of type 'ProductModel'.
//  Type 'undefined' is not assignable to type 'ProductModel'.

dewey92

interface ProductModel {
  id: number;
  name: string;
  price: number;
  tax: number
}

const productList: ProductModel[] = [
  { id: 100, name: 'deluxe', price: 28, tax: 2.5 },
  { id: 101, name: 'giftcard', price: 30, tax: 3 },

dewey92

interface ProductModel {
  id: number;
  name: string;
  price: number;
  tax: number
}

const getFinalPrice = (product: ProductModel) =>
  product.price + product.tax;

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declare const _phantom: unique symbol;
export type NewType<Name, Type> = Type & { [_phantom]?: Name };
  
export type Celcius = NewType<'Celcius', number>;
export type Fahrenheit = NewType<'Fahrenheit', number>;

// ...etc

dewey92

type Brand<Name, Type> = Type & { _brand?: Name } // optional
  
type Celcius = Brand<'Celcius', number>;
type Fahrenheit = Brand<'Fahrenheit', number>;
  
const fiveC: Celcius = 5; // typechecked :)