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Using fp-ts for Functional Programming in TypeScript

Solution Review: Higher-Order Function

Understand how to implement higher-order functions in TypeScript by creating reusable and modular solutions. This lesson guides you through designing a calculatePrice function and composing it within a buyTicketBase function to handle ticket purchasing logic effectively.

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Solution

We have to create three new functions. Let’s look at the solution below.

TypeScript 3.3.4
type Customer = {
    name: string,
    age: number,
    wealthy: boolean
};
const saveInDatabase = (show: string, customer: Customer, price: number) => {
    console.log(`REGISTERED: ${customer.name} has requested  a ticket for ${show}. Price: ${price}`);
};
const buyTicket = (show: string, customer: Customer) => {
    let price = 10;
    if (customer.age > 18) {
        price = price + 10;
    }
    saveInDatabase(show, customer, price);
};
const calculatePrice = (age: number) => {
    const basePrice = 10;
    return age > 10 ? basePrice + 10 : basePrice;
};
const buyTicketBase = (calculate: (age: number) => number) => (show: string, customer: Customer) => {
    const price = calculate(customer.age);
    saveInDatabase(show, customer, price);
};
const newBuyTicket = buyTicketBase(calculatePrice);
buyTicket("Pakistan", {name:"Ali",age:28,wealthy:true}); // current situation
// newBuyTicket("Pakistan", {name:"Ali",age:28,wealthy:true}); // with higher-order function

Explanation

Here’s a line-by-line explanation of the solution ...