Functional Programming

// Pure function — same input, same output, no side effects
function add(a, b) { return a + b; } // ✅ pure
let count = 0;
function impure() { count++; return count; } // ❌ impure — side effect

// Immutability — original change mat karo
const original = [1, 2, 3];
const added = [...original, 4]; // new array!
console.log(original); // [1, 2, 3] — unchanged

// Higher-order functions
function multiply(factor) {
  return (num) => num * factor; // returns function!
}

const double = multiply(2);
const triple = multiply(3);

console.log(double(5));  // 10
console.log(triple(5));  // 15

// Compose functions
const compose = (...fns) => x => fns.reduceRight((v, f) => f(v), x);

const addTax = price => price * 1.1;
const addShipping = price => price + 50;
const formatPrice = price => `Rs. ${price.toFixed(0)}`;

const getTotal = compose(formatPrice, addShipping, addTax);
console.log(getTotal(1000)); // Rs. 1150