Functions as first-class values

In most languages, functions can be passed around just like numbers or strings. That's the foundation of everything from callbacks to React hooks.

Write a function applyTwice that takes:

• a function f that takes one integer and returns one integer
• a starting integer n

…and returns the result of applying f to n twice.

applyTwice(x => x + 3, 7)  →  13   // (7+3)+3
applyTwice(x => x * 2, 5)  →  20   // (5*2)*2

Your program receives two command-line arguments:

1. The operation: add:<k> or mul:<k>
2. The starting integer

Print the result.

Constraints

• applyTwice must accept a function as its first argument — do not hardcode the operation inside it.
• Supported ops: add:<k> and mul:<k>.