Implementing the Curry Function in JavaScript

The curry function is a powerful functional programming technique that allows you to transform a function that takes multiple arguments into a sequence of functions, each taking a single argument. This can improve code reusability, readability, and enable partial application of functions. Your task is to implement a curry function in JavaScript that takes a function and the desired number of arguments and returns a new function that behaves as a curried version of the original.

Problem Description

You need to implement a curry function that accepts a function fn and an arity (number of arguments the original function expects). The curry function should return a new function that, when called with a single argument, returns another function. This process should continue until the original function fn is called with all its required arguments. At that point, the original function fn should be invoked with the accumulated arguments, and its result should be returned.

Key Requirements:

• The curry function should handle functions with any arity.
• The returned curried function should accept arguments one at a time.
• The curried function should return a function until all arguments are provided.
• When all arguments are provided, the original function should be called with those arguments, and its result returned.
• The this context of the original function should be preserved.

Expected Behavior:

The curried function should behave as if the original function was called with all the arguments passed to the curried functions in sequence.

Edge Cases to Consider:

• What happens if the original function takes no arguments (arity of 0)?
• What happens if the original function is not a function?
• What happens if the arity provided to curry is incorrect? (While not strictly required, handling this gracefully is good practice).

Examples

Example 1:

Input: curry(add, 2)
Output: (x) => (y) => x + y
Explanation: The curry function takes the `add` function and arity 2. It returns a function that takes `x`, and then returns another function that takes `y` and returns `x + y`.

Example 2:

Input: curry(multiply, 3)
Output: (x) => (y) => (z) => x * y * z
Explanation: The curry function takes the `multiply` function and arity 3. It returns a function that takes `x`, then returns a function that takes `y`, and finally returns a function that takes `z` and returns `x * y * z`.

Example 3:

Input: curry(greet, 1)
const sayHello = curry(greet, 1);
const greeting = sayHello("Alice");
Output: "Hello, Alice!"
Explanation: `greet("Alice")` returns "Hello, Alice!". The curry function allows us to partially apply the `greet` function.

Constraints

• The curry function must be implemented in JavaScript.
• The original function fn can be any valid JavaScript function.
• The arity must be a non-negative integer.
• The solution should be reasonably efficient. While performance is not the primary concern, avoid unnecessary overhead.

Notes

• Consider using closures to maintain the accumulated arguments.
• Think about how to handle the this context of the original function. While not explicitly required, preserving it is a good practice.
• The curry function should return a function, even if the original function takes no arguments. In that case, the returned function should immediately invoke the original function and return its result.
• You can use arrow functions for conciseness.
• Test your solution thoroughly with various arities and functions.