#498 Sum Function

Create a sum() function that supports currying and chaining. The function should allow partial application and infinite chaining of arguments.

Requirements

1. Currying support – sum(1) returns a function that can accept more arguments
2. Chaining – sum(1)(2)(3) should work and return the total sum
3. Value comparison – when compared with ==, it should return the numeric sum
4. Flexible arguments – support any number of arguments in any combination

Key Behaviors

• Partial application – sum(1) returns a function
• Infinite chaining – sum(1)(2)(3)... continues indefinitely
• Value coercion – the returned function should coerce to its numeric value
• Multiple arguments – each call can accept multiple arguments

Example

const sum1 = sum(1);
sum1(2) == 3;           // true
sum1(3) == 4;           // true

sum(1)(2)(3) == 6;      // true
sum(5)(-1)(2) == 6;     // true
sum(1, 2)(3) == 6;      // true (if multiple args supported)

Signature

function sum(...args: number[]): SumFunction;
interface SumFunction {
  (...args: number[]): SumFunction;
  valueOf(): number;
}

Key Challenge

The function needs to return an object that behaves like both a function (for chaining) and a number (for comparison).