Chapter 7, Transforming Functions – Currying and Partial Application

7.1 Hard by hand: It would work; sum(3) returns a function with 3 already bound; sum(3)() returns the same, and sum(3)()(5) produces the result.

7.2 Sum as you will: The following sumMany() function does the job:

const sumMany = (total: number) => (value?: number) =>
  value === undefined ? total : sumMany(total + value);
sumMany(2)(2)(9)(6)(0)(-3)(); // 16

In JavaScript, the function poses no problem; with TypeScript, we’ll get an objection because it cannot determine that sumMany(2) is a function, not a number.

A small detail: can you fix the function so sumMany() will return 0?

7.3 Curry with eval? Let’s see this in JavaScript first:

// curryByEval.js
function curryByEval(fn) {
  return eval(`${range(0, fn.length)
    .map((i) => `x${i}`)
    .join("=>")} => ${fn.name}(${range(0, fn.length...