Function currySum

Intermediate/00-advanced-functions.js:120–128

(a)

// Currying

function currySum(a) {
    return function (b) {
        return function (c) {
            return function (d) {
                return sum(a, b, c, d)
            }
        }
    }
}

const sumAB = currySum(1)(2)
const sumC = sumAB(3)