Kumite

const fn = (f) => (...args) => args.reduce((f, arg) => f(arg), f);

// ==================================

const sum = fn(a => b => c => (a + b + c));

console.log(sum(1, 2, 3)); // 6
console.log(sum(1, 2)(3)); // 6
console.log(sum(1)(2)(3)); // 6

const doubleInc = sum(1)(1);
console.log(doubleInc(4)); // 6