const fn = (b) => (c) => (d) => {
  return 3;
};

const foo = (a, b) => (c) => (d) => {
  return 3;
};

const bar = (a) => (b) => (c) => a + b + c;

const mw = (store) => (next) => (action) => {
  return next(action);
};

const middleware = (options) => (req, res, next) => {
  // ...
};