Church encoding in JavaScript

church_encoding.js

var inc = function (n) {
  return n + 1;
};

var zero = function (f) {
  return function (x) { return x; };
};

var church = function (n) {
  var loop = function (n, acc) {
    if (n === 0) return acc;
    
    return loop(n-1, function (f) {
      return function (x) {
        return f(acc(f)(x));
      };
    });
  };
  return loop(n, zero);
};

var unchurch = function (f) {
  return f(inc)(0);
};