How to use the fantasy-land.extend function in fantasy-land

return Z.map (other.value, this);
};

Identity.prototype[FL.chain] = function(f) {
  return f (this.value);
};

Identity.prototype[FL.reduce] = function(f, x) {
  return f (x, this.value);
};

Identity.prototype[FL.traverse] = function(typeRep, f) {
  return Z.map (Identity, f (this.value));
};

Identity.prototype[FL.extend] = function(f) {
  return Identity (f (this));
};

Identity.prototype[FL.extract] = function() {
  return this.value;
};

Identity.prototype.inspect =
Identity.prototype['@@show'] = function() {
  return 'Identity (' + show (this.value) + ')';
};

module.exports = Identity;

return map (other.value) (this);
};

Identity.prototype[FL.chain] = function(f) {
  return f (this.value);
};

Identity.prototype[FL.reduce] = function(f, x) {
  return f (x, this.value);
};

Identity.prototype[FL.traverse] = function(typeRep, f) {
  return map (Identity) (f (this.value));
};

Identity.prototype[FL.extend] = function(f) {
  return Identity (f (this));
};

Identity.prototype[FL.extract] = function() {
  return this.value;
};

Identity.prototype.inspect =
Identity.prototype['@@show'] = function() {
  return 'Identity (' + show (this.value) + ')';
};

module.exports = Identity;

const extend = (fn, tx) => tx[$.extend](fn)
const extract = (tx) => tx[$.extract]()

const result = []
  if (Constructor[$.of]) result.push('of')
  if (Constructor[$.empty]) result.push('empty')
  if (Constructor[$.chainRec]) result.push('chainRec')
  if (Constructor[$.zero]) result.push('zero')
  if (Constructor.prototype[$.equals]) result.push('equals')
  if (Constructor.prototype[$.map]) result.push('map')
  if (Constructor.prototype[$.bimap]) result.push('bimap')
  if (Constructor.prototype[$.promap]) result.push('promap')
  if (Constructor.prototype[$.concat]) result.push('concat')
  if (Constructor.prototype[$.ap]) result.push('ap')
  if (Constructor.prototype[$.alt]) result.push('alt')
  if (Constructor.prototype[$.reduce]) result.push('reduce')
  if (Constructor.prototype[$.traverse]) result.push('traverse')
  if (Constructor.prototype[$.chain]) result.push('chain')
  if (Constructor.prototype[$.extend]) result.push('extend')
  if (Constructor.prototype[$.extract]) result.push('extract')
  return result
}