Here's an example that uses context

```js
var Person = function (gender) { this.gender = gender; };
var isMale = function () { return this.gender === 'male'; };
Person.prototype.isMale = isMale;
Person.prototype.isFemale = _.complement(isMale);
var larry = new Person('male');
ok(larry.isMale());
ok(!larry.isFemale());
```