Either
- Functor and Bifunctor, lesson 5: Two maps in one
- Functor and Bifunctor, lesson 7: Laws of the bifunctors
- Functor and Bifunctor, lesson 6: More than a sum
- The Validation Course
- Validation, lesson 5: Refactoring with Either
- Validation, lesson 6: Working with newtypes
- Validation, lesson 7: Introducing Applicative