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