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Contravariant Functors: The Other Side of the Coin

YOW! Lambda Jam 2018

Since their introduction, Applicative and its sidekick Alternative have become ubiquitous and beloved type classes in Haskell and similar languages such as Purescript. By contrast, their contravariant counterparts are relatively unknown. These contravariant structures are useful, and their time has come!

In this talk, we will learn about Contravariant, and its subclasses Divisible and Decidable. How do they work? How do they relate to the classes we know? Are they useful? For what? This talks aims to demystify these classes in an approachable way, by demonstrating their use with practical motivating examples.