#readwise
# Functors, Applicatives, and Friends
## Metadata
- Author: [[Mark Seemann]]
- Full Title: Functors, Applicatives, and Friends
- URL: https://blog.ploeh.dk/2018/03/19/functors-applicatives-and-friends/
## Summary
Functors, Applicatives, and Friends is a blog series which covers category theory concepts such as monads and functors.
Here's a list of articles that belong to this series, retrieved on March 17, 2023:
- [[Functors]]
- [[Applicative functors]]
- Bifunctors
- Tuple bifunctor
- Either bifunctor
- Rose tree bifunctor
- Contravariant functors
- The Command Handler contravariant functor
- The Specification contravariant functor
- The Equivalence contravariant functor
- Reader as a contravariant functor
- Functor variance compared to C#'s notion of variance
- Contravariant Dependency Injection
- Profunctors
- Reader as a profunctor
- [[Invariant functors]]
- Endomorphism as an invariant functor
- Natural transformations as invariant functors
- Functors as invariant functors
- Contravariant functors as invariant functors
- [[Monads]]
- [[Functor Relationships]]
## Highlights
**Functors and related data structures are containers of values.** It's a family of abstractions. ^cxhp17
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Not all generic types are functors. In order to be a functor, a generic type must obey a couple of intuitive laws.
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