JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

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This collection intends to provide viewers with examples of the different Algebraic Data Types that are commonly used in programming. All of these ADTs can be found within the Fantasy Land specification which consists of common algebraic data types used in the realm of web development. By adhering to the different laws that each ADT is built upon, users of the spec are provided with interoperability when using different algebras, ultimately providing them with an incredibly powerful set of tools.

### Resources

* [Fantasy Land Github](https://github.com/fantasyland/fantasy-land)

The term functor comes from category theory in which a functor is a date type used to preserve the structure of data as it's transformed from one category to another. We can recreate these data types in JavaScript by using regular factory functions. 

In this lesson, we learn about the properties our data type must have in order to be considered a true functor. By the end of the lesson you will have created a factory function for creating `Identity` functors.

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Get Acquainted with Functor Data Types in JavaScript by creating an Identity Functor

As its name suggests, a `Maybe` is a type that may or may not hold a value. In JavaScript, we can use `Maybe`s to check whether a value is undefined or null prior to passing it through to a transformer function and ultimately give us better control over the flow of our 

In this lesson, we walk through the process of writing a factory function for creating objects that implement a `Maybe` functor. The overall goal of the lesson is to become more comfortable working with the functor data type while learning about `Maybe`, a widely-known implementation in the functional programming world

Use a Maybe functor to halt transformer functions from acting on null or undefined values

Semi-groups are an important part of functional programming. They're not quite monoids, however, they provide us with the foundation we need to create monoids.

In this video, we'll learn about semigroups and see how they provide us with a generic interface for combining values using a `.concat` method. By the end of the lesson, you will have learned about the properties that a type must possess in order to be considered a valid semigroup.


[Fantasyland Docs - Semigroup](https://github.com/fantasyland/fantasy-land#semigroup)

Creating Semigroup Data Types from Scratch

Semigroup Data Types provide users with a `.concat` function which must abide by the associative law. As a result of that, it doesn't matter how we append `.concat` as it will always produce the same result. 


[Fantasyland Docs - Semigroup](https://github.com/fantasyland/fantasy-land#semigroup)

Testing Semigroups to Ensure They Abide by the Law of Associativity

This lesson extends upon our knowledge of semigroups and shows viewers how to create `Max` and  `Min` semigroups which provide us with an interface for comparing numerical values.


[Fantasyland Docs - Semigroup](https://github.com/fantasyland/fantasy-land#semigroup)

Leveraging Semigroups to Create Reusable Max & Min Interfaces

This lesson extends upon our knowledge of semigroups and shows viewers how to create `Any` and  `All` semigroups which provide us with an interface for comparing `boolean` values.


[Fantasyland Docs - Semigroup](https://github.com/fantasyland/fantasy-land#semigroup)

Leveraging Semigroups to Create Reusable Any & All Interfaces

In this lesson, we'll begin working with monoids by creating some of our own. Specifically, we will upgrade a previously defined semigroup (`Product`) so that it takes the form of a valid monoid. To ensure that we have a valid monoid, we will wrap up this video by testing `Product` so that it holds the laws of `Right` identity and Left` identity.

[Fantasy Land Docs - Monoid](https://github.com/fantasyland/fantasy-land#monoid)





Upgrading Semigroup Data Types to Monoids

This lesson shows viewers how to transform the following semigroups to be valid monoid instances: `All`, `Any`, `Max`, `Min`. 

Transforming All, Any, Max, & Min from Semigroups to Monoids

This lesson continues on the topic of monoids by teaching viewers how to create a generic `fold` function that consumes a monoid as well as an array which that monoid will perform a reduction on.

By the end of the lesson, you'll have created a helpful utility function for creating other specialized functions that are enclosed with a particular monoid.

Exploring Common Algebraic Data Types Used in Functional Programming

Thomas Greco

Resources

Course Content