Plain English not Crazy Jargon The necessity of monads in Haskell maintains the pure functionality of the language but can test the patience of its programmers. An understanding of monads is essential if you want to work with Haskell. This tutorial offers a quick look at the structure of the typeclass. While you’ll need familiarity with Haskell, specifically, to understand how to tackle its typeclass, the concepts presented in this tutorial are easily transferred to other languages. We’ll also be covering the and typeclasses. Let’s start with the boring, technical definition. A monad is a particular typeclass that is primarily composed of 2 functions, and . This is simple enough, right? Now let’s break down some terminology and find out why these 2 functions are so powerful and how all of this affects your real world code. [Monad](http://hackage.haskell.org/package/base-4.11.1.0/docs/Control-Monad.html) Monad [Applicative](http://hackage.haskell.org/package/base-4.11.1.0/docs/Control-Applicative.html) [Functor](http://hackage.haskell.org/package/base-4.11.1.0/docs/Data-Functor.html) bind return You may be a bit confused, what’s a typeclass? Think of a typeclass as an interface that defines a set of functions. You can define an instance of the typeclass for a data type. Now let’s look at these 2 functions, and . The first, , takes a value and applies a data constructor to it. Then the second function, , allows you to use the value in your data type in a sequential computation. Why would you use monads in your code? The simple answer is so you can do useful work such as manipulation and management of input and output and asynchronous programming. Next let’s talk about 2 other important concepts in Haskell: and . bind return return bind Applicative Functor A data type that is an instance of the typeclass will implement . This function allows you to run an arbitrary function on the value or values in your data type. The typeclass defines an infix operator, , which applies a value in a data type to another value in a data type. For example, applying a function to two lists since each list has an instance of . Adding instances of these typeclasses to an instance of enables you to do more with your data types. Next let’s look at some data types that are instances of and their practical operation in your every day programming life. Functor fmap Applicative <*> Functor Monad Monad The first data type we’ll examine is . has an instance of . This data type allows you to represent a value or the lack of a value. Let’s talk about this type in terms of the 2 functions we learned about earlier. First wraps a value in the data constructor . acts like a function and when we try to a value to a name or use the value somehow will either give us our value or will and return . Finally, let’s look at another data type, . Just like there is an instance of for . Along the same lines as the last implementation this wraps a value in the data constructor . Functions that operate on lists use to take all the values in the list as input. This can be thought of as similar to a for loop for . Then the function will return a new list which is still an instance of the data type. [Maybe](http://hackage.haskell.org/package/base-4.11.1.0/docs/Data-Maybe.html) Maybe Monad return Just Just bind Just fail Nothing [List](http://hackage.haskell.org/package/base-4.11.1.0/docs/Data-List.html) Maybe Monad List return List bind [] List You can’t write effective Haskell without a few data types with instances. In the end calling something “a monad” makes it sound like a special entity. Rather, everything that people call a monad is really just a data type with some implementation of the typeclass. I hope this article helped further your understanding of an overcomplicated topic. Monad Monad Thanks for reading, my colleague and I do freelance mobile and fullstack development. Keep us in mind for your next project!
