In computer programming, a functor refers to an object or function that can be treated as if it was a regular function. Functors are commonly found in functional programming languages and allow operations to be more abstract and adaptable. They enable the manipulation of functions as data, allowing them to be passed, created, or altered dynamically.


The phonetics of the keyword “Functor” is: /ˈfʌŋktər/

Key Takeaways

  1. A Functor is a programming concept that represents a type which can be “mapped” over. This means you can apply a function to a value wrapped in a Functor.
  2. Functors must follow two laws: the composition law and the identity law. These laws ensure that Functors behave predictably when working with function compositions and don’t cause side effects.
  3. Common examples of Functors include lists, arrays, and promises in various programming languages. They all provide a map function that allows you to apply a function to their wrapped values.


The term “functor” is important in technology mainly due to its significance in computer programming and functional programming languages like Haskell and Scala.

A functor is a type of structure that, simply put, allows applying a function over a container without altering the structure itself.

Functors promote modularity, code reusability, and abstraction by providing a flexible way to manipulate data while preserving the underlying structure.

They form a building block for more advanced functional programming concepts, such as applicatives and monads, contributing to the development of efficient and maintainable code.

In summary, functors play a vital role in promoting a more organized and expressive programming paradigm that ultimately fosters better software development practices.


Functors serve a vital role in the world of functional programming, where functions are treated as first-class citizens. The purpose of a functor lies in its ability to enable the manipulation and composition of functions without altering the functions’ internal structure or external behavior.

By doing so, functors foster a modular approach to programming, in which different computations can be elegantly combined to achieve greater flexibility and reusability. In practice, functors are entities that follow a predefined contract or structure, often consisting of a type constructor and a mapping function.

The mapping function allows data or functions to be safely wrapped and transformed within a context, such as lists, optional values, or promises. This capability helps to control side effects and maintain the purity of functional programming.

As a real-world example, in financial systems, the concept of a “maybe” functor expands the traditional binary model of success/failure, allowing developers to adapt calculations smoothly even in uncertain situations. Overall, the utility of functors lies in their ability to encapsulate and transform complex operations while preserving the core principles of functional programming.

Examples of Functor

Functors, which are mathematical objects and functions that can be manipulated similarly to other data, are a concept in computer science and functional programming languages, rather than specific technologies. However, they are commonly used in different programming libraries and di frameworks. Here are three real-world examples of libraries and utilities where functors play a significant role:

Haskell (Programming Language):Haskell is a statically-typed functional programming language that heavily utilizes the concept of functors. The Functor type class provides a way to apply a function to a value inside a structure, for example, a container type such as List, Maybe, or Tree. Functors allow for abstract manipulation of values in containers using fmap, enabling a more functional and composable programming style. In Haskell, functor instances can be created for different data structures, making the code more expressive and reusable.

Boost C++ Libraries (Boost.Functional):Boost.Functional is a set of libraries for the C++ programming language that allow users to harness the power of functional programming. One of the key libraries is Boost.Function, which provides a functor-like utility known as “function objects.” These objects can represent anything that can be called as functions, allowing users to treat functions as data and manipulate them accordingly. Functors in Boost.Functional enable a higher level of abstraction, which is essential in improving the overall modularity and maintainability of C++ applications.

Scala (Programming Language)””Scala, which combines the power of functional and object-oriented programming, also uses the functor concept heavily. Scala has a “map” function that can be used with various data structures, such as Option, List, and Future, to manipulate data. The map function wraps around the Functor concept, allowing developers to apply transformations to data within those structures with minimal boilerplate code. This approach promotes more concise and reusable code, a core principle in the functional programming paradigm.

Functor FAQ

What is a Functor?

A Functor is a programming concept that represents an object or data structure that can be mapped over functions. Simply put, it is a function object that can be manipulated as if it were a value.

What is the purpose of Functors in programming?

Functors provide a way to create reusable functions, which can be combined with other functions or data structures to create complex behavior. They are primarily used to enable functional programming techniques, where functions or expressions are treated as values and can be easily manipulated.

How are Functors different from functions?

Functions are specific pieces of code that take arguments, process them, and return a result. Functors represent an object containing a function that can be manipulated as a value. This distinction allows functors to provide additional functionality and flexibility in how they are used in comparison to functions.

How are Functors used in functional programming?

Functors play a crucial role in functional programming, allowing developers to create and manipulate higher-order functions. For example, Functors can be used to apply a series of transformations to a list of data, where each transformation is represented by a separate Functor object. This enables a more modular and composable approach to writing code in a functional style.

Can you give an example of a Functor in programming?

One common example of a Functor is the “Maybe” or “Optional” Functor, which is used to handle values that might not exist or could contain an error. The Maybe Functor wraps a value and provides a way to apply a function to the wrapped value only if the value is present. It helps create safe and composable functions that won’t cause runtime errors due to missing or invalid data.

Related Technology Terms

  • Morphism
  • Category Theory
  • Natural Transformation
  • Monads
  • Applicative

Sources for More Information


About The Authors

The DevX Technology Glossary is reviewed by technology experts and writers from our community. Terms and definitions continue to go under updates to stay relevant and up-to-date. These experts help us maintain the almost 10,000+ technology terms on DevX. Our reviewers have a strong technical background in software development, engineering, and startup businesses. They are experts with real-world experience working in the tech industry and academia.

See our full expert review panel.

These experts include:


About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

More Technology Terms

Technology Glossary

Table of Contents