Top Functional Programming Languages in 2022

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Functional programming is a fast-growing paradigm. In this guide, we will see the most famous functional programming languages. Along the way, we'll learn what functional programming is, the features that are common in functional languages, and explore languages that are not functional but that have some functional features.

People learn functional programming for many reasons. Some want to expand their understanding of programming, while others want to find a new job. Yet others find that functional programming is more natural to the way they think. Whatever reason is right for you, I have categorized the languages to help you find one that's right for you.

Table of Contents

Functional languages in alphabetical order

Click any language for more details.

What is functional programming?

Functional programming is hard to define. You will find conflicting definitions everywhere. I like to define functional programming like this:

Functional programming is a way of programming where you distinguish between:

  • actions—code that affects or is affected by the outside world, such as a function that sends an email or a function that reads from a microphone
  • calculations—computations from inputs to outputs, such as a function that calculates the tax on an sale amount
  • data—facts about events, such as the price of a product

Making this distinction separates the easy code (calculations and data) from the hard code (actions) so you can spend more attention on the hard stuff.

For a more comprehensive tutorial about functional programming, I recommend my book on the topic, Grokking Simplicity.

What is a functional programming language?

There is no absolute way to determine if a language is a functional programming language. However, by convention, functional programming languages encourage and support functional programming as the major mindset to use in the language. They do this through what they make easy, hard, and impossible.

What are some features of functional programming languages?

It is hard to define what features make a language functional. However, some features are more common in functional languages than in non-functional languages:

Many languages provide these features today. However, having these features does not make them functional. The predominant mindset is still procedural or object-oriented. For instance, JavaScript has first-class functions, but I do not consider it a functional language.

Non-functional languages with functional features

Is Java a functional programming language?

Classic object-oriented language

Java
Functional features
  • Lambdas (first-class closures)
  • Streams
  • Functional interfaces
Why it's not a functional langugage
  • Mutable by convention
  • Predominantly object-oriented
  • Mixes actions and calculations
Bottom Line
Java is predominantly object-oriented. Recently, some functional features have been added. Their utility is questionable.

Is JavaScript a functional programming language?

The language of the browser

JavaScript
Functional features
  • First-class functions
  • Pervasive use of higher-order functions
  • Functional tools (map/filter/reduce)
  • Data-orientation
Why it's not a functional langugage
  • Mutable by convention
  • Pervasive use of side-effects
Bottom Line
JavaScript does support functional programming, but it requires a lot of discipline. It might be okay for writing functional code, but it's not great for learning functional programming.

Is Python a functional programming language?

Popular language

Python
Functional features
  • First-class functions
  • List comprehensions
  • Functional tools (map/filter/reduce)
Why it's not a functional langugage
  • Mutable by convention
  • Predominantly procedural
  • Lambdas limited to one line
Bottom Line
Python is a popular and practical language. Though it does have some functional features, it is hard to do functional programming in it.

Functional languages with details

Clojure

A functional Lisp on the JVM

Clojure
Homepage
Company behind it
Try it online
Platforms
Description from their website
Clojure is a robust, practical, and fast programming language with a set of useful features that together form a simple, coherent, and powerful tool.

Elixir

Dynamic language for fault-tolerant systems

Elixir
Install guide
Try it online
Platform
Description from their website
Elixir is a dynamic, functional language designed for building scalable and maintainable applications. Elixir leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant systems, while also being successfully used in web development and the embedded software domain.

Elm

Frontend language with no runtime errors

Elm
Homepage
Install guide
Try it online
Platform
Description from their website
A delightful language for reliable webapps. Generate JavaScript with great performance and no runtime exceptions.

Erlang

Fault-tolerant, functional, actor-based

Erlang
Homepage
Creators
Company behind it
Install guide
Try it online
Platform
Description from their website
Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecoms, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution, and fault tolerance.

F#

Functional language on the .NET platform

F#
Homepage
Creator
Companies behind it
Install guide
Tutorial
Try it online
Platform
Description from their website
F# is a mature, open source, cross-platform, functional-first programming language. It empowers users and organizations to tackle complex computing problems with simple, maintainable and robust code.

Haskell

Flagship functional language with expressive types

Haskell
Homepage
Install guide
Tutorial
Try it online
Description from their website
Every expression in Haskell has a type which is determined at compile time. All the types composed together by function application have to match up. If they don't, the program will be rejected by the compiler. Types become not only a form of guarantee, but a language for expressing the construction of programs.

Idris

A functional languge for type-driven development

Idris
Creator
Try it online
Description from their website
Idris is a programming language designed to encourage Type-Driven Development.

Kotlin

Expressive language for the JVM

Kotlin
Homepage url
Company behind it
Install guide and tutorial
Platforms
Description from their website
Kotlin is a modern, cross-platform, multi-purpose programming language. JetBrains started the design and development of the language back in 2010 and has watched it rapidly grow in popularity. Known for its concise syntax and pragmatic design, Kotlin provides ample opportunity for sharing and reusing code between multiple projects and platforms.

OCaml

Functional, expressive, type-safe

OCaml
Homepage
Creators
Try it online
Description from their website
OCaml is a general-purpose, industrial-strength programming language with an emphasis on expressiveness and safety.

PureScript

Typed functional programming that compiles to JavaScript

PureScript
Creator
Install guide and tutorial
Try it online
Platform
Description from their website
A strongly-typed functional programming language that compiles to JavaScript.

Racket

Modern Lisp

Racket
Homepage url
Creator
Company behind it
Install guide
Platform
Description from their website
Racket is a general-purpose programming language as well as the world's first ecosystem for language-oriented programming. Make your dream language, or use one of the dozens already available.

ReasonML

A new syntax and toolchain for OCaml

ReasonML
Homepage url
Company behind it
Install guide
Try it online
Platform
Description from their website
Reason is not a new language; it's a new syntax and toolchain powered by the battle-tested language, OCaml. Reason gives OCaml a familiar syntax geared toward JavaScript programmers, and caters to the existing NPM/Yarn workflow folks already know.

Rust

Language with memory safety and powerful compiler

Rust
Homepage url
Creator
Company behind it
Install guide
Tutorial
Try it online
Platform
Description from their website
Rust is blazingly fast and memory-efficient: with no runtime or garbage collector, it can power performance-critical services, run on embedded devices, and easily integrate with other languages.

Scala

Functional/object-oriented hybrid on the JVM (and JavaScript)

Scala
Companies behind it
Install guide
Try it online
Platform
Description from their website
Scala combines object-oriented and functional programming in one concise, high-level language. Scala's static types help avoid bugs in complex applications, and its JVM and JavaScript runtimes let you build high-performance systems with easy access to huge ecosystems of libraries.

Scheme

Classic minimalist Lisp designed for teaching and exploration

Scheme
Homepage
Creators

Swift

Focused on safety, speed, and expressiveness

Swift
Homepage
Company behind it
Description from their website
Announced in 2014, the Swift programming language has quickly become one of the fastest growing languages in history. Swift makes it easy to write software that is incredibly fast and safe by design. Our goals for Swift are ambitious: we want to make programming simple things easy, and difficult things possible.

Functional languages for different purposes

Functional languages with the most jobs

You may be thinking of learning a new language to get a job doing functional programming. Functional programming jobs are considered rare in the industry, but they do exist. To maximize your chances of learning a language you can get a job in, you should pick one of these languages.

Job count data comes from indeed.com.

Tier 1

Although all of the languages listed previously are production-ready, these four languages have a lot of jobs listed. Ordered roughly from easiest to hardest to get started with.

Tier 2

These three languages don't have as many jobs as the previous list, but there are still many opportunities out there. Ordered roughly from easiest to hardest to get started with.

Functional languages by platform

Another way to organize functional languages is by what's available on the platform you are targeting.

Browser (JavaScript engine)

Ordered roughly from easiest to hardest to get started with.

Web backend

Ordered roughly from easiest to hardest to get started with.

Mobile (iOS and Android)

Embedded devices

Functional languages by learning opportunity

Immersing yourself in a language can help you learn. You can choose a language based on what it can teach you. Here, you'll find the languages organized by prominent features. They can create a wonderful, immersive learning environment.

Static typing

The most advanced type systems found today are in functional languages. These type systems are based on mathematical logic and are proven to be consistent. Types do more than prevent errors. They can also guide you to design better software. Having a good type system is like having a logician on your shoulder, coaching you into good software. If you'd like to learn more, these languages will immerse you:

Functional tools and data transformation

Most functional languages have good functional tools for doing data transformation. But these languages excel at it. Instead of encouraging you to define new types, these languages operate on a small number of data types and a large number of operations on them.

Concurrency and distributed systems

Most functional languages are good at dealing with multiple threads, mostly because of immutable data structures. However, some excel at it by focusing primarily on that task. These languages have great facilities for correctly managing multiple timelines in a straightforward way. They are organized by different classes of facilities.