Among the programming paradigms, functional programming is one that makes code easy to understand because of modularity and conciseness. It focuses primarily on what needs to be done rather than how it should be done. Hence, it is a subset of declarative programming, and its data is immutable, i.e., it cannot be altered after creation.
Although functional programming is less popular than object-oriented programming , it is gaining traction these days due to the rise of machine learning , big data, data science, and parallel computing.
Several programming languages, such as Python, Java, Scala, etc., are popular due to their features, ability to support concurrent and multithreading programming, and huge community. They follow several programming paradigms, including functional programming.
This blog post aims to enlist some of the top and widely used functional programming languages. Before delving into the list, let us briefly discuss functional programming.
What is Functional Programming?
Functional programming is a programming paradigm that leverages pure functions to write programs and solve problems. It primarily focuses on what result a program will yield rather than how. Simply put, functional programming focuses completely on the result rather than the procedure.
In programming, a function is a set of instructions or a code block that performs a certain task or produces a specific result. Pure functions are those that do not interact with outside elements and do not change after their creation.
Features of Functional Programming
- High-order functions
- Immutable data structures
- No exceptions for error handling
- Pattern matching
- First-class functions
- Function composition
- Recursion
- Referential transparency
Advantages of Functional Programming
- The modularity of functional programming makes the code easy to read and understand.
- It is possible to use lambda calculus in a program to solve complex problems.
- Functional programming languages improve the maintainability of code, as some of them support nested functions.
- They use functional constructs, such as the lazy map, lazy evaluation, and list.
- The use of pure functions makes debugging and unit testing easier and quicker. This means it becomes easy to identify and solve errors.
- There is no scope for the race condition to occur, as pure functions do not share their states with other parts of the code.
If you want to read more about it, read our article: Functional Programming .
Top 10 Functional Programming Languages
Let us now take a look at some of the top functional programming languages.
1. Haskell
Stable release: Haskell 2010 (July 2010)
Haskell is a general-purpose, purely functional programming language that first appeared in 1990. It is a statically typed language with lazy evaluation and type inference. The language is named after Haskell Curry, who was a logician.
The major implementation of Haskell can be observed in the Glasgow Haskell Compiler (GHC). It serves as an interpreter and a native code compiler.
Haskell is specially designed for teaching, research, and industrial applications. The semantics of the Miranda programming language forms the basis for Haskell’s semantics.
Features
- Lazy evaluation
- Concurrent
- Pattern matching
- List comprehension
- Lambda expressions
- A strong, static type system based on Hindley–Milner type inference
- Type polymorphism
- A plethora of packages
Applications Developed using Haskell
- Agda, a proof assistant.
- Cabal, a tool for building and packaging Haskell libraries and packages.
- Darcs, a revision control system.
- Git-annex, a tool to manage big data files under Git version control.
- Linspire Linux used Haskell to build system tools development.
- Pandoc, a tool that converts one markup format into another.
- Pugs, a compiler and interpreter for the Raku programming language.
- Xmonad, a Windows manager for X Windows System.
- TidalCycles, a domain language for live coding musical patterns.
Best for: Academia, mathematics & programming research, and industrial applications. Sometimes, data scientists use Haskel for data abstraction, and full-stack developers use it to build websites and software applications.
2. Java
Stable release: Java SE 20 (21 March 2023)
Java is among the most popular general-purpose, functional, and object-oriented programming languages. Originally designed by James Goslings in 1995, the language’s WORA (Write Once, Run Anywhere) feature makes it stand out from others. This implies the compiled Java code can run on all other Java-enabled platforms without recompiling it.
Any Java program or application is first compiled into Java bytecode that can run on any system with a Java Virtual Machine (JVM). The language's syntax is similar to other traditional compiled languages – C and C++ .
Earlier, Java was the official language for Android app development, which is now replaced by Kotlin. Besides, it is widely used in machine learning and data science applications. The robustness, security, portability, and ease of use make Java more popular among software developers, web developers, and data professionals.
Sun Microsystems has defined the following four editions of Java targeting different application environments:
- Java Card for smart cards.
- Java Platform, Micro Edition (Java ME) , targeting environments with limited resources.
- Java Platform, Standard Edition (Java SE) , targeting workstation environments.
- Java Platform, Enterprise Edition (Java EE) , targeting large distributed enterprise or Internet environments.
Features
- Platform-independent
- Portable
- Compiled and interpreted
- Multithreaded
- Object-oriented
- Distributed
- Dynamic and extensible
Dive deep into the details of Java Features .
Applications Developed using Java
- Spotify, a music streaming desktop, mobile, and web application.
- Twitter, a social media platform.
- Opera Mini, a web browser.
- Signal, an encrypted instant messaging service.
- Google Earth, a computer program that renders 3D representations of Earth based on satellite imagery.
- NetBeans IDE, an integrated development environment for Java.
- Cash App, a mobile payment service.
- Hancom Office, an office suite that includes a word processor, spreadsheet software, presentation software, and a PDF editor.
Best for: GUI-based desktop apps, mobile apps, web apps, enterprise apps, IoT apps, games, AI and ML apps, embedded systems, web browsers, and web and application servers.
If you want to learn Java from scratch, you can refer to your Java Tutorial .
3. Python
Stable release: Python 3.11 (October 2022)
Python is also a general-purpose, functional, and object-oriented programming language with a wide range of applications. According to the TIOBE Index of August 2023 , the language tops the list of popular programming languages.
Guido Van Rossum designed Python as the successor of the ABC language and made it publicly available in 1991.
The language is popular and widely employed due to its simple and easy-to-learn syntax. It uses plain English, eliminating complex delimiters like semicolons and curly braces. Its design philosophy emphasizes code readability with the use of significant whitespace indentation.
Moreover, Python’s standard library offers a plethora of useful tools to accomplish several tasks. Hence, it is often referred to as “batteries included”. The official repository of Python’s third-party software is the Python Package Index (PyPI), which consists of over 300,000 Python packages.
Features
- Object-oriented and procedure-oriented
- Interpreted
- Robust and vast standard library
- Portable
- Dynamically typed
- Extensible
- GUI programming support
- Dynamic memory allocation
Applications Developed using Python
- Instagram, a social media platform.
- Pinterest, a social media network allowing users to bookmark images.
- Spotify, a music streaming app.
- Dropbox, a file hosting service.
- Uber, a ride-hailing service offering food delivery and peer-to-peer ridesharing and bicycle-sharing.
- Reddit, a social news aggregator and discussion platform.
- Quora, a platform allowing users to ask and answer questions on a variety of topics.
Best for: GUI-based desktop applications, software development, web applications, task automation/scripting, data analysis , machine learning, data visualization, and web scraping .
Learn the basics of Python with our Python Tutorial .
4. Scala
Stable release: Scala 3.3.0 (May 2023)
Scala is a general-purpose, statically typed programming language that follows object-oriented and functional programming paradigms. The primary aim of designing the language was to address the criticisms of Java.
Martin Odersky, in 2004, designed the language and named it Scala as the combination of scalable and language. The name represents that the language is designed in a way that it grows with the demands of users.
A Scala program can be compiled into Java bytecode, which runs on the Java Virtual Machine (JVM). More interestingly, it can be compiled into JavaScript, allowing it to run inside a web browser. For this, a Scala compiler named Scala.js comes in handy.
Features
- Immutability
- Lazy evaluation
- Concurrency
- Pattern matching
- Type inference
- High-order functions
- String interpolation
- Rich collection set
Technologies Developed Using Scala
- Apache Spark, a distributed computing system.
- Apache Kafka, a distributed event streaming platform.
- Apache Samza, a processing framework.
- Akka, a toolkit and runtime for building distributed and concurrent systems.
- Finagle, a remote procedure call system.
- Scalding, a domain-specific language for Apache Hadoop.
Best for: Data-intensive distributed systems, modular and scalable software, big data applications, enterprise apps, web applications, parallel processing, and real-time data processing.
5. JavaScript
Stable release: ECMAScript 2021 (June 2021)
JavaScript is the language of the Internet that powers the majority of websites. More than 98.7% of websites on the Internet leverage JavaScript for client-side development. It is one of the cornerstone technologies of the World Wide Web (WWW), alongside HTML and CSS .
The language is a high-level language that conforms to the ECMAScript standard. It is a just-in-time compiled language featuring dynamic typing, first-class functions, and prototype-based object orientation. It supports event-driven, functional, and imperative programming paradigms.
Furthermore, JavaScript has application programming interfaces (APIs) that help you work with regular expressions, standard data structures, dates, texts, and Document Object Model (DOM).
The advent of Node.js has made it possible to use JavaScript for back-end development . As a result, developers can stick to a single language, JavaScript, for both the back-end and front-end of web applications.
Want to learn the basics of JavaScript? Check out our JavaScript Tutorial .
Features
- Platform-independent
- Arrow functions
- Dynamically typed
- Event handling
- Client-side validations
- Prototype-based
- Async processing
Applications Developed using JavaScript
- Netflix, a subscription-based, on-demand video streaming service.
- Uber, a ride-hailing service.
- Candy Crush, an engaging puzzle game.
- Facebook, a social networking platform.
- LinkedIn, a professional social networking platform.
Best for: Web applications, websites, desktop applications, presentations, server applications, web servers, games, mobile apps, smartwatch apps, and flying robots.
6. Clojure
Stable release: Clojure 1.11.1 (April 2022)
Clojure is a dynamic, compiled general-purpose programming language and a functional dialect of the Lisp programming language on the Java platform. It combines the interactive development of a scripting language with a robust infrastructure for multithreaded programming.
The language was designed by Rich Hickey, as his aim was to create a modern Lisp for functional programming that should support concurrency.
Though it is a compiled language, Clojure is completely dynamic. This implies every feature of Clojure is supported at the runtime. The language’s syntax is designed using S-expressions. A reader or read function first parses these expressions into data structures and then compiles them.
The read function or reader supports literal syntax for maps, sets, vectors, and lists. Additionally, Clojure treats code as data and features a Lisp macro system. It has immutable and persistent data structures. It also features a software transactional memory system and reactive Agent system to ensure clean and multi-threaded designs.
Features
- Dynamic development
- Functional programming
- Runtime polymorphism
- Concurrent programming
Companies using Clojure
- Nubank
- Walmart Labs
- CircleCI
- Puppet Labs
- Prismatic
- Factual
- Drift
- Onyx
- Preact
Best for: Website development, shell scripts, scraping web pages, HTML templating, and async web servers.
7. Kotlin
Stable release: Kotlin 1.9.10 (August 2023)
Kotlin is a high-level, cross-platform, general-purpose programming language that fully interoperates with Java. Currently, it is the official and preferred language for Android app development. It is statically typed, and its JVM version of the standard library depends on the Java Class Library.
Furthermore, Kotlin was added as an alternative to the standard Java compiler from the release of Android Studio 3.0. The Android Kotlin compiler generates the Java 8 bytecode by default. However, programmers have the flexibility to choose from Java 9 to Java 20.
Regarding syntax, Kotlin is more concise and clear than Java. It does not necessarily require semicolons as statement terminators. Many times, a newline is enough for the compiler to understand that a statement has ended.
Unlike Java, Kotlin does not restrict the static variables and methods to exist only within a class body. It enables programmers to define static objects and functions at the top of the package without requiring a redundant class level.
Besides Java, Kotlin code can be compiled into JavaScript. This comes in handy when there is a need to develop web applications in Kotlin or create the back-end of web applications in Kotlin and the front-end in JavaScript.
Features
- Interoperability with Java
- JavaScript transpilation
- Expressive code
- Null safety
- Concise and clear code
- Statically typed
- Explicit typecast
Applications Developed using Kotlin
- Evernote, a note-taking application.
- Coursera, a global online learning platform.
- Trello, a project management application.
- Postmates, a food delivery service.
- Basecamp 3, a project management application.
Best for: Android development, back-end web development, full-stack web development, multi-platform mobile development, and data science .
8. Rust
Stable release:
Rust is yet another functional and general-purpose programming language. It emphasizes performance, type safety, and concurrency. Also, it ensures memory safety without the use of a garbage collector or reference counting. It features a borrow checker, which enforces memory safety and prevents data races.
Graydon Hoare, a software developer, designed Rust as a personal project but made it publicly available in 2015. Since December 2022, the language has been used in the development of the Linux kernel alongside C and assembly languages.
The syntax of Rust is analogous to C and C++. The language’s ecosystem comprises a compiler, a standard library, and many other components for software development. Rust is faster than other memory-safe languages, as it does not perform garbage collection. It aims to achieve memory safety without sacrificing performance.
Features
- Immutability
- High-order functions
- Algebraic data types
- Pattern matching
- Zero cost abstraction
- Error messages
- Memory safety
Companies using Rust
- Amazon
- Discord
- Dropbox
- Meta
- Microsoft
Best for: Systems programming, web development, game development, command-line tools and utilities, cross-platform development, scientific computing, and networking.
9. Erlang
Stable release: Erlang 26.0.2 (June 2023)
Erlang is a general-purpose programming language that follows concurrent and functional programming paradigms.
There is also a garbage-collected runtime system called Erlang/OTP or Open Telecom Platform. It consists of ready-to-use components written in Erlang and a collection of design principles for Erlang programs or libraries. Additionally, it has a distributed database , applications to interface with other languages, and debugging and release handling tools.
Joe Armstrong, Robert Virding, and Mike Williams designed Erlang. The runtime system was initially a proprietary software within Ericsson. In 1998, it was available publicly. Currently, the Open Telecom Platform (OTP) product unit at Ericsson develops and maintains Erlang/OPT.
The Erlang language is primarily used to develop scalable, soft real-time, distributed, and highly available systems. The runtime system ensures concurrency, distribution, and fault tolerance. You need to write hundreds of small Erlang processes to build a single Erlang application.
Features
- Immutable data
- Pattern matching
- Eager evaluation
- Single assignment
- Dynamic typing
- A powerful model for error containment and fault tolerance
- Ready-to-use Erlang programs or libraries
Applications Developed using Erlang
- RabbitMQ, an open-source message broker software.
- Whatsapp, an instant messaging application.
- Facebook’s chat backend.
- Klarna, an electronic payment system.
Companies using Erlang
- Ericsson
- AdRoll
- Mitel
- Telia
- Wavenet
- Gambit Research
Best for: Software development in telecommunication systems, messaging and chat applications, distributed and fault-tolerant systems, and games.
10. Swift
Stable release: Swift 5.8.1 (June 2023)
Swift is a compiled, high-level, general-purpose programming language developed by Apple Inc. The company designed Swift and released it in 2014 as the replacement for its earlier language, Objective-C. Introducing the new language was due to the lack of modern features in Objective-C.
Apple’s Swift supports multiple features and core concepts of Objective-C, such as dynamic dispatch, late binding, extensible programming, etc. The only difference is that Swift provides these features in a safer way, making it easy to identify software errors.
Some notable features of Swift address common programming errors, such as null pointer dereferencing and pyramid of doom. The language has clear and concise syntax and is completely interoperable with Objective-C.
Features
- Native error handling
- Memory safety
- Automatic Reference Counting (ARC)
- Flexible enumerations
- Closure syntax
- Powerful generics
Applications Developed using Swift
- Lyft, a ride-sharing app.
- LinkedIn, a professional social networking app.
- Airbnb,
- Khan Academy, an online learning platform.
- Coursera, an online learning platform.
- Slack, a professional team communication and collaboration platform.
Note: It is important to note that all these applications were developed using Swift only for iOS and macOS.
Best for: Software development for iOS, macOS, Apple TV, and Apple Watch.
Conclusion
The functional programming paradigm is gaining popularity with the rising use of big data and machine learning. It enables developers and programmers to solve complex problems quickly and easily. Its primary aim is to make the source code readable with the feature of modularity. This helps identify errors and bugs and fix them quickly. Though it differs from object-oriented programming, it aims to achieve concurrency, reliability, and high performance.
After reading the list of the top functional programming languages, we hope that you have a clear idea of the usage and popularity of functional programming. The languages listed above are widely used for different purposes. So, choose any of the above functional programming languages based on your project requirements.
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