What Is Functional Programming

Why Should You Care?

Seattle Web Design
computer programming languages
8 min readMar 4, 2024


Functional programming is a programming paradigm and approach to software development that is almost a ‘way of life’ for how we write code. It emphasizes using pure functions — entities that rely strictly on their inputs to produce specific outputs, eliminating side effects. It also highlights utilizing a declarative approach, defining functions as expressions that connect values to other values and describing what the program should accomplish rather than how it should do it, in contrast to the imperative approach, which has a program operate step-by-step like a list.


It strays away from the traditional ‘imperative’ approaches and instead focuses on building complex programs by composing and applying simple functions.

Functional Programming in the Industry

While functional programming is predictable, maintainable, concise, and expressive, all at the same time, it does have its challenges. Transitioning to functional programming has an incredibly steep learning curve for developers who first learned other paradigms, forcing them to rewire their thinking and problem-solving approaches with new concepts like ‘immutability’ and ‘higher-order’ functions. Even so, a programmer’s efforts are rewarded with its ability to produce clean, maintainable, and scalable code, making it an incredible tool for tackling modern software challenges. Functional programming represents a ‘paradigm shift’ in software development, with its significance lying in its fundamental principles of simplicity, clarity, and efficiency. Companies and corporations often seek programmers who are well-versed in utilizing and leveraging a particular paradigm to address complex issues efficiently and ‘future-proof’ code, key principles that functional programming exemplifies.

What is Functional Programming? Why is it important?

Functional programming is a programming paradigm and approach to software development that uses pure functions such as variables, arguments, and return values to create navigable, maintainable software. ‘Programming paradigms’ are essentially different ways or styles in which a programming language can be organized to achieve one common goal: a functional program. The five main paradigms, imperative, procedural, functional, declarative, and object-oriented, were built by the programming community with a set of ideas or guidelines and consist of specific structures, features, and opinions about how common programming problems should be handled. In functional programming, programmers build complex programs by applying, composing, and maintaining a mass of simple functions for readability, composability, and modularity; it demonstrates what you want to achieve rather than how to reach it through its code. It also structures its code to support, utilize, and apply mainly mathematical functions.

Historical Roots

Functional programming originates from lambda calculus, a formal mathematical logic and computer science foundation system. Alonzo Church developed Lambda calculus in the 1930s as a way for computation and functions. Functional programming languages draw heavily from lambda calculus, and the connection between the two lies in their shared emphasis on functions as fundamental building blocks. Lambda calculus relies on ‘recursion’, a method of solving problems that require computing where the solution depends on solutions to smaller parts of the same problem. It uses variables to represent numbers and defines and manipulates functions to take a particular argument and return an exact result. Functional programming utilizes pure functions and uses lambda calculus’ idea of recursion as a way for iteration in programs to break down big problems into more manageable, smaller ones.

First-Class Citizens

In functional programming, one key concept is that functions are ‘first-class citizens’, meaning they can be assigned as variables, passed as an argument to other functions, and returned as a value from other functions. A function acts as an ‘entity’ which supports all the operations generally available to other ‘entities’. Simply put, first-class citizens are functions that can be assigned as a variable, an argument to other functions, or a way to return functions from other functions. First-class citizens function assigned as a variable, an argument, a function, a string, a way to return functions from other functions or a number, and you can move them around and use them in various ways with how diverse you can utilize them.

Pure Functions

Another key concept of functional programming is the idea of pure functions. A pure function relies only on its inputs to generate its result. Pure functions always produce the same fixed output for a fixed input, with no side effects. They don’t modify external states, variables, or anything outside the function. Wrapping our iteration within a function ensures it doesn’t change anything outside its environment. It creates a variable to process only the information it needs, and once the command is executed, the variable’s role is over. The function and its variable are strictly for ‘one-time use’.

Writing Programs with Functions

With these concepts in mind, functional programming encourages programs written primarily with functions. It supports the idea of code modularity, a programming concept where developers separate program functions into smaller, individual, and independent pieces to eliminate potential side effects, making it easier to identify and separate specific actions. Doing this improves the code’s maintainability and makes the program less prone to bugs and crashes.

The Use of Functions as Building Blocks

This can be thought of with fly screen doors. By using bigger functions, you can imagine fly screens that are generally cheaper, have fewer strands, and have bigger holes. It usually gets the job done and keeps flies out, but small, pesky flies still get through; in our case, ‘bugs’ are getting through our fly screen, which is our program. With fly screens with more strands and smaller holes, the bugs have a significantly diminished chance of getting through our fly screens. This is why functional programming can be so valuable in the eyes of many programmers. Using many functions that might be smaller and simpler but build on each other can be just as mighty as more extensive functions that may have more bugs as more complex code is added onto the program later down the road.

Examples of Programming Languages that use Functional Programming

Some examples of programming languages that utilize functional programming include Haskell, Lisp, Clojure, and Scala, which are mainly functional programming, along with JavaScript, Python, and Java, which utilize many elements of functional programming and other paradigms. These all use functional programming to deliver more concise, modular code that is easier to ‘decipher’ in specific scenarios.

Pros of Functional Programming

Clean and Maintainable code

Functional Programming offers many benefits, including stronger code maintainability and readability. It lets developers focus on the problem-solving aspect of their code and what the program should accomplish instead of how to achieve it. Code is broken down into small, concise functions, allowing for more readable code for users. In addition, when broken into smaller functions, it promotes reusable functions that are easier to debug and test. This ensures code that won’t introduce new bugs that need to be tested and reduces the time used during debugging. Functional programming promotes clean and maintainable code, increases productivity, and fosters improved collaboration among developers within a team. As functional programming becomes more popular, the readability and maintainability aspect of it will become valuable as it provides a strong foundation of code and long-term success within teams.

Reusable Functions and Components

Functional code is split into more concise functions, which create reusable functions. Reusable functions are cleaner, allowing developers to construct other software programs from the reusable components. Using functions that have already been tested and debugged in other programs minimizes the risk of more bugs within a code. In addition, the functions created can be written in a “generic manner, " enabling other developers to adapt and read it quickly in different contexts. Not only does this save development time, but it enhances the quality of the software and code itself. Functional programming is known for its high-level abstractions, which hide the extended details of the code and allow programs to be shorter and easier to use. Overall, functional programming enables developers to work efficiently because it provides precise and fast code writing and reduces the use of testing and debugging.

Cons of Functional Programming

Adjustment and Adaptability

Despite all of the advantages of functional programming, there are some cons to it as well. One major issue with functional programming is that it’s complicated to adjust and adapt to once you know other languages. For instance, functional programming differs from other common programming languages, so people have to learn a new paradigm if they would like to use functional programming. Most developers are accustomed to other languages that differ entirely from functional programming. Due to a more meticulous workload, this can cause an enormous learning curve for those trying to implement functional programming in their code. Furthermore, as you develop these skills and learn functional programming, you experience more complications because you need to be more thought-out. This causes the process to require more effort and becomes time-consuming, requiring a newly rewired way of thinking.

Limited Resources

Another disadvantage to learning functional programming is that more resources must be needed to understand the language. There are few library books and websites on functional programming to learn. Languages like Java and Python are often seen online and in libraries so that people can learn these languages quickly due to their availability. Programs like those have tutorials and videos for beginners, making adapting easier. However, since functional programming is less popular, there are fewer resources worldwide for people to learn and adjust to functional programming. In addition, functional programming is usually used by experienced programmers, making it even harder for beginners to learn. You can find videos like ‘Functional Programming — A General Introduction’ where functional programming is briefly explained but not taught in depth. Overall, the biggest issue of functional programming is the complex learning process.

Coding Examples

Functional Programming in Python

Here are a few examples of codes from different languages that can be used for functional programming that all serve various purposes. Note that languages have their benefits and drawbacks regarding their use in functional programming since these are only considered functional-capable languages. When it comes to functional programming with Python, it is regarded as a multi-paradigm language, and the best way to use functional programming with Python is to keep most of your code at the module level and switch to classes only when you need to. The downside of functional programming with Python is that since Python has classes, it can be difficult to make pure or immutable functions, meaning that they cannot be changed once created.

# Tuples are useful for immutable functions
tuple1 = (0, 1, 2, 3)
tuple[0] = 4

The code causes an error because it tries to reassign an immutable tuple object. Functional Python programs should use immutable data structures to achieve pure functions.

Functions should be used as objects in Python.

# This shows functions as objects
def shout(text):
return text.upper()
# This passes function as parameter
def shout(text):
return text.upper()
def greet(func):
# This has function being stored into a variable
# The output should be in all capitalization because of how 'shout' is the function
greeting = func("Hi, The World Revolves Around Programming")
print (greeting)

Outputs: Hi, The World Revolves Around Programming


Functional programming stands out for its capacity to create highly effective programs, offering versatile solutions across various programming languages such as Python, JavaScript, and Java. Its rise in popularity stems from its efficiency and scalability in tackling modern software challenges, underscoring its value from a programmer’s standpoint. Despite the challenges for first-time developers transitioning to functional programming, its benefits in clean, maintainable, and readable code make it essential. Functional programming is significant because it was created to create pure, immutable functions, drawing from lambda calculus to deal with many complex problems. It allows programmers to have easier and more methodical debugging and testing. As the software industry grows more and more, demanding more complex programs with more efficient coding, so will the relevance of functional programming, making it a cornerstone of both modern software engineering and its future.