Functional programming is a popular paradigm for software design, but it also comes with some trade-offs that you need to consider. In this article, you'll learn about some of the benefits and challenges of functional programming, and how to balance them in your projects.
Functional programming is a style of programming that treats computation as the evaluation of mathematical functions, and avoids changing state and mutating data. Functional programming emphasizes pure functions, which are functions that always return the same output for the same input, and have no side effects. Functional programming also supports higher-order functions, which are functions that can take other functions as arguments or return them as results.
Functional programming can offer several advantages for software design, such as improving readability and maintainability of code, facilitating testing and debugging, enabling parallel and concurrent programming, and promoting code reuse and modularity. By making it easier to reason about the logic and behavior of pure functions, functional programming can reduce the complexity and unpredictability of stateful and mutable code. This also allows for the composition of smaller and simpler functions into larger and more complex ones.
Functional programming is not a silver bullet and comes with some drawbacks and limitations, such as performance overhead due to more intermediate objects and function calls, or higher memory consumption because of immutable data structures. Additionally, it can be challenging to learn, as it uses unfamiliar syntax and concepts like lambda expressions, currying, monads, and functors. Furthermore, it can reduce interoperability by being incompatible or inconsistent with some existing libraries and frameworks that rely on imperative or object-oriented features.
Finding the right balance between functional programming design trade-offs is dependent on the context and goals of a project. Generally, functional programming should be utilized when it makes sense and provides clear benefits for the problem domain and requirements, such as in data processing, mathematical computation, and reactive programming. Imperative or object-oriented programming should be used where necessary for improved performance, compatibility, or simplicity, like user interface, database access, or system interaction. Combining functional and imperative or object-oriented programming can create a balanced and coherent design; for example, core logic and computation of an application can be done using functional programming while peripheral and integration aspects can be done using imperative or object-oriented programming.
If you want to learn functional programming, you have several options to consider. You could delve into a purely functional language such as Haskell, Clojure, or Elixir for a deep and comprehensive understanding; however, this may take more time and effort to master. Alternatively, you could opt for a multi-paradigm language like Scala, Kotlin, or JavaScript for a flexible and pragmatic approach; yet, this may come with some inconsistencies and trade-offs between paradigms. Lastly, you could learn a functional library such as Lodash, Ramda, or RxJS for a practical and convenient way to use functional programming features in your existing language; however, this may limit your exposure to some functional programming concepts and patterns.
If you've only worked with imperative/OOP in the past you might be best served by starting from "scratch" - think about what you did when you first learned programming and apply the same principles. Learn the basic syntax and semantics, then dive in and make some projects of your own. Once you've got the basics down, the best way to learn is practical experience. Perhaps you could translate your OOP projects to FP projects, in order of complexity? If your job involves a multi-paradigm language, it could also be worth refactoring code (where appropriate) to become functional - such as using LINQ to replace a clunky series of foreaches. Doing so could trim down the codebase and make it more readable, which your team will thank you for!
After so many years, the best books to learn functional programming are the Little Schemer, the Reasoned Schemer and the Seasoned Schemer by MIT Press. The best hands-on way to learn is to pick a language like Clojure (JVM) or Elixir (Erlang targets) to develop any backend application needed at work. While doing so, something taught in the MIT books, one learns that functional programming is a way to think about code and data architectures.