This article is the translation based on the original material by Irina Linnik. We decided that these thoughts and considerations she wrote about can be quite useful for our English-speaking audience. Here we will tell you basic pros and cons of functional programming and show why you should consider it.
Programmers are very creative people but at the same time, they tend to follow some trends in choosing their programming language. For instance, PHP is considered ‘lazy’ language, and JavaScript is ‘difficult predictable magic’. Nowadays, functional languages becoming more and more popular and getting the attention of world biggest companies. According to different analytics and a common evaluation of the popularity of languages on GitHub and Stack Overflow, the functional languages (like Elm or Elixir) slowly gaining the momentum. The enormous increase in the popularity of JavaScript also leads to increased interest in functional programming. In addition, developers with experience in functional programming subsequently began to work on SPA frameworks, and as a result, we have Redux, React, MobX and other libraries that millions of people use.
So, what functional programming is and why it became so popular? Let’s take a closer look.
It is worth to start from the start.
The JavaScript world is very active. A few years ago only a few developers had the idea of functional programming. But over the last three years, almost every large application code base was using the ideas from functional programming. And there are objective reasons for that:
The main distinguishing features of software development that uses functional programming (FP):
Functional programming is essentially based on the fundamental, determining principles of the above. When you start with FP it is necessary to switch to the ‘academic’ mode and study all the definitions or terms that you will come across: pure functions, function composition, shared state avoidance, etc. After that, you will be completely different in looking at both the functional and the programming as a whole. Here the example of some terms:
Pure functions are deterministic functions without side-effects. A deterministic function means that it returns the same result for the same set of input values. For FP, the properties of such functions are very important. For example, pure functions have reference transparency – you can replace the function call with its final value, without changing the values of the program.
Function composition means the process of combining two or more functions in order to create a new function or perform calculations.
What is shared state? The main problem of shared states is to understand the effects of a function. You need to know the whole history of each variable that the function uses. Therefore, functional programming avoids shared states, instead relying on immutable data structures and pure computations to extract new data from existing ones. Another nuance that occurs when working with shared states – changing the order of functions calls can lead to the avalanche of errors. That is why avoiding shared states with help you to avoid this problem.
Immutability is the core of functional programming (don’t mix it up with constants). ‘const’ creates is used for variable’s name that cannot be reassigned after creation. But it does not create immutable objects. You will not be able to change the object to which the binding relates, but you can still change the properties of this object.
Side-effects mean that in addition to the return value, the function also interacts with an external variable state. Why FP avoids side-effects? Because in this way the effects of the program are much easier to understand and test. Haskell, for example, uses monads to isolate side effects from pure functions.
The imperative approach follows the principle of workflow control and answers the question ‘how to do’. The declarative approach describes the data flow and answers the question ‘what to do’. In addition, the imperative code most often uses instructions (operators), and declarative relies more on expressions.
So, we seem to figure out what functional programming is and what you need to know about it. And before we move on to discuss its advantages, let’s go through the shortcomings. What is the essence of the stereotype that ‘functional programming is unnatural’.
Some programmers do still think that functional programming is weird. And that is somewhat true. Here’s the quote from the Internet that describes FP with the next words:
Writing a functional code is like writing the code backwards. And it’s more similar to solving the puzzle, rather than explaining the process to a computer.
In fact, this is rather a subjective attitude to the functional programming formed by people who do not want to spend enough time to understand the FP nuances.
Now we’ll move on to
Disadvantages
Check the lists of FP disadvantages on Quora and in the article by Alexander Alvin too.
Okay, the last point we mentioned is not very related to cons because we cannot blame functional programming for what it was not meant to be.
Advantages
You can find other functional programming benefits here.
These days developers try to solve the problem of parallel processing and working with Big Data. By parallelizing the processing of these data you get the desired result quite fast. Plus, do not forget about decentralized (distributed) calculations like blockchain. Due to functional programming principles, the functional code is the most suitable for such computations. The use of all basic API techniques facilitates the parallel execution of the code and its support.
In the beginning, functional programming was used only for solving specific problems. But now it is applied even in classic projects created by large IT companies.
Here you will find some tips that will help you to start with FP.
Find more useful resources to learn elixir we mentioned in Elixir from a Rubyist’s perspective article!
Good luck!
Not so long ago we have published a short comparison of Elixir and Ruby. That might be a useful reading too!