Functional Programming With Elixir

01. Introduction & Un-learning

What’s unlearning has to do with learning ELixir? To explain this let me take you back to your elementary school.

Now Imagine you are sitting in your Maths class and professor tells you a = 1. What does it means to you? In would simply mean that a is equal to 1, it doesn’t say 1 is assigned to variable a.

So, if a is equal to 1 then 1 is also equal to a, isn’t it? Let’s find it out -

a = 1
1 = a

There are no errors, surprising isn’t it? Well there is no surprise, we are just following what we learnt in our elementary Maths class. Let’s try with one more example -

If name is equal to Shivam then Shivam is equal to my name

name = "Shivam"
"Shivam" = name

It works just prefect! So what’s going on, why don’t we see any errors? This is where I want you to unlearn your modern day programming concepts and go back to elementary school. Equal = is a match operator in Elixir and behaves just like what you learned in Maths. If Left Hand Side(LHS) = Right Hand Side(RHS), then RHS = LHS!

Equal = is not a assignment operator as you would think from other programming languages. It is merely matching your LHS and RHS, if they are equal then everything is fine, otherwise we get an error. This is also called as Pattern Matching and this is one of the superpower of Elixir, once you are hooked then there is no going back!

Let’s try one more time -

a = 1
2 = a

This time we get an error! Becuase your LHS is not equal to RHS, on the previous line we say a and 1 are equal, so how can 2 and a be equal?

You can also say that the value of 1 is now bound to the variable a.

Let’s try with one more example, square brackets means a List in Elixir, we will talk about it later on in the tutorial, for now just concentrate on LHS = RHS

[a, a] = [1, 1]

Let’s try with different values and see what happens -

[a, a] = [1, 2]

What happened the second time? a is already bound to 1, so it does not match with 2 and hence we get an error. Again just think of matching your LHS and RHS. This also bring us to one more important concept of functional programming and that is, all variable are Immutable.

02. Understanding Immutability

You must be wondering why are variables Immutable? Well, first having immutable variables feels closer to actual Maths so it feels Natural, second it offers immense Scalability, third as a programmer you don’t have to worry about Accidently Mutating any data, that means the State is naturally preserved.

Well, if everything is immutable, then Elixir must be creating copies of everything, how can this be efficient? That’s a good questions, the answer is compilers are highly optimized for handling immutability, so you don’t have to worry too much about creating copies.

Wait, did I just read compiler, so is Elixir a compiled language? Yes! ELixir is a compiled language and it runs on the Erlang Virtual Machine also knows as BEAM. Just like Java or Kotlin complies to bytecode and runs on the JVM, similarly we have BEAM.

03. Actor Model & Processes

What do you mean by an Actor, you can think of it as an Isolated unit for computation. It has a Mailbox where it received messages, Actor executes these messages and gives back the data. Each Actor has it’s own memory stack and is garbage collected seperately.

These Messages which an Actor receives are executed sequentially in First In First Out (FIFO) manner. You can have millions of Actors running simultaneously without any problem.

Elixir makes use of this Actor model and executes all code in Processes. These Processes are extremely light weight and are easy to spawn and shutdown. Processes form the basis of immense scalability, distributed nature and fault-tolerance offered by Elixir and in fact the BEAM.

04. Modules

All code in Elixir stays inside Modules

defmodule Hello do
  def say(name) do
    IO.puts("Hello #{name}")
  end
end

Hello.say("Shivam")