Recursion (Part 1)

Unlike in imperative languages, functional programming languages (including Elixir) achieve looping through recursion. Why? To explain that, let's consider C:

for(i = 0; i < 5; i++) {
  sum = sum + i;
}

Here we are modifying (mutating) the value of i as well as sum in each interation. Mutation is considered as a bad practice and functional programming languages do not encourage it. Let's see some basic examples of recursion in Elixir.

Say, we want to print the message "hello" five times. How do we do that?

defmodule Recursion do
  def print_hello(n) when n <= 1 do
    IO.puts "hello"
  end

  def print_hello(n) do
    IO.puts "hello"
    print_hello(n - 1)
  end
end

Recursion.print_hello("Hello!", 3)
# Hello!
# Hello!
# Hello!

Here, defmodule is used to define a module (group of several functions). We can have multiple definitions of the same function. In the first function when n <= 1 is a guard. This function will get executed only when the guard condition is satisfied (no wonder why it is called a guard!). When there are multiple clauses (definitions) of the same function, Elixir looks for a match and executes it when it finds one. If no matches are found, it will throw error.

In this case, when n = 3 and n = 2, the second clause will be executed. When n = 1, the first clause will get executed. 

Read more:

• Modules
• Recursion

Elixir Language (Part 5)

Binaries

In the last section, we talked about representing strings as UTF-8 encoded binary. But we left a topic for this section: How a character having code point above 255 is represented in binary?

Well, we all know that a single byte can only hold a value between 0 and 255. Let's consider the string hełło. Here ł has a code point 322.

This is where UTF-8 comes into picture. It solves the problem by using 2 bytes to represent each ł, and one byte each to represent h, e and o.

iex> string = "hełło"
"hełło"
iex> byte_size string
7
iex> String.length string
5

Here, we can see that the byte size of the string is 7 while the string length is 5. The function byte_size/1 can be used to check how many bytes are actually used in the memory to represent the given string.

Read more: Binaries, strings and char lists