Elixir - Loops

Due to immutability, loops in Elixir (as in any functional programming language) are written differently from imperative languages. For example, in an imperative language like C, you will write −

for(i = 0; i < 10; i++) {
   printf("%d", array[i]);
}

In the example given above, we are mutating both the array and the variable i. Mutating is not possible in Elixir. Instead, functional languages rely on recursion: a function is called recursively until a condition is reached that stops the recursive action from continuing. No data is mutated in this process.

Let us now write a simple loop using recursion that prints hello n times.

defmodule Loop do
   def print_multiple_times(msg, n) when n <= 1 do
      IO.puts msg
   end

   def print_multiple_times(msg, n) do
      IO.puts msg
      print_multiple_times(msg, n - 1)
   end
end

Loop.print_multiple_times("Hello", 10)

When the above program is run, it produces the following result −

Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello

We have utilized function's pattern matching techniques and recursion to successfully implement a loop. Recursive definitions are difficult to understand but converting loops to recursion is easy.

Elixir provides us the Enum module. This module is used for the most iterative looping calls as it is much easier to use those than trying to figure out recursive definitions for the same. We will discuss those in the next chapter. Your own recursive definitions should only be used when you dont find a solution using that module. Those functions are tail call optimized and quite fast.