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Elixir: Functions

At a glance, functions in Elixir are like ones in imperative languages. But that only seems true. They are different in many ways and that influences your code organization inside them a lot.

The easiest way to define a function is to use the construction def/do/end:

def hello do
  IO.puts("Hello, World!")
end

If a function accepts no arguments, then we can omit brackets.

With arguments we write it the same way most of the languages has it:

defmodule Math do
  # Write name in snake_case
  def sum_of_values(a, b) do
    # Basic sum
    a + b
  end
end

# We can call functions without brackets!
IO.puts Math.sum_of_values(5, 8) # => 13

In Elixir there's no instruction return that might stop code execution. The result of function execution is always the last expression result. If the function is empty then it returns nil which is equal to null in other languages.

Another feature is that we can call a function without brackets. But there is a trick: in nested calls, it might cause confusion and unexpected behavior: IO.puts IO.puts "huh".

For one-liners Elixir supports a special short declaration syntax:

# Note that we put a comma before _do_ and we omit _end_
def sum_of_values(a, b), do: a + b

# or

def hello, do: IO.puts("Hello, World!")

Functions defined with def are available outside of its module. If we want to make a private function we should define it using defp.

defmodule Solution do
  # We can call the same module functions without specifying its module
  def hello, do: IO.puts(text_for_hello())

  defp text_for_hello, do: "Hello, World"
end

Instructions

Create function print_twice(value) that prints provided value twice

Solution.print_twice("WoW")
# => WoW
# => WoW
The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

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