Elixir: When to use .ex and when .exs files

Question

Elixir\'s documentation states that

In addition to the Elixir file extension .ex, Elixir also supports .exs files for scripting. Elixir treats both

Answer 1

I check it in Elixir version 1.9.1 and both extensions .ex, .exs will be compiled with elixirc. Another words, we get bytecode (.beam file) in both cases.

Answer 2

.ex is for compiled code, .exs is for interpreted code.

ExUnit tests, for example, are in .exs files so that you don't have to recompile every time you make a change to your tests. If you're writing scripts or tests, use .exs files. Otherwise, just use .ex files and compile your code.

As far as pros/cons, interpretation will take longer to execute (as elixir has to parse, tokenize, etc.), but doesn't require compilation to run. That's pretty much it - if the flexibility of running scripts is more important than optimized execution time, use .exs. Most of the time, you'll use .ex.

Answer 3

Elixir will compile the whole .ex file. .exs Files are compiled as well but are meant to be executed when invoked. So, most use cases of .exs files are to execute code immediately when called. Think of using .exs files for testing, migrating data and running scripts. Think of .ex files as being used for your application's main business logic.

Consider this example

.ex sample

sum.ex

defmodule Sum do
  add(a, b) do
     a + b
  end
end

$ iex sum.ex

iex> Sum.add(1,2)
3

.exs sample

sum.exs

defmodule Sum do
  def add(a,b)  do
    a + b
  end
end

#within same file

IO.puts "The sum of 3 + 2 is: #{inspect Sum.add(3, 2}"

$ elixir sum.exs

 ->> "The sum of 3 + 2 is: 5"