Daniel Strunk

Web Developer

Using Erlang in Elixir

Originally written on Saturday, July 29, 2017.

Erlang is a first-class citizen of Elixir. This isn't a surprise; Elixir compiles down to BEAM, Erlang's VM, which means we get to leverage the power of Erlang for free.

We can see this functionality demonstrated in translating an Erlang library function into Elixir code. First, a look at the Erlang version:


client() ->
    SomeHostInNet = "localhost", % to make it runnable on one machine
    {ok, Sock} = gen_tcp:connect(SomeHostInNet, 5678,
                                 [binary, {packet, 0}]),
    ok = gen_tcp:send(Sock, "Some Data"),
    ok = gen_tcp:close(Sock).
        

Probably most important to note is the syntax for calling an Erlang library in Elixir: :gen_tcp (note the colon). This lets Elixir's compiler know that a call to a native Erlang libary will be performed. Now, in Erlang:

  • Functions are indented until the end of the call. Functions in Elixir are wrapped in a def do, end block.
  • Multiline functions have commas, and the end of the function is terminated with a dot. Elixir doesn't need any of these. Note that this is simplified for our example, but this Stack Overflow question has a good explanation of when to use semicolons, commas or periods in Erlang.
  • Variables are capitalized. Elixir variables are lowercase and snake case, so SomeHostInNet becomes some_host_in_net.
  • Comments start with a %. In Elixir comments use #
  • Tuples look the same in Erlang vs Elixir. But looking at the first tuple in our Erlang function {ok, Sock}, ok is a symbol. In Elixir we prefix symbols with a colon, so ok becomes :ok. Note that the variable Sock will again become lowercased sock.
  • Library methods are called with the colon, e.g. gen_tcp:connect. In Elixir methods are called with the dot, or :gen_tcp.connect.

After converting the above, here is the Elixir implementation:


def client do
  some_host_in_net = "localhost" # to make it runnable on one machine
  {:ok, sock} = :gen_tcp.connect(some_host_in_net, 5678, [binary, {packet, 0}])
  :ok = :gen_tcp.send(sock, "Hello, World!")
  :ok = :gen_tcp.close(sock)
end
        

Once you understand some of the nuances of Erlang's syntax, you can see that it's a relatively straightforward exercise to convert methods between the two.

Written by Daniel Strunk.

Hi! I'm Daniel Strunk, a PHP developer proficient in Laravel, Craft CMS and Magento development. I'm an advocate for test-driven development, a typography nerd, and a fan of building applications to help keep my life in order.