Hello, World

The classic first program: print the line Hello, BEAM!. Notice how the BEAM languages diverge already on day one - Erlang and LFE reach for io:format, Elixir has a friendly IO.puts, Gleam routes everything through its typed gleam/io module, and Luerl runs plain Lua's print. Watch the surface syntax (S-expressions vs. pipes vs. ML-style) while the underlying runtime stays the same.

Erlang

-module(hello).
-export([main/0]).

main() ->
    io:format("Hello, BEAM!~n").

-module(hello).
-export([main/0]).

main() ->
    io:format("Hello, BEAM!~n").

Erlang wraps code in a -module/-export pair and prints with io:format/1, where ~n is the format control sequence for a newline.

Elixir

defmodule Hello do
  def main do
    IO.puts("Hello, BEAM!")
  end
end

Hello.main()

defmodule Hello do
  def main do
    IO.puts("Hello, BEAM!")
  end
end

Hello.main()

Elixir's IO.puts/1 writes a string and appends the newline for you; modules and functions are defined with defmodule and def.

Gleam

import gleam/io

pub fn main() -> Nil {
  io.println("Hello, BEAM!")
}

import gleam/io

pub fn main() -> Nil {
  io.println("Hello, BEAM!")
}

Gleam keeps side effects explicit: you import gleam/io and call io.println, which returns Nil - the empty type that the public main function also yields.

LFE

(defmodule hello
  (export (main 0)))

(defun main ()
  (io:format "Hello, BEAM!~n"))

(defmodule hello
  (export (main 0)))

(defun main ()
  (io:format "Hello, BEAM!~n"))

Lisp Flavoured Erlang expresses the same module in S-expressions, calling the very same io:format BEAM function with Erlang's ~n newline directive.

Luerl

local function main()
  print("Hello, BEAM!")
end

main()

local function main()
  print("Hello, BEAM!")
end

main()

Luerl runs standard Lua on the BEAM, so the idiomatic choice is Lua's built-in print, which writes its arguments followed by a newline.