-module(hello_world). -export([start/0]). start() -> io:format("Hello, World!~n").
Hello World in Erlang was written by:
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Erlang looks scary when you first look at it, so we'll show the full program and then we'll break it down into parts to fully describe it.
The first key part of an Erlang program is the
-module(). preprocessor directive:
Every Erlang file must start with this directive or you'll get a compiler error like the following:
file.erl:2: no module definition
Next, to use functions from the module we've written we have to export them explicitly.
This exports our
start function, it takes no arguments so we reference the function as
start/0. The number of arguments is called the "arity" of the function.
Functions in Erlang start with an atom (for now, think of these as just lowercase letters + underscores), then the parameters, followed by an arrow
->. The following functions are both valid:
my_function() -> ok. myfunction() -> ok.
start function only does one thing for this simple program, it calls the
format function from the
io module to print characters to standard output by default.
io:format(). The string
"Hello world!~n" includes the newline control sequence
~n - you can see a list of control sequences available for use in the documentation for
io:fwrite here (scroll down to "Available control sequences").
To run this example, you need to follow a few steps:
erlc hello_world.erlin your terminal to compile the program to a BEAM file - this results in the file
l(hello_world).- remember to end with a period! This is to load a module into the shell
hello_world:start().- you should see
Hello, World!printed to the shell.
q().or Ctrl-C, a (abort).