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4d47's solution

to Hello World in the Elixir Track

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Instructions
Test suite
Solution

The classical introductory exercise. Just say "Hello, World!".

"Hello, World!" is the traditional first program for beginning programming in a new language or environment.

The objectives are simple:

  • Write a function that returns the string "Hello, World!".
  • Run the test suite and make sure that it succeeds.
  • Submit your solution and check it at the website.

If everything goes well, you will be ready to fetch your first real exercise.

Running tests

Execute the tests with:

$ elixir hello_world_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

Source

This is an exercise to introduce users to using Exercism http://en.wikipedia.org/wiki/%22Hello,_world!%22_program

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

hello_world_test.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("hello_world.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(trace: true)

defmodule HelloWorldTest do
  use ExUnit.Case

  test "says 'Hello, World!'" do
    assert HelloWorld.hello() == "Hello, World!"
  end
end
defmodule HelloWorld do
  @moduledoc """
  Elixir counts the number of arguments as part of the function name.
  For instance;

      def hello() do
      end

  would be a completely different function from

      def hello(name) do
      end

  Can you find a way to make all the tests pass with just one
  function?

  Hint: look into argument defaults here:
  http://elixir-lang.org/getting-started/modules.html#default-arguments
  """

  @doc """
  Greets the user by name, or by saying "Hello, World!"
  if no name is given.
  """
  @spec hello(String.t) :: String.t
  def hello(name \\ "World") do
    "Hello, #{name}!"
  end
end

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?