[en] Add basic Elixir iex guide (#22454)

guide/english/elixir/iex/index.md

@@ -1,13 +1,85 @@
 ---
-title: IEX
+title: IEx
 ---
-## IEX (Interactive Mode)
+## IEx (Interactive Elixir Mode)
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/elixir/iex/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
+`iex` is *interactive Elixir*. It is a command-line interface to Elixir or your Elixir application.
 
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
+`iex` is [REPL][REPL] that allows you to evaluate any statement with immediate feedback. There's no need for compiling any code or putting your code into a script file.
 
-<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
+### Getting started
+
+With Elixir installed, you should be able to simply run `iex` from your shell and find something like the following:
+
+```shell
+$ iex
+
+Erlang/OTP 21 [erts-10.1.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]
+
+Interactive Elixir (1.7.3) - press Ctrl+C to exit (type h() ENTER for help)
+iex(1)>
+```
+
+Now you can evaluate any valid Elixir statement followed by pressing <kbd>ENTER</kbd> and the result will be displayed on the next line.
+
+```shell
+iex(1) 1 + 1
+2
+```
+
+### Tab completion
+
+`iex` features tab completion. Aside from saving keystrokes, it allows you to see which functions and submodules are available.
+
+For example, type <kbd>Da</kbd><kbd>TAB</kbd>. It should expand to `Date`. Now press <kbd>TAB<kbd> again and you'll see two options: `Date` and `DateTime` as both modules start with `Date`.
+
+Now let's say you want to use a function in the `Date` module but can't remember the name or arity. Type a <kbd>.</kbd> after the module name, press <kbd>TAB</kbd> and you'll see all available functions in the module.
+
+```shell
+iex(3)> Date.
+Range               add/2               compare/2
+convert!/2          convert/2           day_of_week/1
+days_in_month/1     diff/2              from_erl!/1
+from_erl!/2         from_erl/1          from_erl/2
+from_iso8601!/1     from_iso8601!/2     from_iso8601/1
+from_iso8601/2      leap_year?/1        months_in_year/1
+new/3               new/4               range/2
+to_erl/1            to_iso8601/1        to_iso8601/2
+to_string/1         utc_today/0         utc_today/1
+```
+
+You'll notice that `Range` at the top of the list. This is a submodule of `Date`. You can continue tab completion with submodules or functions.
+
+### Exiting
+
+To exit `iex`, press <kbd>CTRL</kbd>+<kbd>C</kbd> to bring up the break menu. You can press <kbd>a</kbd>, <kbd>ENTER</kbd> or just press <kbd>CTRL</kbd>+<kbd>C</kbd> a second time to exit.
+
+### Cancelling statement evaluation
+
+If you're writing a complex statement and make a mistake, you may be tempted to press <kbd>CTRL</kbd>+<kbd>C</kbd> to cancel statement evaluation as you would in a standard shell. Unfortunately that won't work in `iex` as it just brings up the break menu.
+
+`iex` allows a magic comment of `#iex:break` to be typed any time, followed by <kbd>ENTER</kbd> to abort statement evaluation.
+
+Let's take this example where you are constructing a map and forgot a quote partway through. You pressed enter to evaluate and get stuck at a statement continuation prompt and you want to abort. Just type `#iex:break` followed by <kbd>ENTER</kbd>:
+
+```shell
+iex(1)> %{ user: "tom, roles: ["admin", "manager"] }
+...(1)> #iex:break
+** (TokenMissingError) iex:1: incomplete expression
+
+iex(1)>
+```
+
+### Loading your Mix application
+
+`iex` can load a script during startup. A common use for this is loading your `mix.exs` script so that your `iex` session contains your whole application and its dependencies loaded and ready to work with.
+
+```shell
+$ iex -S mix
+```
 
 #### More Information:
-<!-- Please add any articles you think might be helpful to read before writing the article -->
+
+* [Official Elixir Documentation](https://elixir-lang.org/getting-started/introduction.html#interactive-mode)
+
+[REPL]: https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop