Implementing TAB autocompletion in Elixir - Need guidance

Challenges
1

Hi CodeCrafters team,

I’m working on the Shell challenge using Elixir and I’m stuck on Stage #QP2 (Tab Autocompletion - Builtin completion).

The Problem: The test expects TAB autocompletion to work, but Elixir/Erlang doesn’t have native readline support in standalone escripts like Node.js does with its built-in readline module.

What I’ve Tried:

  • :io.setopts(:standard_io, [expand_fun: &my_func/1])
  • Application.put_env(:stdlib, :shell_expand_fun, &my_func/1)
  • Manual character-by-character reading with IO.getn/2
  • Various terminal control sequences (ANSI, backspace, etc.)

None of these approaches work because Erlang’s expand_fun only works in an interactive Erlang shell, not in a compiled escript running standalone.

The Issue: In JavaScript (as shown in the community solutions), you can use Node.js’s readline module with a completer function:

javascript

readline.createInterface({
    completer: (line) => { /* autocomplete logic */ }
});

Elixir doesn’t have an equivalent built-in feature. The only solution would be to use an external library like erlang-readline or implement a C NIF binding to libreadline.

My Questions:

  1. Is it expected that Elixir users add external dependencies for this stage?
  2. Can I modify mix.exs to add {:erlang-readline, "~> 1.0"} or similar?
  3. Is there a CodeCrafters-specific solution I’m missing?
  4. Should I skip this stage for now if no native solution exists?

Current Test Output:

Expected: "$ echo "
Received: "$ ech   "

The autocompletion function is never triggered because there’s no way to hook into TAB handling in an Elixir escript without external libraries.

Any guidance would be greatly appreciated!

Thanks,
Illuminaxx

2

Hi, thanks for your post!

I’m currently out of the office for the holidays and will be back on January 5. I’ll get back to you as soon as possible once I return.