nix/modules/home-manager/iex.nix

{
  home.file.".iex.exs" = {
    enable = true;
    text = ''
      Application.put_env(:elixir, :ansi_enabled, true)

      # PROTIP: to break, `#iex:break`

      IEx.configure(
        colors: [enabled: true],
        inspect: [
          pretty: true,
          printable_limit: :infinity,
          limit: :infinity,
          charlists: :as_lists
        ],
        default_prompt: [
          # ANSI CHA, move cursor to column 1
          # "\e[G",
          :magenta,
          # IEx prompt variable
          "%prefix",
          "#",
          # IEx prompt variable
          "%counter",
          # plain string
          ">",
          :reset
        ]
        |> IO.ANSI.format()
        |> IO.chardata_to_string()
      )
    '';
  };
}