Programming Elixir ≥ 1.6

Debugging with IEx

You already know that IEx is the go-to utility to play with Elixir code. It also has a secret and dark second life as a debugger. It isn’t fancy, but it lets you get into a running program and examine the environment.

You enter the debugger when running Elixir code hits a breakpoint. There are two ways of creating a breakpoint. One works by adding calls into the code you want to debug. The other is initiated from inside IEx. We’ll look at both using the following (buggy) code:

tooling/buggy/lib/buggy.ex

defmodule Buggy do
  def parse_header(
    <<
      format::integer-16,
      tracks::integer-16,

    division::integer-16
    >>
  ) do

    IO.puts "format: #{format}"
    IO.puts "tracks: #{tracks}"
 IO.puts  ...