Debugging In Elixir

tl;dr

Use IO.inspect or IEx.pry:

# inspect
[1, 2, 3]
|> IO.inspect(label: "before")
|> Enum.map(&(&1 * 2))
|> IO.inspect(label: "after")
|> Enum.sum

# pry
def some_fun(a, b, c) do
  require IEx; IEx.pry
  ...
end
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Other Resources

Other resources can be found at https://elixir-lang.org/getting-started/debugging.html

IO.Inspect/2

What makes IO.inspect(item, opts \\ []) really useful in debugging is that it returns the item argument passed to it without affecting the behavior of the original code.

(1..10)
|> IO.inspect
|> Enum.map(fn x -> x * 2 end)
|> IO.inspect
|> Enum.sum
|> IO.inspect

[1, 2, 3]
|> IO.inspect(label: "before")
|> Enum.map(&(&1 * 2))
|> IO.inspect(label: "after")
|> Enum.sum

# 3
def some_fun(a, b, c) do
  IO.inspect binding()
  ...
end
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Outputs:

# 1
1..10
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
110

# 2
before: [1, 2, 3]
after: [2, 4, 6]

# 3
[a: :foo, b: "bar", c: :baz]
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IEx.pry/0

Similar to Ruby's binding.pry. Will open an interactive shell.

def some_fun(a, b, c) do
  require IEx; IEx.pry
  ...
end
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