This is a question that originated on the Elixir Slack from David Billskog and I have made only minor changes to the module.

Given this module:

defmodule Dummy do
  def execute(x) do
    with var_a <- get_a(x),
         var_b <- get_b(x) do
      IO.inspect(var_a, label: "a")
      IO.inspect(var_b, label: "b")
      IO.inspect({var_a, var_b})

      if var_a != var_b do
        IO.inspect(var_a, label: "a")
        IO.inspect(var_b, label: "b")
        IO.inspect({var_a, var_b})
      end
    end
  end
  defp get_a(x) do
    IO.puts("get a")
    if Enum.any?(x, & &1 == "A"), do: 3, else: 2
    |> IO.inspect(label: "returning a")
  end
  defp get_b(x) do
    IO.puts("get b")
    if Enum.any?(x, & &1 == "B"), do: 2, else: 1
    #|> IO.inspect(label: "returning b")
  end
end

Dummy.execute(["A", "B"])

I get this unexpected output:

$ elixir sample.exs
get a
get b
a: 3
b: 2
{3, 2}
a: 3
b: 1
{3, 1}

Does anyone understand what is happening here? I don’t expect for the value of b to change within the if statement, and I do expect the returning a inspect to be printed. Tested on elixir 1.11.2-otp-23 and erlang 23.0.2.