Elixir example for using "with" for a "unhappy path" lol.

with_example.exs

#
# Checkout: WithExample.inverse_with
#
defmodule WithExample do

    # Helper functions
    def ok(result), do: {:ok, result}
    def error(error), do: {:error, error}

    # This is what we all have in mind and see in the examples.
    # Following a "happy path" and break if we leave that path.
    def normal_with do
      with {:ok, a} <- ok(1),
           {:ok, b} <- ok(2),
           {:ok, c} <- ok(3) do
        {:ok, a+b+c}
      end
    end

    # But what if we _want_ to find the first "break of the happy path"?
    # We simply need to inverse the "happy path" to a "unhappy path".
    def inverse_with do
      with {:error, a} <- error(:a),
           {:error, b} <- ok(42),
           {:error, c} <- error(:c) do
        {:error, [a, b, c]}
      end
    end

end

IO.inspect(WithExample.normal_with) # {:ok, 6}
IO.inspect(WithExample.inverse_with) # {:ok 42}