Gist fixing Tiago Davi code

tiago_davi.exs

defmodule Tax do
	def get_tax_rates do
		[ NC: 0.075, TX: 0.08 ]
	end
	def get_orders do
		[
		    [ id: 123, ship_to: :NC, net_amount: 100.00 ],
		    [ id: 124, ship_to: :OK, net_amount: 35.50 ],
		    [ id: 125, ship_to: :TX, net_amount: 24.00 ],
		    [ id: 126, ship_to: :TX, net_amount: 44.80 ],
		    [ id: 127, ship_to: :NC, net_amount: 25.00 ],
		    [ id: 128, ship_to: :MA, net_amount: 10.00 ],
		    [ id: 129, ship_to: :CA, net_amount: 102.00 ],
		    [ id: 120, ship_to: :NC, net_amount: 50.00 ]
		]
	end
	def calculate(orders, tax_rates), do: _calculate(orders, tax_rates)
	defp _calculate(orders, tax_rates) do
		Enum.map(orders, &(_add_tax(&1,tax_rates)))
	end
	defp _add_tax(order = [id: id, ship_to: ship_to, net_amount: net_amount], tax_rates) do
		tax_rate = Keyword.get(tax_rates, ship_to, 0)
		total = (net_amount * tax_rate) + net_amount
		Keyword.put(order, :total_amount, total)
	end
end