List Comprehension Over Two Lists in Elixir

list_comprehension.exs

tax_rates = [NC: 0.075, TX: 0.08]

orders = [
  [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]
  ]

for {tax_state, tax_rate} <- tax_rates, current_order = [_, {:ship_to, order_state}, {:net_amount, amount}] <- orders do
  total_amount = case tax_state do
    order_state -> (1 + tax_rate) * amount
    _ -> amount
  end
  Keyword.put(current_order, :total_amount, total_amount)
end