Same thing in ruby

tax_bands.rb

Infinity = 1.0/0
SAVINGS_INCOME_TAX_200910 = [[0, 6475], [0.1, 8915], [0.2, 43875], [0.4, Infinity]]
INCOME_TAX_200910         = [[0, 6475], [0.2, 43875], [0.4, Infinity]]

def tax(income, bands=INCOME_TAX_200910)
  rate, threshold = bands.first
  if income <= threshold
    rate * income
  else
    lowered_remaining_bands = bands[1..-1].map {|r, t| [r, t - threshold]}
    rate * threshold + tax(income - threshold, lowered_remaining_bands)
  end
end