charges.hs

data Rule = Rule {bytes :: Int,
                  cost :: Double}

charges :: [Rule] -> Int -> Double
charges = foldr applyCharge (const 0)
  where applyCharge _ _ 0 = 0
        applyCharge (Rule n mult) cont used = (mult * (fromIntegral $ min n used))
                                              + cont (max 0 (used - n))

value = charges (zipWith Rule [1024, 51200, 512000, 512000, 5120000, 1024000]
                      [0.0671, 0.0659, 0.0648, 0.0637, 0.0626, 0.0626])
                100000