gistfile1.hs

taxRate threshold rate (total, amount)
    | amount > threshold = (total + (amount - threshold) * rate, threshold)
    | otherwise = (total, 0)

taxTable = [taxRate 60000 0.45, taxRate 30000 0.30, taxRate 15000 0.15]

tax amount = fst (calc(0, amount) taxTable)
    where calc (total, remainder) [] = (total, remainder)
          calc (total, remainder) (f:fs) = calc (f (total, remainder)) fs

> tax 72000
=> 16500.0