Table of Content
Just like what I said in previous, there is other way to calculate.
Flatly 0 until 50 million: 5% > 50 until 250 million: 15% - 5 million > 250 until 500 million: 25% - 30 million > 500 million : 30% - 55 million
This will hold the same result as previous:
50 million: 2.5 million 250 million: 32.5 million 500 million: 95 million 1000 million: 245 million
The math for above equation derived as shown in figure below:
Guard and Recursive
We can simply rephrase the previous function, as below to get the code done:
-- taxable income pkp :: Int pkp = 1000000000 -- income tax using progressive tariff pph :: Int -> Int pph pkp = round(pkpr pkp) where pkp_d = fromIntegral(pkp) pkpr pkp | pkp <= 50000000 = pkp_d * 0.05 | pkp <= 250000000 = pkp_d * 0.15 - 5000000 | pkp <= 500000000 = pkp_d * 0.25 - 30000000 | otherwise = pkp_d * 0.30 - 55000000 main = putStrLn $ show $ pph pkp
Code above will also result as below
The code is very nice and intuitive. The only isuuse here is there are too many constant.
Can we make it simpler ?
By taking out the constant, we can prepare this code below:
[t1, t2, t3, t4] = map (*million) [0, 50, 250, 500] (d1, d2, d3, d4) = (0, 5, 30, 55) [dj1, dj2, dj3, dj4] = [fromIntegral(x * million) | x <- [d1, d2, d3, d4]] pkp_d = fromIntegral(pkp) million = 1000000
Or in a more complete fashion,
put the prepared constant inside
-- taxable incomes pkps :: [Int] pkps = [10^7, 10^8, 10^9] -- income tax using progressive tariff pph :: Int -> Int pph pkp = round(pkpr pkp) where pkpr pkp | pkp > t4 = pkp_d * p4 - d4 | pkp > t3 = pkp_d * p3 - d3 | pkp > t2 = pkp_d * p2 - d2 | pkp > t1 = pkp_d * p1 - d1 -- guard limit [t1, t2, t3, t4] = map (*million) [0, 50, 250, 500] -- tariff rate in percent (p1, p2, p3, p4) = (0.05, 0.15, 0.25, 0.30) -- difference, in million rupiah [d1, d2, d3, d4] = map (fromIntegral . (*million)) [0, 5, 30, 55] -- Typecast, such as to Double pkp_d = fromIntegral(pkp) -- to avoid typo in writing digit million = 1000000 main = print $ map pph pkps
Code above will result a list as below
Oouuch… the code look ugly. and it lost the intuitive feels.
Am I fail yet ?
What is Next ?
We can get rid of the guard. Consider continue reading [ Haskell - Tax Tariff - Part Three ].
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