I-Access trading fee

trading_fee_i-access.hs

import System.IO
import Text.Printf

round' :: (RealFrac a, Integral b) => a -> b
round' x = truncate (x + 0.5)

roundAmount :: (RealFrac a) => a -> a
roundAmount x = fromIntegral ((round' (x * 100)) :: Integer) / 100

inputItem :: (Read a) => String -> IO a
inputItem description = do
    putStr description
    getLine >>= return . read

outputItem :: String -> Double -> IO ()
outputItem description value = do
    putStr description
    printf "%.2f\n" value

main :: IO ()
main = do
    hSetBuffering stdout NoBuffering
    price <- inputItem "Price: " :: IO Double
    n_shares <- inputItem "Shares bought/sold: " :: IO Int
    dutiable <- inputItem "Stamp-dutiable (0 or 1): " :: IO Int
    let sell = n_shares < 0
        n_shares_abs = abs n_shares
        amount = roundAmount (price * fromIntegral n_shares_abs)
        duty = fromIntegral $ ceiling (amount / 1000) * dutiable
        trading_fee = roundAmount (amount * 0.00005)
        levy = roundAmount (amount * 0.000027)
        settlement = max (roundAmount (amount * 0.00005)) 2.0
        tariff = 0.5
        system_fee = 0.5
        total = duty + trading_fee + levy + settlement + tariff + system_fee
    putStr "Action: "
    putStrLn (if sell then "Sell" else "Buy")
    putStr "Number of shares: "
    print n_shares_abs
    _ <- sequence $ map (uncurry outputItem) [("Transaction amount: ", amount),
        ("Stamp duty: ", duty),
        ("Trading fee: ", trading_fee),
        ("SFC levy: ", levy),
        ("Clearing fee: ", settlement),
        ("HKEx trading tariff: ", tariff),
        ("ISSnet system fee: ", system_fee) ]
    putStrLn ""
    _ <- sequence $ map (uncurry outputItem) [("Total fee: ", total),
        ("Settlement amount: ", amount * (if sell then 1 else -1) - total)]
    return ()