Blood pressure calculator

Blood.hs

import System.Console.GetOpt (ArgOrder(..), getOpt)
import System.Environment (getArgs, getProgName)


data BloodPressureCategory = Normal
                           | Prehypertension
                           | Hypertension1
                           | Hypertension2
                           | HypertensiveCrisis

instance Show BloodPressureCategory where
    show Normal = "Normal"
    show Prehypertension = "Prehypertension"
    show Hypertension1 = "Hypertension (Stage I)"
    show Hypertension2 = "Hypertension (Stage II)"
    show HypertensiveCrisis = "Hypertensive Crisis"


bloodPressureCategory s d | s >= 180  = HypertensiveCrisis
                          | d >= 110  = HypertensiveCrisis
                          | s >= 160  = Hypertension2
                          | d >= 100  = Hypertension2
                          | s >= 140  = Hypertension1
                          | d >=  90  = Hypertension1
                          | s >= 120  = Prehypertension
                          | d >=  80  = Prehypertension
                          | otherwise = Normal


parseArgs = getOpt RequireOrder []


main = do
    argv <- getArgs
    let cat = case parseArgs argv of
                ([], (d:s:_), []) -> bloodPressureCategory (read d :: Int) (read s :: Int)
    putStrLn $ show cat