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-- [(8.52 − Desired change in serum 25-hydroxyvitamin D level)                                                                                                                                              
--      + (0.074 × Age)                                                                                                                                                                                     
--      – (0.20 × BMI)                                                                                                                                                                                      
--      + (1.74 × Albumin concentration)                                                                                                                                                                    
--      – (0.62 × Starting serum 25-hydroxyvitamin D concentration)]/(−0.002)                                                                                                                               
                                                                                                                                                                                                            
data Equation = Equation {                                                                                                                                                                                  
    desiredChange :: Double                                                                                                                                                                                 
  , age           :: Double                                                                                                                                                                                 
  , bmi           :: Double                                                                                                                                                                                 
  , albumin       :: Double                                                                                                                                                                                 
  , serum         :: Double                                                                                                                                                                                 
  } deriving Show                                                                                                                                                                                           
                                                                                                                                                                                                            
calculate :: Equation -> Double                                                                                                                                                                             
calculate Equation{..} =                                                                                                                                                                                    
    ((8.52 - desiredChange)                                                                                                                                                                                 
  + (0.074 * age)                                                                                                                                                                                           
  - (0.20 * bmi)                                                                                                                                                                                            
  + (1.74 * albumin)                                                                                                                                                                                        
  - (0.62 * serum)) / (-0.002)                                                                                                                                                                              
                                                                                                                                                                                                            
getArg :: IO Double                                                                                                                                                                                         
getArg = read <$> getLine                                                                                                                                                                                   
                                                                                                                                                                                                            
main :: IO ()                                                                                                                                                                                               
main = do                                                                                                                                                                                                   
  print =<<                                                                                                                                                                                                 
    calculate <$>                                                                                                                                                                                           
      do Equation                                                                                                                                                                                           
           <$> do putStrLn "Desired change:" >> getArg                                                                                                                                                      
           <*> do putStrLn "Age:" >> getArg                                                                                                                                                                 
           <*> do putStrLn "BMI:" >> getArg                                                                                                                                                                 
           <*> do putStrLn "Albimun:" >> getArg                                                                                                                                                             
           <*> do putStrLn "Serum:" >> getArg