Hola! Hallo!
I made my first program to understand lists and something about datat types. I have some question about the following code...




import Data.List

data Student = 
     Student { id     :: Int,
               nombre :: String
             } deriving (Show, Eq)

main :: IO ()
main = do putStrLn "---\nStudent Magnament Program\n---"
          loop []
 
ashow :: [Student] -> IO ()
ashow []    = putStrLn "Empty list"
ashow [x]   = putStrLn $ show x
ashow (x:xs)= do putStrLn $ show x
                 ashow xs
 
aadd :: [Student] -> IO ()
aadd xs = do putStrLn "Enter the id"
             id <- getLine
             putStrLn "Enter name"
             name <- getLine
             loop $ (Student (read id) (read name) ) : xs
             
aremove :: [Student] -> IO ()
aremove xs = do putStrLn "Enter the id"
                id <- getLine
                putStrLn "Enter name"
                name <- getLine
                loop $ delete (Student (read id) (read name) ) xs
             
 
loop :: [Student] -> IO ()
loop xs = do putStr $ "\n-------\nSelect an option\n"
                        ++ "1) Add student\n"
                        ++ "2) Remove student\n"
                        ++ "3) Show all students\n"
                        ++ "4) Exit\n"
                        ++ "\t Your option: "
             option <- getLine
             putStrLn "\n------"
             case read option of
                  1 -> aadd xs
                  2 -> aremove xs
                  3 -> do ashow xs
                          loop xs
                  4 -> putStrLn "God bye!"

• When i ask for the data fof a student i repeat the code, cause i have to use fuctions using IO (), cuase i have to put something in the screen. Therefore i cant have a fuction that only return a Student.
• loop $ (Student $ read id $ read name), is wrong why?
• i think that there are best way to achive that i have done. Or is ok for a begginer that doesn't know functors or monads.

Sorry for my bad english, i am Argentinean.

Thanks in advance.