CODEWITHSUNDEEP
haskell
RedoColor
RedoColor

Reputation: 145

How Can I Make a Simple Exit in Haskell?

This is the code:

main :: IO()
main =  do 
{
         putStrLn ("Meniu: ");
         putStrLn ("1. menu 1");
         putStrLn ("2. menu 2");
         putStrLn ("3. menu 3");
         putStrLn ("4. menu 4");
         putStrLn ("5. Exit - Iesire)");
         putStrLn ("-------------------------");
         putStr ("Enter option: ");
         opt <- getLine;
         if(opt == "1") then do
         {
            Code one etc
            main
         }
            else if(opt == "2") then do
         {
            Code 2 etc
            main
         }
            else if(opt == "3") then do
         {
            code 3 etc
            main
         }
         else if(opt == "4") then do
         {
            code 4 etc
            main

         }
         else if(opt == "5") then do
         {
            ??????????? ()
         }
         else putStrLn "Option is not exist";
}

The Problem: In the option 5 (opt == 5) I need to make an code to stop the menu, but I dont know how I can do this. I tried to find more examples on Google and StackOverflow, but I really can't find a solution.

Upvotes: 1

Views: 678

Answers (1)

leftaroundabout
leftaroundabout

Reputation: 120711

return () will work here. In this case, return actually behaves like it would in a procedural language (but watch out, this is not generally true).

Note on style: chains of if...else with equality comparisons are very un-idiomatic in Haskell. The right way to do this is a case:

main =  do 
     putStrLn "Meniu: "
     sequence_ [ putStrLn $ [n]++". menu "++[n] | n<-['1'..'5'] ]
     putStrLn "-------------------------"
     putStr "Enter option: "

     opt <- getLine
     case opt of
      "1" -> do
        Code one etc
        main
      "2" -> do
        Code 2 etc
        main
      "3" -> do
        code 3 etc
        main
      "4" -> do
        code 4 etc
        main
      "5" -> return ()
      _ -> putStrLn "Option does not exist"

Braces and semicolons aren't needed if you correctly indent the code.

What return () does here is simply... nothing at all, it's the no-op. Because main ends after the case switch, the program will then also end if you don't recurse back to main like in the other options.

Upvotes: 9

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