flow - Haskell: Continue program execution

Question

I am very new to Haskell. My question might be very basic for you. Here I go-

I am writing a program to create a series of numbers using a specific mathematical formula. After creating this series, I am supposed to perform some operation on it like finding the maximum/minimum out of those numbers.

I could write the program but after getting a single input from the user, my program displays the output and then exits. What should I do if I have to wait for more commands from the user and exit on command END?

line <- getLine

I am using this command to get a command and then calling the necessary function according to the command. How should I proceed?

Answer 1

A basic input loop:

loop = do
  putStr "Enter a command: "
  input <- getLine
  let ws = words input -- split into words
  case ws of
    ("end":_)       -> return ()
    ("add":xs:ys:_) -> do let x = read xs :: Int
                              y = read ys
                          print $ x + y
                          loop
    ... other commands ...
    _ -> do putStrLn "command not understood"; loop


main = loop

Note how each command handler calls loop again to restart the loop. The "end" handler calls return () to exit the loop.