Dear Haskell programmers,

I'm very confused, because I really don't know how to handle with IO's and other datatypes, such as Int or String.

If I want to build a haskell program can I only use IO() method outputs ? How can I "give" a Int result from a different method back to the main?

Would this mean that I have to create only IO() outputs? Is this correct?

-- A User has to choose something, so I need a IO() datatype

main :: IO()

main = do 

[...]

let listtournementTime = [8,20,10,15]  

-- This is wrong: Couldn't match expected type `IO t0' with actual type `Int'

-- The results of the method dauer is a Int. Do I have to transform the method to an IO() Output

a <- Dauer listtournementTime

[...]

-- the methods

dauer:: [Int] -> Int

dauer (x:xs)

    | laenge(x:xs) == 1 = 0

    | mod (laenge (x:xs)) 2 == 0 = (tmp x xs) + dauer xs

    | mod (laenge (x:xs)) 2 /= 0 = dauer xs

    | otherwise = 999999 -- failure

tmp:: Int -> [Int] -> Int

tmp y (x:xs) = x-y

laenge        :: [a] -> Integer

laenge []     =  0

laenge (x:xs) =  1 + laenge xs

The last three methods are working correct, if I directly put some data into the methods, like: 

dauer [10,15] 

===Result===> 5

Thank you for any help

Best greetings from Namibia