[Haskell-cafe] IO() and other datatypes

Kevin Clees k.clees at web.de
Sun Mar 4 19:41:43 CET 2012

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?

For example:

-- 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
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