Just use this rule of thumb. If it is a monad (like IO Int, IO
String) use do <- notation. If it isn't a monad (like Int, String),
just use let syntax, same as you did with the first list.
main = do
let ttime = [8,20,10,15]
a = dauer ttime (OPTIONAL let a = dauer ttime)
putStrLn a
On Sun, Mar 4, 2012 at 1:41 PM, Kevin Clees
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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