Thanks , it's working now like this :

loop :: Int -> IO ()
loop n = do
    if n <= 100
    then do
        putStrLn (show n );
        putChar ' ';
        putStrLn (show (n * n )) ;
        loop (n + 1);
    else
       return () ;

main :: IO ()
main = loop 1

But the outcome looks like this:

1
   1
2
   4

Can I somehow make it like this

1   1
2    4
3    9

Roelof