In an attempt to get a deeper understanding of several monads (State, ST, IO, ...) I skimmed over some of the research papers (but didn't understand all of it, I lack the required education) and decided to write a little program myself without using any prefab monad instances that should mimic the following: main = do putStrLn "Enter your name:" x <- getLine putStr "Welcome " putStrLn x putStrLn "Goodbye!" But instead of using IO, I wanted to make my own pure monad that gets evaluated with interact, and does the same. However, I get the following output: Enter your name: Welcome ...... So the Welcome is printed too soon. This is obvious since my monad is lazy, so I tried to put a seq at some strategic places to get the same behavior as IO. But I completely failed doing so, either the program doesn't print anything and asks input first, or it still prints too much output. Of course I could just use ST, State, transformers, etc, but this is purely an exercise I'm doing. So, I could re-read all papers and look in detail at all the code, but maybe someone could help me out where to put the seq or what to do :-) The code is at http://hpaste.org/fastcgi/hpaste.fcgi/view?id=8316 Oh btw, the usage of DList here might not be needed; intuitively it felt like the correct thing to do, but when it comes to Haskell, my intuition is usually wrong ;-) Thanks a lot, Peter Verswyvelen