Thanks, but that doesn't really matter in my example, my code is just buggy, and I'm not sure why. For example if I change my test function so that it outputs lines only, then it still prints Welcome first before asking for input. See e.g. http://hpaste.org/fastcgi/hpaste.fcgi/view?id=8316#a8328
On Wed, Aug 19, 2009 at 5:00 PM, David Leimbach <[email protected]> wrote: > Try LineBuffering. > I do linewise stuff with interact a lot. You'll find stuff like > > unlines . lines > > may help too. In fact I just wrote a blog post about this. > > http://leimy9.blogspot.com > > I'm trying to write some interactive code to automate working with serial > console controlled power strips, so I need to either use Expect (yuck) or do > my own thing. > > Dave > > On Wed, Aug 19, 2009 at 7:35 AM, Peter Verswyvelen <[email protected]>wrote: > >> Apparently this particular example happens to work on Mac and Linux >> because of different buffering (thanks Martijn for the help!) >> To make sure we have no buffering at all, the main function should be: >> >> main = do hSetBuffering stdout NoBuffering hSetBuffering stdin NoBuffering >> test >> >> Now I think it should also be *incorrect* on Unix systems. >> >> I guess the way I'm concatenating the strings is not correct, not sure. >> >> I would like to use a graphical tool to show the graph reduction step by >> step, to get a better understanding of the laziness & strictness. Does such >> a tool exist? I know people often say this is not usable because the amount >> of information is too much, but I used to be an assembly language programmer >> so I still would like to give it a try :-) >> >> >> >> On Wed, Aug 19, 2009 at 1:07 PM, Peter Verswyvelen <[email protected]>wrote: >> >>> 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 >>> >>> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> [email protected] >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >
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