I posted a reply to your paste with a stricter version of S and some cleanup.
Untested, though I believe it should work without "seq". "case" provides all the strictness you need, I think! -- ryan On Wed, Aug 19, 2009 at 9:28 AM, Peter Verswyvelen<[email protected]> wrote: > Expect more bugs with this though :-) Just found out that looping does not > work, it hangs, e.g. > > test = do > out "Enter your first name:" > fstName <- inp > out "Enter your second name:" > sndName <- inp > out ("Welcome "++fstName++" "++sndName) > out "Goodbye!" > test > > Doesn't seem to work :-) Back to the drawing board. > > On Wed, Aug 19, 2009 at 5:55 PM, Peter Verswyvelen <[email protected]> > wrote: >> >> Not at all, use it for whatever you want to :-) >> I'm writing this code because I'm preparing to write a bunch of tutorials >> on FRP, and I first wanted to start with simple console based FRP, e.g. >> making a little text adventure game, where the input/choices of the user >> might be parsed ala parsec, using monadic style, applicative style, and >> arrows, and then doing the same with FRP frameworks like Yampa, Elera, >> Reactive, etc... >> After that I would start writing tutorials that use OpenGL, making some >> very simple games, again with the above approaches, and ending with a >> conversion of a very old game of mine (Zarathrusta written in assembler from >> 1991, which was based on Thrust from 1986, converted by myself in C++ to >> PocketPC as G-Pod, and so I would like to make a version in Haskell that >> runs on the iPhone :-) >> This of course is a lot of work, and I would like to put this on the >> Haskell wiki or a blog or something, so others can contribute and comment. I >> would like to show real examples that explain the shortcomings of the FRP >> approaches, because now this is still a bit blurry to me. >> >> On Wed, Aug 19, 2009 at 5:43 PM, David Leimbach <[email protected]> wrote: >>> >>> This Monad you've created is quite excellent. I was trying to do >>> something like this about a year ago, to make the input and output handling >>> of an interactive bowling score card work nicely. I kept running into >>> issues, and did not believe that seq was going to do the trick. Nice work! >>> This is a very useful monad I think, it could be called "Prompter" or >>> something to that effect. >>> Do you mind if I use it in some of my code? >>> Dave >>> >>> On Wed, Aug 19, 2009 at 8:42 AM, Peter Verswyvelen <[email protected]> >>> wrote: >>>> >>>> LOL. Maybe we should have that coffee together ;-) at least virtually! >>>> On Wed, Aug 19, 2009 at 5:39 PM, David Leimbach <[email protected]> >>>> wrote: >>>>> >>>>> Argh... I too have been up too late :-). I edited THE WRONG FILE! No >>>>> wonder your change didn't take effect! :-/ >>>>> Time for coffee I suppose. >>>>> >>>>> On Wed, Aug 19, 2009 at 8:38 AM, David Leimbach <[email protected]> >>>>> wrote: >>>>>> >>>>>> This doesn't seem to be working for me interactively though on a Mac. >>>>>> I still get "Welcome" before I've entered text. >>>>>> >>>>>> On Wed, Aug 19, 2009 at 8:25 AM, Peter Verswyvelen <[email protected]> >>>>>> wrote: >>>>>>> >>>>>>> I fixed it myself but it's really tricky :-) >>>>>>> http://hpaste.org/fastcgi/hpaste.fcgi/view?id=8316#a8330 >>>>>>> The idea is, that when the input is requested, the output that is >>>>>>> then generated must be in sync with the input. >>>>>>> >>>>>>> inp = S $ \s i -> let r = (s `D.append` (i `seq` D.empty), head i) in >>>>>>> (tail i, r) >>>>>>> >>>>>>> >>>>>>> I first had >>>>>>> >>>>>>> inp = S $ \s i -> let r = (i `seq` s, head i) in (tail i, r) >>>>>>> >>>>>>> But that was too eager, since i syncs the input not with the output, >>>>>>> but with the function that will generate the output. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> Okay, now I can sleep again :-) >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> On Wed, Aug 19, 2009 at 5:12 PM, Peter Verswyvelen >>>>>>> <[email protected]> wrote: >>>>>>>> >>>>>>>> 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 >>>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>> >> > > > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe > > _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
