[Haskell-cafe] HXT and xhtml page encoded in cp1251
Greetings, I'm writing a small webcrawler. Usually I used tagsoup for such tasks but this time I decided to give hxt a try. Unfortunately, I ran into the troubles with character encodings. The site I'm targeting uses cp1251, which is the one of the most popular among sites in Russian. Pages contain the following meta tag meta http-equiv=content-type content=text/html; charset=windows-1251 / The readDocument arrow fails with the following message: fatal error: encoding scheme not supported: WINDOWS-1251 Can someone suggest a workaround for my use case? Best regards, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] handling multiple versions of a data structure
On 17.12.2010 01:09, Jeremy Shaw wrote: Hello, You should use happstack-data for this (you do not need the other happstack components to use happstack-data)*. It was created to solve this exact problem. happstack-data builds on type of the 'binary' library and adds versioned data types and automatic version migration. Thanks! Looks like what I need. There is a one problem, though. I don't have a time machine. I mean right now I have A primitive format based on Show instance and I'd like to maintain the compatibility with it. Is it possible to force a particular on-disk format for a particular version of data type? I guess I should write a Serialize instance myself. Are there any pitfalls awaiting me? Best wishes, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] handling multiple versions of a data structure
Greetings, while developing my neural net simulator I stumbled upon a problem. I have a data type NeuralNet and use Show and Read instances for saving and loading configurations. As time passed, I changed the data type, so the program can no longer load files saved in previous versions. I want fix it. My current idea looks as follows. I'm going to create a bunch of types NN1, NN2, NN3..NNn for different versions and write converters c12 :: N1 - N2, c23 :: N2 - N3 and so on. But how to organize the whole process of parsing String into NNn so it's easy to change formats? Something based on using a list of parsers [read, c43 . read, c43 . c23 . read, c43, c23 . c12 . read, c43 . c32 . c21 . read] looks rather verbose and grows quadratically with N. I'm sure there must be a more elegant way. Any ideas? Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] CBRef, a wrapper around IORef with callbacks
Hello,
while building GUIs using Gtk2HS I always struggled with the following
question: how to sync the state of the GUI with the state of the rest
application. I usually make several IORefs store the state there. But
it's quite easy to forget to update relevant parts of GUI when state
changes, especially then it's done in several places, say, by user's
request and by some internal event.
Some time ago I realized a pattern which proved to be useful for me
several times. I wrapped IORef in a type:
data CBRef a = CBRef {v_ref :: IORef a, callbacks :: IORef [a - IO()] }
now I add callbacks using
addCB :: CBRef a - (a - IO()) - IO ()
addCB r cb = modifyIORef (callbacks r) (++[cb])
which fires then the value is changed:
writeCBRef :: CBRef a - a - IO ()
writeCBRef r v = do
writeIORef (v_ref r) v
cbs - readIORef (callbacks r)
mapM_ ($ v) cbs
all the remaining IORef-like interface is present too.
By using these callbacks for updating GUI I can be sure all it's parts
are in sync.
I suspect it's a special case of more general idea. Can anyone give a hint?
Also, do you think it's useful enough to be uploaded to Hackage? Or
maybe something similar is already there?
How do you organize your GUI applications?
Best wishes,
Dmitry
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Re: [Haskell-cafe] Re: Does it deserve to be a hackage package?
On 27.10.2010 13:16, Andy Stewart wrote: Christopher Donechrisd...@googlemail.com writes: On 27 October 2010 10:13, Dmitry V'yalakam...@gmail.com wrote: While ago I had a question about opening the url in the default browser from haskell program. I didn't get any immediate answers so I wrote my own solution. On Linux it uses xdg-open and on Windows - ShellExecute Api. Does it deserve to be a hackage package? If it's not in an existing small library, yes. If I have to have a dependency on gtk2hs just to do that, I'd rather have a small library. Does it work on OS X? If not, I'm sure someone would submit a patch for that. This can also be used for opening the file browser and such, right? It's APIs in GIO library (a sub-library in gtk2hs), you just need depend on GIO don't need depend any other library. Dmitry, it's unnecessary since GIO can do better with same experience both Windows and Linux, don't need any external program help. Infact, GIO not just call default browser for url, it can call any program to open any format. Ok then. I'll wait for it. I hope binary package for Windows would be provided too. Currently I can't figure out how build gtk2hs there. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Does it deserve to be a hackage package?
Hello haskellers, While ago I had a question about opening the url in the default browser from haskell program. I didn't get any immediate answers so I wrote my own solution. On Linux it uses xdg-open and on Windows - ShellExecute Api. Later I received a letter saying what similar functionality was recently implemented in trunk version of gtk2hs but is currently unavailable as binary package. Code I wrote works quite well for my purposes and I copied it into several my programs. In order to make maintenance easier I recently thought about uploading it to hackage. But given a wast amount of half-dead packages with intersecting functionality there I'd like to ask the opinion of community. Does such library look helpful to you? Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Opening a gtk2hs link in default browser
Hello list, I'm trying to make a clickable link in gtk2hs program. Clicking it should open an url in the default browser. Can I hope to find some portable solution in gtk2hs (it should work in linux and windows) or should I start searching platform specific ones, like /usr/bin/xdg-open or something? Can any examples be found in existing haskell software? Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] a couple of cabal related questions
Hello, recently I've cabalized my program and it brought some problems. First of all, I made use of 'import Paths_package name' functionality to get the path of installed data files. It works great, but now I can no longer run my program in ghci because this module is auto-generated by cabal. I tried to supply my own. This way ghci works, but my stub module gets compiled into the binary in place of auto-generated. And things break again. What's the best way to overcome it? And another question. I'd like to make my program output it's version string. Of course, I can hardcode it into sources, but I've already specified one in the cabal file. Is there any way to get it back in the run time? Thanks, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a couple of cabal related questions
On 12.10.2010 13:45, Magnus Therning wrote: On Tue, Oct 12, 2010 at 10:20, Dmitry V'yalakam...@gmail.com wrote: Hello, recently I've cabalized my program and it brought some problems. First of all, I made use of 'import Paths_package name' functionality to get the path of installed data files. It works great, but now I can no longer run my program in ghci because this module is auto-generated by cabal. I tried to supply my own. This way ghci works, but my stub module gets compiled into the binary in place of auto-generated. And things break again. What's the best way to overcome it? Create a file called .ghci in the directory where you run ghci and make it contains something like this: :set -idist/build/autogen And another question. I'd like to make my program output it's version string. Of course, I can hardcode it into sources, but I've already specified one in the cabal file. Is there any way to get it back in the run time? It's in Paths_package name as the variable 'version'. /M That's perfectly what I was looking for, thanks a lot! By the way, the 'version' variable doesn't mentioned in Cabal user guide, or at least I missed it. Is it documented somewhere? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Packaging a Gtk2hs based program for Windows
Hello, haskellers. Recently I stumbled upon a problem. It may sound quite off-topic for this list, but, I'm sure, almost every haskell programmer runs into it sooner or later. It sounds: How to make a neat Windows installer for a nice Gtk2hs program I wrote last week? How to solve the problem of dependency on GTK? Should I ask my users to install a GTK package or it would be better to package all the dynamic libraries needed along with my program? Are there any troubles with different character encodings used in Windows? How to change the application icon? And so on.. I understand, there is no ultimate answer, but I hope there is some wisdom to share. I've been a Linux user for more then five years and now I've found myself completely illiterate on how to make my code easily accessible for a nontechnical Windows user. I would appreciate any thoughts and advises Best wishes, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Spiking neural networks in Haskell
Greetings anyone, Some time ago I with a friend of mine implemented a toy interactive simulator of neural network activity. It has a totally imperative design and uses Gtk2hs for user interface parts. The darcs repository is available here: http://vyal.ru/code/spiking_neuro Now we decided to develop it further to try out some nice biologically inspired ideas. At first I wanted to rewrite the simulator in C++, since that language seems to match the current design more closely. But recently I've read some FRP related papers and have decided to rethink the overall approach. I'd like to hear some comments from the community on the current code and advises on possible improvements and other designs and their pros and conses. The performance is not critical for me, I'm looking for maximal flexibility and clearness so the model can easily be modified and extended. Best wishes, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Happstack basic question
Hello haskellers, I want to host a simple happstack application behind a reverse proxy. So ideally would be to bind it to localhost only. According to http://hackage.haskell.org/packages/archive/happstack-server/0.4.1/doc/html/Happstack-Server-HTTP-Types.html#t%3AConf Conf datatyle has only Port field. Does it mean, there is currently no way to prevent binding happstack to all available interfaces? Regards, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GUI and background processing
Greetings, fellow haskellers. Currently I'm writing some kind of web crawler in haskell with gtk2hs gui. All network operations are run in separate thread, but sometimes input from user is needed. Afaik, gtk2hs is not thread safe, so I came up with following: I create two mvars, A and B, one for question, one for answer. Worker thread puts question in A and blocks trying to take B. Gui thread checks for question by polling with tryTakeMVar. Then question is ready, it asks user and puts his answer into B. Worker awakens and continues processing. Also, for progress report, I use a Chan which is written to by worker and is read by polling by gui thread. This scheme works, but I don't like it. All these mvars and chans create too much clutter, and polling looks rather ugly too. Is there a better way for implementing similar patterns of interaction? Best regards, Dmitry. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to get glyph outline from ttf font.
Greetings. I'm trying to render some glyphs from ttf font to svg image using gtk2hs cairo binding. Since I can find nothing appropriate in gtk2hs API, I decided to draw outlines with bezier curves myself. But how to get them out of font? As far as I know, freetype library is capable of extracting outlines, but is there any haskell binding for it which supports this functionality? Here [1] one such lib was mentioned, but it wasn't availible online that time. Have situation changed today? Thanks in advance [1] http://www.nabble.com/Re%3A-Rendering-TTF-fonts-in-Haskell-and-OpenGL-p15635659.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what GUI library should i select?
Iván Pérez Domínguez wrote: I'm using Gentoo Linux. We obviously don't use prebuilt packaged versions, but installing it is just doing emerge wxhaskell and 'playing the... waiting game'. Gtk2hs support under Gentoo is mostly missing (the package is included, but doesn't work at all). Hmm, that strange. I emerged both gtk2hs-0.9.10 and ghc-6.4.2 just fine. Probably you should update your portage tree. I don't remember exactly, but I used portage snapshot from late spring of 2006. Now I'm waiting for ghc-6.6 being added to official portage tree. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what GUI library should i select?
Bulat Ziganshin wrote: it is what i say about. threaded RTS + multipls threads that does computations + one thread that interfaces with Gtk2Hs. afaiu, the only problem is that i need to manage both Gtk events and periodically check queue of commands from other threads, but using timer + Chan should allow to implement this I wrote multi threaded gui application in Haskell last spring as a educational project. That was a tool for analyzing and extracting contents of FAT volumes. Then i started my project, i was completely unaware of these threading issues and freely called gtk2hs routines from several threads. All worked fine at first, but when i added some disk I/O to my threads, my program became unstable. While on linux it just crashed from time to time, on windows i saw more curious behavior. At random spots threads lost ability to call WinAPI functions. Basically they got an error code meaning something weird like insufficient memory to complete call in return. That was not easily reproducible and depended on exact version of Windows. At some point my app was fully functional on WinXP and didn't even start on Win2000. I spent a lot of time trying to debug these issues and finally refactored my program to make use of approach you describe. Worked fine after that. All you have to do is to choose appropriate timer interval, otherwise your app becomes too jerky or CPU hungry. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] what GUI library should i select?
Duncan Coutts wrote: The problem at the moment with GUIs and GHC's threaded RTS is that there is now way to specify that all the Haskell threads that want to do GUI stuff must run on a single OS thread. It's not impossible to solve but it requires either more support from the RTS or it needs a totally different approach, perhaps using a Haskell-level threading GUI monad rather than the IO monad. Looks interesting for me. It's not too haskellish imo, when one ends with 2/3 of code being in the IO monad. Although situation probably gets better then more complex algorithms for processing data involved. Are there any attempts to fine grain allowed side effects using several monads? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Profiling Gtk2HS applications
Hello. How can one profile a program which uses gtk2hs? I get this: $ ghc --make MainGui.hs -prof Chasing modules from: MainGui.hs Could not find module `Graphics.UI.Gtk.Mogul': use -v to see a list of the files searched for (imported from ./TreeViewHelpers.hs) I tried to specify gtk2hs source path using -i option with no success. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] UTF-8 Strings and GHC
Hi, all. I'm writing a GUI app using Haskell and Gtk2HS. All goes well besides one thing. I need to display some messages in russian and I can't figure out, how to handle that. Gtk uses UTF-8 internally, so i have to pass UTF-8 strings to it somehow. But how to define them in source file? I get lexical error in string/character literal message then compiling using GHC-6.4.1. I tried to bypass it by using koi8-r in sources and converting strings to UTF-8 on the fly using ffi binding to iconv I found in MissingH (iirc). Works fine on Linux though is a little awkward, but I get wried results on Win32. Is there any way to use unicode strings in sources? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] reading binary files
Hello, Bulat
I'm currently working on some kind of program for analysing FAT partitions.
Don't ask why did I chose to implement it in Haskell :) Just for fun.
My program needs to read scattered chunks of binary data from a huge file and to
do a good amount of deserialisation.
I implemented basic functionality using Handles and Ptr's and now I'm starting
to regret for it. I have some pieces of code like:
type PtrAdvancer a b = StateT (Ptr a) IO b
peek_one :: Storable b = PtrAdvancer a b
peek_one = do
p - get
res - lift $ peek $ castPtr p
put $ plusPtr p $ sizeOf res
return res
peek_many :: Storable b = Int - PtrAdvancer a [b]
peek_many 0 = return []
peek_many n = do
first - peek_one
rest - peek_many $ n-1
return $ first:rest
data DirEntry = DirEntry
{ name :: String,
attr :: Word8,
crt_time_tenth :: Word8,
crt_time :: Word16,
crt_data :: Word16,
lst_acc_data :: Word16,
wrt_time :: Word16,
wrt_date :: Word16,
fst_cluster :: Word32,
file_size :: Word32
} deriving Show
instance Storable DirEntry where
sizeOf _ = 32
alignment _ = 32
peek = evalStateT peek_dir_entry
peek_dir_entry = do
n - peek_many 11 :: PtrAdvancer a [Word8]
at - peek_one
peek_one :: PtrAdvancer a Word8
ctt - peek_one
ct - peek_one
cd - peek_one
lad - peek_one
fch - peek_one :: PtrAdvancer a Word16
wt - peek_one
wd - peek_one
fcl - peek_one :: PtrAdvancer a Word16
fs - peek_one
return $ DirEntry (words_to_str n) at ctt ct cd lad wt wd
((fromIntegral fch `shiftL` 16) + fromIntegral fcl) fs
or:
read_cluster_chain32 :: Handle - FatAddress - Cluster - IO [Cluster]
read_cluster_chain32 h start cluster = do
allocaBytes 4 $ \p - chain32' p cluster True
where
chain32' p c need_seek = do
when need_seek $ hSeek h AbsoluteSeek (fromIntegral $ start + c * 4)
hGetBuf h p 4
val - peek p :: IO Word32
let val28 = val .. 0x0fff
case val28 of
0x0 - return []
0x0fff - return [c]
otherwise - do rest - if c+1 == val28 then chain32' p val28 False
else chain32' p val28 True
return $ c:rest
It works with a mediocre speed (about 10Mb/s when extracting files), but design
is ugly IMO. For example I need to write twice as much number of lines of
marshalling code compared to C. For data type declaration and then for Storable
instance. Is there a way to avoid it?
with my lib, you can either read data directly from file (through
implicit 512-byte buffer) or read whole file into the automatically
allocated buffer with `readFromFile`. what is better - depends on what
you plan to do with rest of file
Now I'm going to rewrite my code to make use of io library. So my question is
whether your library is well suited for such application (frequent positioning
and reading small pieces of data).
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Re: [Haskell-cafe] GUI-Woes
Duncan Coutts wrote: You didn't do anything wrong. By default that's what happens with large libs built with ghc. However, the current development version (and so the next release version) of Gtk2Hs has support for ghc's split objects feature. With this, a simple Gtk2Hs Hello world program is only 30% larger than a trivial Haskell hello world program (main = putStr Hello World!). Duncan Then I'm waiting impatiently for the next release. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GUI-Woes
Christophe Poucet wrote: I have to concur with Duncan. I started using Gtk2Hs for a small project and literally within a couple hours I had a good understanding upon which to build a nice gui as well as the gui itself. I haven't tried out wxhaskell, but trying gtk2hs and it's cairo bindings, I fell in love with the simplicity. Cheers I like gtk2hs too. I used it to make gui for my several toy projects. My experience was mostly positive, but I had some troubles: First of all, it's just a binding to GTK+, so if you don't have an expirience with it (as in my case), you have to learn both GTK+ and gtk2hs simultaneously. Secondly, I'm absolutely not satisfied with a size of produced binaries. I hope, I just made something wrong, but I got a 3 megabyte behemot after compiling and stripping my 300-line program. I compiled it with ghc-6.4.1 with ghc --make Main.hs. objdump -T shows a myriad of symbols with gtk_ prefix and I have a hard time guessing what most of them are doing where :) I haven't looked at wxhaskell yet. Personally I don't like wxWidgets because of it's overall orientation on GDI API and resemblance with MFC. What is about size of binaries produced using it? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Lists of Lists
zell_ffhut ?: Last attempt, as its due in a couple of hours Here's what i have so far.. charToGrid :: Char - Position - Grid - Grid charToGrid c [] (row,col) xs = xs charToGrid c (row,col) xs = (changeValue c (concat xs (row*9 + col))) Using changeValue - changeValue x 0 (y:ys) = (x:ys) changeValue x n (y:ys) = y:(changeValue x (n-1) ys) Would really appritiate any help -- View this message in context: http://www.nabble.com/Lists-of-Lists-t1245394.html#a3315187 Sent from the Haskell - Haskell-Cafe forum at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe You can easily do it using updateList as Robert Dockins proposed. updateList :: (a - a) - Int - [a] - [a] updateList f i l = begin ++ (f x : end) where (begin, x : end) = splitAt i l changeGrid :: Char - (Int,Int) - Grid - Grid changeGrid c (row,col) grid = updateList updateRow row grid where updateRow l = updateList (const c) col l Here we replace a row with a new one, using a helper function updateRow which, given the row, changes one symbol at position col in it. updateList is used twice here. First it's applied to outer list and then to inner one. It is possible because of higher-order nature of updateList. It's behavior can be changed by suppling an appropriate function f as it's first argument. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Infinite loop?
Barbier de Reuille Pierre wrote: And how can you, in Haskell, detect symbolic links ? One can use System.Posix.Files.isSymbolicLink function for that purpose. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Concurrency question
Donald Bruce Stewart wrote: Can I ask if just using a `seq` works as well? That was enough (now I recall) for the watchdog code I posted earlier. -- Don In my case this doesn't work timeout :: DeepSeq a = Int - IO a - IO (Maybe a) timeout n t = do res - par_io timer thr --timer return res where thr = do res - t return $! Just res timer = do threadDelay $ n * 1000 return Nothing It's probably because resolve function has type resolve :: CNF - (Bool, [(Int,Int)]) So it should be sequenced deeper. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Concurrency question
I believe you're just observing lazy evaluation at work. The IO computation that you're forking is (return $ resolve cnf). `resolve` is a pure function. Hence the forked computation succeeds immediately--and the thread terminates (successfully)--without evaluating (resolve cnf). It isn't until the case arm that begins Just (ans, stats) - that the result of (resolve cnf) is demanded and hence evaluation of (resolve cnf) begins. But this is too late for the timeout to have the intended effect. How to fix? You need to demand (enough of) the result of (resolve cnf) before returning from the IO computation. What enough of means depends on how `resolve` is written. You may find the DeepSeq module I wrote (see http://www.mail-archive.com/haskell@haskell.org/msg15819.html) helpful. Dean I've just tried DeepSeq as you proposed. timeout :: DeepSeq a = Int - IO a - IO (Maybe a) timeout n t = do res - par_io timer thr --timer return res where thr = do res - t return $!! Just res timer = do threadDelay n return Nothing All works perfectly now! From now I'll pay more attention to evaluation order. Thank you for your help and attention. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
