Re: [Haskell-cafe] Yampa vs. Reactive
On 21 Dec 2008, at 13:10, Henrik Nilsson wrote: Hi Tom, In reactive, one doesn't. All behaviors and events have the same absolute 0 value for time. Right. I believe the possibility of starting behaviors later is quite important. And from what Conal wrote in a related mail, I take it that this is recognized, and that this capability is something that is being considered for reactive? Yep, it is indeed. Thanks for this series of emails by the way. It's helped clarify in my head exactly what problems Yampa solved, and exactly which of them Reactive does or doesn't solve. Thanks Tom Davie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Trouble with FFI on Windows2000...
Hi Kyra (I tried to email you directly, but, for some reason, my mail bounced...), Hi Haskellers, dlltool -d cproj1.def -l libcproj1.a ghc --make testFFI_2.hs -optl-lcproj1 -optl-L. [...] This leads to an error box with message: DLL (null) not found on specified path dlltool -d cproj1.def -l libcproj1.a -D cproj1.dll Thanks very much for this answer, short and effective (an ideal one)! Just an additional question, just for curiosity: Does anyone know why this -D option doesn't appear in the following two pages? - http://www.haskell.org/haskellwiki/GHC/Using_the_FFI#Setting_up_your_build_environment_.28Visual_Studio_Specific.29 - http://www.haskell.org/haskellwiki/GHC:FAQ#GHC_on_Windows (parag. 1.4.3.4) Is this because the behavior I got is Win2K specific (hence very few people run into in 2008)? Thanks again Kyra for your precious help. --Serge ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Time for a new logo?
On Sun, 14 Dec 2008 16:50:11 -0500, sam lee skyn...@gmail.com wrote: http://i35.tinypic.com/mjon83.png used this: http://www.simwebsol.com/ImageTool/Default.aspx This logo still has not been uploaded to the Haskell logos/New logo ideas (http://haskell.org/haskellwiki/Haskell_logos/New_logo_ideas) page. Could you please upload it before it is forgotten? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Can I build and install GHC 6.10.1 without previous installed ghc
On Mon, 2008-12-22 at 11:53 +0800, Wang, Chunye (NSN - CN/Beijing) wrote: I tried to install the ghc 6.8.0 last year but failed for some reason. Now I decide to do it again, because I'd like to try some examples in Real World Haskell Now I remember why I try to install it from source code, because the binary version has the following problem. I guess ``timer_create '' is failed because of library confliction. I suggest you use the binary for ghc-6.8.2 (not 6.8.3) or earlier because those were built on an old Red Hat 9 server and are thus compatible with older versions of glibc and the Linux kernel. If you really need ghc-6.10 (you probably do not if you're just trying examples from the Real World Haskell book) then you can build ghc-6.10.x from source once you have the ghc-6.8.2 binary installed. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Removing/Uninstalling cabal packages ?
On Sun, 2008-12-21 at 13:30 -0600, brian wrote: On Sun, Dec 21, 2008 at 12:12 PM, Laurent Giroud m...@niaow.com wrote: I have been doing a few experiments with cabal packages lately and I wish to uninstall these to return to a cleaner package base. However, there doesn't seem to be a cabal uninstall command and reading the documentation at http://www.haskell.org/ghc/docs/latest/html/Cabal/index.html does not tell much about how to do that manually. I think you want 'ghc-pkg list' and 'ghc-pkg unregister'. If you also want to remove the files then that also has to be done manually at the moment. If any volunteers would like to help us implement tracking of installed files that would be most welcome. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc
Hi Duncan, wget http://haskell.org/ghc/dist/6.8.2/ghc-6.8.2-x86_64-unknown-linux.tar.bz2 tar -jxvf ghc-6.8.2-x86_64-unknown-linux.tar.bz2 cd ghc-6.8.2 ./configure checking build system type... x86_64-unknown-linux-gnu checking host system type... x86_64-unknown-linux-gnu checking target system type... x86_64-unknown-linux-gnu Which we'll further canonicalise into: x86_64-unknown-linux checking for path to top of build tree... pwd: timer_create: Invalid argument configure: error: cannot determine current directory Even though I can fixed this by ``cp /bin/pwd utils/pwd/pwd'' , there is still similar error ``ghc-pkg.bin: timer_create: Invalid argument'' I guess any executable file generates same error message. Best Regards Chunye Wang chunye.w...@nsn.com -Original Message- From: ext Duncan Coutts [mailto:duncan.cou...@worc.ox.ac.uk] Sent: Monday, December 22, 2008 5:38 PM To: Wang, Chunye (NSN - CN/Beijing) Cc: Haskell-Cafe@haskell.org Subject: RE: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc On Mon, 2008-12-22 at 11:53 +0800, Wang, Chunye (NSN - CN/Beijing) wrote: I tried to install the ghc 6.8.0 last year but failed for some reason. Now I decide to do it again, because I'd like to try some examples in Real World Haskell Now I remember why I try to install it from source code, because the binary version has the following problem. I guess ``timer_create '' is failed because of library confliction. I suggest you use the binary for ghc-6.8.2 (not 6.8.3) or earlier because those were built on an old Red Hat 9 server and are thus compatible with older versions of glibc and the Linux kernel. If you really need ghc-6.10 (you probably do not if you're just trying examples from the Real World Haskell book) then you can build ghc-6.10.x from source once you have the ghc-6.8.2 binary installed. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Trouble with the ST monad
Hello Andre, Monday, December 22, 2008, 4:44:34 AM, you wrote: Is there any difference between using freeze/thaw from Data.Array.MArray versus freezeSTArray/thawSTArray from GHC.Arr? portability, at least -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Threads with high CPU usage
Hello Günther, Monday, December 22, 2008, 1:57:22 AM, you wrote: try -threaded, +RTS -N2, and forkOS simultaneously. it may work - i don't see reasons why other threads should be freezd why one does unsafe call nother solution is to compile library with unsafe call changed to safe. this change is always safe but make call ~10mcs slower :) Hi Mads, I just noticed that too. I had been wondering why this problem does not occur with the sample app from RWH eventhough I was employing the same technics as they did. It just occured to me that all the DB interactions in their app are fairly short and thus the problem never becomes apparent. Thanks everyone, I was going crazy here, couldn't figure out what I was doing wrong. Would anyone happen to know of a safe alternative to HDBC? Günther Am 21.12.2008, 23:39 Uhr, schrieb Mads Lindstrøm mads_lindstr...@yahoo.dk: Hi Günther, Hi Mads, I'm using HDBC with sqlite3 Looking at http://software.complete.org/software/repositories/entry/hdbc-sqlite3/Database/HDBC/Sqlite3/Connection.hs and http://software.complete.org/software/repositories/entry/hdbc-sqlite3/Database/HDBC/Sqlite3/Statement.hsc you can see that HDBC-sqlite's foreign calls are indeed marked unsafe. /Mads Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANN: HLint 1.0
Hi Lennart, It would be nice if HLint didn't suggest things that it will object to in the next round. Like LLVM/Core/CodeGen.hs:176:1: Eta reduce Found: applyArgs f g = apArgs 0 f g Why not: applyArgs f = apArgs 0 f The idea is to specify things one step at a time, so the user learns from the hints, as well as fixing them. However, in the case of eta reduction, doing several reductions at a time does make sense. I'll add it to the todo list. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Don Stewart d...@galois.com wrote: Modify the 'unsafe' inports to be 'safe'? I don't think HDBC is going to call back in, so should be fine. John? For those who are puzzled, Don is suggesting that foreign import ccall unsafe foo :: Bar - Baz should simply be changed to foreign import ccall safe foo :: Bar - Baz And in case anyone is wondering whether fiddling with safety declarations is entirely wise: unsafe means I, the programmer, guarantee that this foreign function cannot call back into Haskell land, so you, the compiler, are free to do unsafe things when implementing the call. safe means I the programmer, cannot guarantee that this foreign function is safe, so please, you the compiler, make sure that you add extra checks and assurances to ensure that the call really will be safe in case it calls back into Haskell land. The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] new Haskell logos/Logo design tools - HaskellWiki page [Was: Re: Time for a new logo?]
In order to encourage participation in The Great 2009 Haskell Logo Contest, I have created a new Haskell logos/Logo design tools - HaskellWiki page (see http://haskell.org/haskellwiki/Haskell_logos/Logo_design_tools). This page is still a stub; if you have any further information on logo design tools or logo design-related resource sites, including design advice, please feel free to add to it. The more participation, the better! -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] understanding enumerator/iteratee
So an iteratee is not like a cursor because it does not own the collection -- it just tells us how to step it. The enumerator owns the collection and provides a way to scope resource use? -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] understanding enumerator/iteratee
Hi Jason! 2008/12/22 Jason Dusek jason.du...@gmail.com: So an iteratee is not like a cursor because it does not own the collection -- it just tells us how to step it. The enumerator owns the collection and provides a way to scope resource use? Iteratee does not know anything about resources, it doesn't need to. It is just a function which, given an input stream (which is either EOF, block of data or an IO error string), decides what to do, one of: * yield with some (useful) results (and with the rest of the input) * request more input by returning a continuation The enumerator on the other hand, decides when to open the resource (a file, for example), when to close it, and how to step through it. Iteratee only gets the fruits of this hard work. :) it just tells us how to step it I would say that it just tells us how to react to various forms of input. :) This is much like the function you pass to foldr. I hope this clarifies iteratees a bit (and that my understanding is correct). Cheers, Artyom Shalkhakov. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc
On Mon, 2008-12-22 at 17:53 +0800, Wang, Chunye (NSN - CN/Beijing) wrote: Hi Duncan, wget http://haskell.org/ghc/dist/6.8.2/ghc-6.8.2-x86_64-unknown-linux.tar.bz2 tar -jxvf ghc-6.8.2-x86_64-unknown-linux.tar.bz2 Ahh, x86-64. Those have always been built on Fedora Core 5. My only suggestion is to try older ones, eg 6.6.1. That version should still be able to built 6.10.1 from source and should still be usable for the RWH book. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
On Mon, 2008-12-22 at 10:30 +, Malcolm Wallace wrote: For those who are puzzled, Don is suggesting that foreign import ccall unsafe foo :: Bar - Baz should simply be changed to foreign import ccall safe foo :: Bar - Baz And in case anyone is wondering whether fiddling with safety declarations is entirely wise: unsafe means I, the programmer, guarantee that this foreign function cannot call back into Haskell land, so you, the compiler, are free to do unsafe things when implementing the call. safe means I the programmer, cannot guarantee that this foreign function is safe, so please, you the compiler, make sure that you add extra checks and assurances to ensure that the call really will be safe in case it calls back into Haskell land. The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. For example in a database library it might make sense to use 'unsafe' on the data-access functions that extract data from a local query result but we should always use 'safe' on any DB function that might want to talk to the network (eg to get more query results). Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
On Sun, Dec 21, 2008 at 6:03 PM, Andrzej Jaworski hims...@poczta.nom.plwrote: I just want to say Hello to let you know that there are some serious entities watching you besides monads and FBI:-) There has been a hell of a discussion recently about logos, languages and religion and I want to add to this. First let me disassociate Haskell from Taoism which to may taste has left us in an unhealthy climate. It suffices to say that Taoism is a school of clever trics and cute aphorisms but without the slightest attempt to explain or generalize let alone produce an abstract idea or a system. That is why its wisdom is non transferable in spite of majority of humans desending from it. Haskell on the contrary is a minority school that implements abstract ideas for problem solving in the most transferable way to date, so that other languages look into it for their share. But don't worry, thay will choke becouse it is them who practice Taoizm. Playing too many tricks will eventually trick them, even if some are powerful enough to brainwash dicent professors to preach interoperability or the like. Every viable complexity needs a single underlying concept to survive, including you and the universe. Microsoft and the like excluding;-) Haskell has all that: consistency, transparency and self-contained concept. I associate Haskell with Zen, due to one of my favorite dialogues: If it's purely functional, how do you *do* anything? You don't ;-) (Courtesy of Conal Elliott) Haskell and Zen both happen to be my favorites in their respective fields (and exactly which field that is for both is somewhat fuzzy) Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] understanding enumerator/iteratee
I'm taking a stab at composable streams, starting with cursors. I managed to make a derived cursor today -- as I work through this stuff, I hope to understand Iteratee/Enumerator better. -- Jason Dusek http://github.com/jsnx/streams/tree/554dd69339f027f113a6cfa16f552727ba9d92b3/Control/Stream/OneWay.hs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Defining a containing function on polymorphic list
I am trying to define a containing function to see if a value is one of the elements within a list which is polymorphic, but failed with the following codes: contain :: a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys it seems that the problem is the 'operator' == does not support a polymorphic check? Any way can solve the problem? or any alternative solution to achieve the purpose? Thanks! Raeck _ It’s the same Hotmail®. If by “same” you mean up to 70% faster. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_hotmail_acq_broad1_122008___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Takusen
Hi all, where can I find some sample code or other examples to familiarize me with Takusen? Does Takusen use safe ccall only, or does it also use ccall unsafe? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys The Eq a in the type signature says that 'a' must be a member of the 'Eq' typeclass. That says, in turn, that 'a' must have == defined for it. Fortunately, most types have, or can easily derive that definition. Here is the definition of the typeclass: class Eqhttp://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#t%3AEqa where(==)http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#v%3A%3D%3D:: a - a - Boolhttp://haskell.org/ghc/docs/latest/html/libraries/ghc-prim/GHC-Bool.html#t%3ABool (/=)http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#v%3A%2F%3D:: a - a - Boolhttp://haskell.org/ghc/docs/latest/html/libraries/ghc-prim/GHC-Bool.html#t%3ABool That is, for 'a' to be a member of 'Eq', it must have a == operator which can take 2 values of that type and return a Boolean, saying whether or not they're equal, and it must also have a definition for the /= operator, which is not equal. These two are also defined in terms of each other, so if you define ==, you get /= for free, and vice versa. That's probably more information than you needed to know, but I hope it helps. 2008/12/22 Raeck Zhao ra...@msn.com I am trying to define a containing function to see if a value is one of the elements within a list which is polymorphic, but failed with the following codes: contain :: a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys it seems that the problem is the 'operator' == does not support a polymorphic check? Any way can solve the problem? or any alternative solution to achieve the purpose? Thanks! Raeck -- It's the same Hotmail(R). If by same you mean up to 70% faster. Get your account now.http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_hotmail_acq_broad1_122008 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell for windows mobile 6 on Intel PXA270 processor
Hi All. I'm looking for haskell interpreter/compiler for windows mobile 6 (I have an Asus A696 PDA with intel PXA270 processor). Somebody head about any haskell implementation for this platform? -- With best regards, Constantine Potapov. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Duncan Coutts wrote: On Mon, 2008-12-22 at 10:30 +, Malcolm Wallace wrote: The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. For example in a database library it might make sense to use 'unsafe' on the data-access functions that extract data from a local query result but we should always use 'safe' on any DB function that might want to talk to the network (eg to get more query results). It's difficult to anticipate the needs here. For instance, some people may be using a few very-long-running queries measured in minutes, such as the original poster. Other people, such as web app developers, may be issuing literally millions of queries, right after another, where the difference matters. I had initially used unsafe because of the documented performance benefit, plus I certainly am not expecting Sqlite to call back into the Haskell runtime. It seems to me strange that using unsafe instead of safe would have negative implications for threading. After all, as Malcolm said above, it is always OK to convert an unsafe declaration into a safe one. So could the compiler be made to be smart enough to do so when it is advantageous for threading purposes? What's the best way to make this suitable for both people with many queries and those with long-running queries? I should also add that I suspect the C calls that are bothering the original poster here are the standard ones for reading results, and could be called many, many times on even a single query. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
2008/12/22 Andrew Wagner wagner.and...@gmail.com: The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool Please note that the syntax here should be: contain :: Eq a = a - [a] - Bool Denis ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
Yes, of course, sorry for the typo. On Mon, Dec 22, 2008 at 9:17 AM, Denis Bueno dbu...@gmail.com wrote: 2008/12/22 Andrew Wagner wagner.and...@gmail.com: The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool Please note that the syntax here should be: contain :: Eq a = a - [a] - Bool Denis ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Control.Monad.IfElse
Provides useful anaphoric and monadic versions of if-else and when, as well as infix operators for the actions to allow things like this: -- Allow the clause to be in m a whenM (Gtk.widgetIsFocus win) $ do this that -- anaphoric if. If the condition is nonempty, pass the conditional value to the then clause, otherwise do an action that requires no parameter. aif (lookup name list) (\file - Right `liftM` hGetLine file) (do f - openFile name l - hGetLine file return $ Right (f,l)) -- infix version of Control.Monad.When (x5) ? putStrLn x -- infix version of anaphoric when lookup name list =? \value - putStrLn value -- infix version of anaphoric whenM Gtk.widgetIntersect win rect =? \intersectingRectangle' - Gtk.invalidate intersectingRectangle' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
On 22 Dec 2008, at 15:18, Andrew Wagner wrote: Yes, of course, sorry for the typo. On Mon, Dec 22, 2008 at 9:17 AM, Denis Bueno dbu...@gmail.com wrote: 2008/12/22 Andrew Wagner wagner.and...@gmail.com: The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool Please note that the syntax here should be: contain :: Eq a = a - [a] - Bool Denis Of note, unless this is an exercise, such a function already exists -- it's called elem. How do you find such a function? You search on haskell.org/hoogle. http://haskell.org/hoogle/?hoogle=Eq+a+%3D%3E+a+-%3E+%5Ba%5D+-%3E+Bool Bob___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] A hell of a question
Hi Luke, When neurosurgeons split the brain into left and right hemisphere cutting it along corpus callosum the patient will talk to you with his left half and right half independently - each time unaware what his other half was talking about a moment earlier. I believe Zen emulates such split on a microscopic scale. We all go thru similar state when we conceive an original idea - if we do not write this down or formulate it immediately the discovery will loose its punch and sense of depth. The best documented and most prominent example is Hegel's discovery of dialectical logic - after extensive writing about that at some point he honestly admits loosing the original concept. But if not for his western oververbosity we might not today use the term 'naive' set theory. Every serious mathematician touching foundations is today perfectly aware of the price we pay for formulating things. But I am unaware of any virtue of trying to clap with one hand;-) Regards, -Andrzej ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: forkIO on multicore
Duncan Coutts wrote: On Fri, 2008-12-19 at 10:42 -0600, Jake McArthur wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Paul Keir wrote: fibs = 0 : 1 : zipWith (+) fibs (tail fibs) This is a CAF (Constant Applicative Form). Since it is actually a constant it is never garbage collected, and is always shared, so each thread is only calculating it once. You have essentially created a lookup table. Though note that with all our obvious suggestions there is still no speedup: heavytask m n = putMVar m $! (fibs !! 10) where fibs = n : (n+1) : zipWith (+) fibs (tail fibs) -- so now fibs is not globally shared but is used per-heavytask -- it is also evaluated by heavy task rather than just putting a thunk -- into the MVar main = do ms - sequence $ replicate 8 newEmptyMVar sequence_ [ forkIO (heavytask m n) | (m, n) - zip ms [0..] ] ms' - mapM takeMVar ms mapM_ print ms' Looking at the GC stats (+RTS -t -RTS) we see that the majority of the time in this program is spent doing GC and that when we run with -N4 the time spent doing GC is even higher. This is an interesting example. It shows up a weakness in the GC that I'm working on fixing right now. The interesting aspect of this example is that the thread stacks get large. You can see this by using +RTS -hT: a large chunk of the heap is taken up by TSOs. Each of those (fibs !! 10) requires linear stack, because (fibs 10) depends on (fibs 9), and so on. That could probably be fixed by adding some strictness, but that's not the goal here - we should still be able to run the program in parallel. So when there are large stacks around, GC takes a long time because it has to traverse stacks. But we should be able to alleviate the problem by (a) using a larger heap, and (b) using parallel GC. Not doing parallel GC is seriously going to hurt peformance, because the data will have to be moved from one CPU's cache to another. But it turns out that parallel GC is misbehaving on this example too, because it doesn't force each stack to be scanned by the same thread that is executing it - I'm working on fixing that. Having each CPU be able to GC independently would be a big improvement, of course. We think we understand how this can be done in the context of GHC, it's just a matter of doing it, but it's a big job. Parallel performance is something that we expect to make dramatic improvements over the next few months as we investigate more programs and improve the tools. The current HEAD is already a lot better than 6.10.1. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Defining a containing function on polymorphic list
Thank you very much for your reply! It is really helpful! But I just found another 'problem', I just realize that the list does not support the user-defined data type? the list is also depending on the Eq function? For example, data Shape = Square | Triangle | Circle when I type either [Square, Triangle, Circle] or Square == Square there are errors! So there is no way to construct a truly polymorphic List? any way to extend the list to support some user-defined data type? Or... I define the Shape in a wrong way actually? Thanks Raeck Date: Mon, 22 Dec 2008 09:02:53 -0500 From: wagner.and...@gmail.com To: ra...@msn.com Subject: Re: [Haskell-cafe] Defining a containing function on polymorphic list CC: haskell-cafe@haskell.org; beginn...@haskell.org The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys The Eq a in the type signature says that 'a' must be a member of the 'Eq' typeclass. That says, in turn, that 'a' must have == defined for it. Fortunately, most types have, or can easily derive that definition. Here is the definition of the typeclass: class Eq a where (==) :: a - a - Bool (/=) :: a - a - Bool That is, for 'a' to be a member of 'Eq', it must have a == operator which can take 2 values of that type and return a Boolean, saying whether or not they're equal, and it must also have a definition for the /= operator, which is not equal. These two are also defined in terms of each other, so if you define ==, you get /= for free, and vice versa. That's probably more information than you needed to know, but I hope it helps. 2008/12/22 Raeck Zhao ra...@msn.com I am trying to define a containing function to see if a value is one of the elements within a list which is polymorphic, but failed with the following codes: contain :: a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys it seems that the problem is the 'operator' == does not support a polymorphic check? Any way can solve the problem? or any alternative solution to achieve the purpose? Thanks! Raeck It's the same Hotmail®. If by same you mean up to 70% faster. Get your account now. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe _ Life on your PC is safer, easier, and more enjoyable with Windows Vista®. http://clk.atdmt.com/MRT/go/127032870/direct/01/___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Hi, I am not yet 100% certain that the unsafe calls are indeed the cause of the problem, eventhough I strongly suspect there are. I can tell you more once I have managed to rewrite all unsafe calls into safe once, reinstall HDBC.Sqlite3 and then run my app again to see the effects. My first attempt doing so was not successful, I'm not certain whether I missed an unsafe call or the app is using an old version of HDBC.Sqlite3 or whatever. I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Günther Am 22.12.2008, 15:15 Uhr, schrieb John Goerzen jgoer...@complete.org: Duncan Coutts wrote: On Mon, 2008-12-22 at 10:30 +, Malcolm Wallace wrote: The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. For example in a database library it might make sense to use 'unsafe' on the data-access functions that extract data from a local query result but we should always use 'safe' on any DB function that might want to talk to the network (eg to get more query results). It's difficult to anticipate the needs here. For instance, some people may be using a few very-long-running queries measured in minutes, such as the original poster. Other people, such as web app developers, may be issuing literally millions of queries, right after another, where the difference matters. I had initially used unsafe because of the documented performance benefit, plus I certainly am not expecting Sqlite to call back into the Haskell runtime. It seems to me strange that using unsafe instead of safe would have negative implications for threading. After all, as Malcolm said above, it is always OK to convert an unsafe declaration into a safe one. So could the compiler be made to be smart enough to do so when it is advantageous for threading purposes? What's the best way to make this suitable for both people with many queries and those with long-running queries? I should also add that I suspect the C calls that are bothering the original poster here are the standard ones for reading results, and could be called many, many times on even a single query. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
There are two ways to fix this. Let me see if I can get my syntax right this time :) 1.) Let GHC work out the Eq instance: data Shape = Square | Triangle | Circle deriving Eq 2.) Tell GHC how to do it explicitly: data Shape = Square | Triangle | Circle instance Eq Shape where Square == Square = True Triangle == Triangle = True Circle == Circle = True _ == _ = False Note that the last line here means that any other comparisons are false. On Mon, Dec 22, 2008 at 9:35 AM, Raeck Zhao ra...@msn.com wrote: Thank you very much for your reply! It is really helpful! But I just found another 'problem', I just realize that the list does not support the user-defined data type? the list is also depending on the Eq function? For example, data Shape = Square | Triangle | Circle when I type either [Square, Triangle, Circle] or Square == Square there are errors! So there is no way to construct a truly polymorphic List? any way to extend the list to support some user-defined data type? Or... I define the Shape in a wrong way actually? Thanks Raeck -- Date: Mon, 22 Dec 2008 09:02:53 -0500 From: wagner.and...@gmail.com To: ra...@msn.com Subject: Re: [Haskell-cafe] Defining a containing function on polymorphic list CC: haskell-cafe@haskell.org; beginn...@haskell.org The problem here is even slightly deeper than you might realize. For example, what if you have a list of functions. How do you compare two functions to each other to see if they're equal? There is no good way really to do it! So, not only is == not completely polymorphic, but it CAN'T be. There is a nice solution for this, however, and it's very simple: contain :: Eq a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys The Eq a in the type signature says that 'a' must be a member of the 'Eq' typeclass. That says, in turn, that 'a' must have == defined for it. Fortunately, most types have, or can easily derive that definition. Here is the definition of the typeclass: class Eqhttp://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#t:Eqa where (==)http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#v:%3D%3D:: a - a - Boolhttp://haskell.org/ghc/docs/latest/html/libraries/ghc-prim/GHC-Bool.html#t:Bool (/=)http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Eq.html#v:/%3D:: a - a - Boolhttp://haskell.org/ghc/docs/latest/html/libraries/ghc-prim/GHC-Bool.html#t:Bool That is, for 'a' to be a member of 'Eq', it must have a == operator which can take 2 values of that type and return a Boolean, saying whether or not they're equal, and it must also have a definition for the /= operator, which is not equal. These two are also defined in terms of each other, so if you define ==, you get /= for free, and vice versa. That's probably more information than you needed to know, but I hope it helps. 2008/12/22 Raeck Zhao ra...@msn.com I am trying to define a containing function to see if a value is one of the elements within a list which is polymorphic, but failed with the following codes: contain :: a - [a] - Bool contain x [] = False contain x (y:ys) = if x == y then True else contain x ys it seems that the problem is the 'operator' == does not support a polymorphic check? Any way can solve the problem? or any alternative solution to achieve the purpose? Thanks! Raeck -- It's the same Hotmail(R). If by same you mean up to 70% faster. Get your account now.http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_hotmail_acq_broad1_122008 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Life on your PC is safer, easier, and more enjoyable with Windows Vista(R). See how http://clk.atdmt.com/MRT/go/127032870/direct/01/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Threads with high CPU usage
Hello John, Monday, December 22, 2008, 5:15:46 PM, you wrote: And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. the other way to look at it is to measure overhead of safe call. on 1 GHz Duron i measured 66.000 calls of trivial safe function per second, meaning 16.000 cpu ticks per call (ghc 6.8). it's rather large overhead for many trivial functions, but for calls to sql engine it seems rather small -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Günther Schmidt wrote: Hi, I am not yet 100% certain that the unsafe calls are indeed the cause of the problem, eventhough I strongly suspect there are. I can tell you more once I have managed to rewrite all unsafe calls into safe once, reinstall HDBC.Sqlite3 and then run my app again to see the effects. My first attempt doing so was not successful, I'm not certain whether I missed an unsafe call or the app is using an old version of HDBC.Sqlite3 or whatever. That is an interesting data point indeed. You might try to isolate the problem into some small section of code that reproduces it, so that we can do some more testing on our own systems. -- John I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Günther Am 22.12.2008, 15:15 Uhr, schrieb John Goerzen jgoer...@complete.org: Duncan Coutts wrote: On Mon, 2008-12-22 at 10:30 +, Malcolm Wallace wrote: The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. For example in a database library it might make sense to use 'unsafe' on the data-access functions that extract data from a local query result but we should always use 'safe' on any DB function that might want to talk to the network (eg to get more query results). It's difficult to anticipate the needs here. For instance, some people may be using a few very-long-running queries measured in minutes, such as the original poster. Other people, such as web app developers, may be issuing literally millions of queries, right after another, where the difference matters. I had initially used unsafe because of the documented performance benefit, plus I certainly am not expecting Sqlite to call back into the Haskell runtime. It seems to me strange that using unsafe instead of safe would have negative implications for threading. After all, as Malcolm said above, it is always OK to convert an unsafe declaration into a safe one. So could the compiler be made to be smart enough to do so when it is advantageous for threading purposes? What's the best way to make this suitable for both people with many queries and those with long-running queries? I should also add that I suspect the C calls that are bothering the original poster here are the standard ones for reading results, and could be called many, many times on even a single query. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc
I've recently built 6.10.1 on fairly archaic RHEL servers, both 64 and 32 bit, and the incantation that worked most seamlessly for me was to grab a really old binary release (in my case 6.2 worked) that installs without intervention, and then build up to the latest version (6.10.1) in steps -- I built 6.6 with 6.2, then 6.10.1 with 6.6, and it all worked without a problem. Of course, I'd try 6.6/binary first, but if that doesn't work, all is not lost, older binary releases may still work, and you can then bootstrap from those. Rob - Original Message From: Wang, Chunye (NSN - CN/Beijing) chunye.w...@nsn.com To: Haskell-Cafe@haskell.org Sent: Monday, December 22, 2008 4:53:53 AM Subject: RE: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc Hi Duncan, wget http://haskell.org/ghc/dist/6.8.2/ghc-6.8.2-x86_64-unknown-linux.tar.bz2 tar -jxvf ghc-6.8.2-x86_64-unknown-linux.tar.bz2 cd ghc-6.8.2 ./configure checking build system type... x86_64-unknown-linux-gnu checking host system type... x86_64-unknown-linux-gnu checking target system type... x86_64-unknown-linux-gnu Which we'll further canonicalise into: x86_64-unknown-linux checking for path to top of build tree... pwd: timer_create: Invalid argument configure: error: cannot determine current directory Even though I can fixed this by ``cp /bin/pwd utils/pwd/pwd'' , there is still similar error ``ghc-pkg.bin: timer_create: Invalid argument'' I guess any executable file generates same error message. Best Regards Chunye Wang chunye.w...@nsn.com -Original Message- From: ext Duncan Coutts [mailto:duncan.cou...@worc.ox.ac.uk] Sent: Monday, December 22, 2008 5:38 PM To: Wang, Chunye (NSN - CN/Beijing) Cc: Haskell-Cafe@haskell.org Subject: RE: [Haskell-cafe] Can I build and install GHC 6.10.1 withoutprevious installed ghc On Mon, 2008-12-22 at 11:53 +0800, Wang, Chunye (NSN - CN/Beijing) wrote: I tried to install the ghc 6.8.0 last year but failed for some reason. Now I decide to do it again, because I'd like to try some examples in Real World Haskell Now I remember why I try to install it from source code, because the binary version has the following problem. I guess ``timer_create '' is failed because of library confliction. I suggest you use the binary for ghc-6.8.2 (not 6.8.3) or earlier because those were built on an old Red Hat 9 server and are thus compatible with older versions of glibc and the Linux kernel. If you really need ghc-6.10 (you probably do not if you're just trying examples from the Real World Haskell book) then you can build ghc-6.10.x from source once you have the ghc-6.8.2 binary installed. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
John Goerzen schrieb: Günther Schmidt wrote: Hi, I am not yet 100% certain that the unsafe calls are indeed the cause of the problem, eventhough I strongly suspect there are. I can tell you more once I have managed to rewrite all unsafe calls into safe once, reinstall HDBC.Sqlite3 and then run my app again to see the effects. My first attempt doing so was not successful, I'm not certain whether I missed an unsafe call or the app is using an old version of HDBC.Sqlite3 or whatever. That is an interesting data point indeed. You might try to isolate the problem into some small section of code that reproduces it, so that we can do some more testing on our own systems. -- John I'd love to provide you with it but you'd have to manage a query that takes a long time to finish yourself. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Re: Threads with high CPU usage
From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Alistair * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: Threads with high CPU usage
Hello Alistair, Monday, December 22, 2008, 7:28:03 PM, you wrote: safe). I also was not aware of unsafe calls blocking other threads. they don't to it directly. but without -threaded +RTS -N (or forkOS) there is only 1 OS thread that runs all haskell threads. unsafe call blocks it untill call finished, while safe call allows to reuse it for other haskell threads execution. i've attached old ghc commentary on this topic, although things may be significantly changed ATM -- Best regards, Bulatmailto:bulat.zigans...@gmail.com The GHC Commentary - Supporting multi-threaded interoperation.htm Description: Binary data ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] monad constraint + record update
I'd like to define a monad Set for types in the class Eq. But how can the arguments of Set be constrained when Set is defined as an instance of Monad? instance Eq a = Monad Set where ... obviously cannot work. Is there a standard update function for fields in data types, something that OO programmers do with assignments like obj.attr := value ? Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell re-branding exercise
On 21 dec 2008, at 22:26, Sebastian Sylvan wrote: I am very shortly travelling abroad for several weeks and will not have (reliable access to) a computer, but isn't this a task for one of the haskell web-apps people (HSP, HAppS, Turbinado, etc.) to show us once and for all why *their* library is better than the competition? :-) Hmm, right. I started on a thing in HAppS. See http://github.com/eelco/voting/ for the source code (contributors more than welcome!) and http://code.tupil.com/voting/ for a live demo. It relies heavily on javascript, needs some work on the UI and there are a lot of features that could be added, but it works. -- Regards, Eelco Lempsink PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell re-branding exercise
2008/12/22 Eelco Lempsink ee...@lempsink.nl: Hmm, right. I started on a thing in HAppS. See http://github.com/eelco/voting/ for the source code (contributors more than welcome!) and http://code.tupil.com/voting/ for a live demo. It relies heavily on javascript, needs some work on the UI and there are a lot of features that could be added, but it works. Great. Could it be further hacked to accept ties, as suggested by Sebastian? Something like: thingie1 thingie1bis thingie3 thingie4 thingie4bis Regards, Loup ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problems Installing Takusen with Sqlite Backend
Hi Alistair, what does it take to install Takusen on Win32 with Sqlite backend? I did manage to install *plain* Takusen via cabal install by downgrading to Cabal-1.4 but when I want to cabal-install takusen -fsqlite it complains about a missing sqlite3. What do I need to fix? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
On Mon, 2008-12-22 at 08:15 -0600, John Goerzen wrote: Duncan Coutts wrote: On Mon, 2008-12-22 at 10:30 +, Malcolm Wallace wrote: The terminology seems counter-intuitive, but in other other words, a safe call is slower but more flexible, an unsafe call is fast and dangerous. Therefore it is always OK to convert an unsafe declaration into a safe one, but never OK to convert from safe to unsafe without looking at what the foreign side actually does. And in general we would not even bother with considering using unsafe for calls that are already expensive. It's only worth considering when the length of the call is always very short. For example in a database library it might make sense to use 'unsafe' on the data-access functions that extract data from a local query result but we should always use 'safe' on any DB function that might want to talk to the network (eg to get more query results). It's difficult to anticipate the needs here. For instance, some people may be using a few very-long-running queries measured in minutes, such as the original poster. Other people, such as web app developers, may be issuing literally millions of queries, right after another, where the difference matters. The cost of a safe call is not really that high. In comparison to something a C function that just extracts a member from a structure it's high, but compared to executing even a simple SQL query I expect it's not even measurable. I had initially used unsafe because of the documented performance benefit, plus I certainly am not expecting Sqlite to call back into the Haskell runtime. It seems to me strange that using unsafe instead of safe would have negative implications for threading. After all, as Malcolm said above, it is always OK to convert an unsafe declaration into a safe one. So could the compiler be made to be smart enough to do so when it is advantageous for threading purposes? I think it could only do it by turning all unsafe functions into safe ones. As I understand it, the ability to switch rts capability is the more expensive of the properties that safe provides (compared to allowing the function to be re-entrant) because it involves pthread mutexes. What's the best way to make this suitable for both people with many queries and those with long-running queries? If the squlite API distinguishes executing a query (potentially long running) from extracting data from the result set (always quick) then it would be possible to mark the former safe and the latter unsafe and still not impose any great overhead on any user. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] ANN: HLint 1.0
Well, sort of. Ok, we can parse that. Let's assume a variable x holds the output of :show modules as a String. We call lines on it, then map words on it, do a !! 2 on it, and we get [Util.hs,, Recorder.hs,, Game.hs,, Monadius.hs,, Demo.hs,]. Chuck in a map (filter (\= ',')), and we get a good list. We can turn the list into a string suitable for hlint with a quick unwords. So our long sought after command becomes ':def hoogle (\_ - return $ :! ++ (unwords $ map (filter (\= ',')) $ (map words $ lines x) !! 2))'. But wait, how do we get 'x'? How do we call :show modules inside a Haskell expression? I have carefully looked over http://haskell.org/haskellwiki/GHC/GHCi#Using_GHCi and http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-commands.html and my conclusion is that you can't. You can't do a let x = :show modules, there is no function which will take :show modules, and so on. :functions can accept Haskell output, but it's a one-way barrier. It's no good writing Haskell functions which need information from the :functions. The first url includes a link to a .ghci mini-tutorial (section 4) that, among other things, implements :redir var cmd -- execute cmd, redirecting stdout to var Happy Holidays!-) Claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
On 22 Dec 2008, at 17:35, Raeck Zhao wrote: But I just found another 'problem', I just realize that the list does not support the user-defined data type? Don't worry, it does. the list is also depending on the Eq function? No, it doesn't. data Shape = Square | Triangle | Circle [Square, Triangle, Circle] Should work fine. or Square == Square Wouldn't work unless you declare your type Shape an instance of class Eq - which can be done automatically. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Defining a containing function on polymorphic list
2008/12/22 Raeck Zhao ra...@msn.com Thank you very much for your reply! It is really helpful! But I just found another 'problem', I just realize that the list does not support the user-defined data type? the list is also depending on the Eq function? For example, data Shape = Square | Triangle | Circle when I type either [Square, Triangle, Circle] This is perfectly legal, but GHCi won't be able to print it, because there is no Show instance for Shape. You can declare one: instance Show Shape where show Square = Square show Triagle = Triangle show Circle = Circle This can be generated automatically when you declare the type, by using: data Shape = Square | Triangle | Circle deriving (Show) or Square == Square Similarly, to use (==), you need an Eq instance, which can be defined much in the same way as the Show instance above (deriving also works on Eq -- don't generalize too hastily; not all classes work with deriving). Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monad constraint + record update
You can use a continuation trick I describe below. First of all, I would like to work in a more general situation. So, instead of working with Set, I'd like to declare two classes: class Returnable m a where ret :: a - m a and class Bindable m a b where bind :: m a - (a - m b) - m b I'm sure you're able to define instances like instance Ord a = Returnable Set a by yourself. You'll need MultiParamTypeClasses and FlexibleInstances for that to work. Now, the trick: newtype Restricted r m a = Restricted ((a - m r) - m r) instance Monad (Restricted r m) where return x = Restricted $ \h - h x Restricted g = f = Restricted $ \h - g $ \x - let Restricted g' = f x in g' h Quite simple, and doesn't mention pseudo-monadic structure of m at all. Now, the fun part: embed :: Bindable m a r = m a - Restricted r m a embed mx = Restricted (bind mx) unembed :: Returnable m r = Restricted r m r - m r unembed (Restricted g) = g ret You may also want another class class Summable m a where zero :: m a plus :: m a - m a - m a and now you can have instance Summable m r = MonadPlus (Restricted r m) where mzero = Restricted $ const zero Restricted g1 `mplus` Restricted g2 = Restricted $ \h - g1 h `plus` g2 h From now on, you can do something like that: unembed $ do x - embed $ Set.fromList [6,2,3] (do y - return x z - embed $ Set.fromList [1..2] guard $ y 5 return $ y + z) `mplus` return 10 and have fromList [3,4,5,10], as expected On 22 Dec 2008, at 20:19, Peter Padawitz wrote: I'd like to define a monad Set for types in the class Eq. But how can the arguments of Set be constrained when Set is defined as an instance of Monad? instance Eq a = Monad Set where ... obviously cannot work. Is there a standard update function for fields in data types, something that OO programmers do with assignments like obj.attr := value ? Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
Arnaud Bailly kindly exposed my mistake: I cited Leibniz Monadology attributing it to Spinoza. Call me idiot but it wasn't thoughtless mistake, I really mixed up Spinoza's concept of 'modes' with Leibniz's concept of 'monad'. But it is because of my laziness rather than foolishness (at least this time). My argument is that in his final writings Leibniz's 'monads' encompass reality as perceptions and emanate from God as thought emanates from the mind, which is exactly what Spinoza's 'modes' are about. So monads and modes being equal I prefer Spinoza as a patron for Haskell for his purity of cause-effect treatment. Arnold adds another Haskell-Spinoza nicety, I hope he won't mind my including his all letter. Thank you Arnold, it is encouraging to find guys like you. Philosophy is not my thing but I believe every man should tackle it as exercise. Hello Andrzej, Thanks a lot for your bit of rationalism among all these devotions :-) I think however that you are confusing Spinoza with Leibniz in the following assertion. Monads are a concept invented by the latter, together with the famous the best possible world ever mocked by Voltaire in Candide. The comparison between Haskell and spinozism is rather interesting though, especially when one considers that Spinoza's Ethic is based on the idea that the ultimate goal of one self is to increase its power to live, an affect which it calls Joy. Thinking of Haskell as a way to increase one's joy and one's power is a nice thought. Regards, Arnaud Bailly ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] concurrent haskell: thread priorities
From what i understand (correct me if I'm wrong): The threaded RT creates an OS thread for each CPU/core on the system and uses them to multiplex userland threads. These are context switched whenever they block/yield/gc and no priorities can be assigned. It seems like we could get some priority based scheduling (and still be slackers) if we allow marked green threads to be strictly associated with a specific OS thread (forkChildIO?). Its not a very good solution, but it seems easy to implement and would be nice for the few problems that really need priority based scheduling. How many of those problems involve having 1 thread running at high/realtime priority? Maybe most? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Rewrite thunk action rule?
Peter Todd wrote: Not quite. If I have a thunk, at the low level somewhere it must refer to the transform function, the transform matrix, and the element that is to be transformed. If I apply another transform to that unevaluated thunk, my understanding is that haskell will represent it as such: thunk transform Ta (thunk transform Tb e) When I want the following: thunk transform (Ta * Tb) e Is this an example of a Thunktor? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monad constraint + record update
On Mon, Dec 22, 2008 at 6:19 PM, Peter Padawitz peter.padaw...@udo.edu wrote:
I'd like to define a monad Set for types in the class Eq. But how can the
arguments of Set be constrained when Set is defined as an instance of Monad?
instance Eq a = Monad Set where ... obviously cannot work.
Shouldn't you impose the constraint when defining functions operating
on Set values? I guess that the contraint should be enforced not only
when dealing with monadic code, but also whenever it appears in your
program.
Is there a standard update function for fields in data types, something that
OO programmers do with assignments like obj.attr := value ?
Your statement doesn't make much sense in the functional world of Haskell.
There's a record update construct which may resemble the OO data
update operation but it makes a whole new copy of the original value,
i.e.:
foo a = a { attr = value }
which is basically like doing:
foo a = a + 2
Cristiano
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] concurrent haskell: thread priorities
Hello Neal, Monday, December 22, 2008, 11:07:32 PM, you wrote: The threaded RT creates an OS thread for each CPU/core on the system and uses them to multiplex userland threads. These are context switched whenever they block/yield/gc and no priorities can be assigned. not exactly. amount of OS threads created controlled by +RTS -N option to the program; unless program has special function that RTS calls to set up this value they are switched on every minor GC which by default occurs after each 256kb allocated which is rather frequent event It seems like we could get some priority based scheduling (and still be slackers) if we allow marked green threads to be strictly associated with a specific OS thread (forkChildIO?). forkOS creates new haskell thread and new OS thread specially for it -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] OpenAL
Does the example code at http://articles.bluishcoder.co.nz/Haskell/OpenAL work for anyone? I added some putStrLns to see the device and context, and get $ ./Main2 Device (ALCdevice 0x08a744c8) Context (ALCcontext 0x08aabda0) AL lib: alSource.c:2291: alcDestroyContext(): 1 Source(s) NOT deleted AL lib: alBuffer.c:1097: exit() 2 Buffer(s) NOT deleted and no sound. I had more complex code using OpenAL working some time ago, but the sound was crackly because my distribution used the original OpenAL implementation. Now that people are switching to OpenAL Soft, Haskell's OpenAL seems to be acting strangely. I mailed Sven in September, but didn't hear back. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
On Mon, Dec 22, 2008 at 04:28:03PM -, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Makes sense. I will make the similar change in all HDBC backends. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Hi guys, I just tried to forkIO-off the database code to keep the UI responsive using Takusen with Sqlite this time. The problem persists though, the UI freezes. AFAIK the sqlite-Takusen code does not use unsafe ccall which would block the thread, so that might not be the cause of the problem after all. Before you guys make the effort to fix this you might see if you can reproduce the problem maybe uploading a 50 MB file into an Sqlite database, for instance, or something else that will keep the database busy for some time in a row. I did not use -threaded and forkOS though. Günther Am 22.12.2008, 21:59 Uhr, schrieb John Goerzen jgoer...@complete.org: On Mon, Dec 22, 2008 at 04:28:03PM -, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Makes sense. I will make the similar change in all HDBC backends. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pattern combinators
On Sun, Dec 21, 2008 at 10:14 PM, Andrew Wagner wagner.and...@gmail.com wrote: I'd love to see a copy of this go up on hackage for experimentation. Would you care to upload your code, or send it to me so I can upload it? I've uploaded my latest version to http://hpaste.org/13263. It explicitly makes patterns polymorphic over the answer type of the case statement by making Pattern a newtype and universally quantifying the (un)currying and matching functions. For example, (-) :: Pattern a () vec - Curry vec ans - Case a ans I'm not sure it makes sense to create a package just yet. At the very least, you should ask Morten Rhiger first. The type signatures are mine, but the code is mostly straight transcriptions from his paper. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
On Mon, 2008-12-22 at 22:12 +0100, Günther Schmidt wrote: Hi guys, I just tried to forkIO-off the database code to keep the UI responsive using Takusen with Sqlite this time. The problem persists though, the UI freezes. You might need to provide us more details on the GUI code. As I understand if you're using gtk2hs. You need to make sure that you're not blocking the GUI event loop by making blocking calls in event handlers. All blocking stuff has to be run via forkIO and the event handler must be allowed to return so that Gtk+ can redraw windows etc. In this context, by blocking I mean blocking a single Haskell thread, which is of course different from the safe/unsafe foreign calls which blocks a whole OS thread and thus all the Haskell threads. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Hi, I put in on hpaste: http://hpaste.org/13264 slightly simplified Günther Am 22.12.2008, 22:36 Uhr, schrieb Duncan Coutts duncan.cou...@worc.ox.ac.uk: On Mon, 2008-12-22 at 22:12 +0100, Günther Schmidt wrote: Hi guys, I just tried to forkIO-off the database code to keep the UI responsive using Takusen with Sqlite this time. The problem persists though, the UI freezes. You might need to provide us more details on the GUI code. As I understand if you're using gtk2hs. You need to make sure that you're not blocking the GUI event loop by making blocking calls in event handlers. All blocking stuff has to be run via forkIO and the event handler must be allowed to return so that Gtk+ can redraw windows etc. In this context, by blocking I mean blocking a single Haskell thread, which is of course different from the safe/unsafe foreign calls which blocks a whole OS thread and thus all the Haskell threads. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?
I wrote my own implementation of MaybeT (which was a usefull exercise), but a quick google showed: http://www.haskell.org/haskellwiki/New_monads/MaybeT But I'm wondering why it's not in the standard library. The standards committee just hasn't gotten around to it yet? Or was there some discussion of this in the past on some (public) maillist, that my admittedly shallow googling failed to uncover, that someone could point me at? Thanks. Brian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] concurrent haskell: thread priorities
It seems like we could get some priority based scheduling (and still be slackers) if we allow marked green threads to be strictly associated with a specific OS thread (forkChildIO?). I think you want the GHC-only GHC.Conc.forkOnIO Suggestions like this are more motivation for the suggestion [1] to adopt a re-engineered / haskell-based RTS [2]. Tom [1] http://www.reddit.com/r/haskell_proposals/comments/7itaz/simple_robust_maintainable_rts_for_ghc_io_pdf/ [2] http://www.seas.upenn.edu/~lipeng/homepage/papers/lmpjt07hw.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell re-branding exercise
(responding with just a bit of possibly relevant context, not always directly) Paul Johnson wrote: I've lived through a couple of corporate rebranding exercises in my time, and I've read about some others. They follow a pattern: ... 2. The new branding is released with as much fanfare as possible. Press releases are released. Staff are given briefings about the significance of the whole exercise and the bold new future that it symbolises. I don't think our choice of logo is quite as significant as a corporate logo. We could even use more than one logo if we wanted (maybe different people or different places). The current logo is prominent on the haskell.org (and wikipedia), mainly... places I rarely see, when working on Haskell. I see a couple things people are trying to do - Self-descriptive, without trying to change the way we are as a community or a language - Inviting to newcomers, mostly independent of how we actually work (although better if we advertize things we can actually provide, of course) I don't think it's trying to create a change in the language or the community, mostly it's to reflect the change that has already happened. 3. The staff universally agree that the new logo is not a patch on the old one. The old one was a much loved friend; it stood for something; people have spent years working for it. The new one is obviously a piece of cheap gimcrackery yup, I'll miss the old logo. To me, it still looks beautiful, clean and fitting. A paradox of the Haskell world is that, while the language is Vulcan, the community around it is dominated by Warm Fuzziness. Clearly the two are not mutually exclusive. nice observation! A rebranding exercise needs to start with a short list of adjectives that the brand is to represent, good idea... although we could just be attracted by whatever proposed logo happens to have beauty instead, if our only purpose is not to be stuck with an ugly logo. and I think that the Haskell community needs to decide this before it fires up Inkscape. or in parallel with :-) -- random creativity can help us start thinking about what we don't want to see, and why we don't want to see it, too -Isaac ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Thanks John! I've been running into this quite a bit with the ODBC backend as well. Having an entire server app freeze because MS SQL Server decides to deadlock is rather unpleasant. Cheers, Sterl. On Mon, Dec 22, 2008 at 3:59 PM, John Goerzen jgoer...@complete.org wrote: On Mon, Dec 22, 2008 at 04:28:03PM -, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Makes sense. I will make the similar change in all HDBC backends. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?
On Mon, Dec 22, 2008 at 3:31 PM, Brian Hurt bh...@spnz.org wrote: I wrote my own implementation of MaybeT (which was a usefull exercise), but a quick google showed: http://www.haskell.org/haskellwiki/New_monads/MaybeT But I'm wondering why it's not in the standard library. The standards committee just hasn't gotten around to it yet? Or was there some discussion of this in the past on some (public) maillist, that my admittedly shallow googling failed to uncover, that someone could point me at? Yeah, it'd be useful. Doesn't really matter, though, because it's on Hackage (http://hackage.haskell.org), so it's just a cabal install MaybeT away. Now that cabal and cabal-install are reasonably mature, we really don't have to worry about what's blessed as standard anymore. :-) Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
On Mon, 2008-12-22 at 22:55 +0100, Günther Schmidt wrote: Hi, I put in on hpaste: http://hpaste.org/13264 slightly simplified Ok, that works fine when the action is something like threadDelay so it's clearly not blocking the UI. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Hi Duncan, are you saying then that the db-code is what's blocking the UI? Günther Duncan Coutts schrieb: On Mon, 2008-12-22 at 22:55 +0100, Günther Schmidt wrote: Hi, I put in on hpaste: http://hpaste.org/13264 slightly simplified Ok, that works fine when the action is something like threadDelay so it's clearly not blocking the UI. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Haskell re-branding exercise
On 22 dec 2008, at 19:14, Loup Vaillant wrote: 2008/12/22 Eelco Lempsink ee...@lempsink.nl: Hmm, right. I started on a thing in HAppS. See http://github.com/eelco/voting/ for the source code (contributors more than welcome!) and http://code.tupil.com/voting/ for a live demo. It relies heavily on javascript, needs some work on the UI and there are a lot of features that could be added, but it works. Great. Could it be further hacked to accept ties, as suggested by Sebastian? Something like: thingie1 thingie1bis thingie3 thingie4 thingie4bis Yes. Done. It's quite tricky to get the dragging and dropping interface to work nice, but I think I'm getting close. If anybody with jQuery experience has some ideas how to improve it, please do :) -- Regards, Eelco Lempsink PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
2008/12/22 Luke Palmer lrpal...@gmail.com: Andrzej Jaworski hims...@poczta.nom.pl First let me disassociate Haskell from Taoism... I associate Haskell with Zen... The relationship between Taoism and Zen is actually very close. The notion of stillness practice is essentially Chinese. Indian schools of meditation and schools of Buddhism not originating in China, tend to emphasize an /object/ of meditation -- a God, a candle, what-have-you. The practice of sitting still, doing nothing finds its way into Buddhism when Chan Buddhism is formed in China. It is an adaption of a Taoist practice with a long history -- and in fact, Chan was seen as a Taoist renewal. It is Chan that makes its way to Japan to become the Zen we all know. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
Andrzej Jaworski hims...@poczta.nom.pl wrote: First let me disassociate Haskell from Taoism which to may taste has left us in an unhealthy climate. It suffices to say that Taoism is a school of clever trics and cute aphorisms but without the slightest attempt to explain or generalize let alone produce an abstract idea or a system. That is why its wisdom is non transferable in spite of majority of humans desending from it. Taoist religion in China is very much a popular religion, closely associated with festivals, weddings and magic tricks. As a popular religion, Taoism is indeed deeply compromised; but then again, so is Zen in Japan, Christianity in Europe and indeed, most popular religions in the place where they became popular. As a philosophy, Taoism is more concerned with doubt than knowledge; with humility than pride of understanding; of course it makes litte attempt to explain or generalize. An essential notion in Taoism is that signs and symbols do not communicate the truth -- to appreciate Taoist practice, you must engage in the practice of Taoism for a spell. Thus it is in practical arts -- Chinese medicine, Taiji, strategy -- that one comes to appreciate the Way and its Power. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
You shouldn't need forkOS, but without -threaded (and related RTS switches to enable multithreading) I think you are sunk. Without enabling multithreading support, you are saying that your program (which might use concurrency features of Haskell) will run on a single OS thread. During a foreign call that never calls back into Haskell, then, there's no place for the RTS to pre-empt and switch back to Haskell code. It's kind of confusing with multiple things named threads; call a Haskell thread a lightweight thread, and an OS thread a heavy thread. Each heavy thread can either be executing Haskell lightweight threads, or inside a foreign out-call. Once you jump across to foreign-land, the heavy thread can't do anything (even for a safe out-call) until the out-call either makes an in-call back into Haskell code, or returns. Enabling -threaded allows the Haskell runtime to create more heavy threads; even without -threaded you can make as many lightweight threads as you like and the runtime will handle scheduling them for you; a heavy thread can carry many light threads. But a foreign call takes a whole heavy thread no matter what. -- ryan On Mon, Dec 22, 2008 at 1:12 PM, Günther Schmidt red...@fedoms.com wrote: Hi guys, I just tried to forkIO-off the database code to keep the UI responsive using Takusen with Sqlite this time. The problem persists though, the UI freezes. AFAIK the sqlite-Takusen code does not use unsafe ccall which would block the thread, so that might not be the cause of the problem after all. Before you guys make the effort to fix this you might see if you can reproduce the problem maybe uploading a 50 MB file into an Sqlite database, for instance, or something else that will keep the database busy for some time in a row. I did not use -threaded and forkOS though. Günther Am 22.12.2008, 21:59 Uhr, schrieb John Goerzen jgoer...@complete.org: On Mon, Dec 22, 2008 at 04:28:03PM -, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Makes sense. I will make the similar change in all HDBC backends. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
On Mon, 2008-12-22 at 17:14 -0800, Jason Dusek wrote: Andrzej Jaworski hims...@poczta.nom.pl wrote: First let me disassociate Haskell from Taoism which to may taste has left us in an unhealthy climate. It suffices to say that Taoism is a school of clever trics and cute aphorisms but without the slightest attempt to explain or generalize let alone produce an abstract idea or a system. That is why its wisdom is non transferable in spite of majority of humans desending from it. ... Thus it is in practical arts -- Chinese medicine, Taiji, strategy -- that one comes to appreciate the Way and its Power. But nonetheless, Haskell is not a practical art, no more than theoretical physics or abstract algebra. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A hell of a question
Jonathan Cast jonathancc...@fastmail.fm wrote: Jason Dusek wrote: Thus it is in practical arts -- Chinese medicine, Taiji, strategy -- that one comes to appreciate the Way and its Power. But nonetheless, Haskell is not a practical art, no more than theoretical physics or abstract algebra. I guess the question is whether we are treating Haskell as a means to appreciate Taoism or as Taoism itself. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?
2008/12/22 Luke Palmer lrpal...@gmail.com: Yeah, it'd be useful. Doesn't really matter, though, because it's on Hackage (http://hackage.haskell.org), so it's just a cabal install MaybeT away. Now that cabal and cabal-install are reasonably mature, we really don't have to worry about what's blessed as standard anymore. :-) Although I still had to use my own because I wanted a MonadPlus instance. I would offer a patch, but since there's more than one useful MonadPlus instance for MaybeT it probably still wouldn't be right for everyone. -Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal Install Links to Source from Haddock Docs
Thank you. As it turns out, I was aware of that recipe. What I wanted was to be able to use cabal install's nice dependency following features and still get source links in my documentation. Personally, I feel that inclusion of source and docs should be the DEFAULT for cabal, as well as for binary distributions of ghc. -rhayes On Dec 21, 2008, at 1:11 AM, Thomas Hartman wrote: the answer: not cabal install, just cabal. thart...@thartman-laptop:~/haskellInstalls/smallInstalls/ pureMD5-0.2.3 thart...@thartman-laptop:~/haskellInstalls/smallInstalls/ pureMD5-0.2.3cabal --help | grep -i doc haddock Generate Haddock HTML documentation. thart...@thartman-laptop:~/haskellInstalls/smallInstalls/ pureMD5-0.2.3cabal haddock --help | grep -i link --hyperlink-source Hyperlink the documentation to the source code thart...@thartman-laptop:~/haskellInstalls/smallInstalls/ pureMD5-0.2.3cabal haddock --hyperlink-source 2008/12/21 R Hayes rfha...@reillyhayes.com: Is there a way I can get Haddock Docs WITH links to source (local) from modules installed with cabal install xxx? Getting the docs themselves is pretty easy by changing either ~/.cabal/config or using --enable-documentation. Automatically generating the source (colourised or not) and integrated links eludes me. -r ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Is this related to monomorphism restriction?
Hi, On Sun, Dec 21, 2008 at 11:45 AM, Luke Palmer lrpal...@gmail.com wrote: 2008/12/21 Iavor Diatchki iavor.diatc...@gmail.com g :: TestClass a = a - Integer g = fst (a :: (a - Integer, a - Integer)) Which I believe needs to be written: g :: forall a. TestClass a = a - Integer g = fst (a :: (a - Integer, a - Integer)) quite right! sorry for not testing my code. -iavor Here we are using another GHC extension called scoped type variables to associate the a in the type signature of g with the a in the type annotation for the value a. Hope that this helps, Iavor On Sun, Dec 21, 2008 at 9:21 AM, Maurício briqueabra...@yahoo.com wrote: Why isn't the last line of this code allowed? f :: (TestClass a) = a - Integer f = const 1 a = (f,f) g = fst a The only thing I can think about is monomorphism restriction, but it's allowed (...) (...) The reason is that a has type a :: (TestClass a, TestClass b) = (a,b) and then when we take 'fst' of this value (as in g) we get g :: (TestClass a, TestClass b) = a which is an ambiguous type, (...) Is there some version (i.e., set of extensions) of Haskell where this would be allowed? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Time for a new logo?
Looking over the New_logo_ideas page, my vote is for the snowflake logo: http://haskell.org/sitewiki/images/9/98/Haskell-Symstar.png (I would simplify it, though, by removing the motto pure - lazy - fun.) I like this logo because it works well on two different levels. For those in the know, the lambda and = symbols suggest monads and first-class functions, two important features of the language. For those unfamiliar with Haskell or functional programming, the logo still looks pretty cool and manages to suggest mathematical beauty. -- View this message in context: http://www.nabble.com/Time-for-a-new-logo--tp21004746p21138458.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Hi Ryan, BINGO! that did it. Thanks a lot. It certainly works now, finally, eventhough I don't really know what the implications are. Günther Am 23.12.2008, 02:14 Uhr, schrieb Ryan Ingram ryani.s...@gmail.com: You shouldn't need forkOS, but without -threaded (and related RTS switches to enable multithreading) I think you are sunk. Without enabling multithreading support, you are saying that your program (which might use concurrency features of Haskell) will run on a single OS thread. During a foreign call that never calls back into Haskell, then, there's no place for the RTS to pre-empt and switch back to Haskell code. It's kind of confusing with multiple things named threads; call a Haskell thread a lightweight thread, and an OS thread a heavy thread. Each heavy thread can either be executing Haskell lightweight threads, or inside a foreign out-call. Once you jump across to foreign-land, the heavy thread can't do anything (even for a safe out-call) until the out-call either makes an in-call back into Haskell code, or returns. Enabling -threaded allows the Haskell runtime to create more heavy threads; even without -threaded you can make as many lightweight threads as you like and the runtime will handle scheduling them for you; a heavy thread can carry many light threads. But a foreign call takes a whole heavy thread no matter what. -- ryan On Mon, Dec 22, 2008 at 1:12 PM, Günther Schmidt red...@fedoms.com wrote: Hi guys, I just tried to forkIO-off the database code to keep the UI responsive using Takusen with Sqlite this time. The problem persists though, the UI freezes. AFAIK the sqlite-Takusen code does not use unsafe ccall which would block the thread, so that might not be the cause of the problem after all. Before you guys make the effort to fix this you might see if you can reproduce the problem maybe uploading a 50 MB file into an Sqlite database, for instance, or something else that will keep the database busy for some time in a row. I did not use -threaded and forkOS though. Günther Am 22.12.2008, 21:59 Uhr, schrieb John Goerzen jgoer...@complete.org: On Mon, Dec 22, 2008 at 04:28:03PM -, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther Schmidt I understand that Takusen does not use unsafe calls and would like to try it with that one then, but haven't find enough docs yet on how to use Takusen. Not a lot of detailed examples exist for Takusen. I'm hoping the documentation for Database.Enumerator is a reasonable place to start. http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html I just reviewed the Takusen code and, for no apparent reason, the ODBC module specifies unsafe for all of its FFI imports, but the other modules do not (so they get the default, which I assume is safe). I also was not aware of unsafe calls blocking other threads. I'll change the ODBC imports to be safe (or rather, unspecified). Makes sense. I will make the similar change in all HDBC backends. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Günther Schmidt wrote: Hi Ryan, BINGO! that did it. Thanks a lot. It certainly works now, finally, eventhough I don't really know what the implications are. Did it still work with the unmodified HDBC as well? Just curious. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Threads with high CPU usage
Thanks to you all for inspiration. My web app (which otherwise ran ok) was getting stuck while getting harassed by ab (apache-benchmark) after receiving some 800+ requests in short succession (not less, never gotten to 900, what was weird that running like 500 reqs - pause - 500 reqs ... went ok). After compiling with -threaded and running with +RTS -N2 it handles 10k+ requests (with 10 concurrent request running at once) without missing a beat. Well, at least I double checked everything else ;-))) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Takusen
Hi Günther, 2008/12/22 Günther Schmidt red...@fedoms.com: where can I find some sample code or other examples to familiarize me with Takusen? The best resource I've found is: http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html Cheers, Artyom Shalkhakov. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] intercalate and (byte)strings
I encountered the following code : -- B == Data.ByteString ; L == Data.ByteString.Lazy contents' = B.intercalate B.empty $ L.toChunks contents with a previously unencountered function intercalate. A quick google query later i knew that it's just intersperse concat nicely bundled and started wondering why anybody would do this, as simple contents' = B.concat $ L.toChunks contents would do (probably nearly) the same. The only thing I am able to come up with is that it somehow helps streamline the memory usage (if it has some meaning). Is there some reason to use intercalate empty list instead of concat list (probably when dealing with non-lazy bytestrings) ? Thx, wman. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Byte8] - ByteString
Hello, I have been reading through Data-ByteString. What is the is most elegant and efficient way to map/unmap [Byte8] - ByteString? Thanks, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Byte8] - ByteString
2008/12/22 Galchin, Vasili vigalc...@gmail.com Hello, I have been reading through Data-ByteString. What is the is most elegant and efficient way to map/unmap [Byte8] - ByteString? pack and unpack. You might need a fromIntegral in there, depending on whether Byte8 and Word8 are the same. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?
On Mon, Dec 22, 2008 at 6:52 PM, Antoine Latter aslat...@gmail.com wrote: 2008/12/22 Luke Palmer lrpal...@gmail.com: Yeah, it'd be useful. Doesn't really matter, though, because it's on Hackage (http://hackage.haskell.org), so it's just a cabal install MaybeT away. Now that cabal and cabal-install are reasonably mature, we really don't have to worry about what's blessed as standard anymore. :-) Although I still had to use my own because I wanted a MonadPlus instance. I would offer a patch, but since there's more than one useful MonadPlus instance for MaybeT it probably still wouldn't be right for everyone. There are? The only two I can think of are the left-biased and its dual, in which case the convention is to choose the left-biased one. Is there another? Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?
On Mon, Dec 22, 2008 at 2:31 PM, Brian Hurt bh...@spnz.org wrote: But I'm wondering why it's not in the standard library. The standards committee just hasn't gotten around to it yet? Or was there some discussion of this in the past on some (public) maillist, that my admittedly shallow googling failed to uncover, that someone could point me at? It's equivalent to ErrorT () - but ErrorT String is almost always a better option anyway. /g -- I am in here ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Byte8] - ByteString
sorry actually ByteString - [Word8] On Tue, Dec 23, 2008 at 12:49 AM, Luke Palmer lrpal...@gmail.com wrote: 2008/12/22 Galchin, Vasili vigalc...@gmail.com Hello, I have been reading through Data-ByteString. What is the is most elegant and efficient way to map/unmap [Byte8] - ByteString? pack and unpack. You might need a fromIntegral in there, depending on whether Byte8 and Word8 are the same. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
