Re: [Haskell-cafe] Storables and Ptrs
This can be used to call into C code expecting pointer input or output types to great effect: wrapperAroundForeignCode :: InputType - IO OutputType wrapperAroundForeignCode in = alloca $ \inPtr - alloca $ outPtr - do poke inPtr in c_call inPtr outPtr peek outPtr There is also 'with' (:: Storable a = a - (Ptr a - IO b) - IO b), which is exactly the combination of 'alloca' and 'poke' you use on 'in'. Erik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
In short: I can't cabal install xmonad-contrib. Longer version: It a appears that a program which does not exist on my computer seems to insist on a package version which does not exist in my universe, I'm starting to wonder whether I have lost my marbles. Could some kind soul please point me in some sensible direction? cabal install xmonad-contrib Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version =0.9.0 is required but it could not be found. cabal: Error: some packages failed to install: X11-xft-0.3 failed during the configure step. The exception was: ExitFailure 1 xmonad-contrib-0.9.1 depends on X11-xft-0.3 which failed to install. cabal install x11-xft Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version =0.9.0 is required but it could not be found. cabal: Error: some packages failed to install: X11-xft-0.3 failed during the configure step. The exception was: ExitFailure 1 X11-xft version 0.9.0 doesn't even exist, as far a I can tell: 0.3 seems to be the highest. So what is making cabal believe that such a version is needed? Is it pkg-config? I'm not at all familiar with pkg-config, and, as far as I can tell it's not even installed on the Mac on which I am trying to do this. Curiously, its man page *does* work (it's in /usr/X11/man, for some reason). Does Cabal have some sort of embedded pkg-config? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 6 December 2010 11:02, Jacek Generowicz jacek.generow...@cern.ch wrote: It a appears that a program which does not exist on my computer seems to insist on a package version which does not exist in my universe, I'm starting to wonder whether I have lost my marbles. Could some kind soul please point me in some sensible direction? cabal install xmonad-contrib Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version =0.9.0 is required but it could not be found. X11-xft version 0.9.0 doesn't even exist, as far a I can tell In the development version of cabal we have changed that error message to try and make it clear that it is looking for a program called pkg-config, not a Haskell package or a C lib. cabal: The program pkg-config version =0.9.0 is required but it could not be found. Do you think that message would have helped avoid your confusion? Is there an alternative message that would have been better? pkg-config [1] is a tool used by C libraries to describe things like dependencies on other C libs and what C compiler flags are needed to use the packages. The Haskell package X11-xft is a binding to the C library xft. On most modern unix systems xft C library provides meta-data that pkg-config can use. For example, on my system I can run: $ pkg-config --cflags xft -I/usr/include/freetype2 $ pkg-config --libs xft -lXft -lXrender -lfontconfig -lfreetype -lX11 Cabal does exactly the same thing, to work out what flags are needed to use the xft C library. The problem on your system is that the pkg-config program is not installed. Perhaps on OSX it comes with Xcode, I'm not sure. It may well also be the case that you don't have the development files for X11 or xft installed either (e.g. C header files). Hopefully some OSX person can advise you on what you need to install to do X11 development on OSX. [1]: http://pkg-config.freedesktop.org/wiki/ Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On Mon, Dec 6, 2010 at 7:15 AM, Duncan Coutts duncan.cou...@googlemail.com wrote: On 6 December 2010 11:02, Jacek Generowicz jacek.generow...@cern.ch wrote: It a appears that a program which does not exist on my computer seems to insist on a package version which does not exist in my universe, I'm starting to wonder whether I have lost my marbles. Could some kind soul please point me in some sensible direction? cabal install xmonad-contrib Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version =0.9.0 is required but it could not be found. X11-xft version 0.9.0 doesn't even exist, as far a I can tell In the development version of cabal we have changed that error message to try and make it clear that it is looking for a program called pkg-config, not a Haskell package or a C lib. cabal: The program pkg-config version =0.9.0 is required but it could not be found. Do you think that message would have helped avoid your confusion? Is there an alternative message that would have been better? pkg-config [1] is a tool used by C libraries to describe things like dependencies on other C libs and what C compiler flags are needed to use the packages. The Haskell package X11-xft is a binding to the C library xft. On most modern unix systems xft C library provides meta-data that pkg-config can use. For example, on my system I can run: $ pkg-config --cflags xft -I/usr/include/freetype2 $ pkg-config --libs xft -lXft -lXrender -lfontconfig -lfreetype -lX11 Cabal does exactly the same thing, to work out what flags are needed to use the xft C library. The problem on your system is that the pkg-config program is not installed. Perhaps on OSX it comes with Xcode, I'm not sure. It may well also be the case that you don't have the development files for X11 or xft installed either (e.g. C header files). Hopefully some OSX person can advise you on what you need to install to do X11 development on OSX. On my Mac 'which -a pkg-config' returns: /opt/local/bin/pkg-config /opt/local/bin/pkg-config I'm not sure why it prints twice. The folder means I've installed it from MacPorts, which also means I guess you'll need to install the MacPorts version of X11-xft, but I'm not sure. However building Haskell libraries against MacPorts often leads to nightmarish scenarios involving libiconv, but I haven't run into that on my current installation yet. Antoine [1]: http://pkg-config.freedesktop.org/wiki/ 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
[Haskell-cafe] Berlin Haskell Meeting
The Berlin Haskell meeting is due again: Date: Tuesday, December 7th Time: from 20:00 Location: c-base, Rungestrasse 20, 10179 Berlin See you there. Sönke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
Problem solved: 2 solutions described below. On 2010 Dec 6, at 14:15, Duncan Coutts wrote: On 6 December 2010 11:02, Jacek Generowicz jacek.generow...@cern.ch wrote: It a appears that a program which does not exist on my computer seems to insist on a package version which does not exist in my universe, I'm starting to wonder whether I have lost my marbles. Could some kind soul please point me in some sensible direction? cabal install xmonad-contrib Resolving dependencies... Configuring X11-xft-0.3... cabal: pkg-config version =0.9.0 is required but it could not be found. X11-xft version 0.9.0 doesn't even exist, as far a I can tell In the development version of cabal we have changed that error message to try and make it clear that it is looking for a program called pkg-config, not a Haskell package or a C lib. cabal: The program pkg-config version =0.9.0 is required but it could not be found. Do you think that message would have helped avoid your confusion? Oooh, that's a difficult question to answer, as I had read your earlier paragraph before coming to this question. After your explanation explained the error message (to the extent that I now wonder how on earth I ever took it to mean that it's looking for X11- xft version =0.9.0, when it quite clearly states pkg-config version =0.9.0 is required but could not be found), I have no idea whether the new message would have been better. Is there an alternative message that would have been better? Well, if I try to understand how I could have misunderstood the original message, I suspect that it is because of the common style of error message where the program generating the message precedes the actual message on the same line, just like cabal: ... precedes the message in this case. So I guess that I parsed it something like ... pkg-config: version =0.9.0 is required ... and inferred that 'version' refers to the package mentioned in an earlier message. In which case, maybe something like cabal: version =0.9.0 of pkg-config is required ... would have prevented me from making this particular mistake in this particular case. pkg-config [1] is a tool used by C libraries to describe things like dependencies on other C libs and what C compiler flags are needed to use the packages. The Haskell package X11-xft is a binding to the C library xft. On most modern unix systems xft C library provides meta-data that pkg-config can use. For example, on my system I can run: $ pkg-config --cflags xft -I/usr/include/freetype2 $ pkg-config --libs xft -lXft -lXrender -lfontconfig -lfreetype -lX11 Cabal does exactly the same thing, to work out what flags are needed to use the xft C library. The problem on your system is that the pkg-config program is not installed. Perhaps on OSX it comes with Xcode, I'm not sure. It may well also be the case that you don't have the development files for X11 or xft installed either (e.g. C header files). Hopefully some OSX person can advise you on what you need to install to do X11 development on OSX. Solution 1 (more complicated version): Although I never use XCode itself, I thought that I had it installed along with all the developer tools in order to get at GCC etc. Apparently not. Anyway, pkg-config seems to be available through darwinports, but I don't use darwinports (as, many years ago, I concluded that it's more trouble than it's worth, because of the strange places where it puts the stuff it manages). However, a plain manual compilation Just Works (for me): curl http://pkgconfig.freedesktop.org/releases/pkg-config-0.25.tar.gz -o pkgconfig.tgz tar zxf pkgconfig.tgz cd pkgconfig.tgz ./configure make sudo make install and I now have pkg-config If I try pkg-config --cflags xft it complains about the package not being found, and mentions the relevant environment variable. I *do* have /usr/X11/lib/pkgconfig/xft.pc, and popping its directiory into PKG_CONFIG_PATH makes the above pkg-config call now work. In this state, cabal install xmonad-contrib also works. = = = Solution 2 (simpler): I did manage to get xmonad-contrib to cabal install (without pkg- config) by asking for it not to use xft cabal install xmonad-contrib --flags=-use_xft Presumably cabal uses pkg-config for only a subset of the things it manages, and xft is the only one of those on which xmonad-contrib depends. Thank you Duncan for your concise, clear and complete answer: it was just what I needed to unblock me. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 2010 Dec 6, at 15:05, Antoine Latter wrote: On my Mac 'which -a pkg-config' returns: /opt/local/bin/pkg-config /opt/local/bin/pkg-config I'm not sure why it prints twice. Same happens with my hand-installed version when I use the -a flag: it only shows it once when invoked without -a. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 2010 Dec 6, at 15:39, Jacek Generowicz wrote: On 2010 Dec 6, at 14:15, Duncan Coutts wrote: In the development version of cabal we have changed that error message to try and make it clear that it is looking for a program called pkg-config, not a Haskell package or a C lib. cabal: The program pkg-config version =0.9.0 is required but it could not be found. Do you think that message would have helped avoid your confusion? Oooh, that's a difficult question to answer, as I had read your earlier paragraph before coming to this question. After your explanation explained the error message (to the extent that I now wonder how on earth I ever took it to mean that it's looking for X11- xft version =0.9.0, when it quite clearly states pkg-config version =0.9.0 is required but could not be found), I have no idea whether the new message would have been better. Is there an alternative message that would have been better? Well, if I try to understand how I could have misunderstood the original message, I suspect that it is because of the common style of error message where the program generating the message precedes the actual message on the same line, just like cabal: ... precedes the message in this case. So I guess that I parsed it something like ... pkg-config: version =0.9.0 is required ... and inferred that 'version' refers to the package mentioned in an earlier message. In which case, maybe something like cabal: version =0.9.0 of pkg-config is required ... would have prevented me from making this particular mistake in this particular case. Another thing that would probably have made it easier to understand: the message is strictly correct, but is *too* specific: it talks about pkg-config version =0.9.0 not being found, while the problem was that *no version at all* was present. I would understand if making the error message change according to such subtle distinctions would be more effort that it is worth. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] the beginning of the end
On Mon, Dec 6, 2010 at 2:33 AM, David Virebayre dav.vire+hask...@gmail.com wrote: Level 5 I'm out of layers here. I think this is all there is to it. Level 5 is after you've spent way too much time writing questions and/or answers that people like and have over 10k reputation. This unlocks some basic moderation tools for helping deal with spam and other problematic content. SO is a largely community-driven site, rather than having a bunch of moderators appointed by the administrators. There's also other things that some people track, like weekly scores and per-tag rankings. For instance, I'm apparently SO's foremost expert on lazy-evaluation and typeclass, and the only user so far to get a tag badge for monads. This is obviously a very significant accomplishment. But seriously, it's mostly just a medium for providing QA in a structured, searchable way. In fact, you missed the most important part by far: Level 0: You have an unresolved programming problem. You search the web for information and the first Google hit is a question on StackOverflow that describes your problem exactly. You look at the accepted answer, find that it has the solution you need, and go on your way in a matter of minutes. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 6 December 2010 14:48, Jacek Generowicz jacek.generow...@cern.ch wrote: Another thing that would probably have made it easier to understand: the message is strictly correct, but is *too* specific: it talks about pkg-config version =0.9.0 not being found, while the problem was that *no version at all* was present. I would understand if making the error message change according to such subtle distinctions would be more effort that it is worth. Yes. The version is there so that when you do go and install it, you will know what version to look for, so you don't end up in the situation where you've gone to all the effort of installing pkg-config, only to find it now complains that it found it, but it was too old. Perhaps something like this would be better: cabal: The program 'pkg-config' is required but it could not be found on the system (version 0.9.0 or later of pkg-config is required). Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] An Haskell implementation of a sweep line algorithm for the detection of segments intersection
Hi, Here is my Haskell implementation of the Shamos and Hoey algorithm for detecting segments intersection in the plane: http://neonstorm242.blogspot.com/2010/12/sweep-line-algorithm-for-detection-of.html I'm new to Haskell, so any useful comments will be appreciated. - Eran ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Trying out GHC 7
OK, so the other day I decided to take GHC 7.0.1 for a spin. Suffice it to say, it definitely compiles stuff. So far, I've only tried running it in a Windows XP virtual machine with a single core, so I haven't been able to test what multicore performance is like. One thing that did interest me is the conflicting information about whether or not dynamic linking is supported on Windows. Half the User Guide claims that this /is/ supported, and the other half still contains statements that it is /not/ supported. So I thought I'd just go physically try it and see if it works. Well... it compiles stuff. Hello World goes from being 518KB to being a piffling 13KB. Which is nice. I almost didn't bother actually trying to /run/ the resulting binary... But when I did, I discovered that it immediately crashes, whining that it can't find the DLL it wants. So, out of the box, the Windows setup is broken. (Obviously the Windows section of the User Guide makes no mention of how DLLs are located; it only explains the situation for Linux and Mac OS. I especially liked the bit where it says that there are three modes, and then proceeds to list only two...) In the interests of science, I wanted to see if I could make it run by just putting the necessary DLLs into the same folder as the binary. But first I had to /find/ them. I had expected to find a folder somewhere with all the DLLs in it... but no, the installer appears to have sprinkled them around the filesystem more or less at random. Some of them are in folders named for the package, some of them just sit in the root folder. After about 20 minutes of searching, I found the RTS DLL. Running the program, it now instantly crashes because of a /different/ DLL. This one didn't take quite so long to find (now that I know roughly where to look). I fixed that, and now the binary crashes with yet another missing DLL. And so on and so forth. In the end, Hello World required 5 DLLs. Better still, together these totalled 8MB of data. (!) So the distribution package is now about 16x bigger than with static linking. Oh joy. Clearly if you just want to distribute one executable binary, you're going to use static linking. (E.g., darcs.exe will hopefully remain statically linked.) But I suppose if I had a whole heap of Haskell programs then the extra complexity of delivering half a dozen DLLs might may off in terms of space reductions. And of course, on /my/ development box, I don't need a zillion redundant copies of the RTS code, etc. (Or at least, I won't if I can figure out how to make the programs able to actually /find/ the necessary DLLs...) Actually, of all the DLLs, only base is actually large - it's approximately 6MB on its own. GHC-Prim is 0.5MB, and the others are all relatively tiny. It feels slightly irritating that I need to inclide the FFI DLL when I'm not doing and FFI - but of course, the entire Haskell I/O subsystem /is/ doing FFI. Similarly, I'm not using arbitrary-precision integers, but various I/O operations return file sizes as Integer, so GMP must also be included. Neither of these things are actually especially large. It's rather confusing that the User Guide is out of date in so many places. (And not just regarding dynamic linking on Windows. For example, one section claims that +RTS -f will tell you what options are supported, but that actually yields unknown RTS opion: -f. It seems that -? is the correct option name.) If I can get a suitable Linux VM going, I might have a go at contributing some updates. Just for completeness, I tried asking for dynamic linking with an older version of GHC (6.10, IIRC) - one that supports it on Linux but not Windows. I was expecting to get either dynamic linking is not supported on this platform, or at worst unknown option -dynamic. In fact, what I got was gcc: cannot find file Main.dyn_hi. Oh, that's graceful failure then. _ I did also briefly see if the LLVM backend would work under Windows. I wasn't entirely sure if LLVM comes with the installer binary or you need to get it seperately. (You might say obviously it's seperate, but the installer already contains the entire GCC system, for example.) Attempting to use this resulted in a summary error message (cannot run: opt) which doesn't make it especially clear that the problem is that LLVM isn't installed. Perhaps there's no better way of detecting this condition, I don't know, but something more illuminating would be nice. I briefly had a look at how to install LLVM, but it appears that you have to build it from source. This is not my idea of a fun time, so given the minimal speed difference, I just won't bother. I haven't had time to play with any of the other new good stuff in GHC 7. (The multicore performance, the new GC stuff, etc.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org
Re: [Haskell-cafe] An Haskell implementation of a sweep line algorithm for the detection of segments intersection
2010/12/6 vince vegga megatron...@gmail.com: Here is my Haskell implementation of the Shamos and Hoey algorithm for detecting segments intersection in the plane: http://neonstorm242.blogspot.com/2010/12/sweep-line-algorithm-for-detection-of.html Quite good, actually. Myself, I rarely write code that is on par with yours. ;) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 12/6/10 7:25 AM, Duncan Coutts wrote: cabal: The program 'pkg-config' is required but it could not be found on the system (version 0.9.0 or later of pkg-config is required). Looks good. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] LLVM, getElementPtr?
On Sun, Dec 5, 2010 at 12:45 PM, Lally Singh lally.si...@gmail.com wrote: Is that how it's intended? I think that's correct, (it at least fits the pattern for 'with' functions in Haskell). They're idiomatically used with syntax like this: buildReaderFun :: String - CodeGenModule (Function (IO ())) buildReaderFun nm = do puts - newNamedFunction ExternalLinkage puts :: TFunction (Ptr Word8 - IO Word32) withStringNul nm $ \greetz - createFunction ExternalLinkage $ do tmp - getElementPtr greetz (0 :: Word32,(0 :: Word32, ())) call puts tmp -- Throw away return value. ret () ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trying out GHC 7
Inlcuding the ghc-users list. On Mon, Dec 6, 2010 at 10:10 AM, Andrew Coppin andrewcop...@btinternet.com wrote: OK, so the other day I decided to take GHC 7.0.1 for a spin. Suffice it to say, it definitely compiles stuff. So far, I've only tried running it in a Windows XP virtual machine with a single core, so I haven't been able to test what multicore performance is like. One thing that did interest me is the conflicting information about whether or not dynamic linking is supported on Windows. Half the User Guide claims that this /is/ supported, and the other half still contains statements that it is /not/ supported. So I thought I'd just go physically try it and see if it works. Well... it compiles stuff. Hello World goes from being 518KB to being a piffling 13KB. Which is nice. I almost didn't bother actually trying to /run/ the resulting binary... But when I did, I discovered that it immediately crashes, whining that it can't find the DLL it wants. So, out of the box, the Windows setup is broken. (Obviously the Windows section of the User Guide makes no mention of how DLLs are located; it only explains the situation for Linux and Mac OS. I especially liked the bit where it says that there are three modes, and then proceeds to list only two...) In the interests of science, I wanted to see if I could make it run by just putting the necessary DLLs into the same folder as the binary. But first I had to /find/ them. I had expected to find a folder somewhere with all the DLLs in it... but no, the installer appears to have sprinkled them around the filesystem more or less at random. Some of them are in folders named for the package, some of them just sit in the root folder. After about 20 minutes of searching, I found the RTS DLL. Running the program, it now instantly crashes because of a /different/ DLL. This one didn't take quite so long to find (now that I know roughly where to look). I fixed that, and now the binary crashes with yet another missing DLL. And so on and so forth. In the end, Hello World required 5 DLLs. Better still, together these totalled 8MB of data. (!) So the distribution package is now about 16x bigger than with static linking. Oh joy. Clearly if you just want to distribute one executable binary, you're going to use static linking. (E.g., darcs.exe will hopefully remain statically linked.) But I suppose if I had a whole heap of Haskell programs then the extra complexity of delivering half a dozen DLLs might may off in terms of space reductions. And of course, on /my/ development box, I don't need a zillion redundant copies of the RTS code, etc. (Or at least, I won't if I can figure out how to make the programs able to actually /find/ the necessary DLLs...) Actually, of all the DLLs, only base is actually large - it's approximately 6MB on its own. GHC-Prim is 0.5MB, and the others are all relatively tiny. It feels slightly irritating that I need to inclide the FFI DLL when I'm not doing and FFI - but of course, the entire Haskell I/O subsystem /is/ doing FFI. Similarly, I'm not using arbitrary-precision integers, but various I/O operations return file sizes as Integer, so GMP must also be included. Neither of these things are actually especially large. It's rather confusing that the User Guide is out of date in so many places. (And not just regarding dynamic linking on Windows. For example, one section claims that +RTS -f will tell you what options are supported, but that actually yields unknown RTS opion: -f. It seems that -? is the correct option name.) If I can get a suitable Linux VM going, I might have a go at contributing some updates. Just for completeness, I tried asking for dynamic linking with an older version of GHC (6.10, IIRC) - one that supports it on Linux but not Windows. I was expecting to get either dynamic linking is not supported on this platform, or at worst unknown option -dynamic. In fact, what I got was gcc: cannot find file Main.dyn_hi. Oh, that's graceful failure then. _ I did also briefly see if the LLVM backend would work under Windows. I wasn't entirely sure if LLVM comes with the installer binary or you need to get it seperately. (You might say obviously it's seperate, but the installer already contains the entire GCC system, for example.) Attempting to use this resulted in a summary error message (cannot run: opt) which doesn't make it especially clear that the problem is that LLVM isn't installed. Perhaps there's no better way of detecting this condition, I don't know, but something more illuminating would be nice. I briefly had a look at how to install LLVM, but it appears that you have to build it from source. This is not my idea of a fun time, so given the minimal speed difference, I just won't bother. I haven't had time to play with any of the other new good stuff in GHC 7. (The multicore performance, the new GC stuff, etc.)
Re: [Haskell-cafe] Trying out GHC 7
andrewcoppin: [100 lines snipped] Andrew, if you have a bug report, please use the bug tracker: http://hackage.haskell.org/trac/ghc/wiki/ReportABug Keep your reports concise and to-the-point, for the best hope of getting useful stuff done. Cheers, Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trying out GHC 7
On Mon, Dec 06, 2010 at 10:04:35AM -0800, Don Stewart wrote: Andrew, if you have a bug report, please use the bug tracker: http://hackage.haskell.org/trac/ghc/wiki/ReportABug Or reddit, of course. ;-) -- You've been warned. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Storables and Ptrs
On Mon, Dec 6, 2010 at 12:03 PM, Tyler Pirtle tee...@gmail.com wrote: On Sun, Dec 5, 2010 at 9:46 PM, Antoine Latter aslat...@gmail.com wrote: On Sun, Dec 5, 2010 at 10:45 PM, Tyler Pirtle tee...@gmail.com wrote: Hi cafe, I'm just getting into Foreign.Storable and friends and I'm confused about the class storable. For GHC, there are instances of storable for all kinds of basic types (bool, int, etc) - but I can't find the actual declaration of those instances. I'm confused that it seems that all Storable instances operate on a Ptr, yet none of these types allow access to an underlying Ptr. I noticed that it's possible via Foreign.Marshal.Utils to call 'new' and get a datatype wrapped by a Ptr, but this isn't memory managed - I'd have to explicitly free it? Is that my only choice? The Storable class defines how to copy a particular Haskell type to or from a raw memory buffer - specifically represented by the Ptr type. It is most commonly used when interacting with non-Haskell (or 'Foreign') code, which is why a lot of the tools look like they require manual memory management (because foreign-owned resources must often be managed separately anyway). Not all of the means of creating a Ptr type require manual memory management - the 'alloca' family of Haskell functions allocate a buffer and then free it automatically when outside the scope of the passed-in callback (although 'continuation' or 'action' would be the more Haskell-y way to refer to the idea): alloca :: Storable a = (Ptr a - IO b) - IO b This can be used to call into C code expecting pointer input or output types to great effect: wrapperAroundForeignCode :: InputType - IO OutputType wrapperAroundForeignCode in = alloca $ \inPtr - alloca $ outPtr - do poke inPtr in c_call inPtr outPtr peek outPtr The functions 'peek' and 'poke' are from the Storable class, and I used the 'alloca' function to allocate temporary storage for the pointers I pass into C-land. Is there a particular problem you're trying to solve? We might be able to offer more specific advice. The Storable and Foreign operations may not even be the best solution to what you're trying to do. Hey Antoine, Thanks for the clarity, it's very helpful. There is in fact a particular problem I'm trying to solve - persisting data structures. I'm a huge fan of Data.Vector.Storable.MMap, and I'm interested in other things like it - but i realize that the whole thing is built up/on/around storables, and building vectors with storables (read == peek, write == poke, etc), because i'm trying to write the raw structures themselves to disk (via mmap). I am aware of Data.Binary, but I feel that this kind of serialization for the application I'm building would be too cumbersome considering the number of objects I'm dealing with (on the order of hundreds-of-millions to billions), especially considering that the application I'm building has some very nice pure-ish semantics (an append-only list). I'd like the application to able to simply load a file and interact with that memory - not have to load the file and then deserialize everything. If you have any suggestions here, or if anyone has any general feelings about the design or implementation of Data.Vector.Storable.MMap I'd be very interested in hearing them. Or about any ideas involving persisting native data structures in an append-only fashion, too. ;) If you took the approach of Data.Vector.Storable.MMap, every time you read an element out of the array you would be un-marshalling the object from a pointer into a Haskell type - in effect, making a copy. There are probably ways to do this for ByteStrings to make this copy free, but that's about it. So depending on your data and usage patterns, that might be a great approach. Just rember that operations involving Storable make copies of your data. For large and complex types you would have a trade-off - each read might be more expensive than otherwise, but depending on your usage patterns you could save a lot on how much you keep in memory at a given time. If you're lucky, you might be able to write your Storable instance such that you can take advantage of Haskell's laziness, so that common operations only need to unmarhsall part of the object. But this might be overkill. Maybe you could email the maintainer of the vector package, to see if they have used the 'MMap' backed vector, or have any feedback from anyone that has. Most of what I've written is speculation - I've never tried that sort of thing. Take care, Antoine Thanks, Tyler Take care, Antoine Is there a way that given just simply an Int I could obtain a Ptr from it, and then invoke the storable functions on it? Or for that matter, if I go and create some new data type, is there some generic underlying thing (ghc-only or otherwise) that would let me have a Ptr of it? Thanks, Tyler
Re: [Haskell-cafe] Cabal, xmonad-contrib, X11-xft, pkg-config ... questioning my sanity
On 2010 Dec 6, at 16:25, Duncan Coutts wrote: Perhaps something like this would be better: cabal: The program 'pkg-config' is required but it could not be found on the system (version 0.9.0 or later of pkg-config is required). That looks pretty good. I'm having trouble finding any holes in it. There is also the issue (if my understanding is correct) that cabal install only needs pkg-config for some packages. So it is possible that someone has happily been using cabal install for some time, and then suddenly it doesn't work. And then they are left wondering what broke: But I'm sure it worked last week, and I haven't changed anything etc. At which point it could be helpful to be told that it's a circumstantial rather than a fundamental problem. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about TagSoup
Hi David,
I see no reason not to use TagSoup for this, assuming it does what you
want. It wasn't really designed for either modification or round
tripping, so be careful that things like entities don't become
corrupted. Also note that this won't replace all the contents of the
Content tag, only the first text node, so if someone writes
ContentiText/i/Content you won't hit it. But if it works, I'd
stick with it - it's light weight and easy to get to grips with.
Also your use of recursion seems perfectly reasonable. I often find
the easiest way to encode some kind of multiple element search (i.e.
for the Content tag and it's following text) is with direct
recursion - although I'm certain some kind of fold would also work.
Thanks, Neil
On Fri, Dec 3, 2010 at 1:45 PM, Alex Rozenshteyn rpglove...@gmail.com wrote:
I really wouldn't use tag soup for this. Haskell has libraries specifically
for XML processing which might be better suited to your needs.
On Fri, Dec 3, 2010 at 5:59 AM, David Virebayre dav.vire+hask...@gmail.com
wrote:
Hello café,
I have seen tutorials about extracting information from a tag soup, but I
have a different use case:
I want to read a xml file, find a tag, change its content, and write the
xml file back.
This is an example of the files
?xml version=1.0 encoding=UTF-8 standalone=yes?
idPkg:Story
xmlns:idPkg=http://ns.adobe.com/AdobeInDesign/idml/1.0/packaging;
DOMVersion=7.0
Story Self=ub9fad AppliedTOCStyle=n TrackChanges=false
StoryTitle=$ID/ AppliedNamedGrid=n
StoryPreference OpticalMarginAlignment=false
OpticalMarginSize=12 FrameType=TextFrameType
StoryOrientation=Horizontal StoryDirection=LeftToRightDirection/
InCopyExportOption IncludeGraphicProxies=true
IncludeAllResources=false/
ParagraphStyleRange
AppliedParagraphStyle=ParagraphStyle/prix
CharacterStyleRange
AppliedCharacterStyle=CharacterStyle/$ID/[No character style]
Contentzzznba5/Content
/CharacterStyleRange
/ParagraphStyleRange
/Story
/idPkg:Story
Assuming I want to change the content of the Content tag, this is what I
came up with (simplified), I'm using direct recursion. Is there a better way
?
ts = do
soup - parseTags `fmap` readFile idml/h00/Stories/Story_ub9fad.xml
writeFile test $ renderTagsOptions renderOptions{optMinimize = const
True}
$ modif soup
modif [] = []
modif (x@(TagOpen Content []):TagText _m : xs) = x : TagText modified
: modif xs
modif (x:xs) = x : modif xs
David.
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Re: [Haskell-cafe] Storables and Ptrs
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 12/6/10 13:22 , Antoine Latter wrote: On Mon, Dec 6, 2010 at 12:03 PM, Tyler Pirtle tee...@gmail.com wrote: On Sun, Dec 5, 2010 at 9:46 PM, Antoine Latter aslat...@gmail.com wrote: On Sun, Dec 5, 2010 at 10:45 PM, Tyler Pirtle tee...@gmail.com wrote: Hi cafe, I'm just getting into Foreign.Storable and friends and I'm confused about the class storable. For GHC, there are instances of storable for all kinds of basic types (bool, int, etc) - but I can't find the actual declaration of those instances. I'm confused that it seems that all Storable instances operate on a Ptr, yet none of these types allow access to an underlying Ptr. I noticed that it's possible via Foreign.Marshal.Utils to call 'new' and get a datatype wrapped by a Ptr, but this isn't memory managed - I'd have to explicitly free it? Is that my only choice? The Storable class defines how to copy a particular Haskell type to or from a raw memory buffer - specifically represented by the Ptr type. It is most commonly used when interacting with non-Haskell (or 'Foreign') code, which is why a lot of the tools look like they require manual memory management (because foreign-owned resources must often be managed separately anyway). Not all of the means of creating a Ptr type require manual memory management - the 'alloca' family of Haskell functions allocate a buffer and then free it automatically when outside the scope of the passed-in callback (although 'continuation' or 'action' would be the more Haskell-y way to refer to the idea): alloca :: Storable a = (Ptr a - IO b) - IO b This can be used to call into C code expecting pointer input or output types to great effect: wrapperAroundForeignCode :: InputType - IO OutputType wrapperAroundForeignCode in = alloca $ \inPtr - alloca $ outPtr - do poke inPtr in c_call inPtr outPtr peek outPtr The functions 'peek' and 'poke' are from the Storable class, and I used the 'alloca' function to allocate temporary storage for the pointers I pass into C-land. Is there a particular problem you're trying to solve? We might be able to offer more specific advice. The Storable and Foreign operations may not even be the best solution to what you're trying to do. Hey Antoine, Thanks for the clarity, it's very helpful. There is in fact a particular problem I'm trying to solve - persisting data structures. I'm a huge fan of Data.Vector.Storable.MMap, and I'm interested in other things like it - but i realize that the whole thing is built up/on/around storables, and building vectors with storables (read == peek, write == poke, etc), because i'm trying to write the raw structures themselves to disk (via mmap). I am aware of Data.Binary, but I feel that this kind of serialization for the application I'm building would be too cumbersome considering the number of objects I'm dealing with (on the order of hundreds-of-millions to billions), especially considering that the application I'm building has some very nice pure-ish semantics (an append-only list). I'd like the application to able to simply load a file and interact with that memory - not have to load the file and then deserialize everything. If you have any suggestions here, or if anyone has any general feelings about the design or implementation of Data.Vector.Storable.MMap I'd be very interested in hearing them. Or about any ideas involving persisting native data structures in an append-only fashion, too. ;) If you took the approach of Data.Vector.Storable.MMap, every time you read an element out of the array you would be un-marshalling the object from a pointer into a Haskell type - in effect, making a copy. There are probably ways to do this for ByteStrings to make this copy free, but that's about it. IIRC bytestring-mmap uses pinned bytestrings; might be easier/faster to use that directly if the vector package is troublesome. You'd want to use the bytestring internals module for the equivalent of peek/poke. - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkz9Mm0ACgkQIn7hlCsL25UgKgCgqV/BIXRDm5BVEPBzNllpVVD9 QsYAoJMU7kvHWxoAmb2eYV9b5tll9U0d =p1GN -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Offer to mirror Hackage
On 12/6/10 2:35 AM, Vincent Hanquez wrote: I would really like mirrors too. But before that happens it would be nice to have signed packages on Hackage, preventing a mirror to distribute compromised stuff (intentionally or unintentionally). +1. This should be done during sdist, before uploading, so that maintainers can be sure that the central mirror gets the right thing too. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] include modules in DLL? undefined reference
Hello!
I'm trying to compile a Windows DLL and need to include an additional module
(specifically FRP.Yampa).
I was successful with a Hello World type of DLL but when I use Yampa I get:
$ ghc -shared -o hs.dll DLLTest.o DLLTest_stub.o StartEnd.o
Creating library file: hs.dll.a
DLLTest.o:fake:(.text+0x46): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYamp
a_integral_closure'
DLLTest.o:fake:(.text+0x4d): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYamp
aziVectorSpace_zdfVectorSpaceDoubleDouble_closure'
DLLTest.o:fake:(.text+0x194): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYam
pa_embed_closure'
DLLTest.o:fake:(.text+0x381): undefined reference to
`__stginit_Yampazm0zi9zi2zi
3_FRPziYampa_'
DLLTest.o:fake:(.data+0x0): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYampa
_integral_closure'
DLLTest.o:fake:(.data+0x4): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYampa
ziVectorSpace_zdfVectorSpaceDoubleDouble_closure'
DLLTest.o:fake:(.data+0x38): undefined reference to
`Yampazm0zi9zi2zi3_FRPziYamp
a_embed_closure'
collect2: ld returned 1 exit status
How can I define the references of Yampa in the DLL?
I also tried to reinstall Yampa shared with:
$ cabal install --reinstall --enable-shared yampa
Could not find module `Data.IORef':
Perhaps you haven't installed the dyn libraries for package
`base-3.0.3.
2'?
Use -v to see a list of the files searched for.
$ cabal install --reinstall --enable-shared base # :)
Resolving dependencies...
cabal: internal error: impossible
(StartEnd is taken from:
http://www.haskell.org/ghc//docs/latest/html/users_guide/win32-dlls.html )
DLLTest.hs:
{-# LANGUAGE ForeignFunctionInterface, Arrows #-}
module DLLTest
embeddedSF :: Double - Double - Double - IO Double
embeddedSF v0 v1 v2 = return . last $ embed integral (v0, [(1.0, Just v1),
(1.0, Just v2)])
foreign export ccall embeddedSF :: Double - Double - Double - IO Double
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[Haskell-cafe] ANNOUNCE: Haddock 2.9.0
-- Haddock 2.9.0 A new version of Haddock, the Haskell documentation tool, is out! This version is compatible with .haddock files produced by the version of Haddock that comes with GHC 7.0.1. -- Changes in version 2.9.0 Changes in version 2.9.0 * Drop support for ghc 7 * New flag --qual for qualification of names * Print doc coverage information to stdout when generating docs * Include an 'All' option in the A-Z subdivided index * Make TOC group header identifiers validate * Minor changes to the API -- Links Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/package/haddock-2.9.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: hadd...@projects.haskell.org Code repository: http://code.haskell.org/haddock -- Contributors The following people contributed patches to this release: Tobias Brandt Mark Lentczner Ian Lynagh Simon Marlow Simon Michael Ryan Newton David Waern -- Get Involved We would be very happy to get more contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trying out GHC 7
On 06/12/2010 06:04 PM, Don Stewart wrote: Andrew, if you have a bug report, please use the bug tracker: From what I've seen, the GHC devs already have vastly more bug reports than they know what to do with. I tend to hessitate filing tickets until I'm sure I'm looking at an actual bug, rather than just a misunderstanding on my part. Keep your reports concise and to-the-point, for the best hope of getting useful stuff done. There's actually a couple of seperate issues there, which should presumably end up being seperate tickets. The fact that, out of the box, dynamic linking fails is a bug. The fact that I can't work out the reason or rhyme behind where the DLLs get put is more sort of a hey guys, I'm not really sure what you were going for here type of thing than an actual /bug/. I don't know if it's worth filing a ticket for prior versions of GHC failing to build dynamically in a less than graceful way. On one hand, the problem doesn't exist in GHC7. On the other hand, maybe we want to record this information anyway? Regarding the documentation, what's the best way to fix this? Do I just file a bug against every sentence that's wrong, or would it be quicker for me to actually download a copy of the source and fix the problems myself? (I can probably fix some of it myself, but in other cases I actually don't know what the correct information is, so it would have to be written by somebody who knows what they're talking about.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] need help with syntax...
I am having hard time understanding the following code. The code is from Applicative Parser library: http://hackage.haskell.org/packages/archive/uu-parsinglib/2.5.5.2/doc/html/src/Text-ParserCombinators-UU-BasicInstances.html instance (Show a, loc `IsLocationUpdatedBy` a) = Provides (Str a loc) (a - Bool, String, a) a where splitState (p, msg, a) k (Str tts msgs pos del_ok) = let ins exp = (5, k a (Str tts (msgs ++ [Inserted (show a) pos exp]) pos False)) del exp = (5, splitState (p,msg, a) k (Str (tail tts) (msgs ++ [Deleted (show(head tts)) pos exp]) (advance pos (head tts)) True )) in case tts of (t:ts) - if p t then show_symbol (Accepting symbol: ++ show t ++ at position: ++ show pos ++\n) (Step 1 (k t (Str ts msgs (advance pos t) True))) else Fail [msg] (*ins:* if *del_ok* then *[del*] else []) [] - Fail [msg] [*ins*] Specifically I am having hard time understanding how the ins exp and del exp in the let is related to ins: del_ok, [del], [ins]. I don't understand how given the let expression the following expressions are expanded Fail [msg] (*ins:* if *del_ok* then *[del*] else []) and Fail [msg] [*ins*] Appreciate any help. Thanks Daryoush ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Offer to mirror Hackage
Wow, this thread got long. Good! I'm hopeful that we can take some action now. :) My views on the issues that have been raised - The Haskell steering committee is a good thing and I fully support them. I also support the current maintainer of the site; I don't want to take over or anything, only to assist. In fact, I'll go further, please don't anybody attempt to foist any high-level responsibility on me. I'm a bad receptacle for it. But I do have these technological resources at my disposal and there's no reason the community shouldn't benefit from them. Re incorporation, the person who said that it has to happen was dead-on. So the rest of the discussion on that point is moot. But it's quite independent of when and how we set up mirroring. I agree that signed packages are a good idea. We should move with all haste to implement them. But I'm not sure we want to hold up everything else while we wait for that. That's also my take on a peer-peer repository, as I said already. Can somebody who understands the technologies typically used for this suggest one, and possibly also talk to dcoutts directly to make him aware of the discussion and get his thoughts on how to implement it? I've found he often makes points that save me a lot of work. :) I can certainly conceive of life events that could take my attention, despite all good intentions, in much the fashion that the current maintainer's often is. (That's awkward to say - what's his name, again? I know I should know it... It's not dcoutts, is it?) So I want to build something that works well with minimal manual intervention. I was of the impression that most of the members of the steering committee were on this list, which is one reason I posted here. Is there some other way I should contact them? I will talk to dcoutts, and see what the current status of the distributed-operation code is and figure out how much time I can devote to helping with that. -- Dan Knapp An infallible method of conciliating a tiger is to allow oneself to be devoured. (Konrad Adenauer) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hledger 0.13
I've released hledger 0.13, with readline editing and tab completion from Judah Jacobson, more ledger compatibility, a more robust and installable web interface, bugfixes, and a much-deliberated package split. Docs and mac and 64-bit linux binaries are at http://hledger.org , and of course you can cabal update and cabal install hledger, cabal install hledger-web and so on. I didn't manage to build new windows or linux 32-bit binaries today, but they'll appear when I do. Let it be noted that maintaining a non-trivial cross-platform haskell app is currently quite hard. Release notes: * move web, vty, chart commands into separate hledger-web, hledger- vty, hledger-chart packages. This both simplifies (no more build flags) and complicates (more room for dependency hassles), but I hope overall it will be easier and more scalable. * all packages but chart are now marked beta, ie not finished but suitable for everyday use * parsing: ledger compatibility: support D default commodity directive * parsing: ledger compatibility: ignore metadata tags on transactions and postings * parsing: ledger compatibility: ignore cleared flags at the start of postings * parsing: ledger compatibility: ignore C commodity conversion directives * parsing: price precisions no longer affect commodities' display precisions * add: readline-style editing * add: tab-completion for account names * add: add the default commodity, if any, to commodity-less amounts (#26) * add: misc. commodity/precision/defaults-related bugfixes * chart: give a meaningful error message for empty journals * chart: update for current Chart lib (0.14) * web: support files now live in ./.hledger/web/ and will be auto- created at startup * web: page layout is more robust with wide content * web: allow editing of included files * web: handle multiple filter patterns correctly * web: allow single- or double-quoted filter patterns containing spaces * web: update for current yesod lib (0.6.*) * transaction balancing is now based on display precision (#23) * briefer, more informative usage error messages Stats: 91 days and 117 commits since last release, now at 5997 lines of code with 151 tests. hledger is at a point where real-world user and developer input is needed to focus it; participants welcome. Best, -Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bifold: a simultaneous foldr and foldl
On 12/01/10 21:35, Larry Evans wrote:
[snip]
Hi Noah,
The attached is my attempt at reproducing your code
[snip]
However, ghci compilation of bifold produces an error message:
BifoldIfRecur.hs:20:19: parse error on input `='
[snip]
Apparently I had some extra leading spaces in the last line.
Taking those out (as shown in attached) results in a good
reading of the file by ghci.
-Larry
{-
Purpose:
Test bifold code shown in post:
http://article.gmane.org/gmane.comp.lang.haskell.cafe/83874
-}
module Bifold where
{--}
bifold :: (l - a - r - (r,l)) - (l,r) - [a] - (r,l)
bifold _ (l,r) [] = (r,l)
bifold f (l,r) (a:as) = (ra,las)
where (ras,las) = bifold f (la,r) as
(ra,la) = f l a ras
{--}
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[Haskell-cafe] Help defining a Typeable polymorphic-state monad transformer
Hi all,
I gave myself until this evening to figure this out on my own, and
time is up! Hopefully this makes for a good discussion, though the
idea could be dumb.
What I'm trying to do is define a state monad in which the passed
state can change type during the computation. The only constraint is
that the state types must always be of the Typeable class (see:
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Typeable.html
).
The idea is that the new monad would be something like 'StateT s Maybe
a', but where the 's' type is not fixed (indeed is hidden in an
existential type) and where any programmer errors in the chaining of
the polymorphic state will be caught in the Maybe type (or really the
'fail' implementation of any monad).
Here is how I imagine a computation might look:
computation :: TypeableState Maybe String
computation = do
(c:cs) - getTS
putTS (length cs)
return (c ++ was the first letter of the string passed as
initial state.)
So TypeableState is very similar to StateT, except that the state type
is not present as a type argument. In the example above 'Maybe' is the
monad that catches Typeable errors, and String is the return type of
the computation.
getTS and putTS would be get and put functions that constrain their
arguments to the Typeable class.
Here is what I have so far (at least this is my most recent
uncommented attempt):
{-# LANGUAGE ExistentialQuantification #-}
module Main
where
import Control.Monad.State
import Data.Typeable
-- we might have restricted our 'm' to MonadPlus and used the explicit
-- 'mzero', but decided instead to use Monad, with 'fail'. This is
-- more appropriate since we won't be using 'mplus'. See 'liftMaybe'.
data TypeableState m a = forall s0 sN. (Typeable s0, Typeable sN)=
TypeableState (s0 - m (a,sN))
-- this is probably one of the more non-sensical attempts I've made at
-- this... but I'm not sure:
runTypeableState :: (Monad m, Typeable s0, Typeable sN)= TypeableState m a
- s0 - m (a,sN)
runTypeableState (TypeableState st) s0 = (liftMaybe $ cast s0) = st
-- copied from Control.Monad.StateT
instance (Monad m) = Monad (TypeableState m) where
return a = TypeableState $ \s - return (a, s)
m = k = TypeableState $ \s - do
~(a, s') - runTypeableState m s
runTypeableState (k a) s'
fail str = TypeableState $ \_ - fail str
-- I imagine using this with 'cast' to thread the type in our monad
-- transformer
liftMaybe :: (Monad m)= Maybe a - m a
liftMaybe = maybe (fail Monadic failure) return
So is this even feasible? Or do I not grok what we can and can't do
with the Typeable class?
Any thoughts on this are appreciated.
Sincerely,
Brandon Simmons
http://coder.bsimmons.name
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[Haskell-cafe] Question: mime-mail and base64 encoding
Hi all, I've gotten a request for the mime-mail package that I'd like some input on. Right now, there's the ability to fully specify whether or not to base64-encode each part in a message, but the included simpleMail function defaults to non-encoded parts for both its HTML and plain text alternatives. This has apparently caused some issues where long HTML strings have been word-wrapped at bad locations, causing breakage in the meaning of the markup. The request is to make both the HTML and plain text parts use base64 encoding by default. This *seems* to me to make a lot of sense, since it will ensure that your message arrives exactly as you intended it, and will ensure that any non-ASCII code points don't get killed somewhere along the way. On the other hand, I'm not sure what client support is like for base-64 encoding. Don't we need to leave *some* form of non-encoded data for less sophisticated email clients? Thanks, Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Help defining a Typeable polymorphic-state monad transformer
This has nothing to do with a monad. This is just about data. You
want a type that can contain any Typeable type, and a safe way to cast
out of that type into the type that came in. Such a thing exists,
it's called Data.Dynamic.
Then your monad is just StateT Dynamic, where your magical maybeifying get is:
getD :: (Monad m, Typeable a) = StateT Dynamic m a
getD = maybe (fail Type error) return . cast = get
Luke
On Mon, Dec 6, 2010 at 9:09 PM, Brandon Simmons
brandon.m.simm...@gmail.com wrote:
Hi all,
I gave myself until this evening to figure this out on my own, and
time is up! Hopefully this makes for a good discussion, though the
idea could be dumb.
What I'm trying to do is define a state monad in which the passed
state can change type during the computation. The only constraint is
that the state types must always be of the Typeable class (see:
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Typeable.html
).
The idea is that the new monad would be something like 'StateT s Maybe
a', but where the 's' type is not fixed (indeed is hidden in an
existential type) and where any programmer errors in the chaining of
the polymorphic state will be caught in the Maybe type (or really the
'fail' implementation of any monad).
Here is how I imagine a computation might look:
computation :: TypeableState Maybe String
computation = do
(c:cs) - getTS
putTS (length cs)
return (c ++ was the first letter of the string passed as
initial state.)
So TypeableState is very similar to StateT, except that the state type
is not present as a type argument. In the example above 'Maybe' is the
monad that catches Typeable errors, and String is the return type of
the computation.
getTS and putTS would be get and put functions that constrain their
arguments to the Typeable class.
Here is what I have so far (at least this is my most recent
uncommented attempt):
{-# LANGUAGE ExistentialQuantification #-}
module Main
where
import Control.Monad.State
import Data.Typeable
-- we might have restricted our 'm' to MonadPlus and used the explicit
-- 'mzero', but decided instead to use Monad, with 'fail'. This is
-- more appropriate since we won't be using 'mplus'. See 'liftMaybe'.
data TypeableState m a = forall s0 sN. (Typeable s0, Typeable sN)=
TypeableState (s0 - m (a,sN))
-- this is probably one of the more non-sensical attempts I've made at
-- this... but I'm not sure:
runTypeableState :: (Monad m, Typeable s0, Typeable sN)= TypeableState m a
- s0 - m (a,sN)
runTypeableState (TypeableState st) s0 = (liftMaybe $ cast s0) = st
-- copied from Control.Monad.StateT
instance (Monad m) = Monad (TypeableState m) where
return a = TypeableState $ \s - return (a, s)
m = k = TypeableState $ \s - do
~(a, s') - runTypeableState m s
runTypeableState (k a) s'
fail str = TypeableState $ \_ - fail str
-- I imagine using this with 'cast' to thread the type in our monad
-- transformer
liftMaybe :: (Monad m)= Maybe a - m a
liftMaybe = maybe (fail Monadic failure) return
So is this even feasible? Or do I not grok what we can and can't do
with the Typeable class?
Any thoughts on this are appreciated.
Sincerely,
Brandon Simmons
http://coder.bsimmons.name
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Re: [Haskell-cafe] Question: mime-mail and base64 encoding
On 7 December 2010 13:42, Michael Snoyman mich...@snoyman.com wrote: Hi all, I've gotten a request for the mime-mail package that I'd like some input on. Right now, there's the ability to fully specify whether or not to base64-encode each part in a message, but the included simpleMail function defaults to non-encoded parts for both its HTML and plain text alternatives. This has apparently caused some issues where long HTML strings have been word-wrapped at bad locations, causing breakage in the meaning of the markup. The request is to make both the HTML and plain text parts use base64 encoding by default. This *seems* to me to make a lot of sense, since it will ensure that your message arrives exactly as you intended it, and will ensure that any non-ASCII code points don't get killed somewhere along the way. On the other hand, I'm not sure what client support is like for base-64 encoding. Don't we need to leave *some* form of non-encoded data for less sophisticated email clients? What does the wrapping here? My understanding of the symptom is that newlines are sometimes inserted between the and / of a closing HTML tag, breaking the tag and leaving stray markup in the file. Would it be possible to either not do the wrapping, or to avoid putting newlines inside a tag? Conrad. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question: mime-mail and base64 encoding
On Mon, Dec 6, 2010 at 8:42 PM, Michael Snoyman mich...@snoyman.com wrote: The request is to make both the HTML and plain text parts use base64 encoding by default. This *seems* to me to make a lot of sense, since it will ensure that your message arrives exactly as you intended it, and will ensure that any non-ASCII code points don't get killed somewhere along the way. On the other hand, I'm not sure what client support is like for base-64 encoding. Don't we need to leave *some* form of non-encoded data for less sophisticated email clients? The way I've seen it done before was to: - calculate the size of the body in quoted-printable and base64 encoding - select the smaller encoded form of the two quoted-printable is fairly human readable. This strategy also works for encoding headers, particularly Subject: lines (substituting q-encoding for qp). -n ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with syntax...
On 12/6/10 7:26 PM, Daryoush Mehrtash wrote: I am having hard time understanding the following code. The code is from Applicative Parser library: http://hackage.haskell.org/packages/archive/uu-parsinglib/2.5.5.2/doc/html/src/Text-ParserCombinators-UU-BasicInstances.html instance (Show a, loc `IsLocationUpdatedBy` a) = Provides (Str a loc) (a - Bool, String, a) a where splitState (p, msg, a) k (Str tts msgs pos del_ok) = let ins exp = ...1 del exp = ...2 in case tts of (t:ts) - if p t then ...3 else Fail [msg] (*ins:* if *del_ok* then *[del*] else []) [] - Fail [msg] [*ins*] Specifically I am having hard time understanding how the ins exp and del exp in the let is related to ins: del_ok, [del], [ins]. I don't understand how given the let expression the following expressions are expanded The let expressions are binding functions so ins names (\exp - ...1) and del names (\exp - ...2). Thus, when del_ok is true we get, Fail [msg] (ins : if del_ok then [del] else []) == Fail [msg] (ins : if del_ok then del : [] else []) == Fail [msg] (ins : del : []) == Fail [msg] ((\exp - ...1) : (\exp - ...2) : []) and when del_ok is false we get Fail [msg] ((\exp - ...1) : []) -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
