- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Lambda and closures in PHP -- could someone please comment?
by PR Stanley 18 Jun '08

18 Jun '08

> > Now, if you, Jules, Alex or some other wannabe Hitler have a problem with > > my freedom of expression then your best solution is to saddle up > and get the > > hell out yourselves. This is the wrong place for setting up your tinpot > > dictatorship, Doctor! > >Just more evidence... > >http://en.wikipedia.org/wiki/Godwin's_law > >Paul: I think you're missing a big painfully obvious point here, Mr >smarty pants. No, actually, I think I'll leave it at that. I just >can't be bothered. However, I'll say this - anyone sticking his >bloody big hooter into my business in the future will get a similar reaction! Paul >Luke

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Compiling large code with old machine
by Samuel Silva 18 Jun '08

18 Jun '08

Hello I'm using GHC to compile around 700K of Haskell Code generated by HaXml. How I compile this code. My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2. How much time it spend to compile this file? I spent more than 1 hour and it doesn't finished. What flags make compiling fast? I try with -H500m but dont't expect. It is possible GHC running endless cycle at compilation stage? Thanks. -- Don't hug that, Hugs ME! Samuel Silva

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ANNOUNCE: cabal-install 0.5
by Duncan Coutts 18 Jun '08

18 Jun '08

cabal-install 0.5 ================= cabal-install version 0.5 is out: http://haskell.org/cabal/download.html or get it from hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install If you are already using a cabal-install pre-release then you can just: $ cabal update $ cabal install cabal-install New features in cabal-install ============================= Command line improvements ------------------------- The most immediately noticeable thing is that the command line interface now has all the commands that runhaskell Setup.hs has. Of course it still has the features to download and install packages from hackage. It also gained an upload command. So it now provides a command line interface to the whole Cabal/Hackage system. There’s no need to use runhaskell Setup.hs ever again. There is also bash command line completion support included which I find is a great time saver. Installing and upgrading ------------------------ The next big thing is that it includes a new package dependency resolution system that finds correct and sensible solutions more of the time and has better default behaviour. The new behaviour should be similar to other package managers that people are used to. For example, suppose you’ve got xmonad-0.5 installed and version 0.7 is the latest on hackage, then $ cabal install xmonad will install xmonad-0.7. The older version, xmonad-0.5, will remain installed. The behaviour of install is to upgrade as little as possible to satisfy your request, but sometimes you want to upgrade all the dependencies too. Supposing now that we have xmonad-0.7 installed, but we’re still using X11-1.4.1 and the latest version on hackage is X11-1.4.2, then $ cabal upgrade xmonad will install X11-1.4.2 and *re-install* xmonad-0.7, this time built against the newer X11-1.4.2. So in general, the install command will install the latest version of things but will try and use any existing installed versions of dependencies while the upgrade command will also try to use the latest versions of all dependencies. As a special case, cabal upgrade on its own will try to upgrade all the packages that you have installed. For both command there is a --dry-run flag so you can see what would be installed without actually doing it. Hugs ---- Yes, it even works with hugs. That is, cabal-install built by ghc can manage the installation of packages for hugs. In principle cabal-install should be able to be run by hugs but currently the zlib binding is using a function that hugs does not support. Note that for hugs, Cabal does not know what packages are already installed because there is no equivalent of the package database that ghc has. So that means cabal-install cannot do very sensible installation planning. It should work ok so long as all the dependencies are already installed. Windows ------- Yes, it even works on Windows. The one caveat is that cabal-install cannot currently upgrade itself because Windows makes it hard for a process to overwrite its own executable file. It needs more complex trickery with the Win32 API. In the meantime the workaround is to rename the cabal.exe file first eg to cabal-foo.exe, then run cabal-foo install cabal-install. Build reporting --------------- One feature that made it into this release is build reporting. cabal-install keeps logs of all packages that you install (at least packages from hackage, not local ones). It records a bit of information about each package, in particular whether the outcome was successful or not. You can see these build reports in ~/.cabal/packages/$server/build-reports.log. For example, there is one from my machine for xmonad: package: xmonad-0.7 os: linux arch: x86_64 compiler: ghc-6.8.2 client: cabal-install-0.5.1 flags: -testing small_base dependencies: X11-1.4.2 base-3.0.1.0 containers-0.1.0.1 directory-1.0.0.0 mtl-1.1.0.0 process-1.0.0.0 unix-2.3.0.0 install-outcome: InstallOk docs-outcome: NotTried tests-outcome: NotTried The plan in the longer term is to let people upload these build reports to hackage so we can get a wider range of testing data about the packages on hackage. Duncan

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Re: [Haskell-cafe] Compiling large code with old machine
by Samuel Silva 18 Jun '08

18 Jun '08

Hello On Tue, Jun 17, 2008 at 10:24 PM, Niels Aan de Brugh <nielsadb(a)gmail.com> wrote: > On Tue, 2008-06-17 at 13:19 +0100, Samuel Silva wrote: >> >> I'm using GHC to compile around 700K of Haskell Code generated by HaXml. >> How I compile this code. >> My machine is Windows-XP(512MB RAM, 1.5GHz) running GHC-6.8.2. >> >> How much time it spend to compile this file? >> I spent more than 1 hour and it doesn't finished. > > Just out of curiosity, is all that 700K just one big file or did you > split it up into multiple files? It's just two big files with 700K each generated by DtdToHaskell from two big DTD files around 70K each. > Are you using any "expensive" features? I'm not a GHC exert, but I'd > expect things like type manipulations (e.g. phantom types) to be > expensive (please correct me if this assumption is wrong). This large module only contains datatype declarations and instance classes for HTypeable, XmlContent, XmlAttributes and XmlAttrType. > Bottom line: if compiling is so slow consider changing the code > generator so the result is easier to process by GHC instead of fiddling > with command line switches. Since you've chosen to generate the code it > will probably change often and you'll run into this problem more than > once. > > Regards, > Niels > > Each Haskell file have almost 15000 lines. It is huge. It's compiling very fast(some minutes) using -H300m without cabal and -H200m with cabal. GHC it is amazing. This was a valuable help. -- Don't hug that, Hugs ME! Samuel Silva

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ANN: Mueval 0.3
by Gwern Branwen 18 Jun '08

18 Jun '08

Hiya everyone. So I've uploaded Mueval 0.3 (release early, release often) <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval-0.3>. What's new? Well, I changed the printing output to be cleaner, and I made printing the inferred type optional (through a --print-type flag). In addition, I've made sure it can run (for me, at least) under -N4, and the watchdog threads should be sturdier. (Plus extra tests.) However, I've been hearing that a number of people (3 at last count) have been having a lot of trouble with the ResourceLimits stuff. So, I have a few requests of people who install mueval: * First, does it work out of the box, with no tweaking of the resource limits? * Second, if it doesn't work out of the box, which resource limits did you need to disable or increase? * Thirdly, if you changed the resource limits, could you run ./build.sh and tell me whether all the tests pass? Finally, I've been pondering removing the rlimits entirely since they are both very unportable, empirically derived, and apparently don't even work consistently on Linux. Any thoughts? -- gwern PABX MEMEX 868 1* TSCI @ shelter Yukon el ASLET

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Polymorphic QuickCheck arguments
by Hugo Pacheco 18 Jun '08

18 Jun '08

Hi all, There is something about polymorphic tests in QuickCheck that I do not understand. If you write the simplest dummy test function tst :: a -> Bool tst _ = True and evaluate it we get > verboseCheck tst 0: () 1: () ... How come did the polymorphic value a get instanciated to ()? Is this done via the Testable type class? Could someone please explain this to me? I'm not saying it does not make sense, but I would like to understand how it works. Being possible to change this behavior, this is, assign another "default type" whenever polymorphic types occur, would be awesome. Cheers, hugo -- www.di.uminho.pt/~hpacheco

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send in material for the HWN!
by Brent Yorgey 18 Jun '08

18 Jun '08

Hi all, Do you know of a blog post about Haskell that wasn't syndicated on Planet Haskell? Do you have a Haskell-related story to tell or announcement to make? Do you have a link to some great pictures from the latest meetup/hackathon/talk/conference? A funny story about Don Stewart? If so, consider submitting it to the Haskell Weekly News. The HWN isn't really about Haskell so much as it is about the Haskell *community* -- and that means you! In addition to the above sorts of submissions, I am also thinking of adding a "Community News" section with announcements of (not-necessarily-Haskell-related) major events in the lives of community members -- but obviously this depends on submissions, so if you get a new job/move/start a new company/graduate/increment your age/have a comet named after you/bring forth a new life (aka future Haskeller) into the world, please share, and let the community celebrate with you! Submissions can be sent to byorgey at seas dot upenn dot edu. Be sure to include "HWN" in the subject line. For now I'm planning to put an issue out every Wednesday afternoon, so the submission deadline is Wednesday at 11am GMT (6am Eastern US). -Brent

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How to do this in FP way?
by Magicloud Magiclouds 18 Jun '08

18 Jun '08

Hello, I am getting familiar with FP now, and I have a "program design" kind of question. Say I have something like this in C: static int old; int diff (int now) { /* this would be called once a second */ int ret = now - old; old = now; return ret; } Because there is no "variable" in Haskell. So how to do this in a FP way? Thanks.

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Suggestion for implementation of vector library
by Olex P 18 Jun '08

18 Jun '08

Hi guys, Sorry for a silly questions but I didn't find a proper answer in Google. I've started to learn Haskell and would like to implement a library for work with vectors. I found different implementations of this stuff but all of them made just for fun in a short as possible terms using lists or tuples. I suppose there should be a better way to go. First idea came to my mind was using of classes. Something like this: [code] -- Template Vector class class Vector v where (<+>) :: v -> v -> v (<->) :: v -> v -> v (<*>) :: v -> v -> v (*>) :: v -> Float -> v -- other methods here -- Vector3 instance -- Declare new Vector3 type data Vector3 = Vector3 (Float, Float, Float) instance Vector Vector3 where (<+>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 + x2, y1 + y2, z1 + z2) (<->) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 - x2, y1 - y2, z1 - z2) (<*>) (Vector3 (x1, y1, z1)) (Vector3 (x2, y2, z2)) = Vector3 (x1 * x2, y1 * y2, z1 * z2) (*>) (Vector3 (x, y, z)) f = Vector3 (x * f, y * f, z * f) length (Vector3 (x, y, z)) = sqrt (x * x + y * y + z * z) -- the rest of methods [/code] What I don't like here is using of data type constructors when even simple expression like v1 + v2 becomes too long (<+>) (Vector3 (1,2,3)) (Vector3 (4,5,6)) Do I really need a data type constructor (in this particular case)? Or better to declare a vector3 type as: type Vector3 = (Float, Float, Float)? Next question is how to make one instance which derives from several classes? For example from Eq, Num and Vector (if I want to overload +, -, <, >, == etc.) Is it good idea to use classes and ad hoc polymorphism or better to use parametric polymorphism? How you would implement such library? (not just for educational purposes but for development of _very_good_extensible_ software) Thank you, Alex.

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1/0
by Evan Laforge 17 Jun '08

17 Jun '08

So, I know this has been discussed before, but: > 1/0 Infinity > 0/0 NaN ... so I see from the archives that Infinity is mandated by ieee754 even though my intuition says both should be NaN. Every other language throws an exception, even C will crash the program, so I'm guessing it's telling the processor / OS to turn these into signals, while GHC is turning that off. Or something. But then what about this note in Control.Exception: (NOTE: GHC currently does not throw ArithExceptions except for DivideByZero) Doesn't this imply GHC should be throwing DivideByZero? Why is it in the stdlib if it's turned off? And why would it be turned off? I suppose I could accept the above since Infinity *is* an exceptional value meant to represent things like 1/0, and it can be nice to see NaNs in your output instead of crashing everything (this is, I assume, why ieee754 has these modes in the first place), but how about this: > round (0/0) :: Integer (huge negative number) Ok, so integral types don't have that exceptional value. Shouldn't trying to convert NaN or Infinity to an Integral throw something? Is it a performance thing? I'd think if you're converting to Integer you don't really need hardware level performance anyway, so a couple of checks wouldn't kill anyone.

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Re: [Haskell-cafe] Re: How to do this in FP way?
by Thomas Davie 17 Jun '08

17 Jun '08

On 16 Jun 2008, at 19:24, Achim Schneider wrote: > Thomas Davie <tom.davie(a)gmail.com> wrote: > >> >> On 16 Jun 2008, at 18:28, Achim Schneider wrote: >> >>> Thomas Davie <tom.davie(a)gmail.com> wrote: >>> >>>>> >>>>> One half of all Haskell coders will tell you that mutable state >>>>> isn't a >>>>> good starting point to learn Haskell, the other half will tell you >>>>> the same because they want to be cool kids, too. >>>> >>>> And the one left over will point out that he asked how to do this >>>> the FP way, not the imperative way? >>>> >>> There's no difference, as you can't do time-accounting non-strict >>> and still expect it to give meaningful results: I'm merely trying >>> to be helpful. None of the other solutions allow for the IO Monad. >> >> Firstly, I'd phrase that differently -- the IO Monad doesn't allow >> for the other solutions -- the other solutions are the truly >> functional ones. Secondly, I'm curious as to why you think that the >> two are incompatible, are you saying that for any meaningful kind of >> computation we need to resort to IORefs? I'd strongly contest that >> idea. >> > We have to resort to IO actions to get the time, and to IORefs because > we need to chain up different calls to getCurrentTime using the IO > Monad. The rest of the program can work with whatever you like best. And in what way is this incompatible with either FRP as pierre suggested, or with generating an infinite list of times at which we call the function, and scanning it to find the differences? Bob

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ANN: Haddock Trac
by David Waern 17 Jun '08

17 Jun '08

Hi everyone, there's now a Haddock bug-tracker and wiki at http://trac.haskell.org/haddock. Please use it to submit bug reports and feature requests! David

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C-program calling Haskell program?
by Taepke, Bob 17 Jun '08

17 Jun '08

Hello, I am very new to Haskell, and I work in Windows XP. Can anyone please point me to a working C / Haskell program pair that does the following: 1) The C routine passes one or more scalars, arrays, or matrices to the Haskell routine. 2) The Haskell routine reads a comma-delimited, ASCII file from the path, C:\my_directory\input_data\. 3) The Haskell routine writes a comma-delimited, ASCII file to the path, C:\my_directory\output_data\. 4) The Haskell routine returns to the C routine one or more scalars, arrays, or matrices. 5) For what it's worth, I'm only using the C-routine as an interface between MATLAB and Haskell, because MATLAB can call C-routines. Has anyone written C / Haskell code that does the above tasks? If so, would you please be willing to pass it along to me? Thank you! Bob [CONFIDENTIALITY AND PRIVACY NOTICE] Information transmitted by this email is proprietary to Medtronic and is intended for use only by the individual or entity to which it is addressed, and may contain information that is private, privileged, confidential or exempt from disclosure under applicable law. If you are not the intended recipient or it appears that this mail has been forwarded to you without proper authority, you are notified that any use or dissemination of this information in any manner is strictly prohibited. In such cases, please delete this mail from your records. To view this notice in other languages you can either select the following link or manually copy and paste the link into the address bar of a web browser: http://emaildisclaimer.medtronic.com

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FunPtr error?
by Galchin, Vasili 17 Jun '08

17 Jun '08

Hello, I am getting what is to me a mysterious error in a test case that I am writing: vigalchin@ubuntu:~/FTP/Haskell/unix-2.2.0.0/tests/timer$ runhaskell Setup.lhs build Preprocessing executables for Test-1.0... Building Test-1.0... [1 of 1] Compiling Main ( ./timer.hs, dist/build/timer/timer-tmp/Main.o ) ./timer.hs:11:45: Not in scope: data constructor `FunPtr' It seems like the compiler is complaining about the lack of FunPtr in it's symbol table but System.Posix is imported: module Main where import System.Posix import Foreign import Foreign.C import Foreign.Ptr main = do let event = Sigevent{sigevFunction=(FunPtr (notifyFunc))} <<<<<< error here timerId <- timerCreate Clock_Realtime Nothing timerDelete timerId return () notifyFunc :: Sigval -> IO () notifyFunc sigval = do putStrLn "timer POP!!!!!!!" return () I am probably looking right at the answer and not seeing it. ?? Thanks, Vasili

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monomorphism restriction
by Rex Page 17 Jun '08

17 Jun '08

Definition of f: f = foldr (+) 0 Types: 0 :: (Num t) => t foldr (+) 0 :: Num a => [a] -> a f :: [Integer] -> Integer Please remind me, again, of the advantages of f being something different from the formula defining it. - Rex Page

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Lazy IO.
by Sebastiaan Visser 17 Jun '08

17 Jun '08

Hi, I've got a question about lazy IO in Haskell. The most well known function to do lazy IO is the `hGetContents', which lazily reads all the contents from a handle and returns this as a regular [Char]. The thing with hGetContents is that is puts the Handle in a semi-closed state, no one can use the handle anymore. This behaviour is understandable from the point of safety; it is not yet determined when the result of hGetContents will actually be computed, using the handle in the meantime is undesirable. The point is, I think I really have a situation in which I want to use the handle again `after' a call to hGetContents. I think I can best explain this using a code example. readHttpMessage :: IO (Headers, Data.ByteString.Lazy.ByteString) readHttpMessage = do myStream <- <accept http connection from client> request <- hGetContents myStream header <- parseHttpHeader request bs <- Data.ByteString.Lazy.hGetContents myStream return (header, body) The Data.ByteString.Lazy.hGetContents in the example above obviously fails because the handle is semi-closed. So, what I am trying to do here is apply a parser (on that consumes Char's) to the input stream until it has succeeded. After this I want to collect the remainings of the stream in a lazy ByteString, or maybe even something else. I tried to open the handler again using some internal handle hackery, but this failed (luckily). In the module GHC.IO there is a function `lazyRead' that more or less seems to do what I want. But I'll guess there is a good reason for not exporting it. Does anyone know a pattern in which I can do this easily? Thanks, -- Sebastiaan

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Design your modules for qualified import
by Johan Tibell 16 Jun '08

16 Jun '08

Hi! The last two weeks I've seen two new packages that add suffixes to identifiers instead of relying on them being imported qualified to distinguish them from identifiers in other modules. This is not a new thing in Haskell community and there are examples of this practice in libraries shipped with GHC. It is also common in papers (for good reasons as we will see later). Atomic channels and variables under Control.Concurrent.* are examples of using a prefix as a namespacing tool. Let me reiterate the arguments [1,2] against this practice and also speculate why this practice is more common in Haskell than in e.g. Python, Java or Ruby. * Cons of including a namespace prefix/suffix in identifiers 1. From experience these prefixes/suffixes tend to be short and non-descriptive, typically just one letter e.g. foldU or elemB. Very frequently used functions that every Haskell programmer is likely to use often can have shorter name as the cost of memorizing them is amortized over all their uses. Examples of short names that most Haskell programmers know by heart is map, fold*, etc. Given that your library won't see the same use as these functions your functions need more descriptive names (or in this case use a qualified import that makes them more descriptive e.g. Array.fold). 2. If your modules are imported qualified the suffix is redundant and thus wastes space. Consider for example foldU imported qualified from the module Data.Array as Array.foldU. Array.fold would have been better in this case. * Pros of using qualified imports 1. Your code will be more robust against additions to modules you depend on. Consider this snippet: import Some.Module -- An utility function that the author of the above module forgot to include. foo = ... Now the author of Some.Module releases a new version of his or her package which include `foo' and your code no longer compiles. If you have no imports on the form import Some.Module your package can specify more relaxed version dependencies on other packages [3]. 2. It's easier to see from where an identifier is imported. Just check the functions module prefix (e.g. Array in Array.foo). If you renamed the import using import Foo as F you might have to check the import list. * Explicit, unqualified imports An alternative to qualified imports that shares some of benefits is to import names unqualified but explicitly enumerate the function names e.g. import Some.Module (foo, bar) It is still not immediately obvious what module a name refers too when using this style (point 2 under pros above) but it is at least easier to find than when implicitly importing all names from a module. This is my current preference for infix operators as they look quite ugly qualified with a module name. It might also make sense if a few functions (e.g. parser combinators) are used a lot in the same module (e.g. an HTTP parser). * Why is this practice common in Haskell Here are some guesses: 1. It's common in papers. However, papers and libraries are quite different. The former usually build up a small vocabulary and having short names is a big win. Papers rarely make use of the module system at all. The latter are included as pieces of large programs and their names need to be adjusted accordingly. 2. It's the default. You have to add "qualified" to all your imports to make them qualified. In most language imports are qualified by default. I think the latter would have been a better choice but we have to live with the current design so bite the bullet and add those qualified keywords to your imports. 3. Lack of common interfaces. An example would be two different set implementations that essentially have the same interface but since there is no explicitly shared interface, defined using a type class, you sometimes end up with different names. The lack of type families might explain why e.g. collection classes don't share interfaces. 4. Haskell is a very expressive language. You can often write a whole function definition on one line! Adding those module qualifications makes your code slightly longer and it might just break your beautiful one liner into two lines. * Summary Whenever you write a library design it so it works well with qualified imports. That means leaving namespacing issues to the module system. Try to think of how code using your functions will look like if it uses them qualified. * References 1. http://www.haskell.org/haskellwiki/Import_modules_properly 2. http://www.haskell.org/haskellwiki/Qualified_names 3. See section 2 Version numbers - http://www.haskell.org/haskellwiki/Library_versioning_policy Cheers, Johan

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Memory profiling
by Pieter Laeremans 16 Jun '08

16 Jun '08

Hi, Which tools do you recommand for memory profiling haskell programs on a *nix system. I'm using haskell to develop a CGI program/script. The application has to be deployed on shared hosting infrastructure. Since I would like to be a good citizen , I would need to meassure the maximum amount of memory allocated to the program during execution. The best I can do now is look at top but that 's not satisfactory. thanks, Pieter -- Pieter Laeremans <pieter(a)laeremans.org>

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Documenting the impossible
by Andrew Coppin 16 Jun '08

16 Jun '08

I have a small idea. I'm curios if anybody else thinks it's a good idea... How about a {-# IMPOSSIBLE #-} pragma that documents the fact that a particular point in the program *should* be unreachable? For example, you look up a key in a Map. You know the key is there, because you just put it there yourself two seconds ago. But, theoretically, lookup returns a Maybe x so - theoretically - it's possible it might return Nothing. No matter what you do, GHC will insert code to check whether we have Just x or Nothing, and in the Nothing case throw an exception. Obviously there is no way in hell this code path can ever be executed. At least, assuming your code isn't broken... This is where the pragma comes in. The idea is that you write something like case lookup k m of Just v -> process v Nothing -> {-# IMPOSSIBLE "lookup in step 3" #-} When compiled without optimisations, the pragma just causes an exception to be thrown, rather like "error" does. When compiled with optimisations, the whole case alternative is removed, and no code is generated for it. (And if the impossible somehow happens... behaviour is undefined.) So you test your program with your code compiled unoptimised, and when you're "sure" the impossible can't happen, you tell the compiler to remove the check for it. (Actually, it would possibly be a good idea to have a switch to turn this on and off seperately if needed...) Does anybody think this is a useful idea? If so I'll add a feature request ticket to the GHC Trac. But I want to see if folks like the idea first... (I was thinking the message in the pragma would be what gets displayed on screen, along with some auto-generated location info. Just a module name and line number ought to be sufficient...)

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External query interface to HackageDB?
by Dimitry Golubovsky 16 Jun '08

16 Jun '08

Hi, Is there any way to query the latest version of a particular package stored on Hackage, that was successfully built? I mean, not _how_ to do that (I have some ideas that I have to download directory listings, looking for failure logs, etc.), but is there any tool or interface already available that does similar things? Unfortunately, tarfiles provided on Hackage (like 00-index.tar.gz) do not help, e. g. BerkeleyDB failed to build in all three versions, yet its all cabal files are included in the tarball: tar tvf 00-index.tar.gz ... -rw-r--r-- www-data/www-data 1055 2007-04-06 13:03 ./BerkeleyDB/0.1/BerkeleyDB.cabal -rw-r--r-- www-data/www-data 1061 2007-04-06 16:59 ./BerkeleyDB/0.2/BerkeleyDB.cabal -rw-rw-r-- www-data/www-data 1236 2008-01-11 14:42 ./BerkeleyDB/0.3/BerkeleyDB.cabal I remember, in the past, HackageDB was expected to become a database of some sort: is there any database-like backend that would accept queries, other than just parsing Apache dir listings? My final goal, given some master-list of package names, to be able to retrieve latest succesfully built (not just uploaded) releases from Hackage Thanks. -- Dimitry Golubovsky Anywhere on the Web

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(no subject)
by Adrian Neumann 16 Jun '08

16 Jun '08

{- I downloaded the source and put my file in the same directory You may need to adjust the imports -} module Main where import Picture import Draw -- change xWin to 1000 and yWin to 700 for this to work import EnableGUI -- I use a Mac import SOE hiding (Region) import qualified SOE as G (Region) import Data.List import Random -- lines are not Shapes unfortunately linie = ((Shape $ Polygon [(-0.1,-0.01),(-0.1,0.01),(0.1,0.01), (0.1,-0.01)]), (-0.1,0), (0.1,0)) main = enableGUI >> do w <- openWindow "Lindenmayer System" (xWin, yWin) newStdGen g <- getStdGen drawPic w (aufgabe2 g) k <- getKey w if (k=='q') then do closeWindow w return () else do clearWindow w main -- one big ugly line of code, not that interesting though aufgabe2 g= dasBild where r = rotateRegion (pi/2) $ Translate (-2.5,0) $ renderLSystem linie (lSystem 20 g) dasBild = Region White r `Over` Region Black ( Translate (0,-1.8) $ Scale (1,0.3)$ Translate (0,-2.6) $ rotateRegion (pi/2+pi/ 3) $ Translate (0,2.6) $ r) `Over` Region Green (Shape $ Polygon [(-5,-3.5),(-5,-1.5),(5,-1.5),(5,-3.5)]) `Over` Region Yellow (Translate (4,1.5) (Shape $ circle (0.5))) `Over` Region Blue (Shape $ Rectangle 14 7) -- start of the interesting part: -- A - Axiom, the base shape we use for rendering later --F - Forward --Branch - what it says data LSys = A LSys | F LSys | Branch StdGen [LSys] LSys | Done deriving Show -- a Axiom is a region with two connector points type Axiom = (Region, Vertex, Vertex) -- this seems not to be used anymore? scaleAxiom :: Float -> Axiom -> Axiom scaleAxiom f (r,u,v) = (Scale (f,f) r, f .*. u, f .*. v) -- just for testing purposes testLSys = A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (Branch (mkStdGen 5) [A (F ((Branch (mkStdGen 5) [A (F Done), A (F Done)] Done))), A (F Done)] Done), A (F Done)] Done))), A (F Done)] Done) -- a 2D rotation matrix drehM :: Float -> (Float, Float, Float, Float) drehM w = (cos w, -sin w, sin w, cos w) -- matrix vector multiplication (.**.) :: (Float, Float, Float, Float) -> Vertex -> Vertex (.**.) (a,b,c,d) (px,py) = (a*px+b*py, c* px+d*py) -- other vector stuff (.-.) (a,b) (c,d) = (a-c,b-d) (.+.) (a,b) (c,d) = (a+c,b+d) (.*.) l (c,d) = (c*l,d*l) abs' (a,b) = (abs a, abs b) betr (a,b) = sqrt (a*a+b*b) -- SOE doesn't come with a way to rotate Regions, so I wrote my own rotateRegion :: Float -> Region -> Region rotateRegion f (Shape s) = Shape (rotateS f s) rotateRegion f (Translate v r) = Translate ((drehM f).**.v) (rotateRegion f r) -- the scaling part is not right I think. Everything seems to break if I try to incorporate scaling -- into the rendering rotateRegion f (Scale v r) = Scale ((betr v/ betr nv) .*. nv) (rotateRegion f r) where x = ((drehM f).**. (fst v,0)) y = ((drehM f) .**. (0,snd v)) nv = (abs' x) .+. (abs' y) rotateRegion f (Complement r) =Complement (rotateRegion f r) rotateRegion f (Union r1 r2) = Union (rotateRegion f r1) (rotateRegion f r2) rotateRegion f (Intersect r1 r2) = Intersect (rotateRegion f r1) (rotateRegion f r2) rotateRegion f (Xor r1 r2) = Xor (rotateRegion f r1) (rotateRegion f r2) rotateRegion _ s=s rotateS f (Polygon pts) = Polygon (map ((drehM f) .**.) pts) rotateS f x = x -- nondeterministically generate a word in our LSys language -- lots of copy&paste here, any way to do this better? lSystem :: Int -> StdGen -> LSys lSystem n g = f n g (A undefined) where f :: Int -> StdGen -> LSys -> LSys f 0 _ _ = Done f (n+1) g (A _) | choose >= 1 = A (f n ng (F undefined)) | choose == 0 = A (f n ng (Branch ng [f n ng' (A undefined), f n ng'' (A undefined)] undefined)) where (choose, ng) = randomR (0::Int,3::Int) g (ng', ng'') = split ng f (n+1) g (F _) | choose >= 1 = F (f n ng (F undefined)) | choose == 0 = F (f n ng (Branch ng [f n ng' (A undefined), f n ng'' (A undefined)] undefined)) where (choose, ng) = randomR (0::Int,3::Int) g (ng', ng'') = split ng f (n+1) g (Branch h lSys _) | choose >= 1 = Branch h lSys (f n ng (F undefined)) | choose == 0 = Branch h lSys (f n ng (Branch ng [f n ng' (A undefined), f n ng'' (A undefined)] undefined)) where (choose, ng) = randomR (0::Int,5::Int) g (ng', ng'') = split ng -- recursivly render a LSys renderLSystem :: Axiom -> LSys -> Region renderLSystem _ Done = Empty renderLSystem (r,u,v) (A lSys) = r `Union` renderLSystem (r,u,v) lSys renderLSystem (r,u,v) (F lSys) = r'' `Union` renderLSystem (r'', u . +. o , v .+.o) lSys where r'' = Translate o $ r o = (v .-. u) renderLSystem (r,u,v) (Branch g lSys rest) = theBranches `Union` renderLSystem (r,u,v) rest where theBranches = Translate o $ foldr Union Empty $ -- we need to rotate around the u-Connector, not around (0,0) -- thus translation map (Translate u) $ zipWith ($) rotations (map ((Translate ((0,0).-.u)).(renderLSystem (r,u,v))) lSys) rotations = map rotateRegion (randomRs (-pi/4,pi/3) g) -- branches are rotated randomly o = (v .-. u)

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OT: Paper on increasing entropy in software systems
by Magnus Therning 15 Jun '08

15 Jun '08

This is wildly off topic, but since the Haskell community is a rather academic one I thought there might be a good chance to find someone who can point me in the right direction. I was just listening to Brooks' talk at OOPSLA 2007 and in the Q&A part at the end he mentions a paper on increasing entropy in software systems. He mentions the authors' names but I can't quite make it out and Google hasn't been very helpful either. He says the paper “must be 30 years old” and it sounds like he says it's by Les Bellati and Manny Leimann (Lehmann?). As I said, I can't quite make out the names, and the names ring no bells for me. Does anyone on the list know what paper he's referring to? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus．therning＠gmail．com http://therning.org/magnus What if I don't want to obey the laws? Do they throw me in jail with the other bad monads? -- Daveman

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ANN: Topkata
by Brent Yorgey 15 Jun '08

15 Jun '08

On Sat, Jun 14, 2008 at 10:53 AM, Christoph Bauer < c-bauer-olsbruecken(a)t-online.de> wrote: > Hello Neil, > > > Looks cool! Could you upload it to hackage? > > Thank you. Ok, I uploaded the current version. At the moment you have > to run topkata in the topkata-0.0 directory with > ./dist/build/topkata/topkata, because it has to find its texture/sound > files. There's a way to put something in the .cabal file about extra data files, and have it install them in a certain location that you can then find programmatically. I forget the details, but I think it's pretty easy to set up. Maybe take a look through the Cabal documentation. Or maybe Duncan will jump in and explain. =) -Brent

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Template Haskell sugar / spliceing in automatically ?
by Marc Weber 15 Jun '08

15 Jun '08

Hi, I've been thinking about template haskell sugar lately. Some cool libraries are there such as metaHDBC or the template haskell printf library. However they all have one thing in common: $(printf "...") a b c $(runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" ) 2 3 4 Would it make sense to automatically splice those functions? {-# auto-splice: runStmt, printf #-} So that you can just use printf "..." a b c and runStmt "INSERT INTO ( ) VALUES ( ?, ?, ? )" 2 3 4 without $() ? Would this be convinient? Marc Weber

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ANN: Printf-TH
by Marc Weber 15 Jun '08

15 Jun '08

Igloo (Ian Lynagh) allowed me kindly taking over maintainance on his printf library using template haskell written in 2003. I've updated it so that it compiles with ghc-6.8.2. You can get it from hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Printf-TH usage looks like this: {-# OPTIONS_GHC -XTemplateHaskell #-} ... import Language.Haskell.TH.Syntax import Text.Printf.TH (printf) ... putStrLn $ $(printf "Foo %H bar") (Just 5) putStrLn $ $(printf "%6d") 1 putStrLn $ $(printf "%6d") (-1) Short Explanation: $(printf "%d") will be replaced by a auto generated function taking an int etc Benefit: Wrong arg types or wrong printf arg count will result in compile time errors. Enjoy Marc Weber

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const is question
by odtaa48 15 Jun '08

15 Jun '08

hello could someone explain the following differing results const id 0 5 -> 5 -- ie. 'takes' the 'last' one const (id 0) 5 -> 0 -- ie. 'takes' the 'first' one Thanks

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Hoogle totally broken?
by Richard 14 Jun '08

14 Jun '08

It'd seem that (at least the online version of) Hoogle is totally broken and useless. See, for example, the output when looking for: Monad m => m a -> (a -> m b) -> m b (i.e. (>>=)'s type) over at: http://haskell.org/hoogle/?q=Monad+m+%3D>+m+a+->+(a+->+m+b)+->+m+b Data.Generics.Sche... everywhere :: (a -> a) -> a -> a Data.Generics.Sche... everywhere' :: (a -> a) -> a -> a Prelude. ($) :: (a -> b) -> a -> b Prelude. ($!) :: (a -> b) -> a -> b Data.Function. ($) :: (a -> b) -> a -> b Prelude. maybe :: b -> (a -> b) -> Maybe a -> b Data.Maybe. maybe :: b -> (a -> b) -> Maybe a -> b ... and so on. (>>=) isn't there at all!?

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ANN: Mueval 0.21
by Gwern Branwen 14 Jun '08

14 Jun '08

Hiya everyone. I'd like to announce the release of a little CLI program I whipped up. It's called mueval <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>. WHAT: Mueval grew out of my discontent with Lambdabot: it's really neat to be able to run expressions like this: 07:53 < ivanm> > filter (\ x -> isLetter x || x == '\t') "asdf$#$ dfs" 07:55 < lambdabot> "asdfdfs" But lambdabot is crufty and very difficult to install or run. IMO, we need a replacement or rewrite, but one of the things that make this difficult is that lambdabot uses hs-plugins to get that sort of evaluation functionality, and hs-plugins is half the problem. We want some sort of standalone executable which provides that functionality. Now, 'ghc -e' is obviously unsuited because there is no sandboxing, so what I've done is basically marry the GHC API (as rendered less sharp-edged by Hint) with a bunch of resource limits and sandboxing (as largely stolen from lambdabot). EXAMPLES: The end result is an adorable little program, which you can use like this: bash-3.2$ mueval --expression '1*100+1' Expression type: (Num t) => t result: "101" bash-3.2$ mueval --expression "filter (\`notElem\` ['A'..'Z']) \"abcXsdzWEE\"" Expression type: [Char] result: "\"abcsdz\"" Note that mueval will avoid all the attacks I've been able to test on it: bash-3.2$ mueval --expression 'let x = x in x' Expression type: t result: "mueval: Time limit exceeded bash-3.2$ mueval --expression "let foo = readFile \"/etc/passwd\" >>= print in foo" Expression type: IO () result: "<IO ()>" bash-3.2$ mueval --module System.IO.Unsafe --expression "let foo = unsafePerformIO readFile \"/etc/passwd\" in foo" mueval: Unknown or untrusted module supplied! Aborting. SUMMARY: Anyway, it's my hope that this will be useful as an example or useful in itself for people endeavouring to fix the lambdabot situation or just in safely running code period. GETTING: You can download mueval at the usual place: <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mueval>. (There will probably be a darcs repository at some point.) ----- TODO: Mueval isn't feature-complete yet. The last thing I want to add is an ability to change the current user to 'mubot', which presumably the user will have set up to have access to next to nothing much like is already often done with daemons, but I haven't been able to figure out how to do this - the only suitable function I've found is 'setUID', and that requires one to be root... -- gwern SHA Fetish Ceridian Eurosat munitions MCI spies 26 M.P.R.I. ISN

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cgi liftM liftIO
by Cetin Sert 14 Jun '08

14 Jun '08

Hi, Could someone please care to explain what I am doing wrong below in cgiMain2 and how can I fix it? ./Main.hs:25:15: No instance for (MonadCGI IO) arising from a use of `output' at ./Main.hs:25:15-20 Possible fix: add an instance declaration for (MonadCGI IO) In the first argument of `($)', namely `output' In the expression: output $ renderHtml $ page "import" fileForm In the definition of `upload': upload = output $ renderHtml $ page "import" fileForm ./Main.hs:57:29: Couldn't match expected type `CGI CGIResult' against inferred type `IO CGIResult' In the first argument of `handleErrors', namely `cgiMain2' In the second argument of `($)', namely `handleErrors cgiMain2' In the expression: runCGI $ handleErrors cgiMain2 import IO import Network.CGI import Text.XHtml import qualified Data.ByteString.Lazy as BS import Control.Monad (liftM) import Data.Maybe (fromJust) import Interact fileForm = form ! [method "post", enctype "multipart/form-data"] << [afile "file", submit "" "Upload"] page t b = header << thetitle << t +++ body << b cgiMain1 = do getInputFPS "file" ↠ λms → maybe upload contents ms ↠ return where upload = output $ renderHtml $ page "import" fileForm contents = outputFPS cgiMain2 = do getInputFPS "file" ↠ λms → maybe upload contents ms ↠ return where upload = output $ renderHtml $ page "import" fileForm contents = λs → do (i,o,h,_) ← runUnzip BS.hPutStr i s c ← BS.hGetContents o outputFPS c {- (i,o,h,_) ← runUnzip BS.hPutStr i s BS.hGetContents o ↠ outputFPS -} {- liftM :: (Monad m) => (a1 -> r) -> m a1 -> m r liftIO :: (MonadIO m) => IO a -> m a saveFile n = do cont <- liftM fromJust $ getInputFPS "file" let f = uploadDir ++ "/" ++ basename n liftIO $ BS.writeFile f cont return $ paragraph << ("Saved as " +++ anchor ! [href f] << f +++ ".") -} runUnzip = runInteractiveCommand "unzip -l /dev/stdin" main = runCGI $ handleErrors cgiMain2 Best Regards, Cetin Sert P/s: what are lifts o_O?

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LDAP 0.6.3 build failure
by Jason Dusek 14 Jun '08

14 Jun '08

I'm trying to build the LDAP libs, version 0.6.3, on a recent MacBook Air with OpenLDAP 2.3.27 (the version of OpenLDAP shipped by Apple). The "atom sorting error" I get from `ld` is outside my range of knowledge -- if some could advise me on how to get around it, I'd be much obliged. I'm using the Apple toolchain to do do the build. -- _jsn :; Setup configure && Setup build Configuring LDAP-0.6.3... Preprocessing library LDAP-0.6.3... Building LDAP-0.6.3... ar: creating archive dist/build/libHSLDAP-0.6.3.a ld: atom sorting error for _LDAPzm0zi6zi3_LDAPziTypesLL_Berval_closure_tbl and _LDAPzm0zi6zi3_LDAPziTypesLL_CLDAP_closure_tbl in dist/build/LDAP/TypesLL.o ld: atom sorting error for _LDAPzm0zi6zi3_LDAPziTypesLL_Berval_closure_tbl and _LDAPzm0zi6zi3_LDAPziTypesLL_CLDAP_closure_tbl

2 1

Re: [Haskell] ANN: random-access-list-0.1
by Isaac Dupree 14 Jun '08

14 Jun '08

Stephan Friedrichs wrote: > Hello, > > I've implemented Chris Okasaki's random-access list[1] which provides > typical list operations (cons, head, tail) in O(1) and yet offers > indexed random-access in O(log n). It's uploaded on hackage[2]. > > It's still an early version which I'll extend, but especially at this > eary stage I'd appreciate your feedback concerning what's still missing > / to be fixed / to be improved. Great to see it, it deserved implementing, IIRC! I don't remember enough about it.. (and don't have Okasaki anywhere handy). Can it be lazy or infinitely long? (Data.Sequence can't, but it's fast on both ends and has fast concatenation.) Anyway, document that. If it can't be lazy/infinite, does it have any advantage over using Data.Sequence?(constant factor of speed?, possible operations?, something I'm forgetting?) Is "RandomAccessList" the best name for something that's not O(1), just O(log n)? Or just that "RandomAccessList" is just much longer than "[]"? don't use those unorthodox infix function names.. `cons` is hardly worse than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. . Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer an `at` that's the same partial indexing operation, rather than the name .!. (I think this "at" was a new name being put somewhere else? partly because "!" is trying to be gradually used only to refer to strictness?) "extractHead" is an ugly name for a nevertheless standardish-meaning function... what is it usually called? uncons? headTail? (Data.Sequence, which is meant to be left-right symmetric, calls it "viewr"... except your version doesn't have the Maybe, it's partial instead, fails on empty lists) For "index", don't use Monad, use Maybe (I think that's what the recent libraries(a)haskell.org discussion concluded, in the context of switching Data.Map back to Maybe). Also, Data.List has genericLength etc, to support. Isn't "index" (like Data.List.genericIndex) supposed to be a name for a partial operation, not one that returns a Maybe? Shouldn't "size" be named "length" (or exported as both names, since e.g. Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it possible for these RandomAccessLists to be longer than maxBound::Int?)? for e.g. toList, is the O(n) cost spread over traversing/demanding the items of the generated list, or all up-front, or somewhere in between? Why is zip slow with unbalanced lists? Obviously, it could be implemented O(min(m,n)*(log m + log n)) just indexing each one, which would be faster for really unbalanced-size lists... Obviously, I don't understand the implementation. BTW, looking at the file, data RandomAccessList a = RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)] Marking a list strict like that doesn't have much effect because it only makes the first (:) or [] strict. Did you mean for an element-strict or spine-strict(which would necessarily be non-infinite) list? -Isaac > > Regards, > Stephan > > [1] Chris Okasaki: "Purely Functional Data Structures" > [2] > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/random-access-li… > > >

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Cabal-Install Fails To Compile
by Aditya Siram 14 Jun '08

14 Jun '08

Hi all, I downloaded cabal-install and the cabal-1.4 branch from darcs. The following error occurs when building: > runhaskell Setup.hs build Building cabal-install-0.4.9... [19 of 27] Compiling Hackage.SrcDist ( Hackage/SrcDist.hs, dist/build/cabal/cabal-tmp/Hackage/SrcDist.o ) Hackage/SrcDist.hs:58:59: Couldn't match expected type `Char' against inferred type `Distribution.Simple.PreProcess.PPSuffixHandler' Expected type: FilePath Inferred type: [Distribution.Simple.PreProcess.PPSuffixHandler] In the fifth argument of `prepareSnapshotTree', namely `knownSuffixHandlers' In the second argument of `(>>=)', namely `prepareSnapshotTree verbosity pkg mb_lbi tmpDir knownSuffixHandlers' According to ghc-pkg compiling and installing the cabal-1.4 branch added cabal-1.3.12. Is this the problem? -Deech _________________________________________________________________ It’s easy to add contacts from Facebook and other social sites through Windows Live™ Messenger. Learn how. https://www.invite2messenger.net/im/?source=TXT_EML_WLH_LearnHow

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Re: [Haskell] ANN: random-access-list-0.1
by Isaac Dupree 13 Jun '08

13 Jun '08

Stephan Friedrichs wrote: > Isaac Dupree wrote: >> [...] >> >> Great to see it, it deserved implementing, IIRC! I don't remember >> enough about it.. (and don't have Okasaki anywhere handy). Can it be >> lazy or infinitely long? > > No, it has to be finite as it's actually a list of complete binary trees > whose size depend on the skew binary representation of the list's size. > I'll document this. okay then >> [...] >> >> Is "RandomAccessList" the best name for something that's not O(1), >> just O(log n)? Or just that "RandomAccessList" is just much longer >> than "[]"? > > Well Chris Okasaki called them "Skew Binary Random-Access Lists", which > is even longer :) :) hmm.. IndexableList? (just a thought, not sure whether I like it any better) >> >> don't use those unorthodox infix function names.. `cons` is hardly >> worse than .:. , `append` or `mappend` than .+. , and .!. than, hmm.. >> . Export a ++ and ! (!! ?) if you're really dedicated. But I'd prefer >> an `at` that's the same partial indexing operation, rather than the >> name .!. (I think this "at" was a new name being put somewhere else? >> partly because "!" is trying to be gradually used only to refer to >> strictness?) > > Good point! > >> >> "extractHead" is an ugly name for a nevertheless standardish-meaning >> function... what is it usually called? uncons? headTail? >> (Data.Sequence, which is meant to be left-right symmetric, calls it >> "viewr"... except your version doesn't have the Maybe, it's partial >> instead, fails on empty lists) > > Yes, I wasn't happy with that one either. The view-concept of > Data.Sequence is a good idea. yeah, it's a good idea, although I'm not sure how much I like the particular syntax of how it's done in Data.Sequence (the view-types' constructor names, mostly) >> >> For "index", don't use Monad, use Maybe (I think that's what the >> recent libraries(a)haskell.org discussion concluded, in the context of >> switching Data.Map back to Maybe). > > I was just copying the idea from Data.Map and it's usually a good thing > to have functions as general as possible, or why is it not? To summarize: Monad isn't the proper abstraction for failable/Maybe. Maybe is an algebraic data type that *exactly* represents the spirit of what you're trying to do: e.g. Conor McBride said: "Maybe is the most general abstraction. Requiring (>>=), or even (<*>) seems excessive. What we need is "any f with zero and return", so why not pick the canonical, initial, inductively defined such thing?" In this case the typeclass adds no generality to the function's behaviour (Maybe can be trivially converted to any other type, with a combinator even). And the confusion that results, when the function is almost always used at type Maybe anyway. If you want to read the whole discussion... if you haven't been subscribed to libraries(a)haskell.org , it's archived: http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9082 >> Also, Data.List has genericLength etc, to > > At the moment, I'm using the Int type for size and indexing only for one > reason: I haven't found a proper way to generalize it. I'd really like > to use the Ix class, but it doesn't provide enough functionality, it > only works on fixed-size intervals (i. e. for arrays, which don't change > their size, but a list does). Maybe someone has an idea of how to > realize lists with a variable starting index and size? fair enough. If your implementation only supports sizes up to that of Int (which is reasonable for a strict finite type... whereas something like ([1..2^34] `genericIndex` (2^33)) can probably complete in a small amount of memory and only a moderate amount of time on a modern machine, even a 32-bit one, due to laziness and garbage collection) >> support. Isn't "index" (like Data.List.genericIndex) supposed to be a >> name for a partial operation, not one that returns a Maybe? Shouldn't >> "size" be named "length" (or exported as both names, since e.g. >> Data.Map.size, .List.length) (why is it O(1) not O(log n)? Is it >> possible for these RandomAccessLists to be longer than maxBound::Int?)? > > The size function is in O(1) because I cache it, otherwise it would be > > size (RandomAccessList xs) = sum (map fst xs) > > which is O(log n). I consider the caching useful, as most applications > will check 0 <= i < size quite often. sounds good > >> >> for e.g. toList, is the O(n) cost spread over traversing/demanding the >> items of the generated list, or all up-front, or somewhere in between? >> >> Why is zip slow with unbalanced lists? Obviously, it could be >> implemented O(min(m,n)*(log m + log n)) just indexing each one, which >> would be faster for really unbalanced-size lists... Obviously, I don't > > If two lists have exactly the same size, all the complete binary trees > holding the data have the same size as well. This can be zipped directly > and is a bit (~5% in my tests) faster. okay, that sounds like a fair optimization, since zipping same-size lists is a nice thing to do anyway. But the asymptotic speed ideally should still be O(min(m,n)), if possible? >> understand the implementation. BTW, looking at the file, >> data RandomAccessList a >> = RandomAccessList {-# UNPACK #-} !Int ![(Int, CBTree a)] >> Marking a list strict like that doesn't have much effect because it >> only makes the first (:) or [] strict. Did you mean for an >> element-strict or spine-strict(which would necessarily be >> non-infinite) list? > > Oh, you're right, I just meant to mark the Int strict. It obviously was > too late yesterday! > > Thanks for this feedback! > //Stephan >

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Announce: Fortress talk in New York City
by Jeff Polakow 13 Jun '08

13 Jun '08

Hello, There will be a talk on Fortress ( a new OO/Functional language from Sun) on Wednesday June 25 at 6:30pm in Manhattan. Abstract: The Java Programming Language revolutionized programming with two simple concepts: "Write once run anywhere", and Garbage Collection. This led to a big step up in programmer productivity. Project Fortress does it again. This time we give you multiprocessor performance without having to code threads, locks, or load balancing. Can you say "Implicit Parallelism" and "Transactional Memory"? We also give you a growable language (small fixed core), strong static typing (more errors caught at compile time), and mathematical notation. This talk will focus on the strengths of Fortress as a programming language, as well as a deep dive into implementation issues. More information is available at http://lisp.meetup.com/59 -Jeff --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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Difficulty installing hscurses
by Dominic Espinosa 13 Jun '08

13 Jun '08

Hello, I'm trying to install hscurses on debian-testing. I have ghc6 installed, which I've written some toy programs with, but I haven't tried to install any Hackage packages until now. hscurses depends on old-time and old-locale (those names make me raise my eyebrows a bit). In turn, old-time seems to depend on old-locale. So, I tried installing old-locale first. In installed fine. Now I'm trying to install old-time: $ runhaskell Setup.hs configure Warning: defaultUserHooks in Setup script is deprecated. Configuring old-time-1.0.0.0... Warning: The 'build-type' is 'Configure' but there is no 'configure' script. (given these warnings, I don't really expect the next command to succeed, but what the hell:) $ runhaskell Setup.hs build Preprocessing library old-time-1.0.0.0... Building old-time-1.0.0.0... System/Time.hsc:118:7: Could not find module `System.Locale': it was found in multiple packages: old-locale-1.0.0.0 base No idea what to do here. Is old-time conflicting with whatever "time" package superseded it, or what? I'm new to Haskell, and understanding the guts of its packaging system is a bit beyond me right now. Sorry if this is a FAQ or something, but I tried some Google searches and found nothing useful. Any help or tips appreciated.

2 1

-fvia-C error
by Anatoly Yakovenko 12 Jun '08

12 Jun '08

any idea what could be causing this error when i add the -fvia-C option /tmp/ghc32300_0/ghc32300_0.hc:6:23: error: SFMT_wrap.h: No such file or directory make: *** [release] Error 1 I am also passing these options: -O2 -fexcess-precision -funbox-strict-fields -fglasgow-exts -fbang-patterns -lcblas Thanks, Anatoly

4 5

Problems with Validate from HaXML
by Samuel Silva 12 Jun '08

12 Jun '08

Hello I'm working with large DTDs from http://www.recordare.com/dtds/, particulary partwise.dtd and timewise.dtd. I check these DTDs with some tools, like Altova XML Spy and Microsoft Visual Studio, and DTDs are valid. However Validate tool from HaXML doesn't validate same DTDs. Result from Validate is: $ Validate partwise.dtd Validate: In a sequence: in content spec of ELEMENT decl: note When looking for a non-empty sequence with separators: Expected % but found | in file note.mod at line 51 col 45 used by file partwise.dtd at line 120 col 1 when looking for a content particle when looking for a content particle Problematic definition is in "note.mod" file, presented below: <!ELEMENT note (((grace, %full-note;, (tie, tie?)?) | (cue, %full-note;, duration) | (%full-note;, duration, (tie, tie?)?)), instrument?, %editorial-voice;, type?, dot*, accidental?, time-modification?, stem?, notehead?, staff?, beam*, notations*, lyric*)> I'm trying using DtdToHaskell tool from HaXML to build parser from MusicXML to Haskell types. There are other ways to build XML parser using HaXML? I'm already using HaXML, with HaXML combinators, to write MusicXML. Thanks. -- Don't hug that, Hugs ME! Samuel Silva

2 1

Simple list processing
by Andrew Coppin 12 Jun '08

12 Jun '08

OK, so this is a fairly basic question about list processing. Several times now, I have found myself wanting to process a list to produce a new list. However, the way later elements are processed depends on what the earlier elements are - in other words, this isn't a simple "map". What is the best way to handle this? According to the theory, anything that consumes a list and produces a value is some kind of fold. [Assuming it traverses the list in a sensible order!] So it looks like you could implement this as a fold. But should that be a LEFT-fold or a RIGHT-fold? (I always get confused between the two!) Actually, anything that takes a value and processes it repeatedly to produce a list is technically an unfold. [Again assuming a sensible processing order.] So it looks like this function could also be an UNfold. As in, you take a list as input, and keep unfolding until that list becomes empty. So it looks like this can be implemented as a fold or an unfold. But neither way looks especially easy. Both of these patterns seem to be more general than necessary; I only want to take 1 element of input and produce 1 element of output, but keeping track of a running state. I guess I could use some sort of state monad and make the whole thing monadic - but that again is overkill for what I'm trying to do. Any hints here?

6 5

appending an element to a list
by Adrian Neumann 12 Jun '08

12 Jun '08

Hello, I was wondering how expensive appending something to a list really is. Say I write I'd say "longList ++ [5]" stays unevaluated until I consumed the whole list and then appending should go in O(1). Similarly when concatenating two lists. Is that true, or am I missing something? Adrian

10 15

ANN: ieee-0.2
by Patrick Perry 12 Jun '08

12 Jun '08

ieee is a library that provides approximate comparison of floating point numbers based, NaN-aware minimum and maximum, and a type class for approximate comparisons. This version fixes a bug in the comparison implementation for Maybe. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ieee

1 0

ANN: blas-0.4.1
by Patrick Perry 12 Jun '08

12 Jun '08

There were a few hiccups in the release of 0.4, so this version is to make installation go a little smoother for people. There are now installation instructions (the INSTALL file) and configuration settings for some common CBLAS (ATLAS, MKL, vecLib, GSL). The default is now to assume that ATLAS is installed, so hopefully most people won't have to fuss too much with this. Alberto Ruiz reported two small issues with precision in the unit tests, and those have now been fixed. Patrick

1 0

Haskell Weekly News: Issue 72 - June 11, 2008
by Brent Yorgey 12 Jun '08

12 Jun '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080611 Issue 72 - June 11, 2008 --------------------------------------------------------------------------- Welcome to issue 72 of HWN, a newsletter covering developments in the [1]Haskell community. Greetings, Haskellites! As many of you have already heard, Don Stewart has passed on the editorship of the HWN to me (Brent Yorgey). I'd like to thank Don and John Goerzen for their great work putting it together in the past, and I'm excited to make the HWN once again into a reliable, useful compendium of happenings in the Haskell community. You can expect to see a few changes---for example, hackage uploads will no longer be listed in the HWN (unless they are announced on the haskell or haskell-cafe mailing lists), since you can now see a dynamically updated list on the front page of the Haskell wiki. This edition includes all the announcements going back to Issue 71, but only some of the blog posts, since I couldn't find a way to get old feed data from Planet Haskell. Hopefully next week things will settle down to something more normal(ish) and I can begin tinkering with the format. Feel free to send suggestions and/or stories for inclusion to me, byorgey at gmail dot com. Enjoy---'Putting the W back in HWN!' Announcements hfann. Olivier Boudry [2]announced the first release of the [3]hfann module, an interface to the [4]'Fast Artificial Neural Network (FANN)' library. funsat. Denis Bueno [5]announced a release of [6]funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. DEFUN08: Call for talks and tutorials. Matthew Fluet [7]announced the final call for talks and tutorials at [8]DEFUN 2008, to be held in conjunction with [9]ICFP. Cabal-1.4 Release Candidate. Duncan Coutts [10]announced the second release candidate for [11]Cabal-1.4. Programmer's Minesweeper. Bertram Felgenhauer [12]announced a Haskell implementation of [13]Programmer's Minesweeper, which allows programmers to implement minesweeper strategies and run them. hackage RSS feed. Don Stewart [14]announced a new [15]RSS feed for the most recently uploaded packages on [16]Hackage. BLAS bindings. Patrick Perry [17]announced a set of bindings for the [18]BLAS linear algebra library. Xen Control bindings. Thomas DuBuisson [19]announced the [20]hsXenCtrl package, with FFI bindings to [21]Xen. bloomfilter. Bryan O'Sullivan [22]announced the availability of a fast Bloom filter library for Haskell. A Bloom filter is a probabilistic data structure that provides a fast set membership querying capability. It does not give false negatives, but has a tunable false positive rate. HCAR. Janis Voigtlaender [23]announced the 14th edition of the [24]Haskell Community and Activities Report (HCAR). HSmugMug. Daniel Patterson [25]announced [26]HSmugMug, a Haskell wrapper to the photo hosting site [27]SmugMug's API. LIPL. Sam Lee [28]announced the release of [29]LIPL, a tiny functional language implemented as a term project to learn Haskell. Glome 0.51. Jim Snow [30]announced version 0.51 of [31]glome, a raytracer written in Haskell. ChessLibrary. Andrew Wagner [32]announced the [33]ChessLibrary project, and mentioned that he is looking for an experienced haskeller to serve as a mentor for this project. xmonad-utils. Gwern Branwen [34]announced the upload to hackage of [35]xmonad-utils, a couple of small Xlib programs which might be useful for xmonad users. Roguestar. Christopher Lane Hinson [36]announced the release of [37]Roguestar 0.2, a science fiction themed roguelike (turn-based, chessboard-tiled, role playing) game written in Haskell. Streaming Component Combinators. Mario Blazevic [38]announced the 0.1 release of [39]Streaming Component Combinators in Haskell, based on earlier work done in [40]OmniMark. Twitter client. Chris Eidhof [41]announced a simple [42]terminal-based Twitter client. Monad.Reader call for copy. Wouter Swierstra [43]issued a call for copy for [44]The Monad.Reader. The submission deadline for Issue 11 is August 1. category-extras. Edward Kmett [45]announced a new release of the [46]category-extras package, involving all sorts of new categorical goodness. Session Types for Haskell. Matthew Sackman [47]announced the availability of [48]Session Types for Haskell. Session types are a means of describing communication between multiple threads, and statically verifying that the communication being performed is safe and conforms to the specification. Haddock 2.1.0. David Waern [49]announced the release of [50]Haddock 2.1.0. ReviewBoard. Adam Smyczek [51]announced the release of [52]Haskell bindings to [53]ReviewBoard, a development tool designed to monitor code changes and analyze dependencies. diagrams. Brent Yorgey [54]announced the initial release of [55]Graphics.Rendering.Diagrams, an embedded domain-specific language for creating simple pictures and diagrams, built on top of the Cairo vector graphics library. HXT. Uwe Schmidt [56]announced a new release of the [57]Haskell XML Toolbox. GSoC. Malcolm Wallace [58]announced the seven student projects chosen to be funded by the [59]Google Summer of Code. bytestring. Don Stewart [60]announced a new major release of [61]bytestring, the efficient string library for Haskell, suitable for high-performance scenarios. HXQ. Leonidas Fegaras [62]announced the release of [63]HXQ, an [64]XQuery compiler/interpreter for Haskell. Win32-notify. Niklas Broberg [65]announced the first release of [66]Win32-notify, an inotify-alike for Windows. cpuid. Martin Grabmueller [67]announced the new [68]cpuid package, which provides functionality for accessing information about the currently running IA-32 processor. Emping. Hans van Thiel [69]announced version 0.5 of the [70]Emping package, a utility which derives the shortest rules from a table of rules. datapacker. John Goerzen [71]announced the first release of [72]datapacker, a tool to pack files into a minimum number of CDs, DVDs, or any other arbitrary bin. darcswatch. Joachim Breitner [73]announced the release of [74]darcswatch, a tool for tracking darcs patches and repositories. Generic Haskell. Thomas van Noort [75]announced the fifth release of [76]Generic Haskell, an extension of Haskell that facilitates generic programming. drawingcombinators. Luke Palmer [77]announced the release of [78]graphics-drawingcombinators, a wrapper around OpenGL with a functional interface. The Monad.Reader. Wouter Swierstra [79]announced the publication of Issue 10 of [80]The Monad.Reader, a quarterly magazine about functional programming. Well-Typed LLP. Ian Lynagh [81]announced that he, Björn Bringert and Duncan Coutts have set up a Haskell consultancy company, [82]Well-Typed LLP. Their services include application development, library and tool maintenance, project advice, and training. hgdbmi. Evan Martin [83]announced the [84]hgdbmi package, which wraps the operations of attaching GDB to a process and parsing the GDB/MI output. xmonad. Don Stewart [85]announced the release of [86]xmonad version 0.7. Updates include improved integration with GNOME, more flexible "rules", various stability fixes, and of course, many new and interesting features in the extension library. Haskell Server Pages. Niklas Broberg [87]announced a new release of [88]Haskell Server Pages, a programming model for writing dynamic web pages in Haskell, both server-side and client-side. Network.MiniHTTP. Adam Langley [89]announced a release of [90]network-minihttp, a small bytestring HTTP library. Disciplined Disciple Compiler. Ben Lippmeier [91]announced the initial alpha release of the [92]Disciplined Disciple Compiler, an explicitly lazy dialect of Haskell. haskell-src-exts. Niklas Broberg [93]announced a new release for [94]haskell-src-exts, a package for handling and manipulating Haskell source code. omnicodec. Magnus Therning [95]announced the package [96]omnicodec, containing two command line utilities for encoding and decoding data. Blog noise [97]Haskell news from the [98]blogosphere. * [99]Christophe Poucet (vincenz): ICFP Contest 2008 * [100]Real-World Haskell: CUFP 2007 videos now easier to view * [101]Wrap-up: mergesort in haskell * [102]jbofihe and Haskell * [103]Writing a Regular Expression parser in Haskell: Part 3 * [104]Real World Haskell * [105]London Haskell Users Group: Next meeting: Paradise, a DSEL for derivatives pricing * [106]Christophe Poucet (vincenz): Lazy memoization * [107]Neil Mitchell: GSoC Hoogle: Week 2 * [108]Magnus Therning: Google Treasure Hunt primes question * [109]Roman Cheplyaka: Status report: week 2 * [110]Andy Gill: The unknown cost of dictionaries * [111]Edward Kmett: Zapping Adjunctions * [112]Edward Kmett: Representing Adjunctions * [113]Andy Gill: Performance problems with functional representation of derivatives * [114]Conal Elliott: Functional linear maps Quotes of the Week * roconnor: if you click your heels and say ``there is no binding like gtk2hs'' then dcoutts will appear and answer your question. * mauke: the first rule of fix club is "the first rule of fix club is "the first rule of fix club is... * oerjan: so does this mean that a comonad is like a wildlife preserve on an island in a sea of nuclear waste? * quicksilver: head-explosion is the solution, not the problem. * Botje: [on googling for polyvariadic typeclasses] OH GOD THE FIRST HIT IS OLEGS SITE! / *ahum* / I meant, "yay, reading material" * Baughn: From my point of view, anyone who understands everything ghc can do is /scary/. I'm sure that will change once I reach that level myself, but then again, there's also the possibility that I'll be in a permanent state of autophobia. * newsham: I think the problem with people asking homework questions in this channel is that the people in this channel don't have enough homework questions of their own to do. * quicksilver: *** quicksilver beats Deewiant with the i-will-not-use-fail-stick [Deewiant] quicksilver: I'm willing to accept a good alternative. [quicksilver] no. all you are permitted to accept is a beating. * mar77a: MONAD ARGHH GHGRHGH HGHRGHR RUN * Cale: Types are a bit like the nubs on lego bricks which provide structural integrity while suggesting how the bricks should fit together. * quicksilver: zip`ap`tail the aztec god of consecutive numbers About the Haskell Weekly News New editions are posted to [115]the Haskell mailing list as well as to [116]the Haskell Sequence and [117]Planet Haskell. [118]RSS is also available, and headlines appear on [119]haskell.org. Headlines are available as [120]PDF. To help create new editions of this newsletter, please see the [121]contributing information. Send stories to byorgey at gmail dot com. The darcs repository is available at darcs get [122]http://code.haskell.org/~byorgey/code/hwn/ References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41154 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hfann 4. http://leenissen.dk/fann/ 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41167 6. http://churn.ath.cx/funsat.html 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38392 8. http://www.deinprogramm.de/defun-2008/ 9. http://www.icfpconference.org/icfp2008/ 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41059 11. http://www.haskell.org/cabal/ 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40950 13. http://www.ccs.neu.edu/home/ramsdell/pgms/index.html 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41045 15. http://hackage.haskell.org/packages/archive/recent.rss 16. http://hackage.haskell.org/ 17. http://quantile95.com/?p=5 18. http://www.netlib.org/blas/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40790 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsXenCtrl 21. http://xen.org/ 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40745 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40703 24. http://www.haskell.org/communities/ 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40546 26. http://dbpatterson.com/articles/10 27. http://www.smugmug.com/ 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40500 29. http://www.lipl.googlepages.com/index.html#source 30. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40479 31. http://syn.cs.pdx.edu/~jsnow/glome/ 32. http://article.gmane.org/gmane.comp.lang.haskell.cafe/40052 33. http://code.haskell.org/ChessLibrary/ 34. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39773 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad-utils 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39710 37. http://roguestar.downstairspeople.org/ 38. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39654 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/scc-0.1 40. http://www.idealliance.org/papers/extreme/proceedings/html/2006/Blazevic01/… 41. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39648 42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/twitter 43. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39522 44. http://www.haskell.org/haskellwiki/The_Monad.Reader 45. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39492 46. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/category-extras 47. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39482 48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions 49. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39352 50. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haddock-2.1.0 51. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39347 52. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ 53. http://code.google.com/p/reviewboard/ 54. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39342 55. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/diagrams-0.1 56. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39271 57. http://www.fh-wedel.de/~si/HXmlToolbox/index.html 58. http://article.gmane.org/gmane.comp.lang.haskell.cafe/39040 59. http://code.google.com/soc/2008/haskell/about.html 60. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38992 61. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring 62. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38991 63. http://lambda.uta.edu/HXQ/ 64. http://www.w3.org/TR/xquery/ 65. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38965 66. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Win32-notify-0.1 67. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38922 68. http://uebb.cs.tu-berlin.de/~magr/projects/cpuid/doc/ 69. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38870 70. http://home.telfort.nl/sp969709/emp/empug.html 71. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38773 72. http://software.complete.org/datapacker 73. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38736 74. http://darcswatch.nomeata.de/ 75. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38676 76. http://www.generic-haskell.org/ 77. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38542 78. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphics-drawing… 79. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38505 80. http://www.haskell.org/haskellwiki/The_Monad.Reader 81. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38419 82. http://www.well-typed.com/ 83. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38173 84. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hgdbmi 85. http://article.gmane.org/gmane.comp.lang.haskell.cafe/38167 86. http://xmonad.org/ 87. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37996 88. http://code.google.com/p/hsp 89. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37853 90. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-minihttp… 91. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37831 92. http://www.haskell.org/haskellwiki/DDC 93. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37703 94. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/haskell-src-exts… 95. http://article.gmane.org/gmane.comp.lang.haskell.cafe/37688 96. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/omnicodec 97. http://planet.haskell.org/ 98. http://haskell.org/haskellwiki/Blog_articles 99. http://cpoucet.wordpress.com/2008/06/11/icfp-contest-2008/ 100. http://www.realworldhaskell.org/blog/2008/06/10/cufp-2007-videos-now-easier… 101. http://muharem.wordpress.com/2008/06/10/wrap-up-mergesort-in-haskell/ 102. http://chrisdone.com/blog/2008/06/10/jbofihe-and-haskell/ 103. http://blogs.msdn.com/matt/archive/2008/06/09/writing-a-regular-expression-… 104. http://tapestryjava.blogspot.com/2008/06/real-world-haskell.html 105. http://www.londonhug.net/2008/06/09/next-meeting-paradise-a-dsel-for-deriva… 106. http://cpoucet.wordpress.com/2008/04/25/lazy-memoization/ 107. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-2.html 108. http://therning.org/magnus/archives/353 109. http://physics-dph.blogspot.com/2008/06/status-report-week-2.html 110. http://blog.unsafeperformio.com/?p=24 111. http://comonad.com/reader/2008/zapping-strong-adjunctions/ 112. http://comonad.com/reader/2008/representing-adjunctions/ 113. http://blog.unsafeperformio.com/?p=23 114. http://feeds.feedburner.com/~r/conal/~3/304291460/ 115. http://www.haskell.org/mailman/listinfo/haskell 116. http://sequence.complete.org/ 117. http://planet.haskell.org/ 118. http://sequence.complete.org/node/feed 119. http://haskell.org/ 120. http://code.haskell.org/~byorgey/code/hwn/archives/20080611.pdf 121. http://haskell.org/haskellwiki/HWN 122. http://code.haskell.org/~byorgey/code/hwn/

1 0

wanted: Network.Curl examples
by brad clawsie 11 Jun '08

11 Jun '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 in search of some trivial examples using Network.Curl, preferrably posted here: http://haskell.org/haskellwiki/Network.Curl some of this stuff i can figure out, but setting the curl WriteFunction, as discussed here: http://code.haskell.org/~dons/docs/curl/Network-Curl-Opts.html#t%3AWriteFun… is nonobvious. any info would be useful, curl is a great library and it would be nice if using it were more straightforward thanks brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) iEYEARECAAYFAkhPaAAACgkQxRg3RkRK91OQrQCfTt+xzvqIAxDkqq8/P85ZZjON HWgAoK3L/1JUQjdaWHcHfutKvI3nPJUc =BfuR -----END PGP SIGNATURE-----

2 1

running haddock and lhs2TeX
by Samuel Silva 11 Jun '08

11 Jun '08

Hello I'm using haddock to my Literate Haskell code, and it runs very well. I prefer Literate Haskell instead Haskell because old code remain untouched. It also is possible run latex over my code. But running lhs2TeX is even better. However lhs2TeX doesn't proccess with some haddock information. I won't change or format haddock documentation but using two tools is a valuable help at development. I would know that somebody solve thi issue and how? To solve this issue I build processor, using perl, that escapes characters like | and @. This preprocessor just escapes characters within \begin{code} ... \end{code}. ##################################################################### # This scripts process Literate Haskell Script itself to be process # by lhs2TeX with haddock comments. # use strict; use warnings; my @tag=(); while (<>) { if ($_ =~ /\\begin{(.*)}/) {push @tag => $1;} elsif ($_ =~ /\\end{(.*)}/ and $1 eq $tag[@tag-1]) {pop @tag;} if ( elem("code",@tag) and /(.*)--(.*)/) { print $1 => process($2) => "\n"; } else { print; } } sub process{ my ($input) = @_; $input =~ s/\|/\|\|/g; # escapes | $input =~ s/\@/\@\@/g; # escapes @ $input =~ s/\^//g; # drop ^ $input =~ s/\"/\'/g; # change " into ' return "--$input"; } sub elem { my ($x,@xs) = @_; my $res = 0; for (@xs) {$res=1 if $x eq $_} return $res; } ##################################################################### -- Don't hug that, Hugs ME! Samuel Silva

1 0

blas: ghc-6.8.2: unable to load package `blas-0.4'
by Anatoly Yakovenko 11 Jun '08

11 Jun '08

Patric, I am trying to use your blas package, but I am getting a missing symbol error. > import Data.Matrix.Dense.IO > mm::(IOMatrix (Int,Int) Double) <- newListMatrix (1,1) [1.0] Loading package storable-complex-0.1 ... linking ... done. Loading package ieee-0.1 ... linking ... done. Loading package old-locale-1.0.0.0 ... linking ... done. Loading package old-time-1.0.0.0 ... linking ... done. Loading package random-1.0.0.0 ... linking ... done. Loading package QuickCheck-1.1.0.0 ... linking ... done. Loading package blas-0.4 ... linking ... <interactive>: /usr/lib/blas-0.4/ghc-6.8.2/HSblas-0.4.o: unknown symbol `cblas_ddot' ghc-6.8.2: unable to load package `blas-0.4' any ideas what i am missing? Thanks, Anatoly

3 4

Re: [Haskell-cafe] Moving "forall" over type constructors
by Sean Leather 11 Jun '08

11 Jun '08

Hi, > I just found out that it *is* possible to implement the inside function, > > namely as follows: > > > > > inside :: forall t. ((forall a. Wrapper (t a))-> Wrapper (forall a. (t > > > a))) > > > inside x = Wrapper f > > > where f :: forall a. (t a) > > > f = unwrap x > > > unwrap (Wrapper z) = z > > > > I guess this solves my problem. Sorry for bothering you with this > question. > > I still find it a bit weird to write all these obfuscated identity > functions > > to make the type checker happy, though. > > As I said, the types are not isomorphic -- it you think of type > parameters as arguments you will see why. I found these examples interesting, mostly because I don't understand it very well. So, I simplified Klaus' code a bit and derived the following: ----- {-# LANGUAGE Rank2Types #-} -- Wrapper newtype W a = W { unW :: a } inside :: ((forall a. W (t a))-> W (forall a. (t a))) --inside (W x) = W x -- (a) FAILS --inside = W . unW -- (b) FAILS inside x = W (unW x) -- (c) WORKS ----- Can someone comment on the differences between the following in terms of type-checking or inference? Considering the errors I got, I'm guess the issue is the same for the pattern-matching (a) and the point-free (b) versions. Are there any pointers for developing a better understanding or intuition of this? Thanks, Sean

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Unable to hc-build ghc 6.6.1
by Re, Joseph (IT) 11 Jun '08

11 Jun '08

I'm trying to do a registered hc-build on linux2.4 x86 with ghc 6.6.1. After fixing mk/bootstrap.mk to include "-lncurses" in HC_BOOT_LIBS to get past an undefined reference to "tputs" et al, I've gotten stuck with the following undefined reference error: ------------------------------------------------------------------------ == gmake all -wr; in /tmp/ghc-6.6.1/utils/runstdtest ------------------------------------------------------------------------ gmake[1]: Nothing to be done for `all'. Finished making all in runstdtest: 0 ------------------------------------------------------------------------ == gmake all -wr; in /tmp/ghc-6.6.1/utils/genapply ------------------------------------------------------------------------ gcc -o genapply -fno-defer-pop -fomit-frame-pointer -fno-builtin -DDONT_WANT_WIN32_DLL_SUPPORT -D__GLASGOW_HASKELL__=606 -O -I/tmp/ghc-6.6.1/includes -I/tmp/ghc-6.6.1/libraries/base/include -I/tmp/ghc-6.6.1/libraries/unix/include -I/tmp/ghc-6.6.1/libraries/parsec/include -I/tmp/ghc-6.6.1/libraries/readline/include -L/tmp/ghc-6.6.1/rts -L/tmp/ghc-6.6.1/libraries/base -L/tmp/ghc-6.6.1/libraries/base/cbits -L/tmp/ghc-6.6.1/libraries/haskell98 -L/tmp/ghc-6.6.1/libraries/parsec -L/tmp/ghc-6.6.1/libraries/regex-base -L/tmp/ghc-6.6.1/libraries/regex-compat -L/tmp/ghc-6.6.1/libraries/regex-posix -L/tmp/ghc-6.6.1/libraries/Cabal -L/tmp/ghc-6.6.1/libraries/template-haskell -L/tmp/ghc-6.6.1/libraries/readline -L/tmp/ghc-6.6.1/libraries/unix -L/tmp/ghc-6.6.1/libraries/unix/cbits -u "base_GHCziBase_Izh_static_info" -u "base_GHCziBase_Czh_static_info" -u "base_GHCziFloat_Fzh_static_info" -u "base_GHCziFloat_Dzh_static_info" -u "base_GHCziPtr_Ptr_static_info" -u "base_GHCziWord_Wzh_static_info" -u "base_GHCziInt_I8zh_static_info" -u "base_GHCziInt_I16zh_static_info" -u "base_GHCziInt_I32zh_static_info" -u "base_GHCziInt_I64zh_static_info" -u "base_GHCziWord_W8zh_static_info" -u "base_GHCziWord_W16zh_static_info" -u "base_GHCziWord_W32zh_static_info" -u "base_GHCziWord_W64zh_static_info" -u "base_GHCziStable_StablePtr_static_info" -u "base_GHCziBase_Izh_con_info" -u "base_GHCziBase_Czh_con_info" -u "base_GHCziFloat_Fzh_con_info" -u "base_GHCziFloat_Dzh_con_info" -u "base_GHCziPtr_Ptr_con_info" -u "base_GHCziStable_StablePtr_con_info" -u "base_GHCziBase_False_closure" -u "base_GHCziBase_True_closure" -u "base_GHCziPack_unpackCString_closure" -u "base_GHCziIOBase_stackOverflow_closure" -u "base_GHCziIOBase_heapOverflow_closure" -u "base_GHCziIOBase_NonTermination_closure" -u "base_GHCziIOBase_BlockedOnDeadMVar_closure" -u "base_GHCziIOBase_Deadlock_closure" -u "base_GHCziWeak_runFinalizzerBatch_closure" -u "__stginit_Prelude" GenApply.o -lHSreadline -lreadline -lHStemplate-haskell -lHSunix -lHSunix_cbits -lHSCabal -lHShaskell98 -lHSregex-compat -lHSregex-posix -lHSregex-base -lHSbase -lHSbase_cbits -lHSparsec -lHSrts -lgmp -lm -lncurses -ldl -lrt GenApply.o(.text+0x13a55): In function `s5cr_info': : undefined reference to `base_DataziList_zdsintersperse_info' GenApply.o(.text+0x14c11): In function `s58p_info': : undefined reference to `base_DataziList_zdsintersperse_info' GenApply.o(.text+0x17d79): In function `s54x_info': : undefined reference to `base_DataziList_zdsintersperse_info' collect2: ld returned 1 exit status gmake[1]: *** [genapply] Error 1 Failed making all in genapply: 1 gmake: *** [all] Error 1 gmake: Leaving directory `/tmp/ghc-6.6.1/utils' Does anyone know why this might be occuring? The only reference to "base_DataziList_zdsintersperse_info" on google didn't seem to have an answer. For reference my mk/build.mk is: SRC_HC_OPTS = -H32m -O -fvia-C -Rghc-timing -keep-hc-files GhcLibHcOpts = -O GhcLibWays = SplitObjs = NO just as the example one given on http://hackage.haskell.org/trac/ghc/wiki/Building/Porting. Also- in case this is related- I moved AutoApply_thr.thr_hc to AutoApply_thr.hc (and likewise for debug, thr_debug, and thr_p). Thanks, Joseph Re -------------------------------------------------------- NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.

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DEFUN08: Final Call for Talks & Tutorials (deadline: June 27)
by Matthew Fluet (ICFP Publicity Chair) 10 Jun '08

10 Jun '08

Final Call for Talks and Tutorials ACM SIGPLAN 2008 Developer Tracks on Functional Programming http://www.deinprogramm.de/defun-2008/ Victoria, BC, Canada, 25, 27 September, 2008 The workshop will be held in conjunction with ICFP 2008. http://www.icfpconference.org/icfp2008/ Important dates Proposal Deadline: June 27, 2008, 0:00 UTC Notification: July 14, 2008 DEFUN 2008 invites functional programmers who know how to solve problems with functional progamming to give talks and lead tutorials at the The ICFP Developer Tracks. We want to know about your favorite programming techniques, powerful libraries, and engineering approaches you've used that the world should know about and apply to other projects. We want to know how to be productive using functional programming, write better code, and avoid common pitfalls. We invite proposals for presentations in the following categories: How-to talks: 45-minute "how-to" talks that provide specific information on how to solve specific problems using functional programming. These talks focus on concrete examples, but provide useful information for developers working on different projects or in different contexts. Examples: - "How I made Haskell an extension language for SAP R/3." - "How I replaced /sbin/init by a Scheme program." - "How I hooked up my home appliances to an Erlang control system." - "How I got an SML program to drive my BMW." General language tutorials: Half-day general language tutorials for specific functional languages, given by recognized experts for the respective languages. Technology tutorials: Half-day tutorials on techniques, technologies, or solving specific problems in functional programming. Examples: - how to make the best use of specific FP programming techniques - how to inject FP into a development team used to more conventional technologies - how to connect FP to existing libraries / frameworks / platforms - how to deliver high-performance systems with FP - how to deliver high-reliability systems with FP Remember that your audience will include computing professionals who are not academics and who may not already be experts on functional programming. Presenters of tutorials will receive free registration to ICFP 2008. Submission guidelines Submit a proposal of 150 words or less for either a 45-minute talk with a short Q&A session at the end, or a 300-word-or-less proposal for a 3-hour tutorial, where you present your material, but also give participants a chance to practice it on their own laptops. Some advice: - Give it a simple and straightforward title or name; avoid fancy titles or puns that would make it harder for attendees to figure out what you'll be talking about. - Clearly identify the level of the talk: What knowledge should people have when they come to the presentation or tutorial? - Explain why people will want to attend: is the language or library useful for a wide range of attendees? Is the pitfall you're identifying common enough that a wide range of attendees is likely to encounter it? - Explain what benefits attendees are expected to take home to their own projects. - For a tutorial, explain how you want to structure the time, and what you expect to have attendees to do on their laptops. List what software you'll expect attendees to have installed prior to coming. Submit your proposal in plain text electronically to defun-2008-submission-AT-deinprogramm.de by the beginning of Friday, June 27, Universal Coordinated Time. Organizers Kathleen Fisher AT&T Labs Simon Peyton Jones Microsoft Research Mike Sperber (co-chair) DeinProgramm Don Stewart (co-chair) Galois

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ANN: funsat 0.5, a SAT solver written in Haskell
by Denis Bueno 10 Jun '08

10 Jun '08

Hi all, It is my pleasure to announce the first reasonable release of funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. It is available from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat http://churn.ath.cx/funsat.html As well as in a Git repo, which contains many benchmark files funsat can solve. git clone http://churn.ath.cx/funsat Funsat is intended to be reasonably efficient for practical problems and convenient to use as a constraint-solving backend in other software. The former is achieved by using several well-known techniques from the literature including two-watched literals, conflict-directed learning, non-chronological backtracking, a VSIDS-like dynamic variable ordering, and restarts. The latter is supported currently by efficient unsatisfiable core generation, which generates a minimal unsatisfiable problem for a given unsatisfiable problem. In the future, I plan to add support for converting boolean circuits into CNF, as well as support for other types of constraints. Please try it out and report bugs! (This email is the one listed on the website.) -- Denis

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File locking wishlist
by Joachim Breitner 10 Jun '08

10 Jun '08

Hi, for a program of mine (darcswatch[1]), a rather long running process is run at certain events (by cron, and by new emails). I want to achieve that: * Only one instance of the program runs at a time. * If new events come in while the program runs, it should re-run itself * There is information attached to the events (only one Bool ATM) So I’d like to implement something with this, or a similar, interface: ======================================================================= module MyLocking where -- | tries to get the lock. If it fails, notifies the running process -- to re-start itself afterwards, with the given information -- returns True if the lock was aquired lockOrMark :: Show a => FilePath -> a -> IO Bool -- | release the lock. If new events have come in, they are returned -- in the list, and the lock is still kept. If the list is empty, -- the lock was successfully released. releaseLock :: Read a => FilePath -> IO [a] ======================================================================= I would use this module in this way: realWork args = do someStuff args newArgs <- releaseLock "someDir/" unless (null newArgs) $ do -- we missed some events, so re-run and then try again. let newArg = combineInSomeWay newArgs realWork newArg main = do args <- getArgs l <- lockOrMark "someDir/" args when l $ do -- we got the lock, so lets work realWork args I hope this makes the idea clear. How could a possible implementation look like, when all operations should be atomic? I was considering this, would it work fine? lockOrMark would try to create a directory in the path. Whoever creates the directory has the lock. If it works, create. If it fails, because the directory already exists, then write the given args to a temporary file with a unique name, and move it into that directory. If that fails (because the directory has disappeared, i.e. the lock released), start over with trying to create the directory. If it works, then you are done. releaseLock would try to rmdir the directory. If that succeeds, no files have been in there, so no events were missed. If it does not succeed, then there were files. Read and delete them and return the list of arguments contained in them. Greetings, Joachim [1] http://darcswatch.nomeata.de/ -- Joachim Breitner e-Mail: mail(a)joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata(a)joachim-breitner.de

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