- Haskell-Cafe - Haskell.org

template haskell for typeclass synonyms
by Paolino 02 Nov '10

02 Nov '10

Hello. I'd like to have a template haskell function that take some constraints and a class name and write an empty class from those and relative empty instance to simulate typeclass synonyms. As I've never written TH and couldn't find a easily adaptable code around, I ask here for the code, or some hints on how to arrive there. Thanks paolino

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Re: [Haskell-cafe] [ANNAUNCE] ghcjs-0.1.0 Haskell to Javascript compiler
by Martijn Schrage 02 Nov '10

02 Nov '10

On 01-11-10 22:35, Aaron Gray wrote: > On 1 November 2010 16:04, Martijn Schrage <martijn(a)oblomov.com > <mailto:martijn@oblomov.com>> wrote: > > On 29-10-10 22:20, Aaron Gray wrote: >> ... >> What browser are you using, IE8, IE9, FF and Chrome on Windows >> throw up errors, both locally and to your above code. > That's weird, since http://tryout.oblomov.com/ghcjs/ghcjs.html > works fine for me with Firefox both on Mac and Windows (XP & 7). > There is only a small bug that causes a key event to get lost when > the Haskell JavaScript modules are loaded. > > What error messages do you get from Firefox? > > > Right, FF seems okay now on Vista too. > > Chrome :- > ... It works on Firefox, Chrome and Safari now, both on Windows and Mac. The IE problems seem a bit more subtle, as the script goes into an infinite loop. -- Martijn

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DSL libraries (Was: Map constructor in a DSL)
by Dupont Corentin 02 Nov '10

02 Nov '10

Hello Steffen, can you compile AwesomePrelude? I've got error messages (see below). By the way, I've looked at some DSLs made in Haskell, if I don't mistake there are lots of similarities between them. There similarities could be put in a library to help the implementors of a DSL, more or less like AwesomePrelude. Is there already packages on Hackage dealing with that? Cheers, Corentin AwesomePrelude compilation error: I'm using GHC 6.12.1. > cd tomlokhorst-AwesomePrelude-9819315 > cabal install (...) Warning: Lang.Haskell: Instances of type and data families are not yet supported. Instances of the following families will be filtered out: H Then, when trying with a very simple GATD in GHCI, I've got: <interactive>: HSAwesomePrelude-0.1.0.o: unknown symbol `AwesomePreludezm0zi1zi0_ CompilerziLiftDefinitions_inline_closure' ghc: unable to load package `AwesomePrelude-0.1.0' On Thu, Oct 28, 2010 at 2:02 PM, steffen <steffen.siering(a)googlemail.com>wrote: > I think you would love to have a look at AwesomePrelude[1] or a fork > of AwesomePrelude using associated types[2] > Some more background information by Tom Lokhorst [3][4]. > > [1] http://github.com/tomlokhorst/AwesomePrelude > [2] http://github.com/urso/AwesomePrelude > [3] http://tom.lokhorst.eu/2009/09/deeply-embedded-dsls > [4] http://tom.lokhorst.eu/2010/02/awesomeprelude-presentation-video > > On 28 Okt., 12:09, Dupont Corentin <corentin.dup...(a)gmail.com> wrote: > > Thank you for your rich responses. > > > > Indeed I think I miss some thinks in my DSL, that would make things > easier > > to deal with lists and first class functions. > > I don't really know what for now. > > Perhaps a List Constructor? Or a constructor on functions like yours > Ryan? > > EAp :: Exp ref (a -> b) -> Exp ref a -> Exp ref b > > It's from which DSL? It is accessible on the net? > > > > Chris suggested me that I can only define the Foldr constructor and > deduce > > Map from it. > > But maybe I have to add a List constructor for that. > > > > But in the suggestions from Ryan and Brandon I don't understand why I > should > > add an extra type parameter and what it is! > > > > Steffen: Wow nice. I'll integrate that ;) > > > > I'm also looking at the Atom's DSL to get inspiration. > > Something I don't understand in it is that it has two languages, on > typed: > > > > data E a where > > VRef :: V a -> E a > > Const :: a -> E a > > Cast :: (NumE a, NumE b) => E a -> E b > > Add :: NumE a => E a -> E a -> E a > > etc. > > > > And, along with it, an untyped counterpart: > > > > -- | An untyped term. > > data UE > > = UVRef UV > > | UConst Const > > | UCast Type UE > > | UAdd UE UE > > etc. > > > > What that for? What's the use of having beautiful GADT if you have to > > maintain an untyped ADT aside?? > > > > Corentin > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-C...@haskell.orghttp:// > www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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install GHC 7.0.1 RC on OS X?
by Edward Amsden 02 Nov '10

02 Nov '10

I'd like to install the GHC 7.0.1 RC on my mac (Snow Leopard, x86_64), but I don't want it to run over my current GHC 6.12.2 install. If I use the .pkg installer, it doesn't allow me to select the destination, and I worry that it will overwrite my 6.12.2 install. If I try to build from source, that requires me to use my current GHC, which (as I understand) would build for 32 bit. What other options do I have, or am I misunderstanding something? ------ Edward Amsden Undergraduate Computer Science Rochester Institute of Technology

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Haskellers browse users form
by Yitzchak Gale 02 Nov '10

02 Nov '10

I'm using Safari on Snow Leopard. On the "Browse Users" page on Haskellers, there are little buttons that look like number spinners on the two numerical fields, like "Using Haskell since..." When I press one of those, the number -1.7976931348623157e+308 appears in the field. That must be Lennart. Thanks, Yitz

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Generating random tuples
by Jacek Generowicz 01 Nov '10

01 Nov '10

I'm toying with generating random objects (for example tuples) and started wondering what pearls of wisdom Cafe might have on the matter. Two obvious points (relating to my toy code, shown below) are 1) The meaning of the limits required by randomR is not obvious for types such as tuples (you could come up with some definition, but it wouldn't be unique: how would you allow for different ones?[*]; you might decide that having such limits is nonsensical and not want to provide a randomR: would you then leave it undefinded?). [*] I guess this is related to issues such as Num being both a sum and and product monoid. 2) I'm sure there are at least half a dozen prettier definitions of random. But I suspect that the juicy bits will be in offerings about issues that I haven't even dreamed about. Presumably QuickCheck's test-data generation mechanism would be interesting to look at in this context. Is there a gentle explanation of how it works somewhere? Here's my initial effort: import Control.Monad import System.Random main :: IO (Int, Int) main = randomIO instance (Random a, Random b) => Random (a, b) where randomR = undefined random g0 = let (i1,g1) = random g0 (i2,g2) = random g1 in ((i1,i2), g1)

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commutativity
by Patrick Browne 01 Nov '10

01 Nov '10

Hi, Below are two questions on commutative operations in Haskell. infixl 5 `com` com :: Int -> Int -> Int x `com` y = (x + y) commutative com a b = (a `com` b) == (b`com`a) -- 1 + 3 == 3 + 1 -- This gives true by virtue of the value of LHS and RHS being equal after the plus operation -- Question 1 -- commutative com 1 3 -- This also gives true. Is it because of commutative equation or because of the plus operation? -- Question 2 -- In Haskell can commutativity be specified as a property of infix operations? This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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[ANNAUNCE] ghcjs-0.1.0 Haskell to Javascript compiler
by Victor Nazarov 01 Nov '10

01 Nov '10

I've been working on this for some month and I think now I'm ready to share the results. http://github.com/sviperll/ghcjs Haskell to Javascript translator ================================ Project aims to provide solution to * compile modern Haskell libraries to Javascript files and use them in Ajax applications or * develop entire Ajax application in Haskell language Building -------- Code builds as standard haskell package $ runghc Setup configure $ runghc Setup build $ runghc Setup install Usage ----- To compile Haskell module to Javascript use `ghcjs` command. $ ghcjs Test.hs This command is merely equivalent to the following $ ghc --make Test.hs but it compiles to Javascript instead of native code. See examples folder for an example of loading and running haskell code from browser. Status ------ The code is in alpha stage. Feel free to experiment with it as you wish. Implementation -------------- Compiler is implemented as [GHC](http://www.haskell.org/ghc/) backend using GHC API. And been tested with GHC 6.12.1. -- Victor Nazarov

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Edit Hackage
by Andrew Coppin 01 Nov '10

01 Nov '10

Today I uploaded a package to Hackage, and rediscovered something that you already know: I'm an idiot. More specifically, I copied the Cabal description from another package and then updated all the fields. Except that I forgot to update one. And now I have a package which I've erroneously placed in completely the wrong category. Is there any danger that at some point in the future, it might be possible to edit a package /after/ it has been released on Hackage? There are several reasons why you might wish to do this (beyond realising you did something wrong five minutes after hitting the upload button): The maintainer might change. The homepage might move. A better package might come along, making the existing one obsolete. Or you might want to stick a message on the package saying "hey, this version has a serious bug, please use the next version up instead!" (I guess you wouldn't want to actually change the code content of a package. That leaves the potential for several /different/ variants of "the same" package floating around, depending on when people installed it. That would be Bad.) Is there any danger that we might be able to do these kinds of things sometime soon?

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Forall and type synonyms in GHC 7.0
by Mario Blažević 01 Nov '10

01 Nov '10

Before uploading a new version of my project on Hackage, I decided to future-proof it against GHC 7.0. I ran into several compile errors caused by the changes in let generalization, but these were easy to fix by adding extra type annotations. But then I ran into another problem that I can't fix so easily. Here is its trimmed-down reproduction: > {-# LANGUAGE RankNTypes #-} > > module Test where > > data Component c = Component {with :: c} > > pair1 :: (Bool -> c1 -> c2 -> c3) -> Component c1 -> Component c2 -> Component c3 > pair1 combinator (Component c1) (Component c2) = Component (combinator True c1 c2) > > type PairBinder m = forall x y r. (x -> y -> m r) -> m x -> m y -> m r > > pair2 :: Monad m => (PairBinder m -> c1 -> c2 -> c3) -> Component c1 -> Component c2 -> Component c3 > pair2 combinator = pair1 (combinator . chooseBinder) > > chooseBinder :: Monad m => Bool -> PairBinder m > chooseBinder right = if right then rightBinder else leftBinder > > leftBinder :: Monad m => PairBinder m > leftBinder f mx my = do {x <- mx; y <- my; f x y} > > rightBinder :: Monad m => PairBinder m > rightBinder f mx my = do {y <- my; x <- mx; f x y} The general idea here, if you're intrigued, is that pair1 belongs to a generic module that packages things it knows nothing about into Components. The remaining definitions belong to a client of the generic module, and pair2 is a specialization of pair1 to components that have something to do with monads. Now this little test compiles fine with GHC 6.12.1, but GHC 7.0.0.20101029 reports the following error in the pair2 definition: TestForall.lhs:13:42: Couldn't match expected type `forall x y r. (x -> y -> m r) -> m x -> m y -> m r' with actual type `(x -> y -> m1 r) -> m1 x -> m1 y -> m1 r' Expected type: Bool -> PairBinder m Actual type: Bool -> (x -> y -> m1 r) -> m1 x -> m1 y -> m1 r In the second argument of `(.)', namely `chooseBinder' In the first argument of `pair1', namely `(combinator . chooseBinder)' I've tried adding extra type annotations without making any progress. At this point I'm beginning to suspect I ran into a bug in GHC 7.0, but I can't find it in GHC Trac; the only ticket that looks similar is #4347, but that one works for me. Is this a bug? If not, how do I make my code compile?

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Regex lib doesn't load
by Dan Bensen 01 Nov '10

01 Nov '10

Hi Haskellers. I'm trying to read a text file using GHCi on Haskell Platform 2010.2.0.0. The import line in my program is "import Text.Regex". When I run :main it says "unknown symbol `_regerror'" and "unable to load package `regex-posix-0.94.2'". Any clues on how fix this problem? Please let me know if there's a better place to ask about it. --Dan Bensen

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Red links in the new haskell theme
by Victor Oliveira 01 Nov '10

01 Nov '10

Hi Cafe, I really liked the new colors of haskell theme, but... Is really red a good color for links? At least for me, red links looks like broken or already visited ones. And the worst is hackage docs. It is really eye tiring to read. It's just a thought. Maybe it just with me. What about you? []s Victor

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Tsuru Capital Tokyo is looking for Southern Hemisphere summer (Dec 10 - Feb 11) interns
by employment 01 Nov '10

01 Nov '10

We are looking for an intern that has experience programming in a functional language, and is familiar with Haskell and web development. Some experience with Linux/Unix system administration is preferred. Familiarity with Git would be useful. The position is in Tokyo in a small English speaking team. We do algorithmic options market-making. The exact role is not fixed yet but we are looking particularly for someone to help with making a simulation scheduling framework and results visualisation in a web application. Compensation would be a small package including flights and accommodation. If interested please send a resume to jobs(a)tsurucapital.com You can see more details about the company at tsurucapital.com and at the company page on LinkedIn <http://tsurucapital.com/en/jobs.html#programmer>

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Equivalent of withForeignPtr for System.Mem.Weak?
by Matthew Steele 01 Nov '10

01 Nov '10

I have an object to which I have added one or more finalizers via addFinalizer from System.Mem.Weak. I would like to have a function that allows me to make use of the object within a block of IO code, and guarantee that the finalizer(s) will not be called during the code block -- sort of like withForeignPtr, but for arbitrary objects. Does such a function exist, and if not, how could I write one? I can imagine writing something like: \begin{code} withObject :: a -> IO b -> IO b withObject obj action = do result <- action touchObject obj -- touchObject :: a -> IO () return result \end{code} However, I don't know how I should implement touchObject and be confident that it won't ever be optimized out. Any suggestions? Cheers, -Matt

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Data records. Default values initialisation. Reading datatype from string.
by Siim Haugas 01 Nov '10

01 Nov '10

Hello, I need some help with data records. Normally I can use a `read' function to convert string to some data type e.g. `(read somestring) :: Type'. However, sometimes I'd like to read a record with some uninitialised fields. I have also set up a default values for my data record, for example: `defrec = {a=0,b=1, ..., z=0}'. Now I would like to override some values, so I have a string "defrec{l=100,r=88}", but it seems that it can't be done with read `(read "defRec{l=100,r=88}") :: defRec'. Any suggestions? Siim

1 1

who's in charge?
by Günther Schmidt 01 Nov '10

01 Nov '10

Hi all, this may be an odd question to some, but I think it's actually quite an un-extraordinary one. Who's in charge? Of Haskell I mean. If there was some alien from Planet Java to land on Planet Haskell and demand to be taken to our leader, whom would we take him to? Günther

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Generic traversals for GADTs
by Ozgur Akgun 01 Nov '10

01 Nov '10

Café, SYB-style libraries (and especially Uniplate) make it very easy to run generic traversals (queries/transformations) on ADTs. > data Expr = ... > x :: Expr > f :: Expr -> Expr > transform :: (Expr -> Expr) -> Expr -> Expr > transform f x :: Expr -- applies f to x (and its children) in a bottom-up manner Uniplate is very powerful and doesn't require any hand written type-class instances to get going reasonably efficiently. I can simply re-implement the functionality of Uniplate myself, modulo requiring hand-written instances. (I didn't want to go into that road, since I don't need it for this argument.) I did this exercise, because I wanted to understand why we don't have similar generic traversal libraries for GADTs. And, it didn't take long :) I can post my trials but they are really baby steps and they wouldn't be helpful. My question is: Considering how useful generic traversal libraries and GADTs are, has anybody tried implementing a generic traversal library (like Uniplate or similar) for GADTs? Is it a hard (or impossible, or not efficient, or problematic in some other way) thing to implement, or is it just not a requirement for anyone else? Best, Ozgur

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Re: [Haskell-cafe] Parsing workflow
by Stephen Tetley 31 Oct '10

31 Oct '10

On 31 October 2010 16:53, Nils Schweinsberg <ml(a)n-sch.de> wrote: > Am 31.10.2010 17:27, schrieb Stephen Tetley: >> >> Left factoring! :-) > > Stupid question: Whats that? :) > Actually a good question... Its a standard grammar transformation - if you have two alternative productions that share a common prefix A -> a b | a c Left factoring produces: A -> A_part (b | c) A_part -> a Left factoring can quickly lead to the grammar getting quite convoluted, but using 'try' can lead to very fragile parsers that stop working in mysterious ways when you extend them. Because parser combinators are just functions, you can do questionable hacks to make left factoring a bit less tedious: parseA :: Parser A parseA = do a <- a_part (parseB a <|> parseC a) parseB :: a -> Parser A parseB a = do b <- b_part return $ B a b parseC :: b -> Parser A parseC a = do c <- c_part return $ C a c

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Current thinking on CompositionAsDot issue in haskell prime?
by Alexander Kjeldaas 31 Oct '10

31 Oct '10

Hi haskellers. Reading through the Haskell Prime suggestions, one that caught my eye is the CompositionAsDot issue. I'm especially thinking of the Pro issue: * Paves the way for using . as the selection operator in improved record or module systems I think I recognize this issue from common lisp. Basically the code becomes verbose because accessor functions usually need to redundantly encode the name of the module or struct in its name. The alternative is to require users to import qualified, and that doesn't deal with the occasional intra-module collision. This is a typical large-software-system issue and it annoys me a little that Haskell seems to have inherited the problems from common lisp. I worry that in large systems, a very conservative coding standard is needed with quite verbose naming conventions as that's the only safe way to avoid these conflicts in a large system while allowing refactoring code etc. What is the current thinking on this issue? Thanks, Alexander

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Haskell meeting in Berlin
by Sönke Hahn 31 Oct '10

31 Oct '10

Hi all! There will be an informal Haskell meeting in Berlin. Date: Thursday, October 28th Time: from 20:00 Location: c-base, Rungestrasse 20, 10179 Berlin The bi-monthly lisp meeting takes place at the same time and place [1]. This is the first of hopefully more meetings to come, so we will probably discuss the details of following meetings. If you're in Berlin and want to talk to other Haskell users (or want to yell at lisp users for being from the dark side of the force), please come by. Cheers, Sönke [1] http://www.c-base.org/calender/phpicalendar/month.php

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cabal mystery (#562?)
by Conor McBride 30 Oct '10

30 Oct '10

Hi I've just installed cabal-install (just as a user: I am nowhere near root) on our unix server at work. That went fine. Clearly, the sensible thing to do next is get hold of an up-to-date package list. So, I tried conor@cafe:~$ cabal update Downloading the latest package list from hackage.haskell.org cabal: Codec.Compression.Zlib: premature end of compressed stream Here's the verbose version. conor@cafe:~$ cabal -v3 update Downloading the latest package list from hackage.haskell.org Sending: GET http://hackage.haskell.org/packages/archive/00-index.tar.gz HTTP/1.1 User-Agent: cabal-install/0.8.2 Host: hackage.haskell.org proxy uri host: www-cache.strath.ac.uk, port: :8080 Creating new connection to www-cache.strath.ac.uk:8080 Received: HTTP/1.0 200 OK Date: Thu, 28 Oct 2010 12:59:17 GMT Server: Apache/2.2.9 (Debian) mod_python/3.3.1 Python/2.5.2 Last-Modified: Thu, 28 Oct 2010 12:38:17 GMT ETag: "1888003-20bb4e-493ac9dbe6040" Accept-Ranges: bytes Content-Length: 2145102 Content-Type: application/x-tar Content-Encoding: x-gzip X-Cache: MISS from rouble-1.cc.strath.ac.uk X-Cache-Lookup: MISS from rouble-1.cc.strath.ac.uk:8080 Via: 1.1 rouble-1.cc.strath.ac.uk:8080 (squid/2.7.STABLE7) Connection: close Downloaded to /home/s3/conor/.cabal/packages/hackage.haskell.org/00-index.tar.gz cabal: Codec.Compression.Zlib: premature end of compressed stream So I poked about a bit, and I see it's a known issue. As a user, I'm wondering what to do. Just now, wget http://hackage.haskell.org/packages/archive/00-index.tar.gz is chugging away quite nicely. Anyhow, is there (a) something I can do to avoid this problem? I couldn't quite grasp what to do from the TRAC (b) some way to persuade cabal to use the file I'm currently downloading? Any tips to keep the gremlins at bay gratefully appreciated. Thanks Conor

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Monads and Functions sequence and sequence_
by Mark Spezzano 30 Oct '10

30 Oct '10

Hi, Can somebody please explain exactly how the monad functions "sequence" and "sequence_" are meant to work? I have almost every Haskell textbook, but there's surprisingly little information in them about the two functions. From what I can gather, "sequence" and "sequence_" behave differently depending on the types of the Monads that they are processing. Is this correct? Some concrete examples would be really helpful. Even references to some research papers that explain the rationale behind these (and all the other..?) monad functions would be great. Thanks in advance, Mark Spezzano

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Package regex-posix-0.94.2 suddenly failed to link
by Arnaud Bailly 30 Oct '10

30 Oct '10

Hello, All of a sudden, the package regex-posix-0.94.2 failed to link after i installed a couple of other packages (http, json). When I try to reinstall it, I got the folowing errors: D:\projets\crete1941>cabal install --global --reinstall --enable-documentation regex-posix-0.94.2 Resolving dependencies... Configuring regex-posix-0.94.2... Preprocessing library regex-posix-0.94.2... Text\Regex\Posix\Wrap.hsc:107:19: regex.h: No such file or directory Text\Regex\Posix\Wrap.hsc: In function `main': Text\Regex\Posix\Wrap.hsc:149: error: `regoff_t' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:149: error: (Each undeclared identifier is reported only once Text\Regex\Posix\Wrap.hsc:149: error: for each function it appears in.) Text\Regex\Posix\Wrap.hsc:149: error: syntax error before "int" Text\Regex\Posix\Wrap.hsc:384: error: `REG_NOTBOL' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:385: error: `REG_NOTEOL' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:389: error: `REG_EXTENDED' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:390: error: `REG_ICASE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:391: error: `REG_NOSUB' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:392: error: `REG_NEWLINE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:398: error: `REG_NOMATCH' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:399: error: `REG_BADBR' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:400: error: `REG_BADPAT' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:401: error: `REG_BADRPT' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:402: error: `REG_ECOLLATE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:403: error: `REG_ECTYPE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:404: error: `REG_EESCAPE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:405: error: `REG_ESUBREG' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:406: error: `REG_EBRACK' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:407: error: `REG_EPAREN' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:408: error: `REG_EBRACE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:409: error: `REG_ERANGE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:410: error: `REG_ESPACE' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:447: error: `regex_t' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:481: error: syntax error before ')' token Text\Regex\Posix\Wrap.hsc:484: error: `regmatch_t' undeclared (first use in this function) Text\Regex\Posix\Wrap.hsc:510: error: syntax error before ')' token Text\Regex\Posix\Wrap.hsc:510: error: syntax error before "int" Text\Regex\Posix\Wrap.hsc:511: error: syntax error before ')' token Text\Regex\Posix\Wrap.hsc:511: error: syntax error before "int" Text\Regex\Posix\Wrap.hsc:525: error: syntax error before ')' token compiling dist\build\Text\Regex\Posix\Wrap_hsc_make.c failed command was: D:\Program Files\Haskell Platform\2010.2.0.0\mingw\bin\gcc.exe -c -D__GLASGOW_HASKELL__=612 -DHAVE_REGEX_H -DSPLIT_BASE =1 -ID:\Program Files\Haskell Platform\2010.2.0.0\lib\bytestring-0.9.1.7\include -ID:\Program Files\Haskell Platform\2010.2.0.0\lib\ base-4.2.0.2\include -ID:\Program Files\Haskell Platform\2010.2.0.0\lib/include -ID:\Program Files\Haskell Platform\2010.2.0.0\lib/i nclude -ID:/Program Files/Haskell Platform/2010.2.0.0/lib/include/ dist\build\Text\Regex\Posix\Wrap_hsc_make.c -o dist\build\Text\Re gex\Posix\Wrap_hsc_make.o cabal: Error: some packages failed to install: regex-posix-0.94.2 failed during the building phase. The exception was: ExitFailure 1 I am really clueless about the failure and what caused it. Thanks for your help, Arnaud Bailly

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ANNOUNCE: darcs 2.5
by Reinier Lamers 30 Oct '10

30 Oct '10

Hi all, The darcs team is proud to announce the release of darcs 2.5. Darcs 2.5 contains many improvements over the 2.4 series. Most notable are the performance improvements in record and pull and the --bisect option for trackdown. The easiest way to install darcs 2.5 is using the Haskell Platform [1]. If you have installed the Haskell Platform or cabal-install, you can install this beta release by doing: $ cabal update $ cabal install darcs Alternatively, you can download the tarball from http://darcs.net/releases/darcs-2.5.tar.gz and build it by hand as explained in the README file. What's New ---------- A list of important changes since darcs 2.4.4: * trackdown can now do binary search with the --bisect option * darcs always stores patch metadata encoded with UTF-8 * diff now supports the --index option * amend-record now supports the --ask-deps option * apply now supports the --match option * amend-record has a new --keep-date option * inventory-changing commands (like record and pull) now operate in constant time with respect to the number of patches in the repository * the push, pull, send and fetch commands no longer change the default repository address by default * the --edit-description option is now on by default for the send command Issues resolved since darcs 2.4.4: * 64: store metadata as UTF-8 * 121: add --ask-deps support to amend-record * 643: darcs send -o outputs remote repo email address * 1159: avoid bogus repository cache entries * 1176: caches interfere with --remote-repo flag * 1208: add trackdown --bisect * 1210: global cache gets recorded in _darcs/prefs/sources * 1232: darcs convert copies _darcs/prefs/prefs * 1250: check for newlines in setpref values * 1277: percolate repository format errors correctly * 1288: the main darcs code now compiles and runs with witnesses * 1290: support diff --index * 1337: don't show unrelated patches in darcs changes on untracked path * 1389: change predist pref to point people to use 'cabal sdist' * 1427: accept gzipped patch bundles in darcs apply * 1456: make dist write more portable archives * 1473: make annotate accept '.' as argument * 1503: prefer local caches to remote ones * 1713: shorter interactive prompts * 1716: allow mail header lines of all whitespace in test * 1719: do not back up files when no conflict markers are inserted * 1726: don't consider all files with _darcs prefix boring * 1739: make ColorPrinter handle characters > 255 * 1763: use correct filename encoding in conflictors * 1765: refuse to remove non-tracked directories recursively * 1769: add support for --match 'comment ...' * 1784: push and pull print remote address right away * 1815: work around Cabal sdist permissions issue * 1817: fix support for external merge tools * 1824: avoid PACKAGE_VERSION under Windows * 1825: do not omit important prims in unrecordedChanges w/ files * 1860: (un)applying move patches doesn't corrupt pristine * 1861: fix typo in --no-boring help * 1874: recognise network tests on cabal test command line * 1875: avoid accidentally setting default * 1879: notice unexpected commute failure on merge * 1887: add a missing newline to --list-options output * 1893: move fields of conditional builds within scope of condition * 1898: notify user when they can use set-default * 1913: sort changes in treeDiff Reporting bugs -------------- If you have an issue with darcs 2.5, you can report it via the web on http://bugs.darcs.net/ . You can also report bugs by email to bugs(a)darcs.net. Kind Regards, the darcs release manager, Reinier Lamers [1]: You can download the Haskell platform from http://hackage.haskell.org/platform/

1 0

fundata1 -- Karmic Social Capital Benchmark and Shootout
by Alexy Khrabrov 30 Oct '10

30 Oct '10

I am happy to announce fundata1 -- the largest-ever program per RAM allocation in Haskell, originally implemented in Clojure and then OCaml and Haskell for social network modeling. http://github.com/alexy/fundata1 It has now become the first large-scale social networking benchmark with a real dynamic social graph built from the actual Twitter gardenhose, with the data OK'd by Twitter and supplied along with the benchmark. I wrote three reference implementations, all on github as well. Clojure and OCaml are quite basic, while Haskell community had a chance to optimize its data structures and in fact fix a GC integer overflow while working on it. You're welcome to fork and improve all of these implementations, and supply others! There's a Google Group, http://groups.google.com/group/fundata/ to discuss the shootout. There's also a blog about it and other functional things at http://functional.tv/ Let the fun begin! -- Alexy Khrabrov firstname.lastnameATgmaildotcom

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Re: Haskell-Cafe Digest, Vol 86, Issue 63
by John Lato 30 Oct '10

30 Oct '10

Hi Arnaud, > From: Arnaud Bailly <arnaud.oqube(a)gmail.com> > > Hello, > I am trying to wrap my head around the concept of Iteratee reading the > article by John Lato in Monad Reader issue 16 > (http://themonadreader.files.wordpress.com/2010/05/issue16.pdf) I > followed the "advice" on page 34: > > "I have frequently heard reports from Haskellers (including highly-talented > and > experienced users) that the only way they could understand > enumeration-based > I/O was by re-implementing it themselves." > > and so reimplemented this code in Java which is, for better and worse, > my current professional language (and there really is no point in > writing my own 50th iteratee code...). > > I have a question about iteratees composition and their behaviour. I > tried to use the throbber code to display progress while writing a > file, without using enumeratees which are introduced later on in the > article, but failed. I can bind the two iteratees together, but the > writer iteratee consumes the stream of characters to write before > handing over the control to the throbber iteratee which has nothing to > count. Did I miss something ? > This is the expected behavior. When iteratees are composed with bind, the first will consume as much of the stream as it needs to calculate its result, and only then will it pass the remaining stream to the next iteratee in the composition. Since "streamToFile" and "throbber" both consume an entire stream, they won't complete until EOF, and then will pass just that EOF to the next iteratee in the composition. The behavior you want is pretty common, and it can be accomplished by writing either throbber or streamToFile as an enumeratee. Then the enumeratee version would do the work it's supposed to but also pass the stream along to another iteratee. You could write a library function with type (following the types from the article) iterToEnum :: Monad m => Iteratee el m () -> EnumerateeM el el m a which would do this for any data-sink type iteratee. A very similar approach is used in the "iteratee" package to define the "enumPair" function, enumPair :: Monad m => Iteratee s m a -> Iteratee s m b -> Iteratee s m (a,b) I consider "enumPair" to be one of the most powerful functions supplied in iteratee. Since you use Java, you may be interested in an iteratee implementation in Scala, http://apocalisp.wordpress.com/2010/10/17/scalaz-tutorial-enumeration-based… Best, John

2 1

Haddock API and .haddock interface files questions
by Claus Reinke 30 Oct '10

30 Oct '10

Some questions about Haddock usage: 1. Haddock executable and library are a single hackage package, but GHC seems to include only the former (haddock does not even appear as a hidden package anymore). Is that intended? 2. Naively, I'd expect Haddock processing to involve three stages: 1. extract information for each file/package 2. mix and match information batches for crosslinking 3. generate output for each file/package I would then expect .haddock interface files to repesent the complete per-package information extracted in step 1, so that packages with source can be used interchangeably with packages with .haddock files. However, I can't seem to use 'haddock --hoogle', say, with only .haddock interface files as input ("No input file(s)."). 3. It would be nice if the Haddock executable was just a thin wrapper over the Haddock API, if only to test that the API exposes sufficient functionality for implementing everything Haddock can do. Instead, there is an awful lot of useful code in Haddock's Main.hs, which is not available via the API. So when coding against the API, for instance, to extract information from .haddock files, one has to copy much of that code. Also, some inportant functionality isn't exported (e.g., the standard form of constructing URLs), so it has to be copied and kept in synch with the in-Haddock version of the code. It might also be useful to think about the representation of the output of stage 2 above: currently, Haddock directly generates indices in XHtml form, even though much of the index computation should be shareable accross backends. That is, current "backends" seem to do both stage 2 and stage 3, with little reuse of code for stage 2. It seems that exposing sufficient information in the API, and allowing .haddock interface files as first-class inputs, there should be less need for hardcoding external tools into Haddock (such as --hoogle, or haddock-leksah). Instead, clients should be able to code alternative backends separately, using Haddock to extract information from sources into .haddock files, and the API for processing those .haddock files. Are these expectations reasonable, or am I misreading the intent behind API and .haddock files? Is there any documentation about the role and usage of these two Haddock features, as well as the plans for their development? Claus

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Haskellers.com idea: strike forces
by Michael Snoyman 30 Oct '10

30 Oct '10

Hey all, In the recent discussion about the status of email support in Haskell, the idea of strike forces to tackle these big problems came up. I think one dilemma people face when trying to coordinate such a venture is the logistics: where to organize, how to advertise it, where to have discussions that can be publicly accessible. This may be something that the Haskellers website can help address. Here's an idea, please give me any feedback you have (especially the negative kind): * Anyone can create a "strike force", by specifying a name for the strike force and giving a description. That person will automatically be the administrator for the strike force. * Anyone on Haskellers can watch a strike force; this will contribute to its popularity. The most popular strike forces will be shown at the top of the listings, to give an idea of what projects are active and which are dead. * People must apply to be members of a strike force, and be approved by a strike force admin. Strike force admins also have the right to add new admins/remove current admins. * Admins can add links to other websites, list Hackage packages that are part of this strike force's scope, etc. Ideas on this are welcome. * There will be some kind of discussion forum. The only thing I know for certain about this is we want to have a news feed to give updates on what's happening. I'm open to suggestions on what to implement here, but some ideas: ** A request/bug tracker. ** Free-form message boards. Possibly requires moderation for non-members. ** I'm not certain if it should just be a single thread, multi discussion threads, hierarchical discussions like Reddit, etc. Please let me know what you think. And if you think this is a foolish idea that won't help the community out, please let me know that too. Michael

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State & nested structures
by Dupont Corentin 30 Oct '10

30 Oct '10

Hello the list, I have another silly question. In my software I have a very common pattern: --in file A.hs module A where data A = A {b :: B, i :: Int} type SA x = State A x -- many functions with SA x --in file B.hs data B = B {r :: Int} type SB x = State B x -- many functions with SB x Of course in module A I'm calling some functions of module B. I'd like to know if it's possible, in a function of type SA, to call a function of type SB, without actually executing the State SB. I just wanna tell him "Hey look, you can construct a SA from a SB like this!" For now I have this: bToA:: (B -> B) -> A -> A bToA bb = (λa -> a{b = bb (b a)}) useB :: SB () -> SA () useB = modify . bToA . execState Can I get rid of the execState? Also, I can't manage to write the more generic function SB x -> SA x. Cheers, Corentin

4 6

libffi mystery
by Conor McBride 29 Oct '10

29 Oct '10

Hi again This is what happens when you write actual for-users for-running programs, I guess. It's been a while... I've been writing some software with Network.CGI etc, which we run on the deparmental web server for my students to use. But we just had a bit of an upgrade on the system, and now (once cabal was properly installed) everything compiles again but nothing works. The reason appears to be that the executables now depend on a dynamic library libffi.so.5 which is not (and I am told cannot become) available on our web server. The current workaround is to compile with 6.8.2, which is survivable and will hopefully get me through the semester, but not ideal. Is there some way I can get some more static linking to happen? I did poke about online a bit and found some remarks to the effect that GHC got so much more portable after switching to the dynamic libffi. That sounds great, but tough luck for me. So, being both powerless and clueless, I can only ask: how hosed am I? I'd be grateful for any glimmers of light. Thanks Conor

3 4

Does it deserve to be a hackage package?
by Dmitry V'yal 29 Oct '10

29 Oct '10

Hello haskellers, While ago I had a question about opening the url in the default browser from haskell program. I didn't get any immediate answers so I wrote my own solution. On Linux it uses xdg-open and on Windows - ShellExecute Api. Later I received a letter saying what similar functionality was recently implemented in trunk version of gtk2hs but is currently unavailable as binary package. Code I wrote works quite well for my purposes and I copied it into several my programs. In order to make maintenance easier I recently thought about uploading it to hackage. But given a wast amount of half-dead packages with intersecting functionality there I'd like to ask the opinion of community. Does such library look helpful to you? Dmitry

4 5

If Python now has a good email library; how challenging is it to call Python from Haskell?
by caseyh＠istar.ca 29 Oct '10

29 Oct '10

:)

8 7

New repo location for the network package
by Johan Tibell 29 Oct '10

29 Oct '10

Hi all, To ease my maintenance burden, I've moved the network package repo to: http://github.com/haskell/network Patches are accepted either in the git mbox format, as normal (diff) patch files, or as GitHub pull requests. P.S. If you want to get added to the haskell GitHub organization, just drop me an email. Johan

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Re: [Haskell-cafe] concurrency vs. I/O in GHC
by John Lato 28 Oct '10

28 Oct '10

From: Claude Heiland-Allen <claudiusmaximus(a)goto10.org> > > On 23/10/10 23:17, Donn Cave wrote: > > Quoth Claude Heiland-Allen<claudiusmaximus(a)goto10.org>, > > ... > >> The conclusion I drew was that "unsafe" foreign functions block the > >> current "capability" (OS thread) and any "threads" (Haskell forkIO etc) > >> currently scheduled on that capability, but other capabilities and > >> threads continue executing as normal. > > ... until GC time when all capabilities must be ready. (?) > That's quite interesting. Thanks very much to everyone who contributed to this. I think my understanding of the interactions between threads and foreign functions has deepened considerably. I may be able to accomplish what I want after all. I am somewhat surprised that all capabilities must be ready for GC; I thought with the parallel GC that wouldn't be necessary. But I don't know much about GC implementations so I try not to let their behavior surprise me too much. John

3 4

Map constructor in a DSL
by Dupont Corentin 28 Oct '10

28 Oct '10

Hello café, I have a little DSL in my program as follow. Now I'd like to add a Map constructor in it. Thats where I would need help! > data Obs a where > AllPlayers :: Obs [Int] > Plus :: (Num a) => Obs a -> Obs a -> Obs a > And :: Obs Bool -> Obs Bool -> Obs Bool > Vote :: Obs String -> Obs Int -> Obs Bool > *Map :: (Obs a -> Obs b) -> Obs [a] -> Obs [b]* > -- and others Here is the evaluator for Obs: > evalObs :: Obs a -> Evaluator a > evalObs (Konst a) = return $ pure a > evalObs (Not a) = liftE not (evalObs a) > evalObs (Plus a b) = liftE2 (+) (evalObs a) (evalObs b) > evalObs (Minus a b) = liftE2 (-) (evalObs a) (evalObs b) > evalObs (Time a b) = liftE2 (*) (evalObs a) (evalObs b) > evalObs (And a b) = liftE2 (&&) (evalObs a) (evalObs b) > evalObs (Or a b) = liftE2 (||) (evalObs a) (evalObs b) > evalObs (Equ a b) = liftE2 (==) (evalObs a) (evalObs b) > evalObs (If a b c) = liftE3 (if3) (evalObs a) (evalObs b) (evalObs c) How you can see it is quite neat... But how can I write the evaluator for Map? Actually I have some half baked solution, 15 lines long that I don't dare to show ;) Actually compiling code excerpt is here: http://hpaste.org/40897/map_contstructor_in_a_dsl Thanks for your help. Corentin Below is some helper code: type Evaluator a = StateT Game Comm a (Either Actions a) -- | Combined lifters for Evaluator liftE = liftM . liftA liftE2 = liftM2 . liftA2 liftE3 = liftM3 . liftA3 instance Applicative (Either Actions) where pure x = Right x (Right f) <*> (Right x) = Right $ f x (Right _) <*> (Left u) = Left u (Left u) <*> (Right _) = Left u (Left u) <*> (Left v) = Left $ u ++ v

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Re: [Haskell-cafe] New repo location for the network package
by John Lato 28 Oct '10

28 Oct '10

> > From: Magnus Therning <magnus(a)therning.org> > > On Wed, Oct 27, 2010 at 22:53, Johan Tibell <johan.tibell(a)gmail.com> > wrote: > > Hi all, > > > > To ease my maintenance burden, I've moved the network package repo to: > > > > Â Â http://github.com/haskell/network > > > > Patches are accepted either in the git mbox format, as normal (diff) > > patch files, or as GitHub pull requests. > > > > P.S. If you want to get added to the haskell GitHub organization, just > > drop me an email. > > Ah, the use of github is spreading :-) > > If I, as the developer of the FOO Haskell package, want to move to use > github, can I get a source repo under that organisation as well? > I'm asking since I am considering taking some of my packages from > patch-tag to github (it's really github I want, it's unfortunate that > it also means I'll have to leave darcs), it would then be nice to have > those repos as a part of the haskell organisation. > Similarly, what's the remit of the Haskell organization on github? Is the intention to be an umbrella for any haskell package, or more restricted? I have the same question as Magnus (although in my case I took over something on github; if I could move to darcs and preserve history I would). John

3 2

Test command line programs
by Dupont Corentin 28 Oct '10

28 Oct '10

Hello again café, I have a command line program that takes input from various handles (actually network sockets) like this: > s <- hGetLine h > etc. I'd like to unit test this. How can I do? I'd like to inject data on the handle so that all the input chain is tested. How are command line programs' IO automatically tested usually? Another little question: How can I access the name of a function inside a function (for Trace purpose)? I have to use the CPP preprocessor? Thanks for hints, Corentin

4 4

ANN: language-java-0.1.0
by Niklas Broberg 28 Oct '10

28 Oct '10

Hi café, I found myself in need of a source manipulation suite for Java code. A hackage search turned up nothing, so I wrote one: http://hackage.haskell.org/package/language-java I'm sure there are a number of bugs waiting to be discovered, my own testing hasn't been overly extensive. I'm setting up a trac, will follow up with its location once it's up. Known short-coming: Annotations are not yet supported. Cheers, /Niklas

1 1

On being called a troll
by Günther Schmidt 28 Oct '10

28 Oct '10

Hi everyone, this post is to argue my own case. Today I have made the most upsetting experience of being called a troll, twice. I have posted to this list for over 3 years now and until lately it was an enlightening experience. The responses to my questions have usually been helpful and friendly. But for some time now, I have noticed that the tone on this list has changed. It seems to have become ok to respond quite brutally and without regard for the other persons feelings. It also seems to have become ok to chime in. For some reason it has become acceptable to politicalize a subject at the earliest convenience and take the gloves off. I am 42 now and am surprised how much this still hurts, after all I survived the schoolyard bullies and who would have thought that these times would ever come again? I urge you, my fellow haskellers, to show some restraint when we are dealing with one another on this list. And to think twice before you launch a personal attack. Günther

4 3

Need programming advice for Network Protocol Parsing
by Günther Schmidt 28 Oct '10

28 Oct '10

Hi all, I'd like to write a client app that communicates with a server over TCP/IP. My question is in regard which parser to use for the servers responses. I'm quite familiar with parsec (2.x) but I'm not sure if it's the right choice for this. The code would necessarily constantly be switching between checking for input, interpreting and then responding. Any suggestions? Günther

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Haskell Weekly News: Issue 156 - October 27, 2010
by Daniel Santa Cruz 28 Oct '10

28 Oct '10

Welcome to issue 156 of the HWN, a newsletter covering developments in the [1]Haskell community in the week of October 17 - 28. I did not manage to filter out good posts from Haskell-Cafe this week. If you see a thread in -cafe that you think would be good to share with the community, please do share it with me. I need to find a better way of keeping up with the mountain of posts to that list. There were a total of 34 new stories posted to the Haskell Reddit channel (+10), 47 new questions taged with Haskell in StackOverflow (+20), and 332 messages posted to Haskell-Cafe (-76). So, what was hot last week? Announcements John Hughes [2]announced that the Functional Programming group at Chalmers is recruiting a postdoctoral researcher for a two year position, starting as soon as possible. Wouter Swierstra [3]called for workshop and co-located event proposals for the ICFP 2011 in Tokyo, Japan. Zhong Shao [4]informed us that the Department of Computer Science at Yale University is seeking applicants for a PostDoc and PhD positions in the broad area of certified software. Josh Tripplett wrote in to tell us about Ore, a [5]packaging system for Ruby inspired by Haskell's Cabal! According to [6]this haskell community calendar, there are 2 events to take note happening next week: The Haskell Communities & Activities Report submission deadline on Nov 1, and BelHac (in Ghent, Belgium) on Nov 5 - 7. Top Reddit Stories * The Haskell Platform is now in Ubuntu Domain: packages.ubuntu.com Score: 58, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/dtffi/the_haskell_platform_is_now_… Original: http://packages.ubuntu.com/maverick/haskell-platform * ghcjs: Haskell to Javascript: now released Domain: github.com Score: 36, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/dujnb/ghcjs_haskell_to_javascript_… Original: http://github.com/sviperll/ghcjs#readme * GHC Blog: New directions for Template Haskell Domain: hackage.haskell.org Score: 32, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/dtav8/ghc_blog_new_directions_for_… Original: http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal * A brief tale of faster equality Domain: serpentine.com Score: 27, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/dt76u/a_brief_tale_of_faster_equal… Original: http://www.serpentine.com/blog/2010/10/19/a-brief-tale-of-faster-equality/ * MTL 2.0 has been uploaded good bye old mtl, hello monads-fd! Domain: hackage.haskell.org Score: 25, Comments: 6 On Reddit: http://www.reddit.com/r/haskell/comments/dx8ml/mtl_20_has_been_uploaded_goo… Original: http://hackage.haskell.org/package/mtl-2.0.0.0 * Haskell Rapid Transit Domain: mtnviewmark.wordpress.com Score: 23, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/duqp0/haskell_rapid_transit/ Original: http://mtnviewmark.wordpress.com/2010/10/21/haskell-rapid-transit/ * mathblog: A program for creating and managing a static, mathematically-inclined weblog Domain: hackage.haskell.org Score: 20, Comments: 0 On Reddit: http://www.reddit.com/r/haskell/comments/duh1o/mathblog_a_program_for_creat… Original: http://hackage.haskell.org/package/mathblog-0.2 * Lazy Type-Level Programming: nice trick by Max Bolingbroke Domain: haskell.org Score: 20, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/duu54/lazy_typelevel_programming_n… Original: http://www.haskell.org/pipermail/haskell-cafe/2010-October/085307.html * Let's build a compiler (in Haskell): Part 12 - Introducing the State Monad Domain: alephnullplex.appspot.com Score: 19, Comments: 14 On Reddit: http://www.reddit.com/r/haskell/comments/du38c/lets_build_a_compiler_in_has… Original: http://alephnullplex.appspot.com/blog/view/2010/10/19/lbach-introducing-the… * What's the status of Haskell on the iPhone? Domain: self.haskell Score: 18, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/dsyij/whats_the_status_of_haskell_… Original: /r/haskell/comments/dsyij/whats_the_status_of_haskell_on_the_iphone/ Top StackOverflow Questions * Question (votes: 33, answers: 8): Best explanation for Languages without Null Read on SO: http://stackoverflow.com/questions/3989264/best-explanation-for-languages-w… * Question (votes: 16, answers: 6): Saving my running toplevel for later Read on SO: http://stackoverflow.com/questions/3966925/saving-my-running-toplevel-for-l… * Question (votes: 10, answers: 2): What's the difference between undefined in Haskell and null in Java? Read on SO: http://stackoverflow.com/questions/3962939/whats-the-difference-between-und… * Question (votes: 9, answers: 2): Is FC++ used by any open source projects? Read on SO: http://stackoverflow.com/questions/3995942/is-fc-used-by-any-open-source-pr… * Question (votes: 8, answers: 3): What is the difference between forall a. [a] and [forall a. a]? Read on SO: http://stackoverflow.com/questions/3961851/what-is-the-difference-between-f… * Question (votes: 6, answers: 5): In Haskell, is there any way to express that a type should be an instance of a typeclass in more than one way? Read on SO: http://stackoverflow.com/questions/3998732/in-haskell-is-there-any-way-to-e… * Question (votes: 5, answers: 3): Pure exceptions in Haskell Read on SO: http://stackoverflow.com/questions/3961536/pure-exceptions-in-haskell * Question (votes: 5, answers: 1): How to use fromInteger with no implicit prelude in Haskell? Read on SO: http://stackoverflow.com/questions/3969413/how-to-use-frominteger-with-no-i… * Question (votes: 5, answers: 7): Is this Fibonacci sequence function recursive? Read on SO: http://stackoverflow.com/questions/3980756/is-this-fibonacci-sequence-funct… * Question (votes: 5, answers: 1): Any Sparse Linear Algebra package in Haskell? Read on SO: http://stackoverflow.com/questions/3995323/any-sparse-linear-algebra-packag… Quotes of the Week If you'd like to have a quote you see in IRC here, use the following syntax: @remember WhoSaidIt Quote. I'm currently scrapping IRC logs to find this data, so don't worry if lambdabot doesn't cooperate. * chrisdone: Production of two-handed use langes Schwerts with long flambard blades and heavily category-theoretically decorated guards, katzbalgers, axes, mail and Macedonian quality defence pikes. Lambda Knights need to be prepared for the inevitable battle against success. HackageDB Updates Who contributed, and what got uploaded? * AlbertoRuiz: hmatrix-special * AlessandroVermeulen: lhs2TeX-hl * AlexanderSolla: Facts * AlexeyKhudyakov: histogram-fill, monoid-statistics, mwc-random-monad * AntonKholomiov: csound-expression, temporal-media * AristidBreitkreuz: monadLib-compose, xml-monad * AycanIrican: hweblib * BasVanDijk: concurrent-extra, dstring, explicit-iomodes, explicit-iomodes-bytestring, explicit-iomodes-text, repr, string-combinators, threads, usb, usb-enumerator * BryanOSullivan: text * ChrisKuklewicz: regex-tdfa, regex-tdfa-unittest * ClaudeHeilandAllen: gmndl, qd * DanielDiaz: HaTeX * DonaldStewart: plugins * EugeneKirpichov: splot * GregWeber: xss-sanitize * HenkJanVanTuyl: GeBoP * HolgerReinhardt: amqp * HugoPacheco: pointless-rewrite * JamesCook: priority-queue, queue * JeremyShaw: formlets-hsp * JoelCrisp: bindings-gts * JohanTibell: network * JohnMillikin: anansi, cpython, enumerator-fd, enumerator, enumerator-tf, yajl-enumerator, yajl * JonathanDaugherty: mathblog * JudeNagurney: augeas * KetilMalde: a50, flower * MagnusTherning: archlinux, archlinux-web, cabal2arch * MasatakeDaimon: bindings-audiofile, bindings-EsounD * MichaelIlseman: yaml-light * MichaelSnoyman: authenticate, convertible-text, data-object-json, data-object, data-object-yaml, hamlet, mime-mail, wai-handler-devel, wai-handler-webkit, web-encodings, yesod-auth, yesod * MichelBoucey: ip6addr * NeilMitchell: hlint * OlegBelozeorov: xmms2-client-glib, xmms2-client * OscarFinnsson: text-xml-qq * PeterSimons: vty * PetrRockai: darcs-fastconvert * RoelVanDijk: base-unicode-symbols, containers-unicode-symbols * RyanNewton: wordsetdiff * SimonMarlow: stm * StephenBlackheath: hexpat * StephenTetley: wumpus-basic, wumpus-microprint, wumpus-tree * ThomasDuBuisson: control-event, crypto-api, gps, hsXenCtrl, ipc * TomHawkins: fountain * ViktorDevecseri: bloxorz About the Haskell Weekly News New editions are posted to [7]the Haskell mailing list as well as to [8]the Haskell Sequence and [9]Planet Haskell. [10]RSS is also available, and headlines appear on [11]haskell.org. To help create new editions of this newsletter, please send stories to dstcruz * at * gmail * dot * com. The code used to produce this version of the newsletter is not yet publicly available, as it is a complete hack designed to get things started again. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18252 3. http://article.gmane.org/gmane.comp.lang.haskell.general/18260 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18261 5. http://postmodern.github.com/2010/10/25/mining-rubygems-from-ore.html 6. https://sites.google.com/site/haskellcommunitycalendar/ 7. http://www.haskell.org/mailman/listinfo/haskell 8. http://sequence.complete.org/ 9. http://planet.haskell.org/ 10. http://sequence.complete.org/node/feed 11. http://haskell.org/

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Re: [Haskell-cafe] If Python now has a good email library; how challenging is it to call Python from Haskell?
by Brandon Moore 28 Oct '10

28 Oct '10

On Oct 27, 2010, at 12:43 PM, caseyh(a)istar.ca wrote: > :) I will point out that "Python Haskell Interface" has an excellent axiom. Unfortunately, my attempt to write a nice wrapper around the Python FFI foundered years ago chasing segfaults. It doesn't seem like it should be too hard, if you get the reference counting right - and tie everything to the GIL (ick).

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Where has GDK.GC gone?
by Andrew Coppin 28 Oct '10

28 Oct '10

Today I noticed a small but interesting fact: Under Gtk2hs 0.10.x, the module Graphics.UI.Gtk re-exports (amoung countless others) the module Graphics.UI.Gtk.Gdk.GC. However, under Gtk2hs 0.11.x, it does not. After downloading the darcs repo (with took forever, by the way), I discovered that the requisit line still exists in the source code, but it has been commented out. My repeated attempts to force Darcs to tell me exactly which patch did this resulted only in Darcs locking up again and again. (I'm quite surprised at that. Usually all Darcs operations are instantaneous. I guess the local repo is corrupt somehow or something...) So anyway, what I'd like to know is... was this alteration intensional? Or was it just an oversight? PS. The link on the website that says "browse the darcs repo online"? Apache just returns 404 at me. This is not particularly helpful.

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Haskell and a complete mail client lib?
by Günther Schmidt 28 Oct '10

28 Oct '10

Hi all, do we Haskellers have a complete Mail client library? One that goes beyond an unstructured byte string? Günther

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Pretty-printer for Text
by Ivan Lazar Miljenovic 27 Oct '10

27 Oct '10

I'm currently working on a pretty-printer for lazy text [1] values, basing the API on the wl-pprint [2] package. [1]: http://hackage.haskell.org/package/text [2]: http://hackage.haskell.org/package/wl-pprint In terms of API decisions, there are a few things I'm not sure of and am wondering what other people would prefer: * Should the SimpleDoc type still be exported? Or should the rendering functions just return a Builder or lazy Text value? * Is the Pretty class wanted/needed? If so, should the individual combinators (int, bool, etc.) be kept or just use "pretty" for everything? * Should String values be catered for or just have everything be Text-based? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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ANN: timeplot-0.2.1, a tool for visualizing time series from log files.
by Eugene Kirpichov 27 Oct '10

27 Oct '10

Hi cafe, I'm pleased to announce timeplot-0.2.1. http://hackage.haskell.org/package/timeplot This is a tool for visualizing time series from log files. I'm myself using it for diagnosing performance of distributed systems: I aggregate their logs and plot various things, such as the number of tasks executing on each machine of the cluster, or quantiles of database query times, etc. See pretty pictures on haskellwiki: http://www.haskell.org/haskellwiki/Timeplot This version has several changes, which together raised the program's usefulness for me tremendously: - The program now builds and works on Windows! You just need gtk2hs. I got rid of strptime and pcre dependencies (strptime is built from bundled and patched source, and I use regex-tdfa by Chris Kuklewicz). - Support for millisecond precision on charts (thanks to the new 0.14 version of Tim Docker's excellent Chart library) - Support for millisecond precision in input (because I re-did strptime to compile from scratch with support for the %OS pattern, which recognizes fractional seconds) - Support for selecting a range of the input (however, non-interactively) with "-fromTime/-toTime" - Support for "duration" plots: given an event track (where events of something beginning or ending are recorded), you can produce all kinds of plots over the durations of these events. - Support for colored "status" plots: now event tracks represent not purely the presence or absence of an active event, but an event track can be colored, representing several states of a subsystem or subprocess. Please use the program and provide feedback :) I have a hope that it could become a reasonably widely used tool for the kinds of tasks that I use it for. -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

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cross-platform compile
by Hong Yang 27 Oct '10

27 Oct '10

Just curious if Haskell can or will generate cross-platform executable code, e.g., generate code for Linux from a Windows machine. Thanks, Hong

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ANN: Chart v0.14
by Tim Docker 27 Oct '10

27 Oct '10

I'm pleased to announce v0.14 of the haskell chart library. This is a library for drawing 2D data plots. It's features include + Use of the cairo graphics engine, supporting a variety of output types: ps, pdf, png, and gtk windows. + A variety of plot types, including: points, lines, error bars, candlesticks, bar charts and pie charts. + Strong typing. Charts are parameterized by the types of their coordinates. One benefit of this is that labels etc are automatically generated appropriately for the type of the data. Currently axis types include: Double, Int, Log, LocalTime, and Indexed. + (some) support for interactivity. Charts support dynamic resizing, and mapping from device coordinates back to source values. The library is available on hackage. Additional information including details of the mailing list can be found here: http://dockerz.net/software/chart.html Thanks to Malcolm Wallace, Eugene Kirpichov, and Matt Brown for their contributions to this release. Tim Docker ---------------------------------------------------------------------- New features in v0.14 --------------------- * Plot Type: AreaSpots4D Spots with varying area and colour * Plot Type: CandleStick charts A specific type of plot often used in financial markets for stock price series. * Multiline text in Annotation Plots with flexible control over the anchoring. * Picking. The library now contains logic required to map device coordinates back to input elements. This facilitates interactivity. See tests/TestPicking.hs. * Multiple Layers of axis labels This is currently used by the LocalTime axis to show an additional set of context labels - these show the next sensible granularity of time enclosing the more detailed labels and ticks. * Avoid overlapping axis labels The axis rendering code now skips labels where there would be overlaps. This is done dynamically as the chart is rendered. * Code refactor Plots and axes have been split into separate file hierarchies, with one file per type. This makes it easier to understand, and (hopefully) makes it clearer how to add new plot types.

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Help me TH code.
by Andy Stewart 27 Oct '10

27 Oct '10

Hi all, I want use TH write some function like below: data DataType = StringT | IntT | CharT parse :: [(String,DataType)] -> (TypeA, TypeB, ... TypeN) Example: parse [("string", StringT), ("001", IntT), ("c", CharT)] will return: ("string", 001, 'c') So how to use TH write 'parse' function? Thanks! -- Andy

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Understanding Iteratees
by Arnaud Bailly 27 Oct '10

27 Oct '10

Hello, I am trying to wrap my head around the concept of Iteratee reading the article by John Lato in Monad Reader issue 16 (http://themonadreader.files.wordpress.com/2010/05/issue16.pdf) I followed the "advice" on page 34: "I have frequently heard reports from Haskellers (including highly-talented and experienced users) that the only way they could understand enumeration-based I/O was by re-implementing it themselves." and so reimplemented this code in Java which is, for better and worse, my current professional language (and there really is no point in writing my own 50th iteratee code...). I have a question about iteratees composition and their behaviour. I tried to use the throbber code to display progress while writing a file, without using enumeratees which are introduced later on in the article, but failed. I can bind the two iteratees together, but the writer iteratee consumes the stream of characters to write before handing over the control to the throbber iteratee which has nothing to count. Did I miss something ? Thanks in advance, Arnaud

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