- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] How to define an operation in terms of itself (but of different type)?
by Olex P 24 Jan '09

24 Jan '09

Well if telepaths on vacation... class Vector v where (^+^) :: v -> v -> v data Vector3 = V3 !Double !Double !Double instance Vector Vector3 where (V3 x1 y1 z1) ^+^ (V3 x2 y2 z2) = V3 (x1 + x2) (y1 + y2) (z1 + z2) class Matrix m where (^+^) :: m -> m -> m data Matrix3 = M3 !Vector3 !Vector3 !Vector3 instance Matrix Matrix3 where (M3 r11 r12 r13) ^+^ (M3 r21 r22 r23) = M3 (r11 ^+^ r21) (r12 ^+^ r22) (r13 ^+^ r23) Hope this is better :) So yeah... r11 ^+^ r21 just doesn't work.

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Generalizing a filter-making function
by Dominic Espinosa 24 Jan '09

24 Jan '09

Novice question here. Sorry if the post is wordy. In the following code (which doesn't actually compile as-is), I'm trying to generalize these 'make*Filter' functions into a single 'makeFilter' function. However, I can't get the types to work right. Foo is a tuple type on which a large number of accessor functions are defined. All of them have type Foo -> Int, Foo -> String, or Foo -> [a] (so far). I tried defining 'Query' using exsistential types instead, but had difficulty with 'escaped type variables' when I tried to write a generalized 'makeFilter' function. The general point of makeFilter is to take as parameters a Query, a value, a comparison function, and then return a function (Foo -> Bool). This returned function takes as its argument an object of type Foo, applies the function 'q' to it, compares that value to 'val', and finally returns a Bool. Later on in the program, a list of these filter functions is to be used with a list of Foo objects, to determine which Foo objects satisfy all of the filters. Advice would be greatly appreciated. --- code --- data Query a = Query { query_identifier :: String, query_func :: (Foo -> a) } makeIntFilter :: Query Int -> Int -> (Int -> Int -> Bool) -> (Foo -> Bool) makeIntFilter q val cmp = (\k -> val `cmp` (query_func q $ k)) makeStringFilter :: Query String -> String -> (String -> String -> Bool) -> (Foo -> Bool) makeStringFilter q val cmp = (\k -> val `cmp` (query_func q $ k)) -- ??? broken, and the 'cmp' argument is thrown away, which seems wrong makeMemberFilter :: Eq a => Query [a] -> a -> (a -> a -> a) -> (Foo -> Bool) makeMemberFilter q val cmp =(\k -> val `elem` (query_func q $ k))

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Error in HTTP 4.004 + CouchDB?
by Alex Ott 24 Jan '09

24 Jan '09

Hello (i sent this message to the mail of author, specified at hackage, but it returned to me, so i decided to resend it here) I found strange thing during work with latest versions of CouchDB & HTTP module on my Mac OS X 10.4. The problem is, that when i send document to the couchdb server, it name was cut to the 2 characters. After some investigation i found, that this is problem in combination of the CouchDB + HTTP usage. CouchDB module fills out the Request structure, and specify scheme & authority fields. This lead that i see (in network dumps) following data: PUT http://127.0.0.1:5984/test1/Users_ott_tmp_1_tst HTTP/1.1 Content-Type: ... ... Host: 127.0.0.1:5984 ... instead of proper PUT /test1/Users_ott_tmp_1_tst HTTP/1.1 I can eliminate this by explicitly setting of the scheme & authority into empty values, but this lead to improper creation of the Host header in request: PUT /test1/Users_ott_tmp_1_tst HTTP/1.1 Content-Type: ... ... Host: ... I tried to fix this problem myself, but I'm novice in the industrial Haskell programming ;-) P.S. this code from (CouchDB/HTTP.hs) will restore proper behaviour of the code, but break Host header makeURL path query = CouchMonad $ \conn -> do return ( (ccURI conn) { uriPath = '/':path , uriQuery = if null query then "" else '?':(urlEncodeVars query) , uriScheme = "" , uriAuthority = Nothing } ,conn ) -- With best wishes, Alex Ott, MBA http://alexott.blogspot.com/ http://xtalk.msk.su/~ott/ http://alexott-ru.blogspot.com/

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How to define an operation in terms of itself (but of different type)?
by Olex P 24 Jan '09

24 Jan '09

Hello Haskellers! It's probably a simple question but I can't find a proper solution... Suppose we have a class Vector which overloads (+) operation. I'd like to represent a Matrix data type as a set of vectors: data Matrix3 = M3 !Vector3 !Vector3 !Vector3 In this case (+) for matrices could be implemented as: (M3 r11 r12 r13) + (M3 r21 r22 r23) = M3 (r11 + r21) (r12 + r22) (r13 + r23) But GHC says about ambiguous occurrence. I don't understand why because it's should be pretty clear that rows are vectors and (+) has to be vector type as well. I could use Vector.+ instead but it doesn't look good. Probably I'm missing something. Any ideas? Cheers, Oleksandr.

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Employment
by Andrew Coppin 24 Jan '09

24 Jan '09

Is it possible to earn money using Haskell? Does anybody here actually do this? Inquiring minds want to know... ;-)

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mapM_ -> Monoid.Monad.map
by Henning Thielemann 24 Jan '09

24 Jan '09

I always considered the monad functions with names ending on '_' a concession to the IO monad. Would you need them for any other monad than IO? For self-written monads you would certainly use a monoid instead of monadic action, all returning (), but IO is a monad. (You could however wrap (newtype Output = Output (IO ())) and define a Monoid instance on Output.) However our recent Monoid discussion made me think about mapM_, sequence_, and friends. I think they could be useful for many monads if they would have the type: mapM_ :: (Monoid b) => (a -> m b) -> [a] -> m b I expect that the Monoid instance of () would yield the same efficiency as todays mapM_ and it is also safer since it connects the monadic result types of the atomic and the sequenced actions. There was a recent discussion on the topic: http://neilmitchell.blogspot.com/2008/12/mapm-mapm-and-monadic-statements.h…

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Re: [Haskell-cafe] MySQL and HDBC?
by Duncan Coutts 24 Jan '09

24 Jan '09

On Fri, 2009-01-23 at 03:54 -0600, Galchin, Vasili wrote: > On Fri, Jan 23, 2009 at 3:23 AM, Duncan Coutts > <duncan.coutts(a)worc.ox.ac.uk> wrote: > > This was uploaded to hackage yesterday: > > http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-mysql-0.1 > > You might like to test it and give feedback to the > author. > ooops ... cabal install HDBC-mysql doesn't work ....?? > > Vasili Vasili, it's really no good telling me this, especially since you did not cc the author or haskell-cafe. I am not the author of the package. And even if I were you have provided no details on what goes wrong. I'm sure it was not your intention, but to some people your response would sound demanding and unhelpful, possibly even rude. Make sure that when you do contact the author that you send them something that they will find helpful. So when you email the author make sure you provide full details about what you did and about the environment you are using, eg platform, ghc version, where your mysql libraries are installed, what version they are etc. I would guess that the most likely problem is that you do not have the mysql development package installed. It should provide the mysql_config program. If that is not the problem then contact the package author with the full details. Duncan

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Haskell mode for Emacs question
by Peter Verswyvelen 24 Jan '09

24 Jan '09

I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load "src/main.hs" But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load "main.hs" then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter

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Good books on advanced topics
by Mark Spezzano 24 Jan '09

24 Jan '09

Hi, Is there a good book on some of the more advanced or esoteric Haskell topics, like monads, and morphisms, category theory etc. Cheers, Mark No virus found in this outgoing message. Checked by AVG. Version: 7.5.552 / Virus Database: 270.10.12/1910 - Release Date: 22/01/2009 6:28 PM

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Is it possible to model eventually consistent side effects?
by Daryoush Mehrtash 23 Jan '09

23 Jan '09

I am trying to figure out if there is a way to model cloud computing computations in Haskell. My specific problems is that in cloud computing, as in Amazon WebServices, side effects (writes to storage, simple database, queue) follow the eventually consistent model. Which means even if your writes succeeds, it may or may not be immediately available for reads. Each call to the services may also temporarily experience network errors or end-system unavailability. Virtual machines can mount a local disk that does offers consistent storage, but the storage wont survive a reboot (after a crash). I am trying to find out if I can model computation (and its compositions) where I can hide reliability and consistency issues. And also be able to reason about a computation to make sure no combination of errors and inconsistencies would break my logic. Is it possible? If so is there a good starting point? -- Daryoush

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Liskell installation configuration problems in Cygwin on Windows XP Professional, Service Pack 2
by Benjamin L.Russell 23 Jan '09

23 Jan '09

Yesterday, I downloaded Darcs 2.2 and Liskell for Windows XP Professional, Service Pack 2, but the following error message appeared when I ran "./Setup.lhs configure" in Cygwin: Configuring liskell-0.1... Setup.lhs: At least the following dependencies are missing: ghc-paths -any Does anybody know how this issue should be resolved? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Re: [Haskell-cafe] Employment
by George Pollard 23 Jan '09

23 Jan '09

On Fri, 2009-01-23 at 16:19 +1100, Toby Hutton wrote: > On Fri, Jan 23, 2009 at 11:56 AM, Jonathan Cast > <jonathanccast(a)fastmail.fm> wrote: > > > > Not really. My company *advertises* for Haskell developers, and then > > when they come in to interview, informs them that the code base is > > actually written in Perl. Works, too --- we have several Haskellers > > working here. If all you care about is the quality of the developers, > > and not their productivity once you've got them, you don't actually need > > to let them use Haskell after the interview is over... > > I saw this trick recently for a job advertised locally to me, in > Melbourne. I was initially pretty excited that someone in this city > was actually advertising for Haskell programmers, until I realised > they needed to be good at Javascript and Perl so they could work on > their web apps. Argh, I didn't bother applying. I think I saw the same advertisement; unfortunately it was on a joint Australasian website so I was in the wrong country anyway :)

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Moving nobench towards HaBench
by Andy Georges 23 Jan '09

23 Jan '09

Hello, A while back, we had a discussion on #haskell about assembling a Haskell benchmark suite, that is suitable for doing performance tests. A preliminary page was erected athttp://www.haskell.org/haskellwiki/HaBench . In the meantime, Donald Steward extended the original nofib suite with some shootout benchmarks afaik, resulting in nobench. The code base for the latter currently resides at http://code.haskell.org/nobench/ . I have been trying to get it running on GHC 6.10.1. For now, I added a number of type definitions to the code, causing the build/runtime system to compile. The same probably ought to be done for the benchmarks themselves, unless there is a cheat around this using some language extension. Anyhow, I'll post a patch against the current repository as soon as I have a number of benchmarks running. The main issue that still remains is the availability of real life benchmarks. I agree with the fact that micro-benchmarks can be useful for testing purposes or measures the efficacy and effectiveness of certain optimisations, yet I firmly believe any community has need of a set of benchmarks that actually reflects the real life usage of the language. I am think along the lines of something alike to the DaCapo projects, which assembled a number of very good benchmarks for the Java language and its VM. So the question basically boils down to this. Is there anybody interested in making the move toward HaBench, and if so, do you know of real life benchmarks that can serve for this exact purpose? The benchmarks should preferably execute for > 10s on modern machines, using a decent amount of RAM (say somewhere between 50 and 500MB), thus exercising all parts of a modern computing system. The code should not be trivial and the set of benchmarks should eventually cover the most uses of Haskell in the industry. Of course, the benchmarks themselves should be open source. If possible, they should come with multiple inputs, allowing a short (test) run as well as longer measurement runs. If you are able and willing to help out, drop by at the HaBench page and drop a line, -- Andy

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Processor availability
by Louis Wasserman 23 Jan '09

23 Jan '09

How might I go about finding out how many processors are available in a concurrent GHC program? I have some code I'd like to parallelize, but I don't want to spawn a separate (even lightweight) thread for each of thousands of minor tasks. Louis Wasserman wasserman.louis(a)gmail.com

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Big endian vs little endian in Haskell land?
by Galchin, Vasili 23 Jan '09

23 Jan '09

Hello, Are there applications that have to deal with both(!!!) big endian and little endian on persistent store?? I.e. when marshalling out and unmarshalling in "endian-ness" has to be considered?? Regards, Vasili

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Question about allocaArray and friends
by Patrick Perry 23 Jan '09

23 Jan '09

In C, if you try to "alloca" too much memory, then the stack gets overwritten and bad things happen. Does GHC exhibit the same behavior with allocaArray and the like? Is there a way to find out how much is safe to allocate? Thanks in advance for the help, Patrick

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Factoring into type classes
by Patai Gergely 23 Jan '09

23 Jan '09

Hi everyone, I have a general program design question, but I can't really think of good examples so it will be a bit vague. There was a discussion on Show not long ago which brought up the problem that there are several ways to "show" a data structure, and it depends on the context (or should I call it a use case?) which of these we actually want, e.g. human readable form, debug information, serialisation for later reading and so on, and one of the solutions was to propose a family of show functions that carry the intended use in their name. However, there are other type classes that are too general to assign such concrete uses to. For instance, if a data structure can have more than one meaningful (and useful) Functor or Monoid instance, what should one do? Should one refrain from instantiating these classes altogether and just use the names of operations directly? If one still decides to pick a certain set of operations as an instance, what are the factors that should guide this decision? What about designing libraries, how much should one prefer standard classes for their interfaces? It seems to me that there is practically no literature on design issues like these, and it would be nice to hear some opinions from experienced Haskellers. Gergely -- http://www.fastmail.fm - The way an email service should be

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ANN: STM-IO-Hooks-0.0.1
by Peter Robinson 23 Jan '09

23 Jan '09

This library provides an STM monad with commit and retry IO hooks. A retry-action is run (once) in a separate thread if the transaction retries, while commit-actions are executed iff the transaction commits. The code is based on the AdvSTM Monad [1] by Chris Kuklewicz, but in addition also ensures some atomicity guarantees for commit-actions, see documentation for details. Cheers, Peter [1] http://www.haskell.org/haskellwiki/New_monads/MonadAdvSTM

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Comments from OCaml Hacker Brian Hurt
by John Goerzen 23 Jan '09

23 Jan '09

Hi folks, Don Stewart noticed this blog post on Haskell by Brian Hurt, an OCaml hacker: http://enfranchisedmind.com/blog/2009/01/15/random-thoughts-on-haskell/ It's a great post, and I encourage people to read it. I'd like to highlight one particular paragraph: One thing that does annoy me about Haskell- naming. Say you've noticed a common pattern, a lot of data structures are similar to the difference list I described above, in that they have an empty state and the ability to append things onto the end. Now, for various reasons, you want to give this pattern a name using on Haskell's tools for expressing common idioms as general patterns (type classes, in this case). What name do you give it? I'd be inclined to call it something like "Appendable". But no, Haskell calls this pattern a "Monoid". Yep, that's all a monoid is- something with an empty state and the ability to append things to the end. Well, it's a little more general than that, but not much. Simon Peyton Jones once commented that the biggest mistake Haskell made was to call them "monads" instead of "warm, fluffy things". Well, Haskell is exacerbating that mistake. Haskell developers, stop letting the category theorists name things. Please. I beg of you. I'd like to echo that sentiment! He went on to add: If you?re not a category theorists, and you're learning (or thinking of learning) Haskell, don't get scared off by names like "monoid" or "functor". And ignore anyone who starts their explanation with references to category theory- you don't need to know category theory, and I don't think it helps. I'd echo that one too. -- John

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Elegant external sorting
by Bulat Ziganshin 23 Jan '09

23 Jan '09

Hello haskell-cafe, SPJ asked us a few years ago about examples of simple and elegant haskell programs. i want to propose this external sorting program: it reads stdin in chunks of 5000 lines, writes sorted chunks into files and then merges files together: import Data.List import Control.Monad import Control.Arrow main = do -- (Lazily) create sorted sublists sublists <- fmap chop_and_sort getContents -- Write the sublists into files named 1..n n <- fmap length $ zipWithM writeFile (map show [1..]) sublists -- Read (again lazily) contents of these files sublists <- mapM (fmap lines.readFile.show) [1..n] -- Merge them and write result to stdout putStr (unlines (merge_lists compare sublists)) -- Split input list into 5000-line chunks and sort them chop_and_sort = lines >>> recursive (splitAt 5000) >>> map (sort>>>unlines) -- unfoldr variant that stops on empty list recursive splitFunc = unfoldr (\xs -> guard (xs>[]) >> Just (splitFunc xs)) -- Merging sorted lists (kidnapped from Data.List) merge_lists :: (a -> a -> Ordering) -> [[a]] -> [a] merge_lists cmp [] = [] merge_lists cmp [xs] = xs merge_lists cmp xss = merge_lists cmp (merge_pairs cmp xss) merge_pairs :: (a -> a -> Ordering) -> [[a]] -> [[a]] merge_pairs cmp [] = [] merge_pairs cmp [xs] = [xs] merge_pairs cmp (xs:ys:xss) = merge cmp xs ys : merge_pairs cmp xss merge :: (a -> a -> Ordering) -> [a] -> [a] -> [a] merge cmp xs [] = xs merge cmp [] ys = ys merge cmp (x:xs) (y:ys) = case x `cmp` y of GT -> y : merge cmp (x:xs) ys _ -> x : merge cmp xs (y:ys) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Pure Haskell implementation of Float type?
by Tim Chevalier 23 Jan '09

23 Jan '09

Hello, Is there a pure Haskell implementation of Floats, i.e., one that (unlike GHC.Float) doesn't use foreign calls for things like isFloatNegativeZero? I don't care about performance; I'm just looking for something that doesn't use foreign calls. Thanks, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt "It is easy to keep secrets by being honest in an ironic tone of voice." -- Andrew Solomon

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How to make code least strict?
by Robin Green 22 Jan '09

22 Jan '09

What guidelines should one follow to make Haskell code least-strict? -- Robin

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Cabal.exe is available from http://haskell.org/~duncan/cabal/, but is not included in the latest cabal-install tool (version 0.6.0).
by Benjamin L.Russell 22 Jan '09

22 Jan '09

I just tried to install the cabal-install tool (version 0.6.0) (see http://www.haskell.org/cabal/download.html) on Windows XP, Service Pack 2, but when I followed the instructions on the download page and downloaded cabal-install-0.6.0.tar.gz, the gunzipped untarred cabal-install-0.6.0 directory did not include cabal.exe. Further, according to the bundled README file: >Quickstart on Windows systems >----------------------------- > >For Windows users we hope to provide a pre-compiled `cabal.exe` program shortly. >In the mean time you have to build the three dependencies in [the standard way]. > >[the standard way]: > http://haskell.org/haskellwiki/Cabal/How_to_install_a_Cabal_package Running the bundled bootstrap.sh file in Cygwin resulted in an installation error. However, when I then visited the above-mentioned HaskellWiki page, I discovered that cabal.exe, in fact, already existed: >... Windows users can download a binary (cabal.exe) from here. ("Here" currently references http://haskell.org/~duncan/cabal/.) Apparently, this cabal.exe file is in fact the complete cabal-install tool (version 0.6.0) itself: (After adding the cabal.exe installation directory to the path:) >C:\Documents and Settings\Benjamin>cabal --version >cabal-install version 0.6.0 >using version 1.6.0.1 of the Cabal library To facilitate installation for Windows users, perhaps cabal.exe should be bundled with cabal-install-0.6.0.tar.gz, and the README file updated? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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GLUT (glutGet undefined reference)
by Paul Keir 22 Jan '09

22 Jan '09

Hi all, I was hoping to introduce my old pal OpenGL with my new chum, Haskell. I used cabal to install GLUT on my 64-bit Ubuntu machine with GHC 6.8.2 (installed via apt-get/synaptic). I followed the wiki OpenGLTutorial1 until: ghc -package GLUT HelloWorld.hs -o HelloWorld at which point my screen is filled with errors. The errors begin with: /home/paul/.cabal/lib/GLUT-2.1.1.2/ghc-6.8.2/libHSGLUT-2.1.1.2.a(Begin.o): In function `szEn_info': (.text+0x26c): undefined reference to `glutGet' This surprised me a little because I've already seen these same errors recently on two separate Windows boxes. Somehow I'd got the idea it was (on Windows) due to installing from a binary; though I guess the story is the same with apt-get. Should I look for an apt-get switch to reinstall GHC from source instead? Regards, Paul

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tensor product of dynamic-sized bits
by Ahn, Ki Yung 22 Jan '09

22 Jan '09

For some reasons, I am trying to write a small Haskell code for tensor products (See http://en.wikipedia.org/wiki/Tensor_product) of bits, which can expand or shrink their size and dimension as needed. Has anyone already done similar or more general work before? If so, I'd be happy use/consult that and cite the work. Otherwise, I should think about cleaning up and packaging this as a library. My code is like this right now: > data Bits = O -- all 1 bits of any size and dimension > | I -- all 0 bits of any size and dimension > | Bs [Bits] -- row of bits possibly nested > | Rep Bits -- repeating of bits (e.g. O = Rep O = Bs [O,O]) > deriving (Eq,Show) bitwise-and > O .& _ = O > _ .& O = O > (Rep O) .& _ = O > _ .& (Rep O) = O > (Bs (O:xs)) .& _ | all (O==) xs = O > _ .& (Bs (O:xs)) | all (O==) xs = O > I .& y = y > x .& I = x > (Rep I) .& y = y > x .& (Rep I) = x > (Bs (I:xs)) .& y | all (I==) xs = y > x .& (Bs (I:ys)) | all (I==) ys = x > (Bs xs) .& (Bs ys) = reduce $ Bs (zipWith (.&) xs ys) > (Rep x) .& (Bs ys) = reduce $ Bs (xs .&. ys) where xs=repeat x > (Bs xs) .& (Rep y) = reduce $ Bs (xs .&. ys) where ys=repeat y > (Rep x) .& (Rep y) = reduce $ Rep (x .& y) > > (.&.) = zipWith (.&) bitwise-or > O .| y = y > x .| O = x > (Rep O) .| y = y > x .| (Rep O) = x > (Bs (O:xs)) .| y | all (O==) xs = y > x .| (Bs (O:ys)) | all (O==) ys = x > I .| _ = I > _ .| I = I > (Rep I) .| _ = I > _ .| (Rep I) = I > (Bs (I:xs)) .| _ | all (I==) xs = I > _ .| (Bs (I:ys)) | all (I==) ys = I > (Bs xs) .| (Bs ys) = reduce $ Bs (xs .|. ys) > (Rep x) .| (Bs ys) = reduce $ Bs (xs .|. ys) where xs=repeat x > (Bs xs) .| (Rep y) = reduce $ Bs (xs .|. ys) where ys=repeat y > (Rep x) .| (Rep y) = reduce $ Rep (x .| y) > > (.|.) = zipWith (.|) tensor product > O .* _ = O > _ .* O = O > (Rep O) .* _ = O > _ .* (Rep O) = O > (Bs (O:xs)) .* _ | all (O==) xs = O > _ .* (Bs (O:ys)) | all (O==) ys = O > I .* I = I > I .* (Rep y) = I .* y > (Rep I) .* y = I .* y > (Bs (I:xs)) .* y | all (I==) xs = I .* y > I .* y = reduce $ Rep y > x .* (Rep I) = x .* I > x .* (Bs (I:xs)) | all (I==) xs = x .* I > x .* I = x > (Bs xs) .* (Bs ys) = reduce $ Bs (xs .*. ys) > (Bs xs) .* (Rep y) = reduce $ > Bs (map (reduce . Rep) $ xs .*. [y]) > (Rep x) .* y = reduce $ Rep (x .* y) > > [] .*. _ = [] > (x:xs) .*. ys = (reduce $ Bs [x .* y | y<-ys]) : (xs .*. ys) reducing from Bs [O,O,..] to O and from Bs [I,I,..] to I > reduce (Bs (x:xs)) | all (x==) xs = x > reduce (Rep x@(Rep _)) = x > reduce x = x Some example run on Hugs: Main> Bs [I,O] Bs [I,O] Main> Bs [I,O] .| Bs [O,Bs [I,I,I,I] .* Bs [I,O,O,O,O]] Bs [I,Rep (Bs [I,O,O,O,O])] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] Bs [I,Bs [I,Bs [I,O,O,O,O],Bs [I,O,O,O,O],Bs [I,O,O,O,O]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] Bs [I,Bs [I,Bs [I,I,I,O,O],Bs [I,I,I,O,O],Bs [I,O,O,O,O]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] .| Bs [O, Bs [O,I,I,I] .* Bs [O,O,O,I,I]] Bs [I,Bs [I,I,I,Bs [I,O,O,I,I]]] Main> Bs [I,O] .| Bs [O, Bs [I,I,I,I] .* Bs [I,O,O,O,O]] .| Bs [O, Bs [I,O,O,O] .* Bs [I,I,I,I,I]] .| Bs [O, Bs [O,I,I,O] .* Bs [O,I,I,O,O]] .| Bs [O, Bs [O,I,I,I] .* Bs [O,O,O,I,I]] .| Bs [O, Bs [O,O,I,I] .* Bs [O,I,I,O,O]] I

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Re: [Haskell-cafe] A pattern type signature cannot bind scoped type variables `t'
by George Pollard 22 Jan '09

22 Jan '09

On Mon, 2009-01-12 at 20:24 -0200, rodrigo.bonifacio wrote: > Hi all, > > I'm trying to build a library that has the following code: > > hasTypeOf (TermRep (dx,_,_)) (x::t) > = ((fromDynamic dx)::Maybe t) > Could you do something like this? Enforce the types with a signature: hasTypeOf :: (Typeable t) => Dynamic -> t -> Maybe t hasTypeOf x _ = fromDynamic x > hasTypeOf (toDyn (2::Int)) (undefined::Integer) Nothing > hasTypeOf (toDyn (2::Int)) (undefined::Int) Just 2 Or if you just want boolean result: hasTypeOf x y = typeOf y == dynTypeRep x

1 0

1000 libraries
by Don Stewart 22 Jan '09

22 Jan '09

We've done it! http://hackage.haskell.org/cgi-bin/hackage-scripts/stats 274 users have uploaded 3161 versions of 1000 packages. Thanks everyone who has written a library or tool or app and released it, for making hackage and cabal a success! This has gone further, perhaps more than anything else, towards making it possible to use Haskell in industry. The lucky 1000th package is: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/threadPool-0.1 threadPool: Runs other programs in the manner of a thread pool Takes a single, optional argument which is the number of threads (the default is three). Give it the commands to run, one per line, through standard input. Author Brian Jaress Now, onto 10k libraries! -- Don

3 2

Re: Why monoids will abide...
by Andrzej Jaworski 22 Jan '09

22 Jan '09

Monads are monoids in categories of functors C -> C Arrows are monoids in subcategories of bifunctors (C^op) x C -> C Trees are a playing ground for functors in general:-)

5 7

Applicative/Monad for Either
by Tony Morris 22 Jan '09

22 Jan '09

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 In the code below, the Applicative instance accumulates on the Left constructor using Monoid/mappend. Is it possible to write an equivalent Monad such that ap = (<*>) ? I'm finding difficulty in proving to myself either way. import Control.Monad.Instances import Control.Applicative import Data.Monoid newtype Z e a = Z { either :: Either e a } instance Functor (Z e) where fmap f (Z e) = Z (f `fmap` e) instance (Monoid e) => Applicative (Z e) where pure = Z . Right (Z (Left e1)) <*> (Z (Left e2)) = Z (Left (e1 `mappend` e2)) (Z (Left e1)) <*> (Z (Right _)) = Z (Left e1) (Z (Right _)) <*> (Z (Left e2)) = Z (Left e2) (Z (Right f)) <*> (Z (Right a)) = Z (Right (f a)) instance (Monoid e) => Monad (Z e) where return = pure (Z e) >>= f = error "todo" -- ? - -- Tony Morris http://tmorris.net/ S, K and I ought to be enough for anybody. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFJd5vImnpgrYe6r60RAoUNAJ4jn0GfC6zsP9giPGop1ILExiHrLQCfSoc2 0QXf533sWb3HyrL0pQNjMww= =R36O -----END PGP SIGNATURE-----

3 2

Haddock bug for strict unpacked fields?
by Stephan Friedrichs 22 Jan '09

22 Jan '09

Hi, using haddock-2.4.1 and this file: > module Test where > > data Test > = NonStrict Int > | Strict !Int > | UnpackedStrict {-# UNPACK #-} !Int The generated documentation looks like this: data Test Constructors NonStrict Int Strict !Int UnpackedStrict !!Int Note the double '!' in the last constructor. This is not intended behaviour, is it? //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr

3 2

Existencial quantification and polymorphic datatypes
by Mauricio 22 Jan '09

22 Jan '09

Hi, I'm trying, without success, to understand the difference between existencial quantification and polymorphic datatypes. Can you give me a hint, or an example where one is valid and the other is not? Thanks, Maurício

9 13

Re: [Haskell-cafe] haskell-src-meta Package
by Matt Morrow 22 Jan '09

22 Jan '09

Hi, I managed to miss not one, but two separate emails containing patches to haskell-src meta. My sincere apologies to those who've sent me patches. I'll be applying them among other improvement to src-meta and will update the package on hackage in short time (today :). Matt

1 0

(no subject)
by Matt Morrow 22 Jan '09

22 Jan '09

Hi, I managed to miss not one, but two separate emails containing patches to haskell-src meta. My sincere apologies to those who've sent me patches. I'll be applying them among other improvement to src-meta and will update the package on hackage in short time (today :). Matt

1 0

Elevator pitch for functional programming
by Jim Burton 22 Jan '09

22 Jan '09

Hi, I will be a TA on a comparative PL course and I'm looking for small examples (ammunition) which motivate the use of Haskell and functional programming generally. The course is for 1st year Software Engineers, none of whom are likely to have used a functional language. They will all have experience programming Java and a little C++, with a few of them knowing Python, Ruby, PHP etc etc too. If anyone has code snippets which are the equivalent of an elevator pitch for FP, I would be very grateful to see them. What I want are some small concrete examples of idioms which are natural and powerful in Haskell but difficult or impossible in, say, Java. So I can produce examples of some of the things that make FP powerful, elegant, expressive etc: higher order functions, polymorphism, composition (ask them to write (.) in Java :-)), partial application and so on. I will point any interested souls to Hughes' great paper [1]. But I have little time and it might be hard to put across why they would want to do these things in the first place. I was looking for something that speaks directly to the kind of problems they face in languages like Java... Types are a good example because Java programmers generally already appreciate the help they get from compiler messages etc, so you can sell a more flexible, enhanced form of this. Purity might appeal to anyone who has longed to be able to reason about nastily complex code with a lot of shared state. Laziness, streams? Hard to do in Java (I presume) but also quite hard to sell the need. The existence of an O'Reilly book will help, especially one that can be sampled online, so I'll point them at RWH for extended concrete examples. They will need to be already sold before they will bother with that though. Thanks, Jim [1] http://www.cs.chalmers.se/~rjmh/Papers/whyfp.html

8 12

haskell-src-meta Package
by George Giorgidze 22 Jan '09

22 Jan '09

Hi, In my project I needed a function that would parse a string into a template-haskell AST representing the Haskell expression. To be more precise I needed a function with the following type signature. :: String -> Either String Language.Haskell.TH.Syntax.Exp This kind of function should exist in the implementation of template-haskell, however it is not exported for public consumption from template-haskell package. There is haskell-src-exts package that provides a Haskell expression parser however it uses its own Exp data type which differs from the template haskell representation Exp. After that, I found haskell-src-meta package that provided the function I needed: parseExp :: String -> Either String TH.Exp This function uses parser from haskell-src-exts package and after that translates returned Exp representation into the template-haskell representation of Exp. So problem has been solved. However, In the light of recent changes and enhancements in the haskell-src-exts, haskell-src-meta package on Hackage is broken. I have fixed the broken package and contacted its author and maintainer (Matt Morrow). However, he did not reply. I have a number of questions: Was the use of haskell-src-meta really neccessary, I mean, is there any other package that provides the functionality of aforementioned parseExp function? Can I upload the fixed version of haskell-src-meta package to Hackage and assume its maintenance while Matt Morrow is silent? Does anyone know how to contact Matt Morrow? His is not replying on my emails sent to the email address specified in the package description. The thing is that I do not want my package to be dependent on a package that is broken on Hackage. Cheers, George -- George Giorgidze http://www.cs.nott.ac.uk/~ggg/

1 0

Quite confused by simple transformations on this code not working
by Andrew Wagner 22 Jan '09

22 Jan '09

Strange little bit of code: http://moonpatio.com:8080/fastcgi/hpaste.fcgi/view?id=829#a829 If I do any of the following, all of which seem natural to me, it fails to typecheck: 1. move f out of the 'where' clause (with or without a type signature) 2. put the same type signature on f as is on (/\) 3. replace f with (/\) completely What's going on here?

4 4

Type family problem
by Sjoerd Visscher 22 Jan '09

22 Jan '09

Hi all, When I try this bit of code: > class C1 a where > type F a :: * > x :: F a > y :: F a > x = y I get this error: Couldn't match expected type `F a1' against inferred type `F a' In the expression: y In the definition of `x': x = y I can't figure out what is going on or how I should fix this. -- Sjoerd Visscher sjoerd(a)w3future.com

3 2

Re: Re[2]: [Haskell-cafe] ANN: HTTPbis / HTTP-4000.x package available
by Duncan Coutts 21 Jan '09

21 Jan '09

On Sat, 2009-01-17 at 20:34 -1000, Tim Newsham wrote: > > Speaking of proxies, I've been looking into how to find the right proxy > > to use on Windows systems. Turns out that to do it properly you need a > > JavaScript interpreter! Yes, really. > > Uhh.. What!? That's not right. I think you mean it should not be right! :-) Of course it's possible to specify a list of proxies in Windows and that info is kept in the registry. It's also common in corporate networks to use proxy auto-configuration. The client gets told the URL of the these (.pac) files and the client downloads it to work out what proxy to use. You'll notice a space to specify an auto-configuration URL (.pac file) in the proxy setting dialog of any web browser. Proxy auto-configuration files are JavaScript. It uses more or less the full JavaScript language (ECMA these days), though with a small subset of the standard library. Web browsers are ok because they've got a JavaScript interpreter. The MS WinHTTP library uses the Windows scripting host service. The open source pacparser C library links to the Mozilla SpiderMonkey JavaScript engine. Apparently we have Netscape to thank for this mess. Duncan

3 2

ANN: HTTP-4000.0.4 released
by Sigbjorn Finne 21 Jan '09

21 Jan '09

Hi, a new release of HTTP, version 4000.0.4, is now available http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP It is also pointed at via the updated HTTP web page -- http://projects.haskell.org/http/ The main change is the addition of registering a Browser event handler for capturing state changes to the request-response processing pipeline. An experimental change, see Network.Browser.setEventHandler (Feature suggested by Yuval Kogman in order to accommodate load testing.) enjoy --sigbjorn

1 0

ANN: HTTPbis / HTTP-4000.x package available
by Sigbjorn Finne 21 Jan '09

21 Jan '09

Hi, I guess it's time to publish more widely the availability of a modernization of the venerable and trusted HTTP package, which I've been working on off&on for a while. Bunch of changes, but the headline new feature of this new version is the parameterization of the representation of payloads in both HTTP requests and responses. Two new representations are supported, strict and lazy ByteStrings. Some people have reported quietly pleasing speedups as a result of this change. (If they want to report numbers, please do..) Another change/fix in this release is the _alleged_ fix to the long-standing bug in the use of absolute URIs vs absolute paths in requests (for non-proxied and proxied use.) Give it a go.. Notice that the HTTP-4000.x version will require you to make some modifications to your existing HTTP-using code -- I've tried to keep the API backwards compatible minimal despite the change in functionality and underlying types. If you do not want to deal with this right away, please introduce a <4000 dependency on the HTTP package in your .cabal files. I've also taken on the maintainership of the package, with the highly esteemed Bjorn Bingert no longer having the usual abundance of cycles to look after it (hope I'm not misrepresenting facts here, Bjorn!) However, I've yet to gain access to www.haskell.org and update http://www.haskell.org/http, so for now you may pick up a new version the lib via http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP GIT repo for HTTP-4000 / HTTPbis is here git://code.galois.com/HTTPbis.git enjoy --sigbjorn

10 18

some ideas for Haskell', from Python
by Manlio Perillo 21 Jan '09

21 Jan '09

Hi. There are two features found in Python language, that I would like to see in Haskell. 1) In a Python string it is available the \U{name} escape, where name is a character name in the Unicode database. As an example: foo = u"abc\N{VULGAR FRACTION ONE HALF}" 2) In Python it is possible to import modules inside a function. In Haskell something like: joinPath' root name = joinPath [root, name] importing System.FilePath (joinPath) Thanks Manlio Perillo

21 40

Another Windows question - reading the output from a process
by Günther Schmidt 21 Jan '09

21 Jan '09

Hi all, I'm using WinXP with 6.8.3. For some reason the windows version of 6.8.3 ships with a somewhat "castrated" version of package process, one that does not contain "readProcess" among other convenient functions. Is there a way to install the fully fledged version of "process", because I tried using those "rawer" functions and just don't manage. Günther

1 0

MonadTrans lift implementation
by Daryoush Mehrtash 21 Jan '09

21 Jan '09

Is there a reason why the lift function in ReaderT's MonadTrans instance is implemented as: instance MonadTrans (ReaderT r) where lift m = ReaderT $ \_ -> m Instead of just using the monad's return function? Could "lift m" be implemented as "return m"? instance (Monad m) => Monad (ReaderT r m) where * return a = ReaderT $ \_ -> return a* m >>= k = ReaderT $ \r -> do a <- runReaderT m r runReaderT (k a) r fail msg = ReaderT $ \_ -> fail msg Thanks, Daryoush

6 6

Cabal dependencies
by Stephen Hicks 20 Jan '09

20 Jan '09

Hi, I'm having some difficulty specifying dependencies in my .cabal file for a package I'm looking to upload to hackage soon. The difficulty is as follows. I basically want to specify parsec (>= 2.1 && < 3.0.0) || (> 3.0.0 && < 4) The problem is that 3.0.0 as it exists on hackage is missing a constructor that I need (namely, Postfix, in the compatibility module). The bug was fixed and will presumably work fine if a newer version of parsec is ever uploaded to hackage, and my package works fine with older parsecs as well - I just want to exclude this one version. How can I go about doing that? A secondary question is this - I can actually compile with version 3.0.0 by just not using this constructor, although it does reduce the package's functionality. I've seen flags in various .cabal files, and presumably I could invent a flag to make it work with 3.0.0, but I'm confused about how these flags are set. Specifically, cabal-install has never asked me anything about flags, so what's the point? Or does it automatically set whichever flags satisfy the dependencies? Thanks, steve

2 1

xhtml + bytestring
by Joachim Breitner 20 Jan '09

20 Jan '09

Hi Bjorn, hi list, the darcswatch instance I’m running is getting quite big, and it periodically slows down my server. I managed to get quite an improvement with this simple patch to my parsing: http://darcs.nomeata.de/cgi-bin/darcsweb.cgi?r=darcswatch;a=commitdiff;h=20… Since the new HTTP library, my code runs completely on ByteStrings, only the xhtml library expects me to feed strings. I tried to fix this and created a patch against xhtml-3000.2.0.1 to work internally with lazy ByteStrings. It’s API-compatible to the normal xhtml library, it just adds showHtml', renderHtml' and prettyHtml' that output lazy ByteStrings, and that has Html instances for strict any lazy ByteStrings. There were some speed and space improvements, but none horrific (at least for DarcsWatch, most of the time goes into parsing the repositories and mails, and into sorting that data). Unfortunately, I can’t use it in the live installation until I upgrade the machine from Debian etch to lenny, as the bundled bytestring library in ghc-6.6’ base is too old. Nevertheless, I’m sharing my patch here, maybe it’s useful for some, or maybe it can be the base for an official xhtml release with bytestrings inside. To speed things up even more one should probably create a type analogous to ShowS, i.e. (L.ByteString -> L.ByteString), that allows you to concatenate ByteString chunks cheaply. I also noted that the current version of bytestring implements "concatMap" in a way that is guaranteed to rip apart the string into very small chunks, even if the mapped function returns the same character most times (as it is the case for the Html escaping function). Therefore, I wrote this function: -- | More efficient variant of 'L.concatMap' concatMapL' :: (Char -> String) -> L.ByteString -> L.ByteString concatMapL' f s = go s where go s = let (unmodified, modified) = L.span (\c -> f c == [c]) s in case L.uncons modified of Nothing -> unmodified Just (c,rest) -> L.pack (f c) `L.append` go rest Does this make sense? Should it maybe replace the function in the library? Greetings, Joachim [1] http://darcswatch.nomeata.de/ -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

2 2

Haskell and C++ program
by Sukit Tretriluxana 20 Jan '09

20 Jan '09

Hi all, I was looking around Stroustrup's website and found a simple program that he showed how standard library can be used to make the program succinct and safe. See http://www.research.att.com/~bs/bs_faq2.html#simple-program. I wondered how a Haskell program equivalent to it looks like and I came up with the code below. import qualified Control.Exception as E main = E.catch (interact reverseDouble) (\_ -> print "format error") reverseDouble = unlines . doIt . words where doIt = intro . toStrings . reverse . toDoubles . input toDoubles = map (read::String->Double) toStrings = map show input = takeWhile (/= "end") intro l = ("read " ++ (show $ length l) ++ " elements") : "elements in reversed order" : I'm not a Haskell expert and I am pretty sure that this is not the optimal form a Haskell program that's equivalent to the C++ one. So I would like to see, from the Haskell experts in this group, how else (of course better form) such a program can be written. Thanks, Ed

9 11

know a workaround for greedy context reduction?
by Nicolas Frisby 20 Jan '09

20 Jan '09

With these three declarations {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} class C a where c :: a class C a => D a where d :: a instance C a => D a where d = c ghci exhibits this behavior: *> :t d d :: (C a) => a Where I would prefer "d :: (D a) => a". In my actual examples, the context is much larger and I can't involve overlapping instances. Is there a known workaround? I didn't find a related bug on the GHC trac, and I don't know if other compilers behave in the same way.

2 3

LinuxFest Northwest 2009
by Shachaf Ben-Kiki 20 Jan '09

20 Jan '09

LFNW 2009 (<http://linuxfestnorthwest.org/>) is going to be at the end of April, and I was wondering if anyone here is going to be there, or possibly a Haskell-related presentation. Last year I met ac from #haskell there, but it would be nice if more people came, especially with the (relatively) big group in Oregon and such. Perhaps someone here has plans already? Shachaf

2 1

Haskell Weekly News: Issue 101 - January 19, 2009
by Brent Yorgey 20 Jan '09

20 Jan '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090119 Issue 101 - January 19, 2009 --------------------------------------------------------------------------- Welcome to issue 101 of HWN, a newsletter covering developments in the [1]Haskell community. Gee whiz, people, stop being so darn productive or you're going to burn me out. Seriously. Announcements curl-1.3.4. Sigbjorn Finne [2]announced that a new version of [3]curl, a complete Haskell binding to the libcurl API, is now available and have been uploaded to Hackage. The most notable change is the overloading of representation of response buffers (and headers), allowing for the use of ByteStrings. Turbinado V0.4. Alson Kemp [4]announced the release of version 0.4 of [5]Turbinado, an easy to use Model-View-Controller-ish web framework for Haskell. Highlights for the 0.4 release include a dramatically improved ORM which handles foreign keys, and improved documentation. Hackage about to reach 1000 releases. Don Stewart [6]announced that Hackage is about to reach the 1000 release mark, 2 years after it went live. Some pretty charts [7]can be seen here. leapseconds-announced-2009. Bjorn Buckwalter [8]announced the release of the [9]leapseconds-announced package, which contains a single module and a single function implementing the Data.Time.Clock.TAI.LeapSecondTable interface. zipper-0.1. Andres Loeh [10]announced [11]zipper-0.1, a library offering a generic zipper for systems of recursive datatypes. multirec-0.2. Andres Loeh [12]announced [13]multirec-0.2, a library which provides a mechanism to talk about fixed points of systems of datatypes that may be mutually recursive. On top of these representations, generic functions such as the fold or the Zipper can then be defined. ghci-haskeline 0.1. Judah Jacobson [14]announced the first release of [15]ghci-haskeline. This package uses the GHC API to reimplement ghci with the [16]Haskeline library as a backend. Haskeline is a library for line input in command-line programs, similar to readline or editline, which is written in Haskell and thus (hopefully) more easily integrated into other Haskell programs. The Monad.Reader (13) - Call for copy. Wouter Swierstra [17]announced a Call for Copy for Issue 13 of [18]The Monad.Reader. The submission deadline is February 13, 2009. Please get in touch with Wouter if you intend to submit something. Cabal 2.0. Duncan Coutts [19]announced that he has started a [20]wiki page to collect ideas for Cabal 2. The basic idea for Cabal 2 is to learn lessons from our how the existing design has fared and how we can make a better design to tackle an expanded set of goals. Announcing Haskell protocol-buffers 1.4.0 (the smashing recursive edition). Chris Kuklewicz [21]announced version 1.4.0 (the smashing recursive edition) of [22]protocol-buffers, a Haskell interface to Google's "..language-neutral, platform-neutral, extensible way of serializing structured data for use in communications protocols, data storage, and more." Haskell WikiProject. Robin Green [23]asked: is anyone else interested in forming a Haskell WikiProject on Wikipedia, to collaborate on improving and maintaining the coverage and quality of articles on Haskell-related software and topics (broadly defined)? darcs 2.2.0. Petr Rockai [24]announced the release of darcs 2.2.0, with both a [25]source tarball and a [26]cabalized tarball available. This version features many improvements and bug fixes; see Petr's original announcement for a list. hledger 0.3. Simon Michael [27]announced the release of [28]hledger 0.3, a partial haskell clone of John Wiegley's "ledger" text-based accounting tool. It generates transaction and balance reports from a plain text ledger file, and demonstrates a functional implementation of ledger. language-sh-0.0.3.1. Stephen Hicks [29]announced the [30]language-sh package, a set of modules for parsing, manipulating, and printing sh-style shell scripts. It's being developed alongside shsh, the [31]Simple Haskell Shell. Coadjute 0.0.1, generic build tool. Matti Niemenmaa [32]announced version 0.0.1 of [33]Coadjute, a generic build tool intended as an easier to use and more portable replacement for make. dataenc 0.12. Magnus Therning [34]announced version 0.12 of [35]dataenc, a data encoding library currently providing Uuencode, Base64, Base64Url, Base32, Base32Hex, Base16, Base85, and (new in 0.12) yEncoding. 3 applications of "indexed composition" as a language design principle. Greg Meredith [36]announced that he has found a way to generalize the LogicT transformer, and calculated it's [37]application to three fairly interesting examples. HTTPbis / HTTP-4000.x package available. Sigbjorn Finne [38]announced the availability of a modernization of the venerable and trusted [39]HTTP package. The headline new feature of this version is the parametrization of the representation of payloads in both HTTP requests and responses; two new representations are supported, strict and lazy ByteStrings. monad-interleave 0.1. Patrick Perry [40]announced the [41]monad-interleave package, which provides a type class generalizing his two favorite functions in Haskell, "unsafeInterleaveIO" and "unsafeInterleaveST". hs-dotnet, version 0.3.0. Sigbjorn Finne [42]announced the [43]first public release of [44]hs-dotnet, a pragmatic take on interoperating between Haskell (via GHC) and .NET. HEADS UP: finalizer changes coming in GHC 6.10.2. Simon Marlow [45]announced that, by popular demand, GHC 6.10.2 will support finalizers that are actually guaranteed to run, and run promptly. However, there's a catch. If you want to know what the catch is, read his message. split-0.1.1 (doc bugfix; new functions wordsBy and linesBy). Brent Yorgey [46]announced version 0.1.1 of the [47]split library. This version fixes some Haddock bugs, and adds two new convenience functions suggested by Neil Mitchell, wordsBy and linesBy. json-0.4.1. Sigbjorn Finne [48]announced a new release (0.4.1) of the [49]json package. New in this release is a generic JSON encoder contributed by Lennart Augustsson along with a number of other, smaller changes. haskell-platform mailing list. Duncan Coutts [50]announced that anyone interested in helping out with the haskell platform project is invited to subscribe to the [51]haskell-platform mailing list. This mailing list is for discussing practical stuff; policy questions will be discussed on the libraries mailing list. bytestring-trie 0.1.4. wren ng thornton [52]announced version 0.1.4 of the [53]bytestring-trie package. This release fixes a number of bugs, adds functions such as keys, toListBy, fromList{L,R,S}, and separated Data.Trie (the main module for users) from Data.Trie.Internal (gritty details, and core implementation). HLint 1.2. Neil Mitchell [54]announced [55]HLint version 1.2, a lint-like tool for Haskell that detects and suggests improvements for your code. The biggest new feature is list recursion suggestions. Working with HLint from Emacs. Alex Ott [56]announced an [57]emacs module for integration with [58]HLint. Discussion An Alternative Data.List.Zipper. Jeff Wheeler [59]posted [60]an improved version of Data.List.Zipper, and requested feedback or constructive criticism. Comments from OCaml Hacker Brian Hurt. John Goerzen [61]posted a link to a [62]blog post by Brian Hurt, along with some thoughts about naming things in the standard libraries, spawning the longest ML thread in recent history. Blog noise [63]Haskell news from the [64]blogosphere. * Jeff Heard: [65]The Docuverse.. Cool search query visualization for massive numbers of documents. * Ben Moseley: [66]The Category Theory of Appendages. * Galois, Inc: [67]Galois at POPL. * Colin Ross: [68]Does your IDE define you or support you?. * Alson Kemp: [69]ANNOUNCE: Turbinado V0.4. * Jeff Heard: [70]ProteinVis: Visualizing a large tree in Haskell and OpenGL. * ezekiel smithburg: [71]what to do when you can't solve a problem with a hackage library you need?. * Jeff Heard: [72]Simple Futures in Haskell. * Dan Piponi (sigfpe): [73]Haskell Monoids and their Uses. A nice introductory tutorial on Monoids in Haskell. * Real-World Haskell: [74]John Goerzen on Why You Should Learn Haskell. * LHC Team: [75]LLVM is great.. * Jeff Heard: [76]iBiblio traffic, search engine hits, and cross-traffic. * Luke Palmer: [77]Use MonadRandom!. * LHC Team: [78]Why LLVM probably won't replace C--.. * Magnus Therning: [79]Series of posts on testing Haskell code. * Magnus Therning: [80]Useful thing when adopting test-framework after already using HUnit. * Magnus Therning: [81]dataenc 0.12 posted to HackageDB. * Jeff Heard: [82]The new HTTP library. * Jeff Heard: [83]Beautiful Code, Compelling Evidence. * LHC Team: [84]The case against C/LLVM.. * Manuel M T Chakravarty: [85]Some nice code examples showing how to use type families.. * Manuel M T Chakravarty: [86]Enforcing a relation between independent type families.. * Nick Mudge: [87]Zunes, Year 2038 Problem, Real World Haskell, Why, Potion, Games. * Darcs: [88]darcs 2.2.0 is released!. * GHC / OpenSPARC Project: [89]Info tables. * LHC Team: [90]What is LHC?. * LHC Team: [91]Resources.. * LHC Team: [92]Typeclass Blues. * GHC / OpenSPARC Project: [93]Liveness lies. * Galois, Inc: [94]Real World Haskell: Intel Parallel Programming Podcast. * Real-World Haskell: [95]Intel Parallel Programming Podcast: Real World Haskell. * Brent Yorgey: [96]Abstraction, intuition, and the "monad tutorial fallacy". * Luke Palmer: [97]Ha! I can't even get Events right. * GHC / OpenSPARC Project: [98]Bootstrapping 7. * Colin Ross: [99]Finding a member of an infinite list. * LHC Team: [100]The mess with variable ids.. * Luke Palmer: [101]Ridding ourselves of IO before there is a good replacement. * GHC / OpenSPARC Project: [102]Bootstrapping 7. * Colin Ross: [103]Notes on working with finite sorted lists. * Bryan O'Sullivan: [104]Fun with Haskell view patterns. * Conal Elliott: [105]3D rendering as functional reactive programming. Quotes of the Week * luqui: sigh: mathematicians. can't live with 'em, can't prove 'em wrong. * mauke: YO DAWG I HEARD YOU LIKE METACIRCULARITY SO WE PUT AN INTERPRETER IN YOUR INTERPRETER SO YOU CAN RUN CODE WHILE YOU RUN CODE * lament: tuples are proof that haskell is inherently broken and will never work. * roconnor: [after a long -cafe thread on the suckiness of using math terms in Haskell] we don't use Integer anymore. Too abstract. It is now called CountingThingy. * quicksilver: partially applied type synonym = type lambdas = unrestricted type functions = can of pants * ddarius: In the spirit of that article on monoids, we should drop the term "tree" and replace it with the term "free pointed magma" * ski_: unique among types, 'Void -> X' has its own charm. tourists should definitely pay a visit. * pao: Cale: thanks ... I really think you deserve a statue ... or, at least, a portrait in ascii art on haskell.org :-) * byorgey: TDD replaces a type checker in Ruby in the same way that a strong drink replaces sorrows. About the Haskell Weekly News New editions are posted to [106]the Haskell mailing list as well as to [107]the Haskell Sequence and [108]Planet Haskell. [109]RSS is also available, and headlines appear on [110]haskell.org. To help create new editions of this newsletter, please see the information on [111]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [112]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/16792 3. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl 4. http://article.gmane.org/gmane.comp.lang.haskell.general/16788 5. http://www.turbinado.com/ 6. http://article.gmane.org/gmane.comp.lang.haskell.general/16782 7. http://archhaskell.wordpress.com/2009/01/18/open-source-haskell-releases-an… 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16770 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/leapseconds-anno… 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16756 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zipper 12. http://www.haskell.org//pipermail/haskell/2009-January/020925.html 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/multirec 14. http://article.gmane.org/gmane.comp.lang.haskell.general/16751 15. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ghci-haskeline 16. http://trac.haskell.org/haskeline 17. http://article.gmane.org/gmane.comp.lang.haskell.general/16750 18. http://www.haskell.org/haskellwiki/The_Monad.Reader 19. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10568 20. http://hackage.haskell.org/trac/hackage/wiki/Cabal-2 21. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10497 22. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/51037 24. http://www.haskell.org//pipermail/haskell-cafe/2009-January/053732.html 25. http://www.darcs.net/darcs-2.2.0.tar.gz 26. http://hackage.haskell.org/packages/archive/darcs/2.2.0/darcs-2.2.0.tar.gz 27. http://www.haskell.org//pipermail/haskell-cafe/2009-January/053843.html 28. http://joyful.com/hledger 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50907 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/language-sh 31. http://code.haskell.org/shsh/ 32. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50896 33. http://iki.fi/matti.niemenmaa/coadjute/ 34. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50831 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50756 37. http://biosimilarity.blogspot.com/2009/01/3-applications-of-indexed-composi… 38. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50748 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 40. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50648 41. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/monad-interleave 42. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50548 43. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hs-dotnet 44. http://haskell.forkIO.com/dotnet 45. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50477 46. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50421 47. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/split 48. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50362 49. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/json 50. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50336 51. http://projects.haskell.org/cgi-bin/mailman/listinfo/haskell-platform 52. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50292 53. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestring-trie 54. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50283 55. http://www-users.cs.york.ac.uk/~ndm/hlint/ 56. http://article.gmane.org/gmane.comp.lang.haskell.cafe/50264 57. http://xtalk.msk.su/~ott/common/emacs/hs-lint.el 58. http://www-users.cs.york.ac.uk/~ndm/hlint/ 59. http://thread.gmane.org/gmane.comp.lang.haskell.general/16771 60. http://hpaste.org/14030 61. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/50590 62. http://enfranchisedmind.com/blog/2009/01/15/random-thoughts-on-haskell/ 63. http://planet.haskell.org/ 64. http://haskell.org/haskellwiki/Blog_articles 65. http://vis.renci.org/jeff/?p=66 66. http://nattermorphisms.blogspot.com/2009/01/category-theory-of-appendages.h… 67. http://www.galois.com/blog/2009/01/18/galois-at-popl/ 68. http://vcolin.com/2009/01/18/ide-define-support/ 69. http://www.alsonkemp.com/haskell/announce-turbinado-v04/ 70. http://vis.renci.org/jeff/?p=52 71. http://tehgeekmeister.wordpress.com/2009/01/17/what-to-do-when-you-cant-sol… 72. http://vis.renci.org/jeff/?p=27 73. http://sigfpe.blogspot.com/2009/01/haskell-monoids-and-their-uses.html 74. http://www.realworldhaskell.org/blog/2009/01/17/john-goerzen-on-why-you-sho… 75. http://lhc-compiler.blogspot.com/2009/01/llvm-is-great.html 76. http://vis.renci.org/jeff/?p=33 77. http://lukepalmer.wordpress.com/2009/01/17/use-monadrandom/ 78. http://lhc-compiler.blogspot.com/2009/01/why-llvm-probably-wont-replace-c.h… 79. http://therning.org/magnus/archives/436 80. http://therning.org/magnus/archives/437 81. http://therning.org/magnus/archives/434 82. http://vis.renci.org/jeff/?p=8 83. http://vis.renci.org/jeff/?p=4 84. http://lhc-compiler.blogspot.com/2009/01/case-against-cllvm.html 85. http://justtesting.org/post/70895924 86. http://justtesting.org/post/70893530 87. http://nickmudge.info/?post=103 88. http://blog.darcs.net/2009/01/darcs-220-is-released.html 89. http://ghcsparc.blogspot.com/2009/01/info-tables.html 90. http://lhc-compiler.blogspot.com/2009/01/what-is-lhc.html 91. http://lhc-compiler.blogspot.com/2009/01/resources.html 92. http://lhc-compiler.blogspot.com/2009/01/typeclass-blues.html 93. http://ghcsparc.blogspot.com/2009/01/liveness-lies.html 94. http://www.galois.com/blog/2009/01/13/real-world-haskell-intel-parallel-pro… 95. http://www.realworldhaskell.org/blog/2009/01/13/intel-parallel-programming-… 96. http://byorgey.wordpress.com/2009/01/12/abstraction-intuition-and-the-monad… 97. http://lukepalmer.wordpress.com/2009/01/13/ha-i-cant-even-get-events-right/ 98. http://ghcsparc.blogspot.com/2009/01/bootstrapping-7.html 99. http://vcolin.com/2009/01/12/finding-member-infinite-list/ 100. http://lhc-compiler.blogspot.com/2009/01/mess-with-variable-ids.html 101. http://lukepalmer.wordpress.com/2009/01/12/ridding-ourselves-of-io-before-t… 102. http://ghcsparc.blogspot.com/2009/01/bootstrapping-7.html 103. http://vcolin.com/2009/01/11/notes-working-finite-sorted-lists/ 104. http://www.serpentine.com/blog/2009/01/11/fun-with-haskell-view-patterns/ 105. http://conal.net/blog/posts/3d-rendering-as-functional-reactive-programming/ 106. http://www.haskell.org/mailman/listinfo/haskell 107. http://sequence.complete.org/ 108. http://planet.haskell.org/ 109. http://sequence.complete.org/node/feed 110. http://haskell.org/ 111. http://haskell.org/haskellwiki/HWN 112. http://code.haskell.org/~byorgey/code/hwn/

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Haskell WikiProject
by Robin Green 20 Jan '09

20 Jan '09

Is anyone else interested in forming a Haskell WikiProject on Wikipedia, to collaborate on improving and maintaining the coverage and quality of articles on Haskell-related software and topics (broadly defined)? Not just programming topics specific to Haskell, but also ones of interest to the Haskell community. Some of you might already be doing this from time to time, but forming an explicit WikiProject might help to: * Highlight things that could use some attention * Divide up tasks (based on expertise or interest) * Recruit more editors (sticking a banner on article Talk pages can let editors know the WikiProject exists) * Eventually (something for the future, maybe!) work together on a Wikipedia Haskell Portal * And of course, improve the visibility of Haskell on Wikipedia, which should help our community Here's a good example to start with. The article on Eager evaluation could do with some improvement - and possibly should be merged into the Lazy evaluation article, I'm not sure: http://en.wikipedia.org/wiki/Eager_evaluation We could also probably create some more articles on projects written in Haskell, and add more references to Haskell research papers. Software projects don't have to be polished to be covered in Wikipedia - or even working! - they essentially just have to be "notable", as the Wikipedia guidelines define it. By the way (getting a bit offtopic here) an annoying limitation of the Wikipedia category system, that you couldn't run queries like "Give me all the articles in the Haskell category that are also in the Unreferenced category" has now been partially addressed by the experimental prototype of Category Intersection: http://toolserver.org/~dschwen/intersection/ This is slightly better than Googling, because crucially, it searches *recursively* through categories. That means it will turn up articles that are in a subcategory of "Category:Haskell programming language" but don't explicitly mention Haskell. Don't know if there any such articles yet, but it's worth bearing in mind that you can do this. I think it will, in principle, make topic-specific maintenance a bit more convenient - and it's what I've been waiting for before getting involved in topic-specific maintenance. If you want to just express interest in signing up for such a WikiProject (no commitment required whatsoever!), please reply privately via email or publicly on my User Talk page (User talk:Greenrd) - to avoid clogging up this mailing list. -- Robin

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