- Haskell-Cafe - Haskell.org

Takusen and QuickCheck
by Dmitry Olshansky 26 Jan '11

26 Jan '11

Hello, I have a problem with using Takusen in my current project because it uses old QuickCheck 1.*. This leads to conflict with other packages which use QuickCheck 2.*. Could someone help me to decide this problem? Best wishes, Dmitry

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Re: [Haskell-cafe] GPL License of H-Matrix and prelude numeric
by Vivian McPhail 26 Jan '11

26 Jan '11

Hi, > On Wed, 2011-01-26 at 08:18 +1000, Ivan Lazar Miljenovic wrote: > > Or else because the developers _wanted_ to license it under the GPL. > > Some people do, you know. > > Sure, but I agree it would be nice to know whether the authors chose the > GPL, or applied it because of linking with GPLed native libraries and > might be open to relicensing the native stuff. Seems like a good > question to me. > > -- > Chris Smith hmatrix contains a binding to (i) the GNU GSL library (for fast vector optimisations) and (ii) BLAS/LAPACK (for linear algebra). The GNU GSL library _requires_ a LGPL license. In the short term I do not think this can change. In the longer term, once dph and friends are working well and performance is optimised (dph can do fast linear algebra), the reliance on GSL and LAPACK might be removed. The hmatrix package can be configured to use Data.Vector.Storable of the vector package, and there is work being done on improving fast vector operations in that package. As far as I know, the vector package is _not_ intending to supply mathematical operations. Alberto? Cheers, Vivian

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HMatrix Vector/Matrix interpolation ala Matlab interp/interp2 ??
by gutti 26 Jan '11

26 Jan '11

Dear Haskellers, I'm looking for Vector and especially Matric interpolation ala: z = interp2 (xMatrix, yMatrix, zMatrix, x, y) - x and y can be single values or also vectors or matrices - indeally with the options nearest, linear, quadratic, qubic.. Any hope that there is something similar especially using the HMatrix matrices (Matrix Double). - If I have to code it any suggestions ? Cheers Phil -- View this message in context: http://haskell.1045720.n5.nabble.com/HMatrix-Vector-Matrix-interpolation-al… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Monomorphic let bindings and darcs
by Brandon Moore 26 Jan '11

26 Jan '11

The darcs 2.5 package uses the flat -fglasgow-exts, so it picks up MonoLocalBinds. This causes quite a few errors. The error messages are particularly bad in src/Darcs/Commands/Convert.lhs there is code of the form explicitlyPolyMorphicFun arg $- \local -> ... very long body ... let localdef = _ in ... more long body ... where failure to generalize the inner let is reported as insufficient polymorphism at the outer annotation. Glancing over the paper, it seems like the specific problem is just deferring equality constraints between ground types. Can't that be handled with a notion of constrait normalization?

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Re: [Haskell-cafe] Proposal: Applicative => Monad: Call for consensus
by Conor McBride 25 Jan '11

25 Jan '11

Hi Tyson (So OT, I'm switching to cafe.) On 19 Jan 2011, at 18:24, Tyson Whitehead wrote: > On January 17, 2011 16:20:22 Conor McBride wrote: >> Ahem > > : ) > >>> The unfortunate pain you pay for this additional power is manually >>> having to >>> specify the application (<$> and <*>) and merging (join). If the >>> compiler >>> could figure this all out for you based on the underlying types, >>> wow! >> >> To achieve such a thing, one would need to ensure a slightly more >> deliberate separation of "value" and "computation" in the >> presentation >> of types. In Haskell, we use, e.g., [Int], for >> >> * pure computations of lists of integers >> * nondeterministic computations of integers [..] > I'm pretty sure I know what "pure computations of lists of integers" > is, but > I'm not so sure about "nondeterministic computations of integers". > > If it is not too much of an effort, could you clarify with a quick > example? Viewing [] as a monad, you can view [1,2] as a nondeterministic integer with possible values 1 and 2. Lifting operations to this monad gives you "all possible combinations" computation, so, as SHE would have it, (| [1,2] + [3,4] |) = pure (+) <*> [1,2] <*> [3,4] = [4,5,5,6] It's not hard to come up with examples where lifted and unlifted both make sense. With a bit of help from Twitter, we have (courtesy of Andy Gimblett) (["under","over"] ++ ["state","wear"]) = ["under","over","state","wear"] but (|["under","over"] ++ ["state","wear"]|) = ["understate","underwear","overstate","overwear"] and (courtesy of Dan Piponi) (["plan","tan"] ++ ["gent","king"]) = ["plan","tan","gent","king"] but (|["plan","tan"] ++ ["gent","king"]|) = ["plangent","planking","tangent","tanking"] In each case, the former has (++) acting on lists of strings as pure values, while the latter has (++) acting on strings as values given in []-computations. The type [String] determines a domain, it does not decompose uniquely to a notion of computation and a notion of value. We currently resolve this ambiguity by using one syntax for pure computations with [String] values and a different syntax for [] computations with String values. Just as we use newtypes to put a different spin on types which are denotationally the same, it might be worth considering a clearer (but renegotiable) separation of the computation and value aspects of types, in order to allow a syntax in which functions are typed as if they act on *values*, but lifted to whatever notion of computation is ambient. After types for representation, let us have types for explanation. All the best Conor

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getDirectoryContents and sort order
by John Lask 25 Jan '11

25 Jan '11

I have noticed that on my windows box and ghc 6.12.3 I get the return list for System.Direcotry.getDirectoryContents in reverse sorted order. This is a change from previous observed behavior and I would consider it a bug. I would like to verify that it is not just me.

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Data.Ranges show error
by Aaron Gray 25 Jan '11

25 Jan '11

I am getting the following error when trying to do a show on a Ranges object :- C:\Languages\Haskell>ghci rangeTest.hs GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling Main ( rangeTest.hs, interpreted ) Ok, modules loaded: Main. *Main> main Loading package array-0.3.0.1 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package ranges-0.2.3 ... linking ... done. Ranges [(37*** Exception: <stdout>: hPutChar: invalid argument (character is not in the code page) *Main> I have attached the test source also :- import Data.Ranges test = (ranges [ range 32 33, range 34 35, range 37 39 ]) main :: IO () main = do { putStrLn (show test) } I am probably doing something fundermentaly wrong. Many thanks in advance, Aaron

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Tracing applied functions
by Aaron Gray 25 Jan '11

25 Jan '11

Is there anyway to get a list of applied functions in the running of a Haskell program ? Many thanks in advance, Aaron

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Haskell Vim Indentation
by beo wulf 25 Jan '11

25 Jan '11

I am using: http://www.vim.org/scripts/script.php?script_id=1968 and http://projects.haskell.org/haskellmode-emacs/ Indenting a single do-block looks fine. However, let blocks, where blocks, nesting let/where within do's, nesting anything inside of anything -- tend to give ugly looking code. Anyone know of a good vim indenting script? Thanks!

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Chicago Haskell User Group Meetup this Thursday @ 8PM
by Jeremy Shaw 25 Jan '11

25 Jan '11

Hello, The Chicago Haskell User Group will be meeting at the Pumping Station One hackerspace this Thursday @ 8PM. This meeting coincides with a regularly scheduled Haskell class at PS:One. Among other things, we will discuss how to grow the local Chicago Haskell user community, and a possible group project. Haskell users of all levels (including no experience at all) are invited to come! Facebook Invite: http://www.facebook.com/event.php?eid=158855480832147 Pumping Station One website: http://pumpingstationone.org/ Chicago Haskell User Group Facebook Group: http://www.facebook.com/pages/Chicago-Haskell-User-Group/115989593098 Chicago Haskell User Group Mailing List: http://groups.google.com/group/haskell-chicago - jeremy

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Installing a top-level handler on an existing thread
by Leon Smith 24 Jan '11

24 Jan '11

I've been toying with a little thread manager library, and for sanity's sake I really need a way to install another top-level exception handler on an existing thread. I don't want to replace any other handlers, just put my own handler around the thread's continuation. Of course, it would be pretty easy to do if the IO monad had a nice efficient implementation of call/cc and call/cc1, although I don't need the full power of continuations. I really don't want to create my own "Thread" monad (which could use ContT), I want to be able to do it on plain old IO threads. Is there any way to do this in GHC? Best, Leon

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The F# Team are Hiring
by Simon Peyton-Jones 24 Jan '11

24 Jan '11

Dear Haskell'ers The F# team in Seattle/Redmond have an opening for a Senior Program Manager<https://careers.microsoft.com/JobDetails.aspx?ss=&pg=0&so=&rw=1&jid=33994&j…>. A demonstrated love for applied Haskell/OCaml/F# programming would be highly regarded background experience :) We also have positions open for software development engineers specializing in compilers and tools (see https://careers.microsoft.com/JobDetails.aspx?ss=&pg=0&so=&rw=3&jid=34078&j…) Kind regards & best wishes, Don Syme The F# Team are Hiring!!! * Do you have a love for modern, industry-leading programming technologies? * Can you help us take the F# language to the next level? * Do you have the vision to combine functional programming with technologies for data, cloud, web, finance and technical computing? * Do you have a passion for delivering great visual tools and a simple, clear end-to-end experience for F# programmers? * And do you want to work on a talented agile team that releases compiler sources on codeplex.com and has originated major innovations for C# and Visual Basic? If so, we have a great opportunity for you! The Visual Studio Pro team is looking for an experienced Program Manager to drive the F# area. Partnering with your engineering team in Redmond and Microsoft Research in Cambridge, you will define the F# developer experience for Visual Studio and out of band releases such as the F# PowerPack. As a strong customer advocate, you will drive changes into the F# language, libraries and tools. You will develop and update community programs that drive increased awareness and adoption of F#. Being responsible for delivering integrated solutions, you have experience in building strong cross-group partnerships, ensuring alignment of schedules and business goals, and the natural skill of getting things done. Specific responsibilities include: * Travelling to major conferences, user group meetings, and enterprises to get people excited about solving problems using F# * Defining the strategy for marketing F# to the developer community * Owning our content strategy and community engagement programs * Driving multiple concurrent projects for the F# team including Visual Studio and out of band releases * Working closely with groups within Microsoft such as Technical Computing, .NET Framework, SQL and Azure to deliver great experiences for F# developers * Contributing to the design of all aspects of F# from language & libraries to the tools that integrate with Visual Studio Basic Qualifications: * 3-5 years experience in Program Management or related experience, including a proven track record of delivering on challenging projects * A BS or equivalent degree in Computer Science, Electrical Engineering, or a related field. * Passionate for language and user experience design * Knowledge of Visual Studio, .NET & functional programming languages, and the ability to dig deep into technical challenges * Strong sense of teamwork, personal integrity, responsibility and accountability * Excellent verbal and written communication skills * Strong customer advocate, self-starter and problem solver * Strong knowledge of F# or language design on managed platforms is preferred If you'd would like more details, please either contact me (dsyme(a)microsoft.com<mailto:dsyme@microsoft.com>), or Sean Laberee (seanla(a)microsoft.com<mailto:seanla@microsoft.com>) directly. To apply immediately, please fill in the online forms<https://careers.microsoft.com/JobDetails.aspx?ss=&pg=0&so=&rw=1&jid=33994&j…> and drop us a note that you're applying. https://careers.microsoft.com/JobDetails.aspx?ss=&pg=0&so=&rw=1&jid=33994&j… don

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building hslogger error windows
by Gang Yu 24 Jan '11

24 Jan '11

Hi cafe, I just get a build error on install config-file (which depends on hslogger), C:\Documents and Settings\lenovo>cabal install hslogger Resolving dependencies... Downloading hslogger-1.1.1... Configuring hslogger-1.1.1... Preprocessing library hslogger-1.1.1... Preprocessing executables for hslogger-1.1.1... Building hslogger-1.1.1... src\System\Log\Handler\Rotating.hs:48:7: Could not find module `System.FilePath.Windows': It is a member of the hidden package `filepath-1.1.0.4'. Perhaps you need to add `filepath' to the build-depends in your .cabal fil e. Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: hslogger-1.1.1 failed during the building phase. The exception was: ExitFailure 1 I am using platform-2.0, How can I solve it? Thanks in advance Gang

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Re: [Haskell-cafe] Delivery to haskell-platform@projects.haskell.org
by Yitzchak Gale 24 Jan '11

24 Jan '11

Erik de Castro Lopo wrote: > ...my mail server is rejecting the message coming back > to me... > Nun.haskell.org really should have a reverse DNS entry Ah, that is probably a casualty of the recent upgrade of the haskell.org server. As part of that process, control of the domain was moved from Yale to the community. I think someone at Galois is admin for the domain now, I'll see if I can get them to put the reverse DNS back in. I'm also creating a support ticket for community.haskell.org and taking the liberty of making you the "requestor". Regards, Yitz

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Adding a builder to the "bytestring" package?
by John Millikin 24 Jan '11

24 Jan '11

Most people who work with binary data have had to construct bytestrings at some point. The most common solution is to use a "Builder", a monoid representing how to construct a bytestring. There are currently three packages (that I know of) which include builder implementations: binary, cereal, and blaze-builder. However, all of these libraries have additional dependencies beyond just "bytestring". All three depend on "array" and "containers", and blaze-builder additionally depends on "text" (and thus "deepseq"). Since the current implementation of GHC uses static linking, every additional dependency adds to the final size of a binary. Obviously the "Builder" concept is very useful, as it has been implemented at least three times. How about adding it to the "bytestring" package itself? We could have a module Data.ByteString.Builder, with functions (at minimum): toByteString :: Builder -> Data.ByteString.ByteString toLazyByteString :: Builder -> Data.ByteString.Lazy.ByteString fromByteString :: Data.ByteString.ByteString -> Builder fromLazyByteString :: Data.ByteString.Lazy.ByteString -> Builder empty :: Builder append :: Builder -> Builder -> Builder Plus whatever implementation details might be useful to expose. Existing libraries could then add their extra features (word -> builder for binary and cereal, UTF/HTTP for blaze-builder) on top of the existing types. Is this something the community is interested in? Is there any work currently aimed at this goal?

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Is SHE (the Strathclyde Haskell Enhancement) portable?
by Maciej Piechotka 24 Jan '11

24 Jan '11

It may be strange question but: - Is SHE portable (assuming that the compiler have the extensions)? - If yes why there is only information how to use it with GHC? Regards

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ANN: follower 0.0.1
by R. Emre Başar 24 Jan '11

24 Jan '11

Hello Cafe, I'm happy to announce the first version of the anonymous Twitter following tool: follower Basically the tool allows you to follow people's tweets without having a Twitter account. It keeps a list of the people you follow and keeps track of the tweets you already saw. Thanks to the authors of those nice libraries on hackage, it's just a little more than a hundred lines (probably would be much less using the right *morphisms) hacked up in an hour or so. Any comments, bug reports, rants, requests and patches are welcome. Get it from hackage: http://hackage.haskell.org/package/follower -- R. Emre Başar İstanbul Bilgi University Department of Computer Science

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Tool for evaluating "GHCi>" lines in a source file
by Steffen Schuldenzucker 23 Jan '11

23 Jan '11

Hi, some time ago I read of a small tool that extracts lines like "GHCi> some_expression" from a source file and appends GHCi's output to them. Now I can't find it again. Does anyone remember its name? Thanks. Steffen

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Delivery to haskell-platform@projects.haskell.org
by Magnus Therning 23 Jan '11

23 Jan '11

I'm receiving emails saying that email can't be delivered: Delivery to the following recipient has been delayed: haskell-platform(a)projects.haskell.org Message will be retried for 1 more day(s) Technical details of temporary failure: The recipient server did not accept our requests to connect. Learn more at http://mail.google.com/support/bin/answer.py?answer=7720 [projects.haskell.org (1): Connection timed out] Who should I turn to to get this sorted out? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus

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parsing exercise
by Sebastian Fischer 23 Jan '11

23 Jan '11

Hello, I need a function and wonder whether I can copy some existing code so I don't have to write it myself. It should split a string into a list of strings: splitAtTopLevelCommas :: String -> [String] I need something similar to `splitOn ","` from the Text package with the property intercalate "," . splitAtTopLevelCommas = id But it should split the string only on a few commas, not all. You can think of the result list as representations of Haskell values, for example splitAtTopLevelCommas "True,(1,(2,[3,4])),Just ('a',\")\")" should yield ["True", "(1,(2,[3,4]))", "Just ('a',\")\")"] I expect writing this function to be quite tedious (ignore commas in parens, ignore parens in strings, quotation, ...) and would prefer to copy code from some parsing library. Do you have an idea what I could use? Or how to solve it from scratch in a few lines? Sebastian

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Effective function representation.
by Grigory Sarnitskiy 22 Jan '11

22 Jan '11

Hello! I need to deal with functions of type (Double -> Double). I need Fourier transform, integration, + - * / operations, value of a function in a point, probably composition. However it is not very effective to use straightforwardly this type. Since functions in question are rather smooth (if not analytical), the best option would be to use some kind of pointwise representation (e.g. lists, arrays). But in this case the code wouldn't be so easy to understand and implement, compact and so on. Is there some libraries which allow me to work with functions as if their type was (Double -> Double), but indeed it was something faster?

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windows network programming
by Michael Litchard 22 Jan '11

22 Jan '11

I took a quick look on hackage for an interface to windows networking function calls, and didn't find anything that worked. I may have overlooked something. What's the state of windows network programming? Any recommendations for a good package?

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Flushing Cabal's cache
by Aaron Gray 22 Jan '11

22 Jan '11

I am getting the following error :- C:\Languages\Lexer\Haskell>cabal install ranges Resolving dependencies... cabal: Error: some packages failed to install: ranges-0.2.3 failed while unpacking the package. The exception was: user error (TAR checksum error) I am on Windows Vista, is it possible to clean or delete Cabal's cache ? Many thanks in advance, Aaron

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6th Ghent Functional Programming Group Meeting: 17/02/2011
by Jasper Van der Jeugt 22 Jan '11

22 Jan '11

(apologies if you receive multiple copies) Dear all, We would like to announce that the sixth Ghent Functional Programming Group Meeting will take place on Thursday, February 17, in the Technicum Building (Sint-Pietersnieuwstraat 41, 9000 Gent) of Ghent University at 19h. We will use the "Gobelijn" room this time. To bring some variation into the concept, we will host a problem solving meeting instead of talks. Bring your favorite functional programming language, a laptop with a wireless card (if possible), and the willingness to work together in small groups with other attendees on some interesting problems. We would like to note that is not a contest as such, we want to focus on elegance and working together instead of finding a quick and dirty solution. A beamer will be available if someone wants to give a quick explanation on his/her solution. For more information you can follow us at twitter (@ghentfpg) or sign up for our google group (http://groups.google.com/group/ghent-fpg) Hope to see you all then, The GhentFPG organizing committee, Andy Georges Jeroen Janssen Jasper Van der Jeugt

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Re: [Haskell-cafe] Splittable random numbers
by Ryan Newton 22 Jan '11

22 Jan '11

I'm not too familiar with all the Haskell API's for RNGs. This is the first time I've looked at CryptoRandomGen, but I can see the benefit of having a bytestring interface rather than the System.Random Int based one. Is there a reason that the AES implementation in the "AES" or "crypto" packages can't be ripped out and repackage in the way you would like? Cheers, -Ryan On Fri, Jan 21, 2011 at 6:11 PM, Thomas DuBuisson < thomas.dubuisson(a)gmail.com> wrote: > Ryan, > If you make an AES based RNG then consider making an instance for > CryptoRandomGen (see DRBG [1] for example instances). Such an > instance means you can use "splitGen" [2], which can split generators > in the manner described in this thread. If you make the RNG match > NIST SP 800-90 then feel free to send it to me for inclusion in the > DRBG package, I've been meaning to make the block cipher based DRBG > for a while now. > > Finally, any implementation of AES (using NI or not) could probably go > in its own package or a cipher-specific package like CryptoCipher[3]. > Its a shame we don't have an AES implementation on Hackage that 1) > exposes the fundamental block interface instead of some higher-level > wrapping and 2) isn't tied to a large library. > > Cheers, > Thomas > > [1] http://hackage.haskell.org/package/DRBG > and > > http://hackage.haskell.org/packages/archive/DRBG/0.1.2/doc/html/src/Crypto-… > [2] > http://hackage.haskell.org/packages/archive/crypto-api/0.3.1/doc/html/Crypt… > [3] http://hackage.haskell.org/package/cryptocipher > > > On Fri, Jan 21, 2011 at 2:19 PM, Ryan Newton <rrnewton(a)gmail.com> wrote: > > Hi cafe, > > > > I want to add the ability to use AES-NI instructions on Intel > architectures > > to GHC. Mainly I'd like to do splittable random number generators based > on > > AES as was suggested at the outset of this email. (I met Burton Smith > last > > week and this topic came up.) > > > > I was just reading the below thread about the plugin architecture which > got > > me thinking about what the right way to add AES-NI is. (Disregarding for > a > > moment portability and the issue of where to test cpuid...) > > > > > http://www.haskell.org/pipermail/glasgow-haskell-users/2011-January/019874.… > > > > The FFI is always an option. But after reading the first N pages I could > > come across from google I'm still not totally clear on whether "unsafe" > > foreign calls can happen simultaneously from separate Haskell threads > (and > > with sufficiently low overhead for this purpose). > > > > I also ran across the phrase "compiler primitive" somewhere wrt GHC: > > > http://hackage.haskell.org/trac/ghc/wiki/AddingNewPrimitiveOperations > > > > Is that the right way to go? Or would the compiler plugin mechanism > > possibly allowing doing this without modifying mainline GHC? > > > > Thanks, > > -Ryan > > > > On Fri, Nov 12, 2010 at 6:26 PM, wren ng thornton <wren(a)freegeek.org> > wrote: > >> > >> On 11/12/10 5:33 AM, Richard Senington wrote: > >>> > >>> It does not give the results you would want. This may have something to > >>> do with picking "good" parameters for the mkLehmerTree function. > >>> For example, using a random setup, I just got these results > >>> result expected range > >>> 16.814 expected = 16.0 (1,31) > >>> 16.191 expected = 16.5 (1,32) > >>> 16.576 expected = 17.0 (1,33) > >>> 17.081 expected = 17.5 (1,34) > >>> 17.543 expected = 18.0 (1,35) > >> > >> Have you run any significance tests? I wouldn't be surprised to see > +/-0.5 > >> as within the bounds of expected randomness. I'm more worried about it > >> seeming to be consistently on the -0.5 end of things, than I am about it > not > >> matching expectation (how many samples did you take again?). For small > >> ranges like this, a consistent -0.5 (or +0.5) tends to indicate > off-by-one > >> errors in the generator. > >> > >> -- > >> Live well, > >> ~wren > >> _______________________________________________ > >> Haskell-Cafe mailing list > >> Haskell-Cafe(a)haskell.org > >> http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > _______________________________________________ > > Glasgow-haskell-users mailing list > > Glasgow-haskell-users(a)haskell.org > > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > > > > >

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Problems installing the haskell platform
by Henry Laxen 22 Jan '11

22 Jan '11

Dear Group, Greetings. I've been using haskell for about a year now, though I will readily admit I still don't really know what I am doing when I get error messages. Today I decided to reset my haskell environment from scratch, avoiding the debian packages and going straight to the source. 1. Install ghc from http://www.haskell.org/ghc/download_ghc_6_12_3 Success!! ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.3 cabal update Downloading the latest package list from hackage.haskell.org 2. Next I downloaded the haskell platform and ran cabal install Problems!! cabal: Error: some packages failed to install: haskell-platform-2010.2.0.0 depends on stm-2.1.2.1 which failed to install. stm-2.1.2.1 failed during the building phase. The exception was: ExitFailure 1 3. So I tried installing stm manually, which for some unknown reason worked: runghc Setup.hs install Installing library in /usr/local/lib/stm-2.1.2.1/ghc-6.12.3 Registering stm-2.1.2.1... 4. back to the haskell-platform directory and try again: cabal install Resolving dependencies... Configuring haskell-platform-2010.2.0.0... setup: happy version ==1.18.5 is required but the version found at /usr/local/bin/happy is version 1.18.6 cabal: Error: some packages failed to install: haskell-platform-2010.2.0.0 failed during the configure step. The exception was: ExitFailure 1 5. Crap. Okay, maybe it will work with version 1.18.6 after all, so I edit the .cabal and change happy ==1.18.5 to happy >=1.18.5 -- Depending on programs does not work, they are not registered -- We list them to help distro packaging. build-tools: cabal-install ==0.8.2, alex ==2.3.3, happy >=1.18.5 -- haddock ==2.7.2 -- valid, but needs ghc-paths 6. Try again cabal install Resolving dependencies... Configuring haskell-platform-2010.2.0.0... Preprocessing library haskell-platform-2010.2.0.0... Building haskell-platform-2010.2.0.0... Registering haskell-platform-2010.2.0.0... Installing library in /usr/local/lib/haskell-platform-2010.2.0.0/ ghc-6.12.3 Registering haskell-platform-2010.2.0.0... 7. Success!! Now even though I'm not sure what I am doing, it looks like it may have worked. I'm worried, though, about the first time user who tries to go through this process. They will probably stop at the first error, when the haskell-platform fails to install. I know some of you will say use the debian packages. Well I did that, but when I tried to install snap, which is not included in the debian packages, I wound up with conflicting dependencies, and could not find a way out. I hope this dialog is helpful to whomever is in charge of the haskell platform, a wonderful resource by the way. Best wishes, Henry Laxen

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CfP: The 9th International Conference on SOFTWARE ENGINEERING AND FORMAL METHODS (SEFM'11)
by Juan Manuel Crespo 21 Jan '11

21 Jan '11

CALL FOR PAPERS - SEFM 2011 The 9th International Conference on SOFTWARE ENGINEERING AND FORMAL METHODS (SEFM) 14-18 November 2011 Montevideo, Uruguay URL: http://www.fing.edu.uy/inco/eventos/SEFM2011 ++++++++++++++++++++++++++++++++++++++++++ IMPORTANT DATES * Title and abstract submission deadline: 23 April 2011 * Paper submission deadline: 30 April 2011 * Acceptance/rejection notification: 15 June 2011 * Camera-ready version due: 15 July 2011 +++++++++++++++++++++++++++++++++++++++++++++++++++ BACKGROUND AND OBJECTIVES The aim of the conference is to bring together practitioners and researchers from academia, industry and government to advance the state of the art in formal methods, to facilitate their uptake in the software industry and to encourage their integration with practical engineering methods. Papers that combine formal methods and software engineering are especially welcome. Authors are invited to submit original research or tool papers on any relevant topic. These can either be normal or short papers. Short papers can discuss new ideas which are at an early stage of development and which have not yet been thoroughly evaluated. TOPICS Topics of interest include, but are not limited to: * formal requirement analysis, specification and design * programming languages, program analysis and type theory * formal methods for service-oriented and cloud computing * formal aspects of security and mobility * model checking, theorem proving and decision procedures * formal methods for real-time, hybrid and embedded systems * formal methods for safety-critical, fault-tolerant and secure systems * software architecture and coordination languages * component, object and multi-agent systems * formal aspects of software evolution and maintenance * formal methods for testing, re-engineering and reuse * light-weight and scalable formal methods * tool integration * applications of formal methods, industrial case studies and technology transfer KEYNOTE SPEAKERS * Daniel Le Métayer - INRIA, France * More to be announced... SPECIAL TRACK The conference programme will include a special track on "Modelling for Sustainable Development". A separate Call for Papers is available for the special track. All queries on submissions to the special track should be sent to: sefm2011-msd(a)iist.unu.edu. LOCATION The conference will be held at the NH Columbia Hotel located close to the financial center of Montevideo and enjoying excellent views of the Plata river (Río de la Plata) - http://www.nh-hotels.com/nh/en/hotels/uruguay/montevideo/nh-columbia.html. SUBMISSION AND PUBLICATION Submissions to the conference must not have been published or be concurrently considered for publication elsewhere. All submissions will be peer-reviewed and judged on the basis of originality, contribution to the field, technical and presentation quality, and relevance to the conference. All papers must be written in English. Research and tool papers must not exceed 16 pages in the LNCS format while short papers must not exceed 8 pages in the LNCS format (see http://www.springer.de/comp/lncs/authors.html for details). All queries on the submissions should be sent to: sefm2011(a)fing.edu.uy. Papers must be submitted electronically via the Easychair System: http://www.easychair.org/conferences/?conf=sefm11 The proceedings will be published in the Springer Lecture Notes in Computer Science series (LNCS). After the conference, authors of selected papers will be invited to submit an extended version of their work to be considered for publication in a special issue of the SoSyM journal (Software and Systems Modeling, Springer), following the standard reviewing process of the journal. COMMITTEES Conference Chair * Alberto Pardo, Universidad de la República, Uruguay Program Co-chairs * Gilles Barthe, IMDEA Software, Spain * Gerardo Schneider, Chalmers | Univ. of Gothenburg, Sweden Program Committee * Bernhard K. Aichering (Graz University of Technology, Austria) * Luis Barbosa (University of Minho, Portugal) * Gilles Barthe (IMDEA Software, Spain) * Thomas Anung Basuki (UNU-IIST, China) * Alexandre Bergel (University of Chile, Chile) * Gustavo Betarte (Universidad de la República, Uruguay) * Ana Cavalcanti (University of York, UK) * Pedro R. D'Argenio (Univ. Nacional de Córdoba, Argentina) * Van Hung Dang (UNU-IIST, China) * George Eleftherakis (SEERC, Greece) * José Luiz Fiadeiro (University of Leicester, UK) * Martin Fränzle (Oldenburg University, Germany) * Stefania Gnesi (ISTI-CNR, Italy) * Rob Hierons (Brunel University, UK) * Paola Inverardi (University of L'Aquila, UK) * Jean-Marie Jacquet (University of Namur, Belgium) * Tomasz Janowski (UNU-IIST, China) * Jean-Marc Jezequel (IRISA, France) * Joseph Kiniry (IT University of Copenhagen, Denmark) * Paddy Krishnan (Bond University, Australia) * Martin Leucker (TU Munich, Germany) * Xuandong Li (Nanjing University, China) * Peter Lindsay (The University of Queensland, Australia) * Antónia Lopes (University of Lisbon, Portugal) * Nenad Medvidovic (University of Southern California, USA) * Mercedes Merayo (Universidad Complutense de Madrid, Spain) * Stephan Merz (INRIA Nancy, France) * Madhavan Mukund (Chennai Mathematical Institute, India) * Cesar Muñoz (NASA, USA) * Martín Musicante (UFRN, Brazil) * Mizuhito Ogawa (JAIST, Japan) * Olaf Owe (University of Oslo, Norway) * Gordon Pace (University of Malta, Malta) * Ernesto Pimentel (University of Málaga, Spain) * Sanjiva Prasad (Indian Institute of Technology Delhi, India) * Anders Ravn (Aalborg University, Denmark) * Leila Ribeiro (UFRGS, Brazil) * Augusto Sampaio (UFPE, Brazil) * Gerardo Schneider (Chalmers | Univ. of Gothenburg, Sweden) * Sebastian Uchitel (Imperial College London, UK) * Willem Visser (University of Stellenbosch, South Africa) * Sergio Yovine (VERIMAG, France) Organising Committee * Carlos Luna, Universidad de la República, Uruguay * Alberto Pardo, Universidad de la República, Uruguay * Luis Sierra, Universidad de la República, Uruguay Steering Committee * Manfred Broy, TU Munich, Germany * Antonio Cerone, UNU-IIST, Macao SAR, China * Mike Hinchey, Lero-The Irish Software Engineering Research Centre, Ireland * Mathai Joseph, TRDDC, Pune, India * Zhiming Liu, UNU-IIST, Macao SAR, China * Andrea Maggiolo-Schettini, Pisa University, Italy ===================================================

1 0

Looking for criticism and comments on web-mongrel2.
by Clint Moore 21 Jan '11

21 Jan '11

After sufficient hand-wringing I finally uploaded web-mongrel2 up to hackage and I'm interested in criticism of my approach. The module itself is terribly simple as it's meant to provide a lightweight layer between an application or framework and Mongrel2, but if nothing else, it's a start. Anyway, the hackage page is at http://hackage.haskell.org/package/web-mongrel2-0.0.2.2 with a link to the github repo.

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Re: [Haskell-cafe] hledget: mtv vs transformers
by Simon Michael 21 Jan '11

21 Jan '11

You mean mtl 2.*, right ? Yes that is a problem. I'm nervous about requiring mtl 2 because when I bumped hledger 0.13's process dependency to 0.14 for similar reasons it made all kinds of trouble for folks who just want to install the hledger core in standard/older haskell environments. On Jan 20, 2011, at 5:11 PM, Dmitry Astapov wrote: > Since hledger-chart depends on Chart, which in turn depends on > transformers 0.2.*, it will make a sense to bump all mtl > dependencies in hledger to 2.2 > > When one does "make install" with older GHC (like 6.12.1, for > example), and mtl 1.x is available, it would be happily used for > hledger-lib and hledger, but compilation of hledger-chart will pull > in transformers 0.2 (but not the newer mtl) and will fail due to > conflicting instances.

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Where is the CABAL file for haskell-platform 2010.2.0.0?
by Magnus Therning 21 Jan '11

21 Jan '11

I'm not sure I'm reading the release plan for 2011.x.0.0[1] correctly (the switching between 2011.1.0.0 and 2011.2.0.0 is *very* confusing) but it looks like a stable release is scheduled for Feb 1,2011. I was expecting that the link on the front page[2] would lead to the 2010.2.0.0 release until a new stable version was released. This doesn't seem to be the case however: % curl -s http://code.haskell.org/haskell-platform/haskell-platform.cabal | head name: haskell-platform version: 2011.1.0.0 homepage: http://haskell.org/platform license: BSD3 license-file: LICENSE author: libraries(a)haskell.org maintainer: haskell-platform(a)projects.haskell.org category: System synopsis: The Haskell Platform description: Where can I find the cabal file for 2010.2.0.0 until 2011.1.0.0 is formally released (or will it be 2011.2.0.0 as the release plan says)? Will the CABAL file for 2010.2.0.0 not be available *at all* after 2011.x.0.0 is released? /M [1]: http://trac.haskell.org/haskell-platform/wiki/ReleaseTimetable [2]: http://code.haskell.org/haskell-platform/haskell-platform.cabal -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus

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Re: [Haskell-cafe] Are constructors strict?
by Sebastian Fischer 21 Jan '11

21 Jan '11

sorry, forgot to cc cafe. On Fri, Jan 21, 2011 at 7:12 PM, Sebastian Fischer <fischer(a)nii.ac.jp>wrote: > Hi Daryoush, > > On Fri, Jan 21, 2011 at 6:18 AM, Daryoush Mehrtash <dmehrtash(a)gmail.com>wrote: > >> I am having hard time understanding the following paragraph in "Purely >> functional Lazy non-deterministic programing" paper >> http://www.cs.rutgers.edu/~ccshan/rational/lazy-nondet.pdf >> >> The problem with the naive monadic encoding of non-determinism is that the >> arguments to a constructor must be deterministic. If these arguments are >> themselves results of non-deterministic computations, these computations >> must be performed completely before we can apply the constructor to build a >> non-deterministic result. >> >> >> >> Why does the argument to constructors must be deterministic? >> > > Because of the type of the constructor. Say you want to compute a list of > Ints nondeterministically (like in the paper). Than the first argument of > the (:) constructurs in the result must be an Int. A nondeterministic > computation that yields an Int has type (m Int) for some nondeterminism > monad (for example, it has type [Int] in the list monad). That the (:) > constructur is polymorphic and would allow to make a value of type [m Int], > is a coincidence and does not help to make a value of type (m [Int]). > > >> WHy is it that thunks are not used in this case? >> > > Thunks do not model nondeterminism, only laziness. > > Did that help you understand? > > Regards, > Sebastian >

1 0

parsec2 vs. parsec3... again
by Evan Laforge 21 Jan '11

21 Jan '11

Yeah, I know this has been discussed a number of times, but I have some concrete questions I haven't seen asked before. And the "parsec 3 is now as fast as parsec 2" thing I've seen around doesn't seem to be true for me. I have an app that does a lot of parsing of small expressions. It's currently parsec2 operating on lots of little Texts (after an unpack, of course). A few parsing functions show up near the top of the profile output, so I thought an obvious improvement would be to parse Text directly and avoid the overhead and garbage of unpacking. Since parsec3 is now supposed to be as fast as parsec2 I thought I would give it a try. Parsec3 is 3.1.0, parsec 2 is 2.1.0.1: parsec2, String: total time = 10.66 secs (533 ticks @ 20 ms) total alloc = 2,340,113,404 bytes (excludes profiling overheads) parsec3, String: (this is just after upgrading the library and editing it to fix breakage from Parser being a type alias now) total time = 13.76 secs (688 ticks @ 20 ms) total alloc = 2,706,625,256 bytes (excludes profiling overheads) parsec3, Text: (wrote a Text instance similar to the one for ByteString, updated imports, no longer unpacking to String) total time = 15.96 secs (798 ticks @ 20 ms) total alloc = 3,338,005,896 bytes (excludes profiling overheads) This is not very encouraging! Especially strange is how Text generates *more* allocation... I'd expect less since it doesn't unpack all the Texts. The parsing functions are no longer at the top of the profile, but there are new 'unParser' and 'parsecMap' and 'parserBind' up at or near the top. 'unParser' just looks like it's unwrapping the Parsec newtype, so I don't fully understand how it's the most expensive, but it's called on every bind so it does get called a lot. There are no obvious super expensive ones, just lots and lots of them that add up. Parsec 3's unParser covers up the parsing function I wrote, so it's now hard to tell what the expensive parsing function actually is. I've seen a few remarks that you can't just throw together parsers and expect them to be fast, you have to profile them, but nothing on how to actually interpret the results of profiling. For instance, here's one of the main expensive parsers: p_unsigned_float :: P.CharParser st Double p_unsigned_float = do i <- P.many P.digit f <- P.option "" (P.char '.' >> P.many1 P.digit) if (null i && null f) then P.pzero else do let int = List.foldl' (\total c -> 10 * total + fromIntegral (Char.digitToInt c)) 0 i frac = foldr (\c total -> (total + fromIntegral (Char.digitToInt c)) / 10) 0 f return (int + frac) There's an obvious problem where I get the digits as a String and then parse that with list functions, but I can't see any way to get parsec to return a chunk of Text. This is roughly how parsec itself parses numbers, in Text.Parsec.Token. So, my current options are either figure out some way to speed up parsec3+Text, revert to parsec2+String and give up, or try an entirely different parsing library. I've heard attoparsec is fast but I'd have to switch to utf8 bytestring which is a big change, and Text seems like the more correct choice anyway. Any ideas or experience?

7 14

Browser Game Engine
by Tom Hawkins 21 Jan '11

21 Jan '11

I want to create a simple browser game using Haskell. It would be nothing complicated: basic 2D graphics, limited sound, and minimal network traffic. What is the recommended medium? Flash or JavaScript+SVG? Any recommended Haskell libraries for the server-side logic or client code generation? -Tom

5 4

Re: [Haskell-cafe] Building lambdabot
by Max Bolingbroke 21 Jan '11

21 Jan '11

On 20 January 2011 17:30, Gwern Branwen <gwern0(a)gmail.com> wrote: >> * You need to loosen the base upper bound to < 4.4 >> * If using base >= 4, you need to depend on the syb package as well >> (current version 0.3) > > Would this break GHC 6.12 builds? Thats why I suggested the flag stanza. Cabal has a weird kind of flag semantics where it will try every possible combination of flags until it finds one that builds. The solution I suggested uses this behaviour to either depend on base >= 4 && < 4.4 WITH syb, OR base < 4 WITHOUT syb. Because of the default flag setting of True, the first possibility will be tried first, but it if fails Cabal will just fall back on base < 4. In short, it should work perfectly for either GHC 7 or 6.12 clients (modulo syntax issues - I haven't actually tried the syntax I sent you). > data-memocombinators is only the tip of the iceberg; I believe much of > lambdabot would need modifications. (Apparently Control.OldException > has gone away, which alone guarantees many changes.) So there wouldn't > be much point to changing show. Actually, I: * Fixed the show upper bound * Fixed data-memocombinators and data-inttrie upper bounds (and sent a pull request to get Luke to take these changes upstream) * Got Wouter to change the upper bound on IOSpec (will be in the 0.2.2 release, out soon) And after all that lambdabot seemed to compile OK (though I got a link-time error about iconv because I'm on a Mac). So if you fix show GHC 7 users will be able to cabal install lambdabot! Cheers, Max

2 4

A question about monad laws
by C K Kashyap 21 Jan '11

21 Jan '11

Hi, I am trying to get a better understanding of the "monad laws" - right now, it seems too obvious and pointless. I had similar feelings about identity function when I first saw it but understood its use when I saw it in action. Could someone please help me get a better understanding of the necessity of monads complying with these laws? I think, examples of somethings stop working if the monad does not obey these laws will help me understand it better. Regards, Kashyap

4 5

Re: [Haskell-cafe] Haskell, C and Matrix Multiplication
by John Lato 20 Jan '11

20 Jan '11

Rather than commenting on the code provided, here are the two biggest wins I've had recently with Haskell. Both of these are part of a physical modeling project. 1) uu-parsinglib - simple to use and automatic error correction. I really, really enjoy working with this library, and how often can you say that? 2) STM - the original design reads a system and all inputs from a config file, then runs the system and produces output. I wanted to build the system from a file but collect inputs and produce output in real-time. After a few small adjustments, a few TVar's and a TMVar, and three forkIO's, it was working. One concern is that the engine (which is computation-intensive) shouldn't block waiting for input, it should just continue on and catch up later. With STM, this can be expressed as: atomically $ getInputs inputTVar `orElse` return () and there's the desired behavior. Couldn't be easier. John From: Blake Rain <blake.rain(a)gmail.com> > > Dear Haskellers, > > I thought I'd take some time to share something of my weekend with > you all. Not because of anything new, but because it is a > feel-good example of Haskell being win. A good read for Monday > morning, perhaps. > <code snipped> > Now over to you guys! What experiences have you had which make you > glad you use Haskell? Anything make you smile recently? > > - Blake >

5 12

Haskell time line?
by michael rice 20 Jan '11

20 Jan '11

The Haskell language is some twenty years old. Is there a time line for what features were in the language's initial release and what has been added along the way? Michael

4 5

A question about monad based on http://en.wikipedia.org/wiki/Monad_(category_theory)
by C K Kashyap 20 Jan '11

20 Jan '11

Hi, I was going through http://en.wikipedia.org/wiki/Monad_(category_theory) - under Formal Definition I notice that monad is a Functor T:C -> C My question is - when we think of Maybe as a functor T:C -> C .... should we think that C here refers to Hakell types? As in, (Int and Maybe Int are objects in C) and (Int -> Int and Maybe Int -> Maybe Int are arrows in C) and T is an arrow between them. Is that right? For some reason, I was imagining them as two different categories C and D. I am not able to fully understand how those diagrams translate to haskell - I can guess that T^2 -> T referes to things like concat operation but not able to relate it to bind. Regards, Kashyap

4 4

Re: [Haskell-cafe] Building lambdabot
by Gwern Branwen 20 Jan '11

20 Jan '11

On Thu, Jan 20, 2011 at 3:24 AM, Max Bolingbroke <batterseapower(a)hotmail.com> wrote: > On 20 January 2011 01:51, Gwern Branwen <gwern0(a)gmail.com> wrote: >> It had a lot of issues which meant it wouldn't build anywhere, where >> at least the Hackage version worked at some point. I spent this >> evening working on fixing issues (rewriting the show package to use >> QuickCheck 2 rather than QuickCheck 1 was not fun!) and have uploaded >> a lambdabot and show that compile for me on GHC 6.12.1 > > The show package almost compiles on GHC 7, but: > > * You need to loosen the base upper bound to < 4.4 > * If using base >= 4, you need to depend on the syb package as well > (current version 0.3) Would this break GHC 6.12 builds? Since I do not have GHC 7 installed and, given the breakage I experienced when I installed it the other day and tried to cabal-install my usual tools, will not have it installed any time soon, I am leery of any GHC 7-related changes. data-memocombinators is only the tip of the iceberg; I believe much of lambdabot would need modifications. (Apparently Control.OldException has gone away, which alone guarantees many changes.) So there wouldn't be much point to changing show. -- gwern http://www.gwern.net

1 0

sequence and sequence_ for iteratees
by Maciej Wos 20 Jan '11

20 Jan '11

Hello Cafe! I have written some iteratee functions that I found to be very very useful and I hope they will soon make it to the iteratee library. However, I'd like to get some feedback first, particularly about the error handling. I'm sending this here rather than to iteratee mailing list at projects.haskell.org because the latter is (and has been for a while!) down... Anyway, enumSequence and enumSequence_ are inspired by Prelude's sequence and sequence_. They are useful when one has to deal with several iteratees consuming the same data. For instance, one could use enumSequence as follows: > run $ joinIM $ enumPureNChunk [1..100] 3 $ enumSequence [I.head, I.head >>= \x -> I.head >>= \y -> return (x+y), I.last] which produces: [1,3,100] Each iteratee in the list is given the same input stream. Also, enumSequence consumes as much of the stream as the iteratee in the list that consumes the most. In the above example there is no stream left after enumSequence finishes because I.last consumes everything. As an another example, enumSequence below consumes only the first two elements of the stream and the remainder is passed to stream2list: > run $ joinIM $ enumPureNChunk [1..10] 3 $ (enumSequence [I.head, I.head >> I.head] >> stream2list) [3,4,5,6,7,8,9,10] The code for enumSequence is enclosed below (enumSequence_ is almost identical!) To make it complete though I should add some sort of error handling. I'm not quite sure however what would be the best thing to do. For instance, what should happen if the stream is finished, but one of the iteratees is not done yet? Should the whole enumSequence fail? Similarly, should the whole enumSequence fail if one of the iteratees throws an error? I guess throwing some sort of recoverable error could work. But I still need to figure out how to do that! -- Maciej ########## code ########## enumSequence :: forall m s a el . (Monad m, LL.ListLike s el, Nullable s) => [Iteratee s m a] -> Iteratee s m [a] enumSequence is = liftI step where step :: Stream s -> Iteratee s m [a] step s@(Chunk xs) | LL.null xs = liftI step | otherwise = do let is' = map (joinIM . enumPure1Chunk xs) is allDone <- lift (checkIfDone is') if allDone then uncurry idone =<< lift (collectResults is') else enumSequence (updateChunk s is') -- TODO: should return an error if not all iteratees are done step (EOF _) = uncurry idone =<< lift (collectResults . map (joinIM . enumEof) $ is) -- returns true if *all* iteratees are done; otherwise returns false checkIfDone :: [Iteratee s m a] -> m Bool checkIfDone = liftM and . mapM (\i -> runIter i onDone onCont) where onDone _ _ = return True onCont _ _ = return False -- returns a list of result values and the unconsumed part of the stream collectResults :: [Iteratee s m a] -> m ([a], Stream s) collectResults = liftM (id *** foldl1 shortest) . mapAndUnzipM (\i -> runIter i onDone onCont) where onDone a s = return (a,s) onCont _ _ = error "enumSequence: collectResults failed; all iteratees should be done" shortest :: Stream s -> Stream s -> Stream s shortest (Chunk xs) (Chunk ys) | LL.length xs > LL.length ys = Chunk ys | otherwise = Chunk xs shortest s@(EOF _) _ = s shortest _ s@(EOF _) = s -- iteratee in *done* state holds the unconsumed part of the chunk it -- was given; this chunk needs to be discarded when we move further in -- the stream updateChunk :: Stream s -> [Iteratee s m a] -> [Iteratee s m a] updateChunk s = map (\i -> joinIM $ runIter i (\a _ -> return $ idone a s) icontM)

4 3

Wondering about networking programming in Haskell.
by Magicloud Magiclouds 20 Jan '11

20 Jan '11

Hi, Originally, my idea for networking programming is like: read some bytes, judge if this is enough for a packet (defined in certain protocol), if not, read more until the packet is complete, then parse it into a message. Now we have lazy in Haskell. Can I do it as: buffer <- hGetContents handle (message1, leftData1) <- parse1 buffer (message2, leftData2) <- parse2 leftData2 ... -- 竹密岂妨流水过山高哪阻野云飞

2 1

Formal Program verification in Meta-Haskell
by Alexander McPhail 20 Jan '11

20 Jan '11

Hi, I have no understanding of template haskell and thus this message is uninformed speculation. Would it not be possible to write a function verifier in TH that, unlike QuickCheck which provides bounds on a function being probably approximately correct, is given a list over properties which are proven over a quasi-quoted syntax tree? For example: > multiply :: Num a => a -> a -> a > multiply_group :: Proof Bool > multiply_group = group multiply 1 > group :: (a -> a -> a) -> a -> Proof Bool > group f ident = [proof| f, [associative, identity 1]] where `associative` and `ident` are proof-constructing functions that act over the `f` syntax tree. (Maybe some invokation of an Isabelle-like theorem prover or an SMT-like solver as part of the 'proof' module). Then we might even be able to list properties with class declarations. The properties get verified at compile time. > class Monoid a where > mzero :: a > msum :: a -> a -> a > property a [associative msum, identity mzero msum] Any thoughts? Vivian

1 0

Call for Submissions: Special Poetry and Fiction Edition of the Monad.Reader
by Brent Yorgey 20 Jan '11

20 Jan '11

Submissions are now being accepted for a special POETRY AND FICTION edition of the Monad.Reader. Poems about Haskell, short stories about Haskell, poems about poems about Haskell, elaborate monad tutorial allegories, Haskell/Dinosaur Comics crossovers: all fair game! If you want a bit of inspiration, check out the links at the end of this message [1,2,3]. But you are a creative bunch, I'm sure you can come up with all sorts of fun ideas and formats. The submission deadline will be **Friday, February 18** but feel free to send submissions at any time between now and then. Questions That May Be Asked Frequently (QTMBAF) ----------------------------------------------- Q. Are you serious? A. Absolutely. Q. The deadline is only four weeks away! It will take me at least five weeks to write my incredible masterpiece! A. Are you serious? Q. Will you take every submission or will there be some sort of selection process? A. I hope to publish every submission, although not without going through a process of editing and suggested revisions. Ultimately, it depends on the number of submissions. Q. Can I submit the same poem multiple times to increase my chances? A. I have written a sophisticated, 5000-line Haskell program to detect this and alter your submission in a subtle yet highly embarrassing (for you) way. Q. Seriously, this is a dumb idea. A. Please try to phrase your question in the form of a question. Q. Seriously, is this a dumb idea? A. No, I'm pretty sure it is awesome. Submission Details ------------------ Submissions should be sent to (byorgey at cis.upenn.edu) Simple text submissions are fine for short submissions such as poetry. For longer submissions, LaTeX is appreciated. See the guidelines here to get started: http://themonadreader.wordpress.com/contributing/ If submitting in LaTeX is a hardship, text submissions will be accepted. Submissions in Microsoft Word format will be deleted and then overwritten fifty times with random bits. [1] http://haskell.org/haskellwiki/Humor/Poetry [2] http://haskell.org/haskellwiki/Haiku [3] http://www.cis.upenn.edu/~byorgey/haskell-alphabet/index.html

1 0

Haskell Weekly News: Issue 165 - January 19, 2011
by Daniel Santa Cruz 20 Jan '11

20 Jan '11

Welcome to issue 165 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of January 9 to 15, 2011. Announcements Brent Yorgey [2]announced the release of issue 17 of The Monad.Reader, containing the following three articles: List Leads Off with the Letter Lambda by Douglas M. Auclair, The InterleaveT Abstraction: Alternative with Flexible Ordering by Neil Brown, and The Reader Monad and Abstraction Elimination by Petr Pudlak. Andy Stewart [3]sent an invite to anyone interested in joining the Manatee team. Manatee is a Haskell integrated environment written in Haskell. Follow the link to see some videos posted for a better idea of what the tool is. Niklas Broberg [4]announced the release of version 1.10.1 of haskell-src-extensions. Huibiao Zhu [5]sent a call for papers to the 13th International Conference on Formal Engineering Methods to be held in Durham, UK on October 25-28 2011. Read on to see what was hot in the Haskell community around the net... Quotes of the Week * ion: ddarius: Yeah, abstract concepts absolutely hate being anthropomorphized. * gwern: there are no beginnings or ends to the circular list; but a cons cell thunked in Amador... * tac-tics: If you wish to create the universe from scratch, you must first invent the continuation. * sproingie: hm. Â i can't remember how to use @remember * NOTE: Just say @remember :) I'm grepping the logs to find these things * Kaidelong: <Kaidelong> take 6 "bananas" <lambdabot> "banana" <Kaidelong> clearly lambdabot is keeping the bananas to itself and lying about it * hpc: functor and applicative are easy, since you can remember them as "those things what look like function application, sort of" Top Reddit Stories * RFC: migrating GHC development to git Domain: haskell.org, Score: 51, Comments: 66 On Reddit: http://www.reddit.com/r/haskell/comments/ezgvs/rfc_migrating_ghc_developmen… Original: http://www.haskell.org/pipermail/glasgow-haskell-users/2011-January/019752.… * [CCC] On how Haskell’s Arrows are NOT just function compositions with a fancier name Domain: ro-che.info, Score: 38, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/f3e06/ccc_on_how_haskells_arrows_a… Original: http://ro-che.info/ccc/12.html * foldl vs foldl', and why you should always use the latter Domain: reddit.com, Score: 35, Comments: 8 On Reddit: http://www.reddit.com/r/haskell/comments/f25iv/foldl_vs_foldl_and_why_you_s… Original: http://www.reddit.com/r/haskell/comments/f150x/whats_wrong_with_my_haskell_… * ~Haskell 2011 Domain: haskell.org, Score: 32, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/ezmzh/haskell_2011/ Original: http://www.haskell.org/pipermail/haskell/2011-January/022497.html * The Monad.Reader: Issue 17 Domain: themonadreader.wordpress.com, Score: 30, Comments: 10 On Reddit: http://www.reddit.com/r/haskell/comments/ezft9/the_monadreader_issue_17/ Original: http://themonadreader.wordpress.com/2011/01/09/issue-17/ * Painless NP-complete problems: an embedded DSL for SMT solving Domain: donsbot.wordpress.com, Score: 27, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/f3fp6/painless_npcomplete_problems… Original: http://donsbot.wordpress.com/2011/01/16/painless-np-complete-problems-an-em… * Oregon Programming Languages Summer School: Types, Semantics, and Verification Domain: lists.seas.upenn.edu, Score: 22, Comments: 20 On Reddit: http://www.reddit.com/r/haskell/comments/f15rm/oregon_programming_languages… Original: http://lists.seas.upenn.edu/pipermail/types-announce/2011/002241.html * Announcing Web Application Interface 0.3.0 (now with more speed) Domain: docs.yesodweb.com, Score: 20, Comments: 2 On Reddit: http://www.reddit.com/r/haskell/comments/f0e6f/announcing_web_application_i… Original: http://docs.yesodweb.com/blog/announcing-wai-0-3/ * A bran new functional programming (Haskell inter alia) jobs site (corrected link) Domain: functionaljobs.com, Score: 19, Comments: 11 On Reddit: http://www.reddit.com/r/haskell/comments/ezqst/a_bran_new_functional_progra… Original: http://functionaljobs.com/ * [PDF] Orthogonal Serialization For Haskell Domain: mathematik.uni-marburg.de, Score: 17, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/f1o8t/pdf_orthogonal_serialization… Original: http://www.mathematik.uni-marburg.de/~berthold/papers/mainIFL10-withCopyrig… Top StackOverflow Questions * Monads as adjunctions votes: 15, answers: 3 Read on SO: http://stackoverflow.com/questions/4697320/monads-as-adjunctions * What is a VM and why do dynamic languages need one? votes: 11, answers: 8 Read on SO: http://stackoverflow.com/questions/4640809/what-is-a-vm-and-why-do-dynamic-… * Is Haskell a Lisp? votes: 9, answers: 5 Read on SO: http://stackoverflow.com/questions/4696618/is-haskell-a-lisp * Are there any connections between Haskell and LINQ? votes: 8, answers: 4 Read on SO: http://stackoverflow.com/questions/4683506/are-there-any-connections-betwee… * Haskell newbie on types votes: 7, answers: 4 Read on SO: http://stackoverflow.com/questions/4664429/haskell-newbie-on-types * I can't seem to figure out type variables mixed with classes. votes: 5, answers: 2 Read on SO: http://stackoverflow.com/questions/4653102/i-cant-seem-to-figure-out-type-v… * Emacs align-regexp on = but not == votes: 5, answers: 1 Read on SO: http://stackoverflow.com/questions/4653575/emacs-align-regexp-on-but-not * Current status of automatic parallelism in Haskell [closed] votes: 5, answers: 3 Read on SO: http://stackoverflow.com/questions/4701207/current-status-of-automatic-para… About the Haskell Weekly News You can find an html version of this newsletter at: http://contemplatecode.blogspot.com/2011/01/haskell-weekly-news-issue-165.h… To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18419 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/85224 4. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18427 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18428

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Building lambdabot
by Joe Bruce 20 Jan '11

20 Jan '11

I've had a bit of an adventure trying to build and run lambdabot<http://hackage.haskell.org/package/lambdabot-4.2.2.1> on my box. 'cabal install lambdabot' does not work. It states it's not GHC 6.12 (and certainly not 7.0) compatible, but I tried 6.12 anyway and got nowhere. Next, I tried 6.10 but failed on the unix dependency (in the same manner as this thread<http://web.archiveorange.com/archive/v/nDNOvQMXUGwfkyy0ITet>). The thread is unresolved, so I've not tried modifying the cabal build-depends. I'm hoping to find someone who has a working lambdabot setup who can point me in the right direction. What further information about my struggles should I provide? Thanks, Joe

5 14

Community.haskell.org is down
by Neil Mitchell 19 Jan '11

19 Jan '11

http://www.downforeveryoneorjustme.com/http://community.haskell.org Currently community is down for me. I remember some infrastructure/website strike team was set up, but I couldn't find where to get in contact with them? Thanks, Neil

2 1

planet@community.haskell.org and Mailman Images
by Jon Kristensen 19 Jan '11

19 Jan '11

Just two small comments: The e-mail address planet(a)community.haskell.org mentioned at http://planet.haskell.org/ bounces ("connect to community.haskell.org[72.249.126.23]: Connection timed out"). Also, registering on this mailing list to report the problem, I realized that the mailman images at pages such as http://www.haskell.org/mailman/subscribe/haskell-cafe are broken too. Something you might want to take a look at! Warm regards, Jon Kristensen

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Happstack events and web page refreshing
by Corentin Dupont 19 Jan '11

19 Jan '11

Hello again, I have another question for happstack users/experts: I have a program with happstack-state and a web server with happstack-server. What I'd like is, whenever the MACID state is changed, that the web page is refreshed for every clients connected on the web server. So I think the question is 2 fold: - How to add an event handler on happstack-state for that? - How to ask to the web server to refresh every clients? I did not found infos about that in the API. Thanks a lot, Corentin On Thu, Jan 13, 2011 at 9:40 PM, Corentin Dupont <corentin.dupont(a)gmail.com>wrote: > Hello, > > I'm using the combination happstack + digestive-functors + web-routes + > blazeHTML. > I'm not finding any examples on the net... > > I've tried to adapt your example (thanks): > > type NomicForm a = HappstackForm IO String BlazeFormHtml a > > demoForm :: NomicForm (Text, Text) > demoForm = > (,) <$> ((TDB.label "greeting: " ++> inputNonEmpty Nothing) <* br) > <*> ((TDB.label "noun: " ++> inputNonEmpty Nothing) <* br) > <* (submit "submit") > where > br :: NomicForm () > br = view H.br > -- make sure the fields are not blank, show errors in line if they > are > inputNonEmpty :: Maybe Text -> NomicForm Text > inputNonEmpty v = > (inputText v `validate` (TD.check "You can not leave this field > blank." (not . T.null)) <++ errors) > > > But I've got a problem on submit and inputText. I don't see how they are > compatible with HappstackForm. > NomicForm a reduces to: > Form (ServerPartT IO) Input String BlazeFormHtml a > > whereas the type of submit is: > > submit :: Monad m > > => String -- ^ Text on the submit button > > -> Form m String e BlazeFormHtml () -- ^ Submit button > > > Maybe I miss some instance? > > BTW, I also tried to execute your exemple, but I can't install some packages. > > > cabal install digestive-functors-hsp > > cabal: Unknown build tool trhsx > > Whereas trhsx is in my PATH (under linux). > > You said I need the latest happstack from darcs, why? > > Cheers, > Corentin > > > On Sun, Jan 9, 2011 at 8:36 PM, Jeremy Shaw <jeremy(a)n-heptane.com> wrote: > >> Hello, >> >> newRule also needs to have the type, RoutedNomicServer. The >> transformation of RoutedNomicServer into NomicServer is done in the >> handleSite function. Something like this: >> >> >> nomicSpec :: ServerHandle -> Site Route (ServerPartT IO Response) >> nomicSpec sh = >> Site { handleSite = \f url -> unRouteT (nomicSite sh url) f >> ... >> >> main = >> do ... >> simpleHTTP nullConf $ siteImpl (nomicSpec sh) >> >> Or something like that -- it's hard to tell exactly what is going on >> in your app based on the snippets you provided. >> >> Also, I highly recommend using digestive functors instead of formlets. >> It is the successor to formlets. Same core idea, better implementation >> and actively maintained. >> >> I have attached a quick demo of using: >> >> happstack+digestive-functors+web-routes+HSP >> >> To use it you will need the latest happstack from darcs plus: >> >> hsp >> web-routes >> web-routes-hsp >> web-routes-happstack >> web-routes-mtl >> digestive-functors >> digestive-functors-hsp >> >> I plan to clean up this example and document it better in the crash >> course for the upcoming release. Clearly things like the FormInput >> instance and the formPart function belong a library. >> >> let me know if you have more questions. >> - jeremy >> >> On Sat, Jan 8, 2011 at 6:44 PM, Corentin Dupont >> <corentin.dupont(a)gmail.com> wrote: >> > Hello, >> > >> > I have difficulties mixing web-routes and forms: >> > I have put routes in all my site, except for forms which remains with >> the >> > type ServerPartT IO Response. >> > How to make them work together? >> > >> > I have: >> > type NomicServer = ServerPartT IO >> > type RoutedNomicServer = RouteT PlayerCommand NomicServer >> > >> > newRule :: ServerHandle -> NomicServer Response >> > newRule sh = do >> > methodM POST -- only accept a post method >> > mbEntry <- getData -- get the data >> > case mbEntry of >> > Nothing -> error $ "error: newRule" >> > Just (NewRule name text code pn) -> do >> > html <- nomicPageComm pn sh (submitRule name text code pn)) >> > ok $ toResponse html >> > >> > >> > nomicPageComm :: PlayerNumber -> ServerHandle -> Comm () -> >> > RoutedNomicServer Html >> > nomicPageComm pn sh comm = >> > (..) >> > >> > >> > launchWebServer :: ServerHandle -> IO () >> > launchWebServer sh = do >> > putStrLn "Starting web server...\nTo connect, drive your browser to >> > \"http://localhost:8000/Login\ <http://localhost:8000/Login%5C>"" >> > d <- liftIO getDataDir >> > simpleHTTP nullConf $ mconcat [dir "postLogin" $ postLogin, >> > fileServe [] d, >> > dir "Login" $ ok $ toResponse $ >> loginPage, >> > dir "NewRule" $ newRule sh, >> > dir "NewGame" $ newGameWeb sh, >> > dir "Nomic" $ do >> > html <- implSite >> > "http://localhost:8000/Nomic/" "" (nomicSite sh) >> > ok $ toResponse html >> > ] >> > >> > >> > The red line doesn't compile. I don't know how to transform a >> > RoutedNomicServer into a NomicServer. >> > >> > For the future I intend to use formlets: is these some examples of >> programs >> > using happstack + web-routes + formlets? >> > >> > Thanks, >> > Corentin >> > >> > >> > >> > >> > On Fri, Jan 7, 2011 at 5:10 PM, Jeremy Shaw <jeremy(a)n-heptane.com> >> wrote: >> >> >> >> Hello, >> >> >> >> The [(String, String)] argument is for adding query parameters. >> >> >> >> > encodePathInfo ["foo", "bar", "baz"] [("key","value")] >> >> >> >> "foo/bar/baz?key=value" >> >> >> >> Instead of showURL you would use showURLParams. >> >> >> >> hope this helps!d >> >> - jeremy >> >> >> >> On Fri, Jan 7, 2011 at 8:12 AM, Corentin Dupont >> >> <corentin.dupont(a)gmail.com> wrote: >> >> > Hello Jeremy, >> >> > I'm using Web routes with happstack. >> >> > I'm following this tutorial: >> >> > http://tutorialpedia.org/tutorials/Happstack+type+safe+URLs.html >> >> > >> >> > But It seems out of synch with the latest version of web-routes: >> 0.23.2. >> >> > The haddock documentation seems out of date also: >> >> > >> >> > encodePathInfo :: [String] -> [(String, String)] -> String >> >> > >> >> > For example: >> >> > >> >> > encodePathInfo [\"foo\", \"bar\", \"baz\"] >> >> > >> >> > "foo/bar/baz" >> >> > >> >> > And I can't figure out what this [(String, String)] is for ;) >> >> > >> >> > Thanks, >> >> > >> >> > Corentin >> >> > >> > >> > >> > >

5 9

getting fulling qualified names of types from hint/ghc api
by Pasqualino "Titto" Assini 19 Jan '11

19 Jan '11

Hi, I am using hint's Language.Haskell.Interpreter.typeOf function to dynamically get the type of a haskell expression but, unfortunately for my purposes, I see that it returns unqualified names (I see in Hint.Conversions that it uses the GHC function GHC.getPrintUnqual). Is there any function in the GHC api or any other simple way of getting the fully qualified types? Surprisingly, I could not find any. Thanks, titto -- Dr. Pasqualino "Titto" Assini http://quid2.org/

1 0

Building Haskell Platform on PowerPC?
by Tim Chevalier 19 Jan '11

19 Jan '11

Hello, For reference, I'm wondering whether there's an easier way to build the current version of the Haskell Platform on a PowerPC Mac running Mac OS 10.5.8 than the way in which I documented at: http://tim.dreamwidth.org/1715938.html I was installing the platform from scratch as a favor for a colleague who didn't have any version of GHC installed on his machine, and I just couldn't find a simpler way than installing two other versions of GHC first. Just curious if anyone has done it. I realize PPC is unsupported. Cheers, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc/ * Often in error, never in doubt "an intelligent person fights for lost causes,realizing that others are merely effects" -- E.E. Cummings

1 0