- Haskell-Cafe - Haskell.org

haskell-src-meta installation failed
by Qiuchi Jian 10 Apr '11

10 Apr '11

Hi guys, I tried to install haskell-src-meta and got the error below. I checked all dependencies which are listed on the hackage page, they are all installed with the right version. Can anyone tell me what is the problem? Thanks a lot. jqc@ubuntu:~$ cabal install haskell-src-meta Resolving dependencies... Configuring haskell-src-meta-0.3... Preprocessing library haskell-src-meta-0.3... Building haskell-src-meta-0.3... [1 of 7] Compiling Language.Haskell.Meta.Syntax.Translate ( src/Language/Haskell/Meta/Syntax/Translate.hs, dist/build/Language/Haskell/Meta/Syntax/Translate.o ) src/Language/Haskell/Meta/Syntax/Translate.hs:19:0: Bad interface file: /home/jqc/.cabal/lib/haskell-src-exts-1.9.6/ghc-6.12.3/Language/Haskell/Exts/Syntax.hi Data.Binary.getWord8: end of file cabal: Error: some packages failed to install: haskell-src-meta-0.3 failed during the building phase. The exception was: ExitFailure 1 Regards, Jian

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CFP -- Haskell Symposium 2011
by Haskell Symposium 10 Apr '11

10 Apr '11

"Haskell 2011" ACM SIGPLAN Haskell Symposium 2011 Tokyo, Japan 22nd September, 2011 CALL FOR PAPERS http://www.haskell.org/haskell-symposium/2011/ The ACM SIGPLAN Haskell Symposium 2011 will be co-located with the 2011 International Conference on Functional Programming (ICFP), in Tokyo, Japan. The purpose of the Haskell Symposium is to discuss experiences with Haskell and future developments for the language. The scope of the symposium includes all aspects of the design, semantics, theory, application, implementation, and teaching of Haskell. Topics of interest include, but are not limited to: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal treatments of the semantics of the present language or future extensions, type systems, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management as well as foreign function and component interfaces; * Tools, in the form of profilers, tracers, debuggers, pre-processors, testing tools, and suchlike; * Functional Pearls, being elegant, instructive examples of using Haskell; * Applications, using Haskell for scientific and symbolic computing, database, multimedia, telecom and web applications, and so forth; * Practice and Experience, general experience with Haskell in education and industry. Papers in the latter three categories need not necessarily report original research results; they may instead, for example, report practical experience that will be useful to others, reusable programming idioms, or elegant new ways of approaching a problem. (More advice appears on the symposium webpage.) The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a program! Submission Details * Submission Deadline: Monday, 6th June 2011 * Author Notification: Friday, 1st July 2011 * Final Papers Due : Sunday, 10th July 2011 Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (http://www.acm.org/sigs/sigplan/authorInformation.htm) The text should be in a 9pt font in two columns; the length is restricted to 12 pages, except for "Applications, Practice, and Experience" papers, which are restricted to 6 pages. Each submission must adhere to SIGPLAN's republication policy, as explained on the web. Violation risks summary rejection of the offending submission. Accepted papers will be published by the ACM and will appear in the ACM Digital Library. In addition, we solicit proposals for system demonstrations, based on running (perhaps prototype) software rather than necessarily on novel research results. Proposals are limited to 2-page abstracts, in the same ACM format as papers, and should explain why a demonstration would be of interest to the Haskell community. They will be assessed for relevance by the PC; accepted proposals will be published on the Symposium website, but not formally published in the proceedings. Links * http://www.haskell.org/haskell-symposium, the permanent homepage of the Haskell Symposium. * http://www.haskell.org/haskell-symposium/2011, the 2011 Haskell Symposium web page. * http://www.icfpconference.org/icfp2011, the ICFP 2011 web page. Programme Committee * Koen Claessen, Chalmers University of Technology (chair) * Conal Elliott, LambdaPix * Andy Gill, University of Kansas * Ralf Hinze, Oxford University * Graham Hutton, University of Nottingham * John Launchbury, Galois, Inc. * Sam Lindley, University of Edinburgh * Rita Loogen, Philipps-Universität Marburg * Neil Mitchell, Standard Chartered * Matthew Naylor, University of York * Bruno Oliveira, Seoul National University * Dimitrios Vytiniotis, Microsoft Research * Steve Zdancewic, University of Pennsylvania

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ImProve Tutorial
by Tom Hawkins 10 Apr '11

10 Apr '11

ImProve is a Haskell eDSL for embedded control systems -- we use it for automotive and off-highway powertrain control. I've started writing a tutorial for ImProve. So far it has a basic tour of the language and a handful of examples. Comments and suggestions are welcome. In other recent news, ImProve can now generate models in Simulink and Modelica. -Tom [1] http://github.com/tomahawkins/improve/wiki/ImProve

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Deciding equality of functions.
by Grigory Sarnitskiy 10 Apr '11

10 Apr '11

I guess that deciding whether two functions are equal in most cases is algorithmically impossible. However maybe there exists quite a large domain of decidable cases? If so, how can I employ that in Haskell? It is a common situation when one has two implementations of the same function, one being straightforward but slow, and the other being fast but complex. It would be nice to be able to check if these two versions are equal to catch bugs in the more complex implementation.

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ANNOUNCE: hplaylist-0.1
by Tim Chevalier 10 Apr '11

10 Apr '11

Hello, hplaylist is a very simple command-line utility, written in Haskell, for automatically syncing an iTunes playlist to a non-Apple-manufactured MP3 player (anything that mounts as a USB drive should work in principle). For example, if I have an iTunes playlist called "Songs about cheese", hplaylist allows me to type: $ hplaylist "Songs about cheese" which automatically copies the named playlist, and all music files included in the playlist, to my device. Download at: http://hackage.haskell.org/package/hplaylist-0.1 or https://github.com/catamorphism/hplaylist 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

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Testing Implementation vs Model - Records or Type Classes?
by Heinrich Apfelmus 09 Apr '11

09 Apr '11

Hello, I'm writing a small Haskell library for functional reactive programming. The core of the library consists of two data types and several primitives. However, I have programmed this core *twice*: once as a *model* that displays the intended semantics, and once as the actual *implementation* to be used in production code. Of course, I would like to use QuickCheck to test that the implementation gives the same results as the model. My problem is: how to organize this with the minimum amount of boilerplate? It appears that I can use *multiparameter type classes* to solve this, but I'm not sure I'm happy with this, in particular because it makes the generated Haddock less readable (see 3) below). On the other hand, I could also use *record wildcards* to conveniently reify a module into a record data structure. But that will give me problems with combinators that are derived from the core combinators (see 2) below). Haskell Café, what are your suggestions and ideas? In particular, I wish to: 1) Write examples to be QuickChecked only once. I imagine that my main function for testing looks like this test_equal example = forAll $ \input -> example model input == example implementation input where example an expression involving the combinators from my library. The point is that I don't want to write example twice, once for each version. 2) Use derived combinators. For reference, here the full signature of the core combinators: data Event a data Behavior a instance Functor Behavior instance Applicative Behavior instance Functor Event instance Monoid (Event a) filter :: (a -> Bool) -> Event a -> Event a apply :: Behavior (a -> b) -> Event a -> Event b accumB :: a -> Event (a -> a) -> Behavior a When writing tests, I also want to use common derived combinators, like, say filterJust :: Event (Maybe a) -> Event a filterJust = fmap fromJust . filter isJust without implementing them twice. 3) Obtain readable Haddock. I like the simplicity and readability of an ordinary module signature. In contrast, libraries with many type class scare me. Or is there a way to make this less scary? I'm not sure about the last one: 4) Make both model and implementation available to the user, so that he can QuickCheck his own programs as well. Since the implementation makes heavy use of IO, it is a bit harder to test automatically, so the model might be useful to have. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com

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ANNOUNCE: normaldistribution-1.1 – Minimum fuss normally distributed random values.
by Bjorn Buckwalter 09 Apr '11

09 Apr '11

Dear all, Thanks to enlightening advice from Tom Nielsen and Zoltan Novak normaldistribution now generates normally distributed values using the Box-Muller method instead of the Central Limit Theorem. This change provides a 5-10x speedup. The only API impact is that the random values must now be instances of Floating rather than just Fractional. (The pre-canned Random instances that satisfy Fractional, i.e. Double and Float, also satisfy Floating.) Cheers, Bjorn ---------- Forwarded message ---------- From: Bjorn Buckwalter <bjorn.buckwalter(a)gmail.com> Date: Sat, Apr 9, 2011 at 15:21 Subject: ANNOUNCE: normaldistribution-1.0 – Minimum fuss normally distributed random values. Dear all, I'm pleased to announce the immediate availability of the normaldistribution library on hackage: http://hackage.haskell.org/package/normaldistribution This purpose of this library is to have a simple API and no dependencies beyond Haskell 98 in order to let you produce normally distributed random values with a minimum of fuss. This library does not attempt to be blazingly fast nor to pass stringent tests of randomness. It attempts to be very easy to install and use while being "good enough" for many applications (simulations, games, etc.). The API builds upon and is largely analogous to that of the Haskell 98 Random module (more recently System.Random). Pure: > (sample,g) = normal myRandomGen -- using a Random.RandomGen > samples = normals myRandomGen -- infinite list > samples2 = mkNormals 10831452 -- infinite list using a seed In the IO monad: > sample <- normalIO > samples <- normalsIO -- infinite list With custom mean and standard deviation: > (sample,g) = normal' (mean,sigma) myRandomGen > samples = normals' (mean,sigma) myRandomGen > samples2 = mkNormals' (mean,sigma) 10831452 > sample <- normalIO' (mean,sigma) > samples <- normalsIO' (mean,sigma) Internally the library uses the Central Limit Theorem to approximate normally distributed values from multiple uniformly distributed random values. Enjoy, Bjorn

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ANNOUNCE: normaldistribution-1.0 – Minimum fuss normally distributed random values.
by Bjorn Buckwalter 09 Apr '11

09 Apr '11

Dear all, I'm pleased to announce the immediate availability of the normaldistribution library on hackage: http://hackage.haskell.org/package/normaldistribution This purpose of this library is to have a simple API and no dependencies beyond Haskell 98 in order to let you produce normally distributed random values with a minimum of fuss. This library does not attempt to be blazingly fast nor to pass stringent tests of randomness. It attempts to be very easy to install and use while being "good enough" for many applications (simulations, games, etc.). The API builds upon and is largely analogous to that of the Haskell 98 Random module (more recently System.Random). Pure: > (sample,g) = normal myRandomGen -- using a Random.RandomGen > samples = normals myRandomGen -- infinite list > samples2 = mkNormals 10831452 -- infinite list using a seed In the IO monad: > sample <- normalIO > samples <- normalsIO -- infinite list With custom mean and standard deviation: > (sample,g) = normal' (mean,sigma) myRandomGen > samples = normals' (mean,sigma) myRandomGen > samples2 = mkNormals' (mean,sigma) 10831452 > sample <- normalIO' (mean,sigma) > samples <- normalsIO' (mean,sigma) Internally the library uses the Central Limit Theorem to approximate normally distributed values from multiple uniformly distributed random values. Enjoy, Bjorn

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Is there a way to find out the type inferred for a local function inside another function? :)
by KC 09 Apr '11

09 Apr '11

-- -- Regards, KC

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Patch: adding CTR, CMAC and SIV modes to the Crypto API
by klondike 09 Apr '11

09 Apr '11

Hi, After a few weeks of hard work I have managed to add the CTR, CMAC and SIV modes of operation. The implemententation passes all the KATS I could find and is made as efficiently as possible without forgetting the risk of timing attacks over them. The patch is attached here and you can free it along with your library with a BSD-3 license as long as you recognize the authorship. Francisco Blas Izquierdo Riera (klondike) PS: Attached is also a set of commands I used with ghci to check quickly the implementation and which contain parts of the KATS I used, feel free to use them.

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