April 2013 - Haskell-Cafe

Building the Haskell Platform in Linux
by Daniel Díaz Casanueva 14 Apr '13

14 Apr '13

Hi cafe! Probably you all know how to do this, but I myself found confused when building the Haskell Platform in Linux for my first time. I was using Linux for my first time too! The first problem I encountered was to decide what linux packages install to make the ./configure successful in both GHC binary distribution and the Haskell Platform. So I collected the names of the minimum set of packages that you need to have installed before starting with GHC and the Platform in a small blog post: http://deltadiaz.blogspot.com/2013/04/haskell-platform-from-source-in-linux… If I would have to start all over again, forgetting what I have learned so far, I would fine this list very useful! This thought is what brought me here to make it public. Who knows, maybe I am saving somebody of some google searches and trials and errors. With my best intentions, Daniel Díaz. -- E-mail sent by Daniel Díaz Casanueva let f x = x in x

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multivariate normal distribution in Haskell?
by Bas de Haas 14 Apr '13

14 Apr '13

Dear List, I’m implementing a probabilistic model for recognising musical chords in Haskell. This model relies on a multivariate normal distribution. I’ve been searching the internet and mainly hackage for a Haskell library to do this for me, but so far I’ve been unsuccessful. What I’m looking for is a Haskell function that does exactly what the mvnpdf function in matlab does: http://www.mathworks.nl/help/stats/multivariate-normal-distribution.html Does anyone know a library that can help me out? Thanks. Kind regards, Bas de Haas -- dr. W. Bas de Haas Department of Information and Computing Sciences Utrecht University E: W.B.deHaas(a)uu.nl T: +31 30 253 5965 I: http://www.uu.nl/staff/WBdeHaas/

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Re: [Haskell-cafe] <package>-inplace is shadowed by package <package>-<hexstring>
by Niklas Hambüchen 14 Apr '13

14 Apr '13

Hi, I just got the same thing with attoparsec GIT: Preprocessing benchmark 'benchmarks' for attoparsec-0.10.4.0... Building benchmark benchmarks... creating dist/build/benchmarks creating dist/build/benchmarks/benchmarks-tmp /home/niklas/opt/haskell-7.4/bin/ghc --make -fbuilding-cabal-package -O -odir dist/build/benchmarks/benchmarks-tmp -hidir dist/build/benchmarks/benchmarks-tmp -stubdir dist/build/benchmarks/benchmarks-tmp -i -idist/build/benchmarks/benchmarks-tmp -ibenchmarks -idist/build/autogen -Idist/build/autogen -Idist/build/benchmarks/benchmarks-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -hide-all-packages -package-conf dist/package.conf.inplace -package-id base-4.5.1.0-66f22db3dfcd87541c9c7e50e7095d26 -package-id bytestring-0.9.2.1-503e91bb155301fdb1956cb5c26ce6e9 -package-id criterion-0.6.2.1-5bc7e5a96c8208948366b8e3ea536e68 -package-id deepseq-1.3.0.0-c26e15897417ecd448742528253d68f6 -package-id parsec-3.1.3-771f99c8818551756b6f2ec3e86ab039 -package-id text-0.11.2.3-db61832d0c4660614c4ceff234ed4abb -package-id attoparsec-0.10.4.0-inplace -XHaskell98 benchmarks/Benchmarks.hs -o dist/build/benchmarks/benchmarks <command line>: cannot satisfy -package-id attoparsec-0.10.4.0-inplace: attoparsec-0.10.4.0-inplace is shadowed by package attoparsec-0.10.4.0-c391286d724823eaea3d4278acc0acc0 (use -v for more information) I have no clue what's going on!

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Invitation to connect on LinkedIn
by Chatura Roche 14 Apr '13

14 Apr '13

LinkedIn ------------ Chatura Roche requested to add you as a connection on LinkedIn: ------------------------------------------ Steve, I'd like to add you to my professional network on LinkedIn. - Chatura Accept invitation from Chatura Roche http://www.linkedin.com/e/-j6322o-hfici7ky-5i/v4h1gXJ8v-XpaSE4KRp1AY1vvMqM3… View profile of Chatura Roche http://www.linkedin.com/e/-j6322o-hfici7ky-5i/rso/115844279/bO7F/name/25907… ------------------------------------------ You are receiving Invitation emails. This email was intended for Steve Severance. Learn why this is included: http://www.linkedin.com/e/-j6322o-hfici7ky-5i/plh/http%3A%2F%2Fhelp%2Elinke… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

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Fwd: [Haskell-beginners] Monad instances and type synonyms
by Christopher Howard 14 Apr '13

14 Apr '13

I asked this question in Haskell-beginners, but I haven't heard anything yet, so I'm forwarding to Cafe. -------- Original Message -------- Subject: [Haskell-beginners] Monad instances and type synonyms Date: Sat, 13 Apr 2013 17:03:57 -0800 From: Christopher Howard <christopher.howard(a)frigidcode.com> Reply-To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell <beginners(a)haskell.org> To: Haskell Beginners <beginners(a)haskell.org> I am playing around with some trivial code (for learning purposes) I wanted to take code: -------- -- SaleVariables a concrete type defined early -- `Adjustment' represents adjustment in a price calculation -- Allows functions of type (a -> Adjustment a) to be composed -- with an appropriate composition function type Adjustment a = SaleVariables -> a -------- And put it into code: -------- instance Monad Adjustment where (>>=) = ... return = ... -------- If I try this, I get code: -------- Type synonym `Adjustment' should have 1 argument, but has been given none In the instance declaration for `Monad Adjustment' -------- But if I give an argument, then it doesn't compile either (it becomes a "*" kind). And I didn't want to make the type with a regular "data" declaration either, because then I have to give it a constructor, which doesn't fit with what I want the type to do. -- frigidcode.com

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Re: [Haskell-cafe] Fwd: [Haskell-beginners] Monad instances and type synonyms
by Chris Wong 14 Apr '13

14 Apr '13

On Sun, Apr 14, 2013 at 5:10 PM, Christopher Howard <christopher.howard(a)frigidcode.com> wrote: > type Adjustment a = SaleVariables -> a > > [...] > > instance Monad Adjustment where > > (>>=) = ... > return = ... Essentially, you can't partially apply type synonyms. I don't recall the exact reasoning, but if this sort of thing was allowed it would probably poke funny holes in the type system. Also, Control.Monad.Instances already supplies a Monad instance for functions (r -> a). So even if that did pass, you'd bump into overlapping instances anyway. Chris > -------- > If I try this, I get > > code: > -------- > Type synonym `Adjustment' should have 1 argument, but has been given none > In the instance declaration for `Monad Adjustment' > -------- > > But if I give an argument, then it doesn't compile either (it becomes a > "*" kind). And I didn't want to make the type with a regular "data" > declaration either, because then I have to give it a constructor, which > doesn't fit with what I want the type to do. > > -- > frigidcode.com > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Chris Wong, fixpoint conjurer e: lambda.fairy(a)gmail.com w: http://lfairy.github.io/

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case switch covering all possible constructor but still fails
by Nathan Hüsken 13 Apr '13

13 Apr '13

Hey, I am trying to fix (or at least get my head around) this: https://github.com/valderman/haste-compiler/issues/27 Which is an issue of the haste haskell->javascript compiler. Doing so I encounter this problem which makes me think I am not understanding something fundamental here (and I believe this not to be haste specific)... OK, the problem is that this code: genAlt :: Bool -> JSVar -> JSVar -> StgAlt -> JSGen Config JSAlt genAlt tailpos scrut res (con, args, used, body) = do construct <- case con of DEFAULT -> return Def LitAlt l -> Cond <$> genLit l DataAlt c | Right tag <- genDataConTag c -> return $ Cond tag _ -> error "Bad data constructor tag generated!" Looking at StgAlt, I conclude that con must be of type AltCon, which is defined like this (from CoreSyn.lhs of the ghc source): data AltCon = DataAlt DataCon | LitAlt Literal | DEFAULT deriving (Eq, Ord, Data, Typeable) What I do not understand: The case switch covers all possibilities of AltCon. So how can this happen? Using trace, the con seemed to have the type "GHC.Integer.Type.S#" in the case of the erro. Thanks! Nathan

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NaN as Integer value
by Алексей Егоров 13 Apr '13

13 Apr '13

Hello haskellers, is there a reason why Integer doesn't have 'NaN' as value? I think it would be very convenient to be able to handle (1 `div` 0) as regular NaN value and not as exception. Thanks.

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ANNOUNCE: monoid-subclasses-0.1.1, incremental-parser-0.2.2, and SCC-0.8
by Mario Blažević 13 Apr '13

13 Apr '13

The new package monoid-subclasses [1] exports a number of classes that sit between monoids and groups: ReductiveMonoid, CancellativeMonoid, GCDMonoid, MonoidNull, and FactorialMonoid among others. The package also comes with class instances for all applicable data types from base, vector, containers, bytestring, and text packages. These classes were initially a part of the incremental-parser package [2] but they've moved, so incremental-parser-0.2.2 now depends on monoid-subclasses which has added more class methods and instances. The parsers constructed using the incremental-parser library generally work on any ReductiveMonoid, FactorialMonoid or TextualMonoid. You can thus construct a generic parser that operates on String, ByteString, or Text input, or even on Product Integer or a Map if you are so inclined. The version 0.8 of Streaming Component Combinators (a.k.a. SCC) has also been re-designed from the ground up. In the earlier versions, as in the pipes and conduit packages, the types of streams and stream-processing components were parametrized by the type of the individual items flowing through. All sources and sinks are now parametrized instead by the type of the monoid they produce or consume. As a consequence, SCC coroutines can now communicate in chunks of ByteString or Text instead of just lists, and these chunks can be of arbitrary size. The boundaries of producer's chunks are invisible to the consumer (excepting some low-level functions), which must specify the amount of data it wants to receive using a ReadRequest. This change at the heart of SCC has had a positive impact on outer layers, and especially on the Splitter component type which has become much simpler. [1] http://hackage.haskell.org/package/monoid-subclasses-0.1.1 [2] http://hackage.haskell.org/package/incremental-parser-0.2.2 [3] http://hackage.haskell.org/package/scc-0.8

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ANN: psqueue-benchmarks - benchmarks of priority queue implementations
by Niklas Hambüchen 13 Apr '13

13 Apr '13

(This is a slightly detailed email. If you are the maintainer of one of the packages benchmarked here, you might want to read it though.) Today I was looking for a Priority Queue that also allows a delete operation (some call this a "Priority Search Queue"). I found http://stackoverflow.com/questions/6976559/comparison-of-priority-queue-imp… and after looking at the 10 queue alternatives, I got to the following conclusions: * Only 3 of them allow to delete entries (are p*s*queues) * Most of them are outdated or at least unmaintained for the last 3-5 years * There was an effort to get a priority queue into containers (see the stackoverflow link), but it was not agreed on * Those efforts were driven by Louis Wasserman, who wrote one of the 3 psqueues (queuelike), but now only maintains a non-ps-queue (pqueue) that seems to be the most popular priority queue implementation PSQueue implementations ----------------------- The three packages that are psqueues are: - PSQueue (http://hackage.haskell.org/package/PSQueue-1.1) * original implementation from paper of Ralf Hinze * last upload 2008 * no test suite (but small commented out QC properties), no benchmarks * no code repository - fingertree-psqueue (http://hackage.haskell.org/package/fingertree-psqueue-0.3) * last upload 2011 * no tests, no benchmarks * no code repository - queuelike (http://hackage.haskell.org/package/queuelike-1.0.9) * last upload 2009 * no tests, no benchmarks * no code repository Benchmarks ---------- Unfortunately, none of them had tests, code in repositories or any indication about their real-world performance, so I made some criterion benchmarks. You can find them here: https://github.com/nh2/psqueue-benchmarks Graphs: http://htmlpreview.github.com/?https://raw.github.com/nh2/psqueue-benchmark… Benchmark results ----------------- * PSQueue throws a stack space overflow if you try to put in 100000 Ints * PSQueue suffers from some significant worst case in terms of queue creation, sometimes creating a queue from random numbers just takes 5 times longer (1st graph). This only happens sometimes (despite Criterion) * queuelike creation is instant - it seems to work around my benchmark somehow * converting a queuelike queue to a list surprisingly takes 10 times longer than with the other packages * in terms of average performance, the three are quite close to each other (apart from the point above). queuelike seems fastest, fingertree-psqueue is second and PSQueue slowest, with a difference of +30% to the next one My questions to the maintainers ------------------------------- @Scott: Do you have an idea why PSQueue stack overflows? @Louis: Why did you switch from queuelike to pqueue? Could you put the code up somewhere manageable (repo)? Is it possible to make pqueue a full pSqueue implementation? Niklas

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