October 2013 - Haskell-Cafe

Re: [Haskell-cafe] Suppressing HLint on pattern match of files
by Graham Berks 16 Oct '13

16 Oct '13

Ah that sounds good, thanks will incorporate that. G On 11 October 2013 at 17:21:44, Adam Bergmark (adam(a)edea.se) wrote: You can also do this on a module basis with {-# OPTIONS -fno-warn-missing-signatures #-}. I prefer adding type signatures even for cases where I don't think it's important. GHC spits them out so almost no time spent, and someone might find it useful at some point. On Fri, Oct 11, 2013 at 5:53 PM, Dag Odenhall <dag.odenhall(a)gmail.com> wrote: Just add it next to -Wall wherever you‘re setting that, because I think you must be setting that yourself somewhere (it’s not on by default). On Thu, Oct 10, 2013 at 6:11 PM, Graham Berks <graham(a)fatlazycat.com> wrote: Ah good point :) Wonder if I can change it on cabal file somehow. Thanks On 10 October 2013 at 14:05:45, Dag Odenhall (dag.odenhall(a)gmail.com) wrote: Is that actually from HLint though? I think that comes from GHC with -Wall and can be disabled with -fno-warn-missing-signatures. On Thu, Oct 10, 2013 at 7:50 AM, Graham Berks <graham(a)fatlazycat.com> wrote: Hi, would like to disable 'Top-level binding with no type signature' In my test modules that are prefixed with Test. Is this possible ?? Thanks _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell-cafe] Announce: HDBI-1.3 and friends
by Dan 16 Oct '13

16 Oct '13

Thanks Alexey, Any plans for : 1 - Oracle support ? 3 - NoSql databases (Mongo, Cassandra, etc) support ? Cheers, Dan Date: Tue, 15 Oct 2013 23:55:16 +0600 From: Alexey Uimanov <s9gf4ult(a)gmail.com> To: Haskell Cafe <haskell-cafe(a)haskell.org> Subject: [Haskell-cafe] Announce: HDBI-1.3 and friends Message-ID: <CANtkurc-6sQ87Bji=O0OhEteZJFh=tD2yz8ckTLgYc7J2u_SoA(a)mail.gmail.com> Content-Type: text/plain; charset="utf-8" Hello haskellers! HDBI is the fork of HDBC but reworked. It supports SQlite3 and Postgresql for now. It also supports streaming with coduits. There is TH deriving mechanism to map database rows to Haskell structures and back. HDBI is trying to become simple but still powerfull and flexible database interface. It must be suitable to become the common RDBMS interface for higher level interfaces like persistent or haskelldb. The documentation is not very good, while I have no enough time to make some. In this version changed typeclass signatures of Connection and Statement. Now methods `run` and `execute` get any instance of `ToRow` and method `fetch` return an instance of `FromRow`. Note that [SqlValue] is also an instance of `FromRow` and `ToRow` typeclasses so you do not loose the control. Methods `fromRow` and `toRow` for [SqlValue] are just `id`. SQlite and Postgresql drivers are fixed as well as hdbi-conduit. There is also new helper functions, like `onei :: Integer -> [SqlValue]` which helps you to execute queries with one parameter or execute many queries consistinf of one parameter. Prelude Database.HDBI Database.HDBI.SQlite> :set -XScopedTypeVariables Prelude Database.HDBI Database.HDBI.SQlite> :set -XOverloadedStrings Prelude Database.HDBI Database.HDBI.SQlite> c <- connectSqlite3 ":memory:" Prelude Database.HDBI Database.HDBI.SQlite> runRaw c "create table test(val integer)" Prelude Database.HDBI Database.HDBI.SQlite> withTransaction c $ runMany c "insert into test(val) values (?)" $ map one [1..1000] <interactive>:7:76: Warning: Defaulting the following constraint(s) to type `Integer' ......... Prelude Database.HDBI Database.HDBI.SQlite> r :: (Maybe Integer) <- runFetchOne c "select sum(val) from test" () Prelude Database.HDBI Database.HDBI.SQlite> r Just 500500 Note here that the empty set is used as a parameter of query in `runFetchOne`. Empty set is an instance of `FromRow` and `ToRow` and return an empty list of [SqlValue]. Use empty list as a parameters is bad idea, because we could instantiate some another list of things, suppose the [Integer] as `FromRow` and `ToRow` instance. So it would lead to ambigous type because [SqlValue] is also a list instantiating `FromRow` and `ToRow`.

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haskell-platform problems on (latest) knoppix
by dhw＠thedance.net 15 Oct '13

15 Oct '13

Background: I'm an experienced Linuxer, but not experienced with the Debian package-management tools. I recently decided it was time to renew my acquaintance with Haskell, which began before the do-notation, with Hugs. Seeing the warnings on the ghc website, I decided to install a Linux distribution with a strongly checked package system. I chose Knoppix-7.2.0 i386 (the latest, dated mid-2013), which installed with few problems (now fixed). It claimed to be based on wheezy, the stable branch. Even though the version of haskell-platform in wheezy/stable was from mid-2012, I presumed it would be debugged by now - after all, that's what "stable" is supposed to mean. So I hooked it up to the net, and entered apt-get install haskell-platform After a few seconds, it said that there were broken packages - I think they were libglut-dev and libgl-dev - and that it couldn't fix them. Aptitude, which has a menu-item called 'fix broken packages', couldn't fix them, either. If I recall correctly, there were intrinsically unsatisfiable version constraints, i.e. >=V and <V for the same V. So my question is: have I somehow introduced this (I re-used a knoppix-data.img without ensuring it was empty) or is the problem upstream from me? (i.e does anyone else have this problem?) Looking at the open bug list for haskell- package, I can't tell whether it's a recognised bug. Subsidiary question: since I would prefer to spend time on Haskell rather then on the package system, would it be quicker (in days, not in milliseconds :-) to use nhc98 or Hugs98-Sep2006, obsolete though they are? All advice gratefully received, thanks, -David -------------------------------------------------------------------- mail2web.com Enhanced email for the mobile individual based on Microsoft® Exchange - http://link.mail2web.com/Personal/EnhancedEmail

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[ANNOUNCE] hzk - Haskell Zookeeper bindings
by diego souza 15 Oct '13

15 Oct '13

Dear Haskellers, A project that I'm working on depends on Zookeeper and as currently there is no bindings [1] for it I'm glad to announce the first release of a Haskell bindings for Apache Zookeeper. Any feedback will be highly appreciated. All zookeeper functions should be available but multi operations. I currently don't have any needs for them but if someone is interested in having them available let me know. Thanks! ~dsouza [1] Actually there is at least https://github.com/motus/haskell-zookeeper-client, but it is not available on hackage by the time I wrote this.

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Haskell Group Dresden?
by Daniel Trstenjak 15 Oct '13

15 Oct '13

Hi, is there any interest in having something like a Haskell Group in Dresden? Perhaps I could say something about the lens library, which would be more of a practical talk, how to define lenses and working with lenses, traversals, isos and prisms. Greetings, Daniel

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Proposal for a standard collection of algorithms/Data structures in haskell
by satvik chauhan 15 Oct '13

15 Oct '13

Hi cafe, Whenever you search for a library for doing some standard task on hackage there are lots of implementations available and some of them are poorly implemented without any thoughts given to design and speed. Most of them are left as it is without any further improvements/bug fixes. A limited collection of data-structures and associated algorithms are available in base. It would be nice for the community to maintain a standard collection of recommended implementations (both fast and well designed) of data structure and algorithms (similar to Boost for C++). This can again be maintained and moderated by the community. All the implementation in the collection can adhere to a standard design principle and idiomatic haskell. I would really love to hear your thoughts on this proposal. -Satvik

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Xcode 5 support for GHC iOS
by Luke Iannini 14 Oct '13

14 Oct '13

Hi all, Just wanted to let you know I've finished updating GHC iOS to support Xcode 5. The new scripts are at https://github.com/ghc-ios/ghc-ios-scripts/tree/xcode5 and you'll find updated instructions at http://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling/iOS . Please let me know if you have any trouble! Cheers Luke

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No upgrade of GHC version in Ubuntu repository
by Vlatko Basic 14 Oct '13

14 Oct '13

Hi Caffe, deb packages of GHC (and Haskell Platform) in Ubuntu's (LTS Precise, 12.04) "universe" are not upgrading at all. GHC package is almost two years old, still on version 7.4.1, and GHC site still recommends to use Haskell Platform from repository. Even kernel is upgrading more often, and one would expect it is much more difficult. :-) What would be the reason for that? Is it abandoned? Best regards, vlatko

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Increasing memory use in stream computation
by Arie Peterson 14 Oct '13

14 Oct '13

(Sorry for the long email.) Summary: why does the attached program have non-constant memory use? ==== Introduction ==== I've written a program to do a big computation. Unfortunately, the computation takes a very long time (expectedly), and the memory use increases slowly (unexpectedly), until it fills up the entire memory and swap space of the computer (many gigabytes). The rough structure of the program is: • create a long (up to 20 million) list of objects; • compute a number for each of those objects; • compute the sum of the resulting list. I switched the intermediate data structure from a list to a Stream (from the stream-fusion package), hoping to fix the memory issue. It decreased both the memory use and the rate of its increase, but after a long time, the program still uses up all available memory. ==== A simple program After many hours of cutting down my program, I now have a small program (attached) that shows the same behaviour. It uses only said stream-fusion package, and vector. (I haven't yet tried to cut out the use of vector. I hope it is irrelevant, because all vectors are of fixed small size.) I compile the program with ghc-7.6.1 using > ghc --make -threaded -rtsopts -with-rtsopts="-M1G -K128M" -O2 -main-is > Test.main Test The rts options may not be strictly necessary: I added them at some point to allow the use of multiple cores, and to prevent the program from crashing the machine by using all available memory. When running the program, the resident memory quickly grows to about 3.5 MB (which I am fine with); this stays constant for a long time, but after about 7 minutes, it starts to grow further. The growth is slow, but I really would hope this program to run in constant memory. ==== The code ==== Note that I added an instance for Monad Stream, using concatMap. This is implicitly used in the definition of the big stream. The source of Data.Stream contains many alternative implementations of concat and concatMap, and alludes to the difficulty of making it fuse properly. Could it be that the fusion did not succeed in this case? Thanks for any help! Regards, Arie

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Re: [Haskell-cafe] Compiling arbitrary Haskell code
by Daniil Frumin 14 Oct '13

14 Oct '13

For those who are interested (and I already chatted with Chris on IRC), I've implemented a pastebin that is able to (among some other things) to run arbitrary Haskell code: http://paste.hskll.org/ I've also developed a 'restricted-workers' library for managing processes that should run in secured environment. I've described some of my endeavors in a blog post: http://parenz.wordpress.com/2013/07/15/interactive-diagrams-gsoc-progress-r… Bottom line: proper restrictions are hard, the necessary tools operate on a low level, there are some caveats too On Sat, Oct 12, 2013 at 12:30 AM, Christopher Done <chrisdone(a)gmail.com>wrote: > Is there a definitive list of things in GHC that are unsafe to > _compile_ if I were to take an arbitrary module and compile it? > > E.g. off the top of my head, things that might be dangerous: > > * TemplateHaskell/QuasiQuotes -- obviously > * Are rules safe? > * #includes — I presume there's some security risk with including any old > file? > * FFI -- speaks for itself > > I'm interested in the idea of compiling Haskell code on lpaste.org, > for core, rule firings, maybe even Th expansion, etc. When sandboxing > code that I'm running, it's really easy if I whitelist what code is > available (parsing with HSE, whitelisting imports, extensions). The > problem of infinite loops or too much allocation is fairly > straight-forwardly solved by similar techniques applied in mueval. > > SafeHaskell helps a lot here, but suppose that I want to also allow > TemplateHaskell, GeneralizedNewtypeDeriving and stuff like that, > because a lot of real code uses those. They only seem to be restricted > to prevent cheeky messing with APIs in ways the authors of the APIs > didn't want -- but that shouldn't necessarily be a security—in terms > of my system—problem, should it? Ideally I'd very strictly whitelist > which modules are allowed to be used (e.g. a version of TH that > doesn't have runIO), and extensions, and then compile any code that > uses them. > > I'd rather not have to setup a VM just to compile Haskell code safely. > I'm willing to put some time in to investigate it, but if there's > already previous work done for this, I'd appreciate any links. > > At the end of the day, there's always just supporting a subset of > Haskell using SafeHaskell. I'm just curious about the more general > case, for use-cases similar to my own. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Sincerely yours, -- Daniil

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