October 2017 - Haskell-Cafe

[Announce] ZuriHac 2018 - 8-10 June in Zurich, Switzerland
by Jasper Van der Jeugt 17 Oct '17

17 Oct '17

It is our pleasure to announce that, like in previous years, ZuriHac will also take place in 2018 -- from Friday June 8th to Sunday the 10th. It will be hosted at the Hochschule Rapperswil right besides the beautiful lake Zurich, like last year. The Zurich Haskell Hackathon is a free (as in beer), international, grassroots collaborative coding festival whose goal is to expand the community and to build and improve Haskell libraries, tools, and infrastructure. This is already the 7th Haskell Hackathon in Zurich! This year, we will enjoy keynotes from: - Niki Vazou - Edward Kmett - Stephen Diehl More keynote speakers will be announced. This event is open to any experience level, from beginners to gurus. This year, Julie Moronuki, co-author of Haskell Programming from first principles [1], has kindly agreed to teach a beginners course in one of the classrooms we have available. Additionally, there will be mentors on site whom you can directly approach during the whole event with any Haskell-related question you have. This is a great opportunity to meet your fellow Haskellers in real life, find new contributors for your project, improve existing libraries and tools or even start new ones! We will have space for 300 attendees. Registration will open on 6th of December. You can find more information on our website [2]. We would also like to thank our sponsors Digital Asset [3] and HSR [4] for supporting this great event! Looking forward to see you there, the Zurich HaskellerZ meetup group [1]: https://www.goodreads.com/book/show/25587599-haskell-programming [2]: https://zurihac.info/ [3]: https://digitalasset.com/careers.html [4]: https://www.hsr.ch/

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Exposing a GADT-provided dictionary
by Kosyrev Serge 17 Oct '17

17 Oct '17

Good day, cafe! I found a way to expose a GADT-provided dictionary, but I don't quite like it: > {-# LANGUAGE GADTs, RankNTypes #-} > > import Data.Function ((&)) > > class HasDict a where > > data GADT a where > G1 :: HasDict a => a -> GADT a > -- ... > Gn :: HasDict a => a -> GADT a > > -- | Execute @body with the dictionary for HasDict extracted from the > -- GADT. > withGADTDict :: > (forall b. (b ~ a, HasDict b) => GADT b -> c) -> GADT a -> c > withGADTDict body x = x & case x of > G1 _ -> body > -- ... > Gn _ -> body The problem is in withGADTDict's proportionality to the number of GADT's clauses, as it is somewhat anti-modular. Is that the only light-weight option? I can imagine there is a way to leverage generic programming, but that's a bit heavy.. -- с уважениeм / respectfully, Kosyrev Serge PGP Key ID: 3F62F118E38BED6D -- “Most deadly errors arise from obsolete assumptions.” -- Frank Herbert, Children of Dune

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Re: [Haskell-cafe] Network Connect Timeouts
by Chris Wong 16 Oct '17

16 Oct '17

Hi Mark, >From reading the source code for *runTCPClient* [1], it looks like a thin wrapper around *getSocketFamilyTCP* and *close*. It should be sufficient to copy that definition into your project and wrap the *getSocketFamilyTCP* call in a *timeout*. You might need to import *Data.Streaming.Network.Internal* to get access to the *AppData* constructor. Hope this helps! [1] https://hackage.haskell.org/package/streaming-commons-0.1.18/docs/src/Data-… On Sun, Oct 15, 2017 at 9:08 AM, Mark Fine <mark.fine(a)gmail.com> wrote: > Hi Chris, > > In my application, I'm using *Data.Conduit.Network* from *conduit-extra* directly > (*Data.Streaming.Network* from *streaming-commons* indirectly). The > timeout I'm interested in managing is the connection establishment timeout > - how long does the connect call wait to establish a connection. I haven't > been able to figure out how to control this outside of applying a > non-conditional timeout to the connect call (which is a timeout on the > lifetime of a connection, not a timeout on the establishment of a > connection). Thanks! > > Mark > > On Sat, Oct 14, 2017 at 3:09 AM, Chris Wong <lambda.fairy(a)gmail.com> > wrote: > >> Hi Mark, >> >> What networking library are you using? >> >> There should be a lower level interface which allows for managing the >> lifetime of a connection by hand. >> >> Chris >> >> On Oct 14, 2017 15:17, "Mark Fine" <mark.fine(a)gmail.com> wrote: >> >>> I'd like a configurable network connect timeout. Has anyone solved this >>> reasonably? >>> >>> *System.Timeout.timeout* times out connections, but works on the >>> granularity of the life of the connection. Is there a reasonable way to >>> configure a timeout around just establishing the connection? Maybe >>> something like a conditional timeout that enables an action to disable the >>> timeout once it expires? >>> >>> As a workaround, I'm spinning trying to successfully connect first >>> before trying to connect for real: >>> >>> -- | Try the TCP connection and see if you can connect... >>> -- >>> tryTCPClient :: Int -> ClientSettings -> IO () >>> tryTCPClient microseconds settings = do >>> ok <- newIORef False >>> void $ timeout microseconds $ runTCPClient settings $ const $ >>> writeIORef ok True >>> ok' <- readIORef ok >>> unless ok' $ >>> tryTCPClient microseconds settings >>> >>> -- | Wrap runTCPClient with a connect timeout. >>> -- >>> -- Tries the TCP connection first, and the runs the regular runTCPClient. >>> -- Of course, this only enforces a TCP connect timeout on the first >>> connect. >>> -- The second TCP connect has no timeout :( >>> -- >>> runTCPClient' :: Int -> ClientSettings -> (AppData -> IO a) -> IO a >>> runTCPClient' microseconds settings action = do >>> tryTCPClient microseconds settings >>> runTCPClient settings action >>> >>> I've also tried running the *tryTCPClient* in its own thread >>> concurrently with *runTCPClient* and throwing an exception if it can't >>> connect in *microseconds*. None of these offer an actual true >>> connection establishment timeout. >>> >>> Has anyone found a way to solve this? Thanks! >>> >>> Mark >>> >>> >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> To (un)subscribe, modify options or view archives go to: >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>> Only members subscribed via the mailman list are allowed to post. >>> >> > -- Chris Wong (https://lambda.xyz) "I had not the vaguest idea what this meant and when I could not remember the words, my tutor threw the book at my head, which did not stimulate my intellect in any way." -- Bertrand Russell

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Re: [Haskell-cafe] Your haskell-cafe message [Was: random library]
by jpaugh＠gmx.com 16 Oct '17

16 Oct '17

Ian, Thanks for the note. I work for a secondary school, so that explains the block. I'll keep that in mind, and send mail from home. Thanks, Jon On October 14, 2017 12:29:03 PM CDT, Ian Zimmerman <itz(a)very.loosely.org> wrote: >On 2017-10-10 22:46, jpaugh(a)gmx.com wrote: > >> Interesting library! Here's a link: >> >http://hackage.haskell.org/package/DRBG-0.5.5/docs/Crypto-Random-DRBG.html > >The address from which you posted this is listed by spamhaus: > > ahiker!2 itz$ rblcheck 172.56.6.158 >172.56.6.158 not listed by sbl.spamhaus.org >172.56.6.158 listed by xbl.spamhaus.org >172.56.6.158 listed by pbl.spamhaus.org >172.56.6.158 not listed by bl.spamcop.net >172.56.6.158 not listed by psbl.surriel.com >172.56.6.158 not listed by dul.dnsbl.sorbs.net > >This often happens when people post from cafes and similar, and if this >is the case here not much can be done, unfortunately - other than >perhaps trying a different cafe next time :-) > >-- >Please don't Cc: me privately on mailing lists and Usenet, >if you also post the followup to the list or newsgroup. >Do obvious transformation on domain to reply privately _only_ on >Usenet. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.

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Where to import Id from?
by David Banas 16 Oct '17

16 Oct '17

Hi all, Would someone tell me where I can import Id from, please? I’ve struck out with both Hoogle and Google searches. Thanks! -db

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Re: [Haskell-cafe] haskell-cafe brown out [Was: random library]
by dominic＠steinitz.org 14 Oct '17

14 Oct '17

I get a daily digest from the mailing list and then cut out the bit that seemed relevant fwiw. Well done for caring about mailing lists :) > On 11 Oct 2017, at 17:28, Ian Zimmerman <itz(a)very.loosely.org> wrote: > > On 2017-10-11 13:50, dominic(a)steinitz.org wrote: > >>> Interesting library! Here's a link: >>> http://hackage.haskell.org/package/DRBG-0.5.5/docs/Crypto-Random-DRBG.html >>> <http://hackage.haskell.org/package/DRBG-0.5.5/docs/Crypto-Random-DRBG.html> >>> >>> Thomas, >>> >>> In the linked docs, there's a claim that Hash DRBG is the fastest >>> cryptographically secure RNG on Hackage. Do you have a link to the >>> benchmark results, or perhaps some updated ones? Unlike Viktor, I'm >>> interested in less secure applications, but if the performance is >>> good, it might be worth switching from the defacto random package. >>> >>> Thanks, Jonathan > >> No-one should be using the de facto random package. It is slow and >> produces surprising results. >> >> I think one of the posters suggested using mwc-random and splitting by >> using a different seed. Although mwc-random has reasonably good >> properties, there is no guarantee about how correlated the various >> streams of random numbers will be. QuickCheck uses tf-random to avoid >> such problems. There is also a version of SplitMix >> https://hackage.haskell.org/package/splitmix >> <https://hackage.haskell.org/package/splitmix> but I don’t think this >> has been heavily road-tested. >> >> But in this case, cryptographically secure randomness is required so I >> would follow Thomas’ suggestion. >> >> PS I just noticed my spellchecker changed defacto to defect! Perhaps >> AI is taking over. > > Hello, may I ask how exactly you posted the above message? > > Your message has no threading headers (In-Reply-To or References), but I > _think_ I never received the message to which you appear to be reacting > (that one by "Jonathan"). I cannot prove it beyond doubt because of the > missing headers. Was "Jonathan"'s message posted on the haskell-cafe > mailing list at all? Or what else is going on here? > > Ian, who cares about his mailing lists > > -- > Please don't Cc: me privately on mailing lists and Usenet, > if you also post the followup to the list or newsgroup. > Do obvious transformation on domain to reply privately _only_ on Usenet. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Network Connect Timeouts
by Mark Fine 14 Oct '17

14 Oct '17

I'd like a configurable network connect timeout. Has anyone solved this reasonably? *System.Timeout.timeout* times out connections, but works on the granularity of the life of the connection. Is there a reasonable way to configure a timeout around just establishing the connection? Maybe something like a conditional timeout that enables an action to disable the timeout once it expires? As a workaround, I'm spinning trying to successfully connect first before trying to connect for real: -- | Try the TCP connection and see if you can connect... -- tryTCPClient :: Int -> ClientSettings -> IO () tryTCPClient microseconds settings = do ok <- newIORef False void $ timeout microseconds $ runTCPClient settings $ const $ writeIORef ok True ok' <- readIORef ok unless ok' $ tryTCPClient microseconds settings -- | Wrap runTCPClient with a connect timeout. -- -- Tries the TCP connection first, and the runs the regular runTCPClient. -- Of course, this only enforces a TCP connect timeout on the first connect. -- The second TCP connect has no timeout :( -- runTCPClient' :: Int -> ClientSettings -> (AppData -> IO a) -> IO a runTCPClient' microseconds settings action = do tryTCPClient microseconds settings runTCPClient settings action I've also tried running the *tryTCPClient* in its own thread concurrently with *runTCPClient* and throwing an exception if it can't connect in *microseconds*. None of these offer an actual true connection establishment timeout. Has anyone found a way to solve this? Thanks! Mark

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Pattern Matching with Different Types
by Yotam Ohad 11 Oct '17

11 Oct '17

Hello cafe, I am trying to do the following: data Foo = Foo { a1 :: Int -> Int, a2 :: Int -> Char } data Bar = Bar { a1 :: Int -> Int } func :: a -> Maybe (Int -> Int) -- a is either Foo or Bar func (x::(Bar/Foo) = Just $ a1 x func _ = Nothing I'm not sure how to implement this. All I know that the types are matching so I think it could be possible. Thanks for your help -Yotam

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Galois is hiring
by Eric Mertens 11 Oct '17

11 Oct '17

Hello, Galois is growing again! We're looking for researchers, principal investigators, software engineers, including those with expertise in functional programming, formal methods, machine learning, embedded systems, computer security, or networking. For the exact available positions, please have a look at our website: http://galois.com/careers We now have three locations: Portland, Ore.; Arlington, Va.; and Dayton, Ohio. There are positions available at all locations. We are looking for people to work on-site, not remotely. Mostly, we are looking for candidates who are already authorized to work in the US, but in exceptional situations we can work with the candidate to obtain the necessary documentation. If you are interested, please apply through the web site. If you have questions about working at Galois, you're welcome to contact me directly. Best regards, Eric Mertens glguy

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random library
by Kazu Yamamoto 11 Oct '17

11 Oct '17

Hello, I'm preparing for a major release of the dns package version 3.0.0. https://github.com/kazu-yamamoto/dns/issues/88 Before the release, I would like to replace the random package since it is slow. I'm looking for a random library which is - fast - thread-safe (good for concurrent use) Any recommendations? // Kazu

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