- Haskell-Cafe - Haskell.org

windows crashes (bsod) during link phase
by Han Joosten 07 Jan '15

07 Jan '15

Hi, When I build ampersand (sources from https://github.com/AmpersandTarski/ampersand ) everything compiles correctly. However, during link time, windows crashes and I get a blue screen of death. A colleque of mine has exactly the same experience. However, when I do this on another windows 7 machine, I get a working executable. I would say that any program that compiles correctly cannot cause the linker to fail. I am not very familiar with the build system, but this is a serious blocking issue for me working on that project. Any help is very much appreciated. Thanks!

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GHC 7.8.4 for Windows x86
by Anton Dessiatov 07 Jan '15

07 Jan '15

Hello, Haskell Café! Does anybody know what’s the reason for the lack of GHC 7.8.4 windows x86 build? I could only find x64 version on the official website and it seems like minghc project doesn’t offer x86 build too. Best regards, Anton.

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Significant compilation slowdown when using Data.CaseInsensitive.mk
by Brendan Hay 06 Jan '15

06 Jan '15

Hi, I've recently run into an issue whereby changing textual case comparison to use the Data.CaseInsensitive.mk <http://hackage.haskell.org/package/case-insensitive-1.2.0.3/docs/Data-CaseI…> smart constructor causes substantial differences to outputted core language and a related compilation speed regression. The code which seems to cause this is here: https://github.com/brendanhay/amazonka/blob/release/0.1.4/core/src/Network/… With the downstream project having about 68 call sites for the above function starting here: https://github.com/brendanhay/amazonka/blob/release/0.1.4/amazonka-ec2/gen/… For comparison, the previous version used Attoparsec.Text.takeText <http://hackage.haskell.org/package/attoparsec-0.12.1.2/docs/Data-Attoparsec…> and Text values. Here are some hand wavy points of interest: * Before (Case Sensitive) Function: takeText = Attoparsec.Text.takeText Time (real): 2m27.735s amazonka-ec2/gen/Network/AWS/EC2/Types.hs (simpl): {terms: 242,688, types: 310,463, coercions: 31,215} * After (Case Insensitive) Function: takeCI = Data.CaseInsensitive.mk <$> Attoparsec.Text.takeText Time (real): 11m31.937s amazonka-ec2/gen/Network/AWS/EC2/Types.hs (simpl): {terms: 1,384,779, types: 465,656, coercions: 33,510} I'm finding the outputted core rather unwieldy to analyse, but the main difference seems to be the inclusion of huge swathes of case statements like: https://gist.github.com/brendanhay/5a57f073d5a7d196a1ad It would be appreciated if someone could help me to understand in simple terms why the use of case-insensitive causes this.

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typeclass woes...how to constain a typeclass to be "closed" under an operation....
by Nicholls, Mark 06 Jan '15

06 Jan '15

This is reposted from the beginnners….I’ve not done Haskell for a while and was struggling to get anything to work, I’ve hopefully refound my feet. Its quite common in maths to have operations in a theory that are (set) closed, i just want to translate that notion to a typeclass I have a suggestion that does work class Foo m where op :: m a -> m (S a) That is closed, but now were working on types of kind • -> • (S can be a type family or a data type…lets say it’s a type family….probably an associated type (if I know what that means)) Is this the idiom/pattern i should follow? Or can the closure contraint be expressed directly in a typeclass any other way? From: Haskell-Cafe [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Brandon Allbery Sent: 06 January 2015 1:59 PM To: Rob Leslie Cc: Haskell Cafe Subject: Re: [Haskell-cafe] Haskeline and asynchronous messages On Tue, Jan 6, 2015 at 3:27 AM, Rob Leslie <rob(a)mars.org<mailto:rob@mars.org>> wrote: Does anyone have a suggestion on using Haskeline in an environment where another thread may be writing messages to the terminal -- is it possible to somehow print incoming messages above the input line without disturbing the input line? Terminals don't really work that way; you need to be looking at something like curses or vty. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com<mailto:allbery.b@gmail.com> ballbery(a)sinenomine.net<mailto:ballbery@sinenomine.net> unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net CONFIDENTIALITY NOTICE This e-mail (and any attached files) is confidential and protected by copyright (and other intellectual property rights). If you are not the intended recipient please e-mail the sender and then delete the email and any attached files immediately. Any further use or dissemination is prohibited. While MTV Networks Europe has taken steps to ensure that this email and any attachments are virus free, it is your responsibility to ensure that this message and any attachments are virus free and do not affect your systems / data. Communicating by email is not 100% secure and carries risks such as delay, data corruption, non-delivery, wrongful interception and unauthorised amendment. If you communicate with us by e-mail, you acknowledge and assume these risks, and you agree to take appropriate measures to minimise these risks when e-mailing us. MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe. MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.

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Haskeline and asynchronous messages
by Rob Leslie 06 Jan '15

06 Jan '15

Greetings, Does anyone have a suggestion on using Haskeline in an environment where another thread may be writing messages to the terminal -- is it possible to somehow print incoming messages above the input line without disturbing the input line? Thanks for any advice. -- Rob Leslie rob(a)mars.org

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Postgresql Intervals with Opaleye
by info＠rotnetix.com 06 Jan '15

06 Jan '15

Another opaleye question: What type should I use for the postgresql interval type? Thanks Riaan

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Installing grapefruit: "lexical error at character 'i'"
by Jeffrey Brown 06 Jan '15

06 Jan '15

Dear list, I am trying to install grapefruit on Kubuntu 14.04. Most of the dependencies seemed to install without incident, but I am running into the following error: jeff@jeff-Lenovo:~$ cabal install grapefruit-ui-gtk grapefruit-examples Resolving dependencies... Configuring grapefruit-ui-0.1.0.5... Building grapefruit-ui-0.1.0.5... Preprocessing library grapefruit-ui-0.1.0.5... src/Internal/UIItem.hs-boot:12:2: lexical error at character 'i' Failed to install grapefruit-ui-0.1.0.5 cabal: Error: some packages failed to install: grapefruit-examples-0.1.0.5 depends on grapefruit-ui-0.1.0.5 which failed to install. grapefruit-ui-0.1.0.5 failed during the building phase. The exception was: ExitFailure 1 grapefruit-ui-gtk-0.1.0.5 depends on grapefruit-ui-0.1.0.5 which failed to install. jeff@jeff-Lenovo:~$ I wanted to find the offending 'i' character, but the file "src/Internal/UIItem.hs-boot" I was unable to find anywhere: jeff@jeff-Lenovo:/$ pwd / jeff@jeff-Lenovo:/$ sudo find . -name *UIItem.hs* [sudo] password for jeff: jeff@jeff-Lenovo:/$ Any ideas? Thanks, Jeff

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Concurrency problems with mysql bindings?
by Elliot Cameron 05 Jan '15

05 Jan '15

Hello Fellow Haskellers, I am not experienced with the FFI, but I have suspicions that Haskell's "mysql" package falls short in terms of its support for concurrency. A tiny bit of discussion has occurred here: https://github.com/bos/mysql/issues/11 Since it appears that "mysql" is the de-facto binding for MySQL (see reverse dependencies at http://www.stackage.org/package/mysql ), it seems that this lack has far-reaching effects on the Haskell ecosystem at large. What attracts many to Haskell is it's strengths in writing parallel /concurrent code, but it seems we lose this benefit when interacting with MySQL. I for one have a beautiful Haskell program using MySQL which I would love to push into production, but it's performance pales in comparison to a Python script that builds up calls to bash and actually achieves concurrency. At this point I have not been able to gain traction for this problem, and since I'm not an experienced Haskell developer, my contributions are slow and tedious. I'm hoping that I can garner some help in the following: 1) Confirm or deny my suspicions as represented in the issue linked above 2) If they are confirmed to any degree, I hope for some help in working through the solution Please let me know if you would like to help in either of these ways! Even the smallest comments will be highly valued! Elliot Cameron Covenant Eyes Software Developer elliot.cameron(a)covenanteyes.com 810-771-8322

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New Functional Programming Job Opportunities
by Functional Jobs 05 Jan '15

05 Jan '15

Here are some functional programming job opportunities that were posted recently: Senior Software Engineer at McGraw-Hill Education http://functionaljobs.com/jobs/8775-senior-software-engineer-at-mcgraw-hill… Cheers, Sean Murphy FunctionalJobs.com

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Class constraints on associated types ...
by aditya siram 05 Jan '15

05 Jan '15

Hi all, I'd like to be able to constrain an associated type. I used to have an instance that looked like: class Dispatch a b c | a b -> c where runF :: a -> b -> c instance (C a) => Dispatch D1 D2 ( a -> IO ()) where runF d1 d2 = (\_ -> return ()) Since I upgraded to 7.8 from 7.5 that instance declaration is no longer accepted is no longer accepted since it violates FD's. I have been updating my code to use type families like so: class Dispatch a b where type Impl a b :: * runF :: a -> b -> Impl a b instance (C a) => Dispatch D1 D2 where type Impl D1 D2 = a -> IO () runF d1 d2 = (\_ return ()) Unfortunately the `type Impl ...` line in the instance is rejected because it uses `a` on the RHS. In this one case I could just package it up into a newtype or something but I would ideally like to be able to constrain any number of arguments like: instance (C a, C b ... C z) => Dispatch D1 D2 where type Impl D1 D2 = a -> b -> ... -> z -> IO () ... This was something I could do in 7.6 (although I realize this is way safer). How do I go about getting that constraint back? Thanks! -deech

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