- Haskell-Cafe - Haskell.org

Fwd: Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

> > * Would using a snapshot-based revision control system like Git be an > option? If yes, you could use the [filestore] library. > It's not exactly what I had in mind but I'll think about it. > > * Another option is to run an insertion-only relational model on > really any database system you want like PostgreSQL. There is > nothing about preserving history that needs special handling to be > efficient. > I assume that some sort of structural sharing is needed once the collections grow above a certain size. Also some support for caching would be nice. > * Yet another option is to model your application state with history > and use [acid-state]. However, acid-state only makes an in-memory > Haskell value (the "database") persistent with ACID guarantees. If > you mostly work with the current state, keeping the whole history in > memory all the time would be a waste. Therefore this option may be > less useful. > The database will probably grow bigger than the memory so this is not an option. ...and thanks for the pointers

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Lenses: Changing/creating values deep inside JSON or HashMap
by Jan von Löwenstein 23 Dec '16

23 Dec '16

Hi, I want to have code that produces the following result no matter if input A or B was given: Result: { "outer" : { "inner" : "new-value" } } A: { "outer" : { "inner" : "old-value" } } B: {} `json & key "outer"._Object.key "inner" .~ "new-value"` didn't work. Is what I want even possible with lenses? Best Jan

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Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

Is there any package in Haskell that provides something similar to Datomic http://www.datomic.com/? Basically what I am looking for is a database which could keep all the versions of my data in an efficient way, the same way the persistent data structures do. Ideally it should be implemented over some scalable storage. I looked at Datomic itself but I couldn't find a Haskell client library. The only way to connect to it from a Haskell application is through the REST server which they have just deprecated ( http://docs.datomic.com/rest.html) Thanks!

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Work on mail.haskell.org beginning, please report any problems
by John Wiegley 23 Dec '16

23 Dec '16

Hello Haskellers, Beginning today, I am upgrading our Postfix installation on mail.haskell.org, and introducing some new options to reduce the amount of spam that hits our mailman server. If you experience delivery problems, or any bounced mail, please send a copy of the full bounce message to my address: jwiegley(a)gmail.com. I'll be making more changes gradually over the next few days, and watching the mail logs, but it's possible that mail accepted before will suddenly start getting rejected, depending on how well-behaved your sending mail server is. Activities planned for this Christmas break are: - [x] Upgrade Postfix to 2.11 - [X] Enable postscreen for pre-queue RBL filtering - [ ] DKIM sign messages sent from mailman - [ ] Implement DMARC policy (i.e., reject incoming messages improperly DKIM signed, or failing SPF check) - [ ] Prevent mail being spoofed from haskell.org addresses - [ ] Tighten sender and recipient restrictions - [ ] Re-assess inbound and outbound rate limits - [ ] Use SpamAssassin for post-queue filtering - [ ] If helpful, enable deep protocol pre-filtering - [ ] Document all the above, so others can help with e-mail admin Thank you, John Wiegley Haskell.org, infrastructure team

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Re: [Haskell-cafe] Work on mail.haskell.org beginning, please report any problems
by Viktor Dukhovni 23 Dec '16

23 Dec '16

> On Dec 22, 2016, at 11:09 PM, John Wiegley <jwiegley(a)gmail.com> wrote: > >> If available as a package for your O/S, might as well use 3.1 > > I'll consider that a second migration, after the dust settles this time > around. I'd need to gain experience with 3.x first on my own server, before > being comfortable enough to do that. The 2.11-based setup I've been running > for a month now on another server. Wietse maintains a strong commitment to backwards-compatibility. While Postfix 3.0 (could equally have been 2.12) brings in new features for distribution maintainers, with dynamically-loadable table drivers on multiple platforms it remains compatible with 2.x releases for users. Your 2.11 configuration will work with 3.1, you may just need to install additional table driver packages, if your O/S maintainer has just started delivering Postfix as multiple components. > >>> - [X] Enable postscreen for pre-queue RBL filtering > >> This makes it possible to combine multiple lower-weight RBLs, that >> individually are not sufficient to reject mail, but you should still use the >> SpamHaus zen RBL in smtpd(8). > > Why is it helpful to run it in smtpd as well? I'm already using: > > postscreen_dnsbl_sites = zen.spamhaus.org*2 ... This is because the TTLs on postscreen whitelists are rather longer than RBL TTLs. If an IP address is added to an RBL, you'll want to refuse access in a timely manner. -- Viktor.

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RebindableSyntax and fail in GHC 8
by Chris Smith 21 Dec '16

21 Dec '16

Hey everyone, Can someone explain to me by GHC 8 causes list comprehension bindings to desugar to use 'fail', when RebindableSyntax is enabled in GHC 8? Note that I do not have monad comprehensions enabled. If I define fail, everything works (apparently regardless of what I define fail to do?!?), but I'd like to understand why it's necessary. Thanks, Chris

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emit custom signal from gtk3 haskell side
by Ruben Astudillo 21 Dec '16

21 Dec '16

Hi all I implement the following custom signal in my code import qualified System.Glib.Signals as Sig updateSignal :: ButtonClass self => Sig.Signal self (IO ()) updateSignal = Sig.Signal $ Sig.connectGeneric "updateSignal" Such, will be called inside of "model" phase of the app. But looking on the gtk3 documentation (and grepping also) I can't find a equivalent of `gtk_signal_emit_by_name`. I don't believe this omission is accidental. Can Anybody guide where to look at? -- -- Ruben

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We're recruiting … why not join us?
by Simon Thompson 21 Dec '16

21 Dec '16

We’re recruiting, and if you’re interested in programming languages, types, logics, or more practical aspects like refactoring and other tools, we’d really welcome an application from you. Simon T. Lecturer in Computing (2 posts) University of Kent - School of Computing We are seeking to appoint two Lecturers in Computing (the equivalent of tenure track, assistant professors), based at our Canterbury campus. We are particularly interested in appointments in Security, or Programming Languages but are happy to consider excellent candidates in other areas that would complement or enhance the School’s existing research strengths. Job description https://www11.i-grasp.com/fe/wrapdev_SendFile.asp?key=49170934&c=3362126282… Additional Information https://www11.i-grasp.com/fe/wrapdev_SendFile.asp?key=49170934&c=3362126282… Please apply at https://www11.i-grasp.com/fe/tpl_kent01.asp?newms=jj&id=40606&aid=14243 Closing date for applications: 6 February 2017 The School of Computing [1] is a welcoming and diverse environment whose commitment to gender equality has been recognised with a Bronze Athena SWAN [2] award. We are keen to enhance the balanced, inclusive and diverse nature of the community within our School and would particularly encourage female candidates to apply for these posts. We are committed to delivering high quality research and education. Our research is focused on five broad research areas: Programming Languages and Systems; Computer Security; Computational Intelligence; Data Science; and Computing Education. Full details can be found at: https://www.cs.kent.ac.uk/research. The 2014 Research Excellence Framework (REF) ranked our school 12th for research intensity [3], and we are well placed to improve on this in the next REF. The University of Kent has campuses in Canterbury and Medway, and specialist postgraduate centres in Athens, Brussels, Paris and Rome. It was ranked 16th in the UK in The Guardian University Guide 2016. It ranked 4th for overall student satisfaction (NSS, 2016) and 17th for the intensity of its excellent research (REF 2014). It has 20,000 students and 1,872 academic, teaching and research staff. Overlooking the city centre, and with 125 nationalities represented, the Canterbury campus has a very cosmopolitan feel. Canterbury is a small city that retains parts of its medieval walls. Famous for its heritage (Canterbury Cathedral; Chaucer’s Tales; etc), Canterbury is a vibrant community whose culture and leisure facilities are enhanced by hosting three universities. The city and surrounding region combines an attractive and affordable environment, good schools, and fast transport links to London and mainland Europe. Links: [1] https://cs.kent.ac.uk/ [2] http://www.ecu.ac.uk/equality-charters/athena-swan/ [3] https://www.timeshighereducation.com/sites/default/files/Attachments/2014/1… Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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ANNOUNCE: pdf-slave-1.0 tool for PDF generation from haskintex templates
by NCrashed . 21 Dec '16

21 Dec '16

I am glad to announce first release of pdf-slave, a tool for generation of PDF documents from LaTeX templates with embedded Haskell. Hackage: http://hackage.haskell.org/package/pdf-slave Github: https://github.com/NCrashed/pdf-slave Description ======= In many real-world systems we need to produce reports, cheque and other documents to users. One possible solution is rendering LaTeX files, but it is not flexible enough as you need to solve burden with generation of LaTeX file from varying inputs, manage static files like images and handling dependencies between pieces of document. The new tool takes the burden away. Now all static files and generation code is located within a single template project, that describes how to build your PDF document in a declarative way. Common work flow with pdf-slave: * Develop template from several LaTeX files with embedded Haskell (thanks to haskintex tool) * Pack the template project into bundle all-in file. * Distribute the bundle (for instance, to your service server). * Call pdf-slave with bundle and inputs in JSON file to generate new PDF document. Status ==== pdf-slave is designed as part of commercial Haskell system. The tool is very young and need time approval, although it already has all needed features one may need from such tool. Special thanks to hint authors and Daniel Díaz, developer of awesome HaTex and haskintex, without these packages pdf-slave wouldn't be possible! Reports, feature request, PR are always welcome! Anton Gushcha aka NCrashed

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stack on Windows and C Preprocessor
by Olaf Klinke 20 Dec '16

20 Dec '16

Dear Cafe, not sure who the culprit is, thus trying on this list: My project builds fine with stack on Linux. I installed the latest (1.3.0 x86_64) stack on a Windows box and ran 'stack.exe setup' inside my project's directory. The build fails at the depencency HaXml-1.25.3 with a lexer error on line 34 of this file: http://hackage.haskell.org/package/HaXml-1.25.3/docs/src/Text-XML-HaXml-Wra… lexical error in string/character literal at character '\r' It seems the line (VERSION) is processed by the C preprocessor which somehow messes it up. Unfortunately, stack deletes its temporary files after running into the error, which deprives me of handles to further debug this. Does anyone have an idea how to continue from here? Thanks, Olaf

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