May 2017 - Haskell-Cafe

Adding support for user defined data types to cassandra-cql
by Cody Goodman 26 May '17

26 May '17

Hello all, I wrote some template Haskell code that looks up data in a cassandra database in the system.schema_columns table using this library: https://github.com/the-real-blackh/cassandra-cql/blob/master/Database/Cassa… Currently cassandra-cql lets you make queries like this: getColFamInfo :: Query Rows () (Text, Text, Text, Text, Text) getColFamInfo = "select keyspace_name, columnfamily_name, column_name, type, validator from system.schema_columns" And then it returns type (Text,Text,Text,Text,Text). I'd prefer to be able to write a query like: data MyRecord = MyRecord { a :: Text, b :: Text, c :: Text, d :: Text } getColFamInfo :: Query Rows () (Maybe MyRecord) getColFamInfo = "select keyspace_name, columnfamily_name, column_name, type, validator from system.schema_columns" Point being: I have types being generated from cassandra, but I have no idea where I'd start modifying the cassandra-cql library to use those types. Could anyone offer any direction? Also... Below is a snippet of how Query is implemented, but you can find the full code here: https://github.com/the-real-blackh/cassandra-cql/blob/master/Database/Cassa… Query Looks like: { - START CODE -} -- | The first type argument for Query. Tells us what kind of query it is. data Style = Schema -- ^ A query that modifies the schema, such as DROP TABLE or CREATE TABLE | Write -- ^ A query that writes data, such as an INSERT or UPDATE | Rows -- ^ A query that returns a list of rows, such as SELECT -- | The text of a CQL query, along with type parameters to make the query type safe. -- The type arguments are 'Style', followed by input and output column types for the -- query each represented as a tuple. -- -- The /DataKinds/ language extension is required for 'Style'. data Query :: Style -> * -> * -> * where Query :: QueryID -> Text -> Query style i o deriving Show queryText :: Query s i o -> Text queryText (Query _ txt) = txt instance IsString (Query style i o) where fromString = query . T.pack -- | Construct a query. Another way to construct one is as an overloaded string through -- the 'IsString' instance if you turn on the /OverloadedStrings/ language extension, e.g. -- -- > {-# LANGUAGE OverloadedStrings #-} -- > ... -- > -- > getOneSong :: Query Rows UUID (Text, Text, Maybe Text) -- > getOneSong = "select title, artist, comment from songs where id=?" query :: Text -> Query style i o query cql = Query (QueryID . hash . T.encodeUtf8 $ cql) cql { - END CODE -} Thanks, Cody Goodman

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Munich Haskell Meeting, 2017-05-29 @ 19:30
by Christian Neukirchen 25 May '17

25 May '17

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, May 29 at Max Emanuel Brauerei at 19h30. We'll try to get seats outside, so please be on time. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-may-2017/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Haskell performance when it comes to regex?
by Bram Neijt 24 May '17

24 May '17

Dear reader, I decided to do a little project which is a simple search and replace program for large text files. Written in Haskell, it does a few different regex matches on each line and stores them in a leveldb key-value store to create a consistent/reviewable search-replace index. It should provide for some simple/brute-force anonymization of data and therefore I called it hanon (sorry, could not think of a better name). https://github.com/BigDataRepublic/hanon The code works, but I've done some benchmarking to compare it with Python and the code is about 80x slower then doing the same thing in Python, making it useless for larger data files. I'm obviously doing something wrong. Could you give me tips on improving the performance of this code? Probably mainly looking at https://github.com/BigDataRepublic/hanon/blob/master/src/Mapper.hs where the regex code lives? Greetings, Bram

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Accepted projects for Summer of Haskell 2017
by Niki Vazou 24 May '17

24 May '17

Hey all, We are happy to announce the 15 projects accepted for Summer of Haskell 2017 and that the community bonding period has begun. If there are people who would like to co-mentor a project, please let us know. # Haskell.org projects 1. Safe streaming with linear types Student: Edvard Hübinette Mentor: Arnaud Spiwack 2. Improve the GHC Performance test suite Student: Shivansh Rai Mentor: Ben Gamari 3. Haskell IDE Engine Student: Zubin Duggal Mentor: Alan Zimmerman 4. Last Mile for cabal new-build Student: Francesco Gazzetta Mentor: Daniel Wagner 5. Totality checking base with Liquid Haskell Student: Sean Leffler Mentor: Niki Vazou Co-mentor: Eric Seidel 6. Modularizing haskell-mode and improving haskell-interactive-mode Student: Vasantha Ganesh Kanniappan Mentor: Gracjan Polak 7. Haskey (an embedded key-value store modeled after LMDB) Student: Henri Verroken Mentor: Steven Keuchel Co-mentor: George Karachalias 8. Improve the Shake-Based Hadrian Build System for GHC Student: Zhen Zhang Mentor: Andrey Mokhov 9. GHC Performance improvements Student: Igor Popov Mentor: Jose Calderon 10. Improvement of Hackage Matrix Builder Student: Andika Demas Riyandi Mentor: Herbert Valerio Riedel 11. WebGHC (a WebAssembly backend for GHC) Student: Michael Vogelsang Mentor: Will Fancher # code.world projects 12. Better collaborative coding features for CodeWorld Student: Parv Mor Co-mentor: Michael Chavinda Co-mentor: Anthony Green 13. Improvements to parsing, compiling, and errors for CodeWorld Student: Pranjal Tale Primary Mentor: Kyle Butt Secondary Mentor: Chris Smith 14. Exporting and sharing CodeWorld projects Student: Venkatraman Srikanth Primary Mentor: Theo Belaire Secondary Mentor: Han Wang 15. Improve editor tooling for CodeWorld Student: Eric Roberts Primary Mentor: Emin Karayel Secondary Mentor: Fernando Alegre We would like to thank all students who applied for the quality proposals. We received 68 so selecting the projects was extremely difficult. Yet, three new positions opened during selection period to accept high quality applications. Summer of Haskell 2017 is made possible by our generous sponsors: - [haskell.org](http://haskell.org) kicked things off this year by funding a student and organizing the Summer of Haskell 2017 after a successful [Summer of Haskell 2016]( https://mail.haskell.org/pipermail/haskell-cafe/2016-December/125702.html) - [Asahi Net](https://asahi-net.jp/en/) is a Japanese Internet service provider that has been running stable systems for over 25 years. They are a proud sponsor of the Summer of Haskell, and contribute to the Japanese Haskell community. - [Awake Networks](http://www.awakenetworks.com/) is building a next generation network security and analytics platform. They are a proud sponsor of the Summer of Haskell and contribute broadly to the Haskell community. - [CodeWorld](http://code.world/) is an educational project that blends mathematics and Haskell programming into a visual playground. Chris Smith has volunteered to fund two students to work on CodeWorld in particular. - [Digital Asset](http://digitalasset.com/) provides Distributed Ledger solutions for financial institutions globally. They have developed a pure, typed, functional, domain specific language for writing contracts, called DAML. They are a proud sponsor of the Summer of Haskell and contribute broadly to the Haskell community. - [Facebook](http://facebook.com/) uses Haskell in its [anti-abuse infrastructure]( https://code.facebook.com/posts/745068642270222/fighting-spam-with-haskell/) and as part of that effort we open-sourced the [Haxl]( https://github.com/facebook/Haxl) framework which is being used at scale in production to automatically parallelise data-fetching code. We're delighted to be able to support the Haskell community's efforts by sponsoring a student for this year's Summer of Haskell. - [Fugue Inc.](http://fugue.co/) radically simplifies cloud operations with its software-defined system for dynamically orchestrating and enforcing cloud infrastructure at scale. Fugue uses Haskell in its product and is proud to sponsor a student to improve the ecosystem. - [Galois](http://galois.com/) applies cutting-edge computer science and applied mathematics to solve difficult technological problems, delivering practical solutions tailored to our clients’ needs. Haskell and other functional programming languages are key tools we use in providing these solutions. - [IOHK](https://iohk.io/) is a technology company committed to using peer-to-peer technologies to provide financial services to the three billion people who don't have them. We implement our first-principles cryptographic research in Haskell and we are committed to the development of the Haskell ecosystem. - [Tweag I/O](http://tweag.io) is a network of software innovation labs across Europe. We develop novel solutions and products for our clients around the world. Haskell is key to delivering fast, correct and maintainable code. We have shipped Haskell in anything from tiny web services to large high-performance compute clusters with custom hardware. We're particularly keen to help the community grow Haskell into the strongest systems programming language and ecosystem out there. We're very proud to sponsor a student this summer to help make it happen. Davean has volunteered to fund a student expressly to work on the [Hadrian build system for GHC](/ideas.html#hadrian-ghc). Steven Keuchel has provided funds for a student to work on Haskey. Niki Vazou & Jasper Van der Jeugt

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ANNOUNCE: Haskell Communities and Activities Report (32nd ed., May 2017)
by Mihai Maruseac 24 May '17

24 May '17

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (32nd edition, May 2017) is now available, in PDF and HTML formats: http://haskell.org/communities/05-2017/report.pdf http://haskell.org/communities/05-2017/html/report.html All previous editions of HCAR can be accessed on the wiki at https://wiki.haskell.org/Haskell_Communities_and_Activities_Report Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of September 2016: target deadline for contributions to the November 2017 edition of the HCAR Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in November (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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Re: [Haskell-cafe] [ghc-proposals/cafe] Partially applied type families
by Anthony Clayden 24 May '17

24 May '17

> On Wed May 24 07:57:09 UTC 2017, Alejandro Serrano Mena wrote: > I know I am just jumping in the middle of an already long > discussion. Hi Alejandro, your input is very welcome. I know there have been many posts, so Richard's right the idea now needs writing up in detail in one place. > > > > Bottom line: You win. I'm convinced. Apartness guards .. > > > > Even better, I think apartness guards would be very easy > > to implement. All the plumbing is already installed: we > > basically just have to add a switch. > > > I would like to advise against this idea of apartness > guards. I've tried myself some years ago, and I remember > them being quite complicated to describe. ... That's interesting. What did you try? How did you test for apartness? I roughed out the rules a few posts back. Bottom of https://mail.haskell.org/pipermail/haskell-cafe/2017-May/127103.html The body of that post has worked examples. I can also translate guards into Haskell2010 + MPTCs, providing there's a primitive for type-level type comparison. (Which we could write today with Closed Type Families.) See https://mail.haskell.org/pipermail/haskell-cafe/2017-May/127090.html discussion of (?~). This is essentially the 'case-preparing' technique from HList [2004]. > The main problem is that apartness may end up > introducing some sort of backtracking > in the type checking process -- something > completely undesirable. I agree that's not just undesirable, but unacceptable. (Backtracking is a weakness of Instance chains IMO.) With the guards I'm thinking of, an instance either applies at a usage site or does not (after taking guards into account). Or type refinement hasn't advanced enough to decide. Then that instance remains 'in play'. This is exactly the same process as currently. If an instance does apply (with guards) then it is guaranteed to be the only instance. IOW all other instances are excluded. So: > Furthermore, they make the work of > the overlapping checks much harder. The guards remove any need for overlapping checks. Instead the compiler must unify the usage site with the instance head, then substitute into the guards. If a guard comes out false under that subst, reject the instance. If all guards come out true, select the instance. If some guards come out 'not proven', it needs more type refinement. So you can't have OverlappingInstances as well as InstanceGuards. (Or at least not for the same class/type family. That's a bit of backwards compatibility awkwardness I mentioned.) AntC

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Re: [Haskell-cafe] Nomyx V1.0, the only game where you can change the rules
by Corentin Dupont 24 May '17

24 May '17

Hi Ben! Thanks a lot, it's corrected. The GUI tutorial is based on an old version of the GUI, although the principles remain the same. The new GUI is much more intuitive (I hope). Cheers! On Wed, May 24, 2017 at 10:00 AM, Ben Kolera <ben.kolera(a)gmail.com> wrote: > Hi Corentin, > > I notice that you've got some broken links on that first page. Namely: > > part 1 Nomyx GUI > <http://www.corentindupont.info/blog/posts/2014-09-23-first-Nomyx-tutorial.h…> > part 2 Nomyx Language > <http://www.corentindupont.info/blog/posts/2014-09-23-Nomyx-Language.html> > > Just thought that you may want to know. Your game looks fun! :) > > Cheers, > Ben > > On Wed, 24 May 2017 at 03:27 Corentin Dupont <corentin.dupont(a)gmail.com> > wrote: > >> Hi Haskellers, >> in case you didn't see it on Reddit (sorry for cross-posting): >> >> I released Nomyx V1.0 <http://www.nomyx.net/>! >> Nomyx is a unique game where you can change the rules of the game itself >> while playing it. >> The major novelty in this version is that you can play even without >> knowing how to program. There is a library of rules that are ready to be >> proposed. >> >> A match is going on on the theme "Foundation" (and we need more players). >> Please join! >> >> You can login here: http://www.nomyx.net:8000/Nomyx >> The games are discussed on the mailing list: nomyx-game(a)googlegroups.com >> >> Here is a video introduction of the game: http://vimeo.com/58265498 >> I created a tutorial to learn how to play: http://www.corentindupont. >> info/blog/posts/Programming/2014-09-23-Nomyx-Language.html >> >> Some background: this is an implementation of a Nomic [1] game in Haskell >> (I believe the first complete implementation of a Nomic game on a >> computer). At the beginning, the initial rules are describing: >> >> - how to add new rules and change existing ones. For example a >> unanimity vote is necessary to have a new rule accepted. >> - how to win the game. For example you win the game if you have 5 >> rules accepted. >> >> But of course even that can be changed! >> >> Cheers, Corentin >> >> [1] https://en.wikipedia.org/wiki/Nomic >> _______________________________________________ >> 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. > >

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Nomyx V1.0, the only game where you can change the rules
by Corentin Dupont 23 May '17

23 May '17

Hi Haskellers, in case you didn't see it on Reddit (sorry for cross-posting): I released Nomyx V1.0 <http://www.nomyx.net/>! Nomyx is a unique game where you can change the rules of the game itself while playing it. The major novelty in this version is that you can play even without knowing how to program. There is a library of rules that are ready to be proposed. A match is going on on the theme "Foundation" (and we need more players). Please join! You can login here: http://www.nomyx.net:8000/Nomyx The games are discussed on the mailing list: nomyx-game(a)googlegroups.com Here is a video introduction of the game: http://vimeo.com/58265498 I created a tutorial to learn how to play: http://www.corentindupont.info/blog/posts/Programming/2014-09-23-Nomyx-Lang… Some background: this is an implementation of a Nomic [1] game in Haskell (I believe the first complete implementation of a Nomic game on a computer). At the beginning, the initial rules are describing: - how to add new rules and change existing ones. For example a unanimity vote is necessary to have a new rule accepted. - how to win the game. For example you win the game if you have 5 rules accepted. But of course even that can be changed! Cheers, Corentin [1] https://en.wikipedia.org/wiki/Nomic

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Re: [Haskell-cafe] How to define a type in a TemplateHaskell function and use it in the same function?
by Anthony Clayden 23 May '17

23 May '17

> On Mon May 22 09:45:49 UTC 2017, Saurabh Nanda wrote: > Is there any way to have as single TH function, define a type, > and use the type, as well? In short, no. You must define/compile the TH function in a separate module, then import to where you want to use it. See second bullet of this: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_ext… And any intro to TH will also explain why it's hard. At first I was puzzled why you didn't get an error message explaining that more clearly, but I can see your usage of the TH function is also incorrect. You're trying to make a data declaration. So that must appear at top level in the program. It makes no sense to appear inside a monad. Also I suspect the imported TH function `makeAdaptorAndInstance` is trying to generate an instance declaration. This must also appear at top level, not inside a monad. > Cross-posted from StackOverflow: ... Yes, that answer has also moved the $( ... ) to top level. AntC

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How to define a type in a TemplateHaskell function and use it in the same function?
by Saurabh Nanda 22 May '17

22 May '17

Cross-posted from StackOverflow: http://stackoverflow.com/questions/44107336/how-to-define-a-type-in-a-templ… Is there any way to have as single TH function, define a type, and use the type, as well? Relevant code below. `PersonPoly2` is being defined by `makeRecordSplice` and then being passed to `makeAdaptorAndInstance` (provided by Opalaye), which is also a TH function. Relevant code given below: {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE TemplateHaskell #-} module Lib where import Data.Profunctor.Product.TH (makeAdaptorAndInstance) import Language.Haskell.TH makeRecordSplice :: Q [Dec] makeRecordSplice = [d| data PersonPoly2 a b = Person2 { id :: a , name :: b } |] makeRecordAndAdapter :: Q [Dec] makeRecordAndAdapter = do record <- makeRecordSplice adapter <- makeAdaptorAndInstance "pPerson2" (mkName "PersonPoly2") return $ record ++ adapter ------------- /home/Projects/scratch/app/Main.hs:26:1: error: ‘PersonPoly2’ is not in scope at a reify Failed, modules loaded: Lib. -- Saurabh.

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