- Haskell-Cafe - Haskell.org

working my way through Data.Type.Equality...my head hurts...
by Nicholls, Mark 13 Jan '15

13 Jan '15

Full code here… https://github.com/goldfirere/nyc-hug-oct2014/blob/master/Equality.hs Lets start at the beginning… Ø data a :~: b where Ø Refl :: a :~: a Looks reasonable….” a :~: b” is inhabited by 1 value…of type “a :~: a” Ø sym :: (a :~: b) -> (b :~: a) Ø sym Refl = Refl hmmm… (a :~: b) implies that a is b so (b :~: a) brilliant Ø -- | Transitivity of equality Ø trans :: (a :~: b) -> (b :~: c) -> (a :~: c) Ø trans Refl Refl = Refl Ø -- | Type-safe cast, using propositional equality Ø castWith :: (a :~: b) -> a -> b Ø castWith Refl x = x fine…. But…. Ø -- | Generalized form of type-safe cast using propositional equality Ø gcastWith :: (a :~: b) -> ((a ~ b) => r) -> r Ø gcastWith Refl x = x I don’t even understand the signature What does “~” mean…(it’s something that comes out in error messages when my types are all messed up)….and then there’s a “=>” going on…in the middle of a signature….I know “=>” in the context of “Num a => a -> a -> a” What would a value of type “((a ~ b) => r)” look like? 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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--disable-{executable-}profiling cabal-install-1.22.0.0 with ghc-7.6.3
by Ozgur Akgun 13 Jan '15

13 Jan '15

A recent change in cabal-install's command line interface seems not to be compatible with ghc-7.6.3. cabal-install-1.22.0.0 doesn't like --disable-executable-profiling as a command line option any more. (I could only find this related to this change: https://github.com/haskell/cabal/pull/2286) $ cabal install --disable-executable-profiling cabal: unrecognized 'install' option `--disable-executable-profiling' I try --disable-profiling instead. $ cabal install transformers --disable-profiling -j3 Resolving dependencies... Notice: installing into a sandbox located at [snip] Configuring transformers-0.4.2.0... Failed to install transformers-0.4.2.0 Build log [snip]: unrecognized 'configure' option `--disable-profiling' cabal: Error: some packages failed to install: transformers-0.4.2.0 failed during the configure step. The exception was: ExitFailure 1 Using the following versions of cabal and ghc. $ cabal -V cabal-install version 1.22.0.0 using version 1.22.0.0 of the Cabal library $ ghc -V The Glorious Glasgow Haskell Compilation System, version 7.6.3 --disable-profiling works fine with ghc-7.8.3, this is only a problem with 7.6.3. PS: transformers is only a dependency of an executable I am trying to build. But this happens with all the other dependencies as well. -- Ozgur Akgun

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FP Complete is hiring: Software engineer
by Mathieu Boespflug 13 Jan '15

13 Jan '15

Hi list, FP Complete is expanding yet again! We are looking to hire for several new engineers to join our Haskell development team, both to build great new core products and in partnership with our clients to apply Haskell at a large scale. Some of our recently announced core products include the Integrated Analysis Platform, Stackage and LTS Haskell, with much more to come. If you’d like to be part of our team and shape the future of Haskell, please send a resume or CV to jobs%2Bdev(a)fpcomplete.com. Any existing work - either a running website or an open source codebase - which you can include as links be greatly appreciated as well. We will want you to start right away. Depending on your current jurisdiction, this will either be a full-time contractor position, or an employee position. This is a telecommute position: you can work from home or wherever you choose, with little or no travel. Location in North America preferred; but you will work with colleagues who are both on North American and European hours. Activities: * distribute existing and new code over large clusters, * code parallelization and performance tuning, * interface with foreign math and scientific libraries, * relentlessly refactor for composability, testability and clarity, * identify performance bottlenecks and debug known issues, * implementing unit tests, integration tests, acceptance tests, * write clear and concise documentation. Skills: * strong experience writing process driven application code in Haskell. * experience building reusable components/packages/libraries and demonstrated ability to write well structured and well documented code, * ability to evolve and refactor large code bases, * experience working under test driven methodologies, * Ability to interact with a distributed development team, and to communicate clearly on issues, in bug reports and emails. These further skills are a plus: * Bachelor’s or Master’s degree in computer science or mathematics, * experience developing products in a regulated environment (avionics/medical/finance). * experience building scalable server/Web applications, * (web) UI design and implementation experience, * an understanding of the implementation of GHC’s multithreaded runtime, * experience as an architect and/or a creator of technical specs.

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ANNOUNCE: picoparsec-0.1
by Mario Blazevic 13 Jan '15

13 Jan '15

The newly released package picoparsec [1] is a fork of attoparsec that works with a much wider variety of input types than just ByteString and Text. Parsers written with Picoparsec will generally perform a bit slower than Attoparsec on strict ByteString and Text, somewhat faster than Attoparsec on lazy Text, and much faster than Parsec on any of the mutually-supported input types. That being said, the main point of the library is to enable the writing of generic parsers that are not constrained to any single input type. Depending on the parser primitives used, Picoparsec will take any input whose type is an instance of either NullMonoid, LeftGCDMonoid, FactorialMonoid, or TextualMonoid. These are some of the subclasses of Monoid defined in the monoid-subclasses package [2]. Some of the input types that are fully supported out of the box would be: - Text - String - Seq Char - Vector Char - ByteStringUTF8, a thin newtype wrapper around ByteString - Stateful (Map String a) Text, if you need to parse Text and keep track of the the symbol table state - OffsetPositioned String, in case you need to keep track of the current input position - LinePositioned Text, to keep track of the current line and column This release can be seen as the belated completion of the work described in my Haskell Symposium 2013 presentation [3]. The name Picoparsec seemed to fit in just the right place between Parsec and Attoparsec, especially since Nanoparsec [4] has already been taken. [1] http://hackage.haskell.org/package/picoparsec [2] http://hackage.haskell.org/package/monoid-subclasses [3] https://github.com/blamario/monoid-subclasses/wiki/Files/HaskellSymposium20… [4] http://hackage.haskell.org/package/nanoparsec

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Vacancies: 4 PhD students Software Technology Utrecht University
by Johan Jeuring 13 Jan '15

13 Jan '15

============================================================ 4 x PhD position in Software Technology ============================================================ The research group of Software Technology is part of the Software Systems division of in the department of Information and Computer Science at the Utrecht University. We focus our research on functional programming, compiler construction, program analysis, validation, and verification. Financed by the Netherlands Organisation for Scientific Research (NWO), the EU, Technology Foundation STW and Utrecht University we currently have job openings for four PhD researchers (PhD students) in Software Technology. We are looking for PhD students to work on some of the following topics: * Version control of structured data The theory and practice underlying structure-aware version control systems capable of handling more than just text files. * Intelligent tutoring technologies Technologies for tutoring subjects such as functional programming, statistics, algebra, etc. * Serious games Domain-specific languages and technologies for specifying strategies for serious games. * iTasks iTasks is a formalism for specifying distributed tasks. Specify and test properties of iTasks, and give run-time feedback for iTasks. Besides research, the successful candidate will be expected to help supervise MSc students and assist teaching courses. We prefer candidates to start no later than September 2015. --------------------------- What we are looking for --------------------------- The candidate should have an MSc in Computer Science, be highly motivated, speak and write English well. Furthermore the successful candidate should be proficient in reporting scientific findings. Knowledge of and experience with at least some of the following areas (depending on the topic chosen to work on for your PhD) is essential: * functional programming, such as Haskell or ML; * datatype generic programming; * intelligent tutoring systems; * serious games; * strategies, rewriting, parsing; * modern version control systems such as git, mercurial, or darcs. ------------------ What we offer ------------------ The candidate is offered a full-time position for 4 years. A part-time position of at least 0.8 fte may also be possible. Salary starts at 2083 euro and increases to 2664 euro gross per month in the fourth year of the appointment. The salary is supplemented with a holiday bonus of 8% and an end-of-year bonus of 8.3% per year. In addition we offer: a pension scheme, partially paid parental leave, flexible employment conditions. Conditions are based on the Collective Labour Agreement Dutch Universities. The research group will provide the candidate with necessary support on all aspects of the project. ---------------- How to apply ---------------- To apply please attach a letter of motivation, a curriculum vitae, and (email) addresses of two referees. Make sure to also include a transcript of the courses you have followed (at bachelor and master level), with the grades you obtained, and to include a sample of your scientific writing, such as your master thesis. It is possible to apply for this position if you are close to obtaining your Master's. In that case include a letter of your supervisor with an estimate of your progress, and do not forget to include at least a sample of your technical writing skills. Application deadline is March 8, 2015. You can apply online through the University's website: http://tinyurl.com/qhlco6s --------------------------- Additional information --------------------------- If you have any questions regarding these positions, please contact Johan Jeuring +31 (0)640010053 J.T.Jeuring(a)uu.nl Wouter Swierstra +31 (0)30 253 9207 w.s.swierstra(a)uu.nl

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May I have some examples on Kinds and Data.Type.Equality?
by Magicloud Magiclouds 12 Jan '15

12 Jan '15

Hi, I am trying to learn some advanced stuff of Haskell. But haskell wiki seems only giving some concepts and so. May I have some code example? Also other documents are welcomed. Thanks. -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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Re: [Haskell-cafe] Typesafe API calls
by Fabian Bergmark 12 Jan '15

12 Jan '15

I have uploaded a new version of the library https://hackage.haskell.org/package/apis-0.0.1 I'have included 15 more APIs from Facebook and Dropbox. I have also uploaded documentation to Hackage. I have been working on creating an autotools installation script that builds a makepkg package with the FFI bindings for Python and Java. I have tried it on Arch and it seems to work. If you want to try it out, check out the github repository. Building on top of this, Im working on a library that uses Pipes to create producers (triggers) and consumers (actions), allowing one to create effects (recipes) of the kind, when I am tagged in a photo on Facebook, notify me via email. This very much resembles IFTTT but with static and typesafe compositions. Im experimenting with using my javascript interpreter to allow for more dynamic compositions. 2014-12-18 21:59 GMT+01:00 Jonathan Paugh <jpaugh(a)gmx.us>: > Hello Fabian, > > I have been dreaming of something like this for Haskell since I wrote a > (non type-safe) python library to access any REST API generically[1]. > This comes from a different (and more ambitious) angle than I had imagined. > > I don't have time to test this just now, but I will keep it bookmarked. > Thanks for sharing your hard work! > > Regards, > Jonathan > > [1]: http://github.com/jpaugh/agithub (unmaintained, but maybe interesting) > > On 12/12/2014 07:01 AM, Fabian Bergmark wrote:> I just released a > library on hackage >> (https://hackage.haskell.org/package/apis-0.0.0) The goal of the >> library is to provide typesafe API calls to a large amount of existing >> APIs. By typesafe I mean that, for each API the library provides two >> types, Input and Output, and a function :: Input -> IO Output. >> Internally the library knows how to serialize Input to make an HTTP >> request and how to deserialize the response into Output. >> >> Whats cool about this library is that it uses Template Haskell to >> generate the API interfaces. A combination of Open Data Tables, an >> internal YQL engine and JSON Schemas, all written in Haskell makes >> this possible. >> >> Right now only two APIs are included (Swedish weather data and Swedish >> public announcement), but more APIs are soon to follow. >> >> I have also implemented FFI exports of all types and functions so >> that, in combination with SWIG, this library can be used in almost any >> language. So far I have tried Java and Python with success. >> >> If anyone would like to try it and respond with feedback it would be >> greatly appreciated! If you want any specific API supported, I can try >> to import that right away >> >> Fabian Bergmark >> >

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why can it never go smoothly, language-c-0.4.7 edition
by briand＠aracnet.com 12 Jan '15

12 Jan '15

Hi, setup-Simple-Cabal-1.22.0.0-x86_64-linux-ghc-7.8.4: The program 'happy' is required but it could not be found. so i installed happy. then it wanted alex. which i was also able to install. and then language-c-0.4.7 successfully installed. I have seen this sort of thing many times across all sorts of different packages. So my question is : are these dependency bugs that should be reported to the package maintainer ? or is that certain packages can't be built as a dependency target for some reason ? Thanks, Brian

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ghc-mod split feature
by Tobias Pflug 11 Jan '15

11 Jan '15

Hi, i just wanted to try some of the ghcmod features that I haven't used before in order to hopefully add them to my vim haskell workflow somehow. What I apparently can't get to work is the split command: $ ghc-mod split src/Foo.hs Foo 47 7 which points to exactly the code listed in the ghc-mod help: f :: [a] -> a f x = _ It does however not yield any output at all. Am I missing something obvious here ? I'm using version 5.2.1.1 Thanks, Tobi

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new haskell music track: Mother Is Waiting
by Anton Kholomiov 11 Jan '15

11 Jan '15

Dear Haskellers I'd like to present yet another piece of music made in Haskell. https://soundcloud.com/anton-kho/mother-is-waiting It's very soothing piece that can be used as a helper for dreaming or meditation. It's dedicated to my friend. She's waiting for her second child to be born. This time it contains no samples. All sounds are made out of waves and filters. So I can attach the source code right in the mail. The track relies on new versions of the packages `csound-expression`, `csound-sampler` and `csound-catalog`. So you can do > cabal update > cabal install csound-sampler csound-catalog Ad the we can load the file in the ghci and run the main function. > ghci Mother.hs > main and the Csound should be installed to render the synths. Cheers, Anton

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