- Haskell-Cafe - Haskell.org

Type-class predicates head-normal forms
by sheng chen 01 Jul '16

01 Jul '16

Hello, I got a question about what the form of types in Haskell are allowed. Specifically, what are the requirements of the context of a type? The paper Typing Haskell in Haskell required the type to be in the form P => t, where P to be in head-normal form or in other words shouldn't be something like Num Bool. Now what about multi-parameter classes? The paper Type classes: an exploration of the design space listed several potential choices but didn't say exactly what. The Haskell 2010 report covered single-parameter type classes only. Given the following definition. class Collects ce e | ce -> e where empty :: ce insert :: e -> ce -> ce insert2 c = insert True (insert False c) The function insert2 has the following type insert2 :: Collects ce Bool => ce -> ce This shows that the definition of head-normal forms for multi-parameter class differs from that for single-parameter classes. Is there any definite specification about the context of Haskell types? Thank you, Sheng

2 1

ICFP 2016 Student Research Competition: Call for Submissions
by Lindsey Kuper 01 Jul '16

01 Jul '16

====================================================================== CALL FOR SUBMISSIONS SRC at ICFP 2016 Nara, Japan 18-24 September 2016 http://conf.researchr.org/info/icfp-2016/student-research-competition Co-located with the International Conference on Functional Programming (ICFP 2016) ====================================================================== Student Research Competition ---------------------------- This year ICFP will host a Student Research Competition where undergraduate and postgraduate students can present posters. The SRC at ICFP 2016 consists of three rounds: * Extended abstract round. All students are encouraged to submit an extended abstract of up to 800 words outlining their research. * Poster session. Based on the abstracts, a panel of judges will select the most promising entrants to participate in the poster session which will take place at ICFP. Students who make it to this round will be eligible for some travel support to attend the conference. In the poster session, students will have the opportunity to present their work to the judges, who will select three finalists in each category (graduate/undergraduate) to advance to the next round. * ICFP presentation. The last round will consist of an oral presentation at ICFP to compete for the final award. Prizes ------ * The top three graduate and the top three undergraduate winners will receive prizes of $500, $300, and $200, respectively. * All six winners will receive award medals and a two-year complimentary ACM student membership, including a subscription to ACM's Digital Library. * The names of the winners will be posted on the ACM SRC web site. * The first-place winners will be invited to participate in the ACM SRC Grand Finals, an on-line round of competition among the winners of conference-hosted SRCs. * Grand Finalists and their advisors will be invited to the Annual ACM Awards Banquet for an all-expenses-paid trip, where they will be recognized for their accomplishments along with other prestigious ACM award winners, including the winner of the Turing Award (also known as the Nobel Prize of Computing). * The top three graduate Grand Finalists will receive an additional $500, $300, and $200. Likewise, the top three undergraduate Grand Finalists will receive an additional $500, $300, and $200. All six Grand Finalists will receive Grand Finalist certificates. * The ACM, Microsoft Research, and our industrial partners provide financial support for students attending the SRC. You can find more information about this on the ACM website. Eligibility ----------- The SRC is open to both undergraduate (not in a PhD programme) and graduate students (in a PhD programme). Upon submission, entrants must be enrolled as a student at their universities, and are ACM student members. Furthermore, there are some constraints on what kind of work may be submitted. Previously published work: Submissions should consist of original work (not yet accepted for publication). If the work is a continuation of previously published work, the submission should focus on the contribution over what has already been published. We encourage students to see this as an opportunity to get early feedback and exposure for the work they plan to submit to the next ICFP or POPL. Collaborative work: Students are encouraged to submit work they have been conducting in collaboration with others, including advisors, internship mentors, or other students. However, submissions are individual, so they must focus on the contributions of the student. Submission Details ------------------ Each submission should include the student author's name, institutional affiliation, e-mail address, and postal address; research advisor's name; ACM student member number; category (undergraduate or graduate); research title; and an extended abstract addressing the following: * Problem and Motivation: Clearly state the problem being addressed and explain the reasons for seeking a solution to this problem. * Background and Related Work: Describe the specialized (but pertinent) background necessary to appreciate the work. Include references to the literature where appropriate, and briefly explain where your work departs from that done by others. * Approach and Uniqueness: Describe your approach in attacking the problem and clearly state how your approach is novel. * Results and Contributions: Clearly show how the results of your work contribute to computer science and explain the significance of those results. The abstract must describe the student's individual research and must be authored solely by the student. If the work is collaborative with others and/or part of a larger group project, the abstract should make clear what the student's role was and should focus on that portion of the work. The extended abstract must not exceed 800 words and must not be longer than 2 pages. The reference list does not count towards these limits. To submit an abstract, please register through the submission page and follow the instructions. Abstracts submitted after the deadline may be considered at the committee's discretion, but only after decisions have been made on all abstracts submitted before the deadline. If you have any problems, don't hesitate to contact the competition chair. Please submit your abstract at the EasyChair submission page: https://easychair.org/conferences/?conf=icfp2016src Important Dates --------------- * Deadline for submission: 3 August * Notification of acceptance: 10 August Selection Committee ------------------- To include: Chair: David Van Horn, University of Maryland Ronald Garcia, University of British Columbia Ilya Sergey, University College London

1 0

Deadline extended: Commercial Users of Functional Programming Call For Tutorials
by Lindsey Kuper 01 Jul '16

01 Jul '16

The 2016 Commercial Users of Functional Programming (CUFP) call for tutorials have passed the initial deadlines, but we have more seat for tutors. CUFP tutorial is a good opportunity if you have some idea you want to spread to the real world, say, your favorite programming language (Clojure, Erlang, F#, F*, Haskell, ML, OCaml, Scala, Scheme...), concepts (e.g. Lens, Liquid-Haskell, Proof Assistance, ...), applications (Web, high-performance computing, finance...,) tools and techniques (QuickCheck, Elm, ...), or theories. If you are interested, we kindly invite you to submit a proposal for the Call For Tutorials from here: http://cufp.org/2016/call-for-tutorials.html , before July 3rd. If you have any questions, please do not hesitate to contact us: Roman Gonzalez: roman(a)unbounce.com Takayuki Muranushi: muranushi(a)gmail.com best regards, Takayuki

1 0

Compose :: Conference, Melbourne, 2016, Call for Presentations!
by Noon van der Silk 30 Jun '16

30 Jun '16

(Web version: http://www.composeconference.org/2016-melbourne/cfp/) # Call for Presentations Compose Melbourne - http://www.composeconference.org/ - is pleased to announce its call for presentations. Compose Melbourne is a new functional programming conference focused on developing the community and bringing typed functional programming to a wider audience. It is a 2-day event being held in Melbourne, Australia on the 29th and 30th of August 2016. The first day features a single track of presentations followed by a second day of workshops and an unconference. It is the new sister-conference of the NY based Compose Conference. Submit your presentation proposal here: https://easychair.org/conferences/?conf=cmc2016 # Important Dates - CFP Launch Party - 19th May - CFP Opens - 19th May - CFP Closes - June 30th - Notify Presenters - July 15th - Conference Day 1: Presentations - Monday, 29-Aug-2016 - Conference Day 2: Unconference - Tuesday, 30-Aug-2016 # Talk and Workshop Submission ## Day 1 - Presentations Submit a Presentation Proposal via Easy Chair: https://easychair.org/conferences/?conf=cmc2016. ## Day 2 - Unconference and Workshops Contact us (composemel-admin(a)googlegroups.com) with your workshop proposals. # Submission Guidelines Talk slots will be 30 minutes: 25 minute talk and 5 minutes for questions. Provide sufficient detail in your submission to enable the reviewers to understand your proposal and clearly identify what an attendee will gain from attending your session. You should include the following information in the submission system: - Authors - The details of each of the presenters - Title - Title of the presentation (please keep it brief and specific) - Abstract - A 300-500 word description of your presentation, ideally including... - Description of the content - Goal - Keywords - List any keywords that will help the program committee and attendees categorise your presentation. Also indicate the functional programming languages that you will be targeting. Nothing upsets an audience more than a speaker that stands on stage blatantly promoting his or her company, product or achievements. Please keep the content of your talk on-topic and do not use this speaking opportunity as a sales pitch. # Feel We want Compose Melbourne to be all about the community. We're aiming to help foster the growth of Functional Programming in Melbourne and unite all interested parties to spark a unified presence and a feeling of camaraderie amongst FP and Theory proponents in this wonderful city! # Audience Functional-Programming and Programming-Language-Theory professionals and enthusiasts. Newcomers, experts, anyone from other disciplines of fields who is interested in what FP is or how it could help them with their work, or simply make life more enjoyable! # Diversity Just like Compose-Conference, we would also like to put an emphasis on soliciting a diverse set of speakers - anything you can do to distribute information about this CFP and encourage submissions from under-represented groups would be greatly appreciated. We welcome *all* (new and established) contributions and encourage you to apply! # Day One All topics for proposals for presentations are invited, but not limited to explore the following topics: ## New Languages The development of new and emerging Functional Languages, and the toolsets around them. ## Libraries and Tools Exploring the use and development of new and underrepresented tools and libraries. ## Production Systems 2016 has seen many previously undeployed languages and systems break through into production. We're looking for war-stories, success-stories and sob-stories! ## Theory Theory is the cutting edge of new functional programming. Show the world what is rising over the horizon. ## Art and Music Exciting and innovative usage of functional programming language in the arts! # Day Two The second day will be dedicated to workshops and unconferences. ## Workshops We will be running a beginners Haskell workshop. If you wish to run a workshop on the second day of the conference, then please let us know. Alternatively, if there is a workshop that would interest you as an attendee, then please also let us know. ## Unconference Got something random you want to talk about? The unconference will run the second day. There will be a whiteboard with spaces where anyone can write their name down to speak. There's no need to bring anything but yourself and your ideas and speaking voice. # Sponsors We are seeking sponsors to support us in putting on this conference. If you or your company would like to sponsor us, please get in contact via composemel-admin(a)googlegroups.com. You can find our prospectus here: https://github.com/composeconference/Compose-Melbourne/blob/master/ComposeM… . -- Compose Conference Melbourne Organising Committee http://www.composeconference.org/

1 1

Announcing Blocks for CodeWorld
by Stefan 30 Jun '16

30 Jun '16

Hi everyone, (this is somewhat cross-posted from reddit) I'm announcing Blocks for CodeWorld, which is a functional based drag-and-drop programming environment. The project is part of Haskell Summer of Code. The aim of the project is to create a web application with which users can drag-and-drop blocks in order to create CodeWorld <https://code.world/> applications, The project is primarily educational based, and more advanced applications may be created with the regular CodeWorld text UI. The application uses Blockly to allow users to drag-and-drop blocks, which can then be snapped together in order to build programs, in a Scratch-esque manner. The generated code is Haskell, which is then sent to the regular CodeWorld server and compiled with GHCJS, the resulting JavaScript is then run on the site. Code is generated as students are introduced to programming concepts with the Blocks and will later be exposed to a more text based environment. The majority of the code, aside from Blockly, is in Haskell, which is compiled to JavaScript using GHCJS. Currently, in this initial release, the user is able to: - Build and run simple CodeWorld programs, mostly pictures and transformations thereof - Save and Load projects, load a program by its URL. - Use polymorphic blocks, such as an if-then-else block and some others - Use Let definition blocks to create top level bindings Later, more advanced functional features such as pattern matching and some support for first-class functions might be covered. For anyone interested, an initial version can be found at code.world/blocks. If you want to follow on the progress you can check out my blog <http://stefanj.me/funblocks/>.

1 0

Re: [Haskell-cafe] Help to choose a library name
by Corentin Dupont 29 Jun '16

29 Jun '16

Wow, it is very impressive. I need to give it more time. I have one question regarding this example: main = keep $ do th <- liftIO myThreadId -- thread 89 r <- async (do threadDelay 1000000; return "hello") -- thread 90 <|> async (return "world") -- thread 91 th' <- liftIO myThreadId -- thread 90 and 91 liftIO $ print (th, th', r) -- thread 90 and 91 Output: (ThreadId 89,ThreadId 91,"world") (ThreadId 89,ThreadId 90,"hello") For me it's counter-intuitive that there are two outputs. What is the reason behind? It seems that the use of the <|> affects the rest of the program. It looks strange to me because the two lines situated after the <|> does not look "syntactically" involved, if you see what I mean. Instead I was expecting only one output, with the first thread to finish "wins". In fact I implemented it like that: http://www.corentindupont.info/blog/posts/Programming/2014-09-23-Nomyx-Lang… Cheers Corentin On Mon, Jun 27, 2016 at 8:22 PM, Geraldus <heraldhoi(a)gmail.com> wrote: > Sorry, here is some links: > Wiki paga on GitHub > https://github.com/agocorona/transient/wiki/Transient-tutorial > Programming at specification level > https://github.com/agocorona/transient/wiki/Programming-at-the-specificatio… > > пн, 27 июн. 2016 г. в 23:19, Geraldus <heraldhoi(a)gmail.com>: > >> Hi! Have you looked at Transient by Alberto Gomez Corona? >> >> пн, 27 июн. 2016 г. в 18:27, Corentin Dupont <corentin.dupont(a)gmail.com>: >> >>> Hi Joachim, >>> I agree... I looked hard at them :) >>> https://wiki.haskell.org/Functional_Reactive_Programming >>> >>> I need a library with a DSL able to create forms on the fly, in a >>> "demand driven" way. >>> I.e. if at some point in time the user program needs a boolean from the >>> user, a radio button will be created on the screen of that user. The >>> objective is to retrieve the boolean, creating the form is just a way to do >>> that. Complex forms can be created, capable of generating full ADTs. The >>> styling of the form is not important. >>> Other requirements: >>> - it should be possible to run the event DSL in a monad different from >>> IO. >>> - the event DSL need to be instance of Alternative: events can be put in >>> concurrence, the first to fire wins. >>> >>> >>> >>> >>> On Mon, Jun 27, 2016 at 10:25 AM, Joachim Breitner < >>> mail(a)joachim-breitner.de> wrote: >>> >>>> Hi, >>>> >>>> Am Montag, den 27.06.2016, 09:38 +0200 schrieb Corentin Dupont: >>>> > I need it for the game Nomyx, but couldn't find the features I wanted >>>> > from the existing libraries. >>>> >>>> any chance to extend existing libraries to support what you need? >>>> Library proliferation does not really help the ecosystem. >>>> >>>> Greetings, >>>> Joachim >>>> -- >>>> >>>> Joachim “nomeata” Breitner >>>> mail(a)joachim-breitner.de • https://www.joachim-breitner.de/ >>>> XMPP: nomeata(a)joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F >>>> Debian Developer: nomeata(a)debian.org >>>> _______________________________________________ >>>> 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. >>>> >>> >>> _______________________________________________ >>> 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. >> >>

3 6

Fwd: Delivery Status Notification (Failure)
by A Smith 29 Jun '16

29 Jun '16

Hi I'm a Haskell noob, and decided to experiment with a simple package to get me started; ansi-terminal. However, I found a bug in one of the functions. How and to whom do I send a bug report ? Andrew in Scotland

3 2

Using streams to clarify (?) the signature of Data.Text.replace
by Daniel Díaz 28 Jun '16

28 Jun '16

In the "text" package, the signature of Data.Text.replace <http://hackage.haskell.org/package/text-1.2.2.1/docs/Data-Text.html#v:repla…> always sends me looking into the haddocks: replace :: Text -> Text -> Text -> Text Which argument is the text to replace, which is the replacement and which is the text that should be scanned? Imagine a generalized version of replace that 1) works on streams, and 2) allows replacing a sequence of texts (like, say, chapter headers) instead of replacing the same text repeatedly. It could have the following signature: replace' :: Stream (Stream (Of Text) m) m () > -> Stream (Stream (Of Text) m) m Void > -> Stream (Of Text) m r > -> Stream (Of Text) m r Do you find easy to intuit, just by looking at that signature, which is the function of each argument?

4 6

Help to choose a library name
by Corentin Dupont 28 Jun '16

28 Jun '16

Hi community, I'm writing a reactive programming library (yet another). I need it for the game Nomyx, but couldn't find the features I wanted from the existing libraries. Now the library is called Nomyx-Events. But I'd like to find a cool name that is not related to Nomyx... Some propositions: - Nomev - Noa Some French names: - Imprevu (French for unforseen, like in "unforseen event"). - Rendez-vous - Dejavu I like a lot Imprevu. How does it sound to English native speakers? Thanks

3 3

Instances for (->) a (b :: * -> *)?
by Oleg 28 Jun '16

28 Jun '16

Jim Pryor wrote: > If one wants to declare instances for a type schema `a -> _`, one writes > something like this: > instance Context => Class parameters ... ((->) a) where { ... } > But what if you want to declare instances for a type schema `a -> b _`, > that is, where the slot to be filled is not just the result of (->) a, > but rather the composition of that together with another type operation > b :: * -> *? Then one defines a new type: newtype TwoArrow a b x = TwoArrow{unTA:: a -> b -> x} instance MyClass (TwoArrow a b) where ... Ditto for the composition. Alas, one is stuck with adding the dummy conversions TwoArrow/unTA at various places. > Concretely, here's what I'm trying to achieve. I wrote a typeclass for > MonadReaders that are embedded inside (one level) of other MonadReaders, > like this: > {-# LANGUAGE FunctionalDependencies FlexibleInstances > UndecidableInstances #-} > class MonadReader w m => DeepMonadReader w r m | m -> r where > { deepask :: m r > ; deepask = deepreader id The first instance of the curly-braces notation on this list in more than a decade! I think you are trying to build a monad with several pieces of environment. Assuming that just making a record with two different pieces (and making that record the single environment) doesn't work for you, you can find many solutions on Hackage. For example, various extensible effects libraries offer the desired functionality right out of the box. Or, if you really want to define a new class, why not to do something more general, like class Monad m => MonadMReader var r m | var m -> r where ask :: var -> m r to be used like data Var1 = Var1; data Var2 = Var2 do x <- ask Var1 y <- ask Var2 return $ x + y (and implement it, that is, define the instance any way you wish, e.g., with a Free or a Freer monad). For completeness, the old `reflection' trick, see https://hackage.haskell.org/package/reflection offers multiple pieces of configuration data.

1 0

International summer school on metaprogramming (Cambridge, 8-12 Aug 2016)
by Jeremy Yallop 27 Jun '16

27 Jun '16

==================================================================== International summer school on metaprogramming Robinson College, Cambridge, United Kingdom 8th-12th August, 2016 http://www.cl.cam.ac.uk/events/metaprog2016/ ==================================================================== Metaprogramming is an approach to improving programs by treating program fragments (such as expressions or types) as values that the program can manipulate. Metaprogramming comes in various forms, including * staged programming: treating expressions as program values. The execution of a staged program is spread over several phases, with each stage using the available data to generate specialized code. Staged programming has a wide variety of applications — numeric computations, parsing, database queries, generic programming, domain specific languages, and many more. Precompiling the staged code can have dramatic performance improvements, in some cases an order of magnitude or more. * generic programming: treating types as program values. Generic programming can improve code flexibility, allowing to give a single definition of a function that operates in a predictable (but not uniform) way on many different types. Generic programming techniques can be used to define a wide variety of functions, including traversals, comparisons, pretty printers, serialization functions, and many more. The goal of the summer school is to explore the state-of-the art in metaprogramming and its applications, covering both theory and practice. -------------------------------------------------------------------- Lecturers and courses Philip Wadler, Sam Lindley and Shayan Najd (University of Edinburgh) Normalisation and embedding Simon Peyton Jones (Microsoft Research) Oleg Kiselyov (Tohoku University) Type-safe embedding and optimizing domain-specific languages in the typed final style Laurence Tratt (Kings College London) The highs and lows of macros in a modern language Jeremy Yallop (University of Cambridge) Staging generic programming Martin Berger (University of Sussex) Foundations of meta-programming José Pedro Magalhães (Standard Chartered) -------------------------------------------------------------------- Prerequisites The school is aimed at graduate students in programming languages and related areas, but is open to researchers, practitioners and strong masters students with the support of a supervisor. Some experience of typed functional programming in Haskell, OCaml, Scala, or a similar language will be assumed. -------------------------------------------------------------------- Costs Thanks to generous industrial sponsorship, we are able to offer places with significantly reduced fees. There are three categories of fees, all of which cover registration, accommodation in Robinson College from Monday to Friday, and all meals and refreshments. Participants who can pay the full fees will help allocate more fully-subsidised slots to less financially-able students. Your category of fees will not have any direct bearing on your acceptance into the school, but could affect how many slots we can offer. * The full fee is £800. * The standard (partly-subsidised) fee is £295. * We also have a limited number of fully-subsidised places available for a nominal registration fee of £50. We will notify you of your fee upon acceptance. -------------------------------------------------------------------- Application procedure You will need to complete the online registration form at: http://www.cl.cam.ac.uk/events/metaprog2016/application.html and ensure your referees send your references to: metaprog-2016(a)cl.cam.ac.uk by the application deadline. TIMETABLE * 30 June: Application and reference letters deadline. * 10 July: Notification of acceptance. * 24 July: Registration deadline. * 8 August: Summer school. -------------------------------------------------------------------- Further information For questions relating to the material of the school, please contact Jeremy Yallop (jeremy.yallop(a)cl.cam.ac.uk) Ohad Kammar (ohad.kammar(a)cs.ox.ac.uk) For administrative questions, please contact Gemma Gordon (gg417(a)cl.cam.ac.uk)

1 1

Haskell contract position in US (TX)
by Dave Carlson 27 Jun '16

27 Jun '16

I have a client located in the US, Texas who is looking for a Haskell developer ideally with 8+/- years of development experience. If someone is interested in the position below please contact me ASAP. Thanks- Dave Location: TX (potential for some remote/ off-site work) Duration: 6+ months Position Title: Haskell Developer Duties: Client is looking for a Sr. level Haskell developer who has recent experience to work on an AI platform for their product team. Candidate will be assisting building the infrastructure and writing in Haskell coding. Candidate will need to come in from a mentor stand-point and help mentor and train/build- out of platform. Candidate needs to have functional programming experience and be able to do an implementation stack that is based on Haskell & Haskell programming. Candidate needs to be familiar with ECO system tools within Haskell. Candidate needs to have some experience with basic micro services in Haskell & have some Big Data process experience and know how to move data through a pipeline. Candidate needs to understand best practices and bring in the right tools to get the problem done. Necessary Experience: 8+ years of recent Haskell Experience (coding experience & build out) Experience with Functional Programming Able to do implementation stack Exp. with ECO system tools within Haskell Exp. with Basic Micro Services in Haskell Exp. with Big Data process & how to move data through Pipeline Understanding best practices and bring in right tools to get the problem done Desired Experience: Scala Experience GO experience F# Experience Ocamel Language __________________________________ Dave Carlson Senior Recruiting Executive, Software & Hardware Oxford International 100 Cummings Center Suite 365G Beverly, MA 01915 877.258.9982 Office 978.717.7659 Direct david_carlson(a)oxfordcorp.com<mailto:david_carlson@oxfordcorp.com> NYSE: ASGN oxfordcorp.com<http://www.oxfordcorp.com> | LinkedIn<https://www.linkedin.com/company/oxfordinternational> | facebook<https://www.facebook.com/OxfordOGR> | twitter<https://twitter.com/oxfordindex> | Oxford Index Blog<http://info.oxfordcorp.com/oxfordindexblog> The Right Talent. Right Now. The information transmitted, including attachments, is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon this information by persons or entities other than the intended recipient is prohibited. If you received this e-mail in error, please notify the sender immediately by replying to the message and deleting the material from your computer.

2 2

Extensionality in category theory RE: User Requirements Survey for CT Software (Beta)
by Carter Schonwald 27 Jun '16

27 Jun '16

Hey Joie, I'll cc the list because certain list members (Dan, Gershom, and others) can better clarify / expound on this topic Probably the simplest example is function extensionality , that is the reasoning principle that if forall X , g X == f X , then g == f My understanding is that it can be derived in a homotopy type theory setting, but in in more standard type theories like vanilla coq / Agda / lean that folks often use to model certain categorical objects, this is at best a not computable axiom. The very definitions of an epimorphism and monomorphism (the categorical generalization of the dual pair of surjective and injective mappings) Have a sort of function extensional equality! https://ncatlab.org/nlab/show/equality Touches a wee bit On the topic of equalities. There's a number of approaches to treating / deciding when two ... Things (a very technical term 😉)are the same / equal. -Carter _____________________________ From: Breiner, Spencer J. (Fed) <spencer.breiner(a)nist.gov> Sent: Monday, June 27, 2016 9:44 AM Subject: RE: [Haskell-cafe] User Requirements Survey for CT Software (Beta) To: Carter Schonwald <carter.schonwald(a)gmail.com>, Murphy, Joie R. (Assoc) <joie.murphy(a)nist.gov> Cc: Subrahmanian, Eswaran (Assoc) <eswaran.subrahmanian(a)nist.gov> Carter, Thanks for your reply. I removed the Haskell mailing list from the cc because I don’t know the list’s etiquette, but please forward this response back to the list if you are aiming for a public discussion. I’m not quite sure what you mean by “extensional elements”? Is this extension in the sense of “one class extends another” (in which case this would be expressed explicitly by functors). Or extension in the (related) sense of “the extension of a proposition”, the elements which satisfy it. These sorts of issues would probably be expressed as functors into (some computational implementation of) finite sets. Let me know and I’m happy to talk some more. Thanks again, Spencer Breiner NIST From: Carter Schonwald [mailto:carter.schonwald@gmail.com] Sent: Friday, June 24, 2016 8:35 PM To: Murphy, Joie R. (Assoc) <joie.murphy(a)nist.gov> Cc: haskell-cafe(a)haskell.org; Subrahmanian, Eswaran (Assoc) <eswaran.subrahmanian(a)nist.gov>; Breiner, Spencer J. (Fed) <spencer.breiner(a)nist.gov> Subject: Re: [Haskell-cafe] User Requirements Survey for CT Software (Beta) How do you plan to handle extensional elements of category theory? On Friday, June 24, 2016, Murphy, Joie R. (Assoc) <joie.murphy(a)nist.gov> wrote: Hello, My name is Joie Murphy and I am a Summer Research Student at the US National Institute of Standards and Technology (NIST), working with Drs. Spencer Breiner and Eswaran Subrahmanian. We are currently gathering user requirements for category theoretic software to be developed by or with NIST in the future. This questionnaire will give us insight about your past or present use of CT software and your ideal uses for such software. Providing us with the information on how you would like to use this type of software will help us to make the right design choices in development. The survey is available on Google Forms:http://goo.gl/forms/vfOgR26dHnKynHU23 If you have any colleagues who might be willing to fill out this survey, you can forward our message or you can provide us with their contact information at the end of the survey. If you have any questions or concerns, please feel free to contact us by replying to this email. We would like to thank you for your participation in this initial step of the development process. Regards, Joie Murphy

2 1

Re: [Haskell-cafe] [Haskell] The Haddock documentation is not showing up on the Hackage
by Henning Thielemann 27 Jun '16

27 Jun '16

On Mon, 27 Jun 2016, KwangYul Seo wrote: > I uploaded a package named enchant on the Hackage last week, but the > Haddock documentation is not showing up yet. The Status field says "Docs > pending" and "Build status unknown". This is certainly not for haskell(a)haskell.org. I am answering to haskell-cafe and cabal-devel. > https://hackage.haskell.org/package/enchant-0.1.0.0 > > enchant uses c2hs as a build tool to generate the FFI binding and > requires libenchant-dev to be installed on the machine. I wonder how I > can tell these build requirements to the Hackage server. I assume that it is not a good idea to install many additional packages on the Haskell server. Thus I think the best you can do is to upload the documentation yourself via the package maintenance site. Here is a script that should help creating the docs locally and upload them to Hackage: https://raw.githubusercontent.com/ekmett/lens/master/scripts/hackage-docs.sh

3 3

Re: [Haskell-cafe] [Haskell] The Haddock documentation is not showing up on the Hackage
by Francesco Ariis 27 Jun '16

27 Jun '16

On Mon, Jun 27, 2016 at 01:28:57PM +0900, KwangYul Seo wrote: > Hi, > > I uploaded a package named enchant on the Hackage last week, but the > Haddock documentation is not showing up yet. The Status field says "Docs > pending" and "Build status unknown". > > https://hackage.haskell.org/package/enchant-0.1.0.0 > > enchant uses c2hs as a build tool to generate the FFI binding and requires > libenchant-dev to be installed on the machine. I wonder how I can tell > these build requirements to the Hackage server. I had a similar problem a few months ago, resolved to upload a 0.1.0.1 version, that triggered the build. p.s.: I am replying in haskell-cafe(a)haskell.org , which is probably more suited (haskell@ is for announcements, etc.)

4 3

Munich Haskell Meeting, 2016-06-29 @ 19:30 Augustiner-Keller
by Christian Neukirchen 25 Jun '16

25 Jun '16

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, June 29 at Augustiner-Keller Arnulfstr. at 19h30. **Please note the different day and location!** For details see here: http://muenchen.haskell.bayern/dates.html (Yes, we got a new domain!) 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-jun-2016/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

1 0

User Requirements Survey for CT Software (Beta)
by Murphy, Joie R. (Assoc) 25 Jun '16

25 Jun '16

Hello, My name is Joie Murphy and I am a Summer Research Student at the US National Institute of Standards and Technology (NIST), working with Drs. Spencer Breiner and Eswaran Subrahmanian. We are currently gathering user requirements for category theoretic software to be developed by or with NIST in the future. This questionnaire will give us insight about your past or present use of CT software and your ideal uses for such software. Providing us with the information on how you would like to use this type of software will help us to make the right design choices in development. The survey is available on Google Forms: http://goo.gl/forms/vfOgR26dHnKynHU23 If you have any colleagues who might be willing to fill out this survey, you can forward our message or you can provide us with their contact information at the end of the survey. If you have any questions or concerns, please feel free to contact us by replying to this email. We would like to thank you for your participation in this initial step of the development process. Regards, Joie Murphy

2 1

up-to-date glfw examples
by briand＠aracnet.com 24 Jun '16

24 Jun '16

Hi, I've been looking but the examples are all fairly old and are broken in both imports from glfw and opengl. Just looking for very basic examples that work with the current versions of glfw-b and opengl. Thank you, Brian

4 6

Backtracking when building a bytestring
by David Turner 24 Jun '16

24 Jun '16

Hi, I'm working on a network protocol that involves sending frames of data prefixed by their length and a checksum. The only realistic way to work out the length of a frame is to actually write the bytes out, although the length and checksum take up a fixed number of bytes. If I were working in C I'd be filling a buffer, leaving space for the length/checksum, and then go back and fill them in at the end. So this is _almost_ what ByteString.Builder does except for the backtracking bit. Does anyone know if there's an implementation of a thing that's a bit like ByteString.Builder but also allows for this kind of backtracking? Ideally I want to be able to batch up a number of frames into a single buffer, and deal gracefully with overflowing the buffer by allocating some more, much as Builder does. I can't think of a terribly good way of doing this using the existing Builder implementation as it stands, although it looks quite easy to modify it to add this functionality so I might just do that locally if needs be. Cheers, David

3 3

Haskell in Leipzig 2016: Final Call for Papers
by Joachim Breitner 23 Jun '16

23 Jun '16

Haskell in Leipzig September 14-15, 2016 HTKW Leipzig, Germany http://hal2016.haskell.org/ This is the third and last call for submissions for the Haskell in Leipzig workshop. In case you were hesitating whether you want to submit something, the answer is „Yes!“. I’m looking forward to receiving your contribution on July 1st (next Friday). == About HaL == The workshop series “Haskell in Leipzig”, now in its 11th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts and Haskell beginners to listen to talks, take part in tutorials, and join in interesting conversations. Everything related to Haskell is on topic, whether it is about current research, practical applications, interesting ideas off the beaten track, education, or art, and topics may extend to functional programming in general and its connections to other programming paradigms as well. This year, HaL is colocated with two related conferences, * the Workshop on Functional and (Constraint) Logic Programming (WFLP) and * the Workshop on (Constraint) Logic Programming (WLP), to form the Leipzig Week of Declarative Programming (L-DEC): http://nfa.imn.htwk-leipzig.de/LDEC2016/ In order to accommodate and welcome a more international audience, this year’s HaL will be held in English. == Invited Speaker == Unsure about whether HaL is interesting to you? No need to worry: Alejandro Russo (from Chalmers) is our keynote speaker and will talk about his work on information-flow control (i.e. SecLib, LIO, MAC, HLIO) – a great topic that is of interest to researchers, practitioners and beginners alike. == Submissions == Contributions can take the form of * talks (about 30 minutes), * tutorials (about 90 minutes), * demonstrations, artistic performances, or other extraordinary things. Please submit an abstract that describes the content and form of your presentation, the intended audience, and required previous knowledge. We recommend a length of 2 pages, so that the PC and the audience get a good idea of your submission, but this is not a hard requirement. You can submit your abstract, as an PDF document, at https://easychair.org/conferences/?conf=hal2016 until Friday, July 1, 2016. You will be notified by July 15, 2016. == Program committee == * Andreas Abel, Chalmers and Gothenburg University, Sweden * Heinrich Apfelmus, Leipzig, Germany * Joachim Breitner, Karlsruhe Institute of Technology, Germany (Chair) * Matthias Fischmann, Zerobuzz, Germany * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Institute of Cybernetics at Tallinn University of Technology, Estonia * Andres Löh, Well-Typed LLP, Germany * Alejandro Serrano Mena, Universiteit Utrecht, Netherlands * Neil Mitchell, Standard Chartered Bank, UK * Katie Ots, Facebook, UK * Peter Stadler, University of Leipzig, Germany * Henning Thielemann, Freelancer, Germany * Niki Vazou, University of California, San Diego, USA If you have any questions, please do not hesitate to contact Joachim Breitner <breitner(a)kit.edu>. -- Dr. rer. nat. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.ipd.kit.edu/~breitner

1 0

PEPM 2017 Call for Papers
by Jeremy Yallop 23 Jun '16

23 Jun '16

CALL FOR PAPERS Workshop on PARTIAL EVALUATION AND PROGRAM MANIPULATION (PEPM 2017) http://conf.researchr.org/home/PEPM-2017 Paris, France, January 16th - 17th, 2017 (co-located with POPL 2017) PEPM is the premier forum for discussion of semantics-based program manipulation. The first ACM SIGPLAN PEPM symposium took place in 1991, and meetings have been held in affiliation with POPL every year since 2006. PEPM 2017 will be based on a broad interpretation of semantics-based program manipulation, reflecting the expanded scope of PEPM in recent years beyond the traditionally covered areas of partial evaluation and specialization. Specifically, PEPM 2017 will include practical applications of program transformations such as refactoring tools, and practical implementation techniques such as rule-based transformation systems. In addition, the scope of PEPM covers manipulation and transformations of program and system representations such as structural and semantic models that occur in the context of model-driven development. In order to maintain the dynamic and interactive nature of PEPM and to encourage participation by practitioners, we also solicit submissions of short papers, including tool demonstrations, and of posters. Scope ----- Topics of interest for PEPM 2017 include, but are not limited to: * Program and model manipulation techniques such as: supercompilation, partial evaluation, fusion, on-the-fly program adaptation, active libraries, program inversion, slicing, symbolic execution, refactoring, decompilation, and obfuscation. * Program analysis techniques that are used to drive program/model manipulation such as: abstract interpretation, termination checking, binding-time analysis, constraint solving, type systems, automated testing and test case generation. * Techniques that treat programs/models as data objects including metaprogramming, generative programming, embedded domain-specific languages, program synthesis by sketching and inductive programming, staged computation, and model-driven program generation and transformation. * Application of the above techniques including case studies of program manipulation in real-world (industrial, open-source) projects and software development processes, descriptions of robust tools capable of effectively handling realistic applications, benchmarking. Examples of application domains include legacy program understanding and transformation, DSL implementations, visual languages and end-user programming, scientific computing, middleware frameworks and infrastructure needed for distributed and web-based applications, embedded and resource-limited computation, and security. This list of categories is not exhaustive, and we encourage submissions describing applications of semantics-based program manipulation techniques in new domains. If you have a question as to whether a potential submission is within the scope of the workshop, please contact the programme chairs. Submission categories and guidelines ------------------------------------ Three kinds of submissions will be accepted: Regular Research Papers, Short Papers and Posters. * Regular Research Papers should describe new results, and will be judged on originality, correctness, significance and clarity. Regular research papers must not exceed 12 pages in ACM Proceedings style (including appendix). * Short Papers may include tool demonstrations and presentations of exciting if not fully polished research, and of interesting academic, industrial and open-source applications that are new or unfamiliar. Short papers must not exceed 6 pages in ACM Proceedings style (including appendix). * Posters should describe work relevant to the PEPM community, and must not exceed 2 pages in ACM Proceedings style. We invite poster submissions that present early work not yet ready for submission to a conference or journal, identify new research problems, showcase tools and technologies developed by the author(s), or describe student research projects. At least one author of each accepted contribution must attend the workshop and present the work. In the case of tool demonstration papers, a live demonstration of the described tool is expected. Suggested topics, evaluation criteria, and writing guidelines for both research tool demonstration papers will be made available on the PEPM 2017 web site. Student participants with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses and other support. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC programme, see its web page. Publication and special issue ----------------------------- All accepted papers, short papers and posters included, will appear in formal proceedings published by ACM Press. Accepted papers will be included in the ACM Digital Library. Authors of selected papers from PEPM 2016 and PEPM 2017 will also be invited to expand their papers for publication in a special issue of the journal Computer Languages, Systems and Structures (COMLAN, Elsevier). Best paper award ---------------- PEPM 2017 continues the tradition of a Best Paper award. The winner will be announced at the workshop. Submission ---------- Papers should be submitted electronically via HotCRP. https://pepm17.hotcrp.com/ Authors using LaTeX to prepare their submissions should use the new improved SIGPLAN proceedings style, and specifically the sigplanconf.cls 9pt template. Important Dates --------------- For Regular Research Papers and Short Papers: * Abstract submission : Tuesday 13th September 2016 * Paper submission : Friday 16th September 2016 * Author notification : Monday 24th October 2016 * Camera ready : Monday 28th November 2016 For Posters: * Poster submission : Sunday 30th October 2016 * Author notification : Friday 10th November 2016 * Camera ready : Monday 28th November 2016 PEPM workshop: * Workshop : Monday 16th - Tuesday 17th January 2017 The proceedings will be published 2 weeks pre-conference. AUTHORS TAKE NOTE: The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of your conference. The official publication date affects the deadline for any patent filings related to published work. (For those rare conferences whose proceedings are published in the ACM Digital Library after the conference is over, the official publication date remains the first day of the conference.). PEPM'17 Programme Co-Chairs ------------------- Ulrik Schultz (University of Southern Denmark), ups(a)mmmi.sdu.dk Jeremy Yallop (University of Cambridge), jeremy.yallop(a)cl.cam.ac.uk

1 0

[oleg.grenrus@iki.fi: Re: Easy type-level math]
by Lana Black 22 Jun '16

22 Jun '16

Forwarding Oleg's message to the list. ----- Forwarded message from Oleg Grenrus <oleg.grenrus(a)iki.fi> ----- Date: Tue, 21 Jun 2016 05:27:13 +0300 From: Oleg Grenrus <oleg.grenrus(a)iki.fi> To: Lana Black <lanablack(a)amok.cc> Subject: Re: [Haskell-cafe] Easy type-level math X-Mailer: iPhone Mail (13F69) ghc-typelits-natnormalise can dismiss equality constraints, like `n + m ~ m + n`. OP needs to conjure KnownNat dictionary though, and that plugin cannot do. You can do it unsafely and manually with `reifyNat` from `reflections`: http://hackage.haskell.org/package/reflection-2.1.2/docs/Data-Reflection.ht… - Oleg > On 21 Jun 2016, at 03:12, Lana Black <lanablack(a)amok.cc> wrote: > > GHC currently lacks an ability to normalize type level arithmetic equations. There is a plugin however [1] that implements this feature. I believe that's what you are looking for. > > [1] ‎https://hackage.haskell.org/package/ghc-typelits-natnormalise > > From: Станислав Черничкин > Sent: Monday, June 20, 2016 11:37 PM > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Easy type-level math > > With DataKinds and TypeOperators and GHC.TypeLits and, probably, KindSignatures I have: > > test :: (KnownNat i, KnownNat (i + 4)) => MyType i ((i + 4) + 4) > > and it's typecheck perfectly. > > But what I really want to have is: > > test :: (KnownNat i) => MyType i (i +8) > > and it does not typecheck. > > Does not ((i + 4) + 4) == (i +8)? > > Does not (KnownNat i) implies (KnownNat (i + 4))? > > Did I miss something about Haskell? > > -- > Thanks, Stanislav Chernichkin. > > _______________________________________________ > 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. ----- End forwarded message -----

1 0

Help with triple stack monad
by Christopher Howard 22 Jun '16

22 Jun '16

Hi, I was expanding on my earlier learning, to try a triple monad stack: {-# LANGUAGE GeneralizedNewtypeDeriving #-} <...snip...> import System.Random import Control.Monad.Random import Control.Monad.State.Lazy import Control.Monad.Reader newtype ReaderStateRandom r s g a = RSR { rSR :: ReaderT r (StateT s (Rand g)) a } deriving (Monad, MonadReader r, MonadState s) However, it seems that I must implement MonadRandom myself, as there is no instance for this sort of arrangement already. Probably this is trivial, but I'm having trouble wrapping my mind around how to do it. Would anybody perhaps assist me in implementing one function, to help guide me in the correct direction? instance MonadRandom (ReaderStateRandom r s g) where getRandom = ...? -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

4 5

Easy type-level math
by Станислав Черничкин 21 Jun '16

21 Jun '16

With DataKinds and TypeOperators and GHC.TypeLits and, probably, KindSignatures I have: test :: (KnownNat i, KnownNat (i + 4)) => MyType i ((i + 4) + 4) and it's typecheck perfectly. But what I really want to have is: test :: (KnownNat i) => MyType i (i +8) and it does not typecheck. Does not ((i + 4) + 4) == (i +8)? Does not (KnownNat i) implies (KnownNat (i + 4))? Did I miss something about Haskell? -- Thanks, Stanislav Chernichkin.

2 2

Programming in Haskell - 2nd Edition
by Graham Hutton 21 Jun '16

21 Jun '16

Dear all, I'm delighted to announce that the 2nd edition of Programming in Haskell will be published in August 2016! The new edition has been extensively updated and expanded to include recent and more advanced features of Haskell, new examples and exercises, selected solutions, and freely downloadable lecture slides and example code. Further details, including how to preorder and obtain inspection copies, are provided below. Best wishes, Graham ================================================================= *** BOOK ANNOUNCEMENT *** Programming in Haskell - 2nd Edition Graham Hutton, University of Nottingham Cambridge University Press, August 2016 320 pages, 120 exercises, ISBN 9781316626221 http://tinyurl.com/PIH-2e ================================================================= DESCRIPTION: Haskell is a purely functional language that allows programmers to rapidly develop clear, concise, and correct software. The language has grown in popularity in recent years, both in teaching and in industry. This book is based on the author's experience of teaching Haskell for more than twenty years. All concepts are explained from first principles and no programming experience is required, making this book accessible to a broad spectrum of readers. While Part I focuses on basic concepts, Part II introduces the reader to more advanced topics. This new edition has been extensively updated and expanded to include recent and more advanced features of Haskell, new examples and exercises, selected solutions, and freely downloadable lecture slides and example code. The presentation is clean and simple, while also being fully compliant with the latest version of the language, including recent changes concerning applicative, monadic, foldable, and traversable types. ================================================================= CONTENTS: Foreword Preface Part I. Basic Concepts: 1. Introduction 2. First steps 3. Types and classes 4. Defining functions 5. List comprehensions 6. Recursive functions 7. Higher-order functions 8. Declaring types and classes 9. The countdown problem Part II. Going Further: 10. Interactive programming 11. Unbeatable tic-tac-toe 12. Monads and more 13. Monadic parsing 14. Foldables and friends 15. Lazy evaluation 16. Reasoning about programs 17. Calculating compilers Appendix A. Selected solutions Appendix B. Standard prelude Bibliography Index ================================================================= AUTHOR: Graham Hutton is Professor of Computer Science at the University of Nottingham. He has taught Haskell to thousands of students and received numerous best lecturer awards. Hutton has served as an editor of the Journal of Functional Programming, Chair of the Haskell Symposium and the International Conference on Functional Programming, and Vice-Chair of the ACM Special Interest Group on Programming Languages, and he is an ACM Distinguished Scientist. ================================================================= FURTHER DETAILS: The following web page includes details for how the book can be preordered, and how lecturers can obtain inspection copies: http://tinyurl.com/PIH-2e ================================================================= This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

Where am I going wrong with my bounding box function?
by Michael Litchard 20 Jun '16

20 Jun '16

I am writing a bounding box module for the octree <https://github.com/BioHaskell/octree/tree/master> library. You can find my branch here <https://github.com/mlitchard/octree/tree/MBB>. In the function below, I try to make explicit the implicit bounding boxes of an Octree. The problem is, not all bounding boxes are valid. This is the function in question, followed by a way to replicate the problem in ghci. explicateMBB :: (BBox3, Octree a) -> [BBox3] explicateMBB (mbb, (Leaf _)) = [mbb] explicateMBB (mbb, (Node { split = split', nwu = nwu', nwd = nwd', neu = neu', ned = ned', swu = swu', swd = swd', seu = seu', sed = sed' })) = mbb:concatMap explicateMBB octList where octList = zip boxList children boxList = [swdBox, sedBox, nwdBox, nedBox, swuBox, seuBox, nwuBox, neuBox] children = [swd',sed',nwd',ned',swu',seu',nwu',neu'] swdBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (minX mbb) (minY mbb) (minZ mbb) neuCorner = Vector3 (v3x split') (v3y split') (v3z split') sedBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (v3x split') (minY mbb) (minZ mbb) neuCorner = Vector3 (maxX mbb) (v3y split') (minZ mbb) nwdBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (minX mbb) (v3y split') (minZ mbb) neuCorner = Vector3 (v3x split') (maxY mbb) (v3z split') nedBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (v3x split') (v3y split') (minZ mbb) neuCorner = Vector3 (maxX mbb) (maxY mbb) (v3z split') swuBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (minX mbb) (minY mbb) (v3z split') neuCorner = Vector3 (v3x split') (v3y split') (maxZ mbb) seuBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (v3x split') (minY mbb) (v3z split') neuCorner = Vector3 (maxX mbb) (v3y split') (maxZ mbb) nwuBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (minX mbb) (v3y split') (v3z split') neuCorner = Vector3 (v3x split') (maxY mbb) (maxZ mbb) neuBox = bound_corners swdCorner neuCorner where swdCorner = Vector3 (v3x split') (v3y split') (v3z split') neuCorner = Vector3 (maxX mbb) (maxY mbb) (maxZ mbb) To replicate problem: git clone https://github.com/mlitchard/octree.git git checkout MBB stack ghci In ghci, do the following : :m + Data.List Data.Vector.Class System.Random System.Random.Shuffle Data.BoundingBox.B3 let infinity = (read "Infinity") :: Double let swdCorner = Vector3 (-infinity) (-infinity) (-infinity) let neuCorner = Vector3 (infinity) (infinity) (infinity) let rbb = bound_corners swdCorner neuCorner xGen <- getStdGen yGen <- newStdGen zGen <- newStdGen let xPoints = shuffle' [-256 .. 256] 513 xGen let yPoints = shuffle' [-256 .. 256] 513 yGen let zPoints = shuffle' [-256 .. 256] 513 zGen let xPoints' = map fromInteger xPoints :: [Double] let yPoints' = map fromInteger yPoints :: [Double] let zPoints' = map fromInteger zPoints :: [Double] let tup513 = zip3 xPoints' yPoints' zPoints' let construct_vect = (\(x,y,z) -> Vector3 x y z) let vect513 = map construct_vect tup513 let pre_oct513 = zip vect513 [1 .. 513] let octree513 = fromList pre_oct513 length $ filter (== False) $ map isValidMBB $ explicateMBB (rbb,octree513) The answer will be 9, but should be 0. I feel like one of the fooBox where clauses is wrong, but I have gone over each one several times, and I am not seeing which one it is. If you needed a visual aid like I did, I found this pic <https://geidav.files.wordpress.com/2014/08/full_octree.png?w=820> to be helpful. My sample does 2 subdivisions. Any insight into what is going wrong would be appreciated.

1 0

AFL + Haskell
by Krzysztof Skrzętnicki 20 Jun '16

20 Jun '16

Hello, There was an interesting post today [1] on Hacker News about fuzzing Rust with american-fuzzy-lop (AFL). Interestingly the AFL instrumentation gets applied as LLVM pass. I started to wonder if it would be possible to do the same with Haskell binaries? I know there are plenty of tools designed specifically for Haskell but still it might be interesting to see how AFL performs in this setting. Cheers, Krzysztof Skrzętnicki [1] https://news.ycombinator.com/item?id=11936983

1 0

How to avoid expensive and unnecessary type conversions?
by David Fox 20 Jun '16

20 Jun '16

Suppose you have a class ListLike (which you do have, actually) and it has methods for operations on types that are like lists, and in particular it has a method fromListLike which converts any ListLike value to any other: fromListLike :: ListLike full' item => full' -> full the default implementation of this is simply fromListLike = fromList . toList but this means that if you happen to apply fromListLike to a value which is already the desired type, two unnecessary and possibly expensive conversions take place. My question is, how can one write code that implements fromListLike in such a way that when the two type parameters are the same type it just uses fromListLike = id I've thought about using a class Convert a b class and writing an instance for every pair of ListLike instances. I haven't convinced myself this would work, and if it does it means that adding a new instance involves writing a bunch of Convert instances. Maybe one could somehow have a default implementation (fromList . toList) but then you run into overlapping instances. Anyone have better ideas about any of this? Hopefully I'm missing something dead simple...

2 2

ST Vector / STRef -- Performances and allocation
by Guillaume Bouchard 20 Jun '16

20 Jun '16

Hello. I read a reddit post [0] which ends in a debate about haskell performances. Someone gives a C implementation which runs in 15ms on some dataset. I wanted to learn about mutable vector and ST and got something in haskell which runs in 50ms. Code is here [1]. [0] https://www.reddit.com/r/haskell/comments/4ojsn0/counting_inversions_haskel… [1] https://github.com/guibou/inversionsCount/blob/syntax/inversions.hs When I'm profiling the code, I'm surprised to see more than 50% of the %alloc in function which, from my point of view, must not allocate. For example, this function : inc :: forall s. STRef s Int -> ST s () inc v = modifySTRef' v (+1) Is responsible for 10% of the allocation in this program. I was hoping that the "unboxing magic" of GHC may have replaced my Int somewhere by an unboxed one, but I guess the allocation means that the STRef is somehow pointing to a heap allocated Int. Do you know a way to remove theses allocations? As a second question, if you see any other way to improve this implementation, I'll be happy to learn something new ;) Finally, if you read my code, you'll see that I implemented a small DSL around ST / STRef / MVector to make my main function more readable. How do people write readable code in real life ? Especially, I was annoyed when I tried to convert this piece of C code : if (x1 < mid && (x2 == sz || tmp[x1] <= p[x2])) { a; } else { b; } In my haskell code, x1, x2 are STRef, and tmp and p are MVector. This was highly painful to write in haskell and I had to write something such as: x1 <- readSTRef x1' x2 <- readSTRef x2' cond <- if x1 < mid then if x2 == sz then return True else do tmp_x1 <- Vector.read tmp x1 p_x2 <_ Vector.read p x2 return (tmp_x1 <= p_x2) else return False if cond then a else b This is painful, complex and error prone, so is there another solution ? Thank you.

5 8

Problem binding GEGL library
by nek0 19 Jun '16

19 Jun '16

Hello fellow haskellers, I am currently working on Haskell bindings to the GEGL [0] library. Since it's my first time working with the FFI and the whole idea of binding a library into Haskell, I have now run into a problem I can't resolve myself. The GEGL headers expose a function "gegl_buffer_iterator_new" which returns an iterator over a selected area in a buffer. This iterator contains a float pointer with pixel data. My problem is to make the iterator and the data it contains accessible to Haskell and to iterate over it. Can someone of you please help me with this problem? One of my initial thoughts was to wrap it into a monad, but I am totally inexperienced with that. My project can be found on my Github profile [1]. Many thanks in advance, nek0 links: [0]: http://www.gegl.org/ [1]: https://github.com/nek0/gegl

2 1

My responses to challenge problems in Bartosz Milewski's "Category Theory for Programmers", thru Ch. 10.
by David Banas 18 Jun '16

18 Jun '16

Hi all, I just finished chapter 10 in Bartosz Milewski’s “Category Theory for Programmers”, and thought I’d share my responses to his challenge problems: https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/… I’d love to hear anyone’s feedback. Cheers, -db

1 0

Trying to test natural transformations, in Haskell.
by David Banas 18 Jun '16

18 Jun '16

Got it: {-# LANGUAGE Rank2Types AllowAmbiguousTypes FlexibleContexts #-} type NatTran f f' a = (Functor f, Functor f') => f a -> f' a to_assert :: (Functor f, Functor f', Eq (f' b)) => (a -> b) -> NatTran f f' a -> NatTran f f' b -> f a -> Bool to_assert g h h' f = (fmap g . h) f == (h' . fmap g) f maybe_to_list :: NatTran Maybe [] a maybe_to_list Nothing = [] maybe_to_list (Just x) = [x] test_func :: Num a => a -> (a, a) test_func x = (x, x + 1) success = all (to_assert test_func maybe_to_list maybe_to_list) [Nothing, Just 1] main :: IO () main = do if success then print "Success!" else print "Failure." main Running this code produces: "Success!" ================================================= Hi all, In doing the challenge problems at the end of chapter 10 (Natural Transformations) in Bartosz Milewski’s “Category Theory for Programmers”, I’m trying to write a generic naturality checker: {-# LANGUAGE Rank2Types AllowAmbiguousTypes #-} type NatTran a = (Functor f, Functor f') => f a -> f' a to_assert :: (Functor f, Eq b) => (a -> b) -> NatTran a -> NatTran b -> f a -> Bool to_assert g h h' f = (fmap g . h) f == (h' . fmap g) f which is later made specific to a particular natural transformation: maybe_to_list :: Maybe a -> [a] maybe_to_list Nothing = [] maybe_to_list (Just x) = [x] test_func :: Num a => a -> (a, a) test_func x = (x, x + 1) assertions = map (to_assert test_func maybe_to_list) [Nothing, Just 1] but I’m getting this from ghc: Could not deduce (Functor f0) arising from a use of ‘fmap’ from the context (Functor f, Eq b) bound by the type signature for interactive:IHaskell465.to_assert :: (Functor f, Eq b) => (a -> b) -> interactive:IHaskell465.NatTran a -> interactive:IHaskell465.NatTran b -> f a -> Bool at :2:14-83 The type variable ‘f0’ is ambiguous Note: there are several potential instances: instance Monad m => Functor (Data.Vector.Fusion.Bundle.Monadic.Bundle m v) -- Defined in ‘Data.Vector.Fusion.Bundle.Monadic’ instance Functor Data.Vector.Fusion.Util.Box -- Defined in ‘Data.Vector.Fusion.Util’ instance Functor Data.Vector.Fusion.Util.Id -- Defined in ‘Data.Vector.Fusion.Util’ ...plus 27 others In the first argument of ‘(.)’, namely ‘fmap g’ In the expression: fmap g . h In the first argument of ‘(==)’, namely ‘(fmap g . h) f’ Can anyone offer some advice? Thanks, -db

2 1

How to spot Monads, Applicatives ...
by martin 18 Jun '16

18 Jun '16

Hello all, I am at a stage, where I can use some of the Monads and Applicatives which are out there. But I hardly ever wrote my own instances. I am curious to learn about the thought processes which lead to the insight "hey that can be written nicely as an Applicative Functor" I suppose you can write everything without these type classes. Is it a promising approach to try without and then spot an element of repetition and factoring out that naturally leads to one of these typeclasses? Paticularly I am having difficulties with the *->* instances. E.g. why is the state "s" in the state monad the fixed type and the "a" the type parameter? When I am writing state code without the State monad the two look like equal candidates. Why not have "State a" monad, which threads an a-typed value and spits out states? While we're at it: would someone be so kind and explain what exactly is meant by an "effect"? I know that in haskell this is not the same as a "side effect" as there are no side-effects in haskell.

6 11

Monad Stack - State + Rand?
by Christopher Howard 18 Jun '16

18 Jun '16

Hi. I'm working through "Haskell Design Patterns" and got inspired to try to create my first monad stack. What I really wanted though (not shown in the book) was to combine State and Rand. I daresay I got something to compile: walk :: RandomGen g => StateT (Float, Float) (Rand g) (Float, Float) walk = do (x, y) <- get put (x + 1, y + 1) get >>= return However, the moment I try to insert a getRandomR or something in it, I get an error Could not deduce (MonadRandom (StateT (Float, Float) (Rand g))) arising from a use of `getRandomR' <...snip...> add an instance declaration for (MonadRandom (StateT (Float, Float) (Rand g))) I see there are instances MonadRandom m => MonadRandom (StateT s m) RandomGen g => MonadRandom (Rand g) in Control.Monad.Random.Class, so I am not quite sure what is expected of me. -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

3 4

INLINABLE and SPECIALIZE, GHC 8.0.1
by Jyotirmoy Bhattacharya 18 Jun '16

18 Jun '16

I'm trying to write a mutable hash table library that would work both in the IO and ST monads, so I'm using the PrimMonad typeclass [see JmoyHash.hs in the attached archive]. For efficiency, I would like the functions to be specialized to the concrete monad at the call site. According to Section 9.31.9.2 of the GHC User's Guide <https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_ext…> The optimiser *also* considers each *imported* INLINABLE overloaded function, and specialises it for the different types at which it is called in M. So I marked all the functions in my library as INLINABLE. Yet adding a SPECIALIZE pragma in Main.hs (currently commented out) for an imported function improves runtime performance by 3x, which should not be happening since, if I understand the manual right, the function should have been specialized anyway since it is marked INLINABLE. I am writing to this list rather than filing a bug since I'm not sure if I'm reading the manual right and I have not explicitly verified that the specialization is not happening. I would greatly appreciate any help on both counts. I'm using GHC 8.0.1 with the -O2 flag. Marking the function as INLINE might solve the problem but that's something I don't want to do as it seems to me that specialization and not inlining is what's appropriate here. Regards, Jyotirmoy Bhattacharya

2 4

Macros For Cabal Version
by aditya siram 18 Jun '16

18 Jun '16

Hi all, I have a non-trivial build script that I'm trying to make compatible with Cabal 1.22 and Cabal 1.24. So far the only macro I can find that helps me determine which version I'm using is __GLASGOW_HASKELL__. Is there a better one? Thanks! -deech

2 1

partial solved problem installing postgreSQL-libpq on Windows?
by Phyx 17 Jun '16

17 Jun '16

Hi Kees, Would It be possible for you to try with GHC 7.10.3 or 8.0.1? A bunch of things have changed with the linker in these two versions which should make linking against packages easier. <command line>: can't load .so/.DLL for: > d:/PROGRA~2/POSTGR~1/9.3/lib\libpq.dll (addDLL: could not load DLL) ghc.exe: d:/PROGRA~2/POSTGR~1/9.3/lib\libpq: %1 is not a valid Win32 > application. This seems to be coming from the runtime linker, if indeed d:/PROGRA~2/POSTGR~1/9.3/lib\libpq.dll can be found then either it's the wrong bitness/image type or libpq.dll has dependencies on other dlls. 7.10.1 is not able to load these then as the search path won't be correct. To test this you can add d:/PROGRA~2/POSTGR~1/9.3/lib\ to your path and try loading it again. If that doesn't work and you want to know what's really going on, you can enable loader snaps in gflags for GHC.exe and GHCi.exe (or runHaskell, what ever it is you're using) and attach a debugger like gdb or windbg. https://msdn.microsoft.com/en-us/library/windows/hardware/ff556886(v=vs.85)… You'll then be able to see the OS's trace messages for the loader and it should tell you exactly what's wrong. >From the msys prompt: pexports "d:\program > files\postgreSQL\9.3\bin\libpq.dll" > libpq.def >From the msys prompt: dlltool -d libpq.def -l libpq.a Import libraries are supported by the GHC but not ghci or any other interpreted mode (until 8.0.2) So this would only work for the compiled program without Template Haskell. Regards, Tamar

3 3

Instances for (->) a (b :: * -> *)?
by lists+haskell-cafe＠jimpryor.net 17 Jun '16

17 Jun '16

If one wants to declare instances for a type schema `a -> _`, one writes something like this: instance Context => Class parameters ... ((->) a) where { ... } But what if you want to declare instances for a type schema `a -> b _`, that is, where the slot to be filled is not just the result of (->) a, but rather the composition of that together with another type operation b :: * -> *? I'd like to write something like this: instance Context => Class parameters ... ((->) a (b :: *->*)) where { ...} or: instance Context => Class parameters ... ((->) a (b *)) where { ...} but these don't work. Is it possible to do this? Concretely, here's what I'm trying to achieve. I wrote a typeclass for MonadReaders that are embedded inside (one level) of other MonadReaders, like this: {-# LANGUAGE FunctionalDependencies FlexibleInstances UndecidableInstances #-} class MonadReader w m => DeepMonadReader w r m | m -> r where { deepask :: m r ; deepask = deepreader id ; deeplocal :: (r -> r) -> m a -> m a ; deepreader :: (r -> a) -> m a ; deepreader f = do { r <- deepask; return (f r) } } instance MonadReader r m => DeepMonadReader w r (ReaderT w m) where { deepask = lift ask ; deeplocal = mapReaderT . local ; deepreader = lift . reader } It'd be nice to also provide an instance something like this: instance MonadReader r m => DeepMonadReader w r ((->) w (m :: * -> *)) where { deepask = \w -> ask ; deeplocal f xx = \w -> local f (xx w) ; deepreader xx = \w -> reader xx } -- Jim Pryor jim(a)jimpryor.net

1 0

Trying to test natural transformations, in Haskell.
by David Banas 17 Jun '16

17 Jun '16

Hi all, In doing the challenge problems at the end of chapter 10 (Natural Transformations) in Bartosz Milewski’s “Category Theory for Programmers”, I’m trying to write a generic naturality checker: {-# LANGUAGE Rank2Types AllowAmbiguousTypes #-} type NatTran a = (Functor f, Functor f') => f a -> f' a to_assert :: (Functor f, Eq b) => (a -> b) -> NatTran a -> NatTran b -> f a -> Bool to_assert g h h' f = (fmap g . h) f == (h' . fmap g) f which is later made specific to a particular natural transformation: maybe_to_list :: Maybe a -> [a] maybe_to_list Nothing = [] maybe_to_list (Just x) = [x] test_func :: Num a => a -> (a, a) test_func x = (x, x + 1) assertions = map (to_assert test_func maybe_to_list) [Nothing, Just 1] but I’m getting this from ghc: Could not deduce (Functor f0) arising from a use of ‘fmap’ from the context (Functor f, Eq b) bound by the type signature for interactive:IHaskell465.to_assert :: (Functor f, Eq b) => (a -> b) -> interactive:IHaskell465.NatTran a -> interactive:IHaskell465.NatTran b -> f a -> Bool at :2:14-83 The type variable ‘f0’ is ambiguous Note: there are several potential instances: instance Monad m => Functor (Data.Vector.Fusion.Bundle.Monadic.Bundle m v) -- Defined in ‘Data.Vector.Fusion.Bundle.Monadic’ instance Functor Data.Vector.Fusion.Util.Box -- Defined in ‘Data.Vector.Fusion.Util’ instance Functor Data.Vector.Fusion.Util.Id -- Defined in ‘Data.Vector.Fusion.Util’ ...plus 27 others In the first argument of ‘(.)’, namely ‘fmap g’ In the expression: fmap g . h In the first argument of ‘(==)’, namely ‘(fmap g . h) f’ Can anyone offer some advice? Thanks, -db

1 0

($) and ApplicativeDo
by amindfv＠gmail.com 16 Jun '16

16 Jun '16

foo :: Applicative f => f String foo = do x <- pure "this works" pure x ... but replace "pure x" with "pure $ x" and it doesn't typecheck: a monad instance is required! Tom

5 6

Testing Msgpack system
by Jonn Mostovoy 16 Jun '16

16 Jun '16

Dear friends, we have a distributed system written in Haskell, consisting of three types of nodes with dozen of instances of each of two types and a central node of the third type. Each node is started by executing a binary which sets up acid-state persistence layer and sockets over which msgpack messages are sent around. It is trivial to write low level functionality quickcheck test suites, which test properties of functions. We would like, however, to have a quickcheck-esque suite which sets up the network, then gets it to an arbitrary valid state (sending correct messages between nodes), then rigorously testing it for three high-level properties: 1. Chaos monkey test (disable random node, see if certain invariants hold); 2. Evil node test (make several nodes work against the system, see if certain properties hold); 3. Rigorous testing of network-wide invariants, if all the nodes operate correctly. The problem we're facing is the following — if we want to inspect state of nodes in Haskell-land, we have to write a huge machinery which emulates every launch of node via thread. There will be bugs in this machinery, so we won't be able to get quality testing information before we fix those; if we want to run things as processes, then the best thing we can do is to inspect either acid-state dbs of each node (it poses resource locking problems and forces us to dump the state on every change, which is undesirable), or make an observer node, which dumps the consensus as Text and then parsing the data into Haskell terms, making decisions about the required properties based on that (so far, it feels like the best option). Am I missing something? How is something like this achieved in culture? How would you approach such a problem? Links to source files of test suites which do something similar are highly appreciated.

3 5

base version numbers
by Tom Ellis 16 Jun '16

16 Jun '16

Since each version of GHC depends precisely on one version of base, would it not be more clear to name them after their version of GHC, rather than 4.x.y.z? Could this be done? Tom

3 4

WST 2016, 2nd call for papers
by Salvador Lucas 16 Jun '16

16 Jun '16

========================================================================== WST 2016 - 2nd Call for Papers 15th International Workshop on Termination September 5-7, 2016, Obergurgl, Austria http://cl-informatik.uibk.ac.at/events/wst-2016/ ========================================================================== The Workshop on Termination (WST) traditionally brings together, in an informal setting, researchers interested in all aspects of termination, whether this interest be practical or theoretical, primary or derived. The workshop also provides a ground for cross-fertilization of ideas from term rewriting and from the different programming language communities. The friendly atmosphere enables fruitful exchanges leading to joint research and subsequent publications. The event is held as part of CLA 2016 http://cl-informatik.uibk.ac.at/events/cla-2016/ IMPORTANT DATES: * submission June 22, 2016 * notification July 12, 2016 * final version August 3, 2016 * workshop September 5-7, 2016 TOPICS: The 15th International Workshop on Termination welcomes contributions on all aspects of termination and termination analysis. Contributions from the imperative, constraint, functional, and logic programming communities, and papers investigating applications of complexity or termination (for example in program transformation or theorem proving) are particularly welcome. Topics of interest include all aspects of termination. This includes (but is not limited to): * certification of termination and complexity proofs * challenging termination problems * comparison and classification of termination methods * complexity analysis in any domain * implementation of termination and complexity methods * implicit computational complexity * infinitary normalization * non-termination analysis and loop detection * normalization in lambda calculi * operational termination of conditional rewrite systems * ordinal notation and subrecursive hierarchies * SAT, SMT, and constraint solving for (non-)termination analysis * scalability and modularity of termination methods * termination analysis in any domain * well-founded relations and well-quasi-orders COMPETITION: There will be a live complexity and termination competition during the workshop, including time to present both the results and the tools of the participants. More details will be provided in a dedicated announcement on the competition. PROGRAM COMMITTEE: * Ugo Dal Lago Bologna University * JÃ¶rg Endrullis VU University Amsterdam * Yukiyoshi Kameyama University of Tsukuba * Salvador Lucas Universidad PolitÃ©cnica de Valencia * Aart Middeldorp University of Innsbruck, co-chair * Andrey Rybalchenko Microsoft Research * Thomas StrÃ¶der RWTH Aachen * RenÃ© Thiemann University of Innsbruck, co-chair * Andreas Weiermann Ghent University INVITED SPEAKERS: * Reiner HÃ¤hnle TU Darmstadt SUBMISSION: Submissions are short papers/extended abstract which should not exceed 5 pages. There will be no formal reviewing. In particular, we welcome short versions of recently published articles and papers submitted elsewhere. The program committee checks relevance and provides additional feedback for each submission. The accepted papers will be made available electronically before the workshop. Papers should be submitted electronically via the submission page: http://www.easychair.org/conferences/?conf=wst2016 Final versions should be created using LaTeX and the LIPIcs style file http://drops.dagstuhl.de/styles/lipics/lipics-authors.tgz

1 0

partial solved problem installing postgreSQL-libpq on Windows?
by Kees Bleijenberg 16 Jun '16

16 Jun '16

Maybe I've found a part of the solution. I changed in postgresql-libpq.cabal Extra-Libraries: from pq to libpq. Then runHaskell xx configure -ghc, runHaskell xx build and then runHaskell xx install. No errors.. I'am happy. But. if I try to install postgresql-simple or hasql I get this error : .. <command line>: can't load .so/.DLL for: d:/PROGRA~2/POSTGR~1/9.3/lib\libpq.dll (addDLL: could not load DLL) ghc.exe: d:/PROGRA~2/POSTGR~1/9.3/lib\libpq: %1 is not a valid Win32 application. ... dir d:\PROGRA~2\POSTGR~1\9.3\lib\libpq.dll finds the dll, but d:/PROGRA~2/POSTGR~1/9.3/lib/libpq.dll gives: 'Parameter format not correct'. These mangled filenames come from pg_config.exe. Is this a filename mangling problem? Any idea what is going on? Kees --------------------------- I want to install postgreSQL-libpq on Windows 7 64 bits with ghc version 7.10.1 and cabal version 1.22.4.0 This is what I did: Installed mingw >From the msys prompt: pexports "d:\program files\postgreSQL\9.3\bin\libpq.dll" > libpq.def >From the msys prompt: dlltool -d libpq.def -l libpq.a The file libpq.a is created. I copied the file to d:\program files\postgreSQL\9.3\bin\ and then from de cmd prompt: cabal install postgreSQL-libpq --extra-include-dirs="d:\program files\postgreSQL\9.3\include" --extra-lib-dirs="d:\program files\postgreSQl\9.3\bin" I get: Resolving dependencies... Configuring postgresql-libpq-0.9.1.1... Failed to install postgresql-libpq-0.9.1.1 Build log ( C:\Users\kees\AppData\Roaming\cabal\logs\postgresql-libpq-0.9.1.1.log ): [1 of 1] Compiling Main ( D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.hs, D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\Main.o ) Linking D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.exe ... Configuring postgresql-libpq-0.9.1.1... setup.exe: Missing dependency on a foreign library: * Missing C library: pq This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. What can I do? Kees

1 0

problem installing postgreSQL-libpq on Windows
by Kees Bleijenberg 16 Jun '16

16 Jun '16

I want to install postgreSQL-libpq on Windows 7 64 bits with ghc version 7.10.1 and cabal version 1.22.4.0 This is what I did: Installed mingw >From the msys prompt: pexports "d:\program files\postgreSQL\9.3\bin\libpq.dll" > libpq.def >From the msys prompt: dlltool -d libpq.def -l libpq.a The file libpq.a is created. I copied the file to d:\program files\postgreSQL\9.3\bin\ and then from de cmd prompt: cabal install postgreSQL-libpq --extra-include-dirs="d:\program files\postgreSQL\9.3\include" --extra-lib-dirs="d:\program files\postgreSQl\9.3\bin" I get: Resolving dependencies... Configuring postgresql-libpq-0.9.1.1... Failed to install postgresql-libpq-0.9.1.1 Build log ( C:\Users\kees\AppData\Roaming\cabal\logs\postgresql-libpq-0.9.1.1.log ): [1 of 1] Compiling Main ( D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.hs, D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\Main.o ) Linking D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.exe ... Configuring postgresql-libpq-0.9.1.1... setup.exe: Missing dependency on a foreign library: * Missing C library: pq This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. What can I do? Kees

1 0

This non-exhaustive pattern match seems exhaustive
by Mitchell Rosen 15 Jun '16

15 Jun '16

I'm emulating a "closed typeclass" using a closed type family: * {-# LANGUAGE ExistentialQuantification #-}* * {-# LANGUAGE GADTs #-}* * {-# LANGUAGE LambdaCase #-}* * {-# LANGUAGE TypeFamilies #-}* * import GHC.Exts (Constraint)* * -- This is like* * --* * -- class Thing a -- instance Thing Int --* * type family Thing a :: Constraint where* * Thing Int = ()* * data Foo = forall a. Thing a => Foo (Bar a)* * data Bar a where* * Bar1 :: Bar Int* * Bar2 :: Bar Bool* * inspectFoo :: Foo -> ()* * inspectFoo = \case* * Foo Bar1 -> ()* * Foo Bar2 -> () -- This is required to suppress a warning* Here, it's not possible to create a Foo using "Foo Bar2", because there is no "Thing Bool" constraint in scope. Yet, when picking apart a Foo, I must still pattern match on this impossible data. Is there some smarter way to write this code? I thought of using `constraints`, and adding a catch-all clause to Thing: * type family Thing a :: Constraint where Thing Int = ()* * Thing a = Bottom* This would at least allow users of a Foo to use some * absurd :: Bottom => a* thing to discharge the Bottom constraint brought in scope by pattern matching: * inspectFoo :: Foo -> () inspectFoo = \case Foo Bar1 -> () Foo Bar2 -> absurd bottom* but better still would be to avoid having to write these impossible cases. Thanks!

1 0

benchmarks game -- invalid Haskell fasta programs
by Isaac Gouy 15 Jun '16

15 Jun '16

The guidelines for the benchmarks game "fasta" programs changed to: -- "match a random number against those cumulative probabilities to select each nucleotide (use linear search or binary search)". I'd appreciate it if someone familiar with Haskell could confirm that the old Haskell programs are not compatible with the changed guidelines. Here are those old programs: http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… best wishes, Isaac

1 0

Help with Data.Conduit.List.mapAccum
by bruno＠ruomad.net 15 Jun '16

15 Jun '16

Hello, I'm trying to use Data.Conduit, but I get stuck with mapAccum as how to get and retrieve the result. If I use it, I get a simple conduit like : testC :: ConduitM () Int IO Int testC = Src =$= cdt where src = CL.sourceList [1..10] cdt = CL.mapAccum (\x s ->(x+s, x) 0 I can get the output with testC $$ CL.consume but how do I retrieve the accumulated sum ? Bruno

3 5

ANN: eccrypto, aka Hecc, hF2
by Marcel Fourné 15 Jun '16

15 Jun '16

Dear Haskell Community! It was a long~ish time ago I released hecc[1], which had an unfortunate but funny (to me) name, later together with hF2[2]. Since I have neither released hyperelliptic curve crypto support, nor my pairing based crypto, a generalising change in names would be in order. Today I am releasing eccrypto[3], which contains the code of both (to allow easier refactoring of new ideas) and something new: A pure Haskell, timing-attack resistant Ed25519[4] implementation! ...well, a very rough one at least. The code is not "done", gives wrong results, is _very_ slow, but it might serve as reading material as well as a primer what I plan to do in the future. I do not plan to add embedded C or assembler code, but plan to make the code comparatively fast to some common implementations as well as timing attack resistant (see: [5]), even if it will never be as fast as the best code used in contemporary benchmarks. Sadly, due to health issues, I am not able to work on said code and have not been for a time longer than I care to admit. All comments are welcome, but I will not be able to guarantee answers. ;) Best of wishes to a thriving community, Marcel Fourné [1]: https://hackage.haskell.org/package/hecc [2]: https://hackage.haskell.org/package/hF2 [3]: https://hackage.haskell.org/package/eccrypto [4]: https://ed25519.cr.yp.to/ [5]: https://mail.haskell.org/pipermail/haskell-cafe/2015-February/118213.html

1 0

[ANN] Budapest Haskell Hackathon 2016, 6-7th Aug 2016
by Gmail 15 Jun '16

15 Jun '16

Hi everybody, I'm happy to announce that our local user group will hold a Haskell Hackathon in Budapest this year (this will be the second)! We will hold it from August 6th to the 7th (Saturday & Sunday). You can find out more on the following link: https://wiki.haskell.org/Budapest_Hackathon_2016 We will reguraly update the site with new information. If you decide to come, please fill out the following Google Form: http://goo.gl/forms/pqgh6fvK8F8a2pAg1 If you have a project, demo, or talk that you want to bring to the event please contact us, and we can talk about the details. You can find our contact info the events wiki site, or you can just contact me directly. The event will be open to people of all experience levels, from beginners to gurus. The only requisite is that you’re interested in the Haskell language, and want to hang out with us, and have a good time! Greetings from Daniel, and the other BP-HUG organizers.

2 1