- Haskell-Cafe - Haskell.org

FFI and a struct containing a string and allocating memory space
by Brian Sammon 11 Aug '17

11 Aug '17

If I have a struct like struct EventInfo { char * event_name; int year; int month; int date; } and an associated haskell datatype that I want to marshall into it, it seems to me that I can't take advantage of the speed advantages of alloca (and its friends like "with") The only safe way I've thought of to do this is to do this is to have the poke function for EventInfo (the associated haskell type) call malloc (or newCAString or something) and then poking the string into the newly allocated space. I realized after a few successful runs of using withCString in the poke function for EventInfo, that I don't think that this (calling withCString from the poke function) was a safe approach, and I'm thinking it was just dumb luck that this worked at all. Thoughts? Am I on the right track? Am I missing any better approaches? (I'm using Haskell 8.0.1 and a Storable instance for EventInfo, BTW)

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Investigating single-letter type variables
by Jeffrey Brown 11 Aug '17

11 Aug '17

Haskellers tend to use uninformative single-letter type variables. A case in point: Megaparsec> :i ParsecT type role ParsecT nominal nominal representational representational newtype ParsecT e s (m :: * -> *) a ... I've gotten used to the conventions that "a" stands for anything and "m" stands for monad -- but without digging into the code it wasn't initially obvious to me whether "s" stood for stream or state. Single-letter type variables don't seem to always be the standard, though: Megaparsec> :i between between :: Applicative m => m open -> m close -> m a -> m a -- Defined in ‘Control.Applicative.Combinators’ My questions are: (1) Are the brevity gains worth the confusion costs? (2) If I'm looking at a new library for the first time and trying to figure out what a type variable stands for, is there a canonical way to do it? Flailing through documentation at random? Unifying types by hand? -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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DSLDI 2017: Final Call for Talk Proposals (deadline extended)
by Lindsey Kuper 08 Aug '17

08 Aug '17

********************************************************************* FINAL CALL FOR TALK PROPOSALS DSLDI 2017 Fifth Workshop on Domain-Specific Language Design and Implementation October 22, 2017 Vancouver, Canada Co-located with SPLASH http://2017.splashcon.org/track/dsldi-2017 https://twitter.com/wsdsldi ********************************************************************* **Deadline for talk proposals extended to Friday, 11 August 2017** Well-designed and implemented domain-specific languages (DSLs) can achieve both usability and performance benefits over general-purpose programming languages. By raising the level of abstraction and exploiting domain knowledge, DSLs can make programming more accessible, increase programmer productivity, and support domain-specific optimizations. ## Workshop Goal Domain-Specific Language Design and Implementation (DSLDI) is a workshop intended to bring together researchers and practitioners interested in discussing how DSLs should be designed, implemented, supported by tools, and applied in realistic contexts. The focus of the workshop is on all aspects of this process, from soliciting domain knowledge from experts, through the design and implementation of the language, to evaluating whether and how a DSL is successful. More generally, we are interested in continuing to build a community that can drive forward the development of modern DSLs. ## Workshop Format DSLDI is a single-day workshop and will consist of an invited speaker followed by moderated audience discussions structured around a series of short talks. The role of the talks is to facilitate interesting and substantive discussion. Therefore, we welcome and encourage talks that express strong opinions, describe open problems, propose new research directions, and report on early research in progress. Proposed talks should be on topics within DSLDI’s area of interest, which include but are not limited to: * solicitation and representation of domain knowledge * DSL design principles and processes * DSL implementation techniques and language workbenches * domain-specific optimizations * human factors of DSLs * tool support for DSL users * community and educational support for DSL users * applications of DSLs to existing and emerging domains * studies of usability, performance, or other benefits of DSLs * experience reports of DSLs deployed in practice ## Call for Talk Proposals We solicit talk proposals in the form of short abstracts (max. 2 pages). A good talk proposal describes an interesting position, open problem, demonstration, or early achievement. The submissions will be reviewed on relevance and clarity, and used to plan the mostly interactive sessions of the workshop day. Publication of accepted abstracts and slides on the website is voluntary. * Deadline for talk proposals: August 11th, 2017 * Notification: September 11th, 2017 * Workshop: October 22nd, 2017 * Submission website: https://dsldi17.hotcrp.com/ ## Workshop Organization Co-chairs: * Lindsey Kuper (lindsey(a)composition.al) Intel Labs * Eric Walkingshaw (eric.walkingshaw(a)oregonstate.edu) Oregon State University Follow us on Twitter at https://twitter.com/wsdsldi Program committee: * Nada Amin (EPFL/University of Cambridge) * Eric Holk (Google) * Gabriele Keller (Data61, CSIRO (formerly NICTA) and UNSW) * Rebekah Leslie-Hurd (Intel Labs) * Chris Martens (NCSU) * Lee Pike (Galois) * Jonathan Ragan-Kelley (UC Berkeley) * Jesús Sánchez Cuadrado (Autonomous University of Madrid) * Vincent St-Amour (Northwestern University) * Philip Wadler (University of Edinburgh)

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Combining pool and Conduit
by Pieter Laeremans 07 Aug '17

07 Aug '17

Hello, I would like to combine a "Connection Pool" with the conduit library. I have an application were a stream of results from a web api needs to be analysed and stored in a database. Since the analysis is composed of different parts, I combine some parts together ( .|) Some of those parts need a database connection to do their work. Initially I created a Connection and passed it around to each part that needed it, this is sub-optimal. So I wanted to try the "resource-pool" library to address this problem. (https://hackage.haskell.org/package/resource-pool) So instead of a Connection I pass around a (Pool Connection) But I run into problems , and I don't know how to fix them. Here is a simple snippet of code that demonstrates the problem: ------------------------------------------- {-# LANGUAGE RankNTypes #-} module Lib where import Data.Pool import Database.HDBC import Database.HDBC.ODBC import Data.Conduit import Conduit createConnectionPool :: Pool Connection createConnectionPool = undefined processFoo :: Pool Connection -> Consumer String IO () processFoo pool = withResource pool $ \conn -> do mapM_C print ------------------------- I can not get this to compile: src/Lib.hs:15:19: error: • No instance for (MonadBaseControl IO (ConduitM String o IO)) arising from a use of ‘withResource’ • In the expression: withResource pool In the expression: withResource pool $ \ conn -> do { mapM_C print } In an equation for ‘processFoo’: processFoo pool = withResource pool $ \ conn -> do { mapM_C print } But I have no Idea how to tackle this problem. Any suggestions ? Thanks, Pieter -- Pieter Laeremans pieter(a)laeremans.org

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Extended deadline: IFL 2017 (29th Symposium on Implementation and Application of Functional Languages)
by publicityifl＠gmail.com 07 Aug '17

07 Aug '17

<div dir="ltr">Hello, Please, find below the third call for papers for IFL 2017. Note that some of the deadlines have been extended. Details are given below. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL --- IFL 2017 - CALL FOR PAPERS: DEADLINES EXTENDED ============================================== 29th SYMPOSIUM ON IMPLEMENTATION AND APPLICATION OF FUNCTIONAL LANGUAGES ======================================================================= University of Bristol, UK In cooperation with ACM SIGPLAN Wednesday 30 August - Friday 1 September, 2017 <a href="http://iflconference.org/">http://iflconference.org/</a> Scope ----- The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2017 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Peer-review ----------- Following the IFL tradition, IFL 2017 will use a post-symposium review process to produce the formal proceedings. All participants of IFL 2017 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: <a href="http://www.sigplan.org/Resources/Policies/Republication">http://www.sigplan.org/Resources/Policies/Republication</a> The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. Hence, publications that appear only in the draft proceedings are not subject to the ACM SIGPLAN republication policy. After the symposium, authors will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal review process. From the revised submissions, the program committee will select papers for the formal proceedings considering their correctness, novelty, originality, relevance, significance, and clarity. The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. Important dates --------------- Note that the original deadlines for submission and registration have been extended. | | | | ----------------------| -----------------------------------------------------------| | Thu 17 August 2017 | Submission deadline draft papers | | Fri 18 August 2017 | Notification of acceptance for presentation | | Mon 21 August 2017 | Early registration deadline | | Mon 21 August 2017 | Submission deadline for pre-symposium proceedings | | Fri 25 August 2017 | Late registration deadline | | Wed 30 August 2017 - Fri 1 September 2017 | IFL Symposium | | Mon 4 December 2017 | Submission deadline for post-symposium proceedings | | Wed 31 January 2018 | Notification of acceptance for post-symposium proceedings | | Mon 12 March 2018 | Camera-ready version for post-symposium proceedings | Submission details ------------------ Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English. Papers must use the new ACM two columns conference format, which can be found at: <a href="http://www.acm.org/publications/proceedings-template">http://www.acm.org/publications/proceedings-template</a> For the pre-symposium proceedings we adopt a 'weak' page limit of 12 pages. For the post-symposium proceedings the page limit of 12 pages is firm. Authors submit through EasyChair: <a href="https://easychair.org/conferences/?conf=ifl2017">https://easychair.org/conferences/?conf=ifl2017</a> Topics ------ IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools in the context of functional programming. If you are not sure whether your work is appropriate for IFL 2017, please contact the PC chair at <a href="mailto:nicolas.wu@bristol.ac.uk">nicolas.wu(a)bristol.ac.uk</a>. Topics of interest include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications Peter Landin Prize ------------------ The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Programme committee ------------------- Chair: Nicolas Wu, University of Bristol, UK - Kenichi Asai, Ochanomizu University, Japan - Sandrine Blazy, University of Rennes 1, France - Carlos Camarao, Universidade Federal de Minas Gerais, Brazil - Stephen Dolan, University of Cambridge, UK - Jurriaan Hage, Utrecht University, Netherlands - Yukiyoshi Kameyama, University of Tsukuba, Japan - Benjamin Lerner, Brown University, USA - Bas Lijnse, Radboud University, Netherlands - Garrett Morris, University of Kansas, USA - Miguel Pagano, Universidad Nacional de C√≥rdoba, Argentina - Tomas Petricek, Alan Turing Institute, UK - Maciej Pir√≥g, University of Wroclaw, Poland - Exequiel Rivas, Universidad Nacional de Rosario, Argentina - Neil Sculthorpe, Nottingham Trent University, UK - Melinda Toth, Eotvos Lorand University, Hungary - Phil Trinder, Glasgow University, UK - Kanae Tsushima, National Institute of Informatics, Japan - Marcos Viera, Universidad de la Republica, Uruguay - Meng Wang, University of Kent, UK Venue ----- The IFL 2017 will be held in association with the Department of Computer Science, University of Bristol, UK. Bristol is located in South West England, and can be easily reached from Bristol Airport. See the website for more information on the venue. </div>  <a style='display: block; margin: 32px 0 40px 0; padding: 10px; font-size: 1em; text-align: center; border: 0; border-top: 1px solid gray; ' href='https://goo.gl/2ksdRv'>powered by GSM. Free mail merge and email marketing software for Gmail.</a>

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Convert Data.Vector.Unboxed.Mutable.MVector to Data.Vector.Unboxed.Vector
by Cody Goodman 06 Aug '17

06 Aug '17

I want to do this so I can use the Data.Vector.Unboxed.Generic functions requiring the Vector constraint, namely the maxIndex function. Implementing maxIndex for Data.Vector.Unboxed.Mutable.MVector would be useful as well, but I'm even more confused at how to do that or where to begin. Here is some stubbed out code demonstrating this. {-# Language ScopedTypeVariables #-} module Main where import Control.Monad.Primitive import qualified Data.Vector.Unboxed import qualified Data.Vector.Generic as VG import qualified Data.Vector.Unboxed.Mutable as VM import qualified Data.Vector.Unboxed as V toImmutable :: VM.MVector RealWorld Int -> V.Vector Int toImmutable = undefined main :: IO () main = do v :: VM.MVector RealWorld Int <- VM.new 1 VM.write v 0 (3 :: Int) x <- VM.read v 0 -- y <- VG.head . toImmutable $ v -- print y print $ VM.length v {- Thanks, Cody -}

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Job opening: compiling to categories
by Conal Elliott 05 Aug '17

05 Aug '17

I have a job opening to work closely with me (at Target Digital) on the GHC plugin described in the paper *Compiling to Categories* <http://conal.net/papers/compiling-to-categories> as well as on applications, including machine learning. I’m especially looking for someone used to working inside of GHC and/or on GHC plugins. Mathematically oriented, solid background in programming language theory, denotationally inclined. Remote work is perfectly fine (and is what I do). – Conal

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ANN: stack-1.5.1 released
by Emanuel Borsboom 05 Aug '17

05 Aug '17

See https://haskellstack.org for installation and upgrade instructions. Bug fixes: * Stack eagerly tries to parse all cabal files related to a snapshot. Starting with Stackage Nightly 2017-07-31, snapshots are using GHC 8.2.1, and the `ghc.cabal` file implicitly referenced uses the (not yet supported) Cabal 2.0 file format. Future releases of Stack will both be less eager about cabal file parsing and support Cabal 2.0. This patch simply bypasses the error for invalid parsing.

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Re: [Haskell-cafe] Running ghci in a Cabal sandbox
by Emil Axelsson 04 Aug '17

04 Aug '17

Thanks for your reply! But I actually don't want `cabal repl`. The bigger picture is explained here: http://fun-discoveries.blogspot.com/2017/08/building-haskell-projects-with-… Towards the end of that post I suggest using `cabal exec` to integrate with a Cabal sandbox; however, as Daniel Trstenjak pointed out, that shouldn't be needed since `cabal-cargs` already sets the `-package-db` flag for GHC. So my question is why `cabal exec` is needed (in this particular case) even though `-package-db` is given? I know `cabal exec` sets a few environment variables (`CABAL_SANDBOX_CONFIG`, `CABAL_SANDBOX_PACKAGE_PATH` and `GHC_PACKAGE_PATH`). I've checked that these are all set correctly, so Cabal seems to be doing its job. But it's not clear why ghci gets confused when these variables are not set (and `-package-db` is given), but not when the variables are set. Cheers / Emil Den 2017-08-04 kl. 15:31, skrev nek0: > Hi Emil, > > What you want is hidden behind the `cabal repl` command, which starts > ghci with the package-db of the sandbox. > > Greetings, > > nek0 > > On 4.8.2017 13:41, Emil Axelsson wrote: >> Hi! >> >> I have a small file Test.hs alone in a directory: >> >> {-# LANGUAGE DeriveGeneric #-} >> >> module Test where >> >> import Data.Hashable >> import Data.Scientific >> import GHC.Generics >> >> data Sc = Sc Scientific deriving (Generic) >> >> instance Hashable Sc >> >> To be able to load this file, I set up a Cabal sandbox: >> >> $ ghc --numeric-version >> 8.0.2 >> >> $ cabal --numeric-version >> 1.24.0.2 >> >> $ cabal sandbox init >> ... >> >> $ cabal install hashable-1.2.6.0 scientific >> ... >> >> (Note: not the latest version of hashable.) >> >> Now, if I try to run GHCi and point it to the sandbox' package database >> I get this error: >> >> $ ghci >> -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d >> Test.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help >> [1 of 1] Compiling Test ( Test.hs, interpreted ) >> >> Test.hs:12:14: error: >> • No instance for (Hashable Scientific) >> arising from a use of >> ‘hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt’ >> • In the expression: >> hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc >> In an equation for ‘hashWithSalt’: >> hashWithSalt >> = hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc >> In the instance declaration for ‘Hashable Sc’ >> >> Somehow it mixes in version 1.2.6.1 of hashable, even though this >> package isn't installed (neither in the sandbox nor the global database). >> >> It turns out that wrapping the command in `cabal exec` fixes the problem: >> >> $ cabal exec -- ghci >> -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d Test.hs >> GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help >> [1 of 1] Compiling Test ( Test.hs, interpreted ) >> Ok, modules loaded: Test. >> *Test> >> >> Any idea what's going on? >> >> / Emil >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post.

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Call for participation: FARM (early reg ends today)
by Mark Santolucito 04 Aug '17

04 Aug '17

5th ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design Oxford, UK September 9, 2017 (co-located with ICFP 2017) http://functional-art.org/2017 The ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design (FARM) gathers together people who are harnessing functional techniques in the pursuit of creativity and expression. Functional Programming has emerged as a mainstream software development paradigm, and its artistic and creative use is booming. A growing number of software toolkits, frameworks and environments for art, music and design now employ functional programming languages and techniques. FARM is a forum for exploration and critical evaluation of these developments, for example to consider potential benefits of greater consistency, tersity, and closer mapping to a problem domain. This year FARM presents paper and demo sessions during the day, as well as a performance in the evening. The evening performance feature computer music performances of artists integrating functional programming techniques into their work. To register for FARM, visit the ICFP registration page - early registration ends August 4. Some funding support is available for the main ICFP conference and related workshops like FARM. This information can be found on the travel support page. Registration ------------ You can register via the ICFP 2017 registration:http://icfp17.sigplan.org/attending/registration Early registration deadline is August 4. Program --------------- 9:00 - 9:10 Welcome Michael Sperber, Jean Bresson 09:10 - 10:00 A Categorial Grammar for Music and Its Use in Automatic Melody Generation Halley Young Demo - Representation of Musical Notation in Haskell Edward Lilley 10:30 - 11:30 Demo - The Arpeggigon: A Functional Reactive Musical Automaton Henrik Nilsson Demo - Vivid: Sound Synthesis with Haskell and SuperCollider Tom Murphy Demo - African Polyphony and Polyrhythm Chris Ford 12:00 - 12:30 Modelling the Way Mathematics Is Actually Done Joe Corneli, Ursula Martin, Dave Murray-Rust, Alison Pease, Raymond Puzio, Gabriela Rino Nesin 14:00 - 15:00 FAUST Tutorial for Functional Programmers Yann Orlarey, Stéphane Letz, Dominique Fober, Romain Michon 15:30 - 16:20 GALE: A Functional Graphic Adventure Library and Engine Ivan Perez Demo - Ait: A Concatenative Language for Creative Programming Stian Veum Mollersen 16:50 - 17:40 Unified Media Programming: An Algebraic Approach Simon Archipoff, David Janin Demo - Octopus: A High-Level Fast 3D Animation Language Simon Archipoff, David Janin Performances 19:30-22:00 @ Old Fire Station Workshop Organisation --------------------- - Workshop Chair: Mike Sperber, Active Group GmbH - Program Chair: Jean Bresson, UMR STMS IRCAM/CNRS/UPMC Sorbonne UniversitÃ©s - Publicity Chair: Mark Santolucito, Yale University - Performance Chair: Alex McLean, Deutsches Museum, Munich Program Committee: --------------------- - Renick Bell, Tama Art University, Tokyo - Beatrice Berard, LIP6, Universite Pierre et Marie Curie - Jean Bresson, UMR STMS IRCAM/CNRS/UPMC Sorbonne Universités - Richard Gabriel, IBM Research - Jean-Louis Giavitto, UMR STMS IRCAM/CNRS/UPMC Sorbonne Universités - Stéphane Letz, Grame - José Pedro Magalhães, Standard Chartered Bank - Ivan Perez Dominguez, University of Nottingham - Donya Quick, Southern Methodist University - Christophe Rhodes, Goldsmiths, University of London - Andrew Sorensen, Australian National University - Michael Sperber, Active Group GmbH - Charlotte Truchet, LINA, UMR 6241, Université de Nantes

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[ANN] brittany - haskell source code formatting tool - hackage release
by lennart spitzner 04 Aug '17

04 Aug '17

Greetings, I am happy to (finally) announce the first hackage release of brittany, a configurable haskell source code formatter based on ghc-exactprint [2]. https://hackage.haskell.org/package/brittany https://github.com/lspitzner/brittany *Introduction* Brittany aims to nicely layout the code and retain empty lines and comments as they appear in the input. For that it uses a fundamentally different approach (see [7]/theory) than other formatters. The project is not finished, yet it already is usable and produces better results than other formatters in many cases. Of course these words come from its creator, so see for yourself: I have included some examples at the bottom of this mail; see [3] and [4] for some more. I wish to stress that this project will only progress at a very slow speed barring support from the community. I hereby offer to work on this and ask for funding. See the "future" paragraph below. *Changelog* Since the "alpha-release" announced previously [5] the most important changes are: - Release under the AGPL-v3; - Release on hackage; - Make horizontal alignment less aggressive by default (see example [6]); - Add high-level documentation (see [7]). This might be of interest to anyone considering to write a formatter (haskell or even otherwise); - Improve testsuite setup; - Improve layouting in many many cases and fix various bugs; - Add a library interface (this integrates with haskell-ide-engine [8]); Brittany still.. - does not touch anything other than top-level type signatures and bindings (imports, classes, instances, data decls, .. are not modified); - contains some bugs (but it checks its own output for validity and aborts); - does not handle many "uncommon" syntactic constructs/extentions (e.g. arrow notation); In preparation of this release the `butcher` and `czipwith` packages were published on hackage as well. I will cover those in separate announcements. *Building* Brittany currently requires ghc-8.0 (no support for previous ghc versions is planned, but 8.2 will be). Now that this package is on hackage, cabal users should be able to install it directly; stack users will currently have to clone and go from there (a stack.yaml is provided). Detailed building guides for cabal, cabal-new and stack are in the project README. Inclusion in stackage is coming as soon as all dependencies are included. *Known issues* - Bad performance for large inputs (really noticeable at >1k loc). The cause is already determined - quadratic instead of linear complexity in one specific function (see issue #34 [9]). Should be fixable and has high priority. - The config (file) lacks documentation. - Comments are not always reproduced exactly when reformatting. There is a lack of testcases for comments in the testsuite. There is the known case of comments in List/MonadComprehensions that currently breaks idempotency (the comments move further left each roundtrip through brittany) where a solution will most likely involve some non-trivial changes in ghc-exactprint (see [10]). - As mentioned above: only certain module elements are transformed, and not all syntactical constructs are supported. re-layouting of imports, data decls, classes and instances are on the radar, but all require a good amount of work. - CPP is not officially supported. This is mostly a WONTFIX. One can enable it by force, and it works to a degree, but it is relatively easy to find cases where it will break (conditional code not being reformatted, leading to syntax errors and theoretically also to change semantics)). - No fine-grained (per file or even per-function) control/configuration, e.g. it is not yet possible to add some pragma/comment to disable reformatting this one carefully layouted-by-hand function that brittany messes up. - No adaption to ghc-8.2 yet. *Future/Outlook* As far as I can tell brittany already works rather well - I use it all the time, even though I still run into issues from time to time. Still, brittany is not finished (these projects never really are, are they?). Up on my list are ghc-8.2 adaption, fixing the performance bug mentioned above, layouting of data decls, layouting of instances, and controlling behaviour/config via flags in the source (as comments). But implementing new functionality costs a lot of time, even with the DSL used internally: One has to understand the GHC AST (which is not always documented), think of all possible interactions ("do users really use record syntax when having more than one constructor?" "are GADT records a thing?"), write the layouting transformation and test it. I have already invested a good amount of my free time into this project but its scope is too large and I decided to put a limit on my personal investment. This means that barring some form of support from the community I don't see new features being implemented at any certain pace. This leaves the following paths: 1) This project is supported monetarily: I hereby offer to (part-time) work on this provided appropriate funding. I am not sure who exactly might be interested in providing this kind of support - I am no student anymore so GSoC is out of the question. Feel free to contact me on- or off-list if interested. 2) (More) Contributors add tests, report (and maybe fix) bugs and most importantly implement new functionality (layouting for any syntactic constructs of the haskell language not yet supported, etc.) I realize that this is not a trivial project to dive into, and there is a good amount of stuff one has to get familiar with before one can start making use of the abstractions (the DSL) provided. On the other hand, I _think_ that the project source code is relatively well-structured (although in-source comments are really sparse, admittedly) and the high-level (markdown) documentation <strike>will scare everyone away due to their length</strike> will allow understanding the project relatively quickly. 3) The project will progress only rather slowly. Regardless I plan to continue maintaining this project, fix bugs as they come up and also work on expanding functionality when I find the time. *Contributing* In ascending order of involvement, you can contribute by: - Reporting issues, especially instances of bad layouting (especially when it is not a pure matter of opinion); - Add to the testsuite, specifically to the `tests.blt` file of the `littests` test. It contains a large number of tests already, but the coverage is not very good. - If you want to really help implementing more stuff, the high-level docs [7] are the right place to get a rough overview, especially the theory document [11]. I have not documented how to write new layouters yet, so for now I recommend looking at the existing ones, e.g. in `Expr.hs`. -- lennart [1] https://hackage.haskell.org/package/brittany https://github.com/lspitzner/brittany/ [2] https://mpickering.github.io/posts/2015-07-23-ghc-exactprint.html https://hackage.haskell.org/package/ghc-exactprint [3] https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865… [4] https://github.com/lspitzner/brittany/tree/master/doc/showcases [5] https://mail.haskell.org/pipermail/haskell-cafe/2016-September/124793.html [6] https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865… [7] https://github.com/lspitzner/brittany/blob/master/doc/implementation/index.… [8] https://github.com/haskell/haskell-ide-engine [9] https://github.com/lspitzner/brittany/issues/34 [10] https://github.com/alanz/ghc-exactprint/issues/53 [11] https://github.com/lspitzner/brittany/blob/master/doc/implementation/theory… -- some layouting examples - would be (re)produced in exactly this way by brittany: > main = do > > now <- getCurrentTime > let (_, _, week) = toWeekDate . utctDay $ now > putStrLn $ ("it's "++) $ case week of > 6 -> "the weekend" > 7 -> "the weekend" > _ -> "a weekday" > > localtime <- utcToLocalZonedTime now > let hr = todHour . localTimeOfDay . zonedTimeToLocalTime $ localtime > case hr of > _ | hr < 12 -> putStrLn "it's before noon" > | otherwise -> putStrLn "it's after noon" > -- Newlines are used sparingly: Only after "do" and when the > -- `liftBaseOpDiscard` application would lead to overflowing 80 columns. > main :: IO () > main = do > pool <- createPostgresqlPool (toS databaseConnectionString) 10 > initiate $ \chan -> forever $ do > flip runDbConn pool $ do > makeSureQueueIsFull chan > void $ liftBaseOpDiscard (consumeMsgs chan responseQueue Ack) > (uncurry processMsg) > threadDelay 1000000 > -- Alignment of patterns > go [] "" = True > go [WildCard ] "" = True > go (WildCard :rest) (c:cs) = go rest (c : cs) || go (WildCard : rest) cs > go (Union globs:rest) cs = any (\glob -> go (glob ++ rest) cs) globs > go [] (_:_) = False > go (_:_) "" = False

1 0

Running ghci in a Cabal sandbox
by Emil Axelsson 04 Aug '17

04 Aug '17

Hi! I have a small file Test.hs alone in a directory: {-# LANGUAGE DeriveGeneric #-} module Test where import Data.Hashable import Data.Scientific import GHC.Generics data Sc = Sc Scientific deriving (Generic) instance Hashable Sc To be able to load this file, I set up a Cabal sandbox: $ ghc --numeric-version 8.0.2 $ cabal --numeric-version 1.24.0.2 $ cabal sandbox init ... $ cabal install hashable-1.2.6.0 scientific ... (Note: not the latest version of hashable.) Now, if I try to run GHCi and point it to the sandbox' package database I get this error: $ ghci -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d Test.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Test ( Test.hs, interpreted ) Test.hs:12:14: error: • No instance for (Hashable Scientific) arising from a use of ‘hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt’ • In the expression: hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc In an equation for ‘hashWithSalt’: hashWithSalt = hashable-1.2.6.1:Data.Hashable.Class.$dmhashWithSalt @Sc In the instance declaration for ‘Hashable Sc’ Somehow it mixes in version 1.2.6.1 of hashable, even though this package isn't installed (neither in the sandbox nor the global database). It turns out that wrapping the command in `cabal exec` fixes the problem: $ cabal exec -- ghci -package-db=.cabal-sandbox/x86_64-linux-ghc-8.0.2-packages.conf.d Test.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Test ( Test.hs, interpreted ) Ok, modules loaded: Test. *Test> Any idea what's going on? / Emil

1 0

Question?
by Casey Newsome 04 Aug '17

04 Aug '17

Hello, I am a new user of Haskell. I was wondering if this is where I can ask a question on a program I am attempting to write. If this is the wrong place. I apologize. Sorry if there was an inconvenience, Casey :D

4 3

Low-level idea: Aligned tagged ByteArray#
by Zemyla 03 Aug '17

03 Aug '17

I had an idea for a way to attach small-but-necessary amounts of information to a ByteArray# or MutableByteArray# (and potentially also to Array# and ArrayArray#). The type would look something like "TaggedByteArray# 8#". This, for instance, would represent the address of a primitive array of bytes, with an alignment of 8, and with the last 3 bits having a number between 0 and 7 in them. Code to access the elements of the ByteArray# would disregard the last bits, and the garbage collector would simply ensure that the tag was retained after collection passes. "ByteArray#" itself would simply become an alias for "TaggedByteArray# 1#", and the existing functions would have their types changed to work with the new TaggedByteArray#s. The primary potential problems I see are how to have a KnownNat-style typeclass before Integer is defined, and how to store both the array and the tag in an ArrayArray#.

1 0

Haskell in Leipzig 2017: submission deadline shifted by two weeks
by Wolfgang Jeltsch 02 Aug '17

02 Aug '17

Hi! We have shifted the submission deadline for Haskell in Leipzig 2017 by two weeks. The new deadline is at 18 August 2017. Looking forward to your contribution. 😉 Event: Haskell in Leipzig 2017 Time: October 26–28, 2017 Place: HTWK Leipzig, Germany Homepage: https://hal2017.softbase.org/ About ===== Haskell is a modern functional programming language that allows rapid development of robust and correct software. It is renowned for its expressive type system, its unique approaches to concurrency and parallelism, and its excellent refactoring capabilities. Haskell is both the playing field of cutting-edge programming language research and a reliable base for commercial software development. The workshop series Haskell in Leipzig (HaL), now in its 12th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts, and Haskell beginners to listen to talks, take part in tutorials, join in interesting conversations, and hack together. To support the latter, HaL will include a one-day hackathon this year. The workshop will have a focus on functional reactive programming (FRP) this time, while continuing to be open to all aspects of Haskell. As in the previous year, the workshop will be in English. Contributions ============= 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. 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 program committee and the audience get a good idea of your contribution, but this is not a hard requirement. Please submit your abstract as a PDF document at https://easychair.org/conferences/?conf=hal2017 until Friday, August 18, 2017. You will be notified by Friday, September 8, 2017. Hacking Projects ================ Projects for the hackathon can be presented during the workshop. A prior submission is not needed for this. Invited Speaker =============== * Ivan Perez, University of Nottingham, UK Invited Performer ================= * Lennart Melzer, Robert-Schumann-Hochschule Düsseldorf, Germany Program Committee ================= * Edward Amsden, Plow Technologies, USA * Heinrich Apfelmus, Germany * Jurriaan Hage, Utrecht University, The Netherlands * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Tallinn University of Technology, Estonia (chair) * Andres Löh, Well-Typed LLP, Germany * Keiko Nakata, SAP SE, Germany * Henrik Nilsson, University of Nottingham, UK * Ertuğrul Söylemez, Intelego GmbH, Germany * Henning Thielemann, Germany * Niki Vazou, University of Maryland, USA * Johannes Waldmann, HTWK Leipzig, Germany Questions ========= If you have any questions, please do not hesitate to contact Wolfgang Jeltsch at wolfgang-it(a)jeltsch.info.

1 0

What code is generated for binary functions of data types with multiple constructors?
by Clinton Mead 02 Aug '17

02 Aug '17

Assume the following: 1. We have a type T with multiple constructors, but lets assume we're on a 64 bit machine and have at least 4 but no more than 7 constructors so we can still use pointer tagging. 2. And a function "f :: T -> T -> T" 3. Each combination of constructors (16 in the 4 constructor case, 49 in the 7 constructor case) has an implementation (naturally many of these will call helper functions). There's no wildcard matches. How will GHC generate the code for "f"? Will pushing through LLVM make any difference? Do we take the number of the first constructor, and then multiply the number of the second constructor by say 7, and then do one jump via a jump table? Is there a bunch of nested jump tables, each with 7 options? Is there a fall through if statement? Something else? I understand this probably a complex answer and perhaps doesn't have a simple answer, but I just wanted to get some sort of idea in my head of how GHC attempts to resolve code like this.

2 1

What can be UNPACK'ed?
by Tom Ellis 02 Aug '17

02 Aug '17

What types can be UNPACK'ed? From my vague understanding of what UNPACK does, it can only be types whose size is bounded by a known value, so whilst data Foo = Foo {-# UNPACK #-} !Float {-# UNPACK #-} !Int is fine, presumably data Foo = Foo {-# UNPACK #-} ![Float] is not fine. Or is it? Technically it could be possible to reserve enough space in Foo to store either a [] or a (:) Float [Float]. And if that is possible could we also UNPACK polymorphic fields? data Storable a => Foo a = Foo {-# UNPACK #-} a or data Foo a where Foo :: Storable a => {-# UNPACK #-} a -> Foo a if either DatatypeContexts worked or my imaginary GADT UNPACK syntax worked (I'm not sure if either does). What are the limits of what we could reasonably get to UNPACK in GHC? Thanks, Tom

5 9

Problems with Type family and Typeable
by Kai Zhang 01 Aug '17

01 Aug '17

I got an error when compiling the following codes: {-# LANGUAGE TypeOperators #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE UndecidableInstances #-} import Data.Type.Bool import Data.Type.Equality import Data.Tagged (Tagged(..)) import Data.Typeable type family Elem x xs :: Bool where Elem _ '[] = 'False Elem a (x ': xs) = a == x || Elem a xs elemTag :: forall a s t ts . Proxy s -> Tagged (t ': ts) a -> Bool elemTag _ _ = if typeOf (Proxy :: Proxy (Elem s (t ': ts))) == typeOf (Proxy :: Proxy 'True) then True else False GHC says: • No instance for (Typeable (Data.Type.Equality.EqStar s t || Elem s ts)) arising from a use of ‘typeOf’ • In the first argument of ‘(==)’, namely ‘typeOf (Proxy :: Proxy (Elem s (t : ts)))’ In the expression: typeOf (Proxy :: Proxy (Elem s (t : ts))) == typeOf (Proxy :: Proxy True) In the expression: if typeOf (Proxy :: Proxy (Elem s (t : ts))) == typeOf (Proxy :: Proxy True) then True else False My question: why is ghc unable to deduce that "Data.Type.Equality.EqStar s t || Elem s ts" resolves to "Bool" which should be an instance of Typeable? How to fix this?

3 6

Many packages blocked on Stackage nightly for GHC 8.2.1
by Dan Burton 01 Aug '17

01 Aug '17

Please be advised that many packages were dropped from the Stackage nightly build plan in order to arrive at a successful build with the new ghc. (Note that this does not affect the build plans for LTS 9.) This is to be expected whenever ghc gets a major version bump. For details, see: https://github.com/fpco/stackage/blob/master/MAINTAINERS.md We have attempted to contact package authors whose packages were dropped. However, comprehensive notification is not fully automated, and there may be many who have not been directly contacted. You can check your section of build-constraints.yaml, as well as stackage.org/nightly, to see which of your packages are currently absent from the build plan. You may restore your packages to the nightly build plan (once they are buildable with ghc 8.2.1) in the same way they were added: by opening a PR, uncommenting your packages in build-constraints.yaml. Thank you for your efforts to keep the Haskell ecosystem up to date.

2 1

DSLDI 2017: Second Call for Talk Proposals
by Lindsey Kuper 31 Jul '17

31 Jul '17

********************************************************************* SECOND CALL FOR TALK PROPOSALS DSLDI 2017 Fifth Workshop on Domain-Specific Language Design and Implementation October 22, 2017 Vancouver, Canada Co-located with SPLASH http://2017.splashcon.org/track/dsldi-2017 https://twitter.com/wsdsldi ********************************************************************* Deadline for talk proposals: 7th of August, 2017 Well-designed and implemented domain-specific languages (DSLs) can achieve both usability and performance benefits over general-purpose programming languages. By raising the level of abstraction and exploiting domain knowledge, DSLs can make programming more accessible, increase programmer productivity, and support domain-specific optimizations. ## Workshop Goal Domain-Specific Language Design and Implementation (DSLDI) is a workshop intended to bring together researchers and practitioners interested in discussing how DSLs should be designed, implemented, supported by tools, and applied in realistic contexts. The focus of the workshop is on all aspects of this process, from soliciting domain knowledge from experts, through the design and implementation of the language, to evaluating whether and how a DSL is successful. More generally, we are interested in continuing to build a community that can drive forward the development of modern DSLs. ## Workshop Format DSLDI is a single-day workshop and will consist of an invited speaker followed by moderated audience discussions structured around a series of short talks. The role of the talks is to facilitate interesting and substantive discussion. Therefore, we welcome and encourage talks that express strong opinions, describe open problems, propose new research directions, and report on early research in progress. Proposed talks should be on topics within DSLDI’s area of interest, which include but are not limited to: * solicitation and representation of domain knowledge * DSL design principles and processes * DSL implementation techniques and language workbenches * domain-specific optimizations * human factors of DSLs * tool support for DSL users * community and educational support for DSL users * applications of DSLs to existing and emerging domains * studies of usability, performance, or other benefits of DSLs * experience reports of DSLs deployed in practice ## Call for Talk Proposals We solicit talk proposals in the form of short abstracts (max. 2 pages). A good talk proposal describes an interesting position, open problem, demonstration, or early achievement. The submissions will be reviewed on relevance and clarity, and used to plan the mostly interactive sessions of the workshop day. Publication of accepted abstracts and slides on the website is voluntary. * Deadline for talk proposals: August 7th, 2017 * Notification: September 11th, 2017 * Workshop: October 22nd, 2017 * Submission website: https://dsldi17.hotcrp.com/ ## Workshop Organization Co-chairs: * Lindsey Kuper (lindsey(a)composition.al) Intel Labs * Eric Walkingshaw (eric.walkingshaw(a)oregonstate.edu) Oregon State University Follow us on Twitter at https://twitter.com/wsdsldi Program committee: * Nada Amin (EPFL/University of Cambridge) * Eric Holk (Google) * Gabriele Keller (Data61, CSIRO (formerly NICTA) and UNSW) * Rebekah Leslie-Hurd (Intel Labs) * Chris Martens (NCSU) * Lee Pike (Galois) * Jonathan Ragan-Kelley (UC Berkeley) * Jesús Sánchez Cuadrado (Autonomous University of Madrid) * Vincent St-Amour (Northwestern University) * Philip Wadler (University of Edinburgh)

1 0

Re: [Haskell-cafe] What can be UNPACK'ed?
by Olaf Klinke 31 Jul '17

31 Jul '17

How is UNPACK and BangPatterns related to WHNF? I used to think that unpacking sort of forces the constructors up to the level where the bangs reside. Hence unpacking a tuple makes sense, whereas unpacking a linked list does not save much memory. -- Olaf

1 0

Shout out for Chinese(?) speakers of Haskell
by Anthony Clayden 30 Jul '17

30 Jul '17

Is there a Chinese language(s) equivalent to StackOverflow or reddit or haskell-cafe? I'm asking because someone keeps posting to Trac with beginner/intermediate level questions. They're posting code that doesn't work/doesn't compile, and expecting Trac support to 'fix' it. Clearly they do not speak good English, because they're not explaining what they want the code to do (despite several requests). There have been some comments via Google translate, which isn't well versed in Haskell terminology (no surprise). Their first few tickets had narrative in Chinese characters. Looks like traditional script, so they're maybe a Cantonese speaker; or in Taiwan(?) Thank you AntC

1 0

Re: [Haskell-cafe] [ANNOUNCE] GHC 8.2.1 available
by Wolfgang Jeltsch 30 Jul '17

30 Jul '17

Am Samstag, den 22.07.2017, 23:03 -0400 schrieb Ben Gamari: > In addition, there are a number of new features, > > * A new, more type-safe type reflection mechanism > > * The long-awaited Backpack module system > > * Deriving strategies to disambiguate between GHC's various instance > deriving mechanisms > > * Unboxed sum types, for efficient unpacked representation of sum > data types > > * Compact regions, allowing better control over garbage collection > in the presence of large heaps containing many long-lived objects. > > * Colorful messages and caret diagnostics for more legible errors > > A more thorough list of the changes in this release can be found in > the release notes, > > https://haskell.org/ghc/docs/8.2.1/docs/html/users_guide/8.2.1-notes.html It seems that the release notes mention the new type reflection mechanism und colorful messages only in the “Highlights” section, not in the “Full details” section, and that they do not mention the Backpack module system and unboxed sums at all. All the best, Wolfgang

4 5

Damn you hmatrix
by Yotam Ohad 29 Jul '17

29 Jul '17

Hi cafe, I have a very annoying problem with hmatrix. I have a project which depends on it. I can use `stack build` with no errors but when I try to load it to GHCi(`stack ghci`) I get the following error: sh-4.3$ stack ghci [0mApple-0.1.0.0: configure (lib) [0m [0mConfiguring Apple-0.1.0.0... [0m [0mApple-0.1.0.0: initial-build-steps (lib) [0m [0mConfiguring GHCi with the following packages: Apple [0m GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help ghc.EXE: addDLL: libblas.dll (Win32 error 126): The specified module could not be found. ghc.EXE: Could not load `libblas.dll'. Reason: addDLL: could not load DLL ghc.EXE: addDLL: liblapack.dll (Win32 error 126): The specified module could not be found. ghc.EXE: Could not load `liblapack.dll'. Reason: addDLL: could not load DLL ghc.EXE: C:\Users\Yotam\Apple\.stack-work\install\ebd7be2b\lib\x86_64-windows-ghc-8.0.2\hmatrix-0.18.0.0-IA7RzrKn1o84vo5PLhGcwQ\HShmatrix-0.18.0.0-IA7RzrKn1o84vo5PLhGcwQ.o: unknown symbol `dgesvd_' ghc.EXE: unable to load package `hmatrix-0.18.0.0' This is really bizarre, and could not find something online to help me fix this. I'm using stack 1.5.0 with ghc 8.0.2 On a side note, I've seen some discussions about why the C libraries can't be added automatically but did not understand most of it, if someone can explain it would be highly appreciated. Yotam

3 5

GHCi and custom preprocessors
by aditya siram 28 Jul '17

28 Jul '17

Hi all, I have a custom file format and custom preprocessor in my project that converts it to Haskell. GHCi is unable to detect when changes are made to the custom file, it only sees that the Haskell file hasn't changed and doesn't reload anything. Is this even supported in GHCi? Thanks! -deech

2 1

How to execute a function loaded via GHCI.ObjLink?
by Saurabh Nanda 28 Jul '17

28 Jul '17

Hi, I'm playing around with https://www.stackage.org/haddock/lts-9.0/ghci-8.0.2/GHCi-ObjLink.html to see if I can come up with some sort of hot-loading/plugin system in Haskell. I've managed to load a shared object (compiled from a Haskell source via -rdynamic) with the following code: {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE MagicHash, UnboxedTuples #-} module Main where import GHC.Exts ( addrToAny# ) import GHC.Ptr ( Ptr(..) ) import System.Info ( os, arch ) import Encoding import GHCi.ObjLink import Debug.Trace main :: IO () main = do traceM "before initObjLinker" initObjLinker traceM "before loadObj" loadObj "/Users/saurabhnanda/projects/test-plugins/test-plugins/app/PluginMarkup.o" traceM "after loadObj" -- NOTE: I've hardcoded the symbol name that I obtained from running `symbols PluginMarkup.o` sym <- lookupSymbol "PluginMarkup_foliage_info" traceM "after lookupsymbol" traceM (show sym) I'm getting the following output, which mean that I'm probably getting the Ptr to the function. before initObjLinker before loadObj after loadObj after lookupsymbol Just 0x0000000104be49a8 Question is, how do I run the function in the same Haskell environment/runtime? The underlying function is actually `foliage :: UtcTime -> Html` The code is available at https://github.com/vacationlabs/hint-test/blob/dll/app/Main.hs and the DLL is available at https://github.com/vacationlabs/hint-test/blob/dll/app/PluginMarkup.o -- Saurabh.

2 2

[ANN] saltine 0.0.1.0 released - Users urged to upgrade
by Max Amanshauser 27 Jul '17

27 Jul '17

Saltine is a Haskell binding to libsodium. === Thomas DuBuisson of Galois Inc. found a serious issue in saltine that can lead to data corruption. Security implications cannot be ruled out. All users are advised to upgrade to saltine 0.0.0.6 or above, which are not affected. Saltine requires libsodium 1.0.11 or higher. === Saltine 0.0.1.0 also features: * Support for detached signatures (contributed by Thomas DuBuisson) -- Cheers, Max.

1 0

Re: [Haskell-cafe] Static analysis engineering at Facebook (Clang/OCaml)
by Don Stewart 27 Jul '17

27 Jul '17

Link moved, apply here: https://www.facebook.com/careers/jobs/a0I1200000LT8aAEAT On Thu, Jul 27, 2017 at 12:39 PM, Shannon Sequeira < shannonsequeira(a)gmail.com> wrote: > Hi Don, the job link appears to be broken. > > Best, > Shannon Sequeira > > On 26 July 2017 at 13:11, Don Stewart <dons00(a)gmail.com> wrote: > >> The Infer static analysis team at Facebook is hiring. We have a >> functional programming engineering role in London to work on the open >> source Clang/C++ frontend to Infer. >> >> Infer is a static analysis suite for C++, Java and Objective C used by >> thousands of engineers at Facebook and elsewhere to find bugs. >> >> The role is a "compiler" role - working on the Clang AST to OCaml, and >> intermediate phases of Infer to improve our C++ analysis capabilities. Good >> FP engineering skills (e.g. Haskell or OCaml) are desirable. >> >> You should have a working knowledge of C++ semantics, language or >> compiler design or experience in a range of C++ projects. >> >> Infer: >> >> http://fbinfer.com/ >> >> Apply via: >> >> https://www.facebook.com/careers/jobs/a0I1200000LT8aA >> >> _______________________________________________ >> 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. >> > >

1 0

GHC Platform-independent object files
by Hugo Pacheco 27 Jul '17

27 Jul '17

Hi cafe, I am wondering if there is any easy way to distribute a Haskell module/library in a platform-independent manner without revealing the source code, that can be seamlessly linked with GHC? I am thinking about some sort of GHC object files or any intermediate representation such as C,LLVM or Haskell Core. My use case would be to release a small utility module as part of a student assignment without revealing its source code to students. Thanks, hugo -- www.di.uminho.pt/~hpacheco

2 4

custom package for Verbosity, info, warn etc. in console programs
by Henning Thielemann 27 Jul '17

27 Jul '17

I have several command-line tools that support a verbosity flag. The Cabal library provides an appropriate data type and related reporting functions: https://hackage.haskell.org/package/Cabal-2.0.0.2/docs/Distribution-Verbosi… https://hackage.haskell.org/package/Cabal-2.0.0.2/docs/Distribution-Simple-… However, Cabal moves pretty fast (frequent version increments) and I do not need all the distribution stuff. Is there a package that provides only the Verbosity and reporting functionality?

1 0

Static analysis engineering at Facebook (Clang/OCaml)
by Don Stewart 26 Jul '17

26 Jul '17

The Infer static analysis team at Facebook is hiring. We have a functional programming engineering role in London to work on the open source Clang/C++ frontend to Infer. Infer is a static analysis suite for C++, Java and Objective C used by thousands of engineers at Facebook and elsewhere to find bugs. The role is a "compiler" role - working on the Clang AST to OCaml, and intermediate phases of Infer to improve our C++ analysis capabilities. Good FP engineering skills (e.g. Haskell or OCaml) are desirable. You should have a working knowledge of C++ semantics, language or compiler design or experience in a range of C++ projects. Infer: http://fbinfer.com/ Apply via: https://www.facebook.com/careers/jobs/a0I1200000LT8aA

1 0

ANN: (unofficial) nightly cabal-install builds for OSX
by Oleg Grenrus 26 Jul '17

26 Jul '17

Dear Haskellers, I set up a semi-automatic system to provide you with `cabal` head builds for OSX / macOS at: https://haskell.futurice.com/ As a single highlight, these builds are useful if you need to setup OSX CI; multi-travis-ghc [1] can be used almost as is, see [2]. Hopefully you find these useful! [1]: https://github.com/hvr/multi-ghc-travis [2]: https://github.com/futurice/haskell-futurice-site/commit/3d9b40c6c61788589d… Best regards, Oleg "phadej" Grenrus

1 0

ANN: stack-1.5.0 released
by Emanuel Borsboom 25 Jul '17

25 Jul '17

See https://haskellstack.org for installation and upgrade instructions. ## 1.5.0 Behavior changes: * `stack profile` and `stack trace` now add their extra RTS arguments for benchmarks and tests to the beginning of the args, instead of the end. See [#2399](https://github.com/commercialhaskell/stack/issues/2399) * Support for Git-based indices has been removed. Other enhancements: * `stack setup` allow to control options passed to ghcjs-boot with `--ghcjs-boot-options` (one word at a time) and `--[no-]ghcjs-boot-clean` * `stack setup` now accepts a `--install-cabal VERSION` option which will install a specific version of the Cabal library globally. * Updates to store-0.4.1, which has improved performance and better error reporting for version tags. A side-effect of this is that all of stack's binary caches will be invalidated. * `stack solver` will now warn about unexpected cabal-install versions. See [#3044](https://github.com/commercialhaskell/stack/issues/3044) * Upstream packages unpacked to a temp dir are now deleted as soon as possible to avoid running out of space in `/tmp`. See [#3018](https://github.com/commercialhaskell/stack/issues/3018) * Add short synonyms for `test-arguments` and `benchmark-arguments` options. * Adds `STACK_WORK` environment variable, to specify work dir. See [#3063](https://github.com/commercialhaskell/stack/issues/3063) * Can now use relative paths for `extra-include-dirs` and `extra-lib-dirs`. See [#2830](https://github.com/commercialhaskell/stack/issues/2830) * Improved bash completion for many options, including `--ghc-options`, `--flag`, targets, and project executables for `exec`. * `--haddock-arguments` is actually used now when `haddock` is invoked during documentation generation. * `--[no-]haddock-hyperlink-source` flag added which allows toggling of sources being included in Haddock output. See [#3099](https://github.com/commercialhaskell/stack/issues/3099) * `stack ghci` will now skip building all local targets, even if they have downstream deps, as long as it's registered in the DB. * The pvp-bounds feature now supports adding `-revision` to the end of each value, e.g. `pvp-bounds: both-revision`. This means that, when uploading to Hackage, Stack will first upload your tarball with an unmodified `.cabal` file, and then upload a cabal file revision with the PVP bounds added. This can be useful—especially combined with the [Stackage no-revisions feature](http://www.snoyman.com/blog/2017/04/stackages-no-revisions-field)&… a method to ensure PVP compliance without having to proactively fix bounds issues for Stackage maintenance. * Expose a `save-hackage-creds` configuration option * On GHC <= 7.8, filters out spurious linker warnings on windows See [#3127](https://github.com/commercialhaskell/stack/pull/3127) * Better error messages when creating or building packages which alias wired-in packages. See [#3172](https://github.com/commercialhaskell/stack/issues/3172). * MinGW bin folder now is searched for dynamic libraries. See [#3126](https://github.com/commercialhaskell/stack/issues/3126) * When using Nix, nix-shell now depends always on git to prevent runtime errors while fetching metadata * The `stack unpack` command now accepts a form where an explicit Hackage revision hash is specified, e.g. `stack unpack foo-1.2.3@gitsha1:deadbeef`. Note that this should be considered _experimental_, Stack will likely move towards a different hash format in the future. * Binary "stack upgrade" will now warn if the installed executable is not on the PATH or shadowed by another entry. * Allow running tests on tarball created by sdist and upload [#717](https://github.com/commercialhaskell/stack/issues/717). Bug fixes: * Fixes case where `stack build --profile` might not cause executables / tests / benchmarks to be rebuilt. See [#2984](https://github.com/commercialhaskell/stack/issues/2984) * `stack ghci file.hs` now loads the file even if it isn't part of your project. * `stack clean --full` now works when docker is enabled. See [#2010](https://github.com/commercialhaskell/stack/issues/2010) * Fixes an issue where cyclic deps can cause benchmarks or tests to be run before they are built. See [#2153](https://github.com/commercialhaskell/stack/issues/2153) * Fixes `stack build --file-watch` in cases where a directory is removed See [#1838](https://github.com/commercialhaskell/stack/issues/1838) * Fixes `stack dot` and `stack list-dependencies` to use info from the package database for wired-in-packages (ghc, base, etc). See [#3084](https://github.com/commercialhaskell/stack/issues/3084) * Fixes `stack --docker build` when user is part of libvirt/libvirtd groups on Ubuntu Yakkety (16.10). See [#3092](https://github.com/commercialhaskell/stack/issues/3092) * Switching a package between extra-dep and local package now forces rebuild (previously it wouldn't if versions were the same). See [#2147](https://github.com/commercialhaskell/stack/issues/2147) * `stack upload` no longer reveals your password when you type it on MinTTY-based Windows shells, such as Cygwin and MSYS2. See [#3142](https://github.com/commercialhaskell/stack/issues/3142) * `stack script`'s import parser will now properly parse files that have Windows-style line endings (CRLF) Thanks to all our contributors for this release: * Aayush Kapoor * Albert Netymk * Alexey Kuleshevich * Anders Kaseorg * Arash Rouhani * Bryan Richter * Dawei LIU * Dmitry Nikulin * Domen Kožar * Emanuel Borsboom * Felix Yan * Ivan Lazar Miljenovic * James Hamilton * Luke Murphy * Marcin Tolysz * Martin Kolinek * Mateusz Kowalczyk * Michael Sloan * Michael Snoyman * Niklas Hambüchen * Noah Doersing * Omari Norman * Paolo G. Giarrusso * Peter Stuart * Ryan Scott * Sergey Vinokurov * Sibi Prabakaran * Tej Chajed * Tim Dysinger * Tomáš Janoušek * Vassil Keremidchiev

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Parallel QuickCheck testing with live counter
by Henning Thielemann 25 Jul '17

25 Jul '17

I like pretty much how QuickCheck counts the number of successful tests until it reports that all tests are performed. It gives me feedback on the difficulty of the tests quickly or how long the tests will still run. I also want to run tests in parallel on multiple computing cores. There are dozens of test frameworks now. I have only tried 'pqc' and 'tasty' so far, both of them only show completed test runs but no live counters. Is there a package that runs QuickCheck tests in parallel and shows test counts live?

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Avoiding ad-hoc with yesod-form
by Yotam Ohad 24 Jul '17

24 Jul '17

Hello cafe, I have a custom data type: data Foo = Foo | Bar | Baz deriving (Show, Bounded, Enum) In my yesod app I need to have two forms, one that get two Foo and a second that recieve three Foo. From What I've seen online I need to create two new data types: data Foo2 = { foo1 :: Foo, foo2 :: Foo } data Foo3 = { foo1 :: Foo, foo2 :: Foo, foo3 :: Foo } This is tedious and very much ad-hoc. In my actual app it goes up to Foo6 :( Is there a better way to do it? This is how I defined the forms: foo2AForm :: AForm Handler Foo2 foo2AForm = Foo2 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..] foo2Form :: Html -> MForm Handler (FormResult Foo2, Widget) foo2Form = renderTable teamAForm foo3AForm :: AForm Handler Foo3 foo3AForm = Foo3 <$> areq (selectFieldList foos) "foo1" Nothing <*> areq (selectFieldList foos) "foo2" Nothing <*> areq (selectFieldList foos) "foo3" Nothing where foos:: [(Text, Role)] foos= map (pack . show &&& id) [minBound..] foo3Form :: Html -> MForm Handler (FormResult Foo2, Widget) foo3Form = renderTable teamAForm Thanks

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[Hiring] Part-time student job in Mannheim, Germany (remote possible)
by Dr. Jann Müller 24 Jul '17

24 Jul '17

We are working on a new approach to financial risk modelling based on recent research. Having obtained some initial funding, we are now looking for a developer to help us implement a prototype. The work will be mostly on the frontend using GHCJS and probably the miso framework (but we are open to other suggestions if you have previous experience in that space). - 10-20h per week at market rates - Flexible hours, remote work possible, but must be able to come to Mannheim for one day each month. Train tickets from anywhere in Germany will be paid for. - Start date: First week of October There is also a lot of potential for thesis projects, if you are interested in domain-specific languages, interpreters, or in dealing with uncertainty, please get in touch. Please send your inquiries and applications to jobs(a)lbrm.de<mailto:jobs@lbrm.de> Regards, Jann Müller

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Peformance digression when using "proc" notation for arrows
by Artem 23 Jul '17

23 Jul '17

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Re: [Haskell-cafe] Feeding a monad into itself
by Olaf Klinke 23 Jul '17

23 Jul '17

MarLinn, you observed well, I swept something under the carpet. So here are the definitions in full glory. Apologies to all the not-so mathematically minded in Haskell-Cafe, the mail has grown rather long. A partially ordered set is a type X together with a function (≤) :: X -> X -> Bool obeying three laws. ∀ x. x ≤ x x ≤ y and y ≤ z implies x ≤ z x ≤ y and y ≤ x implies x == y Note that total orders, like the Ord typeclass, require that either x ≤ y or y ≤ x hold, but not so partial orders. Now suppose you have two partially ordered types, say X and A. By abuse of notation we use ≤ for each of the orders. Suppose we have functions f :: X -> A g :: A -> X Suppose further that f and g are order-preserving, that is x ≤ x' implies f x ≤ f x' a ≤ a' implies g a ≤ g a'. Then f is said to be left adjoint to y if for all x :: X and a :: A, f x ≤ a precisely when x ≤ g a. If X is partially ordered, so is each function space (as you suggested correctly), namely pointwise. Define for f, g :: Z -> X f ≤ g when ∀ z. f z ≤ g z If you like, (->) Z is an applicative functor and the ≤ function for the type Z -> X is built using liftA2 (≤). A bounded lattice is a partially ordered type L that has two nullary and two binary operations: least :: L greatest :: L min :: L -> L -> L max :: L -> L -> L subject to the following laws. ∀ x. least ≤ x ∀ x. x ≤ greatest z ≤ x and z ≤ y precisely when z ≤ min x y x ≤ z and y ≤ z precisely when max x y ≤ z An example is the type Bool where False ≤ True, least = False, greatest = True, min = (&&) and max = (||). Observe that for each x :: L, the partial application (min x) is a monotone function of type L -> L. Hence we can ask when each such function has a right adjoint. If each such right adjoint exists, we call L a Heyting algebra and denote the right adjoint to (min x) by (-->) x. For every MonadPlus m, we can embed Bool into m () using the function Control.Monad.guard. In this reading, False is represented by Nothing and True is represented by Just (). We thus obtain partial orders on Maybe () as well as on any function type X -> Maybe (). Recall that my (/\) function had type m a -> (a -> m ()) -> m a Specialising to a = () we obtain meet = \x y -> x /\ (const y) :: m () -> m () -> m () which you can convince yourself produces the (&&) operator in case of Maybe () == Bool. Likewise, my arrow (-->) has type m a -> m a -> a -> m () from which we can build impl = \x y -> (x --> y) () :: m () -> m () -> m () Now, in the bounded distributive lattice Bool the right adjoint to (&&) x is the logical implication (→) x and we check ghci> guard True `impl` guard True :: Maybe () Just () ghci> guard True `impl` guard False :: Maybe () Nothing ghci> guard False `impl` guard False :: Maybe () Just () ghci> guard False `impl` guard True :: Maybe () Just () Summarising, for some MonadPlus monads m, the type m () looks like a bounded lattice with least = mzero greatest = return () max = mplus min = meet and for a subclass of these monads, including m = Maybe, m () is a Heyting algebra with the right adjoint to min defined as the impl function above. On to a more complicated example. Let R = [0,∞] denote the type of non-negative real numbers, including positive infinity, (totally) ordered by the obvious ≤ relation. Observe that for each r :: R, the multiplication function (*) r :: R -> R is order-preserving if we define 0 * ∞ = 0. Hence we can ask for its right adjoint, which will be a function of type R -> R as well. Exercise: Prove that the right adjoint is division (/) of real numbers, with boundary cases r / 0 = ∞ = ∞ / x for all r and x. This demonstrates the parallels between logical implication and divison: They are both right adjoints in a certain sense. Is there a monad m with m () = R? Yes: The monad G of measures, a.k.a. the Giry monad. Is is not a Haskell monad, though. There is no Haskell type which has R as denotational semantics. But let's pretend. Let's pretend all sets are finite and of Eq class. Then a measure on X can be encoded by a list of type [(X,R)]. It is what packages like probable do. What is (/\) for this monad of measures? Look at the type: (/\) :: G a -> (a -> R) -> G a It modifies a measure by a real-valued function. If x :: X previously had the weight r, then the new weight is r * (f x). Obviously, for each measure dx the operator \f -> dx /\ f is order-preserving, since multiplication is monotone. Hence we can ask for a right adjoint. It must be a function of type G a -> G a -> (a -> R) associating a real-valued function to a pair of measures. For a = () we already know the answer: It is division. For all other types, the right adjoint is known as the Radon-Nikodym derivative [*]. It is an important gadget in machine learning because it can be used to build conditional probabilites. Intuitively, you can see the connection: For a conditional probability, you first filter the list [(X,R)] for all the allowed x, then divide by the sum of all remaining weights to make the total weight 1 again. Hence without division there is no conditional probability. Moral of the story: Logical implication and conditional probabilities are both instances of the same problem, only for different monads. -- Olaf [*] Again, I am sweeping stuff under the carpet. On function space (X -> R), the order ≤ is defined up to sets of measure zero.

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benchmark regression/improvement reporting
by Harendra Kumar 23 Jul '17

23 Jul '17

Hi Cafe, I am looking for a package/tool/way that can tell me the difference in criterion benchmarks that a particular change introduced? If there is a way to just diff two criterion benchmark reports and show the difference in each benchmark result that should also do, I can write a CI script on top of that. Thanks, Harendra

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Haskell modules: Morton's fork?
by Nikita Churaev 22 Jul '17

22 Jul '17

Option 1: module App.Component (Foo, Bar, Qux) -- re-exports module App.Component.Foo (Foo, make, func1, func2) module App.Component.Bar (Bar, make, func1, func2) module App.Component.Qux (Qux, make, func1, func2) API clients will have to write long import lists: import App.Component import qualified App.Component.Foo as Foo import qualified App.Component.Bar as Bar import qualified App.Component.Qux as Qux Option 2: module App.Component (module Foo, module Bar) -- re-exports module App.Component.Foo (Foo, makeFoo, fooFunc1, fooFunc2) module App.Component.Bar (Bar, makeBar, barFunc1, barFunc2) module App.Component.Qux (Qux, makeQux, quxFunc1, quxFunc2) Now you can import easily: import App.Component But now you have to prefix your functions, just like in C... Is there another, cleaner option?

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Re: [Haskell-cafe] Feeding a monad into itself
by Olaf Klinke 22 Jul '17

22 Jul '17

Joshua Grosso wrote: >Could MonadPlus (with mzero) or Alternative (with empty) provide the >termination condition, if this pattern turned out to be more generally >useful? MonadPlus and Alternative provide a way to put the zero into the monad, but no way to check for zeroness. In the Maybe type you have the isNothing function, but the MonadPlus and Alternative classes don't require such a thing, and probably shouldn't. In the following I present a class that allows to do stuff conditional on mzero. The starting observation is that in logic, False => anything == True. Hence the implication arrow is a (binary) function that turns nothing into something. Consider the following binary operation. (Logicians: think conjunction) (/\) :: Monad m => m a -> (a -> m ()) -> m a ma /\ f = (\a -> liftM (const a) (f a)) =<< ma It's a bit like Control.Monad.mfilter but deletes stuff by mapping it to mzero instead of False. For example, ghci> [0,1,2,3] /\ (\n -> replicate n ()) [1,2,2,3,3,3] Some MonadPlus monads are set-like. Think of Nothing as the empty set, Just x as the singleton set {x} and think of the list [x,y,z] as the finite set {x,y,z}, disregarding muliplicities. For such monads m, the types m a have a preorder ≤ which is set inclusion under the "set interpretation". For example, Nothing ≤ Just () [1,2,3] ≤ [1,2,3,4] but not [1,2] ≤ [1,4]. Now consider the following type class. class (Monad m) => Heyting m where (-->) :: (Eq a) => m a -> m a -> a -> m () We reqire that for all x, y and f x /\ f ≤ y if and only if f ≤ x --> y That is, (x /\) is left adjoint to (x -->), which reminds the logician of the Heyting implication arrow. For MonadPlus instances, we suggest that (mzero -->) == const (const (return ())) Here are some instances: instance Heyting [] where ys --> xs = \a -> if (a `notElem` ys) || (a `elem` xs) then [()] else [] instance Heyting Maybe where y --> x = listToMaybe.((maybeToList y) --> (maybeToList x)) Without the Eq constraint, I couldn't have used the elem function, hence the Heyting class carries that constraint. (There is also a Heyting instance for the monad of finite distributions [1], see the package probable [2] and its siblings.) Heyting monads have a sort of negation, turning mzero into something: neg :: (MonadPlus m, Heyting m) => m a -> m () neg x = ((liftM (const ()) x) --> mzero) () Using neg, we can do stuff on mzero: ghci> neg Nothing Just () ghci> neg (Just ()) Nothing ghci> neg [1,2,3] [] ghci> neg [] [()] Finally we implement Jake's function, but more general. untilMZero :: (Heyting m, MonadPlus m) => (a -> m a) -> a -> m a untilMZero f x = (liftM (const x) (neg (f x))) `mplus` ((f x) >>= (untilMZero f)) ghci> untilMZero (\n -> if n > 5 then Nothing else Just (n+1)) 0 Just 6 ghci> untilMZero (\n -> if n > 5 then [] else [n+1,2*n]) 1 [6,10,8,6,6,10,8,6,10,8,6,6,10,8] -- Olaf [1] For the Giry monad, --> computes the Radon-Nikodym derivative. It type-checks. [2] https://hackage.haskell.org/package/probable-0.1.2/docs/Math-Probable-Distr…

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Feeding a monad into itself
by Jake 21 Jul '17

21 Jul '17

I have a function f :: a -> Maybe a that I want to feed into itself with some initial input until it returns Nothing. untilNothing :: (a -> Maybe a) -> a -> a untilNothing f x = case f x of Just x' -> untilNothing f x' Nothing -> x Is there a better way to do this? I feel like there is something more general going on with Monads being fed into themselves, but maybe I'm wrong. Thoughts?

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How is this variable not in scope?
by Jeffrey Brown 21 Jul '17

21 Jul '17

The following compiles and runs perfectly: main = do (inputFile:_) <- getArgs input <- readFile inputFile let pairs = pairFilesToContents $ readSmsnLines input mapM_ f pairs where f :: (FilePath, String) -> IO () f (name, content) = writeFile name content But the following triggers the error "Not in scope: ‘root’". main' = do (root : inputFile :_) <- getArgs input <- readFile inputFile let pairs = pairFilesToContents $ readSmsnLines input mapM_ f pairs where f :: (FilePath, String) -> IO () f (name, content) = writeFile (root+name) content -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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How to deal with last item with concatMapAccumC in Conduit.
by jun zhang 21 Jul '17

21 Jul '17

Dear cafes I use Conduit to parse a huge file. And I need merge lines by condition. I find the concatMapAccumC can do that and I write a demo as blow(with conduit-combinators-1.0.6,lts-6.18). The problem is if the last item didn’t make condition true, the data only keep in the accum but missing in stream. Any one can give me some advises? Thanks ---------------------------- import Conduit test'::Int->Int->(Int,[Int]) test' a s = case (a+s) > 5 of True -> (0,[a+s]) False -> (a+s,[]) testlog::IO [Int] testlog = runConduit $ (yieldMany [1,2,3,4,5,6,3]) $= (concatMapAccumC test' 0 ) $$ sinkList

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getChar (NoBuffering) not working on Windows
by Francesco Ariis 20 Jul '17

20 Jul '17

Hello list, I am writing a small console application. Today I was bitten by #2189 [1] ("hSetBuffering stdin NoBuffering doesn't work on Windows"). To reproduce: import System.IO main :: IO () main = hSetBuffering stdin NoBuffering >> getChar >>= putChar -- on linux you just need to press, say, 'c', on Win you -- need to press <Enter> too. Is there any sensible (cross-platform) way of working around this? [1] https://ghc.haskell.org/trac/ghc/ticket/2189

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runghc and linking in libraries
by Brian Sammon 20 Jul '17

20 Jul '17

If I want to have (and run without explicitly invoking ghc or runghc) a script that starts as follows: #!/usr/bin/runghc module Main where import MyLib I can do it just fine if MyLib is a pure-haskell MyLib.hs -- it doesn't have to be packaged or installed or anything complicated. If I want to create a MyLib that uses C code (that I wrote) through FFI, it doesn't seem to be possible to use it in a runghc script like this, unless I create a package and install it. Am I correct about this? In the course of researching this, I realized that I have a rather poor understanding of what "packages" are in ghc-land. I have a high-level-overview understanding ("It's like rubygems, but for haskell"), but I'm rather unclear about the nuts-and-bolts of it. The tight coupling between packages and the ghc core is rather different than what I've seen in other programming languages I've used (I haven't programmed in Java though) It would be useful if ghc had an argument to take a "MyLib.lib" file (or maybe a directory) and temporarily act like it's an installed package for the one invocation. Unsurprisingly, web-searching for "haskell" and "package" doesn't give me the focused result set that I want. I found the relevant section of the GHC Users Guide https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.ht… but links to other reading materials would be appreciated.

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[ANN] New release of SBV (v7.0), now with incremental solving
by Levent Erkok 20 Jul '17

20 Jul '17

I'm pleased to announce v7.0 release of SBV, a library for integrating SMT solvers into Haskell. This release adds incremental solving capabilities to SBV: Users can now interact with the underlying solver using a typed API capturing the SMTLib language, issuing commands, getting model values, and asserting further constraints on-the-fly. The possibility of issuing multiple check-sat commands allows incremental assertion of facts, a key feature of modern constraint solving systems. Hackage: https://hackage.haskell.org/package/sbv Homepage: http://leventerkok.github.io/sbv/ Release notes: https://github.com/LeventErkok/sbv/blob/master/CHANGES.md SMTLib initiative: http://smtlib.cs.uiowa.edu/ Feedback and bug reports are most welcome! -Levent.

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How to statically link some external libraries?
by Kai Zhang 20 Jul '17

20 Jul '17

I want to produce a statically-linked executable. First I tried "-optl-static -optc-static -optl-pthrea", which statically links all external libraries. But when I ran this executable it gives me "abort (core dumped)" error. I suspect the statically-linked glibc library might be the cause. So I decide to statically link all other libraries and leave the glibc as a dynamic library. How to do this using Cabal? Should I write a custom "Setup.hs"?

3 2

DeepSeq and random generators
by Dennis Raddle 19 Jul '17

19 Jul '17

I'm having trouble using Control.DeepSeq.force (necessary for parallel code) on a StdGen from System.Random. I don't know how to derive NFData. A standalone deriving statement, like this deriving instance NFData StdGen gets me the error "the data constructors of StdGen are not all in scope..." Is it actually possible to derive an NFData instance of StdGen, and how would I do that? Or if not possible, how can I work about this? Note: I'm going to see if I can use tf-random in this application. Maybe it will be easier. D

3 2

any cloud computing services for running Haskell?
by Dennis Raddle 19 Jul '17

19 Jul '17

I'm thinking of using cloud computing services for running my CPU-intensive parallel Haskell code, in order to get results faster. Instead of buying a faster computer, I would take advantage of existing services. Note that my budget is small, so I need something that doesn't have a large minimum charge. I'm thinking $10 - 30 per month. Are there any cloud services like that that run Haskell? D

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