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[ANN] dejafu-2.0.0.0 - a library for unit-testing concurrent programs
by Michael Walker 13 Feb '19

13 Feb '19

I'm pleased to announce a new super-major release of [dejafu][1], a library for testing concurrent Haskell programs. While there are breaking changes, common use-cases shouldn't be affected too significantly (or not at all). There is a brief guide to the changes, and how to migrate if necessary, [on the website][2]. What's dejafu? -------------- dejafu is a unit-testing library for concurrent Haskell programs. Tests are deterministic, and work by systematically exploring the possible schedules of your concurrency-using test case, allowing you to confidently check your threaded code. [HUnit][3] and [Tasty][4] bindings are available. dejafu requires your test case to be written against the `MonadConc` typeclass from the [concurrency][5] package. This is a necessity, dejafu cannot peek inside your `IO` or `STM` actions, so it needs to be able to plug in an alternative implementation of the concurrency primitives for testing. There is some guidance for how to switch from `IO` code to `MonadConc` code [on the website][6]. If you really need `IO`, you can use `MonadIO` - but make sure it's deterministic enough to not invalidate your tests! Here's a small example reproducing a deadlock found in an earlier version of the [auto-update][7] library: ``` > :{ autocheck $ do auto <- mkAutoUpdate defaultUpdateSettings auto :} [fail] Successful [deadlock] S0--------S1-----------S0- [fail] Deterministic [deadlock] S0--------S1-----------S0- () S0--------S1--------p0-- ``` dejafu finds the deadlock, and gives a simplified execution trace for each distinct result. More in-depth traces showing exactly what each thread did are also available. This is using a version of auto-update modified to use the `MonadConc` typeclass. The source is in the [dejafu testsuite][8]. What's new? ----------- The highlights for this release are setup actions, teardown actions, and invariants: - **Setup actions** are for things which are not really a part of your test case, but which are needed for it (for example, setting up a test distributed system). As dejafu can run a single test case many times, repeating this work can be a significant overhead. By defining this as a setup action, dejafu can "snapshot" the state at the end of the action, and efficiently reload it in subsequent executions of the same test. - **Teardown actions** are for things you want to run after your test case completes, in all cases, even if the test deadlocks (for example). As dejafu controls the concurrent execution of the test case, inspecting shared state is possible even if the test case fails to complete. - **Invariants** are effect-free atomically-checked conditions over shared state which must always hold. If an invariant throws an exception, the test case is aborted, and any teardown action run. Here is an example of a setup action with an invariant: ``` > :{ autocheck $ let setup = do var <- newEmptyMVar registerInvariant $ do value <- inspectMVar var when (value == Just 1) $ throwM Overflow pure var in withSetup setup $ \var -> do fork $ putMVar var 0 fork $ putMVar var 1 tryReadMVar var :} [fail] Successful [invariant failure] S0--P2- [fail] Deterministic [invariant failure] S0--P2- Nothing S0---- Just 0 S0--P1--S0-- ``` In the `[invariant failure]` case, thread 2 is scheduled, writing the forbidden value "1" to the MVar, which terminates the test. Here is an example of a setup action with a teardown action: ``` > :{ autocheck $ let setup = newMVar () teardown var (Right _) = show <$> tryReadMVar var teardown _ (Left e) = pure (show e) in withSetupAndTeardown setup teardown $ \var -> do fork $ takeMVar var takeMVar var :} [pass] Successful [fail] Deterministic "Nothing" S0--- "Deadlock" S0-P1--S0- ``` The teardown action can perform arbitrary concurrency effects, including inspecting any mutable state returned by the setup action. Setup and teardown actions were previously available in a slightly different form as the `dontCheck` and `subconcurrency` functions, which have been removed (see the migration guide if you used these). [1]: http://hackage.haskell.org/package/dejafu [2]: https://dejafu.readthedocs.io/en/latest/migration_1x_2x.html [3]: http://hackage.haskell.org/package/hunit-dejafu [4]: http://hackage.haskell.org/package/tasty-dejafu [5]: http://hackage.haskell.org/package/concurrency [6]: https://dejafu.readthedocs.io/en/latest/typeclass.html [7]: http://hackage.haskell.org/package/auto-update [8]: https://github.com/barrucadu/dejafu/blob/master/dejafu-tests/lib/Examples/A… -- Michael Walker (http://www.barrucadu.co.uk)

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Weird defaulting on newEmptyTMVar
by Ruben Astudillo 12 Feb '19

12 Feb '19

Dear list Playing on ghci I encountered the following type GHCi, version 8.6.3: http://www.haskell.org/ghc/ :? for help Prelude> :m +Control.Concurrent.STM Prelude Control.Concurrent.STM> var1 <- atomically $ newEmptyTMVar Prelude Control.Concurrent.STM> :t var1 var1 :: TMVar GHC.Types.Any Prelude Control.Concurrent.STM> I would think `var1 :: TMVar a` as the documentation says it should. Reading on `GHC.Types` `Any` seems to be a type family related to some laws on `unsafeCoerce`. Can anybody explain me why is this sensible defaulting and how to obtain the expected result? -- -- Ruben -- pgp: 4EE9 28F7 932E F4AD

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Taking over haskell-src-meta
by Dan Burton 11 Feb '19

11 Feb '19

I, Dan Burton, intend to take over maintenance of haskell-src-meta. -- Dan Burton

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Re: [Haskell-cafe] ANN:DBFunctor-0.1.1.0 - Functional Data Management / ETL Data Processing in Haskell
by Olaf Klinke 11 Feb '19

11 Feb '19

Dear Nikos, (not CC'ing the list yet because I don't know whether my remarks miss the design goals of DBFunctor) As a data scientist I have some questions regarding the design of DBFunctor. 1. Why is RTable, or rather RDataType a closed type? Was this forced by compatibility to other databases? There might be RTabular Types whose elements are hard to represent as RDataType, or the conversion deletes some of the data's semantics. What is the essence that makes the operations in the Julius language work? For example, the inner join could have the more general type MonadPlus m => (a -> b -> Bool) -> m a -> m b -> m (a,b) 2. Is there a way of saying that a column may not contain NULL values? 3. What about the efficiency of the operations? I see no complexities stated in the documentation of Etl.Julius. 4. I like the feature of named operations (:=>). But can we bind a sub-operation to a Haskell variable without leaving Julius? After all, takeNamedResult can lead to exceptions because the user may reference a name that has not been defined. With haskell variables, the compiler prevents this. Why not make the Julius language a monad, so that one can use do-notation for building the result? E.g. type JuliusExpr = JuliusLang RTable instance Monad JuliusLang where ... Kind regards, Olaf

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erd package looking for maintainer - beginner friendly
by Niklas Hambüchen 11 Feb '19

11 Feb '19

`erd` https://github.com/BurntSushi/erd is a Haskell package that creates pretty diagrams from simple textual descriptions. It's made by @BurntSushi (https://github.com/BurntSushi) author of `ripgrep` and several Rust tools and packages. He's looking for help maintaining this older project of his, which many people still find very useful. >From my judgement, the code is fairly beginner friendly, so if you are new-intermediate in Haskell, understand the concepts involved in the package, and want to get into package maintainership, this might be a good start. Details on https://github.com/BurntSushi/erd/issues/42

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Reminder: Call for papers: DBPL 2019
by Alvin Cheung 10 Feb '19

10 Feb '19

Reminder: deadline approaching soon! ---------------------------------------------------------------------- The 17th International Symposium on Database Programming Languages https://pldi19.sigplan.org/track/dbpl-2019-papers Phoenix, Arizona, USA June 23, 2019 hosted as part of PLDI 2019 Call for Papers For over 25 years, DBPL has established itself as the principal venue for publishing and discussing new ideas at the intersection of databases and programming languages. Many key contributions in query languages for object-oriented data, persistent databases, nested relational data, and semistructured data, as well as fundamental ideas in types for query languages, were first announced at DBPL. Today, this creative research area is broadening into a subfield of data-centric computation, currently scattered among a range of venues. DBPL is an established destination for such new ideas and solicits submissions from researchers in databases, programming languages or any other community interested in the design, implementation or foundations of data-centric computation. Scope ----- DBPL solicits practical and theoretical papers in all topics at the intersection of databases and programming languages. Papers emphasizing new topics or emerging areas are especially welcome. Suggested, but not exclusive, topics of interest for submissions include: - Compiling Query Languages to Modern Hardware - Data-Centric Programming Abstractions, Comprehensions, Monads - Data Integration, Exchange, and Interoperability - Data Synchronization and Bidirectional Transformations - Declarative Data Centers (e.g., distributed query processing, serverless computing platforms, social computing platforms, etc) - Emerging and Nontraditional Data Models - Language-Based Security in Data Management - Language-Integrated Query Mechanisms - Managing Uncertain and Imprecise Information - Metaprogramming and Heterogeneous Staged Computation - Programming Language Support for Data-Centric Programming (e.g., databases, web programming, machine learning, etc) - Query Compilation and In-memory Databases - Query Language Design and Implementation - Query Transformation and Optimization - Schema Mapping and Metadata Management - Semantics and Verification of Database Systems - Stream Data Processing and Query Languages - Type and Effect Systems for Data-Centric Programming Author Guidelines ----------------- Prospective authors are invited to submit full papers in English presenting original research. Submitted papers must be unpublished and not submitted for publication elsewhere. Submissions should be no more than 10 pages long, excluding references, in the two-column ACM proceedings format, following PLDI’s formatting requirements (https://pldi19.sigplan.org/track/pldi-2019-papers#Call-for-Papers) Each submission should begin with a succinct statement of the problem and a summary of the main results. Authors may provide more details to substantiate the main claims of the paper by including a clearly marked appendix at the end of the submission, which is not included in the page limit and is read at the discretion of the committee. At least one author of each accepted paper must attend the symposium to present their work. Short papers of at most 4 pages (same format as long papers) describing work in progress, demos, research challenges or visions are also welcome. Accepted short papers may be included or excluded from the formal proceedings, whichever the author(s) prefer. Full and short papers are both due on the deadline, February 15, 2019. Instructions on how to submit will be posted on the symposium website noted above. Review is single-blind, so authors do not need to anonymize their submissions. PC submissions are allowed, except for the co-chairs. Important Dates --------------- - Paper Submission: February 15, 2019 - Notification: March 29, 2019 - Final versions due: April 16, 2019 - Symposium: June 23, 2019 Proceedings ----------- Accepted papers will appear as part of the PLDI Proceedings for DBPL 2019. Program Committee ----------------- *Program Co-Chairs* Alvin Cheung, University of Washington Kim Nguyễn, Université Paris-Sud *Program Committee* William Cook, University of Texas at Austin Vasiliki Kalavri, ETH Harshad Kasture, Oracle Oleg Kiselyov, University of Tsukuba Sam Lindley, University of Edinburgh Tiark Rompf, Purdue University Stefanie Scherzinger, OTH Regensberg Amir Shaikhha, EPFL / University of Oxford Avi Shinnar, IBM Guido Wachsmuth, Oracle Melanie Wu, Pomona College History ------- The 17th Symposium on Data Base Programming Languages (DBPL 2019) continues the tradition of excellence initiated by its predecessors in Roscoff, Finistere (1987), Salishan, Oregon (1989), Nafplion, Argolida (1991), Manhattan, New York (1993), Gubbio, Umbria (1995), Estes Park, Colorado (1997), Kinloch Rannoch, Scotland (1999), Marino, Rome (2001), Potsdam, Germany (2003), Trondheim, Norway (2005), Vienna, Austria (2007), Lyon, France (2009), Seattle, Washington (2011), Riva del Garda, Italy (2013), Pittsburgh, Pennsylvania (2015), Munich, Germany (2017). DBPL was affiliated with VLDB from 1999-2013 and in 2017. In 2015, it is affiliated with SPLASH for the first time and in 2019, it is affiliated with PLDI for the first time.

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ANN:DBFunctor-0.1.1.0 - Functional Data Management / ETL Data Processing in Haskell
by Nikos Karagiannidis 10 Feb '19

10 Feb '19

Dear all, I am pleased to announce the release of *DBFunctor 0.1.1.0* https://hackage.haskell.org/package/DBFunctor-0.1.1.0 DBFunctor is a Haskell library for ETL (Extract Transform and Load) data processing. It comes with an embedded type-level DSL called *Julius* that enables full SQL functionality over tabular data (e.g., CSV files) but also the ability to write a full ETL data processing flow. Currently, DBFunctor can be used for *in-memory data processing* in Haskell, without the need for some external database. The most notable change in this new release is the full support of *DML (Data Manipulation Language) operations*. I.e., Insert (single tuple), Insert-Into-Select, Delete, Update, *Upsert *(Merge) operations have been implemented along with the corresponding Julius clauses. Other changes includes: - Implemented string aggregate function string_agg (listagg in Oracle) and the corresponding Julius clause - Implemented Julius Aggregate clauses: CountDist and CountStar (count(distinct col) clause and count(*)) - Implemented semi-join operation and corresponding Julius clause - Implemented anti-join operation and corresponding Julius clause - Added support for UTCTime values - Solved CSV orphan instances problem - Various other fixes For any issues/problems with the DBFunctor package please open an issue on github. Happy data processing! Thank you. Best Regards, Nikos

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[TFP'19] first call for papers: Trends in Functional Programming 2019, 12-14 June 2019, Vancouver, BC, CA (corrected dates and instructions)
by Peter Achten 08 Feb '19

08 Feb '19

------------------------------- C A L L F O R P A P E R S ------------------------------- ====== TFP 2019 ====== 20th Symposium on Trends in Functional Programming 12-14 June, 2019 Vancouver, BC, CA https://www.tfp2019.org/index.html == Important Dates == Submission Deadline for pre-symposium formal review Thursday, March 28, 2019 Sumbission Deadline for Draft Papers Thursday, May 9, 2019 Notification for pre-symposium submissions Thursday, May 2, 2019 Notification for Draft Papers Tuesday, May 14, 1029 TFPIE Tuesday, June 11, 2019 Symposium Wednesday, June 12, 2019 – Friday, June 14, 2019 Notification of Student Paper Feedback Friday June 21, 2019 Submission Deadline for revised Draft Papers (post-symposium formal review) Thursday, August 1, 2019 Notification for post-symposium submissions Thursday, October 24, 2019 Camera Ready Deadline (both pre- and post-symposium) Friday, November 29, 2019 The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below at scope). Please be aware that TFP uses two distinct rounds of submissions (see below at submission details). TFP 2019 will be the main event of a pair of functional programming events. TFP 2019 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 11. == Scope == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: Leading-edge, previously unpublished research work Position Articles: On what new trends should or should not be Project Articles: Descriptions of recently started new projects Evaluation Articles: What lessons can be drawn from a finished project Overview Articles: Summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2019 program chairs, William J. Bowman and Ron Garcia. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Instructions to Author == Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2019 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Pre-symposium formal review == Papers to be formally reviewed before the symposium should be submitted before an early deadline and receive their reviews and notification of acceptance for both presentation and publication before the symposium. A paper that has been rejected in this process may still be accepted for presentation at the symposium, but will not be considered for the post-symposium formal review. == Post-symposium formal review == Papers submitted for post-symposium review (draft papers) will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback received at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == There are two types of submission, each of which can be submitted either for pre-symposium or post-symposium review: Extended abstracts. Extended abstracts are 4 to 10 pages in length. Full papers. Full papers are up to 20 pages in length. Each submission also belongs to a category: research position project evaluation overview paper Each submission should clearly indicate to which category it belongs. Additionally, a draft paper submission—of either type (extended abstract or full paper) and any category—can be considered a student paper. A student paper is one for which primary authors are research students and the majority of the work described was carried out by the students. The submission should indicate that it is a student paper. Student papers will receive additional feedback from the PC shortly after the symposium has taken place and before the post-symposium submission deadline. Feedback is only provided for accepted student papers, i.e., papers submitted for presentation and post-symposium formal review that are accepted for presentation. If a student paper is rejected for presentation, then it receives no further feedback and cannot be submitted for post-symposium review. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site (http://www.springer.com/lncs) == Program Committee == Program Co-chairs William J. Bowman University of British Columbia Ronald Garcia University of British Columbia Matteo Cimini University of Massachusetts Lowell Ryan Culpepper Czech Technical Institute Joshua Dunfield Queen's University Sam Lindley University of Edinburgh Assia Mahboubi INRIA Nantes Christine Rizkallah University of New South Wales Satnam Singh Marco T. Morazán Seton Hall University John Hughes Chalmers University and Quviq Nicolas Wu University of Bristol Tom Schrijvers KU Leuven Scott Smith Johns Hopkins University Stephanie Balzer Carnegie Mellon University Viktória Zsók Eötvös Loránd University

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PhD studentships in FP at Bristol
by Meng Wang 07 Feb '19

07 Feb '19

Hi list, The programming language group at the University of Bristol is looking for up to three more PhD students in the broad area of functional programming, verification, and testing to join a very dynamic group of FP researchers. http://www.bristol.ac.uk/engineering/departments/computerscience/people/men… http://www.bristol.ac.uk/engineering/departments/computerscience/people/ste… http://www.bristol.ac.uk/engineering/departments/computerscience/people/nic… The positions are fully funded, and with additional bursaries for attending conferences. The ideal candidates will have a strong background in functional programming, especially Haskell, and an appetite for cutting-edge research. For enquiries, please email meng.wang(a)bristol.ac.uk<mailto:meng.wang@bristol.ac.uk> before February 22nd. Best regards, Meng

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Anyone around Edinburgh or Glasgow second half of April?
by Robin Palotai 07 Feb '19

07 Feb '19

Hello, I'm planning a family trip to Edinburgh late April, thought it would be nice to meet with local Haskellers as well. It would be a plus if could give us a quick tour of the campus. I'm also glad to receive advice on geeky things to see [1] in the area (computer museums, whatever). Thank you! Robin [1] Non-geeky as well, but I expect my spouse to have that area covered.

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