- Haskell-Cafe - Haskell.org

property testing with context
by Ben Franksen 24 Oct '18

24 Oct '18

Hi everyone it seems to be the season for new variations on the "property testing" theme, so I would like to chime in... not to announce a new library, sadly, but with a rough idea how the existing ones could perhaps be improved, based on practical experience in Darcs. The problem I have is that there is a tension between (a) stating a property in a clear and simple way, so its code doubles as a formal specification and (b) writing the property in such a way that when it fails, the reported value(s) give enough information about the context to be useful for finding the cause of the problem. Let me give an example to demonstrate what I mean. There is a simple law that says if a sequential pair of patches A;B commutes to B';A' then B';A' commutes back to A;B. In code this looks (more or less) like this: prop_recommute :: Commute p => (p :> p) wA wB -> Bool prop_recommute (x:>y) | Just (y':>x') <- commute (x:>y) = case commute (y':>x')of Just (x'':>y'') -> x==x'' && y==y'' Nothing -> False | otherwise = True This is a bit more verbose than the informal spec but still quite readable. Now suppose this property fails. So quickcheck reports the counter example pair (X:>Y) for some X and Y. But that isn't too useful in itself. We'd like to know a bit more: * did the second commute fail? * or did it succeed but x/=x'' or y/=y''? * and in the latter case, which of the two? So in practice our property code looks more like this: prop_recommute :: (ShowPatch p, Commute p) => (p :> p) wA wB -> Bool prop_recommute (x :> y) | Just (y' :> x') <- commute (x :> y) = case commute (y' :> x') of Nothing -> failed (redText "failed, where x" $$ displayPatch x $$ redText ":> y" $$ displayPatch y $$ redText "y'" $$ displayPatch y' $$ redText ":> x'" $$ displayPatch x') Just (x'' :> y'') -> if y'' /= y then failed (redText "y'' =/\\= y failed, where x" $$ displayPatch x $$ redText ":> y" $$ displayPatch y $$ redText "y'" $$ displayPatch y' $$ redText ":> x'" $$ displayPatch x' $$ redText "x''" $$ displayPatch x'' $$ redText ":> y''" $$ displayPatch y'') else if x'' /= x then failed (redText "x'' /= x, where x" $$ displayPatch x $$ redText ":> y" $$ displayPatch y $$ redText "y'" $$ displayPatch y' $$ redText ":> x'" $$ displayPatch x' $$ redText "x''" $$ displayPatch x'' $$ redText ":> y''" $$ displayPatch y'') else True | otherwise = True Now this code tells us exactly what went wrong when the property fails but it is ugly and repetitive and the additional code obscures the simple logical content. So this is no longer quite as suitable for a (human readable) formal spec. I wonder if displaying (1) all relevant contextual variables and (2) "where in the code it fails" could be automated away, somehow. I guess this is not trivial and may require syntactic analysis, so perhaps expecting a /library/ to solve the problem is unrealistic, except perhaps by using Template Haskell. I'd also go with a separate tool that extracts properties from a module and enriches them with code that displays the additional information. Tackling this problem might be an interesting theme for a master thesis... ;-) Cheers Ben

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Has twidge stopped working?
by Rider of Giraffes 24 Oct '18

24 Oct '18

Greetings, New on the list, apologies if I break any traditions. Sent here from https://github.com/jgoerzen/twidge/wiki with the question in the header. I sent a tweet via twidge on Oct 22, but since then nothing has got through. Has twidge stopped working? Has Twitter made yet another change to the API, this one incompatible? All assistance and advice welcome. Thank you. -- I don't suffer from stress - I'm a carrier.

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Re: [Haskell-cafe] property testing with context
by Olaf Klinke 24 Oct '18

24 Oct '18

Ben, the solution might be simple: Don't express the property as an atomic function (a -> Bool). This reminds me a bit of the Cutty-Howard correspondence, only that proofs are replaced by counterexamples. A testing library should have an operator for each of the logical connectives, where - a counterexample to True is never found - a counterexample to False is () - a counterexample to (not x) is an example for x - a counterexample to (x && y) is either a counterexample to x or a counterexample to y, whichever is found first - a counterexample to (x || y) is a pair of counterexamples to both x and y - a counterexample to (x ==> y) is an example for x together with a counterexample for y Then, if you build your property out of smaller properties and the connectives above, the counterexample-finder would be able to inform you which part of the property failed. I'm pretty sure at least one of the testing libraries has a system like this. Cheers, Olaf

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ANN: Yampa-0.12 and yampa-test (QuickCheck-based FRP testing)
by Ivan Perez 22 Oct '18

22 Oct '18

Dear all, I am please to announce version 0.12 of Yampa! Yampa is a mature and robust FRP implementation that has been used to create mobile, desktop, and web games and applications, including commercial mobile games available on iTunes and Google Play, and open source games that use devices like wiimotes and kinect [1-2]. This version comes with an accompanying library, yampa-test, which includes QuickCheck-based testing with LTL-based signal predicates. These features are described in the ICFP 2017 paper "Testing and Debugging Functional Reactive Programming" [3]. Thanks to Christina Zeller for reporting bugs. Both libraries can be found here: http://hackage.haskell.org/package/Yampa http://hackage.haskell.org/package/yampa-test This version has been tested against all major GHC versions from 7.6 to 8.6. Some legacy code has been deprecated, which has triggered a major version bump (0.12). I would expect all projects that use Yampa to work by, at most, adapting the version constraints in the cabal files. New versions of Yampa will present a simpler API, better documentation and benchmarks [4]. As always, contributions are welcome. There are a number of issues on the github page that are particularly suitable for beginners [5]. Happy Haskelling! Ivan [1] https://github.com/ivanperez-keera/Yampa#other-examples [2] https://haskell.games [3] https://dl.acm.org/citation.cfm?id=3110246 [4] https://github.com/ivanperez-keera/Yampa/milestones [5] https://github.com/ivanperez-keera/Yampa/labels/help%20wanted

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(Sample) bioinformatics applications
by Vasili I. Galchin 22 Oct '18

22 Oct '18

Hello, Do any of these beasts exist for reference? Regards, Vasily

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Well typed OS
by Yotam Ohad 22 Oct '18

22 Oct '18

Hi, In the last couple of days, I've been toying with the thought of an operating system in which programs (or more accurately, any process) has a distinct type which limits its use of the machine. For example, `echo` (String -> String) won't be able to print an output without a second program which would handle changing stdout. I think it could "break down" the IO monad into other structures that are better at specifying what is changing: A file is read / memory written / etc. I do, however, not sure how to incorporate drivers (which handles IO and external devices) into this. Giving them an `IO a` type feels like cheating. I would be much cooler if there was a way to treat them like the `echo` function from earlier. What are your thoughts/suggestions? I'll be happy to hear them. Yotam

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Why is the Cabal User's Guide left outdated?
by Yuji Yamamoto 20 Oct '18

20 Oct '18

Getting interested in the features since Cabal 2.2 (esp. common stanzas), I looked up with the User's Guide <https://www.haskell.org/cabal/users-guide/>, which is (and should be) listed in the search result first, but can't find because the User's Guide is still about Cabal 2.0. Why is it left outdated? Actually User's Guide (HEAD) <https://cabal.readthedocs.io/en/latest/> is kept updated, but it's hard to find, and can include some information too new to release. Thanks in advance. -- 山本悠滋 twitter: @igrep GitHub: https://github.com/igrep GitLab: https://gitlab.com/igrep Facebook: http://www.facebook.com/igrep Google+: https://plus.google.com/u/0/+YujiYamamoto_igrep

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"Update
by Nikita Fufaev 20 Oct '18

20 Oct '18

-- Nikita Fufaev, +7 999 825-95-07

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BOB - Call for Contributions 2019
by Matthias Fischmann 19 Oct '18

19 Oct '18

Subject: Call for Contributions: BOB 2019 - Berlin, Mar 22, 2019 BOB Conference 2019 "What happens when we use what's best for a change?" http://bobkonf.de/2019/en/cfc.html Berlin, March 22 Call for Contributions Deadline: November 23, 2018 You are actively engaged in advanced software engineering methods, implement ambitious architectures and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! NOTE: The conference fee will be waived for presenters. Travel expenses will not be covered (for exceptions see "Speaker Grants"). Speaker Grants BOB has Speaker Grants available to support speakers from groups under-represented in technology. We specifically seek women speakers and speakers who are not be able to attend the conference for financial reasons. Shepherding The program committee offers shepherding to all speakers. Shepherding provides speakers assistance with preparing their sessions, as well as a review of the talk slides. Topics ------ We are looking for talks about best-of-breed software technology, e.g.: - functional programming - persistent data structures and databases - types - formal methods for correctness and robustness - abstractions for concurrency and parallelism - metaprogramming - probabilistic programming - math and programming - controlled side effects - beyond REST and SOAP - effective abstractions for data analytics - ... everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. We're especially interested in experience reports. Other topics are also relevant, e.g.: - introductory talks on technical background - overviews of a given field - demos and how-tos Requirements ------------- We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. Your proposal should include (in your presentation language of choice): - An abstract of max. 1500 characters. - A short bio/cv - Contact information (including at least email address) - A list of 3-5 concrete ideas of how your work can be applied in a developer's daily life - additional material (websites, blogs, slides, videos of past presentations, …) Submit here: https://bobcfc.active-group.de/en/bob2019/cfp Organisation ------------ - Direct questions to contact at bobkonf dot de - Proposal deadline: November 23, 2018 - Notification: December 7, 2018 - Program: December 21, 2018 Program Committee ----------------- (more information here: http://bobkonf.de/2019/en/programmkomitee.html) - Matthias Fischmann, zerobuzz UG - Matthias Neubauer, SICK AG - Nicole Rauch, Softwareentwicklung und Entwicklungscoaching - Michael Sperber, Active Group - Stefan Wehr, factis research Scientific Advisory Board - Annette Bieniusa, TU Kaiserslautern - Torsten Grust, Uni Tübingen - Peter Thiemann, Uni Freiburg

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Fwd: [Haskell] Help inform GHC's development priorities
by Takenobu Tani 19 Oct '18

19 Oct '18

(It is sending to the correct address of haskell-cafe ML.) ---------- Forwarded message --------- From: Ben Gamari <ben(a)well-typed.com> Date: Fri, Oct 19, 2018 at 4:45 AM Subject: [Haskell] Help inform GHC's development priorities To: GHC developers <ghc-devs(a)haskell.org>, <haskell(a)haskell.org>, Haskell Cafe <haskell-cafe(a)googlegroups.com>, GHC users < glasgow-haskell-users(a)haskell.org> tl;dr. Please a take a minute to express your thoughts on GHC's development priorities via this survey [1]. Hello everyone, The GHC developers want to ensure that we are working on problems that of most importance to you, the Haskell community. To this end we are surveying the community [1], asking how our users interact with GHC and which problems need to be addressed most urgently. We hope you will take a few minutes to give us your thoughts [1]. Thanks in advance for your time and, finally, thanks to the financial supporters that make our work GHC possible. Cheers, - Ben and the rest of the GHC developers [1] https://docs.google.com/forms/d/e/1FAIpQLSdh7sf2MqHoEmjt38r1cxCF-tV76OFCJqU… _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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