- Haskell-Cafe - Haskell.org

Applicative transformers
by Laurent Christophe 16 Feb '17

16 Feb '17

Hi guys, the way `StateT` are implemented as `Applicative` have been buggling my mind for some time. https://hackage.haskell.org/package/transformers-0.5.2.0/docs/src/Control.M… <https://hackage.haskell.org/package/transformers-0.5.2.0/docs/src/Control.M…> instance (Functor m, Monad m) => Applicative (StateT s m) where pure a = StateT $ \ s -> return (a, s) StateT mf <*> StateT mx = StateT $ \ s -> do (f, s') <- mf s (x, s'') <- mx s' return (f x, s'') Using dependant monadic computations, this implementation cannot be expressed in term of applicative. This explains why we cannot have `instance (Applicative m) => Applicative (State s m)`. However using real monadic style computations for implementing `<*>` buggles my mind. Moreover `liftA2 (<*>)` can be used to generically compose applicative functors so why monads are needed? https://www.haskell.org/haskellwiki/Applicative_functor#Applicative_transfo… <https://www.haskell.org/haskellwiki/Applicative_functor#Applicative_transfo…> Any inputs would be greatly appreciated! Cheers, Laurent

3 2

1st call for papers: Trends in Functional Programming, 19-21 june 2017, University of Kent, Canterbury
by Peter Achten 15 Feb '17

15 Feb '17

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2017 =========== 18th Symposium on Trends in Functional Programming 19-21 June, 2017 University of Kent, Canterbury https://www.cs.kent.ac.uk/events/tfp17/index.html 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). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. TFP 2017 will be the main event of a pair of functional programming events. TFP 2017 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on 22 June. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * Soesterberg (The Netherlands) in 2014; * Inria Sophia-Antipolis (France) in 2015; * and Maryland (USA) in 2016. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == 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 2017 program chairs, Scott Owens and Meng Wang. == 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. == SPONSORS == TBD == PAPER SUBMISSIONS == Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp17 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/computer/lncs?SGWID=0-164-6-793341-0 == IMPORTANT DATES == Submission of draft papers: 5 May, 2017 Notification: 12 May, 2017 Registration: 11 June, 2017 TFP Symposium: 19-21 June, 2017 Student papers feedback: 29 June, 2017 Submission for formal review: 2 August, 2017 Notification of acceptance: 3 November, 2017 Camera ready paper: 2 December, 2017 == PROGRAM COMMITTEE == TBD

1 0

Re: [Haskell-cafe] Lenses and records and ecosystem
by Anthony Clayden 15 Feb '17

15 Feb '17

> On Sat, Feb 11, 2017 at 21:04, David Menendez wrote: > > On Fri, Feb 10, 2017 at 7:53 PM, Anthony Clayden wrote: > > > > Certainly (.) for lenses works 'backwards' > > (i.e. suffix style) > > compared to function-prefix style. > > (As any Lens tutorial will say.) > > > > Those tutorials are oversimplifying. Thank you David, ho hum I'm not getting much feedback about ecosystem/ co-existence; nor a specialised composition operator. > Lenses (and their relatives) transform operations, not values. So it must be a stubborn superstition on my part that getting/putting from/to structures is about values. I'm not here to 'knock' lenses (of whichever model), but every time I scratch the surface, the answers wander off into category theory and higher-order types. I'll draw a comparison with another place in Haskell where category theory has huge benefits: monads. There's less than a handful of operators for monads, and those are conveniently handled behind some elegant syntactic sugar (do-notation). So a newbie doesn't really need to grok monads. They can get on and use them; learn the theory later. Can that be said of lenses? I guess part of the trouble is that H98 record operations have gobbled up so much of the syntactic design space. Nevertheless I don't see what syntactic sugar could help with lenses. > Composition of lenses is exactly like composition of functions, with > the inner-most operation on the right. That doesn't seem to say more than "it's composition". If I want to get a foo out of a bar out of a baz in a s, I'd (perhaps naievely) go foo (bar (baz s)) -- i.e. (foo . bar . baz) s And I'm using function application all the way through. I'd only think of doing s.baz.bar.foo If I was trying to mimic OO style methods. And anyway with lenses, that's exactly what I _can't_ do. Lenses do not use function application of the lens to the structure. You need an extra operator (view, over). Then I'm not seeing the syntactic merit of using composition (.) for lenses. It's certainly making the mental machinery incompatible for lenses vs records, even if they can co-exist semantically. > A lens foo :: Lens > O I transforms an operation on I into an operation on O. A > composition outer.inner turns an operation on the target > of inner into an operation on the source of outer. > > This is demonstrated by the way over distributes with (.): > > over (outer . inner) = over outer . over inner > > What confuses people is view, which is contravariant: > > view (outer . inner) = view inner . view outer > > but you can't avoid having one of over and view be > contravariant. OK. (Why did it need so much category theory to explain that?) And why do those nifty equivalences have to intrude so much into the surface syntax, just to get a value out of a structure? AntC

2 1

Haskell.org committee financial statement 2016
by Gershom B 15 Feb '17

15 Feb '17

Dear Haskellers, The Haskell.org Committee [1] manages funds for haskell.org and oversees haskell.org infrastructure. The funds available to Haskell.org have historically come from two sources: 1) Mentor payments from the Google Summer of Code program. 2) Donations [2] from the Haskell community at large. Haskell.org is a registered 501(c)3 nonprofit. A portion of our funds are held by Software in the Public Interest, also a 501(c)3 US non-profit, through which we also accept donations. In 2016 we were not accepted into the GSoC program, and ran a summer of haskell program along similar lines, funded by earmarked donations provided by individual and corporate sponsors and from our pool of general funds. A full list of sponsors is on the soh webpage [3]. According to our charter, "Each year, the committee will post a statement of the haskell.org assets, and the transactions for that year." Included in this message is a brief statement of Haskell.org assets over the period 1 December 2015 - 31 December 2016. Aside from the SOH disbursements, our expenses are nearly entirely hosting, with a small overhead incurred by payment processing. SOH thus accounts for both our increased revenue (in the form of earmarked donations) and expenses this year. We do not have full statements from our SPI account yet, as their treasury reports are only complete through october at this time [4] although I hope that will be changed shortly. So this statement is produced as though the income and expenses on our spi account for the last for months of 2016 were net zero, though that was obviously not the case. Even in this incomplete state, I think it is better to provide this than nothing. Additionally, as this covers holdings in our haskell.org bank account, it does not reflect when funds received via paypal donations, are received by paypal, but rather when the lump sum transfers from them are received by us. So paypal donations made in December 2016, for example, will likely be reflected in our 2017 statement. A portion of the income in 2016 is also attributable to gsoc mentor payment from our participation in the 2015 program. Thanks to many generous donations, despite the substantial haskell summer of code expenditures, we are nonetheless net-positive in income (though the difference just about amounts to the outstanding gsoc payments from 2015). We hope to find good opportunity to put our reserves to use again in the coming year. 1. Income and Expenses Total revenue over 2016: 54,802.56 Total expenses over 2016: 48,344.05 ---- Net income over 2016: 6,458.51 2. Total Balance Balance as of 31 December 2015: 32,882.34 Balance as of 31 December 2016: 39,340.85 [1] https://wiki.haskell.org/Haskell.org_committee [2] https://wiki.haskell.org/Donate_to_Haskell.org [3] https://summer.haskell.org/ [5] http://spi-inc.org/treasurer/reports/ Best, Gershom for the Haskell.org Committee

1 0

Loading JSON into a set of nested index-able structures
by Carl Petersen 15 Feb '17

15 Feb '17

Hello All, I've used Aeson to load a JSON object with nested lists into a set of data structures, but what I really need is to load it into a set of data structures that are index-able such as a HashMap. I've had success loading the JSON into a structure with the lowest level being a HashMap using !Object, but I'm having difficulty in figuring out how to nest the HashMaps. Any hints or direction would be appreciated. Thanks, Carl

1 1

Extensible records & mandatory/optional record fields
by Harendra Kumar 15 Feb '17

15 Feb '17

In my application, I want some of the fields in a record to have default values while others must always be specified by the user. I can implement this using the rawr records library (http://hackage.haskell.org/package/rawr) like so: def :: ("b" := String) -> R ("a" := Int, "b" := String) def t = (R (#a := 0) :*: R t) -- merge with defaults let r = def (#b := "hello") Here field "a" has a default value (i.e. it is optional when "def" is used) but field "b" does not have a default value and has to be explicitly specified by the user. This is made possible by record merging feature of rawr, making the record extensible. I could not find an equivalent way of achieving this using overloaded records (http://hackage.haskell.org/package/overloaded-records) Is record merging possible or can be made possible using overloaded-records or with the ghc overloaded records poposal? If not, is there a plan to make something like this possible in future? Or will this never be possible with the in built record syntax? Note that, this is handy to simulate mandatory and optional keyword arguments to a function by passing them in the form of a record. Something which is available in other languages like python. -harendra

1 0

Myrtle Software is hiring for Haskell positions in Hardware and Machine Learning!
by Joe Hermaszewski 14 Feb '17

14 Feb '17

Myrtle is looking for multiple skilled Haskell developers to join our growing development team writing a compiler for generating highly efficient hardware designs implementing machine learning solutions. We use Haskell for every aspect of our work and developers will get the chance to be involved in every part of the project. As an example, some things we’ve worked on recently are a tiny CPU to implement a custom network protocol to communicate between a PC and an FPGA and a Haskell implementation of part of the Caffe deep learning framework. Specific tasks you could be working on soon include: implementing fixed point neural network evaluation support in our compiler, supporting AWS F1 instances as a backend, investigating and implementing exciting techniques for neural network evaluation such as the Winograd small convolution algorithm and realising full hardware implementations of existing neural networks. A familiarity and interest with hardware design would be viewed positively but is not essential. Applicants should be familiar with Unix based systems; all our development is done on Ubuntu or NixOS. Applicants should send a resume and covering email, stating your suitability for this role, to jobs(a)myrtlesoftware.com. Please include any links to blog posts, repositories or any other media which demonstrates your skill set. Roles will be based at our offices in Cambridge, UK. Closing date for applications 5pm, 13th March 2017 About Myrtle Myrtle is a software company based in Cambridge UK with a long history of working at the forefront of compiler technology. We are best known for having helped produce computer generated images for over twenty major Hollywood movies including the Transformers franchise. Myrtle’s clients have included NYSE and NASDAQ listed companies in LA, Vancouver and London. -- Joe https://www.myrtlesoftware.com/vacancies/

1 0

Re: [Haskell-cafe] Sublime2/3 hsdev patch: testers needed
by Ara Adkins 14 Feb '17

14 Feb '17

Looks like this has fixed an issue I've been having! Seems to have just been merged into master as of ~4 hours ago at the time of writing. Thanks Scott! - Ara > On 13 Feb 2017, at 06:40, Scott Michel <scooter.phd(a)gmail.com> wrote: > > Was wondering if there are any Sublime Text users out there who also use hsdev as their Haskell IDE backend. I'd recently (within the last 2 weeks) encountered random lockups, error messages about resources no longer available. I was able to track them down to half-closed pipes and ended up revamping subprocess interaction. So far, I have left a SublimeText session open for 3 days, done some fair amount of work and haven't had any problems. > > If you are a SublimeText 2/3 hsdev user and are comfortable with checking out Sublime packages directly from github, I could use some extra help shaking out the code to ensure that it is as robust as I think it is. The URL to my Github fork is: > > https://github.com/bscottm/SublimeHaskell.git > > Once you've cloned my fork, check out the 'stderr_stdout' branch and test away -- I'm looking for unexpected lockups (e.g., when you've saved a file and ST's status line says "... Checking and Linting" forever.) > > Thanks! > > > -scooter

2 1

A question about GHC test coverage
by ok＠cs.otago.ac.nz 14 Feb '17

14 Feb '17

Step 1: write a module defining a data type. Step 2: write a module with lots of QuickCheck tests for it. Step 3: Compile with gcc -fhpc to get coverage data. Step 4: run, find bugs, fix bugs, repeat from step 3. Step 5: view coverage .html files, note functions not covered, add tests to step 2 file, repeat. Step 6: Step back with a sigh of content. Coverage high. Step 7, some time later: encounter a bug in an untested function. Why? Because Step 1 includes instance Ord MyType where compare ... ... = ... and the untested function was max. The "inherited" definition is of course fully consistent with compare, and comparison had been tested because I thought of that, but there was an extra requirement which need not detain us here. My problem was that (a) I was too dumb to think of writing tests for a function I hadn't written. (b) Because I hadn't written max, 'hpc' didn't show it to me as something needing a test. Obviously this was my fault: if I have declared instance <some class> <my type> it's my responsibility to test all of the functions in the type-class. But I might not actually *know* what all the functions in the type-class are; Haskell does change from time to type. And being a bear of very little brain, I could use some reminders "Hey, you've inherited this function but not tested it". Is that possible using ghc -hpc?

1 0

Fully funded PhD position in CS at Heriot-Watt University, Edinburgh, Scotland
by Ekaterina Komendantskaya 13 Feb '17

13 Feb '17

Dependable System group, School of Mathematical and Computer Sciences, Heriot-Watt University, Edinburgh, is looking to fill in one PhD position (a PhD stipend of £14,300 per annum, for 48 months, and a fee waiver are offered, no nationality restrictions apply). We are looking for a talented person, with 1st class degree in Mathematics or Computer Science, with keen interest in Logic and Programming languages and good programming skills. The successful candidate will be working under supervision of Dr Ekaterina Komendantskaya (http://www.macs.hw.ac.uk/~ek19/) The exact topic of the PhD dissertation will be determined in the course of discussions with the successful candidate, and will be related to both the student’s and the supervisor's research interests. To apply please contact Ekaterina directly: ek19(a)hw.ac.uk Heriot-Watt University. With a history dating back to 1821, Heriot-Watt University is a research-led university located in Edinburgh, UK. Currently it is Scotland’s most international university, delivering degree programmes to 31,000 students globally and with campuses in Edinburgh, Scottish Borders, Orkney, Dubai and Malaysia. The university is consistently highly ranked, having been The Sunday Times; Scottish University of Year between 2011 and 2013. The university has a strong track record in attracting funding for research from national Research Councils, UK government departments, charities, the European Commission and industrial sponsors. In the REF 2014 survey of all UK universities, 82% of our research was found to be world-class. Dependable Systems group. The Computer Science department, hosting this PhD position, had 78% of its outputs rated `world-leading' or `internationally excellent' in REF 2014.The proposed work will be carried out within the Dependable Systems Group (DSG). With members of staff working on programming languages and compilers (Fensch, Loidl, Michaelson, Scholz), Automated Reasoning and Formal Methods (Georgieva, Grov, Ireland, Komendantskaya), Type Theory (Gabbay), this group will provide an ideal environment for the PhD research. Additionally, the DSG is an active member of the multi-site Mathematical Reasoning Group (joint with U. Edinburgh); the sites holding weekly research meetings and a joint platform grant. ******************************* Dr Ekaterina Komendantskaya Associate Professor in Computer Science School of Mathematical and Computer Sciences Earl Mountbatten Building [ building 21, office G26 ] Heriot-Watt University Edinburgh, UK, EH14 4AS +44 (0)131 451 8283 http://www.macs.hw.ac.uk/~ek19/

1 0