- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Hyper-recursion?
by Olaf Klinke 18 Jan '17

18 Jan '17

If I may step into this discussion, I'd like to suggest you start modelling your world of parcels more concretely, as data types. From there it should be easier to grasp our hyper-recursion. Question: Does every parcel have its own time, or is there a universal clock ticking in the background? If you have a uiversal clock, you could model your world as a linear series of state changes, stretching infinitely into the past and future. Hence two streams going out form a "now" would be the overarching data type. This has been used e.g. for doubly linked lists. Doesn't functional reactive programming use a similar model? Question: How does one identify a parcel of land? Is it a polygon of coordinates in some reference system? Hence can the state be seen as a finite set of (Polygon,Owner) pairs? Question: What is more important: The state or the state change? If the state is more important, a kind of graph might be the appropriate data structure. If the change is important, it might be interesting to model the world (and time) as a network of functions. Question to all mathematicians on this list: Suppose (again assuming a universal clock) there is a type (a set?) X and a function change :: Integer -> (X -> X) where the state of "now" is to be understood as the value now = change 0 . change (-1) . change (-2) . {...ad infinitum} Under which circumstances does this determine the value of "now"? The only instance I can think of are contractions on a (compact) metric space. (Brouwer's/Banach's fixed point theorems) I second the contributors who suggest that this has not much to do with recursion nor corecursion. To me, the essence of recusion is self-reference. A function building e.g. an infinite stream from a seed is not self-referential in itself, it is the resulting data that is self-referential. Olaf

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[ANN] FloatingHex: Hexadecimal floats (quasiquoter and pretty-printer)
by Levent Erkok 17 Jan '17

17 Jan '17

FloatingHex (http://hackage.haskell.org/package/FloatingHex) is a simple package that implement hexadecimal notation for floating point numbers, as described in p57-58 of http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf The package provides a quasi-quoter for hexadecimal floats: hf, and a pretty-printer for floats to show them in this notation: showFFloat. (Note that the latter is not 100% compatible with C's %a modifier for printf, but it does render a faithful representation of its input.) Hex-floats are useful as they allow writing floating-point constants without any loss of precision, while remaining human readable. For instance, the float 2 is written as 0x1p1. (With the quasiquoter, the syntax is [hf|0x1p1|].) This representation is to be preferred over decimal rendering where loss of precision can be a problem: Note that not all floating point numbers have a terminating decimal representation as currently required by the Haskell syntax. It would be nice if Haskell itself allowed for such literals in the language specs itself, following the recent changes to other language standards. (Again, see p57-58 of http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf for the new C standard.) In the mean time, I hope FloatingHex library will provide a workaround for the numerophilias amongst us. Bug reports and improvements always welcome! Cheers, -Levent.

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[ANN] Haskell ITA meetup in Milan, Italy (2017-02-25)
by Francesco Ariis 17 Jan '17

17 Jan '17

Good evening -cafe, the italian Haskell Community (http://haskell-ita.it/) is happy to announce its winter Haskell meetup. The event is going to be hosted in Milano, on February 25th (Saturday). It will be kindly hosted by MIKAMAI [1], Via Giulio e Corrado Venini, 42 - 20127 Milano (MI), IT [1] https://www.mikamai.com/ To register, check: https://www.metooo.io/e/incontro-haskell-ita-inverno-2017 Any haskeller (beginner, experienced, curious) is welcome! *** italian follows *** Buonasera a tutti, abbiamo finalmente deciso la data dell'incontro invernale di Haskell-ITA! Ci riuniremo il 25 Febbraio 2017 (un Sabato), presso MIKAMAI [1], che gentilmente mette i locali a disposizione. [1] https://www.mikamai.com/ L'indirizzo è: Via Giulio e Corrado Venini, 42 - 20127 Milano (MI), IT Per registrarvi: https://www.metooo.io/e/incontro-haskell-ita-inverno-2017

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A question on datakinds syntax
by Haiwei Zhou 17 Jan '17

17 Jan '17

Hi, I am reading the document of spock-0.11, and found two strange definitions in the Web.Spock. ```` type Var a = Path ((:) * a ([] *)) Open var :: (Typeable * a, PathPiece a) => Path ((:) * a ([] *)) Open ```` What's the meaning of the star between Typeable and a ? The kind of Typeable is * -> *. I cannot understand why the Typeable in the var prototype takes two kinds. In the Web.Routing.Combinators of reroute-0.4, those are defined as following: ```` type Var a = Path (a ': '[]) Open var :: (Typeable a, PathPiece a) => Path (a ': '[]) Open ```` Why there are two difference definition about the same thing? Thanks, Haiwei

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Control.Parallel seemingly randomly behaviour
by Juan Luis Martty 17 Jan '17

17 Jan '17

Hello everyone, I'm having a consistency issue with the following piece of code: heavyAm = 500 lightAm = 1000 heavyCalc :: Int -> Int heavyCalc s = sum [1..1000000*s] parallel = (heavyCalc lightAm, heavyCalc heavyAm) `using` (parTuple2 rseq rseq) For some reason, during runtime the RTS sometimes parallelizes the evaluation and sometimes it doesn't. I'm running with all the RTS/compile time options correctly afaik. Here is the output from a couple of runs of the program: jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe Warning: File listed in par.cabal file does not exist: README.md (500000000500000000,125000000250000000) Computation time: 1.557007s real 0m1.732s user 0m2.528s sys 0m0.464s jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe Warning: File listed in par.cabal file does not exist: README.md (500000000500000000,125000000250000000) Computation time: 1.544837s real 0m1.720s user 0m2.544s sys 0m0.712s jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe Warning: File listed in par.cabal file does not exist: README.md (500000000500000000,125000000250000000) Computation time: 2.316537s real 0m2.484s user 0m2.592s sys 0m0.680s jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe Warning: File listed in par.cabal file does not exist: README.md (500000000500000000,125000000250000000) Computation time: 2.318514s real 0m2.489s user 0m2.612s sys 0m0.688s jmartty@walrus:~/hs/parallel$ stack build && time stack exec par-exe Warning: File listed in par.cabal file does not exist: README.md (500000000500000000,125000000250000000) Computation time: 1.544975s real 0m1.718s user 0m2.512s sys 0m0.456s As you can see, sometimes wall time roughly equals userspace time, sometimes it doesn't (meaning it parallelized at least some amount). I'm running on a dual core machine under Ubuntu using stack with lts-7.14 (GHC 8.0.1) and parallel-3.2.1.0. Regards, Juan

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Re: [Haskell-cafe] Hyper-recursion?
by Anthony Clayden 17 Jan '17

17 Jan '17

>> On 16 Jan 2017 04:43, "Lawrence Bottorff" <borgauf at gmail.com> wrote: >> >> A while back I worked at an assessor's office, i.e., the people responsible >> for handling properties as land parcels. ... Hi Lawrence, I too worked on land parcels -- a local government rates billing and land valuation application. >> ... how property changed hands, and especially how property lines >> changed due to properties either merging or being split up. >> That is to say, how the parcel map changed over time. I think the important aspect is that the a parcel can be split, and one of the splits merged with another parcel that was not originally with it. (I don't know how it was in your application. but in mine a legal parcel might consist of discontiguous areas of land -- for example a house in a terrace parcelled with a garage amongst a block of garages at the end of the street,) That is, looking over history you cannot group the parcels into a strict hierarchy of splits. >> Somewhere in the functional paradigm, specifically recursion, >> would seem to be a model for this issue. No I'm not seeing anything specifically functional about this. It's a directed graph, where each node is an instance of parcel ownership. >> So in chapter 1 of any functional programming tutorial is the factorial >> calculation function done with recursion. We beginners see the recursion >> "going out" to the "last one," then "coming back," adding up the results of >> each stage as it returns . . . like a yo-yo winding out, >> then winding up again. Nice image, but there's no "last one" here (nor a "first one" that we could make sense of), There's no boundary from where we could be "coming back". Recursion does not apply [see more below] >> David Turner dct25-561bs at mythic-beasts.com >> Mon Jan 16 07:47:41 UTC 2017 >> >> I suspect you have stumbled onto the dual concept of corecursion: ... Nor corecursion. a) because of the infinite and arbitrary potential for splits/mergers; b) because even if there was some time in the distant past when the whole country was a single parcel with a single owner. (The Emperor? But even empires and countries split and merge. Or no owner, only hunter-gatherers/nomads, which might as well be a single parcel.) We're never going to try to rebuild that history. c) because there's never going to be a future end-state. Arbitrary splits/mergers will continue forever. We can't predict what might be the smallest parcels some area of land could be split into. (Note that one trick to prevent mineral exploitation companies from buying up glorious scenery is to split it into $1-parcels and sell each to a different owner.) >> ... Haskell being the most pure functional language, is, hence, >> my starting point on this question. There's nothing specifically Haskell in this. A better place to ask might be lambda-the-ultimate. Anthony

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dynamic code compilation and loading
by Dennis Raddle 17 Jan '17

17 Jan '17

Hello, I wrote a Haskell program which reads a MusicXML score and plays it through real-time MIDI messages (using the portmidi module) via some algorithms that are customized depending on the MIDI synthesizer that is receiving the messages. The program also plays back the music with musically expressive nuances. In the next version of this program, I am going to add more complicated algorithms for the expressive nuances, and it would be helpful to configure them and express them in actual Haskell code. My workflow will look like this: A. write a score using the music typesetting program Sibelius B. write some Haskell code to provide expressive nuances C. play the music through a MIDI synthesizer and listen. D. based on what I hear and where I want to take the music, modify the score and the Haskell code E. loop back to C Therefore, if I don't want to recompile the program each time I do step D, I need to compile and load code dynamically. Let's say that a data structure which contains a MusicXML score and a nominal rendition into MIDI messages together with time tags is of type Score. Then I want to write, and dynamically compile/load, a function vary :: Score -> Score which varies the MIDI messages and time tags to add expressive nuances. Let's say 'vary' is contained in Vary.hs. I want to write 'vary' in terms of already-compiled functions that provide the basic music-processing operations. Let's say that these functions are in the module MusicBase. Then Vary.hs will look like import MusicBase vary = ... operations in MusicBase ... Can I get some basic idea of how to do this? D

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Hyper-recursion?
by Lawrence Bottorff 17 Jan '17

17 Jan '17

A while back I worked at an assessor's office, i.e., the people responsible for handling properties as land parcels. I was brought in to do GIS. One of the things we wanted was to get a sense of the history of land use, specifically how property changed hands, and especially how property lines changed due to properties either merging or being split up. That is to say, how the parcel map changed over time. Problematic was how the rugged old mainframe system (IBM AS/400 and a Cobol app) simply updated the data -- with no concept of remembering how things used to be. My GIS system (ESRI) also lacked any state memory -- other than simply snapshooting everything ad nauseum. Years later I become familiar with the world of functional programming. Somewhere in the functional paradigm, specifically recursion, would seem to be a model for this issue. That is, the whole issue of parcels changing through merges or splits might be a simple question of recursion. If functional is "beyond state," then changes in a map would only be stages, places in a never-ending outward-growing recursion. Seen as "infinite mirrors," one map change would simply be a mirror layer -- click on it to call it up. So in chapter 1 of any functional programming tutorial is the factorial calculation function done with recursion. We beginners see the recursion "going out" to the "last one," then "coming back," adding up the results of each stage as it returns . . . like a yo-yo winding out, then winding up again. But what I'm describing with changing parcels maps would seem to be a process that never comes out of recursion, rather, lives inside a "hyper-recursion." That is to say, an overarching recursion is the whole world. However, today's mentality would simply say, *Obviously, you want to save off each change you make to your parcel map *. . . again, the whole snapshot idea. This thinking is typical data management coupled, perhaps, with the human penchant to see things in terms of time and timelines. So, again, the standard solution would be to timestamp a parcel change and save it off, i.e., a "change" is a tick on the timeline, mark it, make note of it. But again, couldn't we see this whole issue of parcel changes as (using my yo-you analogy) just levels in what seems like a continual winding out -- which in a topological sense doesn't even need to be seen as geographical? This would seem to put the *process in a recursion,* rather than *recursion(s) in a process.* Haskell being the most pure functional language, is, hence, my starting point on this question. I'm a bright enough person, but I can't believe I'm the first person to notice this Alice in Wonderland situation. . . BTW, we could see a chess game in a similar light. . . . if not many, many other evolving phenomena of supposed (cumulative, consequential?) change. Thanks, Lawrence Bottorff

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BayHac 2017 announcement
by Dan Burton 15 Jan '17

15 Jan '17

I am pleased to announce that BayHac 2017 will be held at the Takt office in San Francisco on the weekend of Friday, April 7th thru Sunday, April 9th. BayHac is a Haskell hackathon weekend event for the San Francisco Bay Area and Silicon Valley. It will be a weekend of learning, hacking, and connecting with fellow Haskell enthusiasts. See the page for BayHac 2017 on the haskell.org wiki for details: https://wiki.haskell.org/BayHac2017 -- Dan Burton

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LambdaConf 2017 CFP
by John A. De Goes 15 Jan '17

15 Jan '17

The LambdaConf 2017 Call for Proposals <http://surveymonkey.com/r/lambdaconf-2017-cfp> (CFP) is open until the end of January: http://surveymonkey.com/r/lambdaconf-2017-cfp LambdaConf is an interdisciplinary functional programming conference held in the Mountain West, and seeks to bring together aspiring and practicing functional programmers, as well as researchers. Traditionally, the conference has had a very large amount of Haskell content (second only to Scala content in some years). The conference takes place May 25 - 27, in Boulder, Colorado, and is preceded by commercial training opportunities and a day of third-party mini-conferences on selected topics. If you are an educator, a researcher, a speaker, a speaker coach, or someone aspiring to one of the preceding, then we warmly welcome you to submit a proposal for LambdaConf 2017. All LambdaConf speakers receive free registration, an appreciation dinner, a special gift, accommodations for up to 4 nights (May 24 - May 28), and ample travel assistance based on need and availability. LambdaConf attracts everyone from the FP-curious to researchers; hobbyists and professionals; academics and commercial developers. Material at all levels, including beginner content and very advanced content, will find an audience at LambdaConf. LambdaConf welcomes the following kinds of proposals: Languages. Proposals that overview or dive into specific features of functional, math, or logic programming languages (both new and existing), with the goal of exposing developers to new ideas or helping them master features of languages they already know. Libraries. Proposals that discuss libraries that leverage functional or logic programming to help programmers solve real-world problems. Concepts. Proposals that discuss functional programming idioms, patterns, or abstractions; or concepts from mathematics, logic, and computer science, all directed at helping developers write software that's easier to test, easier to reason about, and easier to change safely. Aspects. Proposals that discuss how functional programming can help with specific aspects of modern software development, including scalability, distributed systems, concurrency, data processing, security, performance, correctness, user-interfaces, machine learning, and big data. Use Cases. Proposals that discuss how functional programming enabled a project or team to thrive, or deliver more business value than possible with other approaches. Cherry-Picking. Proposals that show how techniques and approaches from functional programming can be adapted and incorporated into mainstream development languages and practices, to the benefit of developers using them. Cracks. Proposals that call attention to difficulties of functional programming (both as a cautionary tale but also to raise awareness), especially such proposals that suggest alternatives or a path forward. Data. Proposals that present data, measurements, or analysis that suggests different techniques, paradigms, languages, libraries, concepts, or approaches have different efficacies for given specified metrics, which provide actionable takeaways to practicing functional and logic programmers. Off-Topic. Proposals that have appeal to a mainstream developer audience (the number of off-topic proposals we accept is small, but we do accept some, especially for keynotes). LambdaConf welcomes proposals for dynamic and static programming languages, category theoretic and otherwise, both functional and logic, or mainstream languages that can benefit from functional programming. Challengers and alternatives are also welcome. We are currently soliciting for the following session formats: Speaker Coaches. Speaker Coaches have extensive experience preparing material and giving polished, well-structured, educational, entertaining talks. Speaker Coaches review material and practice sessions for 5 - 10 speakers, & provide constructive feedback to speakers about how to improve the focus, content, & presentation of material. Coaches receive accommodations, free registration, & airfare reimbursement, & a 10 minute speaking slot (if interested). Leap Workshops. Leap Workshops take place on May 25, and are approximately 6 hours in length. They are in-depth, hands-on workshops designed to teach mainstream functional programming topics in enough detail, attendees can immediately apply what they learn in their jobs. Instructors for Leap Workshops receive accommodations, free registration, airfare reimbursement (including family), and a small stipend. If you are an author with a relevant book, we can also make it easy for attendees to purchase the book as part of registration for your workshop. Workshops must use a containerized cloud environment provided and paid for by LambdaConf. Hop Workshops. Hop Workshops are 2 hours in length. Like Leap Workshops, these workshops are in-depth and hands-on, but they cover reduced content and may be specialized to topics that may not have mainstream appeal. Guides receive accommodations, free registration, and travel assistance based on need and availability. Workshops must use a containerized cloud environment provided and paid for by LambdaConf. De Novo Sessions. De Novo Sessions are 1 hour in length. These sessions are designed to present original work from industry and academia. While the requirements for proposals are more rigorous, there is less competition for De Novo slots. Speakers receive accommodations, free registration, and travel assistance based on need and availability. Educational Sessions. Educational Sessions are 1 hour in length. These sessions are designed to clearly and concisely teach one useful concept, skill, aspect, library, or language to attendees. Teachers receive accommodations, free registration, and travel assistance based on need and availability. Inspire Talks. Inspire talks are 10 minutes in length and focus on clear communication of a single takeaway. These sessions are intended to inspire attendees to learn more about particular subjects or to try new approaches. Speakers receive accommodations, free registration, and travel assistance based on need and availability. Note: While only 10 minutes in length, we require a high-level of polish, structure, and rehearsal for Inspire Talks; despite shorter length, they are as much work to prepare for as other sessions. Keynotes. Keynotes are 40 minutes in length, and are presented before all attendees (there are no other sessions concurrent with keynotes). Keynotes are designed to offer thought-provoking, opinionated, and insightful commentary on topics of interest to the community. Keynotes have more latitude to stray from functional programming and into related areas such as computer science, mathematics, and science. Keynote speakers receive accommodations, free registration, and travel assistance based on need and availability. LambdaConf requires tailored content. This does not mean you cannot reuse existing content, only that you should incorporate updates into your material, respond to feedback from your speaker coach, and tailor the material to the LambdaConf audience as appropriate. Note: The Call for Proposals closes January 31. Submitters will be notified by March 1st at latest. -- John A. De Goes john(a)degoes.net Follow me on Twitter @jdegoes

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The design and use of QuickCheck
by Joe Nelson 15 Jan '17

15 Jan '17

Hey Haskellers, I decided to learn more about QuickCheck because it seems useful, and after a two weeks of reading papers and trying experiments, I wrote about my findings. https://begriffs.com/posts/2017-01-14-design-use-quickcheck.html Hope you find the article useful. Cheers, Joe

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Re: [Haskell-cafe] Strange encoding issue with Text and Servant
by David Turner 14 Jan '17

14 Jan '17

Ok, so there's definitely a difference of some kind client-side. It'd be useful to see the network traffic nonetheless, as the source of the '!D(MISSING)' is still a bit of a mystery and you may see something suggestive in the raw bytes. I can't find the string 'MISSING' anywhere in servant or its dependencies, even looking in libs and binaries. Any chance of tracking its source down using `find` and `grep` and `strings`? On 14 Jan 2017 19:48, "Jan von Löwenstein" <jan.loewenstein(a)gmail.com> wrote: Actually the code I pointed at _is_ the swagger-codegen generated client. I have got a very small wrapper around it: ``` listService :: (MonadIO m, MonadCatch m, MonadReader Config m, MonadLog Text m) => Text -> m ServiceList.ServiceList listService labelSelector = namespacedF $ \namespace -> Kube.listNamespacedService namespace Nothing (Just labelSelector) Nothing Nothing Nothing Nothing listSecret :: (MonadIO m, MonadThrow m, MonadReader Config m, MonadLog Text m) => Text -> m SecretList.SecretList listSecret labelSelector = namespacedF $ \namespace -> Kube.listNamespacedSecret namespace Nothing (Just labelSelector) Nothing Nothing Nothing Nothing namespacedF :: (MonadIO m, MonadThrow m, MonadReader Config m, MonadLog Text m) => NamespacedF model -> m model namespacedF f = do config <- ask result <- let baseUrl = apiEndpoint config tlsSettings = Base.tlsSettings baseUrl (credentials config) kubeNamespace = namespace config in do manager <- liftIO $ newManager $ (mkManagerSettings tlsSettings Nothing) { managerModifyRequest = \req -> return req { checkResponse = \req res -> do Text.IO.hPutStrLn stderr (Text.pack (show req)) responseMessage <- showResponse res Text.IO.hPutStrLn stderr responseMessage return () } } liftIO $ runExceptT $ f kubeNamespace manager baseUrl either throwM return result ``` I call them like: ``` do let Just agentId = ... selector = "agentId" <> "=" <> agentId logMessage $ "listSecret selector: '" <> selector <> "'" secretList <- listSecret selector ``` `logMessage` gives a literal equals sign in both cases. `Text.IO.hPutStrLn stderr (Text.pack (show req))` from namespacedF gives `%3D` and `%!D(MISSING)` depending on which function I call. >From what I understand this is definitely happening on the client side. Do you still think a tcpdump might be worth it? ``` listSecret selector: 'agentId=b49d4406-8020-44e6-7788-6f92d5c0e732' Request { host = "192.168.99.100" port = 8443 secure = True requestHeaders = [("Accept","application/json")] path = "/api/v1/namespaces/default/secrets" queryString = "?labelSelector=agentId%!D( MISSING)b49d4406-8020-44e6-7788-6f92d5c0e732" method = "GET" proxy = Nothing rawBody = False redirectCount = 10 responseTimeout = ResponseTimeoutDefault requestVersion = HTTP/1.1 } ``` ``` listService selector: 'agentId=24f99a4b-1682-44da-7ba4-dba935d107d2' Request { host = "192.168.99.100" port = 8443 secure = True requestHeaders = [("Accept","application/json")] path = "/api/v1/namespaces/default/services" queryString = "?labelSelector=agentId%3D24f99a4b-1682-44da-7ba4- dba935d107d2" method = "GET" proxy = Nothing rawBody = False redirectCount = 10 responseTimeout = ResponseTimeoutDefault requestVersion = HTTP/1.1 } ``` Thanks for the time you already invested. I am completely puzzled because I see no chance how the code could behave as it does. (From my experience that points out I am looking at the wrong place ;) ) Best Jan David Turner <dct25-561bs(a)mythic-beasts.com> schrieb am Sa., 14. Jan. 2017 um 20:08 Uhr: > Grasping at straws a little bit here, but can you (a) do a packet capture > (e.g. `tcpdump -X`) to see what's going back and forth on the wire, just to > make absolutely sure all of the oddness is on the client's end? > > A string like `!D(MISSING)` sorta looks like a decoding error so perhaps > it will be instructive to look at the bytes on the wire it's trying to > decode, although I can't think what could be confused with an equals sign. > It's not like that blooming Greek question mark ( > http://www.fileformat.info/info/unicode/char/037e/index.htm) > > Cheers, > > > > > On 14 January 2017 at 18:47, Nigel Rantor <wiggly(a)wiggly.org> wrote: > > On 14/01/17 17:37, Jan von Löwenstein wrote: > > Oh, it happens with servant on the client side. > > I use a swagger-codegen generated servant based client to access > kubernetes. > Calling https://github.com/soundcloud/haskell-kubernetes/blob/ > master/lib/Kubernetes/Api/ApivApi.hs#L475 works > Calling https://github.com/soundcloud/haskell-kubernetes/blob/ > master/lib/Kubernetes/Api/ApivApi.hs#L473 doesn't. > > From what I see the `QueryParam"labelSelector" Text`is the same in both. > > Logging the value gives the literal `=` as expected. Logging the > (http-client) requests shows the difference. > > > So I went ahead and wrote a simple client by hand and when I call the two > functions on a local endpoint that shows me the request URL I get the > following. > > Same arguments for 'pretty' and 'labelSelector' in both cases. > > Code: > > runListSecret :: Manager -> BaseUrl -> ClientM SecretList > > runListSecret manager baseUrl = listSecret (Just "prettyArg") (Just "=") > Nothing Nothing Nothing Nothing manager baseUrl > > > > runListService :: Manager -> BaseUrl -> ClientM ServiceList > > runListService manager baseUrl = listService (Just "prettyArg") (Just "=") > Nothing Nothing Nothing Nothing manager baseUrl > > Server log: > > 127.0.0.1 - - [14/Jan/2017:18:39:49 +0000] "GET /api/v1/secrets?pretty=prettyArg&labelSelector=%3D > HTTP/1.1" 404 - 0.0003 > 127.0.0.1 - - [14/Jan/2017:18:39:49 +0000] "GET /api/v1/services?pretty=prettyArg&labelSelector=%3D > HTTP/1.1" 404 - 0.0003 > > I haven't used swagger-codegen but the servant-client code works for me so > I would look more into that. > > Swagger codegen looks like it might take me a while to get my head into so > maybe you could look at the generated code, or sling it to me here or > directly. > > The two calls are so similar that I can't see why the generated client > would behave differently in those cases. > > Regards, > > n > > Best > Jan > > Nigel Rantor <wiggly(a)wiggly.org <mailto:wiggly@wiggly.org>> schrieb am > > Sa., 14. Jan. 2017 um 18:11 Uhr: > > On 13/01/17 19:28, Jan von Löwenstein wrote: > > Hi, > > > > I have got a two places with a `QueryParam "q" Text` and call it > with a > > Text that contains a `=` literal. In one place the `=` is correctly > > encoded as %3D, in the other I see a `!D(MISSING)`. > > > > This has to happen somewhere in Servant or the lower layers. Both > Texts > > print out nicely with an `=` sign if I just print them to stdout. > > > > Google does not find `!D(MISSING)` anywhere. > > > > Any idea what could possibly be the problem here? > > It would be really useful to see exactly how you are 'calling' this. > > Do you have a curl command line or are you using some other client? > > n > > _______________________________________________ > Haskell-Cafe mailing list > To (un)subscribe, modify options or view archives go to: > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > Only members subscribed via the mailman list are allowed to post. > > > _______________________________________________ > Haskell-Cafe mailing list > To (un)subscribe, modify options or view archives go to: > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > Only members subscribed via the mailman list are allowed to post. > > >

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Calling Haskell from C
by Dominic Steinitz 14 Jan '17

14 Jan '17

I've been trying to get the example in https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ffi-chap.ht… working. I have a cabal file name: test-via-c version: 0.1.0.0 homepage: TBD license: MIT author: Dominic Steinitz maintainer: idontgetoutmuch(a)gmail.com category: System build-type: Simple cabal-version: >=1.10 executable Foo.dylib main-is: Foo.hs other-extensions: ForeignFunctionInterface build-depends: base >=4.7 && <4.10, primitive >=0.6 && <0.7 hs-source-dirs: src default-language: Haskell2010 include-dirs: src ghc-options: -O2 -shared -fPIC -dynamic extra-libraries: HSrts-ghc8.0.1 which installs /Users/dom/Library/Haskell/ghc-8.0.1/lib/test-via-c-0.1.0.0/bin/Foo.dylib I then compile the C with gcc-6 Bar.c /Users/dom/Library/Haskell/ghc-8.0.1/lib/test-via-c-0.1.0.0/bin/Foo.dylib -I/Library/Frameworks/GHC.framework/Versions/8.0.1-x86_64/usr/lib/ghc-8.0.1/include -L/Library/Frameworks/GHC.framework/Versions/8.0.1-x86_64/usr/lib/ghc-8.0.1/rts -lHSrts-ghc8.0.1 Sadly when I try to run the executable I get ~/Dropbox/Private/TestU01-1.2.3/examples/src $ ./a.out dyld: Library not loaded: @rpath/Foo.dylib Referenced from: /Users/dom/Dropbox/Private/TestU01-1.2.3/examples/src/./a.out Reason: image not found Trace/BPT trap: 5 I am guessing the executable is looking for the dynamic library. I copied Foo.dylib to the current directory but still get the same error. I know this is really an OS X question but I am hoping someone who has done before will be able to help. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

4 8

module is a package module error
by Lana Black 14 Jan '17

14 Jan '17

Hi, I'm trying to use hint [1] to compile in runtime externally supplied haskell code. The compiled code must have certain modules imported. The problem is that I'm getting this error when loading modules >WontCompile [GhcError {errMsg = "<no location info>: error: module >\8216Internal\8217 is a package module"}] I'm not really sure what to do with this. One way to fix this is to move Internal to a separate package so that hint could load it through cabal, but that's something I'd like to avoid. Is there any way I could make hint use the same modules from the package it's being called from? The code is located at [2]. [1]: http://hackage.haskell.org/package/hint [2]: https://github.com/greydot/hint-test/

2 3

Feedback needed: CLI app + guide
by Carlo Matteo Scalzo 13 Jan '17

13 Jan '17

Hi all, I've already posted this in beginners@, but I thought it might be of interest to a wider audience too (apologies for double-posting). I started learning Haskell about a year ago, and I couldn't find any example of a simple, real world application written in Haskell, so as usual I ended up writing my own :-) The code is available for free (it's a simple command-line app), and I've also written a short guide that uses the application as a case study to talk about Haskell's features. Could you guys please download the guide (for free, of course) and let me know if you find it useful? You can get the guide here: https://fifohaskell.com Please send me your feedback either here or to my personal email address (it's on the website), and thank you very much for your help! Carlo

1 0

brainstorm help
by Michael Litchard 13 Jan '17

13 Jan '17

Hi There. I'm looking for ideas to flesh out a writing project I'm beginning. What I am looking for is a set of five games in increasing complexity that would allow for a wide discussion of Haskell. I originally began this project by centering the writing around one large game, but this idea has proven to be brittle. The set of five should include a discussion of: (1) Types (2) folds, maps, filters (3) monoids, functors, applicatives, and monads Thanks for what ever storms your brains bring forth. :)

7 11

Can I allow multiple rigid type variables?
by Cody Goodman 13 Jan '17

13 Jan '17

I know my question doesn't quite make sense and you can't have "multiple rigid type variables" but I couldn't think of a better way to characterize it or explain it. So I'll also try to give more detail below along with the code example and error at the end. I have an inner join function using vinyl which does cool stuff like giving a type error if you try to join on a column that doesn't exist. I previously had an implementation that blindly built an index based on the left argument. I then tried to dispatch based on the lengths of the left and right producer arguments. The problem is my return type is: Rec f (as ++ bs) That means I have two different producers, one of as and one of bs. I then do a case statement on the lengths and I want to store the producer to use for a given piece in that variable. The problem is ghc "pins" the type variable as either (Rec f as) or (Rec f bs) when I need to make that choice at runtime. My code and error is both at github here: https://github.com/codygman/frames-diff/blob/inner-join-fix/Frames/Diff.hs#… and below: -- | Performs an inner join and keeps any duplicate column -- Recommend keeping columns in producers disjoint because accessing -- anything but the leftmost duplicate column could prove difficult. -- see: https://github.com/VinylRecords/Vinyl/issues/55#issuecomment-269891633 innerJoin :: (MonadIO m, Ord k) => Producer (Rec f leftRows) IO () -- leftProducer -> Getting k (Rec f leftRows) k -- leftProducer lens -> Producer (Rec f rightRows) IO () -- rightProducer -> Getting k (Rec f rightRows) k -- rightProducer lens -> m (P.Proxy P.X () () (Rec f (leftRows ++ rightRows)) IO ()) innerJoin leftProducer leftLens rightProducer rightLens = do leftProducerLen <- P.liftIO $ P.length leftProducer rightProducerLen <- P.liftIO $ P.length rightProducer let curProducer = case rightProducerLen < leftProducerLen of True -> rightProducer -- False -> leftProducer let curKeymapProducer = case rightProducerLen < leftProducerLen of True -> leftProducer -- False -> rightProducer let curLensLookup = case rightProducerLen < leftProducerLen of True -> rightLens -- False -> leftLens let curLensInsert = case rightProducerLen < leftProducerLen of True -> leftLens -- False -> rightLens let appender km row = case rightProducerLen < leftProducerLen of True -> case M.lookup (view curLensLookup row) km of Just otherRow -> pure $ rappend otherRow row Nothing -> P.mzero -- False -> case M.lookup (view curLensLookup row) km of -- Just otherRow -> pure $ rappend row otherRow -- Nothing -> P.mzero keyMap <- P.liftIO $ P.fold (\m r -> M.insert (view curLensInsert r) r m) M.empty id curKeymapProducer pure $ curProducer >-> P.mapM (\r -> appender keyMap r) -- error if I uncomment my false cases (specifically the False case for curProducer) -- [5 of 5] Compiling Frames.Diff ( Frames/Diff.hs, interpreted ) -- Frames/Diff.hs:125:32: error: -- • Couldn't match type ‘leftRows’ with ‘rightRows’ -- ‘leftRows’ is a rigid type variable bound by -- the type signature for: -- innerJoin :: forall (m :: * -> *) k (f :: * -- -> *) (leftRows :: [*]) (rightRows :: [*]). -- (MonadIO m, Ord k) => -- Producer (Rec f leftRows) IO () -- -> Getting k (Rec f leftRows) k -- -> Producer (Rec f rightRows) IO () -- -> Getting k (Rec f rightRows) k -- -> m (P.Proxy P.X () () (Rec f (leftRows ++ rightRows)) IO ()) -- at Frames/Diff.hs:113:14 -- ‘rightRows’ is a rigid type variable bound by -- the type signature for: -- innerJoin :: forall (m :: * -> *) k (f :: * -- -> *) (leftRows :: [*]) (rightRows :: [*]). -- (MonadIO m, Ord k) => -- Producer (Rec f leftRows) IO () -- -> Getting k (Rec f leftRows) k -- -> Producer (Rec f rightRows) IO () -- -> Getting k (Rec f rightRows) k -- -> m (P.Proxy P.X () () (Rec f (leftRows ++ rightRows)) IO ()) -- at Frames/Diff.hs:113:14 -- Expected type: Producer (Rec f rightRows) IO () -- Actual type: Producer (Rec f leftRows) IO () -- • In the expression: leftProducer -- In a case alternative: False -> leftProducer -- In the expression: -- case rightProducerLen < leftProducerLen of { -- True -> rightProducer -- False -> leftProducer } -- • Relevant bindings include -- curProducer :: Producer (Rec f rightRows) IO () -- (bound at Frames/Diff.hs:123:7) -- rightLens :: Getting k (Rec f rightRows) k -- (bound at Frames/Diff.hs:119:47) -- rightProducer :: Producer (Rec f rightRows) IO () -- (bound at Frames/Diff.hs:119:33) -- leftLens :: Getting k (Rec f leftRows) k -- (bound at Frames/Diff.hs:119:24) -- leftProducer :: Producer (Rec f leftRows) IO () -- (bound at Frames/Diff.hs:119:11) -- innerJoin :: Producer (Rec f leftRows) IO () -- -> Getting k (Rec f leftRows) k -- -> Producer (Rec f rightRows) IO () -- -> Getting k (Rec f rightRows) k -- -> m (P.Proxy P.X () () (Rec f (leftRows ++ rightRows)) IO ()) -- (bound at Frames/Diff.hs:119:1)

2 3

ANN: `dump-core` a prettier GHC core viewer
by Iavor Diatchki 13 Jan '17

13 Jan '17

Hello, Over the holidays I wrote a small GHC plugin to help me do some low-level optimizations of Haskell code. I thought it might be of use to other people too, so please try it out! When enabled, the plugin will save the Core generated by GHC in JSON format, and also render it in HTML for human inspection. The plugin is available on Hackage: http://hackage.haskell.org/package/dump-core The instructions on how to use it are in the README file. You may also read about it at the github page: http://hackage.haskell.org/package/dump-core There are many things that could probably be improved, just let me know. Also, if you are good at design, I could use some help making things look prettier :) Happy hacking, -Iavor

5 4

[ANN] wiringPi-0.1.0.0
by Patrick Pelletier 10 Jan '17

10 Jan '17

https://hackage.haskell.org/package/wiringPi-0.1.0.0 https://github.com/ppelleti/hs-wiringPi This is a Haskell binding to the wiringPi library, which allows you to interface with the GPIO pins on the Raspberry Pi. Unlike some other solutions for using the Raspberry Pi's GPIO pins, wiringPi provides access to more advanced features, such as enabling the internal pull-up or pull-down resistors. To use this library, you must either run as root, or set the WIRINGPI_GPIOMEM environment variable. (Set it to anything; the value does not matter.) However, PWM will not work if WIRINGPI_GPIOMEM is set. This library will only build on the Raspberry Pi. Before building this library, you must install the "wiringPi" C library on your Raspberry Pi, like this: sudo apt-get install wiringpi Tested on a Raspberry Pi Model B, with Raspbian Jessie Lite, using the system-provided Haskell compiler. (GHC 7.6.3.) This Haskell binding is licensed under the 3-clause BSD license, and the examples in the examples directory are in the public domain. However, be aware that the wiringPi C library itself is licensed under the LGPLv3+. --Patrick

1 0

[ANN] powermate-1.0
by Patrick Pelletier 10 Jan '17

10 Jan '17

As the new maintainer of the "powermate" package, I'm pleased to announce the first new release in nearly 9 years! This library is for interfacing the Griffin PowerMate USB (a big silver knob you can turn and click) with Haskell on Linux. You can read events from the PowerMate, and control the brightness, pulse speed, and pulse waveform of the built-in blue LED. https://hackage.haskell.org/package/powermate-1.0 https://github.com/ppelleti/powermate Version 1.0 is a major release with some breaking changes. The complete list of changes since version 0.1 is: * Now works with GHC 7.2.2 - 8.0.1. * Added Eq, Ord, Show, and Read instances for Event and Status. * Added example programs powermate-print and powermate-pulse. * Added documentation. * An open PowerMate is now represented by the opaque type 'PowerMate' instead of 'Handle'. A new function 'closeDevice' exists to close the opaque 'PowerMate' type. * Fixed a bug where the PowerMate would get confused and start dropping button presses if you set the LED. * Removed extraneous printing to stdout. * Removed getUSBName and readEventWithSkip; I didn't see the utility in these functions. * readEvent no longer returns a Maybe. There was no meaning to 'Nothing' and it just had to be ignored. * Removed the MPD module. It wasn't directly related to the PowerMate functionality, and the "libmpd" package seems to be an alternative which is more complete and better maintained. --Patrick

1 0

Call for interest: Haskell in middle school math education
by Chris Smith 08 Jan '17

08 Jan '17

Hello fellow Haskellers! Are you interested in getting Haskell into middle school (ages 11-14) math or other classes? I'd love to hear from you! Many of you are probably already aware that I've spent the last several years teaching Haskell to children and teens via my CodeWorld project ( http://code.world and http://github.com/google/codeworld) Well, 2017 is my year to make a bigger success of the whole effort. So, let's get Haskell into K-12 schools as a part of mathematics education. By incorporating a programming language like Haskell that's faithful to modeling using true functions, variables, and equations, we can make mathematical modeling and algebraic reasoning tangible and creative in a way it's never been before. There's a lot that's already been done, but the task is still daunting. With some help from some coworkers of mine at Google, and in conjunction with the New York Haskell User Group, I've put together a small budget of around $60K in USD, to start this ball rolling a bit faster with some paid help. Some possible goals include: - Produce quality instructional materials to help teachers around the world incorporate Haskell into their classes and after-school activities. - Produce videos and online resources to support students learning on their own. - Build software features make the CodeWorld tools more helpful, easier to use, easier for students share their work more broadly, and more supportive when students need help. - Make what we already have available to more students, and educate more teachers. - Spread the word and look for more support so we can keep up the effort after the initial investment is finished. Everything produced as part of the project will be distributed under either the Apache 2.0 open source license, or the latest Creative Commons attribution-only license, so that it's freely available for any educational institution (or anyone else) to use, modify, redistribute, etc. So here's where you can step in: - Join the codeworld-discuss@ mailing list (https://groups.google.com/ forum/#!forum/codeworld-discuss) - Introduce yourself, and tell us a bit about what vision you have, and what role you might want to play. This could be a spectator, teacher at a school near you, volunteer contributions on the side, or even a leadership role with a salary attached! Cognizant that solo decisions can be poor ones, I hope to follow some initial sharing of ideas with gathering a small handful of like-minded individuals - I know you're out there - to make decisions about the best way to manage the effort, and go from there. Some background reading: - Blog post on the defining decisions of my effort so far <https://cdsmith.wordpress.com/2016/05/22/codeworlds-big-decisions/> - The web site and its source code <https://github.com/google/codeworld> - A huge bag of partially incomplete stuff already produced <https://drive.google.com/drive/u/1/folders/0B-qIu_nqxaMoYTQ4ODZjMjMtNWRiOC0…> - A similarly motivated project using Racket <http://www.bootstrapworld.org/> that gets a lot right I look forward to hearing from you.

1 0

install of ghc-8.0.1 failing
by Michael Litchard 07 Jan '17

07 Jan '17

I'm trying to install ghc-8.0.1 on ppc64 arch. Below is the truncated config.log, followed by the error that stops make. It was created by The Glorious Glasgow Haskell Compilation System configure 8.0.1, which was generated by GNU Autoconf 2.69. Invocation command line was $ ./configure ## --------- ## ## Platform. ## ## --------- ## hostname = ubuntu-ppc64 uname -m = ppc64 uname -r = 4.4.0-53-powerpc64-smp uname -s = Linux uname -v = #74-Ubuntu SMP Fri Dec 2 16:41:54 UTC 2016 /usr/bin/uname -p = unknown /bin/uname -X = unknown /bin/arch = unknown /usr/bin/arch -k = unknown /usr/convex/getsysinfo = unknown /usr/bin/hostinfo = unknown /bin/machine = unknown /usr/bin/oslevel = unknown /bin/universe = unknown PATH: /home/lambdafan/.cabal/bin PATH: /home/lambdafan/bin PATH: /home/lambdafan/.local/bin PATH: /usr/local/sbin PATH: /usr/local/bin PATH: /usr/sbin PATH: /usr/bin PATH: /sbin PATH: /bin PATH: /usr/games PATH: /usr/local/games PATH: /snap/bin PATH: /home/lambdafan/ghc-8.0.1 <snip> configure: exit 0 Now, the error that make stops at E: Unable to locate package gmake lambdafan@ubuntu-ppc64:~/ghc-8.0.1$ make ===--- building phase 0 make --no-print-directory -f ghc.mk phase=0 phase_0_builds make[1]: Nothing to be done for 'phase_0_builds'. ===--- building phase 1 make --no-print-directory -f ghc.mk phase=1 phase_1_builds utils/genapply/ghc.mk:23: utils/genapply/dist/build/.depend.haskell: No such file or directory utils/genapply/ghc.mk:23: utils/genapply/dist/build/.depend.c_asm: No such file or directory make[1]: *** No rule to make target '/home/kgardas/sfw/ghc-7.10.1/ lib/ghc-7.10.1/base_I5BErHzyOm07EBNpKBEeUv/Prelude.hi', needed by 'utils/deriveConstants/dist/build/Main.o'. Stop. Makefile:129: recipe for target 'all' failed make: *** [all] Error 2 I looked in utils/genapply/dist/build/ to find only this ls -la utils/genapply/dist/build/ total 12 drwxr-xr-x 3 lambdafan lambdafan 4096 Jan 4 13:07 . drwxr-xr-x 3 lambdafan lambdafan 4096 Jan 4 13:07 .. drwxr-xr-x 2 lambdafan lambdafan 4096 Jan 4 13:07 autogen advice on how to proceed?

2 1

Build base with stack
by Robin Palotai 06 Jan '17

06 Jan '17

Hello Cafe, Do you know a way to force a rebuild of base with stack? I don't want to modify it, just want to feed it through a customized ghc pipeline. Using stack is desirable for consistency with how other packages are run through that pipeline. When I download the appropriate base package and put it in a multi project stack directory, I see all the dependent packages are rebuilt, but not base. Thanks! Robin

4 5

Problems with truncate big float values in Haskell
by Henson 06 Jan '17

06 Jan '17

Hi, Firstly I desire one year brilliant for all on group. I have one simple problem but not solved for me for some mistake mine. I have one Rational number (3 + sqrt 5) and I need get the last three digits from integral part of that number. The question is the number is arbitrary and that number always is power of n and n is between 2(Two) and 2000000000(Two billions). I have attempted that on ghci for various values and get same result with different powers: let x = (truncate ((3 + sqrt 5) ^ 2000000)) `mod` 1000 and result is 216. let y = (truncate ((3 + sqrt 5) ^ 20000000)) `mod` 1000 and result is 216. let w = (truncate ((3 + sqrt 5) ^ 200000000)) `mod` 1000 and result is 216. let z = (truncate ((3 + sqrt 5) ^ 2000000000)) `mod` 1000 and result is 216. The result is same for all: 216, and is incorrect because any that expressions have one exclusive value. What I do for complete that task correctly and what I'm mistaken here?! Thank you, Josenildo Silva

4 4

Re: [Haskell-cafe] Problems with truncate big float values in Haskell
by Manuel Gómez 05 Jan '17

05 Jan '17

On Thu, Jan 5, 2017 at 3:51 PM, Henson <jfsihenson(a)gmail.com> wrote: > Ok! I have mistake the correct number. Really the number is Irrational and > the problem is the values are Infinity but How I work with BigFloat precision > for Arbitrary numbers in Haskell?! > > I need get the values for arbitrary precision numbers in haskell about > samples posted not is better implementation for that because range of double > implemented in various languages. > > The correct question here about that is How to resolve that problem?! > > I need get three last digits for arbitrary numbers and after search in > various places not found response for that. > > If exists any material about that but not only for explanations about Floats > and Doubles it's a good start for resolve question. I haven't used it, but this package looks like it might help in your situation: http://hackage.haskell.org/package/cyclotomic

1 0

How to tie knots in XML-style data structures
by Auke Booij 05 Jan '17

05 Jan '17

I am reading an XML file, where some nodes have attributes that refer to other nodes. For example: <blah name="first" type="5"> <yada blah="second"></yada> </blah> <blah name="second" type="3"> </blah> Here, the point is that the inner <yada> refers to a <blah> that is not its parent by means of a "blah" attribute. But there might also be a mistake in the XML file, which I would then want to report: the inner <yada> might refer to a <blah> which does not exist. Using an XML parsing library, this XML file can easily be read into a data type such as the following: data Blah = Blah {blahName :: String, blahType :: Int, blahYadas :: [Yada]} data Yada = Yada {yadaBlah :: String} But for my application, it is useful to have the Yadas refer back to actual Blahs, instead of just their name Strings. So I'd like to parse the XML into the following data structure: data Blah' = Blah' {blah'Name :: String, blah'Type :: Int, blah'Yadas :: [Yada']} data Yada' = Yada' {yada'Blah :: Blah} (the only change is the type of yada'Bla from String to Blah) 1. How can I write a function that takes a Blah, and outputs a Blah', and reports a nice error when there is no <blah> with the name specified in the <yada>? Can it be done at all without using partial functions like fromJust (when using Maybe to "report" errors)? 2. Is there a better way to define the types Blah, Yada, Blah' and Yada' (e.g. with less repetition)? After all, all I'm changing is the type of one field, but I end up having to redefine all my types.

3 4

threadDelay delays less time than expected (Windows)
by Lian Hung Hon 05 Jan '17

05 Jan '17

Dear Haskellers, I am baffled by a strange bug (?) with threadDelay on Windows. It delays for less time than expected (500 seconds vs expected 24 hours), and is consistently reproducible on my system. Can someone have a look (need some patience, ~8 minutes waiting), just to be sure? I glanced around trac but didn't find any related issues. How to reproduce: module Main where import Data.Time import Control.Concurrent import Control.Monad main :: IO () main = do _ <- forkIO thread getLine >>= print -- Just to keep the main thread running thread :: IO () thread = forever $ do now <- getCurrentTime print now threadDelay 86400000000 print "done waiting" Expected result: 2016-12-28 13:07:49.5113098 UTC ... (next timing should be the next day 2016-12-29) Actual result: 2016-12-28 13:07:49.5113098 UTC "done waiting" 2016-12-28 13:16:10.2159485 UTC "done waiting" 2016-12-28 13:24:30.8735845 UTC "done waiting" 2016-12-28 13:32:51.5292203 UTC ... System: Windows 7 Enterprise Service Pack 1, ghc 7.10.3 This seems specific to Windows, it doesn't appear on Debian 8. Help is appreciated! Regards, Hon Rant: It has cost me significant debugging time! Please tell me I made a rookie mistake or misread the docs somewhere!

12 22

Deploying Scotty based web app to Amazon Elastic Bean - One approach
by Guru Devanla 03 Jan '17

03 Jan '17

Hello All, Recently, I have been working on a web app in Haskell using Scotty as the web framework. I had to go through different sources and compile together an approach I took to deploy a dockerized version of web app to Amazon Elastic Beanstalk. There may be other approaches available and I am happy to hear about it. Meanwhile, I documented my experience with a simple Hello World app and documented the steps I had to take to get my app up and running on Elastic Beanstalk. I look forward to suggestions on a better way to do this. https://github.com/gdevanla/helloscotty/blob/master/README.md Hopefully, this documentation is helpful, and does not proposed an anti-pattern! Thanks

1 0

Code review - wrapping servant client to hide required parameters
by Nigel Rantor 02 Jan '17

02 Jan '17

Hello, So, I am still learning and would like someone to cast an eye over some code to see if I am missing something in terms of making it cleaner/more concise. I have begun wrapping the They Work For You API using the Servant Client library. All code is already online for you to grab at; https://github.com/wiggly/twfy-api-client https://hackage.haskell.org/package/twfy-api-client The API is not under my control so I can't change how it works or how it accepts parameters. Every API call requires a Key to be passed as a query string parameter. For a particular session/user this will always be the same, and there is no point in allowing the user to not provide it. Since it is a query parameter Servant forces the type to be within Maybe. For example; type TwfyAPI = "getConstituency" :> QueryParam "key" ApiKey :> QueryParam "name" T.Text :> QueryParam "postcode" T.Text :> Get '[JsonIso8859] Constituency Gives the following function signature; getConstituency :: Maybe ApiKey -- ^ API key -> Maybe T.Text -- ^ Name -> Maybe T.Text -- ^ Post code -> ClientM Constituency To make the API easier to use I have created a Client module that wraps these so that I can hide the passing of the API key for every call, and also allow the user to not have to deal with http client managers or URL parsing if they don't want to. The upshot is that I get a signature that now accepts a data type I have created that contains all the information required to run the client action and return a result, like so (where A.getConstituency is the function above taking a Maybe ApiKey as first argument); getConstituency :: Client -> Maybe T.Text -- ^ Name -> Maybe T.Text -- ^ Post code -> IO (Either ServantError Constituency) getConstituency c = do let key = Just $ clientApiKey c env = clientEnv c in (\name postCode -> (flip runClientM) env (A.getConstituency key name postCode)) So, this wraps up all of the calling of the servant client with an appropriate environment and arguments. I have two questions; 1) What do people think of this style of wrapping the servant client calls? 2) I am now returning a lambda that accepts the remaining arguments to the call, is there any way I can make this cleaner? i.e. is it possible for me to not have to specifically re-write all of the function parameters using something like uncurry or other machinery? I have played with trying to use uncurry but got nowhere fast. Thanks in advance, Nigel

1 0

ANN: hledger 1.1
by Simon Michael 01 Jan '17

01 Jan '17

Two months since last release, I'm pleased to announce hledger 1.1 ! Thank you to contributors Johannes Gerer, Nikolay Orlyuk, and Shubham Lagwankar, along with all others who contributed in other ways. hledger (http://hledger.org) is a dependable, precise, cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple plain text file format. Inspired by the Ledger project, hledger provides command-line, curses and web interfaces, and aims to be a robust, practical tool for daily use. Notable user-visible changes in this release: - hledger-ui --watch live-updates as files or the current date change, useful eg when reconciling or for a time log dashboard - Ledger-style balance assignments are now supported in journal files Full release notes: http://hledger.org/release-notes#hledger-1.1 To install this release: Get stack, eg from http://haskell-lang.org/get-started $ stack install --resolver=nightly hledger [hledger-ui] [hledger-web] [hledger-api] $ ~/.local/bin/hledger or see http://hledger.org/download for more installation options. Our IRC channel is #hledger on Freenode, and you can find out more at http://hledger.org. I hope you enjoy these tools and that they help you achieve your goals. If you like hledger, your support and participation is appreciated! Fund us on Gratipay or Bountysource, give feedback, report bugs, send pull requests, write about it, etc. Happy 2017! Best, -Simon

1 0

How to call python from haskell
by jun zhang 01 Jan '17

01 Jan '17

Dear cafe I had try to use the http://hackage.haskell.org/package/cpython <http://hackage.haskell.org/package/cpython> package. I can call python function once by the package, but when I call function second time it will occur a "Segmentation fault”. Does there any stable package support call python from haskell? Thanks. Julian

2 1

Re: [Haskell-cafe] help with type variable escaping scope/passing lens as function argument
by Li-yao Xia 31 Dec '16

31 Dec '16

Hi Cody, I forgot to keep Haskell-cafe in copy. > Are you saying that my forall applies to both a and b, but not only a? And > that a is what (Lens (Record rs) Chicago -> (...)) expands to? That sounds about right. Try this: dateBetween :: (forall f. Functor f => (Chicago -> f Chicago) -> Record rs -> f (Record rs)) -> Day -> Day -> Pipe (Record rs) (Record rs) IO m Or, a bit refactored: type Lens s a = forall f. Functor f => (a -> f a) -> (s -> f s) dateBetween :: Lens (Record rs) Chicago -> Day -> Day -> Pipe (Record rs) (Record rs) IO m > Where does f1 come from? Does GHC just come up with it because my type > variable doesn't satisfy it? When you write this dateBetween :: forall (rs :: [*]) (m :: *) (f :: * -> *). (Functor f) => ((Chicago -> f Chicago) -> Record rs -> f (Record rs)) -> Day -> Day -> Pipe (Record rs) (Record rs) IO m dateBetween target start end = ... The parameter target is a monomorphic function, with f instantiated at the call site of dateBetween. This means that dateBetween can not assume anything about f apart from the fact that it is an instance of Functor, i.e., f must be abstract. Then we have: let targetDate = rget target r but this is the type of rget: rget :: (forall f . Functor f => (a -> f a) -> Record rs -> f (Record rs)) -> Record rs -> a rget expects a polymorphic function, while target is monomorphic. The compiler tries to unify "f" from the type signature of dateBetween, and "f" from the type signature of rget. To avoid confusion, the compiler does renaming, so that different variables (identified by where they are bound) have different names, and that's where "f1" comes from: rget :: forall a1 rs1. (forall f1 . Functor f1 => (a1 -> f1 a1) -> Record rs1 -> f1 (Record rs1)) -> Record rs1 -> a1 Applying rget to (target :: (Chicago -> f Chicago) -> Record rs -> f (Record rs)), the compiler tries to unify f and f1, and fails because they are "rigid", meaning, they can't be instantiated. f is rigid because it is abstract in the body of dateBetween, f1 is rigid because it is the type parameter of the polymorphic function rget expects. Li-yao On 12/31/2016 09:07 AM, Cody Goodman wrote: > Hi Li-yao, > > Are you saying that my forall applies to both a and b, but not only a? And > that a is what (Lens (Record rs) Chicago -> (...)) expands to? > > In either case, I don't understand what action I can take based on what was > you said and what I understand from it :/ > > Where does f1 come from? Does GHC just come up with it because my type > variable doesn't satisfy it? > > Thanks, > > Cody > > On Sat, Dec 31, 2016 at 2:54 AM, Li-yao Xia <li-yao.xia(a)ens.fr> wrote: > >> Hi Cody, >> >> You wrote something of the shape >> >> forall f. Functor f => a -> b >> >> which means >> >> forall f. Functor f => (a -> b) >> >> but not >> >> (forall f. Functor f => a) -> b >> >> which would be what (Lens (Record rs) Chicago -> (...)) expands to. >> >> Regards, >> Li-yao >> >> >> On 12/31/2016 08:45 AM, Cody Goodman wrote: >> >>> Thanks for the help Li-yao, but I still have a type error after using Rank >>> N Types. I have updated my code on github >>> https://github.com/codygman/frames-credit-card-trans-demo/bl >>> ob/master/src/Main.hs#L45() >>> and pasted below: >>> >>> dateBetween :: forall (rs :: [*]) (m :: *) (f :: * -> *). >>> (Functor f) => >>> ((Chicago -> f Chicago) -> Record rs -> f (Record rs)) >>> -> Day >>> -> Day >>> -> Pipe (Record rs) (Record rs) IO m >>> dateBetween target start end = P.filter go >>> where go :: Record rs -> _ >>> go r = let targetDate = (rget target r) :: Chicago >>> targetDate' = chicagoToZoned targetDate :: ZonedTime >>> targetDay = localDay (zonedTimeToLocalTime targetDate') >>> :: Day >>> in >>> targetDay >= start && targetDay < end >>> -- type error >>> -- src/Main.hs:53:39: error: … >>> -- • Couldn't match type ‘f’ with ‘f1’ >>> -- ‘f’ is a rigid type variable bound by >>> -- the type signature for: >>> -- dateBetween :: forall (rs :: [*]) m (f :: * -> *). >>> -- Functor f => >>> -- ((Chicago -> f Chicago) -> Record rs -> f >>> (Record rs)) >>> -- -> Day -> Day -> Pipe (Record rs) (Record rs) >>> IO m >>> -- at >>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:45:45 >>> -- ‘f1’ is a rigid type variable bound by >>> -- a type expected by the context: >>> -- forall (f1 :: * -> *). >>> -- Functor f1 => >>> -- (Chicago -> f1 Chicago) -> Record rs -> f1 (Record rs) >>> -- at >>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:53:34 >>> -- Expected type: (Chicago -> f1 Chicago) >>> -- -> Record rs -> f1 (Record rs) >>> -- Actual type: (Chicago -> f Chicago) -> Record rs -> f (Record >>> rs) >>> -- • In the first argument of ‘rget’, namely ‘target’ >>> -- In the expression: (rget target r) :: Chicago >>> -- In an equation for ‘targetDate’: >>> -- targetDate = (rget target r) :: Chicago >>> -- • Relevant bindings include >>> -- target :: (Chicago -> f Chicago) -> Record rs -> f (Record rs) >>> -- (bound at >>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:51:13) >>> -- dateBetween :: ((Chicago -> f Chicago) >>> -- -> Record rs -> f (Record rs)) >>> -- -> Day -> Day -> Pipe (Record rs) (Record rs) >>> IO m >>> -- (bound at >>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:51:1) >>> -- Compilation failed. >>> >>> On Sat, Dec 31, 2016 at 2:21 AM, Li-yao Xia <li-yao.xia(a)ens.fr> wrote: >>> >>> Hello Cody, >>>> >>>> Complete the type annotation, using RankNTypes >>>> >>>> dateBetween :: Lens Record Chicago -> ... >>>> >>>> GHC does not infer higher-rank types, because it is an undecidable >>>> problem >>>> in general, so you must annotate polymorphic parameters explicitly. >>>> >>>> Regards, >>>> Li-yao >>>> >>>> >>>> On 12/31/2016 07:56 AM, Cody Goodman wrote: >>>> >>>> I have the following code and error(also seen at >>>>> https://github.com/codygman/frames-credit-card-trans-demo/bl >>>>> ob/master/src/Main.hs#L28 >>>>> ): >>>>> >>>>> >>>>> -- between meaning on or after start but before end >>>>> dateBetween :: _ >>>>> -> Day >>>>> -> Day >>>>> -> Pipe (Record rs) (Record rs) IO r >>>>> dateBetween target start end = P.filter go >>>>> where go :: Record rs -> _ >>>>> go r = let targetDate = rget target r :: Chicago >>>>> targetDate' = chicagoToZoned targetDate :: ZonedTime >>>>> targetDay = localDay (zonedTimeToLocalTime >>>>> targetDate') >>>>> :: Day >>>>> in >>>>> targetDay >= start && targetDay < end >>>>> -- type error >>>>> -- src/Main.hs:48:38: error: … >>>>> -- • Couldn't match expected type ‘(Chicago -> f Chicago) >>>>> -- -> Record rs1 -> f (Record rs1)’ >>>>> -- with actual type ‘t’ >>>>> -- because type variable ‘f’ would escape its scope >>>>> -- This (rigid, skolem) type variable is bound by >>>>> -- a type expected by the context: >>>>> -- Functor f => (Chicago -> f Chicago) -> Record rs1 -> f >>>>> (Record >>>>> rs1) >>>>> -- at >>>>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:33-45 >>>>> -- • In the first argument of ‘rget’, namely ‘target’ >>>>> -- In the expression: rget target r :: Chicago >>>>> -- In an equation for ‘targetDate’: >>>>> -- targetDate = rget target r :: Chicago >>>>> -- • Relevant bindings include >>>>> -- r :: Record rs1 >>>>> -- (bound at >>>>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:12) >>>>> -- go :: Record rs1 -> Bool >>>>> -- (bound at >>>>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:9) >>>>> -- target :: t >>>>> -- (bound at >>>>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:13) >>>>> -- dateBetween :: t -> Day -> Day -> Pipe (Record rs) (Record >>>>> rs) >>>>> IO r >>>>> -- (bound at >>>>> /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:1) >>>>> -- Compilation failed. >>>>> >>>>> Perhaps it's late, but I'm fairly sure I've done something like this >>>>> before. >>>>> >>>>> Thanks, >>>>> >>>>> Cody >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> 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. >>>>> >>>>> >>>>> >>> >

2 1

help with type variable escaping scope/passing lens as function argument
by Cody Goodman 31 Dec '16

31 Dec '16

I have the following code and error(also seen at https://github.com/codygman/frames-credit-card-trans-demo/blob/master/src/M… ): -- between meaning on or after start but before end dateBetween :: _ -> Day -> Day -> Pipe (Record rs) (Record rs) IO r dateBetween target start end = P.filter go where go :: Record rs -> _ go r = let targetDate = rget target r :: Chicago targetDate' = chicagoToZoned targetDate :: ZonedTime targetDay = localDay (zonedTimeToLocalTime targetDate') :: Day in targetDay >= start && targetDay < end -- type error -- src/Main.hs:48:38: error: … -- • Couldn't match expected type ‘(Chicago -> f Chicago) -- -> Record rs1 -> f (Record rs1)’ -- with actual type ‘t’ -- because type variable ‘f’ would escape its scope -- This (rigid, skolem) type variable is bound by -- a type expected by the context: -- Functor f => (Chicago -> f Chicago) -> Record rs1 -> f (Record rs1) -- at /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:33-45 -- • In the first argument of ‘rget’, namely ‘target’ -- In the expression: rget target r :: Chicago -- In an equation for ‘targetDate’: -- targetDate = rget target r :: Chicago -- • Relevant bindings include -- r :: Record rs1 -- (bound at /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:12) -- go :: Record rs1 -> Bool -- (bound at /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:48:9) -- target :: t -- (bound at /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:13) -- dateBetween :: t -> Day -> Day -> Pipe (Record rs) (Record rs) IO r -- (bound at /home/cody/source/frames-credit-card-trans-demo/src/Main.hs:46:1) -- Compilation failed. Perhaps it's late, but I'm fairly sure I've done something like this before. Thanks, Cody

1 0

Netwire woes: creating a wire with mkGen_
by Francesco Ariis 31 Dec '16

31 Dec '16

Hello -cafe, a few days ago I posted this [1] in beginners, I'll pester you too before giving up. tl;dr: I want to create a wire which outputs a stream of 'q's when the letter Q is pressed and a stream of 'a' when the letter A is pressed. What I wrote is not working and I suspect I am not using mkGen_ correctly. Any pointers appreciated! [1] https://mail.haskell.org/pipermail/beginners/2016-December/017276.html

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ANN: rapid, rapid-term: Rapid prototyping for Haskell
by esz＠posteo.de 31 Dec '16

31 Dec '16

Hi everybody, I'd like to officially announce my rapid prototyping suite unimaginatively called [Rapid] along with a helper library called [rapid-term]. The traditional approach to rapid prototyping with Haskell is to have a process running in the background that listens for source code changes and then recompiles/reloads and restarts the application. I'll call this process the *watcher*. This approach has a few drawbacks: * The watcher is separate from the main GHCi instance used for development. This means that the only access to the application state you have is through the interfaces you have explicitly defined in your code. * Restarting the application entails losing all ephemeral state, all network connections, all computed in-memory data, etc. * The watcher typically doesn't understand individual application components, so it's impossible to restart them individually. Rapid uses Chris Done's [foreign-store] library to provide a rapid prototyping framework for GHCi that lets you reload just the relevant parts of your application while keeping everything else running untouched, including all state, database/network connections, etc. It runs directly in the GHCi instance used for development, so you can talk to Rapid as well as your application from the REPL as it runs; no need to define debugging interfaces. The goal is to shorten the development cycle as much as possible. Another example use case is the development of interactive GUI applications. You can keep the GUI window open and preserve all of its run-time state (text you have entered, list items you have created, etc.), while reloading your application logic. It can also be used by batch applications that don't run for extended periods of time, for example to keep expensive resources in memory. For example load and parse your giant data file once and just reuse the resulting value across reloads. There is a detailed [Rapid tutorial] in the documentation of the `Rapid` module. It also walks you through Emacs haskell-mode integration. Rapid-term is a helper library for the development of applications that require an actual terminal. It spawns a separate terminal and keeps it open for the duration of the GHCi session. The application can then access this terminal and reuse it across runs. There is a [rapid-term tutorial] in the documentation of the `Rapid.Term` module, which also explains how to use rapid-term for rapid prototyping of Vty applications (same story as for GUI applications, but for Vty: keep your UI running, preserve your state, reload your application logic). Feedback, bug reports and code contributions are highly welcome! Greets, ertes [foreign-store]: https://hackage.haskell.org/package/foreign-store [rapid tutorial]: https://hackage.haskell.org/package/rapid-0.1.3/docs/Rapid.html [rapid-term tutorial]: https://hackage.haskell.org/package/rapid-term-0.1.0/docs/Rapid-Term.html [rapid-term]: https://hackage.haskell.org/package/rapid-term [rapid]: https://hackage.haskell.org/package/rapid

1 0

Doing the course "Functional Systems in Haskell"
by Damian Nadales 30 Dec '16

30 Dec '16

Hi, I want to follow the material in this course: http://www.scs.stanford.edu/16wi-cs240h/ Is anybody interested in studying the course material and completing the exercises? Has anybody tried to complete earlier versions of the course? Cheers, Damian.

1 0

hackagebot future ?
by Simon Michael 30 Dec '16

30 Dec '16

Hello all, hackagebot is the bot I've been maintaining for a few years which announces new hackage uploads in the #haskell IRC channel. I've tried to keep it "a well-behaved, non-annoying bot". It's configured to announce up to 5 uploads at a time, with at least a 5 minute interval between announcements. As our community grows, upload activity increases, and more megaprojects with many uploads appear, I've seen more complaints about the noise, and noticed channel ops muting it temporarily. A few weeks ago this happened, and also a possible problem with the correctness of the announcements or the feed was reported. I didn't have time to investigate, so I left it offline, inviting feedback if anyone missed it. Since then I've heard nothing. So, even though I personally like seeing the uploads, and the conversations and connections that sometimes result, I'm inclined to let hackagebot rest indefinitely. Or, would a new maintainer like to take it on ? If you have feelings about it one way or the other, please reply on-list. Thanks! -Simon

7 9

many haskell's mails are detected as spam on gmail
by Takenobu Tani 28 Dec '16

28 Dec '16

Hi, I'm using gmail. Recently, many haskell's mails are detected as spam on gmail. (ghc-devs, haskell-cafe, ghc-commit, ...) Does anyone know why? Do you know the workaround? Regards, Takenobu

13 17

References on GADT's
by Damian Nadales 28 Dec '16

28 Dec '16

Hi, I'm climbing up the standardized ladder of functional programming: https://news.ycombinator.com/item?id=13067741 The next topic on my list is to gain some understanding and practice on GADT's (competent section of the ladder). Do you have any resources that you would recommend? Are there any books that cover the topic? Thanks in advance, Damian.

1 0

Multi groupby with foldl' and Map.insertWithKey
by Olaf Klinke 28 Dec '16

28 Dec '16

I'd say the cleanest way to go is to split your Info data structure into an intermediate key and a value part like so: type Key = String data Value = Value {count :: !Int, healthTopics :: ![String]} keyvalue :: Info -> (Key,Value) keyvalue (Info _ h k) = (k,Value 1 [h]) and give Value a Monoid instance: instance Monoid Value where mempty = Value 0 [] mappend (Value c s) (Value c' s') = Value (c+c') (s++s') (Or you could use (Sum Int) instead of Int and have type Value = (Sum Int,[String]). Then the Monoid instance is derived for you.) Now you can transform a list of Infos into a Map using a generic function: makeMap :: [Info] -> M.Map Key Value makeMap = M.fromListWith mappend . map keyvalue Semantically, it's pretty identical to ALeX Kazik's suggestion of using foldl' and alter. Internally, fromListWith uses a strict fold, so strictness should be the same as using foldl'. Olaf

2 3

[NL-FP 2017] 2nd CFP: Dutch Functional Programming Day 2017
by J. Stutterheim 28 Dec '16

28 Dec '16

Second Call for Participation: Dear Friends of Functional Programming, There is still room for more participants for the FP day. Please register until December 31st so we can make arrangements for lunch and dinner. The next Dutch FP Day will be held on Friday, January 6 2017 at the Radboud University in Nijmegen. You are invited to some or all of: participate, give a presentation, join the dinner. For further information, please see the website. https://wiki.clean.cs.ru.nl/NL-FP_dag_2017 Feel free to forward this invitation to colleagues and students who might be interested. Best Regards on behalf of Markus Klinik

1 0

Multi groupby with foldl' and Map.insertWithKey
by Cody Goodman 28 Dec '16

28 Dec '16

My goal is to take data like this: [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] and build a Map like this: [("MA",[("Pregnancy",1)]),("TX",[("Alcohol",2)])] Here is my failed attempt: {-# LANGUAGE ScopedTypeVariables, BangPatterns #-} import qualified Data.Map as M import Data.List (foldl') import Data.Maybe import Debug.Trace data Info = Info { i :: !Int, healthTopic :: !String, state :: !String } deriving Show m :: M.Map String (M.Map String Integer) m = M.fromList [("MA", M.fromList[("Pregnancy",1)]),("TX", M.fromList[("Alcohol",2)])] constantValsPerState = foldl' (\accum currentRow -> do M.insert (state currentRow) "xxx" accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- λ> constantValsPerState -- fromList [("MA","xxx"),("TX","xxx")] -- how can I get something like: -- λ> numTopicsPerState -- fromList [("MA", fromList[("Pregnancy",1)]),("TX", fromList[("Alcohol",2)])] -- so we need to give the modified stae of the new map isntead of M.empty -- λ> m -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- λ> M.insertWith (\new old -> new) "MA" M.empty m -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",2)])] numTopicsPerState = foldl' (\(accum :: M.Map String (M.Map String Integer)) currentRow -> do M.insertWithKey (\k new old -> M.insert (healthTopic currentRow) ((fromMaybe 0 $ M.lookup (healthTopic currentRow) old) + 1) new ) (state currentRow) (fromMaybe (M.empty) (M.lookup (state currentRow) accum)) accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- WRONG OUTPUT -- λ> numTopicsPerState -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",1)])] -- TODO -- turn -- fromList [("Alcohol",fromList []),("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- into -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",3)])]

3 2

Call for new Stackage Curator
by Michael Snoyman 26 Dec '16

26 Dec '16

I'm copying the text from my blog post today[1]. On behalf of the Stackage curators, I'm putting out a call for a volunteer to join the team. The Stackage curators are responsible for the day-to-day management of the Stackage project: merging PRs, managing builds, reporting bounds issues and build or test failures, and every once in a while making a judgement call on when to bump to newer package versions. The curator team currently consists of Adam Bergmark, Dan Burton, Jens Petersen, and me. The processes we follow are documented in the curator guide[2]. We each rotate shifts, taking one week at a time on duty. Overall, the workload is light and straightforward: usually less than 30 minutes a day. We're putting out this call for a new volunteer since we've been running as a four-person show for a while now, and want to make sure we're getting our processes well documented enough for newcomers to easily come up to speed on the process. While we are currently asking for just one new addition to the team, if there are multiple enthusiastic candidates, we will definitely consider expanding the team further. Joining the curator team is a great way to both contribute to the Haskell ecosystem, and to become more familiar with how things work. You'll also get an opportunity to interact (albeit in brief discussions) with many package maintainers in the Haskell community. If you're interested in applying, please send a message to the Stackage mailing list[3] or, if you prefer applying privately, send me an email and I'll pass the message along to the rest of the team. [1] http://www.snoyman.com/blog/2016/12/call-for-new-stackage-curator [2] https://github.com/fpco/stackage/blob/master/CURATORS.md [3] https://groups.google.com/d/forum/stackage

2 1

happy parser generator - stack space overflow error
by Mageshkumar Kuppusamy 25 Dec '16

25 Dec '16

Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh

3 2

Re: [Haskell-cafe] happy parser generator - stack space overflow error
by Tobias Dammers 25 Dec '16

25 Dec '16

In my experience, using one of the excellent parser-combinator libraries out there (megaparsec, attoparsec, trifecta) is usually less painful and perfectly adequate. On Dec 25, 2016 7:49 AM, "Mageshkumar Kuppusamy" <magesh.kuppusamy(a)gmail.com> wrote: Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh _______________________________________________ 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

ANNOUNCE: Haskell Communities and Activities Report (31st ed., November 2016)
by Mihai Maruseac 24 Dec '16

24 Dec '16

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (31st edition, November 2016) is now available, in PDF and HTML formats: http://haskell.org/communities/11-2016/report.pdf http://haskell.org/communities/11-2016/html/report.html All previous editions of HCAR can be accessed on the wiki at https://wiki.haskell.org/Haskell_Communities_and_Activities_Report Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of February 2016: target deadline for contributions to the May 2017 edition of the HCAR Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in November (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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Call for Papers: ICFP 2017
by Lindsey Kuper 24 Dec '16

24 Dec '16

ICFP 2017 The 22nd ACM SIGPLAN International Conference on Functional Programming Oxford, United Kingdom http://icfp17.sigplan.org/ Call for Papers ### Important dates Submissions due: Monday, February 27, Anywhere on Earth https://icfp17.hotcrp.com Author response: Monday, April 17, 2017, 15:00 (UTC) - Thursday, April 20, 2017, 15:00 (UTC) Notification: Monday, 1 May, 2017 Final copy due: Monday, 5 June 2017 Early registration: TBA Conference: Monday, 4 September - Wednesday, 6 September, 2017 ### New this year Those familiar with previous ICFP conferences should be aware of two significant changes that are being introduced in 2017: 1. Papers selected for ICFP 2017 will be published as the ICFP 2017 issue of a new journal, Proceedings of the ACM on Programming Languages (PACMPL), which replaces the previous ICFP conference proceedings. The move to PACMPL will have two noticeable impacts on authors: * A new, two-phase selection and reviewing process that conforms to ACM’s journal reviewing guidelines. * A new, single-column format for submissions. 2. Authors of papers that are conditionally accepted in the first phase of the reviewing process will have the option to submit materials for Artifact Evaluation. Further details on each of these changes are included in the following text. ### Scope ICFP 2017 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Topics of interest include (but are not limited to): * *Language Design*: concurrency, parallelism, and distribution; modules; components and composition; metaprogramming; type systems; interoperability; domain-specific languages; and relations to imperative, object-oriented, or logic programming. * *Implementation*: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimization; garbage collection and memory management; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources. * *Software-Development Techniques*: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling. * *Foundations*: formal semantics; lambda calculus; rewriting; type theory; monads; continuations; control; state; effects; program verification; dependent types. * *Analysis and Transformation*: control-flow; data-flow; abstract interpretation; partial evaluation; program calculation. * *Applications*: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed-systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; multimedia and 3D graphics programming; scripting; system administration; security. * *Education*: teaching introductory programming; parallel programming; mathematical proof; algebra. Submissions will be evaluated according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. ICFP 2017 also welcomes submissions in two separate categories — Functional Pearls and Experience Reports — that must be marked as such at the time of submission and that need not report original research results. Detailed guidelines on both categories are given at the end of this call. Please contact the program chair if you have questions or are concerned about the appropriateness of a topic. ### Preparation of submissions **Deadline**: The deadline for submissions is Monday, February 27, 2017, Anywhere on Earth (<https://en.wikipedia.org/wiki/Anywhere_on_Earth>). This deadline will be strictly enforced. **Formatting**: (NOTE: NEW FORMAT REQUIREMENTS FOR ICFP 2017) Submissions must be in PDF format, printable in black and white on US Letter sized paper, and interpretable by common PDF tools. All submissions must adhere to the "ACM Large" template that is available (in both LaTeX and Word formats) from <http://www.acm.org/publications/proceedings-template>. For authors using LaTeX, a lighter-weight package, including only the essential files, is available from <http://sigplan.org/Resources/Author/#acmart-format>. There is a limit of 24 pages for a full paper or 12 pages for an Experience Report; in either case, the bibliography will not be counted against these limits. These page limits have been chosen to allow essentially the same amount of content with the new single-column format as was possible with the two-column format used in past ICFP conferences. Submissions that exceed the page limits or, for other reasons, do not meet the requirements for formatting, will be summarily rejected. **Submission**: Submissions will be accepted at <https://icfp17.hotcrp.com/> (in preparation at the time of writing). Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. **Author Response Period**: Authors will have a 72-hour period, starting at 15:00 UTC on Monday, April 17, 2017, to read reviews and respond to them. **Supplementary Materials**: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. The material should be uploaded at submission time, as a single pdf or a tarball, not via a URL. This supplementary material may or may not be anonymized; if not anonymized, it will only be revealed to reviewers after they have submitted their review of the paper and learned the identity of the author(s). **Authorship Policies**: All submissions are expected to comply with the ACM Policies for Authorship that are detailed at <https://www.acm.org/publications/authors/information-for-authors>. **Republication Policies**: Each submission must adhere to SIGPLAN's republication policy, as explained on the web at <http://www.sigplan.org/Resources/Policies/Republication>. **Resubmitted Papers**: Authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the program chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. ### Review Process This section outlines the two-stage process with lightweight double-blind reviewing that will be used to select papers for presentation at ICFP 2017. We anticipate that there will be a need to clarify and expand on this process, and we will maintain a list of frequently asked questions and answers on the conference website to address common concerns. **ICFP 2017 will employ a two-stage review process.** The first stage in the review process will assess submitted papers using the criteria stated above and will allow for feedback and input on initial reviews through the author response period mentioned previously. At the PC meeting, a set of papers will be conditionally accepted and all other papers will be rejected. Authors will be notified of these decisions on May 1, 2017. Authors of conditionally accepted papers will be provided with committee reviews (just as in previous conferences) along with a set of mandatory revisions. After five weeks (June 5, 2017), the authors will provide a second submission. The second and final reviewing phase assesses whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. The intent and expectation is that the mandatory revisions can be addressed within five weeks and hence that conditionally accepted papers will in general be accepted in the second phase. The second submission should clearly identify how the mandatory revisions were addressed. To that end, the second submission must be accompanied by a cover letter mapping each mandatory revision request to specific parts of the paper. The cover letter will facilitate a quick second review, allowing for confirmation of final acceptance within two weeks. Conversely, the absence of a cover letter will be grounds for the paper’s rejection. This process is intended as a refinement of the review process that has been used in previous ICFP conferences. By incorporating a second stage, the process will conform to ACM’s journal reviewing guidelines for PACMPL. **ICFP 2017 will employ a lightweight double-blind reviewing process.** To facilitate this, submitted papers must adhere to two rules: 1. **author names and institutions must be omitted**, and 2. **references to authors' own related work should be in the third person** (e.g., not "We build on our previous work ..." but rather "We build on the work of ..."). The purpose of this process is to help the PC and external reviewers come to an initial judgement about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. ### Information for Authors of Accepted Papers * As a condition of acceptance, final versions of all papers must adhere to the new ACM Large format. The page limits for final versions of papers will be increased to ensure that authors have space to respond to reviewer comments and mandatory revisions. * Authors of accepted submissions will be required to agree to one of the three ACM licensing options: copyright transfer to ACM; retaining copyright but granting ACM exclusive publication rights; or open access on payment of a fee. Further information about ACM author rights is available from <http://authors.acm.org>. * At least one author of each accepted submissions will be expected to attend and present their paper at the conference. The schedule for presentations will be determined and shared with authors after the full program has been selected. Presentations will be videotaped and released online if the presenter consents. * We intend that the proceedings will be freely available for download from the ACM Digital Library in perpetuity via the OpenTOC mechanism. * ACM Author-Izer is a unique service that enables ACM authors to generate and post links on either their home page or institutional repository for visitors to download the definitive version of their articles from the ACM Digital Library at no charge. Downloads through Author-Izer links are captured in official ACM statistics, improving the accuracy of usage and impact measurements. Consistently linking to the definitive version of an ACM article should reduce user confusion over article versioning. After an article has been published and assigned to the appropriate ACM Author Profile pages, authors should visit <http://www.acm.org/publications/acm-author-izer-service> to learn how to create links for free downloads from the ACM DL. * The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to *two weeks prior* to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. ### Artifact Evaluation Authors of papers that are conditionally accepted in the first phase of the review process will be encouraged (but not required) to submit supporting materials for Artifact Evaluation. These items will then be reviewed by a committee, separate from the program committee, whose task is to assess how the artifacts support the work described in the associated paper. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Authors of accepted papers will be encouraged to make the supporting materials publicly available upon publication of the proceedings, for example, by including them as "source materials" in the ACM Digital Library. An additional seal will mark papers whose artifacts are made available, as outlined in the ACM guidelines for artifact badging. Participation in Artifact Evaluation is voluntary and will not influence the final decision regarding paper acceptance. Further information about the motivations and expectations for Artifact Evaluation can be found at <http://icfp17.sigplan.org/track/icfp-2017-Artifacts>. ### Special categories of papers In addition to research papers, ICFP solicits two kinds of papers that do not require original research contributions: Functional Pearls, which are full papers, and Experience Reports, which are limited to half the length of a full paper. Authors submitting such papers should consider the following guidelines. #### Functional Pearls A Functional Pearl is an elegant essay about something related to functional programming. Examples include, but are not limited to: * a new and thought-provoking way of looking at an old idea * an instructive example of program calculation or proof * a nifty presentation of an old or new data structure * an interesting application of functional programming techniques * a novel use or exposition of functional programming in the classroom While pearls often demonstrate an idea through the development of a short program, there is no requirement or expectation that they do so. Thus, they encompass the notions of theoretical and educational pearls. Functional Pearls are valued as highly and judged as rigorously as ordinary papers, but using somewhat different criteria. In particular, a pearl is not required to report original research, but, it should be concise, instructive, and entertaining. A pearl is likely to be rejected if its readers get bored, if the material gets too complicated, if too much specialized knowledge is needed, or if the writing is inelegant. The key to writing a good pearl is polishing. A submission that is intended to be treated as a pearl must be marked as such on the submission web page, and should contain the words "Functional Pearl" somewhere in its title or subtitle. These steps will alert reviewers to use the appropriate evaluation criteria. Pearls will be combined with ordinary papers, however, for the purpose of computing the conference's acceptance rate. #### Experience Reports The purpose of an Experience Report is to help create a body of published, refereed, citable evidence that functional programming really works — or to describe what obstacles prevent it from working. Possible topics for an Experience Report include, but are not limited to: * insights gained from real-world projects using functional programming * comparison of functional programming with conventional programming in the context of an industrial project or a university curriculum * project-management, business, or legal issues encountered when using functional programming in a real-world project * curricular issues encountered when using functional programming in education * real-world constraints that created special challenges for an implementation of a functional language or for functional programming in general An Experience Report is distinguished from a normal ICFP paper by its title, by its length, and by the criteria used to evaluate it. * Both in the proceedings and in any citations, the title of each accepted Experience Report must begin with the words "Experience Report" followed by a colon. The acceptance rate for Experience Reports will be computed and reported separately from the rate for ordinary papers. * Experience Report submissions can be at most 12 pages long, excluding bibliography. * Each accepted Experience Report will be presented at the conference, but depending on the number of Experience Reports and regular papers accepted, authors of Experience reports may be asked to give shorter talks. * Because the purpose of Experience Reports is to enable our community to accumulate a body of evidence about the efficacy of functional programming, an acceptable Experience Report need not add to the body of knowledge of the functional-programming community by presenting novel results or conclusions. It is sufficient if the Report states a clear thesis and provides supporting evidence. The thesis must be relevant to ICFP, but it need not be novel. The program committee will accept or reject Experience Reports based on whether they judge the evidence to be convincing. Anecdotal evidence will be acceptable provided it is well argued and the author explains what efforts were made to gather as much evidence as possible. Typically, more convincing evidence is obtained from papers which show how functional programming was used than from papers which only say that functional programming was used. The most convincing evidence often includes comparisons of situations before and after the introduction or discontinuation of functional programming. Evidence drawn from a single person's experience may be sufficient, but more weight will be given to evidence drawn from the experience of groups of people. An Experience Report should be short and to the point: it should make a claim about how well functional programming worked on a particular project and why, and produce evidence to substantiate this claim. If functional programming worked in this case in the same ways it has worked for others, the paper need only summarize the results — the main part of the paper should discuss how well it worked and in what context. Most readers will not want to know all the details of the project and its implementation, but the paper should characterize the project and its context well enough so that readers can judge to what degree this experience is relevant to their own projects. The paper should take care to highlight any unusual aspects of the project. Specifics about the project are more valuable than generalities about functional programming; for example, it is more valuable to say that the team delivered its software a month ahead of schedule than it is to say that functional programming made the team more productive. If the paper not only describes experience but also presents new technical results, or if the experience refutes cherished beliefs of the functional-programming community, it may be better off submitted it as a full paper, which will be judged by the usual criteria of novelty, originality, and relevance. The program chair will be happy to advise on any concerns about which category to submit to. ### Organizers General Chair: Jeremy Gibbons (University of Oxford, UK) Program Chair: Mark Jones (Portland State University, USA) Artifact Evaluation Chair: Ryan R. Newton (Indiana University, USA) Industrial Relations Chair: Ryan Trinkle (Obsidian Systems LLC, USA) Programming Contest Organiser: Sam Lindley (University of Edinburgh, UK) Publicity and Web Chair: Lindsey Kuper (Intel Labs, USA) Student Research Competition Chair: Ilya Sergey (University College London, UK) Video Chair: Jose Calderon (Galois, Inc., USA) Workshops Co-Chair: Andres Löh (Well-Typed LLP) Workshops Co-Chair: David Christiansen (Indiana University, USA) Program Committee: Bob Atkey (University of Strathclyde, Scotland) Adam Chlipala (MIT, USA) Dominique Devriese (KU Leuven, Belgium) Martin Erwig (Oregon State, USA) Matthew Flatt (University of Utah, USA) Ronald Garcia (University of British Columbia, Canada) Kathryn Gray (University of Cambridge, England) John Hughes (Chalmers University and Quvik, Sweden) Chung-Kil Hur (Seoul National University, Korea) Graham Hutton (University of Nottingham, England) Alan Jeffrey (Mozilla Research, USA) Ranjit Jhala (University of California, San Diego, USA) Shin-ya Katsumata (Kyoto University, Japan) Lindsey Kuper (Intel Labs, USA) Dan Licata (Wesleyan University, USA) Ben Lippmeier (Digital Asset, Australia) Gabriel Scherer (Northeastern University, USA) Alexandra Silva (University College London, England) Nikhil Swamy (Microsoft Research, USA) Sam Tobin-Hochstadt (Indiana University, USA) Nicolas Wu (University of Bristol, England) Beta Ziliani (CONICET and FAMAF, Universidad Nacional de Córdoba, Argentina)

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Fwd: Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

> > * Would using a snapshot-based revision control system like Git be an > option? If yes, you could use the [filestore] library. > It's not exactly what I had in mind but I'll think about it. > > * Another option is to run an insertion-only relational model on > really any database system you want like PostgreSQL. There is > nothing about preserving history that needs special handling to be > efficient. > I assume that some sort of structural sharing is needed once the collections grow above a certain size. Also some support for caching would be nice. > * Yet another option is to model your application state with history > and use [acid-state]. However, acid-state only makes an in-memory > Haskell value (the "database") persistent with ACID guarantees. If > you mostly work with the current state, keeping the whole history in > memory all the time would be a waste. Therefore this option may be > less useful. > The database will probably grow bigger than the memory so this is not an option. ...and thanks for the pointers

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Lenses: Changing/creating values deep inside JSON or HashMap
by Jan von Löwenstein 23 Dec '16

23 Dec '16

Hi, I want to have code that produces the following result no matter if input A or B was given: Result: { "outer" : { "inner" : "new-value" } } A: { "outer" : { "inner" : "old-value" } } B: {} `json & key "outer"._Object.key "inner" .~ "new-value"` didn't work. Is what I want even possible with lenses? Best Jan

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Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

Is there any package in Haskell that provides something similar to Datomic http://www.datomic.com/? Basically what I am looking for is a database which could keep all the versions of my data in an efficient way, the same way the persistent data structures do. Ideally it should be implemented over some scalable storage. I looked at Datomic itself but I couldn't find a Haskell client library. The only way to connect to it from a Haskell application is through the REST server which they have just deprecated ( http://docs.datomic.com/rest.html) Thanks!

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