October 2015 - Haskell-Cafe

Avoiding Dependency loops
by martin 25 Oct '15

25 Oct '15

Hello all, I just split up a program I'm working on into several source files and ran into the following difficulty: module Process implements Process which has a field Runner. Runner is a basically a function which alters a 'System' state. So Process needs Runner, Runner needs System and thus Process needs System. module System implements among others a collection of Processes (because Processes can alter their states). So System needs Process. Eh voila, I have a loop. What I did was to leave the type of the Runner unspecified in Process, i.e. I now have (Process r) where r is the type of the Runner. Thus Process no longer needs to know about System. This does work, but it feels strange and I'm a bit worried that this is an indication for a design flaw, but I cannot see it.

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Projectional editing: Separating a program's AST from its presentation
by Jeffrey Brown 25 Oct '15

25 Oct '15

These ideas were touched on in a previous thread [1]. Our work would be easier if, as data, we separated a program's AST from its layout. If, for instance, the order in which a library's functions are presented on the page were stored as a "projection", separate from the AST that defined those functions, then one could reorder the functions without obscuring the history of changes to anything that was "moved". I assume I am not alone in making a lot of edits aimed solely at allowing me to read or traverse the code faster? Those within-function changes of presentation, like across-function changes of order, obscure the record of functional (as opposed to cosmetic) changes. They don't have to. Moreover, if projections and the AST were separate data, one could use contradictory hierarchiies|projections|layouts for the same data. One projection might group functions by their common purpose (an "is-tree"), while another grouped them by priority to the reader-rewriter (a "do-tree"). Given current technology, text folding does allow us to impose a hierarchy on a text document (even a Haskell document! you just need to indent the code relative to the comments that define the hierarchy). However, if the code is stored as text, then only one hierarchy is possible. In particular one is presently forced to choose between an "is-tree" and a "do-tree". https://groups.google.com/forum/#!msg/haskell-cafe/d8h8J8VxZxo/BNlKUjWeAgAJ -- Jeffrey Benjamin Brown

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Google Cloud API
by Tomas Carnecky 24 Oct '15

24 Oct '15

I recently migrated some infrastructure from AWS to Google Cloud and needed a way to upload a file to a storage bucket. For AWS there's an awesome Haskell library (aws), but I couldn't find anything comparable for interacting with the Google Cloud APIs. While it wouldn't be difficult to write a standalone function for that simple task, I decided to package it up in a library. Currently implemented is uploading a ByteString to a bucket and some metadata server queries. That's all I need currently, but I may add a few more selected APIs in the near future (mostly around managing compute instances). Adding support for new APIs should be relatively easy, even without having to change the library itself. All the internals are exposed to users of the library. There is nothing private or hidden. The library gives you access to convenience functions to send HTTP requests. That, coupled with a bit of JSON/aeson parsing, should cover most use cases. http://hackage.haskell.org/package/google-cloud https://github.com/wereHamster/google-cloud#readme

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wxHaskell on Windows compilation problems
by Michael Jones 24 Oct '15

24 Oct '15

I’m trying to compile an established wxHaskell application (Ubuntu) on Windows 7 and after a day of frustration, I wanted to see if anyone had some clues. The problem is getting wxc to compile against wxWidgets, where wxWidgets was compiled with MinGHC (GHC 7.8.4). Following are my steps up to trouble: - On 64 bit Win 7, install MinGHC, which ends up in the AppData path. - Grab wxWidgets with git and using MSYS shell compile like: mingw32-make -f makefile.gcc SHARED=1 UNICODE=1 BUILD=release clean mingw32-make -f makefile.gcc SHARED=1 UNICODE=1 BUILD=release with the goal of compiler compatibility. - Setup some environment variables like: C_INCLUDE_PATH == C:\PCRE\include CPLUS_INCLUDE_PATH == C:\Libs\wxWidgets\3.0.2\include LIBRARY_PATH == C:\PCRE\lib;C:\Libs\wxHaskell\3.0.2\\lib\gcc_lib MSYSTEM == MINGW64 WXCFG == gcc_dll\mswu WXWIN == C:\Libs\wxWidgets\3.0.2 PATH = C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\git-2.4.5.1\cmd;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\git-2.4.5.1\usr\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\bin;C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\bin;C:\Users\michaeljones\AppData\Roaming\cabal\bin; - Tweak wxUSE_GRAPHICS_CONTEXT - Create sandbox for my project with pointer to a local copy of wxHaskell - Apply a few patches to enable some new table support (stable stuff) - Configure with cabal and compile The first problem is it can’t run wx-config because it looks for a script, so I tweaked the Setup.hs to use the exe and it continues to compile. It gets this error: Building wxc C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin\gcc.exe -Isrc/include -IC:/Users/michaeljones /Documents/linti/libs/wxHaskell/wxc -IC:/Users/michaeljones/Documents/linti/libs/wxHaskell/wxc -DWXUSINGDLL -D_UNICODE -D__WXDEBUG __ -D__WXMSW__ -DHAVE_W32API_H -DwxcREFUSE_MEDIACTRL -DBUILD_DLL -c src\cpp\apppath.cpp -o dist\dist-sandbox-95204306\build\src/cp p/apppath.o In file included from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20:0, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:22: fatal error: wx/setup.h: No such file or directory compilation terminated. So, I copy the wxWidgets setup.h file from include/msvc/wx to include/wx and compile to a new error: Build log ( C:\Users\michaeljones\Documents\linti\linti-beagle\.cabal-sandbox\logs\wxc-0.92.0.0.log ): Building wxc C:\Users\michaeljones\AppData\Local\Programs\minghc-7.8.4-x86_64\ghc-7.8.4\mingw\bin\gcc.exe -Isrc/include -IC:/Users/michaeljones /Documents/linti/libs/wxHaskell/wxc -IC:/Users/michaeljones/Documents/linti/libs/wxHaskell/wxc -DWXUSINGDLL -D_UNICODE -D__WXDEBUG __ -D__WXMSW__ -DHAVE_W32API_H -DwxcREFUSE_MEDIACTRL -DBUILD_DLL -c src\cpp\apppath.cpp -o dist\dist-sandbox-95204306\build\src/cp p/apppath.o In file included from C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:0, from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:12:6: error: #error "This file should only be included when using Microsoft Visual C++" In file included from C:\Libs\wxWidgets\3.0.2\include/wx/platform.h:136:0, from C:\Libs\wxWidgets\3.0.2\include/wx/defs.h:20, from C:\Libs\wxWidgets\3.0.2\include/wx/wx.h:14, from src/include/wrapper.h:20, from src\cpp\apppath.cpp:1: C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "/" and "vc_x64_dll" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "vc_x64_dll" and "/" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "/" and "msw" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:1: error: pasting "mswu" and "/" does not give a valid preprocessing token C:\Libs\wxWidgets\3.0.2\include/wx/setup.h:121:27: fatal error: ../../../lib/vc_x64_dll /mswu /wx/setup.h: No such file or directo I assume the problem is that the wxWidget compilation that comes with makefile.gcc is somehow bypassing some linux based compilation method and not leaving the tree in the proper state for wxHaskell. The Wiki page is based on platform, not MinGHC. I used MinGHC because it got me over problems compiling regex-pcre against libpcre where I failed with cygwin. From reading is appeared MinGHC was a good general path. Note, I had the TDM compiler on the machine, but it was taken out, so there is no accidentally use of the wrong compiler or anything going on. Does anyone have any clues how to make wxHaskell and MinGHC work together? Mike

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ICFP 2016 Call for Workshop and Co-located Event Proposals
by Lindsey Kuper 23 Oct '15

23 Oct '15

         CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS                             ICFP 2016  21st ACM SIGPLAN International Conference on Functional Programming                      September 18-24, 2016                           Nara, Japan                http://icfpconference.org/icfp2016/ The 21st ACM SIGPLAN International Conference on Functional Programming will be held in Nara, Japan on September 18-24, 2016. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as tutorials) to be affiliated with ICFP 2016 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on September 18 (the day before ICFP) and September 22-24 (the three days after ICFP). ---------------------------------------------------------------------- Submission details  Deadline for submission:     November 21, 2015  Notification of acceptance:  December 20, 2015 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2016 workshop co-chairs (Andres Loeh and Nicolas Wu), via email to     icfp2016-workshops(a)googlegroups.com by November 21, 2015. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by December 20, 2015, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2016-files/icfp16-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://www.sigplan.org/Resources/Proposals/Sponsored/ ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2016 organizing committee, together with the members of the SIGPLAN executive committee.  Workshop Co-Chair: Andres Loeh                        (Well-Typed LLP)  Workshop Co-Chair: Nicolas Wu                  (University of Bristol)  General Co-Chair : Jacques Garrigue                (Nagoya University)  General Co-Chair : Gabriele Keller     (University of New South Wales)  Program Chair:     Eijiro Sumii                    (Tohoku University) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Andres Loeh and Nicolas Wu), via email to icfp2016-workshops(a)googlegroups.com

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[ANN] haskell-ide project
by Alan & Kim Zimmerman 23 Oct '15

23 Oct '15

The ongoing effort to save us as a community from separately implementing the same functionality over and over around IDEs[1] has found a home in the haskell-ide project on github [2]. This mail serves as a call to collaborate for all parties interested in this space. It is still at a very early stage, but the intent is to pool resources so that we can have really good support for IDEs that can extend through the entire tool chain from changes to GHC to better support tooling through the build environment and community information management. This should mean that people who are familiar with a particular part of the chain can focus their efforts there, knowing that the other parts will be covered too. This is a deliberately broad and vague scope, the reality is likely to be much more limited initially, but the sooner we can get started the sooner we will have something concrete to criticise and improve. For those wishing to get involved the following resources currently exist * the haskell-ide mailing list [3] * the github project page [1] * The #haskell-ide channel on IRC Freenode. This is not aimed at some small inner circle of people, anyone who wants to will be added to the project on github, adress your request to me or @hvr. Regards Alan [1] IDE is a loose term for anything that enables a user to interact with the code. [2] https://github.com/haskell/haskell-ide [3] https://groups.google.com/forum/#!forum/haskell-ide

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New STM Data Structures Collection
by Алексей Семин 23 Oct '15

23 Oct '15

Hi everyone! I want to present a couple of STM data structures which were implemented by me and Ryan Yates this summer (during GSOC 2015). I decided to create only a candidate package [1]. I would be glad if anyone can take a look and/or comment on topic. Since Hackage does not provide the easy way to `cabal install` candidate packages I have written a script [2] which should do all the work for you. It create a directory in /tmp and initialized sandbox along with cloning the library from github [3]. After that it will download Haskell program with an example of data structure usage. Thank you for your attention. [1] https://hackage.haskell.org/package/stm-data-collection-0.1.0.0/candidate [2] https://gist.github.com/Alllex/445f3d74e872fe032596 [3] https://github.com/Alllex/stm-data-collection -- Regards, Alex Semin

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how to create a pipes producer from websockets?
by Dimitri DeFigueiredo 22 Oct '15

22 Oct '15

Hello All, I am trying to use both the websockets library and the pipes library. They seem like a natural fit. However, I wanted to use the websockets library to build a pipes 'Producer' and that does not seem possible without some heavy lifting. The websockets library does not give me a connection I can read from and write to. Instead, I need to supply an IO action (called a clientApp). And execute it using something like: --runClient :: String -- ^ Host -- -> Int -- ^ Port -- -> String -- ^ Path -- -> ClientApp a -- ^ Client application -- type ClientApp a = Connection -> IO a -- -> IO a main :: IO () main = withSocketsDo $ runClient "echo.websocket.org" 80 "/" app The problem happens when you couple this restriction with the requirement that ClientApps have type 'Connection -> IO a'. Pipes producers are Monad transformer stacks. For example, I would like to build something like: messageProducer :: Producer' WebsocketMessage IO () But this does not run in the IO monad and at the same time I cannot get a 'Connection' object unless I use runClient. So, it seems I have a catch22 situation. Or have I overlooked something? I'd rather not have to do "un-lifting" on the monad transformer stack. Has anyone done this before? Any suggestions on how to go about it? Thanks, Dimitri

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Re: [Haskell-cafe] Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`
by Simon Thompson 21 Oct '15

21 Oct '15

Hello all. I write this to be a little provocative, but … It’s really interesting to have this discussion, which pulls in all sorts of well-made points about orthogonality, teaching, the evolution of the language and so on, but it simply goes to show that the process of evolving Haskell is profoundly broken. Other languages do evolve, but in a managed and reflective way. Simply throwing in changes that would have a profound impact on systems that are commercially and potentially safety critical in an à la carte, offhand, way seems like a breakdown of the collective responsibility of the Haskell community to its users and, indirectly, to its future. If we make claims - I believe rightly - that Haskell is hitting the mainstream, then we need to think about all changes in terms of the costs and benefits of each of them in the widest possible sense. There’s an old fashioned maxim that sums this up in a pithy way: “if it ain’t broke, don’t fix it”. Simon Thompson > On 5 Oct 2015, at 10:47, Michał J Gajda <mjgajda(a)gmail.com> wrote: > > Hi, > > As a person who used Haskell in all three capacities (for scientific research, for commercial purpose, and to introduce others to benefits of pure and strongly typed programming), I must voice an supportive voice for this change: > 1. Orthogonal type classes are easier to explain. > 2. Gradual improvements helps us to generalize further, and this in turn makes education easier. > 3. Gradual change that break only a little help to prevent either stagnation (FORTRAN) and big breakage (py3k). That keeps us excited. > > That would also call to split TCs into their orthogonal elements: return, ap, bind having the basic TC on their own. > > So: > +1, but only if it is possible to have compatibilty mode. I believe that rebindable syntax should allow us to otherwise make our own prelude, if we want such a split. Then we could test it well before it is used by the base library. > > That said, I would appreciate Haskell2010 option just like Haskell98 wad, so that we can compile old programs without changes. Even by using some Compat version of standard library. Would that satisfy need for stability? > > PS And since all experts were beginners some time ago, I beg that we do not call them "peripheral". > -- > Best regards > Michał > > On Monday, 5 October 2015, Malcolm Wallace <malcolm.wallace(a)me.com <mailto:malcolm.wallace@me.com>> wrote: > On other social media forums, I am seeing educators who use Haskell as a vehicle for their main work, but would not consider themselves Haskell researchers, and certainly do not have the time to follow Haskell mailing lists, who are beginning to say that these kinds of annoying breakages to the language, affecting their research and teaching materials, are beginning to disincline them to continue using Haskell. They are feeling like they would be > (...) > > > -- > Pozdrawiam > Michał > _______________________________________________ > Haskell-prime mailing list > Haskell-prime(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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[ANN] codex 0.4
by Alois Cochard 21 Oct '15

21 Oct '15

Hello Café, I have released a new version of `codex`[1] (a ctags file generator for cabal/stack projects and their dependencies). This release include some fixes but more important it *include support for `stack`* projects. As `stack` is multi-platform and so is `codex`, it should work seamlessly on any OS but I have only done testing on unix. Cheers [1] https://github.com/ <https://github.com/aloiscochard/codex>aloiscochard/ codex <https://github.com/aloiscochard/codex> -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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