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Future of FPComplete Haskell Center (IDE)
by Thomas Bereknyei 19 Oct '15

19 Oct '15

FPComplete is deprecating Haskell Center and removing support for their hosted IDE at the end of the year. I enjoy using the IDE in many situations and would like to have a similar capability available to the community. I know several people have expressed interest in helping maintain a version that can go on. Michael Snoyman has stated that there are some issues with the existing codebase and that there are many things that can/should be improved. There are some limitations due to NDA, but I believe FPComplete would be willing to hand over much of the codebase. I intend this thread to bring together those people interested in helping with this effort in any way. Personally, I would be willing to provide limited hosting and some development support. My goals would be to upgrade support to 8.x GHC, latest Stackage - LTS and create a path for people to self-host the IDE. -Tom Bereknyei

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[NL-FP 2016] Announcement: Dutch Functional Programming Day 2016
by Atze Dijkstra 19 Oct '15

19 Oct '15

[My apologies for multiple received copies of the same message] Dear all, The next Dutch Functional Programming day (NL-FP 2016) will be held on Friday, January 8, 2016 at the Utrecht University, The Netherlands. You are invited to participate and to give a presentation. At the end of the day we will have a joint dinner. On the web page http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome <http://foswiki.cs.uu.nl/foswiki/NlFpDay2016/WebHome> for the day you’ll find preliminary information which will be further filled in due time. Registration is by letting me know via email (with a subject header that begins with [NL-FP 2016]) whether you want to (1) participate, (2) join dinner, (3) give a presentation (please include title + abstract), also see the webpage for additional details. If you intend to participate, please let me know as soon as possible because we like to know how many people we can expect. Hope to meet you all in Utrecht at the next FP Day! Best regards, - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 .... | Email: atze(a)uu.nl ............... / |___\

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Building 32-bit binaries on a 64-bit system?
by Mike Meyer 19 Oct '15

19 Oct '15

I've got someone who wants to run one of my haskell apps on a 32-bit Windows 10 box. I've pretty much moved to 64-bit everywhere, so don't have such a system to build on. Is it possible to get stack/cabal/ghc to build a 32-bit Windows binary on a 64-bit Windows box? Google found a bunch of things about building 64 bit applications, and the ghc manual doesn't seem to have such an option. So do I need to get a 32-bit system for this?

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STM and garbage collector
by Tomas Carnecky 18 Oct '15

18 Oct '15

If a thread is blocking indefinitely in an STM transaction (reading from a queue to which nobody else has a reference and thus can not write into), is the runtime smart enough to GC the thread? Or do I have to kill the thread manually?

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make an PrimMonad-wrapped FFI call
by Alexey Egorov 18 Oct '15

18 Oct '15

Hello haskellers, I'm writing FFI bindings to C library which uses some allocations across functions call, for example: int *alloc_buf(void); void free_buf(int *); So I need to use newForeignPtr to make sure buffer will be free'd when all pointers to it get collected. But what if I want to do this in PrimMonad (say, ST) and not IO (returned by newForeignPtr)? Thanks.

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How to specialize a type
by martin 18 Oct '15

18 Oct '15

Hello all, Suppose I have a type "Process" which stands either for a Train or a moving Belt. In both cases there is a place of departure and a place of arrival. However the other parameters which describe a Process differ. A Train has departure and arrival times, but a Belt has a speed. I tried the following: type PlaceDep = Int type PlaceArr = Int data Process = Train PlaceDep PlaceArr TP | MovingBelt PlaceDep PlaceArr BP deriving (Eq, Show) data TP = TP Int deriving (Eq, Show) data BP = BP Int deriving (Eq, Show) prc1 = Train 10 11 (TP 1) prc2 = MovingBelt 12 13 (BP 2) What I don't like about this is that the fact that all Processes have PlaceDep and PlaceArr appears somewhat "coincidental". This in contrast, captures the common parts more clearly: type PlaceDep = Int type PlaceArr = Int data ProcessParams = DepartureTime Int | Speed Int deriving (Eq, Show) data Process = Process PlaceDep PlaceArr ProcessParams deriving (Eq, Show) prc1 = Process 10 11 (DepartureTime 1) prc2 = Process 12 13 (Speed 2) Is this the classic way of specializing a type or are there better options See also: http://stackoverflow.com/questions/33156656/subclassing-a-type-in-haskell/3…

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Trying to write an Embedded DSL that threads a monad?
by Oleg 17 Oct '15

17 Oct '15

> Ian Bloom wrote: > I've been hoping to design a domain specific embedded language in > Haskell that would let me pipe a commutative monad throughout an expression > written in the language. Special terms within the language will eventually > have access to this monad. Is there a reason tagless-final approach does not work for you? You can easily thread any monad, even if you don't make any provision for it initially. For example, http://okmij.org/ftp/tagless-final/index.html#call-by-any http://okmij.org/ftp/tagless-final/course/CBAny.hs uses monad to print out traces of the expression and then later to implement lazy evaluation for EDLS (which needs mutable cells).

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Three open positions at Beautiful Destinations
by Tom Nielsen 17 Oct '15

17 Oct '15

The Data Science team at Beautiful Destinations is looking for three full-time developers and researchers with strong quantitative and programming skills. Beautiful Destinations ( http://www.beautifuldestinations.com/) is the world's largest travel influencer with a highly engaged audience of over 7 million followers across Instagram, Facebook and Snapchat. Beautiful Destinations distributes beautiful travel photography to its followers and helps clients to grow their social media channels. Our in-house photographers use drones and still photography to create content for our own accounts and our clients. The data science team has three aims: to predict and enhance the engagement of photographs on specific accounts; to measure influence on social media; and to determine the factors that contribute to the growth of social media accounts. Our internal API and core infrastructure are written in Haskell (using PostgreSQL), our Bayesian statistical time-series models use Stan ( http://mc-stan.org/) as well as some statistical models in Haskell. For image processing we use convolutional neural networks (in Python) and SIFT (C++/CUDA/Haskell). We are open to people bringing their preferred tools and maintain a polyglot environment. We are looking for developers who can fill the gap between data science and software engineering. We are at this stage only looking for full-time employees who can work in our London office. We welcome recent graduates and applicants with non-traditional backgrounds who show strong programming skills and capacity for independent learning. Please email contact(a)beautifuldestinations.com with any questions or with a CV if you are interested in this opportunity. -- <https://instagram.com/beautifuldestinations/>

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Talk at tonight's Haskell Meetup at the Hacker Dojo.
by David Banas 16 Oct '15

16 Oct '15

Hi all, I plan to give a short talk, at tonight’s Haskell Meetup at the Hacker Dojo in Mountain View, CA, on using Conal’s Circat and Lambda-CCC machinery to implement the Fast Fourier Transform (FFT). Hope to see you there, -db

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Specializing argument to forM_, mapM_ & foldM_ in base-4.8
by Amit Aryeh Levy 16 Oct '15

16 Oct '15

I've been running into a relatively small but frequent annoyance with base >= 4.8 (GHC 7.10). `Control.Monad.foldM_`, `Control.Monad.mapM_` and `Control.Monad.forM_` are generalized traverse over any `Foldable a` rather than just arrays (`[a]`). This is great, except I'm finding that, for a lot of my code that works well in previous versions, I need to specialize the argument to `[a]` now. If other people are encoutering a similar patter, I wonder what are your best practices for doing this: ScopedTypeVariables? Deconstruct the reconstruct the array? ... The most common example is when I deserialize a JSON array with aeson and want to traverse over that array (say, to store the objects to a DB): ``` let objArray = eitherDecode myjson case objArray of Left err -> ... Right (objs :: [MyObjType]) -> forM_ objs $ \obj -> saveToDb obj ``` The above fix requires `ScopedTypeVariables` (which is probably OK). Another option is to deconstruct and reconstruct the list: ``` Right (o:objs) -> forM_ (o:objs) $ \obj -> saveToDb obj ``` Does this get optimized away? Penny for your thoughts? Cheers! Amit

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