November 2015 - Haskell-Cafe

User guide for DeriveAnyClass
by Kostiantyn Rybnikov 06 Nov '15

06 Nov '15

Is there a topic for DeriveAnyClass extension in user guide? It is mentioned several times in different places, also I see link to it in from cabal haddocs [0] into its page inside "other type extensions" [1], but it leads nowhere. Thank you. [0]: https://www.haskell.org/cabal/release/cabal-latest/doc/API/Cabal/Language-H… [1]: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/other-type-…

2 2

How to install newest ghcjs-base
by Arie Peterson 05 Nov '15

05 Nov '15

5 days ago a change [1] was made to the ghcjs-base library. How can one obtain a ghcjs that incorporates such a recent version of ghcjs-base? I installed ghcjs from git master yesterday, and installed the boot libraries using "ghcjs-boot --dev". However, I still get "Module ‘JavaScript.Web.MessageEvent’ does not export ‘getData’", so apparently my ghcjs-base lags behind somehow. What determines the version of ghcjs-base that is installed? Regards, Arie [1] <https://github.com/ghcjs/ghcjs-base/commit/e827ded07053a3281c50ee52b3e3ebd3…>

2 1

Yampa: upcoming changes; maintaining the projects we care about
by Ivan Perez 05 Nov '15

05 Nov '15

Dear all I am the current maintainer of the FRP implementation Yampa. (For context: I'm a PhD student at Nottingham, working with Henrik Nilsson.) Yampa contains legacy code that used to be useful to get things running quickly. In the interest of having minimal overhead and using existing robust solutions whenever possible, we'd like to remove some of that old auxiliary code. These changes will not affect the core of Yampa (SF definitions, arrow combinators, switches, etc.), but only auxiliary/miscelaneous stuff (vector spaces, deep strict evaluation type class, tupling/monad aux functions, etc.). We've been introducing these changes progressively over the last year, by first re-structuring the code base and marking some functions as deprecated. The time is coming for backwards incompatible changes, but I'd like to make sure that the projects you care about keep working as before. This may include (but is not limited to): * Code (which may not be on hackage, so it may be difficult for me to even know it exists). * Examples included in papers, slides, blog posts, etc. So, if you may be affected by these changes, please: - Watch the github project [1] and subscribe to yampa-users(a)cs.yale.edu, which is where details will be announced. It's a low traffic mailing list. - If you can deal with it yourself by upgrading your code, please do so. Otherwise, feel free to drop a line. - If your use case does not support easy upgrading (papers? talk videos?) please let me know. For starters, we may be able to concentrate all the potential compilation errors that your users might get in one place in the documentation. - If you are affected in a way that I'm not seeing, please let me know. All the best Ivan [1] http://github.com/ivanperez-keera/Yampa

1 0

Looking for a new maintainer: Bindings-DSL, c2hsc
by John Wiegley 05 Nov '15

05 Nov '15

Hello, The Bindings-DSL libraries, and the c2hsc tool that parses C headers into .hsc files, both on Hackage, are looking for new maintainers. People are using these libraries to get real work done, and I no longer wish to be a stumbling block due to lack of time. If you're interested, please drop me a line. Anyone with experience at C parsing would be great, but those with a desire to learn it are good too. I'd be available to help with questions indefinitely, I just lack the time to stay on top of every bug. Thank you, John Wiegley

3 2

Warnings suppression and examples
by Эдгар Жаворонков 05 Nov '15

05 Nov '15

Hello everyone! This may be a strange question, but nevertheless. I am interested in examples of warnings, thrown by GHC, that you, Haskell programmers, want to suppress. To be more precise, i am interested, what kind of warnings you would like to suppress in: 1. Functions 2. Imports 3. Typeclasses 4. Instances Thank you! P.S. I want to implement possibility of warning suppression with single pragma, that's why i am asking my question here --- С уважением, Жаворонков Эдгар Best regards, Edgar A. Zhavoronkov --- С уважением, Жаворонков Эдгар Best regards, Edgar A. Zhavoronkov

2 1

Re: [Haskell-cafe] [Haskell] ANNOUNCE: polymap 0.1.0.1
by Roman Cheplyaka 04 Nov '15

04 Nov '15

(moving from haskell@ to haskell-cafe@) Hi David, As someone who is not familiar with the concept of polygonal maps, I find this package severely underdocumented. What is a polymap? Why would I want to use one? What is storage and how should I choose it? The example clears it up a bit, but it could also use more prose. And perhaps there could be a more motivated example (showing how polymap solves an actual problem). On 09/24/2015 09:53 PM, David Farrell wrote: > I'm excited to announce the first release of a package I've been working > on over the last week called polymap, a library providing type-safe > polygonal maps whose sides are defined by a kindlist of types zipped > with a storage type for each side. I've tried to match the interface > exposed by the containers package as closely as possible. For example: > > import Data.Set (Set) > import Data.PolyMap.Nat (first, second, third) > import qualified Data.PolyMap as PM > > mEmpty :: PM.PolyMap '[ '(String, Set), '(Int, Set) ] > mEmpty = PM.empty > > mOne :: PM.SimplePolyMap '[String, Int] Set > mOne = PM.singleton ("one", length "one") > > main = do > print mEmpty -- empty PolyMap > print mOne -- PolyMap with one Relation > print mTwo -- PolyMapwith two Relations > print (PM.member first "one" mTwo) -- True > print (PM.notMember first "asdf" mTwo) -- True > --print (PM.notMember second "asdf" mTwo) -- will not typecheck > --print (PM.notMember third "asdf" mTwo) -- will not typecheck > print (PM.lookup first "two" mTwo) -- second Relation of PolyMap > where mTwo = PM.insert ("two", length "two") mOne > > This is a short usage example of most of the functions currently written > for polymap. There's still a long way to go both in terms of exposed > functions and in terms of efficiency and such, but I felt it prudent to > make a public release of my work so far as I feel it's reached a stage > where it could be beneficial to others. Note that GHC 7.10 (base >=4.8, > GHC extensions) is required. > > Git Repository: > https://github.com/shockkolate/hs-polymap > > Issue Tracker: > https://github.com/shockkolate/hs-polymap > > Hackage: > https://hackage.haskell.org/package/polymap > > The code is licensed under the Unlicense license--that is to say, the > code is released into the public domain for the benefit of others. > > I'd love to hear any feedback/suggestions/improvements/anything you want > to say about polymap over the mailing list (which may be more suited to > the haskell-cafe mailing list; I don't know) or in #haskell on Freenode > (I'm usually in there as Shockk). > > N.B. Version 0.1.0.0 of the package will not build due to the use of a > function in containers that has been submitted as a pull request but > does not exist yet/at all. > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell >

4 4

record field names vs. -fwarn-unused-binds
by Evan Laforge 04 Nov '15

04 Nov '15

[ ccing haskell-cafe since while it's a ghc flag, I'll bet most compilers have an equivalent ] I really like -fwarn-unused-binds because it frequently finds bugs where I forgot to call something or use some value. If I put an export list on, it can find dead functions I forgot to delete. However, there's one case where it frequently gives false positives, and that's unused record field names. The problem is that I sometimes use record field names as documentation, but the record itself is internal and small, so I'm comfortable using positional pattern matching to open it (and in fact that can be safer, since then warn-unused-binds will make sure I used all the fields). But GHC sees these as unused functions, so it warns about them. I can work around by putting underscores on field names I haven't used yet, but it's a hassle to go edit them when I want to use them. The warning can be useful if it indicates an unused field, but since fields can also be extracted via the positional syntax it's not reliable. The other use of the warning for dead code or functions you forgot to use doesn't apply to record accessors because they're trivial and compiler generated. So, would it be reasonable to exclude record field accessors from -fwarn-unused-binds? Or is there another way to work around it? I guess GHC doesn't have a "suppress warning" pragma like Java does, but even if we did it wouldn't be much better than changing the name, and more likely to get stale.

4 4

Haskell positions in Moscow, Positive Technologies
by Kosyrev Serge 04 Nov '15

04 Nov '15

Good day! The Moscow office of Positive Technologies (http://ptsecurity.com) seeks Haskell developers with strong C background, as part of an effort to develop a next-generation (of course!) democratic security platform. Think widely available, easy-to-use, dramatically enhanced security. If this kind of thing feels motivating, please send your resume to career(a)ptsecurity.com and CC skosyrev(a)ptsecurity.com. Position: Senior Software Engineer Vague description: - bare-metal, kernel, userland development Required experience: - C programming - experience of applying GHC in FFI-heavy context - experience with kernel development (some of Linux, Windows, Darwin) - experience writing resource-efficient Haskell code - experience with parallelism - taming laziness - taming the GC (desirable) - experience with the Intel system platform (desirable) - some knowledge of GHC runtime internals (desirable) -- respectfully, Kosyrev Serge http://www.ptsecurity.com/ Habr: http://habr.ru/company/pt Twitter: @ptsecurity https://twitter.com/ptsecurity

1 0

Haskell Engineer Needed for Machine Learning Group
by Charles Weitzer 04 Nov '15

04 Nov '15

Voleon Capital Management LP is a quantitative hedge fund located in Berkeley, California. We would like to hire a senior software engineer with strong functional programming experience as soon as possible. Voleon's founders previously worked together at one of the most successful quantitative hedge funds in the world. Our CEO has a PhD in Computer Science from Stanford and has been CEO and founder of a successful Internet infrastructure startup. Our Chief Investment Officer has a PhD in Statistics from Berkeley. Voleon's team includes PhD's from leading departments in statistics, computer science, and mathematics. We have made several unpublished advances in the field of machine learning and in other areas as well. Here is our formal job description: ********************************************************** * Senior Software Engineer * Technology-driven investment firm employing cutting-edge statistical machine learning techniques seeks an exceptionally capable software engineer. You will architect and implement new production trading systems, machine learning infrastructure, data integration pipelines, and large-scale storage systems. The firm researches and deploys systematic trading strategies designed to generate attractive returns without being dependent on the performance of the overall market. Join a team of under 30 people that includes a Berkeley statistics professor as well as over ten PhD's from Berkeley, Chicago, CMU, MIT, Princeton, Stanford, and UCLA, led by the founder and CEO of a successful Internet infrastructure technology firm. The firm's offices are walking distance from BART and the UC Berkeley campus in downtown Berkeley, California. We have a casual and collegial office environment, catered lunches, and competitive benefits packages. We seek candidates with a proven track record of writing correct, well-designed software, solving hard problems, and delivering complex projects on time. You should preferably have experience designing and implementing fault-tolerant distributed systems. Experience with building large-scale data infrastructure, stream processing systems, or latency-sensitive programs is a bonus. We are growing rapidly. Willingness to take initiative and a gritty determination to productize are essential. Required experience: - strong experience developing in a functional programming environment (Haskell, Erlang, others). - developing with C/C++/Python/Go in a Linux environment with a focus on performance, concurrency, and correctness. - working in TCP/IP networking, multi-threading, and server development. - working with common Internet protocols (IP, TCP/UDP, SSL/TLS, HTTP, SNMP, etc.). - architecting and designing highly available systems. - architecting and designing large-scale data management infrastructure. - working in large codebases and building modular, manageable code. Preferred experience.: - debugging and performance profiling, including the use of tools such as strace, valgrind, gdb, tcpdump, etc. - working with build and test automation tools. - working with well-defined change management processes. - diagnosing RDBMS performance problems, exploiting indexing, using EXPLAIN PLAN, optimizing at the code layer, etc. - working with messaging queues (RabbitMQ, Redis, etc.) as well as distributed caching systems. Interest in financial applications is essential, but experience in finance is not a primary factor in our hiring. Benefits and compensation are highly competitive. ********************************************************** The above job description is just a starting point in terms of possible duties and seniority. We can be very flexible for the right person. If you are interested please apply on our website: http://voleon.com/apply/. If you have any questions or if you know of anyone who might be interested, let us know the best way to get in touch and we can discuss details. Thank you, Charles Weitzer Senior Recruiter Voleon Capital Management LP Office: 510.704.9870 x 7012 Mobile: (510) 558-9182 www.Voleon.com<http://www.voleon.com/>

11 19

Streaming a Conduit into a lazy list
by Jules Bean 04 Nov '15

04 Nov '15

Conduits seem like a popular and useful way to compose operations which consume and produce streams at various speeds. I hadn't used them before, so apologies for any obvious mistakes below. Conduits have lots of power in terms of how you can interleave monadic effects with the streaming; but I found that I had a stream with no effects at all and I wanted to convert it back into haskells more simplistic representation, lazy lists. This is probably a well-known trick, but I couldn't find how to do this from googling, so here is the solution I found in case it helps someone else: > {-# LANGUAGE DeriveDataTypeable, FlexibleContexts #-} > module Main where > > import Data.Conduit > import Control.Monad.Catch > import Control.Monad.Trans.Resource > import Control.Monad.Writer > import Control.Monad.Identity > import qualified Data.Conduit.List as CL > import Data.Typeable > > source123Error :: Monad m => Source m Int > source123Error = do > yield 1 > yield 2 > yield 3 > error "error" A source which produces some data and then hangs, to test lazy production. One solution which doesn't work is CL.consume (as its own docs say) - and instead this happens: *Main> :t runIdentity (source123Error $$ CL.consume) runIdentity (source123Error $$ CL.consume) :: [Int] *Main> runIdentity (source123Error $$ CL.consume) *** Exception: error But what we can do instead is push the data out via the Writer monad: > tellEverything :: MonadWriter [a] m => Sink a m () > tellEverything = awaitForever (\x -> tell [x]) *Main> :t source123Error $$ tellEverything source123Error $$ tellEverything :: MonadWriter [Int] m => m () *Main> snd $ runWriter (source123Error $$ tellEverything) [1,2,3*** Exception: error Success! A lazily produced list. If your output is of any size - and depending on the compositions pattern in your code - it may be much faster to use this version: > tellEveryEndo :: MonadWriter (Endo [a]) m => Sink a m () > tellEveryEndo = awaitForever (\x -> tell (Endo (x:))) *Main> ($[]) . appEndo . snd . runWriter $ (source123Error $$ tellOne) [1,2,3*** Exception: error I found a further case where the Conduit I was trying to run was pure but had a 'MonadThrow' constraint. You can use the same approach here, using the ExceptionT transformer to satisfy the MonadThrow constraint. > data MyError = MyError deriving (Show,Typeable) > instance Exception MyError > > source123Throw :: MonadThrow m => Source m Int > source123Throw = do > yield 1 > yield 2 > yield 3 > throwM MyError *Main Control.Monad.Except Control.Monad.Trans.Resource> snd . runWriter . runExceptionT $ (source123Error $$ tellEverything) [1,2,3*** Exception: error *Main Control.Monad.Except Control.Monad.Trans.Resource> snd . runWriter . runExceptionT $ (source123Throw $$ tellEverything) [1,2,3] An aside: I tried to measure the speed difference between the list-mappend and Endo-mappend approaches with the following code. count2N uses a binary-tree shaped recursion so it should be fairly bad for list-mappend with lots of long lists on the left. > count2N :: Monad m => Int -> Source m Int > count2N 0 = yield 0 > count2N n = count2N (n-1) >> count2N (n-1) > speedTest1 = print . length . snd . runWriter $ (count2N 24 $$ tellEverything) > speedTest2 = print . length . ($[]) . appEndo . snd . runWriter $ (count2N 24 $$ tellEveryEndo) With -O or -O2 I measure no speed difference between these, they both take a bit over 2 seconds. With no optimisation flag, speedTest2 is slower, 17 seconds vs 11 seconds. I'm quite surprised the Endo version isn't faster, it seems like something is rewriting those list appends? Cheers, Jules

1 0