- Haskell-Cafe - Haskell.org

Initial public release of Haskell bindings for SLEPc
by Marco Zocca 01 Oct '15

01 Oct '15

Dear all, I have published the first version of my Haskell bindings for the SLEPc parallel eigenproblem library; it's available at https://github.com/ocramz/slepc-hs So far, only the most basic functionality is wrapped, and there is no exception control or high-level types and combinators, but it showcases a number of aspects of Haskell foreign-function interface design (using `inline-c`). I am also developing Haskell bindings for PETSc, thanks to the similar design of the two libraries, and I hope to release it before the end of the year. My biggest hope however is to contribute to the conversation between the functional programming and high-performance computing communities, as I feel the expressiveness and correctness guarantees provided by the former can be of great advantage to the latter. I look forward to your feedback; Kind regards, Marco Zocca

1 0

Haskell Weekly News
by Kim-Ee Yeoh 30 Sep '15

30 Sep '15

*Top picks:* - Neil Mitchell reports a stack overflow with 7.10.2 maximumBy <https://ghc.haskell.org/trac/ghc/ticket/10830> that regresses from 7.8.3. His sixth sense points to the Foldable-Traversable coup <https://ghc.haskell.org/trac/ghc/wiki/Prelude710/FTP> (aka BBP: Burning Bridges Proposal) as culprit. Joachim Breitner investigates and verifies that the bug's indeed caused by BBP's redefinition of maximumBy that changed out foldl1 for foldr1. Neil guesses that with foldl1, "the strictness analysis managed to kick in and optimise things." Joachim opines that "this is more a BBP design issue than a compiler bug." For now, roll your own maximumBy if you're affected. - A reddit question <https://www.reddit.com/r/haskell/comments/3jvyf7/services_for_learners/> asks whether there's a way for "haskell learners to learn haskell from haskell gurus, one-on-one for a fee?" An answer points to CodeMentor <https://www.codementor.io/haskell-experts> where haskellers charge from $15 to $60 per quarter-hour of consultation. Heinrich Apfelmus chimes in to say he's at HackHands <https://hackhands.com/>. - Yair Chuchem, who worked at Google for a year, reveals <https://www.reddit.com/r/haskell/comments/3ij91q/who_works_at_google_and_ho…> how a software engineer's performance metric is gamed to the detriment of the Organizer of the World's Information. Not quite Wally's "I'm gonna write me a new minivan this afternoon" <http://dilbert.com/strip/1995-11-13> but close. To the indignation of his managers, Yair left Google to work with Eyal Lotem on his passion: an Abstract-Syntax-Tree-driven IDE called Lamdu <http://peaker.github.io/lamdu/>, which redditors have already unpacked here <https://www.reddit.com/r/haskell/comments/3k8ek3/lamdu_blog_designing_progr…> . - Ph.D. student Rob Zinkov <http://zinkov.com/posts/2015-08-25-building-a-probabilisitic-interpreter/> demoes a rudimentary Probabilistic Programming Interpreter based on importance sampling. *Quotes of the Week:* - User kyllo on HN: <https://news.ycombinator.com/item?id=10276498#up_10277862> It's an exciting time for Haskell developers right now, we just got an a awesome new build tool (stack), an incredible new server-side framework (servant) and our compile to JS tool (GHCJS) is improving by leaps and bounds. - @gfixler: Was OOP created as a business model to sell complex tooling? @jonruttenberg: <https://twitter.com/jonruttenberg/status/638329205483249664> @gfixler Was #haskell created as a business model to sell complex blog posts? - User breadbox on HN observes: <https://news.ycombinator.com/item?id=10122333#up_10126413> "People think that confidence follows skills, but it’s usually the other way around where skills follow confidence." This is a fact that really needs to be more widely acknowledged. (It also casts the microagressions that have the effect of chipping away at the confidence of women and minorities in a rather uncomfortable light.) - User mgrennan on HN: <https://news.ycombinator.com/item?id=10122784#up_10123667>I understand it is our nature to push away from parents to strike out on our own. I also understand why older people resist change. Magic happens when the young seek to understand the wisdom of their elders and elders hold on to explorer spirit of their youth. -- Kim-Ee

1 0

Haskell Engineer Needed for Machine Learning Startup
by Charles Weitzer 30 Sep '15

30 Sep '15

Voleon Capital Management LP is a startup 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/>

1 0

Data.Foldable.all and empty list
by Lana Black 30 Sep '15

30 Sep '15

Hello, Is there any particular reason why the 'all' function returns True when supplied with an empty list (or any other foldable)? I'm aware that it is implemented via All monoid instance, my question is whether this behaviour is intentional or it can be considered a bug.

5 4

Parsing, infixes and on-the-fly precedence
by Jeffrey Brown 30 Sep '15

30 Sep '15

I imagine a parser that operates on (String,[String]) pairs, for which the second element allows the user to define precedence on the fly. For instance, it would read the pair (x,y) = ("a , b : c", [":" , ","]) as "(a , (b : c))" because y informs the parser that in x the colon binds first, then the comma. I know it is possible, because Haskell does it already! In Haskell we can define novel infix operators on the fly, including their precedence relative to each other. I don't know how, though, so that's my question. -- Jeffrey Benjamin Brown

4 5

Question, re: Typeclassopedia Ex. 4.2.1
by David Banas 29 Sep '15

29 Sep '15

Hi all, In trying to solve exercise 4.2.1 in Typeclassopedia, I’ve come up with the following: To prove: pure f <*> x = pure (flip ($)) <*> x <*> pure f Proof: pure (flip ($)) <*> x <*> pure f = (interchange) pure (flip ($)) <*> pure ($ f) <*> x = (homomorphism) pure (flip ($) ($ f)) <*> x = (definition of flip) pure ($ ($ f)) <*> x = (interchange) x <*> pure ($ f) = (interchange) (Is this step valid?) pure f <*> x Is the last step in my proof valid? Thanks, -db

2 1

Using Parsec with a recursive data as the stream
by Matteo Ferrando 29 Sep '15

29 Sep '15

Hello, I've posted this question in StackOverflow[1], but I thought this would be a good place to ask too: I'm writing an interpreter for functional programming language with with *mixfix operators*, just like Agda[2]. I used their paper[3] as reference. if_then_else_ : Bool -> a -> a -> a if True then x else _ = x if False then _ else x = x _/\_ : Bool -> Bool -> Bool True /\ True = True _ /\ _ = False So that means I had to run a parser (I used Alex/Happy), to get an AST, with this specific part (smaller than actual `Expr`): data Expr = Id String | Apply [Expr] | Forall Type Expr data Type = TypeBind String Expr And with this `Expr`, I have to run a second parser (which I intend to use Parsec) to do the following kind of processing: λ let example = Apply [Id "if", Id "a", Id "/\\", Id "b", Id "then", Id "c", Id "else", Id "d"] λ parseMixfix example Right (Apply [Id "if_then_else_",Apply [Id "_/\\_",Id "a",Id "b"],Id "c",Id "d"]) I started with a Parser that received a `Stream` of `[Expr]`, but this only accepts the lists in a `Apply`, and doesn't go deep in the *tree*, just parses on the top level. So I'm considering the option of instead of using `[Expr]` as the `Stream`, to use `Expr`, having to do the `Stream` instance for it; this is where I'm at: data Tok a = This a | Over (Tok a) deriving (Show) instance (Monad m) => Stream Expr m (Tok Expr) where uncons ex = check ex where check :: Monad m => Expr -> m (Maybe (Tok Expr, Expr)) check ex = case ex of Id s -> return $ Just (This (Id s), Apply []) Apply (x:xs) -> do mst <- check x return $ fmap (\(a, b) -> (Over a, b)) mst Which is using `data Tok` as kind of a Zipper breadcrumb (or at least I see it that way), to indicate how deep in the tree it comes from. I know this is not the correct code, but is for you folks to get the idea. I'm wondering if I'm on the right track or if there's a better solution for this problem. I'm also missing the `Forall` case here; that's because I was making tests with an `Id | Apply` only tree before. [1]: http://stackoverflow.com/posts/32831287 [2]: http://wiki.portal.chalmers.se/agda/pmwiki.php?n=ReferenceManual.Mixfix [3]: http://www.cse.chalmers.se/~nad/publications/danielsson-norell-mixfix.pdf

1 0

Fmap and Map for lists
by Strikingwolf2012 . 28 Sep '15

28 Sep '15

Does anyone have any idea why fmap (Functor map) and the list map are separate functions? I think it would make plenty sense for the Functor map to just be named map and have lists respond to that

2 1

Re: [Haskell-cafe] Parsing Atom feed link
by Francesco Ariis 28 Sep '15

28 Sep '15

On Sat, Sep 26, 2015 at 10:59:12AM +0300, fr33domlover wrote: > Hello, > > I'm using the package 'feed' to parse news feeds and I noticed it fails to > parse the item links of many feeds! I investigated and apparently here is why. > Many Atom feeds in practice seem to publish their item links like this: > > <link href="http://....."/> Checking the code [1] it looks like it is indeed the case linkRel = Right `fmap` pAttr "rel" e [1] http://hackage.haskell.org/package/feed-0.3.10.1/docs/src/Text-Atom-Feed-Im… > I looked at the examples at https://tools.ietf.org/html/rfc4287 and I just > checked Octopress (Ruby) and Ikiwiki (Perl) generated feeds. The RFC's examples > have item links without "alernate" (as the only item link provided) and both > generators I mentioned create feed item links without "alternate". > > > Should 'feed' be fixed to recognize them? Since you have done the homework and this is rfc compliant, have you tried sending an email to the maintainer [1]? It seems an uncontroversial change and they are active (last version released in 2015), I bet they are be willing to fix this. [1] http://hackage.haskell.org/package/feed

2 1

Solutions to Typeclassopedia Ex. 3.3.1?
by David Banas 28 Sep '15

28 Sep '15

Would anyone care to share their solution to exercise 3.3.1 in Typeclassopedia? Thanks, -db

4 4