- Haskell-Cafe - Haskell.org

Questions about concurrency and laziness
by Tony Garcia 11 Jun '15

11 Jun '15

Hi, First of all, apologies if this is not the right place to ask this question. I'm reading the book "Parallel and concurrent programming in Haskell" and I'm having some issues reasoning about the impact of laziness. Looking at the first example in chapter 8 [1] main = do m1 <- newEmptyMVar m2 <- newEmptyMVar forkIO $ do r <- getURL "http://www.wikipedia.org/wiki/Shovel" putMVar m1 r forkIO $ do r <- getURL "http://www.wikipedia.org/wiki/Spade" putMVar m2 r r1 <- takeMVar m1 r2 <- takeMVar m2 print (B.length r1, B.length r2) I don't understand why this function is not just putting an unevaluated thunk in the MVar. Well, I assume that getURL is an eager function, but looking at its code [2] or at the documentation of Network.Browser [3] I don't see why... Am I looking at this wrong? Is there any rule of thumb to be used in these cases? I have the impression that it's really easy to end up creating thunks in parallel threads and evaluating them in the main one... Thanks, Jose. [1] http://chimera.labs.oreilly.com/books/1230000000929/ch08.html [2] https://github.com/simonmar/parconc-examples/blob/master/GetURL.hs [3] http://hackage.haskell.org/package/HTTP-4000.0.8/docs/Network-Browser.html

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US Haskell Developer Position
by Christopher Lewis 11 Jun '15

11 Jun '15

Karamaan Group, a principal investment firm based in Manhattan, is looking for an outstanding software developer to develop tools for financial analysis and knowledge management. We are a growth oriented firm that values people who take a craftsman's pride in their work. Our ideal candidate is an experienced software developer with strong analytical, organizational, and communication skills. A candidate who demonstrates an intense focus on quality, but has the ability to recognize and make the tradeoffs that are a necessary part of day-to-day software development. Candidates should have at least a degree in a quantitative field and a keen interest in building robust and elegant computer programs. This is a high-impact, high-visibility position where successful candidates will be entrusted with a lot of responsibility for products that have a direct effect on the P&L of the firm and influences our workflow. The ideal candidate will have experience with Haskell, relational database technologies, and Java. All new development is performed in Haskell, but our legacy Java code base occasionally requires maintenance. Unlike most finance companies, our atmosphere is informal and intellectual. We don't require previous experience in finance or business, but knowledge in those areas is a plus. Karamaan Group is situated in Manhattan, we are an investment adviser to hedge funds and family offices. We value innovative thinking, encourage an entrepreneurial atmosphere, and enjoy spirited conversations. We also offer lunch, and every once in a while we go bowling. Telecommuting is an option, but you must be located in the Continental United States and authorized to work in the United States. Please send your CV and cover letter to recruitment at karamaan dot com. Please do not reply to the original poster.

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Benchmarking two versions of the same package?
by Alp Mestanogullari 11 Jun '15

11 Jun '15

Hi -cafe, While we can easily benchmark different functions or libraries easily with criterion, I can't think of a reasonably easy (and accurate!) way of benchmarking two versions of the same package. And not necessarily version as in cabal version -- one of the use cases I have in mind would be running a benchmark suite whenever a PR gets merged to the main branch of a library, so the benchmark would need to compare the performance of the library's-code-before-merging and after. This definitely can't be accomplished with something like criterion because we can't have two different instances of a package in scope for a module, even with -XPackageImports. If we separately build the same program against two instances of the same library and run the benchmarks separately, this might happen far apart enough that the machine running this might be under a different load. This does however seem to be the only actual solution? Run separately at two different commits, diff the numbers, report. I have felt the need for a solution to this for quite some time, but have never needed it bad enough that it became a priority. Thinking about it again today, I thought I should drop an email to the list and see if fellow haskellers have an easy-to-use solution for this? I may very well be overlooking something. -- Alp Mestanogullari

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haskell team at megacorp is hiring!
by Carter Schonwald 11 Jun '15

11 Jun '15

Dear Haskell Colleagues, my team at megacorp, one of the largest for profit organizations on the planet, is looking to grow! about the haskell team: currently 3 engineers, though a 4th on the way already, in the past 6 months alone we've deployed customer facing APIs into production (no small feat in megacorp), built self serve generative sampling based data anonymization tools that promise to transform how megacorp customer data gets shared within and without. And thats just to start! We've repeatedly demonstrated that our use of haskell helps us develop and evolve great software for the business. the haskell team is part of a larger "new product / R&D" group whose mission is to build new tools, products and services to help pull megacorp kicking and screaming into the 2010's in terms of technology and services. The new product group is broadly seeking competent thoughtful technologists across a range of skill sets -- frontend, python, java, and haskell -- to join the engineering team. (so even if you're not the perfect fit for the team, we may know great folks we can point you to) *The Perks* *• *our management fully supports upstreaming bugfixes and improvements to the open source tools that we use • amazing view out of our Brooklyn and/or NYC offices (you will need to be in NYC to work with us, though I believe we can help with relocation) • by dint of the sheer scale of megacorp, every successful project will have pretty huge impact • because we're awesome, we will make sure you get your own mac along with the standard megacorp workstation. • picking a new project to work on every 3-6 months is the norm, owing to our role as a sort of prototyping / R&D group. *The Caveats* • it is megacorp, its a huge organization, and while the new product group is shielded from a lot of that, it can still be overwhelming • you will have to live somewhere within commuting distance of Brooklyn New York. • you have to deal with me and a few other interesting colleagues on a daily basis. *Should you apply?* • we welcome candidates of all experience levels, junior or senior. • we'd love it if you have some portfolio work/open source/work experience that demonstrates your ability to tackle engineering projects headon or master some nontrivial technical problem domain. • colleagues who take teaching/learning new things seriously • you'd enjoy working out of Brooklyn NYC. • you enjoy programming / software engineering and try to do it well. *how to apply* •*email me with the subject "functional megacorp job"*, attaching your resume/cv and if you want, a teeny cover letter that articulates your unique strengths and interests as a professional software engineer. •I can tell you more about the company and team via email. I or another member of the engineering team will be screening resumes first before kicking off any interview processes, so there will not be any HR limbo going on. Every email will get a reply. (NB: actual org name is easy to figure out with some googling, but for various reasons cannot be used publicly by its employees without an authorization process that befits a megacorp) also megacorp is is an equal opportunity and affirmative action employer

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Thank you to new maintainers
by Fred Ross 10 Jun '15

10 Jun '15

The libraries I used maintain have all be handed off. Thank you to: Adam Bergmark for taking over hscamwire. Lana Black for taking over hdaemonize. Jose Calderon for taking over serial. And goodbye for now to this wonderful community. Maybe I'll be back in a few years. Unless I become a field ecologist or a florist or something. Fred Ross http://madhadron.com

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Haskell developer role with Strats at Standard Chartered London
by Don Stewart 10 Jun '15

10 Jun '15

Hi all, I'm hiring (another) Haskell dev to join our team in London. Details here: https://donsbot.wordpress.com/2015/06/10/haskell-dev-role-in-strats-at-stan…

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[ANN] Lentil - a frugal issue tracker
by Francesco Ariis 10 Jun '15

10 Jun '15

lentil - a frugal issue tracker If you litter your code with TODOs and FIXMEs, lentil [1] can help you make sense of that big mess into something nice and readable like: src/Lentil/File.hs 49 does upMan work windows? [feature:intermediate] src/Lentil/Parse.hs 26 eliminate lookahead? refactor parsing? [lint] [refactor] 54 add test for rotoscope [test] It supports tags, filtering, exporting and much more. Check the user manual [2] for more information. [1] http://hackage.haskell.org/package/lentil [2] http://www.ariis.it/static/articles/lentil-manual/page.html

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[Haddock] Alphabetize record accessors
by aditya siram 09 Jun '15

09 Jun '15

How would people feel about Haddock alphabetizing record accessors by default? For example: data T { b :: ..., c :: ... , a :: ... } displays as: data T { a :: ..., b :: ... , c :: ... } Seems as though projects that have large records like Cabal & Parsec would benefit from this. Thanks! -deech

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And, Or, Not, and [something atomic] data types: What am I doing?
by Jeffrey Brown 09 Jun '15

09 Jun '15

I am considering the problem of representing search results in a graph database. (Define such a database as a collection N of nodes and E of labeled edges, where a labeled edge consists of a triplet (l, n1, n2), where l is some kind of label and n1 and n2 are members of N.) I think a type something like the following would be useful: data Search = Fan { origin :: Node , label :: Label , members :: [Node] } | And Search Search | Or Search Search | Not Search In a Fan with origin o, members would be the set of Nodes p such that (label, o, p) is an edge. A Search is ultimately built out of Fans. I've seen this kind of thing before, and I believe it will lead me to some substantial problems that other people have already solved. What should I study?

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parsec or attoparsec for 40-50MB text files ?
by briand＠aracnet.com 09 Jun '15

09 Jun '15

Hi, My file is pretty straightforward text file with a small amount of somewhat annoying state: comments* config line comments* data line* if there is no config line it's an error. the data lines can have a variable number of values and it matters how many values there are (hey- it's not my file format !). the data lines can also have a comment at the end. My initial thought was to go with parsec but the data files could be as large as 40-50MB and upon further reading it really seemed like attoparsec would be better. Error handling wouldn't be too sophisticated. if a data line has something other than 1 or more floating point values and the optional comment, failing out with "error line X" is fine. parse time is somewhat critical only because i'll have multiple files to parse, so while 5-10 seconds is ok for one file, i have to multiply that by 5-10. I've seen several comments talking about the fact that parsec can be slow, but so far unable to find anything the quantifies "slow". Any opinions on which would be better for my application (although i think i've just talked myself into using attoparsec) ? In particular- am i going to get at least reasonable "error on line X" error handling using attoparsec ? Thanks, Brian

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