December 2013 - Haskell-Cafe

Question on nested State monads.
by David Banas 29 Dec '13

29 Dec '13

Hi all, If I want to use a second, nested State monad inside another State monad, must I thread the outer monad’s state through the processing of the inner one, even if the inner one falls out of scope before I return from the processing body of the outer one? Thanks, -db

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Fwd: ANN: website for Haskell regex testing
by Andrew M 28 Dec '13

28 Dec '13

Haskellers: I run a website for testing regular expressions and just added support for Haskell and wanted to see if you find it useful/what you think/if you have any suggestions. The site is RegexPlanet, the Haskell testing page is at: http://www.regexplanet.com/advanced/haskell/index.html It uses Text.Regex.TDFA flavor. You can see the source code on github: https://github.com/fileformat/regexplanet-haskell Disclaimer: I'm not a Haskell expert (actually, not even a newbie) and had someone else do the actual coding. Again, any feedback is appreciated. Thanks! Enjoy! Andrew

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Segmentation fault/access violation when CPLUS_INCLUDE_PATH not set correctly
by Henk-Jan van Tuyl 28 Dec '13

28 Dec '13

L.S., When I compile an application against an experimental version of wxHaskell*, the application always ends with the message: Segmentation fault/access violation in generated code , unless I set the environment variable CPLUS_INCLUDE_PATH to C:\Program Files\Haskell Platform\2013.2.0.0\mingw\lib\gcc\mingw32\4.5.2\include\c++\ , which is the same value as used when compiling wxHaskell. If I copy the contents of C:\Programs\Haskell Platform\2013.2.0.0\ to some other location and let CPLUS_INCLUDE_PATH point to the new location of directory c++, the segmentation fault message reappears. Why is this and how can create an application that also works on another computer? Regards, Henk-Jan van Tuyl * wxHaskell is a binding to the wxWidgets GUI library, which is written in C++ -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Name for the following combinators?
by Hans Höglund 28 Dec '13

28 Dec '13

Dear all, Recently I have found myself using these two combinators a lot: http://lpaste.net/97643 They basically allow composition of any m satisfying (Monad m, Traversable m). I have been thinking about moving them to a separate package and giving them better names (in the original paper, they are simply called join and bind). Does anyone have a better suggestion for the name of the package, module and the two combinators? Should they be called joinDefault, or simply called join and bind to be imported with a qualifier? This might be a bicycle-shed question, but I tend to find stylistic questions important when it comes to improving clarity and readability. Best wishes, Hans

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[Fp-nl] Call for participation: Dutch Functional Programming Day 2014
by Doaitse Swierstra 27 Dec '13

27 Dec '13

Dear all, The next Netherlands Functional Programming day (NL-FP 2014) will take place on Friday, January 10, 2014 at the University of Amsterdam at Amsterdam Science Park. You are all cordially invited to participate and, of course, to give a presentation. The day will largely follow the pattern of the previous NL-FP days with a moderately timed start, a day of enjoyable talks in between lunch and coffee breaks and ending with a joint dinner in a nearby restaurant. All further details can be found on the NL-FP 2014 site(s): http://staff.science.uva.nl/~grelck/nl-fp-day-2014.html http://staff.science.uva.nl/~grelck/nl-fp-dag-2014.html Hope to see you all in Amsterdam in January! Best regards, Clemens Grelck -- ---------------------------------------------------------------------- Dr Clemens Grelck Science Park 904 University Lecturer 1098XH Amsterdam Netherlands University of Amsterdam Institute for Informatics T +31 (0) 20 525 8683 Computer Systems Architecture Group F +31 (0) 20 525 7490 Office C3.105 www.science.uva.nl/~grelck ---------------------------------------------------------------------- _______________________________________________ Fp-nl mailing list Fp-nl(a)lists.science.uu.nl http://lists.science.uu.nl/mailman/listinfo/fp-nl

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integrating Happy & Alex monads
by Richard Cobbe 27 Dec '13

27 Dec '13

I'm working on a program in which I'd like to use Alex and Happy to parse the input. I've written the scanner, and it uses Alex's "monadUserState" wrapper to track source location and various other things. Now, the problem is to integrate it with the parser. As far as I can tell from reading the Happy documentation, I need to use a monadic Parser in Happy as well, but the manuals don't relaly provide a lot of information about how to integrate the two. And I haven't really been able to find many examples of this either. Lots of folks cite "the Haskell parser", although I'm not sure which implementation that's referring to. I did check out the GHC source, and while it contains an Alex parser specification, it doesn't look like anything actually *uses* this, preferring instead a handwritten parser. Could anyone point me to a discussion of how to integrate these two tools, or examples of places where folks have done this before? Thanks much, Richard

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finding "good work" in CS
by Dennis Raddle 26 Dec '13

26 Dec '13

It's me again, guy aged 45 thinking about doing graduate work in CS. I read this ebook about a guy's CS PhD, "The PhD Grind": <http://www.pgbovine.net/PhD-memoir.htm> It was enlightening. I used to think that software in the C.S. academic world must be well-written, seeing as it was written by computer scientists. (I didn't like the poorly organized and simple-minded code involved in my last job at NASA.) Turns out that academic code can be very poor indeed, sometimes just a hacked prototype meant to demonstrate an idea to get it published. It may be the youngest PhD students who are assigned the job of cranking out such prototypes. So what do I want to do for my life's work, once I can overcome this illness and get back to work full-time? I hope I can work with beauty in some form. I find Haskell to be beautiful, for instance. I like ideas, but I also like the process of implementing ideas in a quality way. I may not be suited to the academic world because I need to spend at least some of my time as a craftsman of code, doing something well. Is there an area with CS academia that is more about elegance, less about hacking up prototypes? The study of languages? Second, what if I thought of PhD not as a way to enter academia, but as a way to qualify me for the more interesting and creative C.S. jobs out there? What kinds of C.S. jobs involve real creative control, an opportunity to do things in an elegant way? I know that's a very broad question, so maybe those reading could mention single examples or things they've run into. No need to cover everything. Thanks, Dennis

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forever function laziness
by Eduardo Sato 26 Dec '13

26 Dec '13

Hello, guys. Recently I came across the definition of the function 'forever' on hoogle. I am intrigued that it works. The recursive definition does make sense to me in a mathematical way, but I can't figure out how it works under the hood in terms of thunks. To tell you the truth, I don't know how laziness works in general in haskell. Can someone help me understand how it works in this example, and give some pointers to materials on the subject? The "tying the knot" article on the wiki is pretty mind bending too. -- | @'forever' act@ repeats the action infinitely. forever :: (Monad m) => m a -> m b {-# INLINE forever #-}forever a = let a' = a >> a' in a' -- Eduardo Sato

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Re: [Haskell-cafe] Haskell Singapore Meetup
by Corentin Roux 26 Dec '13

26 Dec '13

Hi Jesse, Just saw your email. I started the data science team at Zalora and was behind the adoption of Haskell. As a short background, I didn't know how to program 2 years ago, when I left a finance job for a small startup in Australia. I didn't know anything about business intelligence either, and started with excel sheets. But the work was very repetitive so I picked up programming to try and automate some of it. After I moved to the South East Asian version of the same company, Zalora, I had read up a lot more, including books like SICP, and all of Paul Graham's essays. I liked both his concept of the "blub" ladder of abstraction, and his idea of using a programming language as a "secret weapon". Lisp is nice, but the pure nature of Haskell and the work that was done on the compiler both convinced me that it was a better secret weapon to solve my issue of not having enough budget or time to set up a standard BI setup (I separately was not too happy with SaaS providers anyway, so decided that in-house was the only way we could afford what I wanted). I had picked up enough Haskell to hire the first person (Dat Le) on the basis of his answers to a bunch of exercises we used as a filter (we were also helped by Hisham Zarka, current CMO of another Rocket company, Namshi and former Googler in MV). Dat did an extraordinary amount of work acting as proof of concept, much of it in Haskell, so it worked out even better than expected and we picked up enough budget to build a proper team. We called it "Data Science" because that seems to be the current buzz word for hiring smart guys. Haskell is unique in that: - it has a well defined standard with enormous amounts of research going into it (both the language, and its libraries); - the purity simplifies scaling, which I already needed, as well as all the standard improvements from catching most bugs before compiling, shorter code, etc.; - it is relatively hard to write Haskell that compiles as a beginner, thus acting as a natural talent filter (that can be expanded upon: it also attracts the kind of people who enjoy programming for its own sake, just like Lisps). I would disagree that there are very few people that know the language. I did put up my first ad as Python, with a preference for people with "experience in FPLs, like Haskell, Clojure, Erlang or Scala". I had over 200 applications, of which less than 5% were people we'd consider working with (mostly "Greetings! I believe my extensive experience and considerable skills make me an ideal fit for your company."). Every ad thereafter has been in Haskell, and on average over half the applicants are good enough to be hired (which is a great situation to be in as an employer, although I feel bad for the Haskellers meeting so few opportunities). The community's quality is simply exceptional. I'll post more about its use, which is rapidly expanding beyond "data science", in a few weeks. If anybody is interested: http://www.haskellers.com/jobs/61 Best, Corentin Le samedi 21 décembre 2013 05:59:30 UTC, Jesse Armand a écrit : > > Hi Paul, > > A follow-up from the meetup. I was tired yesterday after work. So, didn't > have the energy to socialize. > > Just a few of my thoughts. First of all, it was a good start to promote > haskell in Singapore. > > I'm very new to Haskell. I did some ruby, python and node.js at a very > small scale before. Most of time I do Objective-C programming as a job. > > Just finished reading Higher Order Functions, and will start learning > about making my own typeclasses. This is based on > http://learnyouahaskell.com. So, I barely know anything about the > language. Though, I'm aware that its popularity is growing, and also the > existence of a haskell web framework such as Yesod. > > So, for this reason, I am curious about how Zalora decided to choose > Haskell as a programming language. Given that, there are very few people > who know the language. It will also be great to understand where is it > being used on the technology stack, and some examples of how Haskell is > really advantageous for a particular use case. > > Thanks > > On Wednesday, December 18, 2013 6:12:52 PM UTC+8, Paul Meng wrote: >> >> Hi all, >> >> I've already posted on the reddit but forgot to post it here. >> >> It's going to be Christmas, and a good way to celebrate it is to have a >> Haskell meetup. On this Friday, Dec 20. We are going to host it at Google >> Singapore office. >> http://www.meetup.com/HASKELL-SG/events/154702892/ >> There would be a short sharing and have some time to meet with other >> Haskell programmers (or FP programmer in general) after the talk. >> If you happen to be in Singapore, welcome to stop by! >> >> For people signed up before, notice that we are moving from Zalora to >> Google's office to have a bigger meeting room. >> And due to the access policy, please fill out your full name, e-mail and >> company in the following form. >> >> https://docs.google.com/forms/d/1pTQA3eK7Qsxbq_Tw8nPPX6MIUnQuGsm23rT5bfhtw-… >> >> Paul Meng >> >

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Re: [Haskell-cafe] Parse HTML that is contain javascript
by akira kawata 25 Dec '13

25 Dec '13

Many thanks for your cooperations. I have decided to use xmlhtml instead of making my own html parser. 2013/12/25 akira kawata <a.kawashiro(a)gmail.com> > Hi, I am Akira. > I want to parse HTML file that is contain javascript. > But I cant come up with how to deal with script tag. > Is there anyone help me? > > Details of probrem > HTML code I want to parse is like following > > <html> > <script> > //<![CDATA[ >  > //]]> > </script> > </html> > > Because '<' is used as normal character in the script region, > I can not use my HTML parser there. > >

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