March 2017 - Haskell-Cafe

CEF3 bindings and game dev in Haskell
by Maksymilian Owsianny 10 Mar '17

10 Mar '17

Hey I'm interested in making gamedev in haskell more viable and one thing that I believe is missing in that part of the environment is a good GUI story. So I decided to create proper bindings to cef3, you can check out what I've done so far [here][1]. In this current version I basically took the work done by Daniel Austin [here][2] split it into parts to prevent my machine from dying from lack of memory and packed it up with some nix glue for convenient usage. Now all this doesn't look like much but it sill took me much more time then I'm willing to admit in public. That's one of the eternal truths of software development, that everything always takes an order of magnitude more time then you suspect it would. Anyway, what I would like to do here is add support for all platforms. Create some nice scripts that help with automatizing building, developing and deployment of code with this library for users. Possibly write a script that automatically generates bindings from c headers to bring this lib up to speed with the current version of cef. Write some proper guides on using this lib for creating game GUI or standalone desktop application. All of that is nice and well to wish for but it is quite a lot of frankly not very fun work. If I had to choose I would rather spend my time working on either something fun or something that pays the rent, so usually at this point I stop and walk away. But this time I decided to go about it differently, and ask for community support. I have set up a BountySource campaign [here][3] so I could focus on making this happen. Alternatively, if that's your thing, I have set up a bitcoin address [4]. Depending on how well this campaign will go I'm also planing on creating a full 2D game engine... but yeah, that's in the future. So yeah, if you'd like to help me build this please support me. Thanks, Max. [1]: https://github.com/haskell-ui/cef3-raw [2]: https://github.com/fluffynukeit/bindings-cef3 [3]: https://salt.bountysource.com/teams/haskell-ui [4]: 1LskxSUyLDLpMCBfUUnqcRT8mEFMW511Eq PS. I have also created a reddit thread for this proposal here <https://www.reddit.com/r/haskell/comments/5yi1b7/cef3_bindings_and_game_dev…>.

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To [] Or Not To []
by Johannes Waldmann 09 Mar '17

09 Mar '17

Dear Cafe, I wrote a text (well, you might call it a rant) on the tragic over-use of lists in Haskell, based on my experience in programming and teaching. http://www.imn.htwk-leipzig.de/~waldmann/etc/untutorial/list-or-not-list/ * If your program accesses a list by index (with the !! operator), then your program is wrong. * If your program uses the length function, then your program is wrong. * If your program sorts a list, then your program is wrong. * If you wrote this sort function yourself, then it is doubly wrong. * The ideal use of a list is such that will be removed by the compiler. * The enlightened programmer writes list-free code with Foldable. Have fun reading, and avoiding lists from here on! - J.W.

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Parsing a bunch of strings without backtracking
by Olaf Klinke 09 Mar '17

09 Mar '17

The tree with internal nodes of type Char and leaves of type v is a representation of a finite state machine, a common tool in parsing certain grammars. I'm not sure your type Compact v captures exactly this, since a value v may be followed by more Chars down in the tree. You'd want type Compact v = [Either (More v) v] -- akin to Data.Tree.Forest data More v = More Char (Compact v) -- akin to Data.Tree.Tree What you may want to look at is a so-called trie [1,2]. In textbooks, it is common to assume that there is a charcter '$' not element of your alphabet. Then '$' is appended to each string before compressing all into a tree structure. This way, one can put both a string and a prefix of it into the same tree. A special kind of trie is the suffix trie. It holds all suffixes of a string and facilitates fast full-text search. More efficient variants are extensively used in bioinformatics [3]. Olaf [1] http://hackage.haskell.org/package/word-trie-0.3.0/docs/Data-Trie.html [2] https://en.wikipedia.org/wiki/Trie [3] http://mummer.sourceforge.net

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Haskell-related PhD studentship
by Meng Wang 09 Mar '17

09 Mar '17

Dear Haskellers, I am seeking a PhD student on Haskell-related projects, particularly in the area of bidirectional programming (lenses), property-based testing (QuickCheck) and refactoring. This would be a good opportunity for someone who is interested in applying Haskell ideas to real problems. The student will be part of the Programming Languages and Systems (PLAS) group in the School of Computing at the University of Kent. A major focus within the group is functional programming (FP), where it has had an international reputation for more than twenty five years. The group currently has 13 FTE academic staff, 4 RAs and 12 doctoral students. . The funding covers maintenance, EU student fees and research related expenses. But non-EU students are welcome to apply too. For Sep 2017 starting, the application deadline is 7 April 2017. If you are interested, please contact me at m.w.wang(a)kent.ac.uk<mailto:m.w.wang@kent.ac.uk>. More information can be found at https://www.cs.kent.ac.uk/research/studyingforaphd/phd-wang-2017.html. Best wishes, Meng Dr. Meng Wang | Lecturer in Computer Science School of Computing, University of Kent Canterbury, Kent, CT2 7NF, UK m.w.wang(a)kent.ac.uk<mailto:m.w.wang@kent.ac.uk> | ☎ +44 (0)1227 827699 www.cs.kent.ac.uk/~mw516<http://www.cs.kent.ac.uk/~mw516>

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[ANN] DataHaskell mailing list
by Marco Zocca 09 Mar '17

09 Mar '17

Dear all, DataHaskell now has a mailing list hosted on haskell.org : https://mail.haskell.org/cgi-bin/mailman/listinfo/data-haskell This is an addition to our current Gitter chatroom ; the purpose is to host longer-form archived discussions on libraries, documentation and more. With kind regards, Marco Zocca (https://github.com/ocramz)

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Re: [Haskell-cafe] formal treatment of module dependencies
by Johannes Waldmann 08 Mar '17

08 Mar '17

> specifying and solving module dependencies related: http://www.mancoosi.org/papers/ (not for Haskell modules, but for Debian-like package specs) PS: keep in mind that even the most elaborated versioned dependency mechanism is just a work-around - as long as we don't have *all* software properties in the types. Only then could we have a formal proof that a module A can use module B2 instead of module B1, etc. And, we do not "just" want correctness w.r.t. a specification, but also resource consumption. - J.W.

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reading and writing Data.Ratio.Rational
by Olaf Klinke 07 Mar '17

07 Mar '17

Dear cafe, when processing text files containing numbers of the form "xxxx.yyyy" I used to parse them into Double using that type's Read instance. Obviously, even with arithmetic no more complicated than the field operations the result might have ugly rounding errors like 12.000000000002 due to the fact that numbers like 0.7 are not dyadic rationals. The math in my program is not complicated and the numbers are not large, so I don't care about Rationals having potentially huge memory footprints. So here's my question. A literal like 0.7 has type Fractional a => a, but the Read instance of Rational rejects the string "0.7". Must it be this way? Do I have to go via toRational.(read :: String -> Data.Scientific.Scientific)? Note that the documentation of Data.Scientific explicitly states that using (/) is unsafe, so I'd rather stay with the field Rational. For the output as decimal expansion, there is of course long division as described here [1], but I wonder whether either this exists in some library or there is even a more efficient solution. Any pointers are appreciated. Thanks, Olaf [1] http://stackoverflow.com/questions/30931369/how-to-convert-a-rational-into-…

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Professor of Cyber Security at Kent
by Simon Thompson 07 Mar '17

07 Mar '17

We’re looking to appoint a professor of Cyber Security at Kent, to head up our existing group, with its Masters course and research activities. The Cyber Security group also sits alongside our Programming Languages and Systems group, and someone with strengths in PL aspects of security would fit very well. The advert for a Professor of Cyber Security is live at https://jobs.kent.ac.uk/fe/tpl_kent01.asp?s=4A515F4E5A565B1A&jobid=40739,21… <https://jobs.kent.ac.uk/fe/tpl_kent01.asp?s=4A515F4E5A565B1A&jobid=40739,21…> and post has been advertised with an associated lectureship in security, so the successful candidate will have a chance to shape that appointment too. If you’re interested, do think about applying, or get in touch with us. I’d be happy to answer emails, as would Richard Jones, head of school: cs-hos AT kent DOT ac DOT uk Simon Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk <mailto:s.j.thompson@kent.ac.uk> | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt <http://www.cs.kent.ac.uk/~sjt>

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Yesod app uses wrong port when connecting to PostgreSQL
by Geraldus 06 Mar '17

06 Mar '17

Hi folks! I'm struggling with following error: libpq: failed (could not connect to server: Connection refused Is the server running on host "localhost" (127.0.0.1) and accepting TCP/IP connections on port 5432? I see such messages in Keter's log (in app folder). The VPS where the app deployed running PostgreSQL 9.6 on port 5433. I have changed default port in: - config/settings - config/keter.yaml - /opt/keter/etc/postgres.yaml on server side None of these steps helped. I wasn't able to find other port configuration places. What else can I do?

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Maintaining fb, yesod-fb, yesod-auth-fb
by Sibi 06 Mar '17

06 Mar '17

Posting here to share my intent on taking the maintainership of fb, yesod-fb and yesod-auth-fb packages. The packages has not been updated for quite some time and are currently not building in GHC 8.0.2. Also, I use this package at my day job and we are planning to switch to GHC 8 soon. Regards, Sibi

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