- Haskell-Cafe - Haskell.org

Arrows and Computation exercises?
by David Banas 17 Oct '16

17 Oct '16

Hi all, I’m wondering if anyone else happens to be working their way through the exercises in Ross Paterson’s *Arrows and Computation*, and would like to compare notes and/or discuss solutions to his exercises. Here are mine, so far: https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/… <https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/…> Thanks, -db

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[ANN] xls-0.1.0 Parse MS Excel spreadsheets
by Harendra Kumar 17 Oct '16

17 Oct '16

I have uploaded the xls package [1] on Hackage [2]. It works pretty well for the basic use case of parsing all sheets in a single stream of rows composed of cells. The cell values are presented as plain strings i.e. no data type based interpretation. Such stuff can be added if required, it is supported by the underlying C library (libxls). One thing that I would like to have added to the API is a way to list all sheets and select sheets to parse in a workbook. It should be pretty easy to do if anyone wants to do it. 1. https://github.com/harendra-kumar/xls 2. https://hackage.haskell.org/package/xls -harendra

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MTL vs Free-monads, what are your experiences
by Oleg 16 Oct '16

16 Oct '16

Matt wrote: > The mtl technique subsumes the free monad technique. if you have a term: > getCurrentTime :: MonadClock m => m UTCTime The relationship between MTL and Free(r) monad approaches is filled with confusion, as you message has just demonstrated. There is nothing specific to MTL in writing the constraints like MonadClock. There is absolutely nothing that prevents you from defining instance Member ClockEffect r => MonadClock (Eff r) or similar with Free monads, instance MonadClock (Free CurrentTimeF) (which are less efficient, compose less well and require the boilerplate of writing functor instances). In short, defining constraints like MonadClock, MonadState etc. is not specific to any approach to effects. The difference between the monad transformer and Free monad is how you build types that satisfy the MonadClock etc. constraint. In MTL, you build by applying monad transformer to a suitable base monad. In Free monad, you define functors like CurrentTimeF and then build the Free monad. In Freer monad approach, your example getCurrentTime will look like getCurrentTime :: Member ClockEffect r => Eff r UTCTime which looks quite like getCurrentTime :: MonadClock m => m UTCTime in your example. Therefore, there is usually no need to define a separate MonadClock class. But nothing stops you from doing that.

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[ANN] HackerNews 1.0
by David Johnson 14 Oct '16

14 Oct '16

Released new API bindings to the HackerNews API ( https://github.com/HackerNews/API) *Changes/Updates:* - Matching GHCJS implementation, all AJAX calls are tested thanks to phantomjs w/ hspec. - All aeson instances derived generically - Nix-based CI w/ travis ensures successful building on the following platforms: - *nixpkgs-16.09* - ghcjs-7103 - ghc-801 - *Stackage LTS * - LTS 7.3 *Release links*: - http://hackage.haskell.org/package/hackernews - https://github.com/dmjio/hackernews More platforms to be added for testing. - David

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Type alias in constraints
by Sylvain Henry 14 Oct '16

14 Oct '16

Hi, I have been using constraints of the form: xxx :: forall x xs ys zs m. ( Monad m , zs ~ Union (Filter x xs) ys , Catchable x xs , Liftable (Filter x xs) zs , Liftable ys zs ) => Variant xs -> (x -> Flow m ys) -> Flow m zs Where "zs" is used as a type alias. Now with GHC8 and -Wredundant-constraints, GHC complaints that "zs" is redundant (indeed it is). Is there a way to do this properly? If not, could we introduce a new syntax to make this kind of local declaration? We could borrow the syntax of local declarations into list-comprehensions: "let zs ~ ..." Thanks, Sylvain

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Req. transfer of maintainership of network-multicast
by Marco Zocca 14 Oct '16

14 Oct '16

To the Hackage trustees, following a communication with Audrey Tang, I would like to become new maintainer of `network-multicast` . My Hackage account name is `ocramz`. Thank you, Marco

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Help wanted for the architecture backing perf-service.haskell.org
by Sebastian Graf 12 Oct '16

12 Oct '16

Hi all, I'm about to wrap up my work for the Haskell committee (think half a summer of code): feed-gipeda <https://github.com/sgraf812/feed-gipeda> It's basically a daemon which will spawn benchmarking jobs for every commit of registered repositories. Much like Travis CI, but for benchmarks. You can see a simple web server, hosting the gipeda <https://github.com/nomeata/gipeda/>-generated sites, at http://perf-service.haskell.org/ghc/#all. While the Haskell part is working smoothly enough for now, I'd really like some help setting up proper sandboxing environments for the benchmark slaves, in such a way that security isn't as much a concern as it currently is. We can go over the details on a less publicly shared medium, but I doubt the current solution (invoking shell scripts from a non-root user) is safe. So, some concrete points I need help with: 1. Administrative expertise: Which part of the architecture runs has which rights, setting up proper sandboxing environments for benchmark slaves 2. Ops stuff: Creating master and slave containers for a low barrier to entry and reproducible environments 3. Distributed protocols: Someone with experience in stuff like SSH-tunneling/CloudHaskell/other useful things I should make the communication protocol of feed-gipeda aware of 4. Some Haskellers which want to take a look at my code and contribute criticism or even code to it :) Thanks in advance! So long, Sebastian Graf

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Announcing binary-parsers
by 韩冬(基础平台部) 12 Oct '16

12 Oct '16

Hi all, I am happy to announce binary-parsers. A ByteString parsing library built on binary. I borrowed lots of design/tests/document from attoparsec so that i can build its shape very quickly, thank you bos! And thanks to binary's excellent design, the codebase is very small(<500 loc). From my benchmark, it’s insanely fast, it outperforms attoparsec by 10%~30% in aeson benchmark. it’s also slightly faster than scanner(a non-backtracking parser designed for speed) in http request benchmark. I’d like to ask you to give it a shot if you need super fast ByteString parsing. These parsers are just binary's Get monads, so you can seamlessly combine them with combinators from binary package. You can now write more complex Binary instances using comprehensive combinators, with serialisation packages like blaze-texual. all these goodies come for free! Happy hacking! Github: https://github.com/winterland1989/binary-parsers Hackage: http://hackage.haskell.org/package/binary-parsers Winterland

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Galois is hiring!
by Iavor Diatchki 12 Oct '16

12 Oct '16

Hello, Galois is hiring again! We're looking for researchers, principal investigators, software engineers, and project leads, including those with expertise in functional programming, formal methods, machine learning, embedded systems, computer security, or networking. For the exact available positions, please have a look at our web-site: http://galois.com/careers We have two offices: one in Portland, OR, and one in Arlington, VA. There are positions available at both locations. Generally, we are looking for people to work on site, not remotely. Mostly, we are looking for candidates who are already allowed to work in the US, but in exceptional situations we can work with the candidate to obtain the necessary documentation. If you are interested, please send us your resume through the web site. Cheers, -Iavor

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 10 Oct '16

10 Oct '16

If you or one of your students recently completed a PhD in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, deadline 31st October 2016. Many thanks, Graham ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 31st October 2016 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the PhD student and PhD advisor/supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 31st October 2016. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 1000 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting in the abstract, but do get in touch if this causes significant problems) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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