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Announce: Software Engineering for Systems Developed in Functional Languages
by Simon Thompson 16 Feb '14

16 Feb '14

The 32nd CREST Open Workshop: Software Engineering for Systems Developed in Functional Languages Date: 24th - 25th March 2014 Venue: University College London, UK Through the kind support of the EPSRC in the form of a platform grant, we have funding to support the workshops, so registration is free (but there is a charge for registering and then *not* attending, since places are limited). Registration includes lunch on both days and light refreshments. Overview: Functional programming has become a mature practical tool for software development. Large complex functional programs require many of the software engineering techniques developed for other languages and paradigms, such as testing, slicing and refactoring. Some of these techniques, originally designed for imperative languages, such as amorphous slicing and refactoring may prove highly amendable to functional styles of programming. This workshop will bring together software engineers and functional programmers to concentrate on aspects of software engineering that can be extended, adapted and augmented for application to functional programs. Confirmed Speakers David Binkley, Computer Science Department, Loyola University Maryland, USA Sebastian Danicic, Department of Computing - Goldsmiths College London, UK Kevin Hammond, School of Computer Science, at the University of St. Andrews, UK Torben Hoffmann, Erlang Solutions, Denmark Yue Jia, CREST Centre, SSE Group, Department of Computer Science, UCL, UK Raghavan Komondoor, Indian Institute of Science, India Alan Mycroft, Computer Laboratory, University of Cambridge, UK Jerry Swan, Computing Science and Mathematics, University of Stirling, UK Don Syme, Microsoft Research, Cambridge, UK Simon Thompson, School of Computing, University of Kent, UK Dimitrios Vytiniotis, MSRC PPT group, Microsoft Research, Cambridge, UK More details and registration at: http://crest.cs.ucl.ac.uk/cow/32/ Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Wheb 0.1 released -- Graceful shutdown, Mongo plugin, blaze example and more.
by Kyle Hanson 16 Feb '14

16 Feb '14

Hello all, This is a small release, but I thought I would tell you about it. I have added some new stuff to my Haskell server framework, Wheb. For those of you (most) who don't know about Wheb, here is Wheb's description from github: > Wheb's a framework for building robust, high-concurrency web applications > simply and effectively. Its primary goal is to extend the functionality of > the base WAI library as well as provide an easy entry point into Haskell > web servers. The only prerequisite is "Learn you a Haskell" or another > introductory Haskell course. I fleshed out some more examples, rewrote some of the documentation and made some feature improvements to make it easier to build plugins. The github repo's readme now contains a small tutorial. Probably the biggest change this release is the addCleanupHook which you can use to hook in and run IO actions after server shutdown to cleanup any open resources. Wheb handles the SIGINT signal and waits for all requests to complete before shutting down. Here is the complete changelog: - Ability to read settings from a file - Add graceful shutdown and cleanup hooks. - Ability to monitor number of active connections. - Remove Data.Default - Add builder helper function - URL encoding You can find Wheb on hackage or github: - http://hackage.haskell.org/package/Wheb - https://github.com/hansonkd/Wheb-Framework In addition to these changes, I have released Wheb-Mongo which provides Auth, Sessions and document manipulation/querying for mongoDB. - http://hackage.haskell.org/package/wheb-mongo If you have any recommendations please feel free to let me know! -- Kyle Hanson

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ANN: aivika-1.1 (the simulation library for DES and SD)
by David Sorokin 16 Feb '14

16 Feb '14

Hi Cafe, Aivika is a multi-paradigm simulation library with a strong emphasis on the Discrete Event Simulation (DES) in the first order and System Dynamics (SD) in the second one. A new version introduces an infinite stream of simulation data. This stream is based on the process-oriented computation of DES (this computation in its turn works on top of the event queue and uses the continuations). So, a random input of arrivals distributed exponentially can be described as such a stream in just one line of code! There is also a processor that just a function that takes an input stream and then returns a resulting stream after the processing. The processor is a Haskell arrow, which means that we can use the proc-notation in case of need, although there is a lot of predefined combinators such as that one which unites parallel processors into one processor. There are finite and infinite queues. The library collects the statistics for theses queues. We can either work with the queue directly, or create a buffer processor for the queue (with loop-back or not). There is also so called the server that provides its own processor. It suits for modeling working places. As before, the library collects the statistics too. In my personal opinion the library was powerful enough already earlier but now it can also allow the modeler to define some models using the mentioned above streams and processors directly in a very high-level Haskell code in such a way as he/she would draw the model on the diagram like those ones which are used by some visual simulation software tools. At the same time, all parts of the library are very well integrated. Actually, all them are inter-connected, where more high-level monads are just based on more low-level ones. Now the top is the mentioned above processor (the Haskell arrow). Unfortunately, the PDF document included in the package is outdated. Moreover, it doesn't cover even 10% of the features of my simulation library. But there are example models that illustrate the most important features. Also I use them for my tests. Best regards, David Sorokin [1] http://hackage.haskell.org/package/aivika [2] http://hackage.haskell.org/package/aivika-experiment [3] http://hackage.haskell.org/package/aivika-experiment-chart

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C++ exception (from *.so) catchable by Haskell??
by Nick Rudnick 16 Feb '14

16 Feb '14

Dear all, after trying around a while this seems to be a good question for Haskell-cafe to me: Is somewhere a place (e.g. some Hackage package) where intercepting exceptions from C++ library code is done, so one can look *how* it is done? Generally, it is the following: 1) Injecting code that throws a an exception in C++ library code, e.g., throw runtime_error("OOOPS..."); 2) then, I tried out everything in reach (Haskell docs, Hackage interfaces to C++ considered to be well-done) to get it caught (try, catch, bracket, finally; various exception types; forkOS). 3) To my surprise, every time the output stays the same: terminate called after throwing an instance of 'std::runtime_error' what(): OOOPS... Is it possible at all to get a grip of this? Is there some place where it is done? Does the terminate call already happen with the C++ execution? Any comment welcome, cheers, Nick

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GHC 7.6.3 (and others) hashes
by Alexander Solla 16 Feb '14

16 Feb '14

Hi everybody, I'm building up a body of SaltStack "states" for developing with and running Haskell web-apps. Since I am hoping my project will go big (don't we all?) I'm hoping to do things right, the first time (up to the constraints of marginal costs...) So, to that end, I'm trying to go a little overboard on the systems security front, since the costs are so low. Is there any where I can find SHA hashes for the official GHC builds? In particular, I'm looking for a hash for the file located at: https://www.haskell.org/ghc/dist/7.6.3/ghc-7.6.3-x86_64-unknown-linux.tar.b… I suppose downloading via an encrypted http connection goes a long way to mitigate MITM, etc. And I realize that long term, I'll want to host my own copy (and I will). But that is quickly sliding up the cost curve. Plus, I won't know if the copy I host will be okay unless I get the hash from a trusted source. Is there some place to get that hash? Thanks!

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Protecting against main thread exit
by Roman Cheplyaka 15 Feb '14

15 Feb '14

When using forkFinally or bracket, I like to have the guarantee that the cleanup action will be executed regardless of how the action or thread is terminated — normally or via an exception. Of course, all guarantees are off when dealing with SIGKILL or power reset, but there's one other annoying exception (no pun intended) — when the main thread terminates, all other threads are silently shut down, without any chance to clean up. Why is it done that way? Why not kill them with an async exception instead? That would be a more uniform behavior. Are there any good ways to protect again the main thread exit? (Note that I'm talking about a library, so I can't have direct control over what's going on in the main thread.) Roman

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[ANN] anonymous-sums
by Omari Norman 15 Feb '14

15 Feb '14

Someone once wondered why there are no anonymous sum types in Haskell: https://groups.google.com/forum/#!topic/haskell-cafe/cIxfLdcJ7aI Wonder no more: http://hackage.haskell.org/package/anonymous-sums Occasionally I have needed this so I split it off into a package. If there is already something like this out there (or some elegant way to do this that doesn't involve hairy extensions), please let me know and I will be all too happy to deprecate this. Omari

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Naming scheme for partial functions
by Michael Snoyman 15 Feb '14

15 Feb '14

Greg Weber and I have been discussing some changes to mono-traversable[1]. One of the modules we provide is Data.NonNull, which provides total versions of functions like `last`. A change we're looking at would require having a partial version of `last` defined in a separate typeclass (IsSequence), which would allowing for more optimized implementations of the total `last` function for datatypes which support it (e.g., strict ByteStrings). But what should we name it? I'm sure everyone's familiar with the `unsafe` naming convention, but that's not appropriate here: standard usage shows `unsafe` meaning a function which can cause a segfault. I initially named it `partialLast`, but partial can also imply partial function application. Greg brought up the idea of suffixing the function with something like `Throws` or `Errors`, which I think I'm a bit partial to myself[2]. So my questions are: * Is there some already used naming scheme out there for partial functions which I've missed? * Do people have any ideas to throw into the mix? Michael [1] https://github.com/snoyberg/mono-traversable/pull/21 [2] Pardon the pun.

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HGamer3D 0.3.0 on Github
by Peter Althainz 14 Feb '14

14 Feb '14

Dear All, HGamer3D version 0.3.0 is finalized and on Github. www.hgamer3d.org www.github.com/urs-of-the-backwoods/HGamer3D News: runs on Linux and Windows, example Games/Cuboid2.hs with FRP regards Peter Althainz

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ANN: asynchronous-exceptions
by Roman Cheplyaka 13 Feb '14

13 Feb '14

It is often useful to distinguish between synchronous and asynchronous exceptions. The common idiom is to run a user-supplied computation catching any synchronous exceptions but allowing asynchronous exceptions (such as user interrupt) pass through. base 4.7 (shipped with GHC 7.8) will have SomeAsyncException type that solves this problem. asynchronous-exceptions is a new package that serves two purposes: * provide compatibility with older `base` versions that lack the `SomeAsyncException` type * define convenient functions for catching only synchronous exceptions Roman

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