- Haskell-Cafe - Haskell.org

ANN: JMacro 0.6 and JMacro-RPC, featuring cross-platform json-rpc, easy AJAX applications, evented reactive panels and more
by Gershom Bazerman 17 Dec '12

17 Dec '12

jmacro: http://hackage.haskell.org/package/jmacro jmacro-rpc: http://hackage.haskell.org/package/jmacro-rpc jmacro-rpc-snap: http://hackage.haskell.org/package/jmacro-rpc-snap jmacro-rpc-happstack: http://hackage.haskell.org/package/jmacro-rpc-happstack I'm happy to announce the release of JMacro 0.6 (0.6.3 actually) which brings a host of improvements. JMacro is a quasiquoted library for the programmatic generation of JavaScript code. It lets you write in a superset of JavaScript with haskell-like syntax and compile-time guarantees of syntactic correctness, and is intended to be used for both embedded javascript and compilers and libraries targeting JavaScript--where hygienic naming, proper scoping, and anti-quotation are especially important. Documentation is on the Haskell Wiki: http://www.haskell.org/haskellwiki/Jmacro This release brings a host of improvements to efficiency, driven largely by user-submitted patches and requests. Text is used more uniformly, as opposed to String, and JSON integration is provided via aeson rather than the json package. Additionally, nearly all of JavaScript is supported, including more obscure operators, as well as labels, and labeled break and continue. The big news, however, is JMacro-RPC, which provides multi-server tools for serving JSON-RPC 2.0 [1] remote procedure calls, as well as binding to them from both Haskell and JavaScript. On the Haskell side, rpc server functions and caller stubs are automatically generated by typeclasses. On the JavaScript side, which is less typed, a function is exposed to marshall javascript function arguments directly into RPC calls to a located URL. [1] http://jsonrpc.org/specification On top of these RPCs, JMacro-RPC provides the conversation page abstraction, which allows the easy creation of web-applications with server side state. The user simply provides a function from JavaScript -> Page that splices in some JavaScript, and a list of functions they wish to be accessible from the page. All JavaScript within the page then has access to these functions, which run, transparently, server-side, with access to page-invocation-local shared state. Backends exist for JMacro-RPC for Happstack and Snap, and can be easily written for any other server or framework. JMacro-RPC now also provides the Panels library, which is even higher-level, providing the convenience of continuation-style web development with no scaling hassle. On the server side, Panels are entirely stateless, storing no client-specific state (so requests can be sharded to multiple servers as well without worrying about session replication). Code is written with a set of combinators over Panels, which package up display and behavior simultaneously. Panels, inspired by FRP, can provide Signals, which are sampleable, Events, which are discrete and can trigger updates, and Sinks which can be bound to Signals (behaving similarly to FRP wormholes). Semantics, by virtue of client-server interaction, are necessarily evented rather than continuous. As such, this is properly a system for declarative, event-driven reactivity rather than genuine FRP. Such a system is impoverished compared to the richer continuous-time or fully stream-based discrete-time semantics provided by of real FRP libraries. However, it is more than powerful enough for the sorts of user interfaces Panels are designed to build, and holds the added advantage of being straightforward, tractable, and a tight fit for client-server interactions. While Signals are applicative and Sinks are contravariant functors, which exposes at least some flavor of FRP, simple Signals and Sinks which don't require server-side processing (and are safely distinguished as such by types) can be bound to one-another purely on the client-side, avoiding unnecessary round-trips. The Panels code combines concepts from FRP [1][2], Self-Adjusting Computation [3], ASP.NET update panels [4], and research in stable naming schemes for bound variables [5]. The JavaScript "rts" driving evented updates is designed to be reasonably efficient and leak-free. Between basic RPCs, Conversations, and Panels, JMacro-RPC is intended to provide the full "power scale" for writing robust AJAX web applications with complex server-side logic. Because it is designed to be usable from any Haskell web framework or server, it is suitable for widespread adaptation. Patches, bug-reports, contributions, feature requests, documentation, etc. all are very welcome. [1] http://www.haskell.org/haskellwiki/Functional_Reactive_Programming [2] http://stackoverflow.com/questions/1028250/what-is-functional-reactive-prog… [3] http://www.umut-acar.org/self-adjusting-computation [4] http://msdn.microsoft.com/en-us/library/bb399001(v=vs.100).aspx [5] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.66.6645 ("I am not a number: I am a free variable", McBride and McKinna. See section four, on hierarchical names.) Cheers, Gershom

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Re: [Haskell-cafe] edge: compile testing
by John Lato 17 Dec '12

17 Dec '12

> > From: Christopher Howard <christopher.howard(a)frigidcode.com> > > On 12/14/2012 07:05 PM, Clark Gaebel wrote: > > Unacceptable argument type in foreign declaration > > Thanks for giving it a try. Could you send off a bug report to the > OpenAL Haskell module maintainer? <sven.panne(a)aedion.de> > > (I might offer to do it, but I tried to e-mail him once about a > different issue and never heard back. Probably didn't make it through > his spam filter.) I think Sven's been incommunicado for a few years now. Most likely somebody else will need to step forward as the OpenAL maintainer, if there's interest in keeping that package current. John L.

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Can cabal be turned into a package manager?
by Janek S. 16 Dec '12

16 Dec '12

In the recent months there was a lot of dicussion about cabal, dependency hell and alike. After reading some of these discussions there is a question I just have to ask: Why not create a package manager (like rpm or apt) for Haskell software? I've been using Linux for years. Software for Linux is mostly written in C and C++. There are thousands of libraries with lots of dependencies and yet: a) Linux distributions manage to have package repositories that are kept in a consistent state b) Linux package managers can avoid dependency hell, automatically update to new packages, etc. Linux people did it! Is there any technical issue that prevents Haskell people from doing exactly the same thing? Or are we just having non-technical problems like lack of money or developers? Janek

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Hackage suggestion: Gather the list of the licenses of all dependencies of a package
by Petr P 15 Dec '12

15 Dec '12

Dear Haskellers, following up the recent discussion about copyleft licenses, I'd suggest a (hopefully minor) improvement of Hackage: For each package, gather the list of the licenses of everything it depends on. I think this would help considerably people who don't want or can't use software licensed under a particular license (most often (L)GPL). In particular, we can have a BSD package that depends on a LGPL package, and this is fine for FOSS developers. But for a commercial developer, this can be a serious issue that is not apparent until one examines *every* transitive dependency. This idea is a bit vague, because a dependency is actually a range of packages, which in theory could have different licenses. But I suppose this will rarely happen in practice, so it'd be safe just to take the last package in the range (or maybe take all licences of the packages in the range). Best regards, Petr

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Hackage down, again?
by Magnus Therning 15 Dec '12

15 Dec '12

It looks like hackage is down again. Is it planned or unplanned downtime this time? There doesn't happen to be some mirror of the packages that is a bit more reliable than the original? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

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A new FFMPEG library?
by Kyle Hanson 15 Dec '12

15 Dec '12

The current hs-ffmpeg library is labeled as "old" on github: https://github.com/anders-/hs-ffmpeg is there a newer one or perhaps an alternative to play media files in haskell? -- Kyle Hanson

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Template Haskell Splicing
by satvik chauhan 15 Dec '12

15 Dec '12

Is there any way to splice declarations inside where? If not, then what is the reason for not supporting this? -Satvik

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ANNOUNCE: timeout-with-results
by Petr P 15 Dec '12

15 Dec '12

A small library that extends System.Timeout.timeout. It adds the possibility of saving partial results. Useful for AI-like algorithms that should return the best result found within a time limit. It comes in two variants: (1) Simple, which only allows computations to save partial results, not retrieve what has been written already. If a computation times out, the last saved partial result is returned. It comes in two flavours: One that converts saved values to WHNF, the other to NF. (This is required so that the producing thread performs the computations, not the consuming thread.) (2) Based on MonadWriter. The types of partial results have to be monoids. Saving a partial result combines it with the saved value using `mappend`. It also adds the ability to run a contained computation within another one, without disturbing its output. See https://github.com/ppetr/timeout-with-results#examples for examples. Repo: https://github.com/ppetr/timeout-with-results Hackage: http://hackage.haskell.org/package/timeout-with-results (I apologize for not being able to come up with a better package/module names. Suggestions welcomed.) Petr Pudlak

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Is it possible to have constant-space JSON decoding?
by oleg＠okmij.org 15 Dec '12

15 Dec '12

I am doing, for several months, constant-space processing of large XML files using iteratees. The file contains many XML elements (which are a bit complex than a number). An element can be processed independently. After the parser finished with one element, and dumped the related data, the processing of the next element starts anew, so to speak. No significant state is accumulated for the overall parsing sans the counters of processed and bad elements, for statistics. XML is somewhat like JSON, only more complex: an XML parser has to deal with namespaces, parsed entities, CDATA sections and the other interesting stuff. Therefore, I'm quite sure there should not be fundamental problems in constant-space parsing of JSON. BTW, the parser itself is described there http://okmij.org/ftp/Streams.html#xml

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edge: compile testing
by Christopher Howard 15 Dec '12

15 Dec '12

Hey guys, to teach myself Haskell I wrote a little arcade game called The Edge, built on gloss. It is in hackage under the package name "edge". Are there a few kind souls who would be willing to compile it on their machines and let me know if there are any problems at the compiling level? In the past, I've had issues with Haskell code compiling fine on my development system but not on others (due to dependency-related issues). I want to double check this before I try to make any distro-specific packages. I developed with GHC 7.4 and cabal-install 1.16.0.2 on a Gentoo system. Requires OpenGL and OpenAL (for sound). cabal update && cabal install edge -- frigidcode.com

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