October 2010 - Haskell-Cafe

Lambda-case / lambda-if
by Max Bolingbroke 08 Oct '10

08 Oct '10

Hi Cafe, I implemented the proposed Haskell' feature lambda-case/lambda-if [1] during the Haskell Implementors Workshop yesterday for a bit of fun. The patches are online [2, 3]. The feature is demonstrated in this GHCi session: $ inplace/bin/ghc-stage2 --interactive -XLambdaCase GHCi, version 7.1.20101002: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> (if then "Haskell" else "Cafe") False "Cafe" Prelude> (case of 1 -> "One"; _ -> "Not-one") 1 "One" Prelude> :q Do you like this feature and think it would be worth incorporating this into GHC? Or is it too specialised to be of use? If there is enough support, I'll create a ticket and see what GHC HQ make of it. Max [1] http://hackage.haskell.org/trac/haskell-prime/ticket/41 [2] http://www.omega-prime.co.uk/files/LambdaCase-Testsuite.patch [3] http://www.omega-prime.co.uk/files/LambdaCase-Compiler.patch

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Pronouncing "Curry" and "currying"
by Petr Pudlak 08 Oct '10

08 Oct '10

Hi all, I have a question for native English speakers: What is the correct pronunciation of the name "Curry" (in "Haskell Curry") and the derived verb "currying"? I found on Wikitonary the name is (probably) of Irish orgin, so I suppose that the pronunciation may by nonstandard. Probably the best way to answer would be either a link to some voice sample or written using some standard phonetic alphabet. Thanks a lot, Petr

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Re: [Haskell-cafe] A model theory question
by Alexander Solla 07 Oct '10

07 Oct '10

On Sep 30, 2010, at 1:39 AM, Patrick Browne wrote: > I think my original question can be rephrased as: > Can type classes preserve satisfaction under the the expansion > sentences > (signature/theory morphisms inducing a model morphism). > > According to [1] expansion requires further measures (programming?) > which you demonstrated. But this raises are further question. Does > Haskell’s multiple inheritance represent a model expansion where the > classes in the context of an instance are combined in the new bigger > model? In principle, the answer is yes (I think). But I kept running into walls when I tried. It is almost as if there is "too big" a gap to be filled between compile-time and run-time. At least for the approaches I tried. I have two suggestions though. First, monadism is a great way to approach this problem from a run-time level. Indeed, a monad is an interpreter, which comes with the associated notions of a free algebra/ model and the like. Injecting a new axiom amounts to creating a new monadic action. Monad transformers can do lifting and lowering in a fairly straight forward way. Another suggestion is to check out the OOHaskell paper. I know they use type level forcing to get stuff done, but I guess they used a different cluster of extensions than I tried. http://homepages.cwi.nl/~ralf/OOHaskell/ Sorry for the delay in responding. -Alex

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Is there a more recent paper or article than "Can GUI Programming Be Liberated From The IO Monad
by caseyh＠istar.ca 07 Oct '10

07 Oct '10

Is there a more recent paper or article than "Can GUI Programming Be Liberated From The IO Monad"? :)

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Notes from "Haskell takes over the world" BoF at ICFP
by Don Stewart 07 Oct '10

07 Oct '10

Here are the notes transcribed from the Future of Haskell BoF held after the Haskell Symposium last week. -- Don = Future of Haskell BoF Notes = A "birds of a feather" meeting was held at ICFP, organized by Bryan and Johan. We had 30 (?) people in a room, for 2 hours, discussing how to ensure Haskell succeeds. These are the transcribed notes. == Libraries == * Need to encourage special interest groups (SIGs) to form around particular domain areas in the libraries. AI, BioInf, Networking, etc. * Document the SIG process: what resources they have, how you get results. * Missing SIGs for certain platforms: Mac, CentOS etc. * More tutorials on use of Haskell in particular domains. * Keen for Hackage 2.0 quality review tools: embedded wikis, voting * Hackage analysis tools: reverse indexing of the code base. * There is no PVP tool. * Library fragmentation occuring due to type duplication (String, Text, ...) * Focus on intitiatives for common, core types. HP polish. * What is the "Son of Containers" going to be? * Build reports would help the community a lot. Integrated with Hackage. Haddock pages on hackage should be editable wikis (per-top-level function, dvcs backed? record history, captchas. roll back spam, by default assume good contributions) * Need to register patches to packages with lost maintainers. * Belgium Hackathon coming up. * Improve libraries process: esp. for small contributions. * Hackage maintainance: + maintainer timeout. + hackage package clobbering. + tweaks. hackage-local .cabal fixes. * Unclear what the rules for contributing are. Document them! * In particular, document how to contribute to: * ghc * cabal * core and HP * hackage * dockathon == IDEs == * A new ghci. + scriptable, scion-server? + repls on top of ghc-api + ruby repl + .ghci + documentation + hpaste/ghci. * IDE + scion. contributions. market places. + documentation. + EclipseFP, scion? + NetBeans. * Special Interest Groups + as the vehicle for domain projects. + formal process for forming a group. + a small amount of structure for groups + document process for forming a strike team. * haskell.org + polishing the wiki. + wikibooks. + call for sig. * haskell visual design group? + consistent color themes across haskell.org sites. + consistent haskell branding. * community server mailing lists in poor state * Move community more online ? Community services. + google groups + digests. + reply at the right point in the threads. + serious lists. + ghc users. libraries. + announces. + stackoverflow for new questions? + keep refering to SO. + reddit for news? == GHC == * ghc status + 50% split in room on moving ghc from darcs to git. + bug reports and interaction load with ghc + well documented workflow for lightweight changes + heavy weight process for major work. + bugs, tickets. + Simon Marlow "contributions are going up, and process is working well" * Release schedule. + RC at ICFP. + GHC release page. + HP/GHC release. + stage releases. + more clearly announced that ghc will be a beta prior to GHC HP. * HP, uses GHC installers as is. GHC zip. == Teaching / tutorials == * Tutorials. Documentation. + Writing a blog post that is wrong is a pretty good way to get feedback. + Find a forum to ask the question, so the answer is findable. + Ask on SO. + Clojure and Scala communities have active blog spheres. + they love descriptions of data structures + e.g. high fanout trees. + Aggregating the ephemera. + Archives: Haskell Reddit has all the interesting blog posts. -- Haskell Wikibook. * Cabal and integration with other languages. + Easier integration with C. + Higher barrier to entry on the Mac. + Playing well with other languages?

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HTML library with DOM?
by Günther Schmidt 07 Oct '10

07 Oct '10

Hi all, is there an HTML parsing library that creates a DOM from a page? Günther

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CFP MSCS Issue: Dependently Typed Programming
by Conor McBride 07 Oct '10

07 Oct '10

(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)- >(p:P s)* OPEN CALL FOR PAPERS for a Special Issue of MATHEMATICAL STRUCTURES in COMPUTER SCIENCE in association with the workshop DEPENDENTLY TYPED PROGRAMMING 2010 editors: Thorsten Altenkirch (Nottingham), Conor McBride (Strathclyde) 2011 timeline: submission Jan 31; notification May 31; final version June 30 (s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)- >(p:P s)* Thorsten Altenkirch and Conor McBride are delighted to invite contributions to a Special Issue of the journal Mathematical Structures in Computer Science (Cambridge University Press), in association with the Workshop on Dependently Typed Programming, which we organised on 9 and 10 July 2010 in Edinburgh, as part of FLoC, associated with LiCS. The workshop had a packed programme of exciting developments, reflecting the strength of work on this topic at this time. More recent workshops and conferences have exhibited a significant contribution from researchers in this area. We are grateful to Editor-in-Chief Giuseppe Longo and to Editor Eugenio Moggi for the opportunity to reflect these welcome developments in the pages of MSCS, and we encourage researchers to consider submitting a paper. submission deadline: January 31 2011 notification: May 31 2011 final versions due: June 30 2011 We invite full journal articles concerning Dependently Typed Programming or related topics, from authors at work in this area. Submissions are particularly welcome from but not limited to contributors to the workshop, and the same journal-standard peer review process will apply in any case. Please feel free to address any enquiries about scope and suitability to the guest editors, Thorsten Altenkirch (University of Nottingham) and Conor McBride (University of Strathclyde). Submissions should usually not exceed 35 pages. Authors should adhere to the guidelines issued by Cambridge University Press for MSCS contributors: http://assets.cambridge.org/MSC/MSC_ifc.pdf. These include directions to the relevant LaTeX resources. We very much look forward to hearing from you. Thorsten and Conor

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EDSL for Makefile
by C K Kashyap 07 Oct '10

07 Oct '10

Hi All, I was thinking about doing an EDSL for Makefile (as an exercise) I put down my line of thought here - http://hpaste.org/40233/haskell_makefile_edsl I'd appreciate some feedback on the approach. Also, I wanted some idea on how(in the current approach) I could make the target name and the dependency available to the action writer - as shown below. r1 = Rule { target = "file1", dependsOn = ["file2"], action = do execute ("gcc -c " ++ dependencyList ++ " -o " ++ target) } -- Regards, Kashyap

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Lazy evaluation from "Why Functional programming matters"
by C K Kashyap 07 Oct '10

07 Oct '10

Hi All, I was going through the paper's "lazy evaluation" section where the square root example is given. It occurred to me that one could implement it in a modular way with just higher order functions (without the need for lazy evaluation that is). function f (within, eps, next, a0){ while(true){ a1=next(a0); if(within(a0,a1,eps)return a0; a0=a1; } } Is this not the case? -- Regards, Kashyap

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Packaging a Gtk2hs based program for Windows
by Dmitry V'yal 07 Oct '10

07 Oct '10

Hello, haskellers. Recently I stumbled upon a problem. It may sound quite off-topic for this list, but, I'm sure, almost every haskell programmer runs into it sooner or later. It sounds: How to make a neat Windows installer for a nice Gtk2hs program I wrote last week? How to solve the problem of dependency on GTK? Should I ask my users to install a GTK package or it would be better to package all the dynamic libraries needed along with my program? Are there any troubles with different character encodings used in Windows? How to change the application icon? And so on.. I understand, there is no ultimate answer, but I hope there is some wisdom to share. I've been a Linux user for more then five years and now I've found myself completely illiterate on how to make my code easily accessible for a nontechnical Windows user. I would appreciate any thoughts and advises Best wishes, Dmitry

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