- Haskell-Cafe - Haskell.org

Happstack: moving the uploaded file
by Nikita Karetnikov 03 Jun '14

03 Jun '14

I’m trying to create a trivial Happstack application based on the example from the “File Uploads” section of the Happstack book [1]. It should work as follows: 1. If there is no file called ‘foo’ on disk, show the upload form at any page. 2. If the file exists, show its contents at ‘localhost:8000/file’ and the upload form at any other page. The difficulty is that initially the uploaded file is placed to a temporary location, but since I want to read the file later, I have to move it somewhere. ‘UploadFile-working.hs’ uses two handlers for that, which doesn’t look right. I’d like the code to look like ‘UploadFile.hs’, but it doesn’t work properly. Could anyone explain why? [1] http://happstack.com/docs/crashcourse/index.html

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ANNOUNCE: jhc 0.8.2
by John Meacham 02 Jun '14

02 Jun '14

Lots of internal improvements in this one, so may be of more interest to developers http://repetae.net/computer/jhc/ - completely replaced the front end parser/lexer with a new more flexible one. My rewritten one is about 3,250 lines shorter. - The new one uses a general precedence parser for application as well as infix operators, allowing consistent handling of bang, irrefutable, and @ patterns and allows prefix and infix operators with a higher precedence than application to be defined. Incidentally, this allows for ~ and @ in expressions. (~) = negate (prefixr 11) gives us a nice strongly binding negative and @ (infixr 12) is perfect for type directed name resolution without further overloading the humble dot. they parse exactly the same as they do in patterns so no new magic is being added to the symbols other than allowing them in expressions. - Layout algorithm is fully in the lexer now, no lexer/parser interaction needed and useful transformations happen between the two simplifying the parser. - updated a lot of the external libraries to new versions - improvements to the build based on feedback, now gives much better error messages about what went wrong. - include an experimental utility to automatically download 3rd party packages from hackage and install them, it has some kinks, but even if it can't do it automatically, it provides a template for easily modifying the package to work. - removed the last of the cabal-cruft from the library build system. - fixed a lot of bugs relating to errors not being caught early by jhc so they produce a cryptic message from the compiler later, attach source location to more errors for better reporting. - ghc 7.8 compatibilty contributed by others. (thanks!) - infix type constructor extension supported - field punning extension now supported - new option -fno-sugar to turn off all desugaring that would introduce any hidden dependencies, all literals are unboxed under it. WYSIWYG. - unboxed kinds now more general, work in more places - record field names may overlap - more efficient binary representation using LEB128 - Data.String added with mild magic. -- John Meacham - http://notanumber.net/

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Haskell jobs in the Silicon Valley?
by David Banas 02 Jun '14

02 Jun '14

Hi all, Just pinging to see if anyone knows of a Haskell job opening in the Silicon Valley. Thanks, -db

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MacOS testing?
by Ian Ross 01 Jun '14

01 Jun '14

Hi all, Does anyone know of a good solution for MacOS testing that doesn't cost much? (Ideally, that costs nothing...) I've been getting a lot of MacOS-specific issues on the C2HS that I maintain and, since I don't have a Mac myself, testing and fixing these things is a bit of a problem. There is no equivalent of Amazon's EC2 for MacOS. There are some hosting services out there, but they're not all that practical, since they cost, they're set up for continuous hosting rather than intermittent use for bug-fixing, and you can't save a machine image snapshot once you've installed all the software you need (as you can on AWS) so you either need to keep your instance running or reinstall everything every time you want to test something. Any ideas? The only thought I've had so far was to try to do something horrible using Travis (Kiwamu Okabe has some slides about building and testing Haskell code on Travis: http://www.slideshare.net/master_q/20131109-kof2013-travisciosx) That's not a good solution for debugging though. Thanks for any thoughts you might have, Ian. -- Ian Ross Tel: +43(0)6804451378 ian(a)skybluetrades.net www.skybluetrades.net

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MonadRandom and traversing infinite streams
by Petr Pudlák 31 May '14

31 May '14

Hi Brent and Wouter, looking at SO questions http://stackoverflow.com/q/14494648/1333025 http://codereview.stackexchange.com/q/52149/15600 threre are monads and applicative functors that support ``` sequenceInf :: S.Stream (f a) -> f (S.Stream a) ``` that is, allow lazy traversals of streams (infinite lists). Namely those that don't produce any additional output. And instances of MonadRandom seem to have valid implementations of `sequenceInf`, which would allow to produce lazy infinite randomized lists (basically a generalization of `getRandoms`). My proposal is to add ``` class Applicative f => LazyApplicative f where sequenceInf :: S.Stream (f a) -> f (S.Stream a) sequenceInf = traverseInf id traverseInf :: (a -> f b) -> S.Stream a -> f (S.Stream b) traverseInf f = sequenceInf . S.map f ``` to a module in Stream package (for example `Control.Applicative.Lazy`), and add its instances into `MonadRandom`. What do you think? I'd be willing to send patches. Best regards, Petr

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Self-contained GHC for Mac
by Bob Ippolito 30 May '14

30 May '14

After seeing some demand for packaged Haskell for Mac for the IHaskell project and by word of mouth at BayHac I decided to take a stab at it. Here you go: http://ghcformacosx.github.io/ (currently GHC 7.8.2 and cabal-install 1.20.0.1) Why? It can be a bit cumbersome to use the GHC builds from haskell.org on Mac, because they don't come "fully baked", you have to ./configure --prefix=/some/path to get them installed and the installation is not relocatable, if you move it the scripts will break and the package.conf.d files will go stale. It also doesn't ship with cabal-install, which is cumbersome as well, especially for new users. How does it work? In https://github.com/ghcformacosx/ghc-dot-app I have a Main.hs script which downloads/builds/etc. all of the prerequisites. Then it patches the shell scripts to use a path relative to themselves (after following symlinks) rather than hard-coding an installation location. It also patches the package.conf.d files to use ${pkgroot} relative paths. Separately, there's an Xcode project that includes all of the metadata to make it look like a real Mac app bundle (icons, Info.plist) and a small Cocoa application that has a button to open the docs and provides instructions for adding it to the PATH in .bashrc. Due to the heuristics in Mac OS X's man, this will automatically make man pages work as well. Using Xcode here also makes it produce a signed build (which I do, since I am already paying for the $99/year license). -bob

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Local .ghci_history
by João Cristóvão 29 May '14

29 May '14

Hello, I raised this on trac ( https://ghc.haskell.org/trac/ghc/ticket/9089 ), but it seems it did not get much attention, but surelly I'm not the only one who finds this useful. With this little change, if there is a .ghci_history in the folder where you launch ghci it will use it instead of the global ~/.ghc/ghci_history. So, if you keep jumping from one project folder to the other, you can have a project specific history on each one (if you want). If you do not create a local .ghci_history file on that folder, the behaviour is exactly the same as it was before. Thus, this is somewhat identical to the local .ghci file. This, coupled with finally discovering the well hidden possibility of increasing the history size: http://trac.haskell.org/haskeline/wiki/UserPrefs Has vastly improved my ghci workflow. What do you think? João

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Haskell in Org Mode Babel
by Chris Warburton 29 May '14

29 May '14

Hello, I'm wondering if anyone's had success using Haskell in "Babel", the literate programming system in Emacs's Org Mode? I'm trying it with a blog post, but am getting mixed results. For those who don't know, Org Mode is an Emacs mode for editing text files, which has a bunch of features controlled by markup in the file. Babel is a feature which allows source code in various languages to be included in-line and executed. For example, I can write some Haskell like this: #+begin_src haskell [1..10] #+end_src Cheers, Chris

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Haskell Weekly News: Issue 295
by Daniel Santa Cruz 29 May '14

29 May '14

Welcome to issue 294 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from May 4 to 24, 2014 Quotes of the Week * dalaing: going from doing a fair bit of haskell recently to doing javascript today... sigh... it feels like the difference between typing at a keyboard and typing with a pair of those sporting-event-foam-hands-with-a-pointing-finger on * monochrom: to be blunt, I believe that "I do X for a living" means nothing. politicians do politics for a living too, what is the result? * Cale: Java seems like it was designed especially to be a strawman for people who hate static type systems * ReinH: Every so often edwardk goes up to the mountain of CT and brings us some new tablets edwardk: hear that dolio? we're going to start calling you the mountain. Top Reddit Stories * #haskell is welcoming and troll resistent (just found this by accident) Domain: gist.github.com, Score: 172, Comments: 19 Original: [1] http://goo.gl/TCiMW On Reddit: [2] http://goo.gl/JZNY3M * $7.5m DoD grant to develop Homotopy Type Theory Domain: cmu.edu, Score: 117, Comments: 70 Original: [3] http://goo.gl/EmSlbE On Reddit: [4] http://goo.gl/sKjGIl * Understanding the Stack Domain: well-typed.com, Score: 102, Comments: 13 Original: [5] http://goo.gl/qo9m5O On Reddit: [6] http://goo.gl/MVvaQn * Elm 0.12.3 - efficient 3D rendering with WebGL Domain: elm-lang.org, Score: 82, Comments: 19 Original: [7] http://goo.gl/iATfSi On Reddit: [8] http://goo.gl/QJ5ttp * An example of a Real World Haskell Application Architecture Domain: self.haskell, Score: 68, Comments: 36 Original: [9] http://goo.gl/ZTcr1x On Reddit: [10] http://goo.gl/ZTcr1x * ezyang: “try a <|> b” considered harmful Domain: blog.ezyang.com, Score: 67, Comments: 29 Original: [11] http://goo.gl/BEkC6W On Reddit: [12] http://goo.gl/3oql5l * 9m URL Shortener (Written in Haskell) Domain: 9m.no, Score: 67, Comments: 27 Original: [13] http://goo.gl/E0NoYv On Reddit: [14] http://goo.gl/n4cyN5 * Announce: JHC 0.8.1 IS OUT Domain: notanumber.net, Score: 66, Comments: 14 Original: [15] http://goo.gl/n6qAcf On Reddit: [16] http://goo.gl/wSMrva * Haskell for Mac OS X, self-contained relocatable GHC builds Domain: ghcformacosx.github.io, Score: 64, Comments: 35 Original: [17] http://goo.gl/CvsYC7 On Reddit: [18] http://goo.gl/WcIBw5 * Binary serialisation: better, stronger, faster (PDF, Duncan Coutts, March 2014) Domain: code.haskell.org, Score: 63, Comments: 39 Original: [19] http://goo.gl/r4xShZ On Reddit: [20] http://goo.gl/xhJRbg * CS240h lecture notes Domain: scs.stanford.edu, Score: 61, Comments: 8 Original: [21] http://goo.gl/F39zHe On Reddit: [22] http://goo.gl/AQqrUj * Haskell-mode documentation Domain: chrisdone.com, Score: 58, Comments: 28 Original: [23] http://goo.gl/XzKMCk On Reddit: [24] http://goo.gl/DZBQtO * PSA: you can now visit status.haskell.org Domain: status.haskell.org, Score: 58, Comments: 19 Original: [25] http://goo.gl/oRHfsn On Reddit: [26] http://goo.gl/Ye9YU2 * Once more into the teach, dear friends Domain: serpentine.com, Score: 57, Comments: 11 Original: [27] http://goo.gl/L8Csnm On Reddit: [28] http://goo.gl/AyF2Fs * What Features Would You Like to Find in a Haskell IDE? Domain: self.haskell, Score: 57, Comments: 90 Original: [29] http://goo.gl/Pvo32I On Reddit: [30] http://goo.gl/Pvo32I * Adventure with Types in Haskell - Simon Peyton Jones [1:33:36] Domain: youtu.be, Score: 57, Comments: 10 Original: [31] http://goo.gl/L9wGWe On Reddit: [32] http://goo.gl/sL3u8i * Ars Technica has Haskell as one of three potential heirs to Fortran's scientific computing throne Domain: arstechnica.com, Score: 56, Comments: 78 Original: [33] http://goo.gl/lxWcdK On Reddit: [34] http://goo.gl/kCxUS9 Top StackOverflow Questions * Why does Haskell's “do nothing” function, id, consume tons of memory? votes: 72, answers: 1 Read on SO: [35] http://goo.gl/8awkSk * Are Ana-/Catamorphisms just slower? votes: 29, answers: 2 Read on SO: [36] http://goo.gl/wcmkQw * Code becomes slower as more boxed arrays are allocated votes: 22, answers: 2 Read on SO: [37] http://goo.gl/qfKo2a * Which part of Real World Haskell is now obsolete or considered bad practise? votes: 22, answers: 1 Read on SO: [38] http://goo.gl/EtT51x Until next time, [39]+Daniel Santa Cruz References 1. https://gist.github.com/quchen/5280339 2. http://www.reddit.com/r/haskell/comments/2516e4/haskell_is_welcoming_and_tr… 3. http://www.cmu.edu/news/stories/archives/2014/april/april28_awodeygrant.html 4. http://www.reddit.com/r/haskell/comments/24rs73/75m_dod_grant_to_develop_ho… 5. http://www.well-typed.com/blog/94/ 6. http://www.reddit.com/r/haskell/comments/2641x0/understanding_the_stack/ 7. http://elm-lang.org/blog/announce/0.12.3.elm 8. http://www.reddit.com/r/haskell/comments/261abs/elm_0123_efficient_3d_rende… 9. http://www.reddit.com/r/haskell/comments/24y6ls/an_example_of_a_real_world_… 10. http://www.reddit.com/r/haskell/comments/24y6ls/an_example_of_a_real_world_… 11. http://blog.ezyang.com/2014/05/parsec-try-a-or-b-considered-harmful/ 12. http://www.reddit.com/r/haskell/comments/25ulsv/ezyang_try_a_b_considered_h… 13. http://9m.no/ 14. http://www.reddit.com/r/haskell/comments/267evu/9m_url_shortener_written_in… 15. http://notanumber.net/archives/178/jhc-haskell-0-8-1-released 16. http://www.reddit.com/r/haskell/comments/25o33n/announce_jhc_081_is_out/ 17. http://ghcformacosx.github.io/ 18. http://www.reddit.com/r/haskell/comments/26bx5n/haskell_for_mac_os_x_selfco… 19. http://code.haskell.org/~duncan/binary-experiment/binary.pdf 20. http://www.reddit.com/r/haskell/comments/25ch8v/binary_serialisation_better… 21. http://www.scs.stanford.edu/14sp-cs240h/slides/ 22. http://www.reddit.com/r/haskell/comments/25i99i/cs240h_lecture_notes/ 23. http://chrisdone.com/posts/haskell-mode-docs 24. http://www.reddit.com/r/haskell/comments/2583sm/haskellmode_documentation/ 25. http://status.haskell.org/ 26. http://www.reddit.com/r/haskell/comments/2653kp/psa_you_can_now_visit_statu… 27. http://www.serpentine.com/blog/2014/05/13/once-more-into-the-teach-dear-fri… 28. http://www.reddit.com/r/haskell/comments/25iqk7/once_more_into_the_teach_de… 29. http://www.reddit.com/r/haskell/comments/25sqvk/what_features_would_you_lik… 30. http://www.reddit.com/r/haskell/comments/25sqvk/what_features_would_you_lik… 31. http://youtu.be/6COvD8oynmI 32. http://www.reddit.com/r/haskell/comments/25vj62/adventure_with_types_in_has… 33. http://arstechnica.com/science/2014/05/scientific-computings-future-can-any… 34. http://www.reddit.com/r/haskell/comments/250558/ars_technica_has_haskell_as… 35. http://stackoverflow.com/questions/23746852/why-does-haskells-do-nothing-fu… 36. http://stackoverflow.com/questions/23664197/are-ana-catamorphisms-just-slow… 37. http://stackoverflow.com/questions/23462004/code-becomes-slower-as-more-box… 38. http://stackoverflow.com/questions/23727768/which-part-of-real-world-haskel… 39. https://plus.google.com/105107667630152149014/about

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[ANN] cartel - specify Cabal files using Haskell
by Omari Norman 29 May '14

29 May '14

The Cabal file format works very well for small projects. However, in big projects with a library, many executables, and test suites, some irritations emerge. You need to specify dependencies in multiple places, leading to redundancy. You also have to manually add in new modules, make sure you list all modules (a real pain with executables, as problems may arise only after you build a distribution tarball), and update your module lists when you refactor. Specifying your Cabal files in Haskell rather than in a plain-text file format helps deal with a lot of these problems. You have the full power of Haskell to make definitions in one place and then reuse them. You can also dynamically read a tree of modules and use the result, thus avoiding the need to manually update your module lists. A disadvantage to Cartel is that it can be a bit more verbose than a vanilla Cabal file. In addition, you also have to remember to generate the new Cabal file whenever you change the script that generates your Cabal file. Cabal already has an AST that it uses. Cartel could, perhaps, have re-used these structures. Cartel does not do this for three reasons. First, the Cabal API is a bit untidy, partially because it has to do things that Cartel doesn't have to worry about, but also because the comments in the Cabal modules themselves indicate that the whole thing could use a refactoring. Second, the Cabal developers make no commitment to keep that API stable. Third, the Cartel API tries only to replicate format of the plain-text Cabal file, which will be much more stable than the Cabal API. Hackage: http://hackage.haskell.org/package/cartel Github: https://github.com/massysett/cartel

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