- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] imports at bottom
by Doug McIlroy 23 Apr '14

23 Apr '14

> A language pragma could be used to select between top imports or bottom > imports (can't use both). > > What do you think? Warning. This one touches a personal hot button, mostly off topic. To my mind, language pragmas are blemishes. Reasonable, assuredly, to announce that code uses some nonstandard feature of a compiler, but generally unreasonable as an integral part of the language definition. As originally promulgated for ALGOL, pragmas had no effect on the meaning of a program or its conformance to the standard, though they could, for example, affect the efficiency of object code. Language pragmas stray far from this intent. As unstable features, often incompletely described (just what does FlexibleInstances permit, anyway?), language pragmas might well be banned from the Haskell Platform. Doug McIlroy

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Contract opportunity
by Ian Ross 22 Apr '14

22 Apr '14

Dear all, This is kind of weird, but it might be of interest to someone and I think it's within the remit of this list, so here goes. Sorry to everyone who's not interested! I'm looking for someone to take over a contract I've been working on -- I've been offered something better and I won't have the time to carry on with this thing. I can't say too much about the details, but it's mostly GIS and geoprocessing work for a smallish business consulting firm, probably expanding to some statistical modelling soon. I've been using PostGIS with postgresql-simple to do some quite complicated geoprocessing of OpenStreetMap data for them: much of the Haskell content is really only using Haskell as a fancy scripting language to run lots of SQL, but there are a couple of more interesting bits. Anyone who was going to take this over would need to be a reasonably proficient Haskeller, know SQL well (including having some idea about query optimisation), have some familiarity with GIS work (data formats, something like QGIS or ArcGIS, ideally PostGIS and/or spatial SQL) and be persistent enough to deal with the places where the OpenStreetMap data isn't all you might hope. The client has a large number of sites in different cities that they're interested in, which means that everything has to be automated as much as possible, and that often means iterating again and again to discover geometrical or metadata problems that you need to work around. It can be quite frustrating. What's there now is pretty solid, I think, but it's quite fragile to changes in the OSM data. The rate of pay is good, there's enough work to occupy someone full-time, and the client is OK. There are the usual on-again-off-again rushes associated with this sort of business consulting. The timescale for me moving on is quite short: 2-3 weeks. I'll be organising notes and things for any potential handover, and there's another Haskell person at the client, so you would have someone to talk things over with. If you're interested, either get in touch with me if you have questions, or directly with Chad Scherrer (the Haskeller at the client: cscherrer(a)melinae.com) Cheers, Ian. -- Ian Ross Tel: +43(0)6804451378 ian(a)skybluetrades.net www.skybluetrades.net

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Job offer at Create-Net, Italy
by Corentin Dupont 22 Apr '14

22 Apr '14

Hi guys, I'm surprised I didn't got any reply from the community to this job offer, that I posted some time ago: http://www.create-net.org/work-with-us/postdoctoral-researcher-cloud-comput… While it's not 100% guarantee to work in Haskell, the position is still very interesting with technologies such as Constraint Programming (I'm currently exploring SMT with the SBV library), Cloud computing and energy efficiency. Ciao, Corentin

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Correctly setting up emacs + ghc-mod
by Arnaud Bailly 22 Apr '14

22 Apr '14

Hello, I am struggling to get my emacs settings right for doing significant Haskell development, eg. something more involved than a bunch of source files in a single directory. The issue I am running in currently is that when trying to load files in the interpreter, most source paths are missing which means loading inevitably fails. This is especially annoying with tests: To get things working correctly I need to explicitly add in the console > :set -iwhere/my/src/are Is there any configuration I should be aware of in my cabal files or .emacs file that would correctly set the source roots? Am I missing something? Here is my .emacs configuration. Thanks for any help. ;; haskell coding (require 'auto-complete) (require 'haskell-mode) (require 'haskell-cabal) (autoload 'ghc-init "ghc" nil t) (add-hook 'haskell-mode-hook (lambda () (ghc-init))) (eval-after-load "haskell-mode" '(progn (setq haskell-stylish-on-save t) (setq haskell-process-args-cabal-repl '("--ghc-option=-ferror-spans" "--with-ghc=ghci-ng")) (define-key haskell-mode-map (kbd "C-,") 'haskell-move-nested-left) (define-key haskell-mode-map (kbd "C-.") 'haskell-move-nested-right) (define-key haskell-mode-map (kbd "C-c v c") 'haskell-cabal-visit-file) (define-key haskell-mode-map (kbd "C-c C-c") 'haskell-compile) (define-key haskell-mode-map (kbd "C-x C-d") nil) (setq haskell-font-lock-symbols t) ;; Do this to get a variable in scope (auto-complete-mode) ;; from http://pastebin.com/tJyyEBAS (ac-define-source ghc-mod '((depends ghc) (candidates . (ghc-select-completion-symbol)) (symbol . "s") (cache))) (defun my-ac-haskell-mode () (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod))) (add-hook 'haskell-mode-hook 'my-ac-haskell-mode) (defun my-haskell-ac-init () (when (member (file-name-extension buffer-file-name) '("hs" "lhs")) (auto-complete-mode t) (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod)))) (add-hook 'find-file-hook 'my-haskell-ac-init))) (add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan) (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) (eval-after-load "which-func" '(add-to-list 'which-func-modes 'haskell-mode)) (eval-after-load "haskell-cabal" '(define-key haskell-cabal-mode-map (kbd "C-c C-c") 'haskell-compile))

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Re: [Haskell-cafe] "add ifM and whenM to Control.Monad" and other discussions like that
by Yuri de Wit 22 Apr '14

22 Apr '14

I haven't been around for long in the Haskell community, but I have seen a few of these discussions taking long email rounds in different mailing lists. I don't have a strong opinion at this point to add my vote here or there one way or the other, and I do appreciate the effort made by everyone to find a sort of consensus, as hard as that can be sometimes. However, the question I keep asking myself is why can't the compiler disambiguate between two definitions with the same name based on the actual argument types? This would allow packages to choose their own names for functions without such global-naming discussions and without much pain when using them. e.g.: > import PackageA (when) > import PackageB (when) > when (Just True) doSomething versus: > when True 1 Is there a theoretical or practical issue that makes this an undesirable feature in Haskell?

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Does this typeclass have a name?
by Bardur Arantsson 21 Apr '14

21 Apr '14

Hi all, I was wondering if anyone out there knows if this type class has a name? class Foo a e where foo :: e -> a -> a bar :: a (I also have a fundep a -> e, but that's not essential.) Essentially the usage is: You have a sequence of "events" e_i and a starting value "bar" and can use the "foo" function to apply all events to that starting value foo e_n $ foo e_{n-1} $ ... $ foo e_0 $ bar and thus get the final value of the a induced by the events e_i. (I've included the "bar" starting value in the type class, but I suppose it could be supplied by a Default instance.) Regards,

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Re: [Haskell-cafe] conduit zips
by Ben Foppa 21 Apr '14

21 Apr '14

Don't know how I missed those. Thanks! On Mon, Apr 21, 2014 at 3:04 PM, Michael Snoyman <michael(a)snoyman.com>wrote: > Instead of functions, they're now newtype wrappers: ZipSource, ZipSink, > and ZipConduit (that last one never existed as a function). Some > information on each of these: > > * http://www.yesodweb.com/blog/2013/09/zipsinks-conduit-extra > * http://www.yesodweb.com/blog/2014/02/conduit-zip-source > * > http://stackoverflow.com/questions/21671688/single-stepping-a-conduit/21684… > > > On Mon, Apr 21, 2014 at 3:52 AM, Ben Foppa <benjamin.foppa(a)gmail.com>wrote: > >> Since conduit-1.1.*, the package hasn't contained conduit zipping >> functions anymore. They don't appear to have been moved to conduit-extra, >> either. Did they get lost in the ether, or are they in a separate package? >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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ANN: v0.0.8 of treeviz package released.
by David Banas 21 Apr '14

21 Apr '14

- Split code into multiple files. - Completed Haddoc documentation. - Changed decimation style flag from Boolean to custom type, DecimationStyle, w/ constructors: DIT & DIF, as per Mark L.’s suggestion. - Introduced type alias: type Radix = Int, for readability. cabal install treeviz http://www.haskell.org/haskellwiki/Treeviz Cheers, -db

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GHC-7.8.2 & Win
by Cédric Chantepie 21 Apr '14

21 Apr '14

Hi, Try to setup GHC 7.8.2 & cabal 1.8 on Windows (7/64bits), using binary distributions from haskell.org I get error when I try to install glib package using cabal : cabal: Missing dependency on a foreign library: * Missing (or bad) header file: primitive-memops.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. If the header file does exist, it may contain errors that are caught by the C compiler at the preprocessing stage. In this case you can re-run configure with the verbosity flag -v3 to see the error messages. Failed to install primitive-0.5.2.1 cabal: Error: some packages failed to install: Command cabal install primitive raise the same error. I have tried either within cygwin or from plain cmd. Thanks for any hint, best.

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conduit zips
by Ben Foppa 21 Apr '14

21 Apr '14

Since conduit-1.1.*, the package hasn't contained conduit zipping functions anymore. They don't appear to have been moved to conduit-extra, either. Did they get lost in the ether, or are they in a separate package?

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