- Haskell-Cafe - Haskell.org

gloss-examples install fails
by Gregory Guthrie 15 Feb '15

15 Feb '15

I installed gloss, and then the binary for llvm (http://llvm.org/builds/ ) But still gloss-examples fail, because it requires gloss-raster, which fails (below). I see some discussion of this from last year (https://mail.haskell.org/pipermail/haskell-cafe/2014-March/113001.html) Do I need to do some path manipulations to get this to work? I see llc & opt as mentioned in that note installed under mingw, but not under the llvm installed site. ------------------------------------------------------------------------ <C:\Windows\System32>cabal install gloss-raster Resolving dependencies... Configuring gloss-raster-1.9.2.1... Building gloss-raster-1.9.2.1... Failed to install gloss-raster-1.9.2.1 Build log ( C:\Users\guthrie\AppData\Roaming\cabal\logs\gloss-raster-1.9.2.1.log ): Building gloss-raster-1.9.2.1... Preprocessing library gloss-raster-1.9.2.1... [1 of 2] Compiling Graphics.Gloss.Raster.Array ( Graphics\Gloss\Raster\Array.hs, dist\build\Graphics\Gloss\Raster\Array.o ) <no location info>: Warning: Couldn't figure out LLVM version! Make sure you have installed LLVM cabal: Error: some packages failed to install: gloss-raster-1.9.2.1 failed during the building phase. The exception was: ExitFailure 1 Running with -v, it adds: <no location info>: Warning: Couldn't figure out LLVM version! Make sure you have installed LLVM 8.3 found on system at: e:\Plang\Haskell Platform\bin\ghc.exe Using ghc-pkg version 7.8.3 found on system at: e:\Plang\Haskell Platform\bin\ghc-pkg.exe No ghcjs found No ghcjs-pkg found No greencard found -------------------------------------------

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Exception safe resource management with dynamic regions, call for review
by Yuras Shumovich 15 Feb '15

15 Feb '15

Hello, I'm asking for code and design review for `io-region` library. It is already on Hackage for convenience and easy access to haddock: https://hackage.haskell.org/package/io-region Manual exception handling in Haskell almost never is a good idea, except probably trivial cases where `bracket` is enough. A number of special libraries where created to help with exception handling. `io-regions` is one of them. Initially it was an attempt to solve the double-throw issue, but I found it unsolvable in library without changes in language itself. So now it is an attempt to design easy to use API with a bit different set of trade-offs. The library is based on idea of regions that own resources. The resources are released when the region is closed. Early releasing and ownership transferring are supported. Types are *not* used to prevent use-after-free errors. The API is not monadic, and it is the biggest difference from other libraries. Regions are first-class citizens, so you can manipulate them, pass as arguments to functions, send to other thread, store in data types. Such flexibility has its cost -- a bit more manual management. The implementation is based on STM and is thread safe, that allows e.g. atomic ownership transferring between threads. The nearest competitor I think is `resourset` package, and I still recommend it by default. Though I convinced myself that `io-region` is good enough, and I'm using it in productions (for two weeks already :) ) Thanks, Yuras

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Refactor unqualified imports to qualified ones automatically?
by Jeffrey Brown 15 Feb '15

15 Feb '15

Hi, In a previous post regarding overlapping images in wx [1], Stephen Tetley suggested I study Blobs [2]. I want to find its wx logic, but as it stands I can't distinguish the wx commands from the others, because wx is too large a library for me to know all the names in it, and Blobs imports most of its modules unqualified. Is there some automatic way of changing an unqualified import to a qualified import, so that every function from the module of interest would be prefixed to indicate where it comes from? If not, is there some other way around the problem? Thanks, Jeff [1] https://mail.haskell.org/pipermail/haskell-cafe/2015-January/117669.html [2] https://hackage.haskell.org/package/Blobs-0.3/src/

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ANN: New Haskell.org Homepage Now Live
by Gershom B 15 Feb '15

15 Feb '15

I’m pleased to announce that http://www.haskell.org has received its first significant design update since 2010! More significantly, for the first time since 2006 it is not a wiki, but an actual language homepage. More significantly still, for the first time ever, the Haskell homepage now runs on a fully Haskell-powered stack. I suppose some people might also be interested in the fact that it looks quite nice, and has significantly cleaned up the information it presents, so as to provide a more focused experience for newcomers looking to explore the language. The page is now includes the collective work of over 230 commits by 17 contributors. First and foremost among those is Chris Done, who conceived the vision, wrote the bulk of the code, and executed the design. Also thanks to our many admins, including Austin Seipp, Ricky Elrod, et al., who managed the deployment, and have been working behind the scenes to continue to modernize and update our creaking infrastructure. Onto a few key things to remember: * The wiki is still around at https://wiki.haskell.org and it is still a fantastic resource. It is now speedy again, and we have an account creation process. By all means, jump in, and help curate and cultivate its wealth of knowledge. * The new site is all on github: https://github.com/haskell-infra/hl — there you will also find an issue tracker as well. We are sure there are many gaffes, gaps, and oddities that remain to be patched up in the site, especially with regards to its content. Tickets, pull requests, and comments are encouraged. * The official home for our mailinglists is now http://mail.haskell.org — hopefully this will cause no problems or confusion, and the redirects should be in place properly. Please let us know if there are any issues. * We think we covered everything, but there is the possibility that some item, service, or redirect broke in the course of this transition. Please let us know if this is the case. * If you have been responsible for some subdirectory under the www.haskell.org banner, then you will find that you do not yet have an account on the new server. Please contact us and we’ll get you set up to continue to maintain that portion of the site. * As always, you can reach the haskell ops and admin team at admin(a)haskell.org, or on freenode irc at #haskell-infrastructure. Regards, Gershom (and also the Haskell.org Committee and Haskell.org Admin Team)

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Re: [Haskell-cafe] [Haskell] ANN: New Haskell.org Homepage Now Live
by Daniil Frumin 15 Feb '15

15 Feb '15

Dear Haskell.org team thank you for your great work! But I was wondering this as well, why there is no mention of the Haskell platform in the Downloads section? I am also a little bit concerned about the "News" section: arguably, the news about GHC and Haskell platform releases are more important than newest stackoverflow questions or reddit posts. The newsfeed on Python.org, for example, is almost exclusively dedicated to releases and real-life events (which is also located on the front page). On Sun, Feb 15, 2015 at 1:31 PM, David Sabel <sabel(a)ki.informatik.uni-frankfurt.de> wrote: > I wonder why the downloads section doesn't link to the Haskell platform. > What's the reason for it? > > David > > Am 15.02.2015 um 08:50 schrieb Gershom B: >> >> I’m pleased to announce that http://www.haskell.org has received its first >> significant design update since 2010! More significantly, for the first time >> since 2006 it is not a wiki, but an actual language homepage. More >> significantly still, for the first time ever, the Haskell homepage now runs >> on a fully Haskell-powered stack. I suppose some people might also be >> interested in the fact that it looks quite nice, and has significantly >> cleaned up the information it presents, so as to provide a more focused >> experience for newcomers looking to explore the language. >> >> The page is now includes the collective work of over 230 commits by 17 >> contributors. First and foremost among those is Chris Done, who conceived >> the vision, wrote the bulk of the code, and executed the design. Also thanks >> to our many admins, including Austin Seipp, Ricky Elrod, et al., who managed >> the deployment, and have been working behind the scenes to continue to >> modernize and update our creaking infrastructure. >> >> Onto a few key things to remember: >> >> * The wiki is still around at https://wiki.haskell.org and it is still >> a fantastic resource. It is now speedy again, and we have an account >> creation process. By all means, jump in, and help curate and cultivate its >> wealth of knowledge. >> * The new site is all on github: https://github.com/haskell-infra/hl — >> there you will also find an issue tracker as well. We are sure there are >> many gaffes, gaps, and oddities that remain to be patched up in the site, >> especially with regards to its content. Tickets, pull requests, and comments >> are encouraged. >> * The official home for our mailinglists is now http://mail.haskell.org >> — hopefully this will cause no problems or confusion, and the redirects >> should be in place properly. Please let us know if there are any issues. >> * We think we covered everything, but there is the possibility that >> some item, service, or redirect broke in the course of this transition. >> Please let us know if this is the case. >> * If you have been responsible for some subdirectory under the >> www.haskell.org banner, then you will find that you do not yet have an >> account on the new server. Please contact us and we’ll get you set up to >> continue to maintain that portion of the site. >> * As always, you can reach the haskell ops and admin team at >> admin(a)haskell.org, or on freenode irc at #haskell-infrastructure. >> >> Regards, >> Gershom >> (and also the Haskell.org Committee and Haskell.org Admin Team) >> >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell -- Sincerely yours, -- Daniil

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Code review. API Guidance.
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 15 Feb '15

15 Feb '15

Hello everyone. I have an application (a calculator repl [1]) and I'm looking to convert it into an package that provides both library and executable. I'm looking for suggestions for what might be a good API for such a library. I'm not looking for an extended code review, just the placement of functions in modules, and which functions to export. The current source tree looks like this. src/ $ tree . . ├── Calculator │ ├── Color.hs -- Colored output │ ├── Evaluator │ │ ├── Base.hs -- Common evaluation functions │ │ ├── Cmd.hs -- Evaluate special commands │ │ ├── Expr.hs -- Expression evaluation │ │ ├── Func.hs -- Convert specification for a function into a mathematical function │ │ └── Statement.hs -- Evaluate either expression or command │ ├── Help.hs -- Help message │ ├── Parser │ │ ├── Base.hs -- Common parsers, number, id etc. │ │ ├── Cmd.hs │ │ ├── Expr.hs │ │ └── Statement.hs │ └── Prim -- Primitives │ ├── Bindings.hs -- Variable and Function Bindings │ ├── Cmd.hs │ ├── Definitions.hs -- Basic definitions, pre-defined variables and functions etc. │ ├── Expr.hs │ ├── Function.hs -- Tried to formalize the notion of a function of multiple arguments without currying. │ └── Statement.hs ├── Main.hs └── Model └── Arithmetic.hs -- A calculator model built using Text.ParserCombinators.Parsec.Expr (for model testing) I'm trying to have a library because I want to use a lot of the functionality provided by calculator in plot-lab [2], which is a plotting application. I want to have a stable API, because I don't want to irresponsibly keep changing it according to my personal needs. [1] : https://github.com/sumitsahrawat/calculator [2] : https://github.com/sumitsahrawat/plot-lab -- Regards Sumit Sahrawat

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ANN: ZuriHac 2015
by Gleb Peregud 14 Feb '15

14 Feb '15

We am glad to announce ZuriHac 2015, a annual three-day Haskell hackathon in Zurich. This year it's sponsored by Google. When: May 29th - May 31st Where: Google office, Zurich, Switzerland ZuriHac is an international Haskell hackathon: a grassroots, collaborative coding festival with a simple focus, to build and improve Haskell libraries, tools, and infrastructure. This is a great opportunity to meet your fellow Haskellers in real life, find new contributors for your project, improve existing libraries and tools, or even start new ones! I am happy to announce that Edward Kmett will give a talk. We are still in progress of nailing down the details, they will be available at the wiki page: http://www.haskell.org/haskellwiki/ZuriHac2015 Registration is not yet open, we will send an additional announcement email when it's open. We look forward to seeing you there! -- The organisers of ZuriHac 2015 Gleb Peregud Simon Meier Johan Tibell Alexander Bernauer

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Changes to Haskell Weekly News: In with the Old, In with the New
by Kim-Ee Yeoh 14 Feb '15

14 Feb '15

Dear Reader, A few days ago Daniel Santa Cruz stepped down from the helm of Haskell Weekly News. With others that read HWN regularly, I thank him for his long service and wish him and his family godspeed. Did you know John Goerzen started HWN in August 2, 2005? Now a week from today, February 21, 2015, Simon and Simon shall close your window of opportunity to opine on drastic changes to the prelude. By sheer coincidence, the very first issue of HWN links to a thread on Updating the Haskell Standard. John himself started the thread. Today the talk is about the Foldable and Traversable type classes. Back then it was about Overlapping and Undecidable instances, the FFI, and a Hierarchical namespace. But these are all features we take for granted today. What sweeping changes took hold over the last ten years. There was no hackage. Only in September 2005 did Isaac Jones and David Himmelstrup announce beta-testing of a cabal prototype. Imagine life without hackage. Today there are 7664 packages all ready to go. So it is with this ladened awareness that I have volunteered and been accepted to the open vacancy at HWN. I seek to alleviate a sorely felt void in the Haskell diaspora by elucidating the newsworthy. The first decision I made might catch you by surprise, so let me explain. You see, Semen Trygubenko has also stepped up to contribute to HWN by continuing the leaderboard format pioneered by Daniel. I proposed and he agreed to alternate weeks between HWN Leaderboard and HWN Light. I'm excited by this dual format. Lower frequency means longer wavelength, which also means looking at events from a wider angle. At the same time the dual format affords continuity from past editions that a readership has grown accustomed to. Even though some readers will be mortified by the loss in uniformity, I trust you won't be among them. I take full responsibility for any untowardness caused by this to-ing and fro-ing, including innocent kittens mysteriously vanishing into the night. The Light edition will come out this Tuesday; the Leaderboard edition next. Thank you for reading Haskell Weekly News. >From the desk of Poobah of HWN, Kim-Ee Yeoh

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Rationale for two separate map functions in ClassyPrelude
by Clinton Mead 14 Feb '15

14 Feb '15

ClassyPrelude has two map functions, namely: 1. "map" 2. "omap" "map" works on any Functor. However, things like "Text" are not functors as they aren't generic containers. As can be seen in the following code: module Main where import Prelude () import ClassyPrelude import qualified Data.Text as T import Data.Char as C main = do let l = [1,2,3] :: [Int] let t = (T.pack "Hello") let m = Just 5 print $ map (*2) l print $ map (*2) m print $ omap C.toUpper t return () Notice one has to use "omap" to deal with the Text. The thing is, I found it trivially easy to get "map" to work for both calls. Here's the code: {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeFamilies #-} module Main where import Prelude hiding (map) import qualified Data.Text as T import Data.Char as C import Control.Monad (Functor) class CanMap a b where type Element a :: * type Container a b :: * map :: (Element a -> b) -> a -> Container a b instance (Functor f) => CanMap (f a) b where type Element (f a) = a type Container (f a) b = f b map = fmap instance CanMap T.Text Char where type Element T.Text = Char type Container T.Text Char = T.Text map = T.map main = do let l = [1,2,3] :: [Int] let m = Just 5 let t = (T.pack "Hello") print $ map (*2) l print $ map (*2) m print $ map C.toUpper t return () All that's required is to add instances to CanMap for any monomorphic containers. ClassyPrelude already does this anyway with "omap" in the Data.MonoTraversable module. I suspect however there's a good reason I'm missing about why there should be two separate map functions to deal with these alternate situations, but I'm wondering what that is.

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Why doesn't TH expose its parser?
by Christopher Done 13 Feb '15

13 Feb '15

What's the reason that there isn't a parseExp :: String -> Q Exp, parseDecl, etc.? It's a pretty common use case to write some syntactic extension that merely extends regular Haskell. We end up with the haskell-src-meta package which doesn't support full GHC Haskell and doesn't know how to parse infix applications. It doesn't give a strong story for quasi-quotes to be useful for extensions to Haskell's syntax itself, as opposed to just mini-DSLs. Here's a case in point: idiom brackets. You'd like to implement them like this: [i|foo bar mu|] → foo <$> bar <*> mu You want it to be full Haskell inside, so foo could easilly be a case or a let, etc., so a trivial way to do that would be to just parse the string "foo bar mu" with parseExp and then do the above simple transformation. Job done. In practice, we can't do this. Our best option is HSE, but it's not ideal. Another way to do this is: $(idiom [|foo bar mu|]) And because [|…|] produces a Q Exp, you can just go ahead and do the rewrite on the resulting Exp. Yay, we now have full GHC Haskell inside the idiom bracket, but we've lost the syntactic convenience. Given that [|…|] already does the String → Q Exp step, why not allow us to re-use this functionality in quasi quotes? Ciao!

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