- Haskell-Cafe - Haskell.org

ANN: Simon Marlow & Edward Kmett @ ZuriHac 2014
by Bas van Dijk 07 Apr '14

07 Apr '14

Dear Haskellers and ZuriHac 2014 attendees, On this lovely day (pun intended), I'm excited to announce that Simon Marlow and Edward Kmett will be giving talks at ZuriHac 2014. When: Friday 6 June 2014 - Sunday 8 June 2014 Where: Erudify offices, 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! 30 people already signed up for ZuriHac 2014 but there's still room for more. If you wish to attend, please register by filling in this form: http://bit.ly/ZuriHac2014 Full details can be found on the wiki page: http://www.haskell.org/haskellwiki/ZuriHac2014 We look forward to seeing you there! -- The organisers of ZuriHac 2014 ZuriHac 2014 is sponsored by Erudify & Google

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GHC and platform versions
by Ian Zimmerman 06 Apr '14

06 Apr '14

On the Haskell Platform webpage, it tells me what GHC version I need for the latest/current version of the platform. Also, there are links to downloads for prior versions of the platform. But, how can I find out what GHC version I need for one of those older platform versions? That information doesn't seem to be on the page, and I see no README or similar file in the platform source tarball itself. -- Please *no* private copies of mailing list or newsgroup messages. gpg public key: 2048R/984A8AE4 fingerprint: 7953 ADA1 0E8E AB57 FB79 FFD2 360A 88B2 984A 8AE4 Funny pic: http://bit.ly/ZNE2MX

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vim-hsimport: only consider modules of direct dependencies
by Daniel Trstenjak 05 Apr '14

05 Apr '14

Hi all, vim-hsimport[1] is a vim plugin that is able to automatically extend the import list of a haskell source file for the symbol under the cursor. It uses hdevtools[2] for finding the symbol in the modules of the installed packages and hsimport[3] for extending the import list. Until now vim-hsimport did consider all packages a project depends on, even if the package was only an indirect dependecy, not listed in the 'build-depends' field. So e.g. if a project directly and indirectly depends on the packages: base, containers, bytestring, binary, text and vector, and the modules for symbol 'foldl' have been requested, then the list of found modules might have been: Data.IntMap Data.IntMap.Lazy Data.IntMap.Strict Data.IntSet Data.Map Data.Map.Lazy Data.Map.Strict Data.Set Data.ByteString Data.ByteString.Char8 Data.ByteString.Lazy Data.ByteString.Lazy.Char8 Codec.Binary.UTF8.Generic Data.String.UTF8 Data.ByteString.UTF8 Data.ByteString.Lazy.UTF8 Data.Text Data.Text.Internal.Fusion.Common Data.Text.Lazy GHC.List Data.Foldable Data.List Prelude Data.Vector.Fusion.Stream.Monadic Data.Vector.Fusion.Stream Data.Vector.Generic Data.Vector.Primitive Data.Vector.Storable Data.Vector.Unboxed Data.Vector But if the project depends directly only on the packages: base and text, then only these modules are really relevant: Data.Text Data.Text.Internal.Fusion.Common Data.Text.Lazy GHC.List Data.Foldable Data.List Prelude This can be now achieved by using cabal-cargs[4] (>= 0.4) for the configuration of hdevtools. Please read the README[5] for detailed instructions. (One might argue, that even the modules Data.Text.Internal.Fusion.Common, GHC.List and Prelude might be left out, but that's another issue.) You might be also interested in a new feature of the 0.3 versions of hsimport and vim-hsimport. Before that version types have been always imported like: import SomeModule (Type) Now there's the option to choose between importing only the type or also importing all constructors/functions of the type: import SomeModule (Type(..)) If you're using hdevtools with the vim plugin syntastic[6] and have projects containing multiple sections (library/executable/testsuite ...) and each section has a separate 'hs-source-dirs', then you might get a more robust hdevtools behaviour by using this little change[7]. Happy Haskell hacking! :) Greetings, Daniel [1] https://github.com/dan-t/vim-hsimport [2] https://github.com/bitc/hdevtools [3] https://github.com/dan-t/hsimport [4] https://github.com/dan-t/cabal-cargs [5] https://github.com/dan-t/vim-hsimport/blob/master/README.md [6] https://github.com/scrooloose/syntastic [7] https://github.com/dan-t/syntastic/commit/7bd9b98342c93b7c7b06ddea199492331…

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Ported a Python script for use with Go to Haskell
by Matt Joiner 05 Apr '14

05 Apr '14

It's been 3 years since my last attempt to use Haskell. I've ported a script from Python, I wonder if anyone might point out areas that I'm not doing things idiomatically for Haskell? I'm hoping to start using Haskell more in place of Go and Python. The Haskell script: http://pastebin.com/SxH3PXgG The original Python script if you're curious: http://pastebin.com/bqUVxB5d

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Call for Contributions - Haskell Communities and Activities Report, May 2014 edition
by Mihai Maruseac 05 Apr '14

05 Apr '14

Dear all, I would like to collect contributions for the 24th edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 1 May 2014 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format) ================================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough --- please reconsider and submit an entry anyway! * If you are interested in an existing project related to Haskell that has not previously been mentioned in the HCAR, please tell me, so that I can contact the project leaders and ask them to submit an entry. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the previous edition --- you will find interesting projects described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Mihai Maruseac and Alejandro Serrano Mena (current co-editors) FAQ: Q: What format should I write in? A: The required format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/05-2013/template.tex There is also a LaTeX style file at http://haskell.org/communities/05-2013/hcar.sty that you can use to preview your entry. If you do not know LaTeX, then use plain text. If you modify an old entry that you have written for an earlier edition of the report, you should already have received your old entry as a template (provided I have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include Haskell code? A: Yes. Please use lhs2tex syntax (http://people.cs.uu.nl/andres/lhs2tex/) The report is compiled in mode polycode.fmt. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg format, then. Q: Should I send files in .zip archives or similar? A: No, plain file attachements are the way. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also ask the editor. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell the editor that there are no changes. The old entry will typically be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. Q: Will I get confirmation if I send an entry? How do I know whether my email has even reached the editor, and not ended up in a spam folder? A: Prior to publication of the final report, the editor will send a draft to all contributors, for possible corrections. So if you do not hear from the editor within two weeks after the deadline, it is safer to send another mail and check whether your first one was received. -- Mihai Maruseac (MM) "If you don't know, the thing to do is not to get scared, but to learn." -- Atlas Shrugged.

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scotty + aeson + ffi: optimising performance
by Miro Karpis 05 Apr '14

05 Apr '14

Hi, I have a C++ program that is doing some IO with one shared library (dll). I made a Haskell program that uses ffi for communicating with external dll. With scotty and aeson I made a web-service that communicates with the dll via REST-API (json). I was expecting that the performance would be a bit slower than the c++ internal dll calls, but I'm getting approx 3x slower performance in my haskell program. I tried to profile it but so far I can see that the bottleneck is Aeson (please correct me if I'm wrong). Is there a way how to optimise it? The data I'm sending via JSON are very small, so that can not be the problem. I have compiled the program with: ghc -O2 --make Service.hs -o eDS_FM -prof -auto-all -L. -lextlib Cheers, Miro profile: Fri Apr 04 23:57 2014 Time and Allocation Profiling Report (Final) eDS_FM.exe +RTS -p -RTS total time = 0.81 secs (810 ticks @ 1000 us, 1 processor) total alloc = 638,446,652 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc MAIN MAIN 65.3 63.1 go/Number Data.Aeson.Encode 22.5 26.2 array_ Data.Aeson.Parser.Internal 7.0 6.6 tableArrayInDataToJSON.json FM.Json 1.5 0.9 go/Array Data.Aeson.Encode 1.4 1.1 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 172 0 65.3 63.1 100.0 100.0 unstream/resize Data.Text.Fusion 419 7 0.0 0.0 0.0 0.0 main.arrayDouble Main 415 2158 0.0 0.2 0.0 0.2 main.retCodeInt Main 414 2158 0.0 0.0 0.0 0.0 main.dataOut Main 413 2158 0.0 0.0 0.0 0.0 getarray.paramLength FM.ModelIO 408 2158 0.0 0.0 0.0 0.0 getarray FM.ModelIO 407 2158 0.1 0.7 0.1 0.7 getarray.rowsReturnedInt FM.ModelIO 412 2158 0.0 0.0 0.0 0.0 getarray.arrayPtr FM.ModelIO 411 2158 0.0 0.0 0.0 0.0 main.resultInt Main 396 1 0.0 0.0 0.0 0.0 main.resultInt Main 395 1 0.0 0.0 0.0 0.0 setmodulestring FM.ModelIO 391 1 0.0 0.0 0.0 0.0 setmodulestring.setVarInArray FM.ModelIO 394 1 0.0 0.0 0.0 0.0 setmodulestring.cValueLength FM.ModelIO 393 1 0.0 0.0 0.0 0.0 setmodulestring.cParamLength FM.ModelIO 392 1 0.0 0.0 0.0 0.0 main.queryString Main 385 1 0.0 0.0 0.0 0.0 stringDataToJSON FM.Json 386 1 0.0 0.0 0.0 0.0 stringDataToJSON.json FM.Json 388 1 0.0 0.0 0.0 0.0 object_ Data.Aeson.Parser.Internal 389 0 0.0 0.0 0.0 0.0 jstring_ Data.Aeson.Parser.Internal 390 4 0.0 0.0 0.0 0.0 stringDataToJSON.retValue FM.Json 387 1 0.0 0.0 0.0 0.0 main.resultInt Main 382 290 0.0 0.0 0.0 0.0 go/Object Data.Aeson.Encode 379 2553 0.0 0.1 24.1 27.5 go/Array Data.Aeson.Encode 416 2158 1.2 0.8 21.7 26.2 go/Number Data.Aeson.Encode 418 63801 20.5 25.4 20.5 25.4 go/Number Data.Aeson.Encode 383 2656 0.1 0.1 0.1 0.1 string Data.Aeson.Encode 380 4814 0.1 0.1 2.2 1.1 go/Number Data.Aeson.Encode 384 0 1.9 0.8 2.0 1.0 go/Array Data.Aeson.Encode 417 0 0.1 0.2 0.1 0.2 break Data.Aeson.Encode 381 4814 0.1 0.0 0.1 0.0 setmoduletable FM.ModelIO 372 290 0.2 0.0 0.4 0.1 setmoduletable.cRows FM.ModelIO 376 290 0.0 0.0 0.0 0.0 setmoduletable.cColumns FM.ModelIO 375 290 0.0 0.0 0.0 0.0 setmoduletable.cParamLength FM.ModelIO 374 290 0.1 0.0 0.1 0.0 setmoduletable.cTable FM.ModelIO 373 290 0.0 0.0 0.0 0.0 main.queryString Main 363 290 0.0 0.0 9.6 7.7 tableArrayInDataToJSON FM.Json 364 290 0.0 0.0 9.6 7.7 tableArrayInDataToJSON.json FM.Json 366 290 1.5 0.9 9.6 7.7 object_ Data.Aeson.Parser.Internal 368 0 0.1 0.0 8.1 6.8 jstring_ Data.Aeson.Parser.Internal 369 1450 1.0 0.2 8.0 6.8 array_ Data.Aeson.Parser.Internal 371 0 7.0 6.6 7.0 6.6 tableArrayInDataToJSON.retValue FM.Json 365 290 0.0 0.0 0.0 0.0 main Main 345 0 0.2 0.7 0.2 0.7 run FM.ModelIO 398 0 0.0 0.0 0.0 0.0 run.result FM.ModelIO 405 103 0.0 0.0 0.0 0.0 run.timeTotal FM.ModelIO 404 103 0.0 0.0 0.0 0.0 run.retData FM.ModelIO 403 103 0.0 0.0 0.0 0.0 CAF GHC.Integer.Logarithms.Internals 343 0 0.0 0.0 0.0 0.0 CAF GHC.Float.ConversionUtils 340 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding.CodePage 327 0 0.0 0.0 0.0 0.0 CAF GHC.Conc.Windows 317 0 0.0 0.0 0.0 0.0 CAF GHC.TopHandler 315 0 0.0 0.0 0.0 0.0 CAF GHC.Float 312 0 0.0 0.0 0.0 0.0 CAF Data.Fixed 301 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Handle.FD 299 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Encoding 295 0 0.0 0.0 0.0 0.0 CAF GHC.IO.Exception 294 0 0.1 0.0 0.1 0.0 CAF Data.Text.Lazy.Builder.Int.Digits 282 0 0.0 0.0 0.0 0.0 CAF Data.Text.Lazy.Builder.Int 281 0 0.0 0.0 0.0 0.0 CAF Data.Text.Array 275 0 0.0 0.0 0.0 0.0 CAF Data.Text.Internal 274 0 0.0 0.0 0.0 0.0 CAF System.Locale 269 0 0.0 0.0 0.0 0.0 CAF Data.Scientific 268 0 0.0 0.0 0.0 0.0 CAF Data.Time.LocalTime.TimeOfDay 265 0 0.0 0.0 0.0 0.0 CAF Data.Time.Clock.POSIX 263 0 0.0 0.0 0.0 0.0 CAF Data.Aeson.Parser.Internal 256 0 0.0 0.0 0.0 0.0 array_ Data.Aeson.Parser.Internal 370 1 0.0 0.0 0.0 0.0 object_ Data.Aeson.Parser.Internal 367 1 0.0 0.0 0.0 0.0 CAF Blaze.ByteString.Builder.HTTP 249 0 0.0 0.0 0.0 0.0 CAF Network.HTTP.Types.Header 227 0 0.0 0.0 0.0 0.0 CAF Network.HTTP.Types.URI 226 0 0.0 0.0 0.0 0.0 CAF Network.HTTP.Types.Status 225 0 0.0 0.0 0.0 0.0 CAF Network.HTTP.Types.Method 224 0 0.0 0.0 0.0 0.0 CAF Network.Socket 220 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Parse 211 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.RequestHeader 203 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.ResponseHeader 202 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Date 199 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Request 197 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Response 196 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Recv 194 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Header 193 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Types 191 0 0.0 0.0 0.0 0.0 CAF Network.Wai.Handler.Warp.Settings 189 0 0.0 0.0 0.0 0.0 CAF Web.Scotty.Trans 187 0 0.0 0.0 0.0 0.0 CAF Web.Scotty.Route 186 0 0.0 0.0 0.0 0.0 CAF Web.Scotty.Types 185 0 0.0 0.0 0.0 0.0 unstreamChunks/inner Data.Text.Lazy.Fusion 349 0 0.0 0.0 0.0 0.0 unstreamChunks/outer Data.Text.Lazy.Fusion 350 1 0.0 0.0 0.0 0.0 CAF Web.Scotty.Action 184 0 0.0 0.0 0.0 0.0 unstreamChunks/outer Data.Text.Lazy.Fusion 353 4 0.0 0.0 0.0 0.0 unstreamChunks/inner Data.Text.Lazy.Fusion 354 28 0.0 0.0 0.0 0.0 unstreamChunks/resize Data.Text.Lazy.Fusion 355 5 0.0 0.0 0.0 0.0 CAF Main 182 0 0.0 0.0 0.0 0.0 unstreamChunks/outer Data.Text.Lazy.Fusion 406 1 0.0 0.0 0.0 0.0 main.resultInt Main 360 1 0.0 0.0 0.0 0.0 main Main 344 1 0.0 0.0 0.0 0.0 go/Object Data.Aeson.Encode 357 1 0.0 0.0 0.0 0.0 go/Number Data.Aeson.Encode 361 1 0.0 0.0 0.0 0.0 string Data.Aeson.Encode 358 1 0.0 0.0 0.0 0.0 go/Number Data.Aeson.Encode 362 0 0.0 0.0 0.0 0.0 break Data.Aeson.Encode 359 1 0.0 0.0 0.0 0.0 unstreamChunks/outer Data.Text.Lazy.Fusion 346 10 0.0 0.0 0.0 0.0 unstreamChunks/inner Data.Text.Lazy.Fusion 347 104 0.0 0.0 0.0 0.0 unstreamChunks/resize Data.Text.Lazy.Fusion 348 20 0.0 0.0 0.0 0.0 CAF FM.Json 180 0 0.1 0.0 0.1 0.0 unstream/resize Data.Text.Fusion 356 14 0.0 0.0 0.0 0.0 CAF FM.ModelIO 179 0 0.0 0.0 0.0 0.0 getarray FM.ModelIO 409 0 0.0 0.0 0.0 0.0 getarray.rows FM.ModelIO 410 1 0.0 0.0 0.0 0.0 run.timeTot FM.ModelIO 399 1 0.0 0.0 0.0 0.0 run FM.ModelIO 397 1 0.0 0.0 0.0 0.0 run.runType FM.ModelIO 402 1 0.0 0.0 0.0 0.0 run.timeNow FM.ModelIO 401 1 0.0 0.0 0.0 0.0 run.timeTot FM.ModelIO 400 0 0.0 0.0 0.0 0.0 setmoduletable FM.ModelIO 377 0 0.0 0.0 0.0 0.0 setmoduletable.firstTimeStepAfterRestart FM.ModelIO 378 1 0.0 0.0 0.0 0.0 initfm FM.ModelIO 351 1 0.0 0.0 0.0 0.0

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What's the status of regular patterns?
by ducis 05 Apr '14

05 Apr '14

The package description of haskell-src-exts says "Apart from these standard extensions, it also handles regular patterns as per the HaRP extension as well as HSX-style embedded XML syntax." So is this HaRP extension still alive in any way? The harp package seems to have nothing to do with syntax and long-abandoned.

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Happybara
by Charles Strahan 05 Apr '14

05 Apr '14

Hey all, I've started a clone of the popular Ruby project "Capybara". Of course, it being written in Haskell, I just had to name it Happybara. It's in the early stages, but I think it's quickly coming together. Here's the mission plan: - Custom build hook to compile capybara-webkit's webkit_server (DONE) - High level interface to webkit_server (DONE) - Design Driver type-class, along with monadic DSL class - Queries/actions built atop the underlying Driver/DSL - Write instances/wrappers for hs-webdriver and others If you're interested, check out development here: https://github.com/cstrahan/happybara Oh, and a personal plug: who's hiring? :) -Charles

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design problem, "varying intermediate types"
by Robert Vollmert 05 Apr '14

05 Apr '14

Dear cafe, I’m working on a project that reads logic puzzle descriptions from yaml files and renders them using the Diagrams framework (https://github.com/robx/puzzle-draw) and am quite unsure what’s a good way of stringing things together. It’s a bit hard to even express the problem… I’ve tried to break it down with limited success, to the following task: 1. Read YAML data like type: “three” x: 3 y: [3, 4, 5] Type is from a fixed (long) list of strings. This type determines the format of the fields x and y (x is required, y is optional). 2. Do something type-specific to produce output based on the parsed data. Two options, one that depends on the x field only, the second can also consult the y field. My problem is how I should deal with these intermediate types that vary based on the input. My current approach below has parsing and printing functions, and then one big function that strings the matching parsers and printers together. I’ve also thought about using one big sum type, or type classes (Parseable, Printable, but doesn’t really seem to help). So far, all of it has felt a bit awkward. Any suggestions for how to attack this much appreciated. Cheers Rob {-# LANGUAGE OverloadedStrings #-} import Control.Applicative import Data.Yaml type Parsers a b = (Value -> Parser a, Value -> Parser b) parse1 :: Parsers Int Double parse1 = (parseJSON, parseJSON) parse2 :: Parsers String Char parse2 = (parseJSON, parseJSON) -- parse3 :: Parsers Int [Int] -- ... lots more of these type Printers a b = (a -> IO (), a -> b -> IO ()) print1 :: Printers Int Double print1 = (print . show, \x y -> print (show y ++ "..." ++ show x)) print2 :: Printers String Char print2 = (const $ print "hello", \x y -> print (show y)) type Composed = (Value -> Parser (IO ()), Value -> Value -> Parser (IO ())) compose :: Parsers a b -> Printers a b -> Composed compose (pp, ps) (rp, rs) = (\v -> rp <$> pp v, \v w -> rs <$> pp v <*> ps w) composeType :: String -> Composed composeType t = case t of "one" -> compose parse1 print1 "two" -> compose parse2 print2 _ -> (f, const f) where f = fail $ "unknown type: " ++ t parseXY :: (String -> Value -> Value -> Parser a) -> Value -> Parser a parseXY f (Object v) = do t <- v .: "type" x <- v .: "x" y <- v .: "y" f t x y parseX :: (String -> Value -> Parser a) -> Value -> Parser a parseX f (Object v) = do t <- v .: "type" x <- v .: "x" f t x printA :: Value -> Parser (IO ()) printA = parseX (fst . composeType) printB :: Value -> Parser (IO ()) printB = parseXY (snd . composeType) main = do flagB <- return False -- command line flag let p = parseEither $ if flagB then printB else printA mv <- decodeFile "input.yaml" v <- maybe (fail "failed to parse yaml") return mv case p v of Left e -> fail $ "failed to parse data: " ++ e Right x -> x

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Building GHC 7.6 with 7.8
by Colin Watson 04 Apr '14

04 Apr '14

Hi, I'm trying to bootstrap GHC on a new architecture (Linux arm64/aarch64). I've been working with Karel Gardas from https://ghc.haskell.org/trac/ghc/ticket/7942, and with a few of my own naïve modifications on top of his patch set I've been able to bootstrap my way to a complete working build of the ghc-7.8 git branch (that is, I was able to cross-build on amd64 and then do a complete native build on arm64). arm64 hardware is still pretty rare and emulation is slow, but I have access to some via work, so given help from somebody who knows GHC rather better than I do I'm in a good position to get this done. What I actually want is to see if I can get this support into Ubuntu 14.04 LTS, which is going to be released in about two weeks. I still just about have enough time to do this if I'm quick. However, we currently ship GHC 7.6.3, it's working pretty well, and I don't want to destabilise things by trying to introduce a new version of GHC even just for some architectures. Thus, I've been trying to build 7.6 using 7.8. I know this is not a supported path - it's pretty obvious from the ways it breaks that nobody has spent much time trying to make it work. It seems as though it ought to be possible in theory, though, and cross-building has improved so much in 7.8 that I really don't want to go back and try to cross-build 7.6 - I tried that before and never managed to get anywhere. I've therefore been trying to apply the obvious tweaks like adding imports and adjusting versions in .cabal files. However, I've run into a roadblock, and I hope somebody here might be able to figure out what's going on. I've attached my current work-in-progress patch set; there's some noise from autoreconf, and it also requires putting an updated libffi tarball in place. I've also attached a script(1) log of a failed build attempt. The patch is actually slightly newer than the typescript, in that I realised that the GHC_CONVERT_CPU output needed to be "aarch64" not "arm64" in order for configuring libffi to work properly; this has no material effect on the build failure, though, and I hope it doesn't cause too much confusion. This typescript is from a build of 7.6 with the cross-compiled ghc-stage2. However, I also tried the same build with the native ghc-stage2 build that I'd bootstrapped off that, and the failure looks basically the same to my eye. If anyone thinks the difference might be important then I'd be happy to prepare an updated typescript, but it takes a while. I'd appreciate any suggestions people might have. Thanks, -- Colin Watson [cjwatson(a)ubuntu.com]

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2nd CFP: FHPC'14 - Functional and High-Performance Computing - due May 15
by Ryan Newton 04 Apr '14

04 Apr '14

There a couple small bugs in the previous CFP. (Dates were right, but day of the week was wrong -- the due date is a Thursday.) Please see the corrected version below. ===================================================================== CALL FOR PAPERS FHPC 2014 The 2nd ACM SIGPLAN Workshop on Functional High-Performance Computing Gothenburg, Sweden September 4, 2014 https://sites.google.com/site/fhpcworkshops/ Co-located with the International Conference on Functional Programming (ICFP 2014) Submission Deadline: Thursday, 15 May, 2014 (anywhere on earth) ===================================================================== The FHPC workshop aims at bringing together researchers exploring uses of functional (or more generally, declarative or high-level) programming technology in application domains where high performance is essential. The aim of the meeting is to enable sharing of results, experiences, and novel ideas about how high-level, declarative specifications of computationally challenging problems can serve as maintainable and portable code that approaches (or even exceeds) the performance of machine-oriented imperative implementations. All aspects of performance critical programming and parallel programming are in-scope for the workshop, irrespective of hardware target. This includes both traditional large-scale scientific computing (HPC), as well as work targeting single node systems with SMPs, GPUs, FPGAs, or embedded processors. It is becoming apparent that radically new and well founded methodologies for programming such systems are required to address their inherent complexity and to reconcile execution performance with programming productivity. Every year, the FHPC workshop has an application area as a theme. Papers touching on this topic are especially encouraged, though all in-scope papers are welcomed. For FHPC 2014, the theme is "Heterogeneous computing". In the systems and parallelism communities, there has been a lot of work on programming systems with CPUs and GPUs (or other mixed parallel architectures), but in the programming languages community this idea has not received as much attention. At their best, high-level languages can have the degrees of flexibility necessary to abstract over platform differences. Proceedings: ============ Accepted papers will be published by the ACM and will appear in the ACM Digital Library. * Submissions due: Thursday, 15 May, 2014 (anywhere on earth) * Author notification: Sunday, 15 June, 2014 * Final copy due: Sunday, 22 June, 2014 Submitted papers must be in portable document format (PDF), formatted according to the ACM SIGPLAN style guidelines (2 column, 9pt format). See http://www.sigplan.org/authorInformation.htm for more information and style files. Typical papers are expected to be 8 pages (but up to four additional pages are permitted). Contributions to FHPC 2014 should be submitted via Easychair, at the following URL: * https://www.easychair.org/conferences/?conf=fhpc14 The submission site is now open. The FHPC workshops adhere to the ACM SIGPLAN policies regarding programme committee contributions and republication. Any paper submitted must adhere to ACM SIGPLAN's republication policy. PC member submissions are welcome, but will be reviewed to a higher standard. http://www.sigplan.org/Resources/Policies/Review http://www.sigplan.org/Resources/Policies/Republication Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC programme, see its web page (http://www.sigplan.org/PAC.htm) Programme Committee: ==================== Mary Sheeran (co-chair), Chalmers University of Technology, SE Ryan Newton (co-chair), Indiana University, USA Lennart Augustsson, Standard Chartered Bank, UK Jost Berthold, University of Copenhagen, Denmark Guy Blelloch, Carnegie Mellon University, USA Marius Eriksen, Twitter, USA Clemens Grelck, University of Amsterdam, Netherlands Vinod Grover, Nvidia, USA Kevin Hammond, University of St. Andrews, UK Ben Lippmeier, University of New South Wales, Australia Liu (Paul) Hai, Intel, USA Rita Loogen, University of Marburg, Germany Greg Michaelson, Heriot-Watt University, UK Marc Pouzet, ENS Paris, France John Reppy, Univesity of Chicago, USA Tiark Rompf, Oracle Labs and EPFL, Switzerland Satnam Singh, Google, USA Dimitrios Vytiniotis, Microsoft Research, UK General Chairs: ==================== Jost Berthold University of Copenhagen

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FLOPS 2014 call for participation (June 4-6, Kanazawa, Japan; early registration deadline on May 13)
by Eijiro Sumii 04 Apr '14

04 Apr '14

Dear colleagues, The registration for FLOPS 2014 (Twelfth International Symposium on Functional and Logic Programming, June 4-6, Kanazawa, Japan) is now open: http://www.jaist.ac.jp/flops2014/registration.html - Early registration deadline on May 13, 2014 - Program http://www.jaist.ac.jp/flops2014/program.html with invited talks by Ranjit Jhala, Shin-ya Katsumata, and Gabriele Keller - Sponsored by JSSST SIGPPL; in cooperation with ACM SIGPLAN, AAFS, and ALP - Proceedings to be published as LNCS 8475 - Hyakuman-goku Matsuri Festival http://www.kanazawa-tourism.com/eng/event/event2.php on the day after the symposium (June 7); accommodation can be extended on request basis via the registration site (use the comments field) - See http://www.jaist.ac.jp/flops2014/ for more information Thank you! FLOPS 2014 Program Co-Chairs Michael Codish and Eijiro Sumii

1 0

What should I use if I want both deriving SQL 'create table' from haskell types automatically and relational queries ?
by ducis 04 Apr '14

04 Apr '14

Persistent and acid-state are both 'No SQL' ? I guess there is only groundhog?

3 2

Fun and Profit with Stongly-Typed Data Schemas
by Chris Dornan 04 Apr '14

04 Apr '14

Folks, I will be giving a talk in London on Wednesday evening at Skills Matter on _api-tools_, a cool new Haskell package Iris Connect have been developing with Well Typed to help us with the new web platform. See the Skills Matter web site for details: https://skillsmatter.com/meetups/6201-fun-and-profit-with-stongly-typed-data -schemas Cheers, Chris

1 0

Inline makes program slow?
by Kai Zhang 03 Apr '14

03 Apr '14

Hi cafe, Inline sometimes can cause problems, at least in following case: import qualified Data.Vector as V import Data.List f ∷ String → (String → Int → Char) → [Int] → String f str g idx = map (g str) idx h ∷ String → Int → Char *{-# INLINE h #-}* h s i = (V.fromList $ sort s) V.! i slow ∷ String → [Int] → String slow str = f str h fast ∷ String → [Int] → String fast str = map ((V.fromList $ sort str) V.!) main = do let testString = replicate 100000 'a' iterations = replicate 1000 100 putStrLn $ fast testString iterations putStrLn $ slow testString iterations Without inline (remove the inline pragma), "slow" would be much faster. I suspect this is because ghc can build a "persistent structure" for the partial applied function. After inline, each call of "g" will try to build a new vector. How can I tell ghc not to inline some specific functions? Or are there other ways to resolve this issue?

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Haskell Weekly News: Issue 289
by Daniel Santa Cruz 03 Apr '14

03 Apr '14

Welcome to issue 289 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from March 1 to 31, 2014 So... where have I been? My wife and I recently welcomed into the world our new baby, and as some of you have already experienced, I was doing good getting *some* sleep at night. Life has slowly started to get back to a more predictable rhythm, and I am sure glad to be back doing this. For a while there I thought that any project of mine before bambina was going to have to be put into permament hold, but things are getting very manageble now. Sorry for the abscense! I was somewhat pleased to see that some in -cafe wondered if this was coming back... this one is for you! Some have mentioned that they wish to see more of the "reviews" that HWN used to have of blog entries, and/or email chains in the different mailing lists. I understand that dessire. I'm probably going to need some extra hands to write those, if there are to be back. Maybe we can start with something "lighter", a la tl;dr. I'm stil trying to work out how we'd do that exacly. I'll keep you all posted. Anyway, enough rambling. Quotes of the Week * acowley: I will push machines-concurrent to hackage one fine day edwardk: not concurrent-machines ? acowley: Man, I walked right into that bike shed * malc: I have a coworker who constantly reads haskell stuff at work, nudged him towards the lens talk, that should push him towards actually doing work at work. * Fuuzetsu: I know someone who pulls in Lens just for & and ?? * Eduard_Munteanu: Don't put your money in monads, you can never get it back. :P Top Reddit Stories * Haskell for all: Introductions to advanced Haskell topics Domain: haskellforall.com, Score: 121, Comments: 23 On Reddit: [1] http://goo.gl/M6ZL9f Original: [2] http://goo.gl/YEKyCc * GHC 7.8.1 RC2 released Domain: well-typed.com, Score: 99, Comments: 36 On Reddit: [3] http://goo.gl/jxlLQl Original: [4] http://goo.gl/05xnqX * Book review: Parallel and Concurrent Programming in Haskell Domain: serpentine.com, Score: 87, Comments: 17 On Reddit: [5] http://goo.gl/BfWSWC Original: [6] http://goo.gl/nDe2UG * The Haskell Cast #6 - Gabriel Gonzalez and Michael Snoyman on Pipes and Conduit Domain: haskellcast.com, Score: 83, Comments: 13 On Reddit: [7] http://goo.gl/PwL2aV Original: [8] http://goo.gl/hwemr6 * Performance in Haskell from a noob's perspective Domain: self.haskell, Score: 74, Comments: 111 On Reddit: [9] http://goo.gl/IuT0uJ Original: [10] http://goo.gl/IuT0uJ * New Haddock -- a visual guide to changes Domain: fuuzetsu.co.uk, Score: 72, Comments: 13 On Reddit: [11] http://goo.gl/KWJSEh Original: [12] http://goo.gl/IXzESN * Full-time position available: computer scientist to create data types for scientific computing, in Haskell. Location: anywhere (telecommute). Domain: self.haskell, Score: 67, Comments: 17 On Reddit: [13] http://goo.gl/Z8y9py Original: [14] http://goo.gl/Z8y9py * Haskell Type Classes Cheatsheet Domain: fundeps.com, Score: 62, Comments: 21 On Reddit: [15] http://goo.gl/oAWk4C Original: [16] http://goo.gl/SqHbro * Malicious link in haskell.org docs for 6 years, 6 months, 6 days Domain: self.haskell, Score: 61, Comments: 6 On Reddit: [17] http://goo.gl/V5y3hk Original: [18] http://goo.gl/V5y3hk * What's your "killer app" for your scientific/statistical programming environment? Domain: self.haskell, Score: 57, Comments: 92 On Reddit: [19] http://goo.gl/jfbwdj Original: [20] http://goo.gl/jfbwdj * Find out the type of an expression/function with typed holes Domain: ro-che.info, Score: 56, Comments: 5 On Reddit: [21] http://goo.gl/hcjX1v Original: [22] http://goo.gl/TWLT5R * Elm 0.12 - making interactive UI elements easy and pure Domain: elm-lang.org, Score: 56, Comments: 5 On Reddit: [23] http://goo.gl/SRoog7 Original: [24] http://goo.gl/7FoFAz * QuickCheck 2.7 released Domain: hackage.haskell.org, Score: 55, Comments: 7 On Reddit: [25] http://goo.gl/RN66bR Original: [26] http://goo.gl/3S38Uz Top StackOverflow Questions * Why is Haskell unable to read "7e7" but able to read "7a7"? votes: 42, answers: 3 Read on SO: [27] http://goo.gl/ZI8qm8 * Strange GHCi lazy evaluation votes: 17, answers: 1 Read on SO: [28] http://goo.gl/aoHvVp * Fast, branchless unsigned int absolute difference votes: 16, answers: 3 Read on SO: [29] http://goo.gl/TT3Oxi * How can I write human-language units as postfixes in Haskell, like `3 seconds`? votes: 15, answers: 2 Read on SO: [30] http://goo.gl/6MJk5C * Running Haskell on Xeon-Phi votes: 14, answers: 1 Read on SO: [31] http://goo.gl/QEIayp Until next time, [32]+Daniel Santa Cruz References 1. http://www.haskellforall.com/2014/03/introductions-to-advanced-haskell-topi… 2. http://www.reddit.com/r/haskell/comments/21bcb5/haskell_for_all_introductio… 3. http://www.well-typed.com/blog/87 4. http://www.reddit.com/r/haskell/comments/1zgaln/ghc_781_rc2_released/ 5. http://www.serpentine.com/blog/2014/03/18/book-review-parallel-and-concurre… 6. http://www.reddit.com/r/haskell/comments/20sdt4/book_review_parallel_and_co… 7. http://www.haskellcast.com/episode/006-gabriel-gonzalez-and-michael-snoyman… 8. http://www.reddit.com/r/haskell/comments/1zfo9g/the_haskell_cast_6_gabriel_… 9. http://www.reddit.com/r/haskell/comments/21g6uo/performance_in_haskell_from… 10. http://www.reddit.com/r/haskell/comments/21g6uo/performance_in_haskell_from… 11. http://fuuzetsu.co.uk/blog/posts/2014-03-24-New-Haddock-released%21-A-visua… 12. http://www.reddit.com/r/haskell/comments/218rov/new_haddock_a_visual_guide_… 13. http://www.reddit.com/r/haskell/comments/202pvl/fulltime_position_available… 14. http://www.reddit.com/r/haskell/comments/202pvl/fulltime_position_available… 15. http://fundeps.com/posts/cheatsheets/2014-03-04-cheat-sheets/ 16. http://www.reddit.com/r/haskell/comments/1zn3h9/haskell_type_classes_cheats… 17. http://www.reddit.com/r/haskell/comments/21959m/malicious_link_in_haskellor… 18. http://www.reddit.com/r/haskell/comments/21959m/malicious_link_in_haskellor… 19. http://www.reddit.com/r/haskell/comments/1zowv1/whats_your_killer_app_for_y… 20. http://www.reddit.com/r/haskell/comments/1zowv1/whats_your_killer_app_for_y… 21. http://ro-che.info/articles/2014-03-13-type-of-local-function.html 22. http://www.reddit.com/r/haskell/comments/20bixd/find_out_the_type_of_an_exp… 23. http://elm-lang.org/blog/announce/0.12.elm 24. http://www.reddit.com/r/haskell/comments/218isr/elm_012_making_interactive_… 25. http://hackage.haskell.org/package/QuickCheck-2.7.1/changelog 26. http://www.reddit.com/r/haskell/comments/213da9/quickcheck_27_released/ 27. http://stackoverflow.com/questions/22689122/why-is-haskell-unable-to-read-7… 28. http://stackoverflow.com/questions/22491700/strange-ghci-lazy-evaluation 29. http://stackoverflow.com/questions/22445019/fast-branchless-unsigned-int-ab… 30. http://stackoverflow.com/questions/22109333/how-can-i-write-human-language-… 31. http://stackoverflow.com/questions/22253311/running-haskell-on-xeon-phi 32. https://plus.google.com/105107667630152149014/about

3 2

I guess this is "Play it again Sam"?? If so, sorry ...
by Vasili I. Galchin 03 Apr '14

03 Apr '14

http://www.infoq.com/presentations/haskell-newsroom-nyt

1 0

Eta Reduction
by Dan Doel 03 Apr '14

03 Apr '14

In the past year or two, there have been multiple performance problems in various areas related to the fact that lambda abstraction is not free, though we tend to think of it as so. A major example of this was deriving of Functor. If we were to derive Functor for lists, we would end up with something like: instance Functor [] where fmap _ [] = [] fmap f (x:xs) = f x : fmap (\y -> f y) xs This definition is O(n^2) when fully evaluated,, because it causes O(n) eta expansions of f, so we spend time following indirections proportional to the depth of the element in the list. This has been fixed in 7.8, but there are other examples. I believe lens, [1] for instance, has some stuff in it that works very hard to avoid this sort of cost; and it's not always as easy to avoid as the above example. Composing with a newtype wrapper, for instance, causes an eta expansion that can only be seen as such at the core level. The obvious solution is: do eta reduction. However, this is not operationally sound currently. The problem is that seq is capable of telling the difference between the following two expressions: undefined \x -> undefined x The former causes seq to throw an exception, while the latter is considered defined enough to not do so. So, if we eta reduce, we can cause terminating programs to diverge if they make use of this feature. Luckily, there is a solution. Semantically one would usually identify the above two expressions. While I do believe one could construct a semantics that does distinguish them, it is not the usual practice. This suggests that there is a way to not distinguish them, perhaps even including seq. After all, the specification of seq is monotone and continuous regardless of whether we unify ⊥ with \x -> ⊥ x or insert an extra element for the latter. The currently problematic case is function spaces, so I'll focus on it. How should: seq : (a -> b) -> c -> c act? Well, other than an obvious bottom, we need to emit bottom whenever our given function is itself bottom at every input. This may first seem like a problem, but it is actually quite simple. Without loss of generality, let us assume that we can enumerate the type a. Then, we can feed these values to the function, and check their results for bottom. Conal Elliot has prior art for this sort of thing with his unamb [2] package. For each value x :: a, simply compute 'f x `seq` ()' in parallel, and look for any successes. If we ever find one, we know the function is non-bottom, and we can return our value of c. If we never finish searching, then the function must be bottom, and seq should not terminate, so we have satisfied the specification. Now, some may complain about the enumeration above. But this, too, is a simple matter. It is well known that Haskell programs are denumerable. So it is quite easy to enumerate all Haskell programs that produce a value, check whether that value has the type we're interested in, and compute said value. All of this can be done in Haskell. Thus, every Haskell type is programatically enumerable in Haskell, and we can use said enumeration in our implementation of seq for function types. I have discussed this with Russell O'Connor [3], and he assures me that this argument should be sufficient even if we consider semantic models of Haskell that contain values not denoted by any Haskell program, so we should be safe there. The one possible caveat is that this implementation of seq is not operationally uniform across all types, so the current fully polymorphic type of seq may not make sense. But moving back to a type class based approach isn't so bad, and this time we will have a semantically sound backing, instead of just having a class with the equivalent of the current magic function in it. Once this machinery is in place, we can eta reduce to our hearts' content, and not have to worry about breaking semantics. We'd no longer put the burden on programmers to use potentially unsafe hacks to avoid eta expansions. I apologize for not sketching an implementation of the above algorithm, but I'm sure it should be elementary enough to make it into GHC in the next couple versions. Everyone learns about this type of thing in university computer science programs, no? Thoughts? Comments? Questions? Cheers, -- Dan [1] http://hackage.haskell.org/package/lens [2] http://hackage.haskell.org/package/unamb [3] http://r6.ca/

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HGamer3D - 0.3.x - Building Fixed
by Peter Althainz 02 Apr '14

02 Apr '14

Dear All, I recognized that there were some serious bugs in build code for HGamer3D, which basically prevented building it successfully. I'm very sorry for this! As always there are some explanations how this could happen, but anyhow, I could imagine how frustrating it is to try, spend time and then: no success. This has been fixed now. The detailed build instructions on http://www.hgamer3d.org/Install.html do work, they have been tested on 4 different linux distros and Windows exactly the way described there. regards Peter

1 0

New GHC Features for 7.10.1 and Beyond
by Gershom Bazerman 01 Apr '14

01 Apr '14

There's been lots of exciting work going into the forthcoming GHC 7.8.1 release. But even with all these new features, our language is far from complete and I wouldn't want the GHC team to rest on their laurels. Especially with so much renewed community involvement in GHC development, it seems appropriate to share some ideas some of us have been discussing for future releases, and take a poll of community consensus regarding which ones people might be excited to jump in and help out with, or might find particularly helpful. One important area that needs work is exceptions. These are famously difficult, and many libraries have been written to provide checked exceptions, or unify error and exceptions in various ways. It seems to me that the problem, all along, has been that we've decided to give Haskell _imprecise exceptions_ with special semantics. It would alleviate a great deal of confusion if we implemented a -fprecise-exceptions flag that remedied this. Additionally, while we have long known that Haskell is not a "lazy" language but a "non-strict" one, our leading compiler only rarely takes advantage of this. It is well known that for every program there is a reduction strategy that preserves non-strict semantics while using as few reductions as possible. This is known as the "optimal reduction" strategy, and it is calculable and well understood. We should put some work into a -foptimal-reduction flag. Another important area of research is quantum computation. The D-Wave Two, with 512 qbits, is a commercially available quantum computer now deployed in a few leading institutions. As more and more people begin to purchase D-Wave systems for home hacking, every language worth its salt will need to be able to target this system. Now that cross compilation is more fully supported, it would be good to start putting work into a dwave backend. We've also seen a lot of interest in distribution and cloud computing. From the articles I've read, efficient concurrent programming involves using node.js, so I think we should put some work into writing a new-new-new-IO Manager built on top of this technology. Furthermore, it's ridiculous that while Haskell allows simple concurrent and distributed programming, it offers no simple way to set up a distributed environment. Work should be put into a compiler mode that provisions cloud resources automatically and distributes the target binary among them, with a flag such as: -fvia-s3 _credit_card_number_ There are a few cases where a good idea in GHC can be taken further, and I don't know why we haven't tried already. For example, we've found that despite introducing some occasional problems, the state hack also has drastically improved performance. Since it works so well, we should provide a dual to -fno-state-hack, -fmore-state-hack, for those who really need every last drop of performance. Similarly, now we have type holes that let us see what types should be inserted in various spots. -fvalue-holes is the next logical step, to tell us what terms we should be writing. Also, while we've put so much emphasis on correctness, we've also loosened the bolts optionally the other way, with flags such as -XIncoherentInstances. Along the same lines, I would like to introduce -XImpossibleInstances to let us express such useful things as "instance Int String," "instance IO Comonad," and "instance data if". -fdefer-type-errors allows us to defer type errors to runtime. Having spent some time with JavaScript lately, I think this doesn't go nearly far enough. It would be good to run programs with other sorts of problems as well, for educational purposes and for quick hacking. So work should be put into a -fdefer-scope-errors flag, as well as -fon-error-resume-next, which has done wonders for the resilience of Visual Basic code (see also the wildly useful ability to set the top level error handler in PHP). With all these features put together, we have a powerful new way to approach Haskell programming, and it would be good to enable them by default on .ilhs files (illiterate haskell). It also was pointed out to me recently by Jason Dagit that while we have had debates and confusion over closed and open type families and functions for years, topologists have solved this problem elegantly. With some basic point set topology under one's belt, a -XClopenTypeFamilies extension seems almost trivial to implement. Finally, I'm very sorry to see that my proposal for youtube syntax has languished, and I hope it can be revived: http://www.haskell.org/pipermail/haskell-cafe/2012-April/100527.html HTH HAND, Gershom

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[TFPIE2014] final call for papers
by Peter Achten 01 Apr '14

01 Apr '14

3rd International Workshop on Trends in Functional Programming in Education (TFPIE 2014) May 25, 2014 Utrecht University Soesterberg, The Netherlands (http://www.cs.uwyo.edu/~jlc/tfpie14/) The 3rd International Workshop on Trends in Functional Programming in Education, TFPIE 2014, will be co-located with the Symposium on Trends in Functional Programming (TFP 2014) at Soesterberg, at the “Kontakt der Kontinenten” hotel in the Netherlands on Sunday, May 25th. TFP will follow from May 26-28. The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2014 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2014 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles not selected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012) and in Provo Utah, USA (2013). ** Invited Speaker ** TFPIE is pleased to announce that professor Johan Jeuring of Utrecht University and Open University, both in The Netherlands is giving an invited talk entitled: "Automatic tutoring and assessing functional programs". ** Program Committee ** James Caldwell, (Program Chair) University of Wyoming Peter Achten, Radboud University, Nijmgen Edwin Brady, University of St Andrews, St Andrews Jurriaan Hage, Universiteit Utrecht Philip Holzenspies, University of Twente Daniel R. Licata, Wesleyan University Marco T Morazan, Seton Hall University Christian Skalka, University of Vermont David Van Horn, Northeastern University ** Submission Guidelines ** There will be two types of presentations at TFPIE 2014. Regular papers and “best lecture” presentations. The best lecture talks are intended to allow for presentations or short lectures of purely pedagogical material. Papers and abstracts can be submitted via easychair at the following link: https://www.easychair.org/conferences/?conf=tfpie2014 ** Papers ** TFPIE 2014 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: * FP and beginning CS students * FP and Computational Thinking * FP and Artificial Intelligence * FP in Robotics * FP and Music * Advanced FP for undergraduates * FP in graduate education * Engaging students in research using FP * FP in Programming Languages * FP in the high school curriculum * FP as a stepping stone to other CS topics * FP and Philosophy ** Best Lectures ** In addition to papers, this year we are requesting “best lecture” presentations. What’s your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. ** Important Dates ** * 1 February 2014: TFPIE submissions open on easychair. * 14 April 2014: Early registration for TFP closes * 21 April 2014: Submission deadline for draft TFPIE papers and abstracts * 27 April 2014: Notification of acceptance for presentation * 15 May 2014: Registration for TFPIE closes - as does late registration for TFP * 25 May 2014: Presentations in Soesterberg, Netherlands * 29 June 2014: Full papers for EPTCS proceedings due * 16 August 2014: Notification of acceptance for proceedings * 8 September 2014: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full paper; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn. At least one author from each accepted presentation must attend the workshop.

1 0

Problems with Network/MVar
by Pierre-Étienne Meunier 01 Apr '14

01 Apr '14

Hello cafe, I’m trying to run a server to synchronize a bunch of machines, and one of the threads keeps crashing every ~50 hours. One of the threads is an HTTP server and stays alive forever, so it’s not a Unix signal problem. I don’t have much information on its stdout/stderr, and the bug is not very reproducible, since it can happen even though very few of its maximum ~200 clients are connected. Is there a reason why the following can stop after some time? server::Config -> MVar State -> IO () server config state=withSocketsDo $ do installHandler sigPIPE Ignore Nothing threads<-Sem.new $ maxThreads config forever $ do E.catch (bracket (listenOn $ port config)) sClose $ \sock->forever $ do (s,a,_)<-accept sock wait threads forkIO $ (reply state s a)`finally`(signal threads)`E.catch`(\e->let _=e::IOException in return ()) (\e->let _=e::IOException in return ()) threadDelay 100000 This was compiled with GHC 7.6.3, -threaded and run on Debian Jessie (I have not tested other settings), and Config and State are both record types. Thanks, Pierre

2 3

[TFP2014] First Call for Participation
by Peter Achten 01 Apr '14

01 Apr '14

--------------------------------- 1ST CALL FOR PARTICIPATION --------------------------------- ======== TFP 2014 =========== 15th Symposium on Trends in Functional Programming May 26-28, 2014 Utrecht University Soesterberg, The Netherlands http://www.cs.uu.nl/wiki/TFP2014/WebHome Registration is now open for the symposium on Trends in Functional Programming (TFP). It is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results. Submission for TFP is now closed, and the complete programme (29 presentations and two invited talks) for TFP can be perused here: http://www.cs.uu.nl/wiki/TFP2014/PresentationSchedule TFP 2014 will be the main event of a pair of functional programming events. The other is the International Workshop on Trends in Functional Programming in Education (TFPIE). TFPIE will take place on May 25th. Its website is located at http://www.cs.uwyo.edu/~jlc/tfpie14/ . The submission deadline for TFPIE is April 21, 2014. INVITED SPEAKERS TFP is pleased to announce talks by the following two invited speakers: John Hughes of Chalmers, Goteborg, Sweden, is well-known as author of Why Functional Programming Matters, and as one of the designers of QuickCheck (together with Koen Claessen); the paper on QuickCheck won the ICFP Most Influential Paper Award in 2010. Currently he divides his time between his professorship and Quviq, a company that performs property-based testing of software with a tool implemented in Erlang. Geoffrey Mainland received his PhD from Harvard University where he was advised by Greg Morrisett and Matt Welsh. After a two year postdoc with the Programming Principles and Tools group at Microsoft Research Cambridge, he is now an assistant professor at Drexel University. His research focuses on high-level programming language and runtime support for non-general purpose computation. IMPORTANT DATES Early registration: April 14, 2014 Late registration: May 15, 2014 TFPIE Workshop: May 25, 2014 TFP Symposium: May 26-28, 2014 Registrations can be made at the following URL: http://www.cs.uu.nl/wiki/TFP2014/Register This page will also point you to the web page of the venue where you can arrange for your stay. hoping to see you there. Jurriaan Hage (General Chair)

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Re: [Haskell-cafe] Haskell Weekly News
by Roman Cheplyaka 01 Apr '14

01 Apr '14

(This was submitted to glasgow-haskell-users, probably by mistake. Redirecting to cafe.) * harry <voldermort(a)hotmail.com> [2014-03-31 00:36:10-0700] > There hasn't been a HWN since mid-December. I've emailed the editor with no > response, and there doesn't seem to have been any (public) online activity > from him since. > > I hope he's OK, but either way, it seems that HWN needs a new editor. Any > volunteers? While we're at it, I suggest to potential editors to look up how HWN looked back when Brent Yorgey was the editor. IMO it was much more interesting to read than a mechanically compiled list of reddit and SO posts which HWN has become lately. That style is more time and effort consuming, though. (http://ro-che.info/ccc/06) Roman

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groupBy without Ord?
by martin 01 Apr '14

01 Apr '14

Hello all, when I groupBy a list in order to cluster elements which satisfy some sort of equality, I usually have to sort the list first, which requires Ord. However groupBy itself does not require Ord, but just Eq. How can I groupBy a List whose elements are only instances of Eq but not of Ord?

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Re: [Haskell-cafe] Groundhog - Given entity, how to retrieve autokey value?
by lykahb＠gmail.com 01 Apr '14

01 Apr '14

Hi Ross, The primary key if it is generated by a database is not part of the entity. However, you can store it in your entity if you supply it yourself. It is a good approach if your entity has a natural primary key (like username). Only default key can be auto-incremented. Here is more detailed description of how keys work in Groundhog https://www.fpcomplete.com/user/lykahb/groundhog#keys-and-references Also you may want to use project instead of select. For example, "project (AutoKeyField, MyConstructor) $ MyField ==. myValue" would return id and the entity. Thank you, Boris Lykah On Sunday, March 30, 2014 12:41:40 AM UTC-4, Ross Pokorny wrote: > > Hello, > > I am trying to build a RESTful web application using Groundhog for > persistence. In order to generate URLs for my entities (e.g. for the > Location HTTP header), I need a way, given that I have an entity, to obtain > its id (its AutoKey). From what I've gathered so far, in normal Groundhog > usage, the primary key is not part of the actual entity datatype. The only > place where I've seen it returned is from the 'insert' functions in > Database.Groundhog. I need the id in cases where I have retrieved an > already-existing entity using 'select', but I cannot find a way to obtain > it. > > I gather that this might not be possible with the current API, and that > instead, I may need to explicitly define a field on the entity type to > store the id instead of using the auto-generated field that Groundhog > normally provides. In that case, my question is how do I set up that field > to be an auto-incrementing key, and not simply a value with a unique > constraint. Also, would Groundhog recognize that field as the AutoKey, and > would it return it from 'insert' calls? > > Thanks, > > Ross Pokorny >

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Re: [Haskell-cafe] [ANN] network-transport-zeromq-0.1.
by Patrick Wheeler 01 Apr '14

01 Apr '14

> Our vision is that send/expect should work according to the default distributed-process semantics, but one ought to be allowed to vary the semantics of channel-based communication (as opposed to actor-based) according to what is relevant to the application. E.g. an application ought to be able to give up reliability for better latency/throughput on a channel-by-channel basis. That pretty exciting. I will have to put aside some time to tryout Cloud Haskell on top of your ZeroMQ layer. I would love to see a simple example of how this would work with different reliability settings in a ping-pong example. On Mon, Mar 31, 2014 at 1:34 PM, Edsko de Vries <edsko(a)well-typed.com>wrote: > Hi Mathieu, > > That sounds great! It's great to see that the redesign of Cloud Haskell > with a pluggable Network.Transport layer is in fact being used. Good stuff! > > Edsko > > -- > You received this message because you are subscribed to the Google Groups > "parallel-haskell" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to parallel-haskell+unsubscribe(a)googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Patrick Wheeler Patrick.John.Wheeler(a)gmail.com Patrick.J.Wheeler(a)rice.edu Patrick.Wheeler(a)colorado.edu

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ghc-mod v4.0.0
by Kazu Yamamoto 01 Apr '14

01 Apr '14

Hello, I'm happy to announce the release of ghc-mod v4.0.0. You can see its changelog here: http://hackage.haskell.org/package/ghc-mod-4.0.0/changelog This version provides an interactive command called ghc-modi. As you can guess, this makes syntax error highlighting much faster. The Emacs front-end resolves the "import hell". If you are an Emacs user, probably it is worth reading this page: http://mew.org/~kazu/proj/ghc-mod/en/emacs.html The entire documentation was re-written. Please give a look at it if you are interested: http://mew.org/~kazu/proj/ghc-mod/en/ P.S. This is not April fool. --Kazu

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Re: [Haskell-cafe] [ANN] network-transport-zeromq-0.1.
by Alexander V Vershilov 31 Mar '14

31 Mar '14

Hi, On 31 March 2014 15:41, Mathieu Boespflug <m(a)tweag.io> wrote: > Hi Edsko, > > no worries. > >> Have you tried running Cloud Haskell on top of 0MQ, or are >> you using Network.Transport for something else? > > We're at a point where all distributed-process-tests pass, not just > network-transport-tests (Alexander can confirm). I need to add a correction, some tests, that implies connection break doesn't work, i.e. they are locking (but very rarely they are passing), and I didn't found a valid reason for it. I will try to prepare a email with description of this problem and everything I've found out in a next few days. -- Alexander

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[ANN] cake3-0.4.0.0 released
by Sergey Mironov 30 Mar '14

30 Mar '14

Hi! I'm glad to announce a new version of cake3 the Makefile generator. http://hackage.haskell.org/package/cake3 https://github.com/grwlf/cake3 Cake3 is a EDSL for building Makefiles, written in Haskell. With cake3, developer can write their build logic in Haskell, obtain clean and safe Makefile and distribute it among the non-Haskell-aware users. Currenly, GNU Make is the only backend supported. === Chagnes === - Automatically generate the 'clean' rule - New genFile and genTmpFile functions embed text files into the Makefile. - The Ur/Web extension improved === The sample program === module Cakefile where import Development.Cake3 import Cakefile_P main = writeMake (file "Makefile") $ do selfUpdate cs <- return $ [file "main.c", file "second.c"] d <- rule $ do shell [cmd|gcc -M $cs -MF @(file "depend.mk")|] os <- forM cs $ \c -> do rule $ do shell [cmd| gcc -c $(extvar "CFLAGS") -o @(c.="o") $c |] elf <- rule $ do shell [cmd| gcc -o @(file "main.elf") $os |] rule $ do phony "all" depend elf includeMakefile d Regards, Sergey

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TLS Handshake fails with 'invalid header type: 1\nFrom:\theader\n\n"'
by Reto Hablützel 30 Mar '14

30 Mar '14

Hello, I'm trying to a establish a TLS connection with the hs-tls library. I got most of the code from the Stunnel.hs, but what I am trying do here is to be able to pass either 'Client' or 'Server' as argument and then, depending on which one it is, act as either one in the handshake. This is the code, that tries to make the handshake: client :: Socket -> IO () client sock = do addr <- sockaddr _ <- connect sock addr ctx <- myCCtx sock contextHookSetLogging ctx logging handshake ctx server :: Socket -> IO () server sock = do sockaddr >>= bind sock listen sock 1 (peer, _) <- accept sock ctx <- mySCtx peer contextHookSetLogging ctx logging handshake ctx The rest of it would probably too much to fit into an email, so I am linking it from here: http://lpaste.net/102014 When I run it, the client fails to parse the handshake: Error_Packet_Parsing "Failed reading: invalid header type: 1\nFrom:\theader\n\n" Whereas the server says 'server hello done' right before it receives the alert from the client. How can this happen? That 'From:\theader...' doesn't even exist as a string in the hs-tls library.. Is there anywhere an example for the hs-tls library with a client as well as a server? Thanks a lot! - Reto

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Parsec Preprocessor
by Alessio Valentini 29 Mar '14

29 Mar '14

Dear Haskellers This is gonna be my first post on here : ) . I am developing some tools to interact with Chemistry packages, and I basically have to write input files for those programs. I would like to be able to write those input in a better way inside the hs code. For example this would be perfect ( {{{+ and +}}} are just labels to mark the "special syntax"): --------------a.hs-------------------------------- main = do writeFile "inputOfChemPack" string string = {{{+ This is the actual input file Formatted like this with some %variable +}}} variable = "foo" -------------------------------------------------- I have written a parser that is reading the code and outputs a file like this (it can handle special characters and variables that are not strings, but let's keep it simple here): ----------------b.hs------------------------------ main = do writeFile "inputOfChemPack" string string = "This is the actual input file\nFormatted like this\nwith some " ++ variable ++ " " variable = "foo" -------------------------------------------------- Now... this file can be compiled and it does exactly what I want: it prints a file like this: --------inputOfChemPack----- This is the actual input file Formatted like this with some foo -------------------------------------- Now the big question... right now I am doing this with some bash scripts (run the parser on the file and then compile its output)... but... is it possible to automatize this using my parser as a sort of preprocessor? the "dream" would be to make an extension that just applies the parser automatically before compilation, such as: -----------------a.hs----------------------------- {-# extensionName #-} main = do writeFile "inputOfChemPack" string string = {{{+ This is the actual input file Formatted like this with some %variable +}}} variable = "foo" -------------------------------------------------- $ ghci a.hs GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Main ( a.hs, interpreted ) Ok, modules loaded: Main. *Main> string "This is the actual input file\nFormatted like this\nwith some foo" I have been browsing stuffs about quasiquotation and preprocessors, but I have the feeling that is a quite simple task compared to those solutions. Any ideas? How can I solve this problem? Thank you Alessio

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Naming/Bikeshedding: Haskell version of Capybara
by Charles Strahan 29 Mar '14

29 Mar '14

A question for you all: what would be a good name for a Haskell version of Ruby's Capybara web testing framework? I'm about to start hacking on some better web testing tools for Haskell, but I'm afraid I'm terrible at coming up with concise, revealing names for things. Any suggestions would be very welcome! -Charles

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Best Actor system?
by james 28 Mar '14

28 Mar '14

Having been introduced to actors by looking at Erlang, I discovered Akka. It seems that the performance is pretty impressive and I like the model. There seem to be several basic Actor libraries in Hackage, but they don't seem to be very actively developed. I'm more interested in the model for programming within a single runtime than I am for distributed systems, but message and dispatch performance definitely is important. Can anyone share experiences with the different packages? Is any one of them stand-out? Thanks James

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Happstack website down?
by Sgeo 28 Mar '14

28 Mar '14

http://www.happstack.com/ is now giving a default-looking "It works!" page. Anyone know why?

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Help getting hcwiid to work
by Ivan Perez 28 Mar '14

28 Mar '14

Hi Café, I'm trying to get the wiimote bindings to work (hcwiid). I can compile them just fine, but trying to open the wiimote with the demo application included in the repo returns a null. I tried using C apps directly (wmgui, etc.) and they work for me. I googled as much as I could, but found no solution there. I tried using previous versions of the package, going back in the history of the repo, but it seems to be "just broken". The maintainer of this package cannot offer any help at this moment. Has any haskeller been able to make this work? Best Ivan

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Haskell article from a friend ... .
by Vasili I. Galchin 28 Mar '14

28 Mar '14

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[ANN] network-transport-zeromq-0.1.
by Alexander V Vershilov 28 Mar '14

28 Mar '14

Hi, I'm happy to announce a new network-transport backend based on the 0MQ brokerless protocol [1]. This implementation makes it possible to the wealth of ZeroMQ transports through a simple and shared API. In particular, ZeroMQ supports authenticated communication channels, encryption, efficient multicast and throughput enhancement techniques such as message batching. Wrapping a subset of the ZeroMQ API behind the network-transport API makes it possible for a wealth of higher-level libraries such as distributed-process and HdpH to communicate over ZeroMQ seamlessly, with little to no modification necessary. Network transport zeromq provides: * basic network transport API, ability to use channels and send messages over reliable connections between endpoints. * multicasting. Multicasting reliable and ordered in absence of a long network failures, i.e. if message A is send before message B, then message A will be delivered before message B to every subscriber in multicast group. * basic plain text authorization. * 0mq driven reliability. (automatic connection restart without message loose). * ability mark connections as broken, this may be required to stop automatic reconnect. We currently have a few performance issues that cause a consistent 30% slowdown in performance of network-transport-zmq over TCP, but we’re working on it. ZeroMQ should in fact *improve* performance over raw TCP in many use cases thanks to intelligent batching of queued messages. Current approach is an early release of the library in order to gather feedback. There is a large TODO list with a set of features that may be useful for a big set of use cases like different authorization mechanisms including certificate based, support of connection encryption, support for unreliable connections, heartbeating and service discovery support. This features will be implemented in short milestones. While we believe network-transport-zmq to be useful in its own right, it is only a stepping stone towards making the rich communication patterns implemented in ZeroMQ available through distributed-process. This will allow for writing ZeroMQ applications with all the power of the Process monad, supervision hierarchies, powerful type based matching abstractions and intuitive message sending primitives. All feedback are appreciated. If you have a commercial interest around this project then feel free to contact [2]. [1] http://zeromq.org/ [2] mailto:sales@tweag.io -- Alexander Vershilov mail-to: alexander.vershilov(a)tweag.io -- Alexander

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Main function variables made global.
by Chapman, Anthony Sergio 27 Mar '14

27 Mar '14

?Hello, My problem is as follows (not actual code), I declare a function outside of the main function func w = w * var I get the value of 'var' from a text file in the main function (as the user types the name of the file into terminal) I need a way for 'func' to see what 'var' is without having to change it's type (ie make it into a function which take a 'w' and a 'var'. The reason I can't change the type is that I then pass the function to a PSO module which has strict declarations of a function and I would rather not change the PSO module. I also can't put 'func' into main because 'w' isn't specified. The PSO will find the best w so I don't get it a value. I have thought about making a dummy function which has an input of 'w' and 'var' and an output of a function of just 'w'. Something like: func w = func' w var. I got the function for PSO to optimise and the function to get the data I want from a text file working great, they both do what they're supposed to do. I just need the function of PSO to see the data I get from the file. If you need any more information (sorry if I've been too vague) please let me know. Thank you for your time.?

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2 PhD positions at McMaster
by Jacques Carette 27 Mar '14

27 Mar '14

[The underlying tools in this work will most likely be done in Haskell] PhD Positions Available in the Computing and Software Department at McMaster University For excellent candidates, two PhD positions are available in the Computing and Software Department at McMaster University, in Hamilton, Ontario, Canada. The positions will focus on developing certifiable scientific and engineering software using a Literate Process that eliminates duplication between software artifacts and explicitly incorporates traceability between these artifacts. The motivating case study for the research will be nuclear safety analysis software. Applicants should have a strong background in software engineering or computer science, mathematical maturity and experience with technology and software development. Knowledge of computational mathematics and physics will be considered an asset. Due to the funding model, preference will be given to domestic students or landed immigrants in Canada. Interested candidates should apply for graduate studies with the Computing and Software Department (http://www.cas.mcmaster.ca/cas/0template1.php?1002) and they should send an e-mail expressing interest to one of the project supervisors: Dr. Spencer Smith (smiths(a)mcmaster.ca) Dr. Jacques Carette (carette(a)mcmaster.ca) or Dr. Ned Nedialkov (nedialk(a)mcmaster.ca) Applicants will be accepted until the two positions are filled. The projected start date is September 2014, but this is negotiable. Please feel free to forward this advertisement to any potentially interested candidates. -- Jacques

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Re: [Haskell-cafe] Why does not Haskell have built-in memoization support?
by Andraž Bajt 27 Mar '14

27 Mar '14

Because that would imply you store all calls(parameters and results) during the program execution. And that would require potentialy infinite memory. You might argue that only some need to be memoized. And this is precisely the case. But this reasoning(which to memoize) cannot be fully automated(yet). On Wednesday, March 26, 2014 8:42:32 AM UTC+1, Cosmia Luna wrote: > > Hi everyone, I'm new to Haskell. > > I'm confused about the pure function and lazy evaluation in Haskell. Why > there is not built-in support for memoization, with the fact that calls > with same parameters returns the same result? > > > ---- > Cosmia > >

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ANN: Haskell bindings for Z3: package z3 0.3.2 released
by Iago Abal 27 Mar '14

27 Mar '14

I am happy to announce a new version of the z3 package http://hackage.haskell.org/package/z3 the (unofficial) Haskell bindings for Microsoft's Z3 theorem prover. We didn't announce this package before, but we believe that now it is stable enough to be useful for a broader audience. These bindings are especially appropriate in the following cases: * If your program runs lot of queries, and probably would benefit from incremental solving. Here the performance benefit w.r.t. translating each query to SMT-LIB and calling an external solver should be significant. * If you need to extract interpretations for arrays and functions. * If you need to access specific Z3 features such as Quantifiers or Solvers. We offer three different interfaces: * Z3.Base: a low-level interface, it just performs marshalling. * Z3.Monad: introduces a class MonadZ3 and a concrete monad Z3 that does some bookkeeping for you. Most people seem to be using this interface. * Z3.Lang: a high-level interface in the form of an embedded language. This interface has been deprecated in the current release, we will continue to develop it, but it will be in separate package. The bindings are still incomplete as there are some API functions that have not been added yet. The infrastructure is there, and adding support for new API functions is (most of the times) straightforward. We appreciate that, if you fork the project and add extra functions, then you send the changes back to us. These bindings still use the old Z3 API of Z3 3.x versions, but there is some support for the new API that some people is using satisfactorily. (Z3 4.0 was released while we were still exploring the design of the library and we preferred not to switch to the new API at that time). Full support for the new API should come in the next release. Iago

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Munich Haskell Meeting
by Heinrich Hördegen 26 Mar '14

26 Mar '14

Dear all, our next Haskell meeting in Munich is scheduled for the 31st of March. Exceptionally, we will meet at 19h30 at Theresienstrasse 39 Room A027, 80333 Munich Rene Brunner will present his inaugural speech on Big Data for us. See also the announcment on our site. Afterwards, we will meet at Cafe Puck, as usually. Please help to reserve enough tables by going to http://www.haskell-munich.de/dates and clicking the button. Until then, have a nice time! Heinrich

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ANNOUNCE: wxHaskell 0.90.1.0
by Henk-Jan van Tuyl 26 Mar '14

26 Mar '14

L.S., I am happy to announce a new version of wxHaskell. This version binds to wxWidgets 2.9 [0]. What is it? ----------- wxHaskell is a portable and native GUI library for Haskell. The goal of the project is to provide an industrial strength GUI library for Haskell, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore built on top of wxWidgets – a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with the native look-and-feel. What's new? ----------- - Added functionality: wxGrid: cell spans, cell renderers (numeric, auto string wrapping), wxScrolledWindow, wxSplitterWindow - Reanimated wxToggleButton, added wxBitmapToggleButton - Solved problem with spaces in pathnames (installation procedure, Windows) - Increased max version of dependencies - The external preprocessor (CPP) is now used - The presence of the wx-config executable is checked at installation time - The bitness of the wxWidgets dynamic libraries is compared to the bitness of the wxHaskell libraries to generate, at installation time; a warning is given when the bitness is incompatible - Documentation improvements - Bugs fixed Links ----- See the homepage of wxHaskell for more information: https://www.haskell.org/haskellwiki/WxHaskell The packages are: - wxc https://hackage.haskell.org/package/wxc - wxdirect https://hackage.haskell.org/package/wxdirect - wxcore https://hackage.haskell.org/package/wxcore - wx https://hackage.haskell.org/package/wx Regards, Henk-Jan van Tuyl [0] https://www.wxwidgets.org/ -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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Haskell practice -- Plotting library
by Kai Zhang 26 Mar '14

26 Mar '14

Hi, I've been playing with Haskell for a while. In order to improve my Haskell skills and also due to the lack of an intuitive plotting library, I decided to write a simplified plotting interface for the haskell-chart library. Any comments or suggestions would be very welcome! https://github.com/kaizhang/haskell-plot Kai

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[ANN] haskintex 0.4.0.0 - Haskell code inside a LaTeX document, now with IO!
by Daniel Díaz Casanueva 25 Mar '14

25 Mar '14

Hello haskellers. Good news for the users of haskintex. This release opens new possibilities and solves some frustrations we had in the past. For those who don't know what haskintex is, here is an overview. Haskintex is a program that reads a LaTeX file and evaluates Haskell expressions contained in some specific commands and environments. For example, if you save the file "foo.htex" with: -- foo.htex \documentclass{article} \begin{document} I have \evalhaskell{2+3} fingers in my right hand. \end{document} -- ...and run "haskintex foo", you will get the following output: \documentclass{article} \begin{document} I have \verb`5` fingers in my right hand. \end{document} Just as you expected. If you want to know more details, visit the haskintex site at: http://daniel-diaz.github.io/projects/haskintex What is new in this release? We have added two new features: * \iohatex{t}, where t :: IO LaTeX. It works exactly as the \hatex command does, but it expects an input of type IO LaTeX. This means you can perform IO computations now! * \begin{haskellpragmas}...\end{haskellpragmas} This will allow to include pragmas in the temporal Haskell module. In addition to these two features, a new flag can be passed to the program: -debug. It writes down in a file the representation of the input that haskintex uses internally. It can be useful in those cases that you are not getting the output you expect. And that's it for now. The code didn't grow much (and I want it to stay small) but I think possibilities have grown substantially. If you want to give it try, run "cabal update" followed by "cabal install haskintex". Good luck, Daniel Díaz.

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Cabal robustness
by Dominick Samperi 25 Mar '14

25 Mar '14

I have seen the dreaded "ExitFailure 1" many times when a package fails to install (under Linux or Windows), and I wonder why something more helpful cannot be printed? Sometimes one gets a variant of this where the message is "this system is not compatible with this package," but the user must study the foo.cabal file to determine what is missing. Also, it seems that the only way to determine if a package will install under Windows is to try and hope for the best (often getting "ExitFailure 1" if it fails). Wouldn't it make more sense to tag packages with the OS and other dependencies and fail with a helpful message like "Windows not supported" if appropriate? It appears that some packages (like lens-4.1) have version dependencies that cannot be satisfied (at least not on my Linux and Windows boxes), so it appears that the Hackage hosting process suffers from a variant of the well-known "dll hell" problem. I tried the new (Cabal 1.18.0) sandbox feature but this did not help in my case. Any comments on these issues would be appreciated. Thanks, Dominick

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HaL-9 - Call for Contributions
by Henning Thielemann 25 Mar '14

25 Mar '14

HaL ist ein lokaler Haskell-Workshop mit überregionaler Bedeutung, der nun bereits das 9. Mal stattfindet. Dieses Jahr laden wir für den 20. Juni ins Institut für Informatik an der Martin-Luther-Universität Halle-Wittenberg ein. Wir suchen Beiträge zu Haskell im Besonderen und der funktionalen Programmierung im Allgemeinen, aber auch Anknüpfungen an andere Programmierparadigmen. Dabei interessieren wir uns unter anderem für die Themenbereiche * Neues von Sprache, Bibliotheken, Werkzeugen, * Anwendungen von Kunst bis Industrie, * Lehre und Forschung an Schulen und Hochschulen. Die Beiträge können präsentiert werden als * Tutorium (etwa 90 min) * Vortrag (etwa 30 min) * Demonstration, künstlerische Aufführung Die Veranstaltungssprache ist Deutsch, nach Absprache auch Englisch. Presentations will be given in German but we can switch to English if requested. Bitte reichen Sie Kurzfassungen der Beiträge ein (max. 3 Seiten), die dem Programmkomitee eine Einschätzung ermöglichen, sowie eine knappe Zusammenfassung von etwa 100 Wörtern. Teilnehmer des Workshops sind Interessenten (keine Erfahrung mit Haskell oder funktionaler Programmierung), Anfänger (wenig Erfahrung) und Experten. Wir bitten die Vortragenden, die Zielgruppe des Beitrags anzugeben und die nötigen Vorkenntnisse zu beschreiben. Bei Tutorien sollen Teilnehmer auf eigenen Rechnern arbeiten. Bitte beschreiben Sie dazu die vorher zu installierende Software. Senden Sie die Beitragsvorschläge als PDF-Dokument bis zum 27. April 2014 an hal-committee(a)iba-cg.de Wir werden Ihnen bis zum 9. Mai mitteilen, ob wir Ihren Beitrag in das Programm aufnehmen. Für das Organisationsteam Henning Thielemann

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Regular Expression Simplification
by Berg, Matias Juho 24 Mar '14

24 Mar '14

?Hi all, I am a final year undergraduate student at a university and I am doing my final honours project on natural language generation from regular expressions. For this to work efficiently I need to simplify the regular expressions before I translate them. It seems that there is some previous work done on this in Haskell but I have only been able to find this code (http://hackage.haskell.org/package/HaLeX-1.1/docs/src/Language-HaLex-RegExp…) which does some elementary simplification. Does anyone have any suggestions on where to look for more examples so I can see what kinds of attempts people have used to try and solve this problem? Also if someone has worked on this kind of problem was Kleene algebra a good starting point? Best regards, Matias

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[ANN] rainbox - print colorful text boxes - good for tabular data
by Omari Norman 24 Mar '14

24 Mar '14

Rainbox helps you create (possibly) colorful text boxes for printing to a UNIX terminal. It uses the rainbow [1] library to permit use of 8 or 256 colors. Rainbox is great for formatting tabular data. One module, Rainbox, permits you to make simple grids--like spreadsheets that do not allow you to split or merge cells. Another module, Rainbox.Box, lets you create boxes of arbitrary complexity. Rainbox is similar to the boxes library [2] but unlike Boxes it's easy to use colors with Rainbox. The Haddocks for both modules will get you started; there is also a tutorial for the simple grid model in the Rainbox.Tutorial module. That file is written in literate Haskell, which HsColour does not fare so well with, so it makes more sense in your text editor or on Github: https://github.com/massysett/rainbox/blob/master/lib/Rainbox/Tutorial.lhs Rainbox is here: http://hackage.haskell.org/package/rainbox --Omari [1] http://hackage.haskell.org/package/rainbow [2] http://hackage.haskell.org/package/boxes

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