- 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 04 Apr '14

04 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 04 Apr '14

04 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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