- Beginners - Haskell.org

Fwd: Can i define a record without defining access method.
by David McBride 09 Jul '11

09 Jul '11

I've never used the main aeson library, but I just tried the aeson-qq library and got this without any real problem. Try this: {-# LANGUAGE QuasiQuotes, TemplateHaskell, DeriveDataTypeable #-} import Data.Text import Data.Aeson import Data.Aeson.QQ import Data.Aeson.Generic import Data.Aeson.Types myReq = [aesonQQ| {age: <|age|>, version: <|version|>} |] where age = 34 :: Integer version = "1.2" myResp = [aesonQQ| {age: <|name|>, version: <|version|>} |] where name = "harold" version = "1.3" >encode $ Data.Aeson.Generic.toJSON myReq Chunk "{\"age\":34,\"version\":\"1.2\"}" Empty >encode $ Data.Aeson.Generic.toJSON myResp Chunk "{\"age\":\"harold\",\"version\":\"1.3\"}" Empty On Sat, Jul 9, 2011 at 12:41 PM, yi huang <yi.codeplayer(a)gmail.com> wrote: > On Sun, Jul 10, 2011 at 12:25 AM, Chaddaï Fouché <chaddai.fouche(a)gmail.com> > wrote: >> >> On Sat, Jul 9, 2011 at 5:59 PM, yi huang <yi.codeplayer(a)gmail.com> wrote: >> > On Sat, Jul 9, 2011 at 6:45 PM, Tom Murphy <amindfv(a)gmail.com> wrote: >> >> >> >> On 7/9/11, yi huang <yi.codeplayer(a)gmail.com> wrote: >> >> > I'm trying to create a haskell implementation of json rpc, I try to >> >> > define >> >> > protocol using record like this: >> >> > >> >> > data Request = Request { >> >> > version :: Integer >> >> > , id :: Integer >> >> > , method :: String >> >> > , args :: [Value] >> >> > } deriving (Typeable, Data, Show) >> >> >> >> > so i can use json library to encode/decode it. >> >> > But this code fails, because haskell will define access function >> >> > automaticlly, and function names conflicts. >> >> > My question is, is there a way i can define record without access >> >> > function, >> >> > so i can have same attribute name in multiple record. >> >> >> >> If you really want to keep those attribute names exactly, you'll have >> to check where the conflict is and find a way not to import the >> conflicting function name. Here I guess "id" is the big problem since >> it comes with the prelude you'll have to use the NoImplicitPrelude >> extension and explicitly "import Prelude hiding (id)", I suggest you >> make a separate module for your type definition so you don't have to >> worry about that in the rest of your code. > > Sorry i don't describe my problem well, actually i have two records, Request > and Response, some attributes have same names, e.g. version, id. > data Request = Request { > version :: Int > ... > } > data Response = Response { > version :: Int > ... > } > And yes, i really want to keep those names exactly, so aeson can > automatically encode them to right json object. > If there are no way to hide access function, then i guess i have to define > them in seperate module, or define them as normal data constructor with > encode/decode precedure defined manually. Both is not pleasant to me. >> >> -- >> Jedaï > > > > -- > http://www.yi-programmer.com/blog/ > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners > >

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iterating over a range of dates
by Rolf Hanson 09 Jul '11

09 Jul '11

Hi, I'm trying to iterate over a range of dates and print them out. Here's how I am doing it in Ruby: 'require 'date' now = Date.parse('2011-07-11') end_date = Date.parse('2011-12-31') (now..end_date).each do |d| # print out a date that looks like: # Monday, July 11, 2011 puts "#{d.strftime('%A, %B %d, %Y')}" end I've been looking at the docs for Data.Time.Format and Data.Time.Calendar and am a bit puzzled at where to begin. Anyone have ideas? I've not found many (any?) examples of time and date manipulation in Haskell. RW

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Can i define a record without defining access method.
by yi huang 09 Jul '11

09 Jul '11

I'm trying to create a haskell implementation of json rpc, I try to define protocol using record like this: data Request = Request { version :: Integer , id :: Integer , method :: String , args :: [Value] } deriving (Typeable, Data, Show) data Response = Response { version :: Integer , id :: Integer , code :: Integer , method :: String , result :: Value } deriving (Typeable, Data, Show) so i can use json library to encode/decode it. But this code fails, because haskell will define access function automaticlly, and function names conflicts. My question is, is there a way i can define record without access function, so i can have same attribute name in multiple record. -- http://www.yi-programmer.com/blog/

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GLfloat cast... have I got it right?
by Sean Charles 08 Jul '11

08 Jul '11

As I chunder on through OpenGL-land with Haskell I find things that sometimes confuse me! Is there some kind of assumption being made here about the remaining two zeros? color $ Color3 (0::GLfloat) 0 0 I can see that is is typing the first zero to GLfloat but why don't I need to do it to the remaining two zeros? Color3 is "Color3 !a !a !a" The !a is, IIUIC, a strictness instruction that ensures that whatever expression I put here is evaluated immediately i.e. no thunk is generated and presumably no space leaks either: something rendering at 60 fps with 'interesting' calculations for RGB values for example could cripple the application! But back to the syntax: I am guessing (and hoping I've got it right for the *right* reasons) that it works because the definition says "a" for all three and that explicitly typing the first one automatically tells (infers!) the type inference system that the other two are to be treated as GLfloat types too. :)

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undefined symbol not allowed?
by Christopher Howard 08 Jul '11

08 Jul '11

I'm one of those evil people who loves to sprinkle Unicode throughout my code. I thought it was pretty cool when I learned about the UnicodeSyntax language extension, as well as the base-unicode-symbols package. However, I am a little perplexed that this symbol is not provided by either of those: ⊥ That is, the "bottom" symbol, Unicode #22A5 (\8869), which I have seen in some programming texts as representing the undefined expression. I tried just defining ⊥ = undefined But ghc won't parse that. Why is this? And is there a way to make it work? -- frigidcode.com theologia.indicium.us

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Does one need a ticket to attend ICFP?
by Sebastien Zany 07 Jul '11

07 Jul '11

There's a "Registration" item on the left menu at http://www.icfpconference.org/icfp2011/ but it doesn't link to anywhere. Can I just show up? Sebastien

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Throughly confused by this error message
by Michael Litchard 07 Jul '11

07 Jul '11

I'd like someone to help me learn what questions to ask about this error. I'm not sure how to contextualize. I will include code segments that I think are important, and trust your questions will reveal what I am leaving out. HtmlParsing.lhs:81:25: The first argument of ($) takes one argument, but its type `URLString' has none In the second argument of `($)', namely `initial $ method_GET' In a stmt of a 'do' expression: curlResp curl $ initial $ method_GET In the expression: do { let initial = urlInitial urlSequence login = urlLogin urlSequence ....; curlResp curl $ initial $ method_GET; curlResp curl $ urlLogin urlSequence $ loginOpts user pass; curlResp curl $ urlFlash1 urlSequence resourceOpts; .... } > generateResourceHtml :: Curl -> String -> String -> FilePath -> IO (Either String String) > generateResourceHtml curl user pass ipFile = do > urlSequence <- popURLrec ipFile > let makeIDPage = do > let initial = urlInitial urlSequence > login = urlLogin urlSequence > flash1 = urlFlash1 urlSequence > flash2 = urlFlash2 urlSequence > showWebForwards = urlShowWebForwards urlSequence > quickCreate = urlQuickCreate urlSequence > getResource = urlGetResource urlSequence > curlResp curl $ initial $ method_GET > curlResp curl $ urlLogin urlSequence $ loginOpts user pass > curlResp curl $ urlFlash1 urlSequence resourceOpts > curlResp curl $ urlFlash2 urlSequence resourceOpts > curlResp curl $ urlShowWebForwards urlSequence resourceOpts > curlResp curl $ urlQuickCreate urlSequence resourceOpts > curlResp curl $ urlGetResource urlSequence resourceOpts > runErrorT makeIDPage > data URLSequence = URLSequence { urlInitial :: URLString > , urlLogin :: URLString > , urlFlash1 :: URLString > , urlFlash2 :: URLString > , urlShowWebForwards :: URLString > , urlQuickCreate :: URLString > , urlGetResource :: URLString > } deriving Show > curlResp :: (Error e, MonadError e m, MonadIO m) => > Curl -> URLString -> [CurlOption] -> m String --CurlResponse > curlResp curl url opts = do > resp <- liftIO $ (do_curl_ curl url opts :: IO CurlResponse) > let code = respCurlCode resp > status = respStatus resp > if code /= CurlOK || status /= 200 > then throwError $ strMsg $ "Error: " ++ show code ++ " -- " ++ show status > else return $ respBody resp

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I get no speedup with RWH examples of parallel sorting
by Kees Bleijenberg 06 Jul '11

06 Jul '11

I've carefully followed the instructions in Real World Haskell for parallel sorting: In SortMain.hs 1. Set testfunction=sort Then del *.o (force recompilation) ghc --make -O2 sortMain.hs run SortMain and I get 500000 numbers => 3.9735 sec. 2. Set testFunction = parSort2 2 del *.o ghc -threaded --make -O2 sortMain.hs run SortMain +RTS -N2 -RTS, I get => 5.3 sec run SortMain +RTS -N1 -RTS, I get => 4.3 sec With the +RTS -s option I get 3 SPARK3 (3 converted, 0 pruned) All other testFunctions are worse. I have a dual core computer that runs Windows XP. I've experimented a lot with par, pseq ... in other programs. I almost always get a few hundred sparks. Half of them are converted and the other half gets pruned. But I never got a faster program (then sequential). What am I doing wrong, any ideas? Kees

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Understandig types
by moowoo9＠fastmail.fm 06 Jul '11

06 Jul '11

Hi everyone. I've got a few questions about the Haskell programming language. 1) what's the difference between these two code statements? I'm convinced they should be the same type T = [Char] type CurrentValue = Char My concern is that in the second one there are no brackets Anyway they are actually declarations arent'they? 2) What is Maybe String? For instance: type P = (Char, Maybe String) Is that a function which has two arguments ? 3) What is Maybe Char ? For instance : type D = ((Maybe Char) , Char) It's another function having three arguments..am I right? Thanks a lot. 777P -- moowoo9(a)fastmail.fm -- http://www.fastmail.fm - The professional email service

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HaXml will not install...
by Sean Charles 04 Jul '11

04 Jul '11

I have just tried to install HaXml after installing htx with no problems, thinking it might have been that I tried ghc-pkg hide hxt and tried again but no luck, that's gotten me out of issues with different version of GLFW but alas not this time. So, can anybody help me out of this one! I've included the output from the install plus the output of running "cabal info base". Thanks Sean. -------- installation output -------- scharles@ubuntu:~/stuff/hackinge/objitsu/trunk/haskell/cimd$ cabal install haxml Resolving dependencies... Configuring HaXml-1.22... Preprocessing library HaXml-1.22... Preprocessing executables for HaXml-1.22... Building HaXml-1.22... src/Text/XML/HaXml/Schema/TypeConversion.hs:8:7: Could not find module `Text.XML.HaXml.Schema.Environment': Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: HaXml-1.22 failed during the building phase. The exception was: ExitFailure 1 scharles@ubuntu:~/stuff/hackinge/objitsu/trunk/haskell/cimd$ cabal install -v haxml Reading available packages... Resolving dependencies... In order, the following would be installed: HaXml-1.22 (new package) Extracting /home/scharles/.cabal/packages/hackage.haskell.org/HaXml/1.22/HaXml-1.22.tar.gz to /tmp/HaXml-1.2215949... Configuring HaXml-1.22... Flags chosen: bytestringinbase=False, splitbase=True Dependency base ==4.2.0.2: using base-4.2.0.2 Dependency bytestring ==0.9.1.7: using bytestring-0.9.1.7 Dependency containers ==0.3.0.0: using containers-0.3.0.0 Dependency filepath ==1.1.0.4: using filepath-1.1.0.4 Dependency polyparse ==1.7: using polyparse-1.7 Dependency pretty ==1.0.1.1: using pretty-1.0.1.1 Dependency random ==1.0.0.2: using random-1.0.0.2 Using Cabal-1.10.2.0 compiled by ghc-6.12 Using compiler: ghc-6.12.3 Using install prefix: /home/scharles/.cabal Binaries installed in: /home/scharles/.cabal/bin Libraries installed in: /home/scharles/.cabal/lib/HaXml-1.22/ghc-6.12.3 Private binaries installed in: /home/scharles/.cabal/libexec Data files installed in: /home/scharles/.cabal/share/HaXml-1.22 Documentation installed in: /home/scharles/.cabal/share/doc/HaXml-1.22 Using alex version 2.3.5 found on system at: /home/scharles/.cabal/bin/alex Using ar found on system at: /usr/bin/ar Using c2hs version 0.16.3 found on system at: /home/scharles/.cabal/bin/c2hs Using cpphs version 1.11 found on system at: /home/scharles/.cabal/bin/cpphs No ffihugs found Using gcc version 4.5.2 found on system at: /usr/bin/gcc Using ghc version 6.12.3 found on system at: /usr/bin/ghc Using ghc-pkg version 6.12.3 found on system at: /usr/bin/ghc-pkg No greencard found Using haddock version 2.6.1 found on system at: /usr/bin/haddock Using happy version 1.18.6 found on system at: /home/scharles/.cabal/bin/happy No hmake found Using hsc2hs version 0.67 found on system at: /usr/bin/hsc2hs No hscolour found No hugs found No jhc found Using ld found on system at: /usr/bin/ld No lhc found No lhc-pkg found No nhc98 found Using pkg-config version 0.25 found on system at: /usr/bin/pkg-config Using ranlib found on system at: /usr/bin/ranlib Using strip found on system at: /usr/bin/strip Using tar found on system at: /bin/tar No uhc found creating dist/build creating dist/build/autogen Preprocessing library HaXml-1.22... Preprocessing executables for HaXml-1.22... Building HaXml-1.22... Building library... creating dist/build /usr/bin/ghc --make -package-name HaXml-1.22 -hide-all-packages -fbuilding-cabal-package -i -idist/build -isrc -idist/build/autogen -Idist/build/autogen -Idist/build -optP-DMYVERSION="\"1.22\"" -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build -hidir dist/build -stubdir dist/build -package-id base-4.2.0.2-d09520f27d14dc38c6981fa942393083 -package-id bytestring-0.9.1.7-253db8fad875ae549d30aec0d8553adf -package-id containers-0.3.0.0-7be04792060ce1514c52e2cb13a5c18a -package-id filepath-1.1.0.4-1425f312faf5b8e9f4babf887e252326 -package-id polyparse-1.7-b5af8124e8aeb60817d4c8a8608def30 -package-id pretty-1.0.1.1-b6652d4fb1f996119a76dcaa986e9d70 -package-id random-1.0.0.2-a4bf29bbfd08ec91d43a4c919e9253f8 -O -XCPP -XExistentialQuantification Text.XML.HaXml.Schema.Schema Text.XML.HaXml Text.XML.HaXml.ByteStringPP Text.XML.HaXml.Combinators Text.XML.HaXml.DtdToHaskell.Convert Text.XML.HaXml.DtdToHaskell.Instance Text.XML.HaXml.DtdToHaskell.TypeDef Text.XML.HaXml.Escape Text.XML.HaXml.Html.Generate Text.XML.HaXml.Html.Parse Text.XML.HaXml.Html.ParseLazy Text.XML.HaXml.Html.Pretty Text.XML.HaXml.Lex Text.XML.HaXml.Namespaces Text.XML.HaXml.OneOfN Text.XML.HaXml.Parse Text.XML.HaXml.ParseLazy Text.XML.HaXml.Posn Text.XML.HaXml.Pretty Text.XML.HaXml.SAX Text.XML.HaXml.Schema.Parse Text.XML.HaXml.Schema.XSDTypeModel Text.XML.HaXml.Schema.HaskellTypeModel Text.XML.HaXml.Schema.NameConversion Text.XML.HaXml.Schema.TypeConversion Text.XML.HaXml.Schema.PrettyHaskell Text.XML.HaXml.Schema.PrimitiveTypes Text.XML.HaXml.ShowXmlLazy Text.XML.HaXml.Types Text.XML.HaXml.TypeMapping Text.XML.HaXml.Util Text.XML.HaXml.Validate Text.XML.HaXml.Verbatim Text.XML.HaXml.Wrappers Text.XML.HaXml.XmlContent Text.XML.HaXml.XmlContent.Parser Text.XML.HaXml.XmlContent.Haskell Text.XML.HaXml.Xtract.Combinators Text.XML.HaXml.Xtract.Lex Text.XML.HaXml.Xtract.Parse src/Text/XML/HaXml/Schema/TypeConversion.hs:8:7: Could not find module `Text.XML.HaXml.Schema.Environment': Use -v to see a list of the files searched for. World file is already up to date. cabal: Error: some packages failed to install: HaXml-1.22 failed during the building phase. The exception was: ExitFailure 1 scharles@ubuntu:~/stuff/hackinge/objitsu/trunk/haskell/cimd$ -------- base output -------- scharles@ubuntu:~$ cabal info base * base (library) Synopsis: Basic libraries (backwards-compatibility version) Versions available: 3.0.3.1, 3.0.3.2, (4.0.0.0), (4.1.0.0), (4.2.0.0), (4.2.0.1), (4.2.0.2), (4.3.0.0), (4.3.1.0) Versions installed: 3.0.3.2, (4.2.0.2) Homepage: [ Not specified ] Bug reports: http://hackage.haskell.org/trac/ghc/newticket?component=libraries/base Description: This is a backwards-compatible version of the base package. It depends on a later version of base, and was probably supplied with your compiler when it was installed. License: BSD3 Maintainer: libraries(a)haskell.org Source repo: http://darcs.haskell.org/packages/base3-compat Dependencies: base >=4.0 && <4.3, syb ==0.1.* Documentation: [ Not installed ] Cached: No Modules: Control.Applicative Control.Arrow Control.Category Control.Concurrent Control.Concurrent.Chan Control.Concurrent.MVar Control.Concurrent.QSem Control.Concurrent.QSemN Control.Concurrent.SampleVar Control.Exception Control.Monad Control.Monad.Fix Control.Monad.Instances Control.Monad.ST Control.Monad.ST.Lazy Control.Monad.ST.Strict Data.Bits Data.Bool Data.Char Data.Complex Data.Dynamic Data.Either Data.Eq Data.Fixed Data.Foldable Data.Function Data.Generics Data.Generics.Aliases Data.Generics.Basics Data.Generics.Instances Data.Generics.Schemes Data.Generics.Text Data.Generics.Twins Data.HashTable Data.IORef Data.Int Data.Ix Data.List Data.Maybe Data.Monoid Data.Ord Data.Ratio Data.STRef Data.STRef.Lazy Data.STRef.Strict Data.String Data.Traversable Data.Tuple Data.Typeable Data.Unique Data.Version Data.Word Debug.Trace Foreign Foreign.C Foreign.C.Error Foreign.C.String Foreign.C.Types Foreign.Concurrent Foreign.ForeignPtr Foreign.Marshal Foreign.Marshal.Alloc Foreign.Marshal.Array Foreign.Marshal.Error Foreign.Marshal.Pool Foreign.Marshal.Utils Foreign.Ptr Foreign.StablePtr Foreign.Storable GHC.Arr GHC.Base GHC.Conc GHC.ConsoleHandler GHC.Desugar GHC.Dotnet GHC.Enum GHC.Environment GHC.Err GHC.Exception GHC.Exts GHC.Float GHC.ForeignPtr GHC.Handle GHC.IOscharles@ubuntu:~$ cabal info base * base (library) Synopsis: Basic libraries (backwards-compatibility version) Versions available: 3.0.3.1, 3.0.3.2, (4.0.0.0), (4.1.0.0), (4.2.0.0), (4.2.0.1), (4.2.0.2), (4.3.0.0), (4.3.1.0) Versions installed: 3.0.3.2, (4.2.0.2) Homepage: [ Not specified ] Bug reports: http://hackage.haskell.org/trac/ghc/newticket?component=libraries/base Description: This is a backwards-compatible version of the base package. It depends on a later version of base, and was probably supplied with your compiler when it was installed. License: BSD3 Maintainer: libraries(a)haskell.org Source repo: http://darcs.haskell.org/packages/base3-compat Dependencies: base >=4.0 && <4.3, syb ==0.1.* Documentation: [ Not installed ] Cached: No Modules: Control.Applicative Control.Arrow Control.Category Control.Concurrent Control.Concurrent.Chan Control.Concurrent.MVar Control.Concurrent.QSem Control.Concurrent.QSemN Control.Concurrent.SampleVar Control.Exception Control.Monad Control.Monad.Fix Control.Monad.Instances Control.Monad.ST Control.Monad.ST.Lazy Control.Monad.ST.Strict Data.Bits Data.Bool Data.Char Data.Complex Data.Dynamic Data.Either Data.Eq Data.Fixed Data.Foldable Data.Function Data.Generics Data.Generics.Aliases Data.Generics.Basics Data.Generics.Instances Data.Generics.Schemes Data.Generics.Text Data.Generics.Twins Data.HashTable Data.IORef Data.Int Data.Ix Data.List Data.Maybe Data.Monoid Data.Ord Data.Ratio Data.STRef Data.STRef.Lazy Data.STRef.Strict Data.String Data.Traversable Data.Tuple Data.Typeable Data.Unique Data.Version Data.Word Debug.Trace Foreign Foreign.C Foreign.C.Error Foreign.C.String Foreign.C.Types Foreign.Concurrent Foreign.ForeignPtr Foreign.Marshal Foreign.Marshal.Alloc Foreign.Marshal.Array Foreign.Marshal.Error Foreign.Marshal.Pool Foreign.Marshal.Utils Foreign.Ptr Foreign.StablePtr Foreign.Storable GHC.Arr GHC.Base GHC.Conc GHC.ConsoleHandler GHC.Desugar GHC.Dotnet GHC.Enum GHC.Environment GHC.Err GHC.Exception GHC.Exts GHC.Float GHC.ForeignPtr GHC.Handle GHC.IO GHC.IOBase GHC.Int GHC.List GHC.Num GHC.PArr GHC.Pack GHC.Ptr GHC.Read GHC.Real GHC.ST GHC.STRef GHC.Show GHC.Stable GHC.Storable GHC.TopHandler GHC.Unicode GHC.Weak GHC.Word Numeric Prelude System.CPUTime System.Console.GetOpt System.Environment System.Exit System.IO System.IO.Error System.IO.Unsafe System.Info System.Mem System.Mem.StableName System.Mem.Weak System.Posix.Internals System.Posix.Types System.Timeout Text.ParserCombinators.ReadP Text.ParserCombinators.ReadPrec Text.Printf Text.Read Text.Read.Lex Text.Show Text.Show.Functions Unsafe.Coerce scharles@ubuntu:~$ GHC.IOBase GHC.Int GHC.List GHC.Num GHC.PArr GHC.Pack GHC.Ptr GHC.Read GHC.Real GHC.ST GHC.STRef GHC.Show GHC.Stable GHC.Storable GHC.TopHandler GHC.Unicode GHC.Weak GHC.Word Numeric Prelude System.CPUTime System.Console.GetOpt System.Environment System.Exit System.IO System.IO.Error System.IO.Unsafe System.Info System.Mem System.Mem.StableName System.Mem.Weak System.Posix.Internals System.Posix.Types System.Timeout Text.ParserCombinators.ReadP Text.ParserCombinators.ReadPrec Text.Printf Text.Read Text.Read.Lex Text.Show Text.Show.Functions Unsafe.Coerce scharles@ubuntu:~$

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