October 2008 - Haskell-Cafe

computational overhead of the "data" declarations
by Daryoush Mehrtash 29 Oct '08

29 Oct '08

I Haskell School of Expression (p172), it says: A newtype declaration is just like a data declaration, except that it can > only be used to defined data types with single constructor. The new data > type is different from the analogous one created by a data declaration, in > that there is no computational overhead in having the constructor.... You > can think of a newtype as defining a "new type" with exactly the same > structure, behaviour, and performance as the underlying type. > What is (or where do you see) the computational overhead of the "data" declrations?

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ANNOUNCE: Data.TCache 0.5.1
by Alberto G. Corona 28 Oct '08

28 Oct '08

I uploaded TCache to hackage.org. Data.Tcache is a transactional cache with configurable persistence. It tries to simulate Hibernate for Java or Rails for Ruby. The main difference is that transactions are done in memory trough STM. There are transactional cache implementations for some J2EE servers like JBOSS. TCache uses STM . It can atomically apply a function to a list of cached objects. The resulting objects go back to the cache (withResources). It also can retrieve these objects (getResources). Persistence can be syncronous (syncCache) or asyncronous, wtih configurable time between cache writes and configurable cache clearance strategy. the size of the cache can be configured too . All of this can be done trough clearSyncCacheProc. Even the TVar variables can be accessed directly (getTVar) to acceess all the semantic of atomic blocks while maintaining the persistence of the TVar updates. Persistence can be defined for each object.: Each object must have a defined key, a default filename path (if applicable). Persistence is pre-defined in files, but the readResource writeResource and delResource methods can be redefined to persist in databases or whatever. There is a sample.hs that explain the main features.

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Functional MetaPost in 5 Steps
by Jared Updike 28 Oct '08

28 Oct '08

I'm interested in using Functional MetaPost on Mac OS X (or FreeBSD). I'm looking for a tutorial like: http://haskell.org/haskellwiki/Haskell_in_5_steps but for FMP. I can't even get a simple example to show up in a PDF file: ------------------- import FMP ... (see full code below) myPicture = text "Hello World" main = do print $ emit $ metaPost 1 myPicture params ---------- When run, this emits MetaPost, which, after running through my shell script, below, won't show up in my PDF... (this same TeX file will show an .eps figure I made with PyX, the Python equivalent of FMP, when I change includegraphics to use that file instead of test.1) What am I missing? If I can get this working I will gladly write the FMP 5 Step Tutorial. I like the idea of using FMP but I can't for the life of me understand why running a toy example is so non-trivial. (Not to mention undocumented... the manual and tutorials are very compelling but they don't mention how to get a viewable PDF out of any of the otherwise enticing examples.) Jared. Relevant almost working code: Test.hs: ------------------- import FMP params = Parameters { prolog = "verbatimtex\n\ \\\documentclass{article}\n\ \\\begin{document}\n\ \etex\n\n\ \input boxes\n\ \input FuncMP\n\n", epilog= "\n\n\\end", defaultDX= 3, defaultDY= 3, textDX= 2, textDY= 2, newmp= True, funcmpRTS= "IGNORE", --"+RTS -H40m -K3M -RTS", funcmpBin= "IGNORE", -- "~/FuncMP-1.2/FuncMP", mpBin= "IGNORE" -- "MPINPUTS=:~/FuncMP-1.2 TEX=latex mpost " } myPicture = text "blah" main = do print $ emit $ metaPost 1 myPicture params ---------- test.tex: ----------- \documentclass[12pt]{article} \usepackage[dvipdfm]{graphicx} \begin{document} \section*{Heading} \begin{figure} \begin{center} \includegraphics{test.1} \end{center} \end{figure} \end{document} --------------- shell script: ------ #!/bin/sh ghc --make Test.hs && \ ./Test > test.mp && \ mpost test.mp && \ latex test.tex && \ latex test.tex && \ dvipdfm test.dvi && \ open test.pdf # MacOS X runs my pdf in preview -----------

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strange ghc output
by brad clawsie 28 Oct '08

28 Oct '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 i have a small program i have been using routinely that has stopped working. the last alteration of my install configuration was to upgrade the haskell-feed package as arch linux recommended. here is the error i get: - ----- $ runghc newspage.hs GHCi runtime linker: fatal error: I found a duplicate definition for symbol fps_minimum whilst processing object file /usr/lib/bytestring-0.9.1.3/ghc-6.8.2/HSbytestring-0.9.1.3.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. - ----- i have reinstalled the haskell-bytestring package, to no avail. here is the actual code i am trying to run: http://hpaste.org/11514#a0 its fairly straightforward. any clues? thanks - brad -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkkF8ScACgkQxRg3RkRK91OosgCfeZIA378PleCnaxwymabNz97F TXAAnRzOhL4zQ9n9RG1oDp146a1b4ajK =qtCU -----END PGP SIGNATURE-----

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using ghc as a library
by Anatoly Yakovenko 28 Oct '08

28 Oct '08

so I am trying to figure out how to use ghc as a library. following this example, http://www.haskell.org/haskellwiki/GHC/As_a_library, i can load a module and examine its symbols: module Main where import GHC import GHC.Paths ( libdir ) import DynFlags ( defaultDynFlags ) import System.Environment import Data.Maybe import Outputable main = do args <- getArgs let file = head $ args rv <- defaultErrorHandler defaultDynFlags $ do runGhc (Just libdir) $ do dflags <- getSessionDynFlags setSessionDynFlags dflags target <- guessTarget file Nothing setTargets [target] load LoadAllTargets gr <- getModuleGraph mi <- getModuleInfo $ ms_mod $ head $ gr return $ fromJust $ mi print $ showSDoc $ ppr $ modInfoInstances $ rv print $ showSDoc $ ppr $ modInfoExports $ rv given Test.hs: module Test where hello = "hello" world = "world" one = 1 two = 2 i get this output: $ ./Main ./Test.hs "[]" "[Test.hello, Test.one, Test.two, Test.world]" which is what i expect. My question is, how do manipulate the symbols exported by Test? Is there a way to test the types? lets say i wanted to sum all the numbers and concatenate all the strings in Test.hs, how would i do that?

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Re: [Haskell-cafe] Haskell syntax inside QuasiQuote
by Matt Morrow 28 Oct '08

28 Oct '08

> Is there a simple way to do this, i.e. using existing libraries? Yes indeed. I'll be traveling over the next two days, and am shooting for a fully functional hackage release by mid next week. > What I need is a Haskell expression parser which outputs values of type > Language.Haskell.TH.Syntax.QExp, but I can't see one available in the TH > libraries, or in the haskell-src(-exts) libraries. My strategy is to use the existing haskell-src-exts parser, then translate that AST to the TH AST. Once I've got settled in one place, I'll follow up with a brain dump :) > Cheers, > Reiner Matt

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Cabal and GHCi
by Reiner Pope 28 Oct '08

28 Oct '08

Hi, Is there a way to use GHCi with code which is cabal-buildable but not "ghc --make"-able? The emacs haskell-mode makes a pretty good guess by :cd-ing into the directory with the .cabal file; however, if there is a different source-dir this doesn't work so well. A number of more advanced cabal features are even harder to handle. Cheers, Reiner

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What's this algebraic structure called?
by Richard O'Keefe 28 Oct '08

28 Oct '08

Is there a special name for an operator monoid where the structure that's acted on is an Abelian group?

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Problems building HOC
by Colin Fleming 28 Oct '08

28 Oct '08

Hi all, I'm trying to get HOC to build because I'd like to take Yi for a spin and see how it works. I followed the instructions in the Yi README, but I can't get HOC to build. It seems like HOC is under pretty heavy development right now, so maybe this is something transient. I didn't build libffi because according to the Yi docs that's not required on Leopard. HOC built and installed ok, however it failed on the bindings generation step - I've pasted the full compile output below. Am I doing something daft? I'm an (almost) total Haskell newbie so this is entirely possible... I'm using GHC 6.8.2 from MacPorts, and OSX 10.5.5. Thanks for any help! Cheers, Colin ~/dev/haskell/hoc/Bindings> bash make-bindings-macos.sh --user *** Processing Framework Foundation *** NSObjCRuntime.h:139:32: NSIntegerMax undefined [ ] NSObjCRuntime.h:139:32: Couldn't handle enum value for NSNotFound ] NSPropertyList.h:13:55: kCFPropertyListImmutable undefined ] NSPropertyList.h:13:55: Couldn't handle enum value for NSPropertyListImmutable ] NSPropertyList.h:14:71: kCFPropertyListMutableContainers undefined ] NSPropertyList.h:14:71: Couldn't handle enum value for NSPropertyListMutableContainers NSPropertyList.h:16:1: kCFPropertyListMutableContainersAndLeaves undefined ] NSPropertyList.h:16:1: Couldn't handle enum value for NSPropertyListMutableContainersAndLeaves NSPropertyList.h:20:65: kCFPropertyListOpenStepFormat undefined ] NSPropertyList.h:20:65: Couldn't handle enum value for NSPropertyListOpenStepFormat NSPropertyList.h:21:65: kCFPropertyListXMLFormat_v1_0 undefined ] NSPropertyList.h:21:65: Couldn't handle enum value for NSPropertyListXMLFormat_v1_0 NSPropertyList.h:23:1: kCFPropertyListBinaryFormat_v1_0 undefined NSPropertyList.h:23:1: Couldn't handle enum value for NSPropertyListBinaryFormat_v1_0 NSNumberFormatter.h:39:57: kCFNumberFormatterNoStyle undefined******* ] NSNumberFormatter.h:39:57: Couldn't handle enum value for NSNumberFormatterNoStyle NSNumberFormatter.h:40:67: kCFNumberFormatterDecimalStyle undefined NSNumberFormatter.h:40:67: Couldn't handle enum value for NSNumberFormatterDecimalStyle NSNumberFormatter.h:41:69: kCFNumberFormatterCurrencyStyle undefined NSNumberFormatter.h:41:69: Couldn't handle enum value for NSNumberFormatterCurrencyStyle NSNumberFormatter.h:42:67: kCFNumberFormatterPercentStyle undefined NSNumberFormatter.h:42:67: Couldn't handle enum value for NSNumberFormatterPercentStyle NSNumberFormatter.h:43:73: kCFNumberFormatterScientificStyle undefined NSNumberFormatter.h:43:73: Couldn't handle enum value for NSNumberFormatterScientificStyle NSNumberFormatter.h:45:1: kCFNumberFormatterSpellOutStyle undefined NSNumberFormatter.h:45:1: Couldn't handle enum value for NSNumberFormatterSpellOutStyle NSNumberFormatter.h:189:73: kCFNumberFormatterPadBeforePrefix undefined NSNumberFormatter.h:189:73: Couldn't handle enum value for NSNumberFormatterPadBeforePrefix NSNumberFormatter.h:190:71: kCFNumberFormatterPadAfterPrefix undefined NSNumberFormatter.h:190:71: Couldn't handle enum value for NSNumberFormatterPadAfterPrefix NSNumberFormatter.h:191:73: kCFNumberFormatterPadBeforeSuffix undefined NSNumberFormatter.h:191:73: Couldn't handle enum value for NSNumberFormatterPadBeforeSuffix NSNumberFormatter.h:193:1: kCFNumberFormatterPadAfterSuffix undefined NSNumberFormatter.h:193:1: Couldn't handle enum value for NSNumberFormatterPadAfterSuffix NSNumberFormatter.h:200:67: kCFNumberFormatterRoundCeiling undefined NSNumberFormatter.h:200:67: Couldn't handle enum value for NSNumberFormatterRoundCeiling NSNumberFormatter.h:201:63: kCFNumberFormatterRoundFloor undefined NSNumberFormatter.h:201:63: Couldn't handle enum value for NSNumberFormatterRoundFloor NSNumberFormatter.h:202:61: kCFNumberFormatterRoundDown undefined NSNumberFormatter.h:202:61: Couldn't handle enum value for NSNumberFormatterRoundDown NSNumberFormatter.h:203:57: kCFNumberFormatterRoundUp undefined NSNumberFormatter.h:203:57: Couldn't handle enum value for NSNumberFormatterRoundUp NSNumberFormatter.h:204:69: kCFNumberFormatterRoundHalfEven undefined NSNumberFormatter.h:204:69: Couldn't handle enum value for NSNumberFormatterRoundHalfEven NSNumberFormatter.h:205:69: kCFNumberFormatterRoundHalfDown undefined NSNumberFormatter.h:205:69: Couldn't handle enum value for NSNumberFormatterRoundHalfDown NSNumberFormatter.h:207:1: kCFNumberFormatterRoundHalfUp undefined NSNumberFormatter.h:207:1: Couldn't handle enum value for NSNumberFormatterRoundHalfUp NSDecimal.h:49:1: problem parsing struct 61% [*************** ] NSDateFormatter.h:40:53: kCFDateFormatterNoStyle undefined*************** ] NSDateFormatter.h:40:53: Couldn't handle enum value for NSDateFormatterNoStyle NSDateFormatter.h:41:59: kCFDateFormatterShortStyle undefined NSDateFormatter.h:41:59: Couldn't handle enum value for NSDateFormatterShortStyle NSDateFormatter.h:42:61: kCFDateFormatterMediumStyle undefined NSDateFormatter.h:42:61: Couldn't handle enum value for NSDateFormatterMediumStyle NSDateFormatter.h:43:57: kCFDateFormatterLongStyle undefined NSDateFormatter.h:43:57: Couldn't handle enum value for NSDateFormatterLongStyle NSDateFormatter.h:45:1: kCFDateFormatterFullStyle undefined NSDateFormatter.h:45:1: Couldn't handle enum value for NSDateFormatterFullStyle NSCalendar.h:16:47: kCFCalendarUnitEra undefined 79% [******************* ] NSCalendar.h:16:47: Couldn't handle enum value for NSEraCalendarUnit NSCalendar.h:17:49: kCFCalendarUnitYear undefined NSCalendar.h:17:49: Couldn't handle enum value for NSYearCalendarUnit NSCalendar.h:18:51: kCFCalendarUnitMonth undefined NSCalendar.h:18:51: Couldn't handle enum value for NSMonthCalendarUnit NSCalendar.h:19:47: kCFCalendarUnitDay undefined NSCalendar.h:19:47: Couldn't handle enum value for NSDayCalendarUnit NSCalendar.h:20:49: kCFCalendarUnitHour undefined NSCalendar.h:20:49: Couldn't handle enum value for NSHourCalendarUnit NSCalendar.h:21:53: kCFCalendarUnitMinute undefined NSCalendar.h:21:53: Couldn't handle enum value for NSMinuteCalendarUnit NSCalendar.h:22:53: kCFCalendarUnitSecond undefined NSCalendar.h:22:53: Couldn't handle enum value for NSSecondCalendarUnit NSCalendar.h:23:49: kCFCalendarUnitWeek undefined NSCalendar.h:23:49: Couldn't handle enum value for NSWeekCalendarUnit NSCalendar.h:24:55: kCFCalendarUnitWeekday undefined NSCalendar.h:24:55: Couldn't handle enum value for NSWeekdayCalendarUnit NSCalendar.h:25:69: kCFCalendarUnitWeekdayOrdinal undefined NSCalendar.h:25:69: Couldn't handle enum value for NSWeekdayOrdinalCalendarUnit NSCalendar.h:70:61: kCFCalendarComponentsWrap undefined NSCalendar.h:70:61: Couldn't handle enum value for NSWrapCalendarComponents NSCalendar.h:93:1: NSIntegerMax undefined NSCalendar.h:93:1: Couldn't handle enum value for NSUndefinedDateComponent NSByteOrder.h:9:45: CFByteOrderUnknown undefined NSByteOrder.h:9:45: Couldn't handle enum value for NS_UnknownByteOrder Parsing Objective-C header files: 100% [*************************] Building initial entities: 100% [*************************] Resolving cross-references: 100% [*************************] Converting types: 100% [*************************] Zapping unconvertable entities: 100% [*************************] Filling in additional instance declarations: 100% [*************************] Combining duplicate entities: 100% [*************************] Resolving name conflicts: 100% [*************************] Eliminating redundant instances: 100% [*************************] Writing binding modules: 100% [*************************] Writing Foundation.hs: 100% [*************************] Writing Foundation.pi: 100% [*************************] done. ~/dev/haskell/hoc/Bindings/Generated/HOC-Foundation ~/dev/haskell/hoc/Bindings/Generated Configuring HOC-Foundation-1.0... Preprocessing library HOC-Foundation-1.0... Building HOC-Foundation-1.0... [ 2 of 154] Compiling Foundation.NSProxy[boot] ( Foundation/NSProxy.hs-boot, dist/build/Foundation/NSProxy.o-boot ) [ 3 of 154] Compiling Foundation.NSObject[boot] ( Foundation/NSObject.hs-boot, dist/build/Foundation/NSObject.o-boot ) [ 4 of 154] Compiling Foundation.NSPort[boot] ( Foundation/NSPort.hs-boot, dist/build/Foundation/NSPort.o-boot ) [ 5 of 154] Compiling Foundation.NSScanner[boot] ( Foundation/NSScanner.hs-boot, dist/build/Foundation/NSScanner.o-boot ) [ 6 of 154] Compiling Foundation.NSScriptCommand[boot] ( Foundation/NSScriptCommand.hs-boot, dist/build/Foundation/NSScriptCommand.o-boot ) [ 7 of 154] Compiling Foundation.NSScriptCommandDescription[boot] ( Foundation/NSScriptCommandDescription.hs-boot, dist/build/Foundation/NSScriptCommandDescription.o-boot ) [ 8 of 154] Compiling Foundation.NSScriptObjectSpecifiers[boot] ( Foundation/NSScriptObjectSpecifiers.hs-boot, dist/build/Foundation/NSScriptObjectSpecifiers.o-boot ) [ 9 of 154] Compiling Foundation.NSSet[boot] ( Foundation/NSSet.hs-boot, dist/build/Foundation/NSSet.o-boot ) [ 10 of 154] Compiling Foundation.NSStream[boot] ( Foundation/NSStream.hs-boot, dist/build/Foundation/NSStream.o-boot ) [ 11 of 154] Compiling Foundation.NSString[boot] ( Foundation/NSString.hs-boot, dist/build/Foundation/NSString.o-boot ) [ 12 of 154] Compiling Foundation.NSTimeZone[boot] ( Foundation/NSTimeZone.hs-boot, dist/build/Foundation/NSTimeZone.o-boot ) [ 13 of 154] Compiling Foundation.NSTimer[boot] ( Foundation/NSTimer.hs-boot, dist/build/Foundation/NSTimer.o-boot ) [ 14 of 154] Compiling Foundation.NSURL[boot] ( Foundation/NSURL.hs-boot, dist/build/Foundation/NSURL.o-boot ) [ 15 of 154] Compiling Foundation.NSValue[boot] ( Foundation/NSValue.hs-boot, dist/build/Foundation/NSValue.o-boot ) [ 16 of 154] Compiling Foundation.NSXMLNode[boot] ( Foundation/NSXMLNode.hs-boot, dist/build/Foundation/NSXMLNode.o-boot ) [ 17 of 154] Compiling Foundation.NSXMLDTDNode[boot] ( Foundation/NSXMLDTDNode.hs-boot, dist/build/Foundation/NSXMLDTDNode.o-boot ) [ 18 of 154] Compiling Foundation.NSXMLDocument[boot] ( Foundation/NSXMLDocument.hs-boot, dist/build/Foundation/NSXMLDocument.o-boot ) [ 19 of 154] Compiling Foundation.NSXMLElement[boot] ( Foundation/NSXMLElement.hs-boot, dist/build/Foundation/NSXMLElement.o-boot ) [ 23 of 154] Compiling Foundation.NSNotification[boot] ( Foundation/NSNotification.hs-boot, dist/build/Foundation/NSNotification.o-boot ) [ 24 of 154] Compiling Foundation.NSMethodSignature[boot] ( Foundation/NSMethodSignature.hs-boot, dist/build/Foundation/NSMethodSignature.o-boot ) [ 25 of 154] Compiling Foundation.NSLocale[boot] ( Foundation/NSLocale.hs-boot, dist/build/Foundation/NSLocale.o-boot ) [ 26 of 154] Compiling Foundation.NSInvocation[boot] ( Foundation/NSInvocation.hs-boot, dist/build/Foundation/NSInvocation.o-boot ) [ 27 of 154] Compiling Foundation.NSIndexSet[boot] ( Foundation/NSIndexSet.hs-boot, dist/build/Foundation/NSIndexSet.o-boot ) [ 28 of 154] Compiling Foundation.NSGeometry ( Foundation/NSGeometry.hs, dist/build/Foundation/NSGeometry.o ) Loading package base ... linking ... done. Loading package array-0.1.0.0 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. Loading package containers-0.1.0.1 ... linking ... done. Loading package old-locale-1.0.0.0 ... linking ... done. Loading package old-time-1.0.0.0 ... linking ... done. Loading package filepath-1.1.0.0 ... linking ... done. Loading package directory-1.0.0.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package fgl-5.4.1.1 ... linking ... done. Loading package parsec-3.0.0 ... linking ... done. Loading package pretty-1.0.0.0 ... linking ... done. Loading package packedstring-0.1.0.0 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package unix-2.3.0.0 ... linking ... done. Loading package HOC-1.0 ... linking ... done. Foundation/NSGeometry.hs:36:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:36:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:36:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:37:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:37:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:37:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:38:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:38:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:38:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:39:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:39:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:39:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:40:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:40:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:40:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:41:8: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:41:16: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:41:30: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:42:9: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:42:17: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:42:31: Not in scope: data constructor `NSSize' Foundation/NSGeometry.hs:43:10: Not in scope: data constructor `NSRect' Foundation/NSGeometry.hs:43:18: Not in scope: data constructor `NSPoint' Foundation/NSGeometry.hs:43:32: Not in scope: data constructor `NSSize'

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Re: [Haskell] IORef sharing
by Bulat Ziganshin 27 Oct '08

27 Oct '08

Hello Rodney, Tuesday, October 28, 2008, 1:27:26 AM, you wrote: > Now I define an IORef and a couple of counters that share > the IORef, >> iio :: IO (IORef Int) >> iio = newIORef 0 >> ic1 = do { io <- iio ; count io 0 } >> ic2 = do { io <- iio ; count io 0 } > So apparently my mental picture of an IORef as a pointer > to a value is wrong. I need a new mental picture. What's > going on here? this part is right. but "iio = newIORef 0" doesn't define IORef, instead it defines *operation* that creates new IORef and returns it then ic1 and ic2 are *operations* that performs iio, creating new IORef on each call, and then use this new IORef in further operation look at http://haskell.org/haskellwiki/IO_inside -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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