March 2006 - Haskell - Haskell.org

Haskell as a markup language
by oleg＠pobox.com 22 Mar '06

22 Mar '06

We demonstrate that Haskell as it is, with no TH or other pre-processors, can rather concisely represent semi-structured documents and the rules of their processing. In short, Haskell can implement SXML (ssax.sourceforge.net) right in its syntax and with the *open* and extensible set of `tags'. The benefit of Haskell is of course in static type guarantees, such as prohibiting an H1 element to appear in the character content of other elements. It also seems that the specification of various pre-post-order and context-sensitive traversals is more concise in Haskell compared to Scheme. Again, we are talking about the existing Haskell, i.e., Haskell98 plus common extensions. No Template Haskell or even overlapping instances are required. The features of our framework are: - extensibility: at any time the user can add new `tags' and new transformation/traversal modes. - static safety: there are no dynamics, and no variant data types for elements or attributes, and thus no possibility of a run-time pattern-match failure. - static guarantees: the framework statically ensures that a `block-level element' cannot appear in the inline (i.e., character) content and that a character-content entity cannot appear in a pure element content. Some entities (e.g., `title') may be either element or attribute. OTH, many other entities may not occur in the attribute context. Thus the generated XML or HTML document will not only be well-formed: it would also satisfy some validity constraints. More validity constraints can be added to the framework. - flexibility of the traversal: the same document can be transformed in pre-, post-, accumulating or other ways, even within the same session. A document can be processed in a pure function, or in a monadic action, including an IO action. In the latter case, we can, e.g., verify URLs as we generate an HTML document. A `tag' can be transformed depending of the transformation modes and tag's context: e.g., the same `(title "title")' expression may appear as an attribute or an element -- and it will be rendered differently by the (X)HMTL serializer. - pleasant syntax, which closely resembles SXML. We can write (p "string" "string1" br "string3") without unnecessary commas and other syntactic distractions. We take polyvariadic functions to the new level (pun intended). We also exploit functional dependencies on a per-instance level -- which is a very useful but, alas, rarely used technique. We introduce two frameworks for representing semi-structured data in Haskell. In one, semi-structured data is truly a heterogeneous structure -- and so can be showed, stored, written and read. In the second approach, semi-structured data are represented as a monadic value, polymorphic over the rendering monad. Different choices of the monad give different views of data. In GHC, this amounts to representing semi-structured data by linked dictionaries; in JHC, both approaches are probably equivalent. The first representation is quite reminiscent of HList; the second has clear SYB3 (``Scratch your boilerplate with class'') overtones, although the realization is quite different. In particular, there is no need for recursive instances. Because of the amount of code involved (to describe common HTML tags and their constraints), this message is not the complete code. The code is available from http://pobox.com/~oleg/ftp/Haskell/HSXML.tar.gz Please see the files HSXML.hs, HSXML_HTML.hs and the sample code sample1c.hs for the data-centric framework. The monad-centric framework is in one self-contained file CSXML.hs. The first framework is more in line with SXML, and so will be considered here. Our running example, inspired by the Haskell.org web site, is: test_haskell = (document (head [title "Haskell" longdash "HaskellWiki"] [meta_tag [description "All about the language" br "Haskell"]]) (body [h1 "Haskell"] [div (attr [title "titleline"]) [p [[a (attr [href (FileURL "/haskellwiki/Image:Haskelllogo.jpg")]) "Haskell" br "A <purely functional> language"]] br ] [p "Haskell is a general purpose," [[em [[strong "purely"]] "functional"]] "programming language"]])) We should point out the absence of commas. The [[x]] syntax can be replaced with a simple [x], but that would require overlapping instances. So far, we have avoided overlapping instances. Incidentally, in many Scheme systems (and, reputedly, in R6RS) square brackets are taken to be synonymous to the round ones. We see that the |br| can be used in various contexts: in the character content of an element and of an attribute (cf. `description' for the latter). However, if we try to replace "Haskell" within the `description' attribute with [[em "Haskell"]] we get an error that Couldn't match `CT_attr' against `CT_inline' Expected type: CT_attr Inferred type: CT_inline OTH, the string "Haskell" that appears within |h1| element may be replaced with [[em "Haskell"]]. However, if we try to enter (h1 [[h1 "Haskell"]]) we get type error Couldn't match `CT_inline' against `CT_block' Indeed, the element |H1| is not allowed in the `inline' context. We can transform the test_haskell data structure in many ways (e.g., extract all the titles, renumber sections, etc). We can also render it in HTML. The result is quite predictable: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd"> <head> <title>Haskell— HaskellWiki</title> <meta name="description" content="All about the language Haskell"></meta> </head> <body> <h1>Haskell</h1> <div title="titleline"> <p><a href="/haskellwiki/Image:Haskelllogo.jpg">Haskell <br> A <purely functional> language</a> <br> </p> <p>Haskell is a general purpose,<em><strong>purely</strong>functional</em>programming language</p> </div> </body> We should note that |title| -- which can be either an element or an attribute -- is indeed rendered differently depending on the context. Just to emphasize the extensibility of the framework, we show how easy it is to add new elements. For example, the `tags' |longdash|, |a|, |div| and |title| are not defined in the base file HSXML.hs. We add these tags in sample1c.hs, as follows: Let us start with an abbreviation for the long dash. It may appear in the character content of an element or an attribute > data LongDash = LongDash deriving Show > longdash :: Check_ia LongDash ct => HW ct LongDash > longdash = HW LongDash > > -- and how to render it in HTML > instance RenderInline (HW ct LongDash) where > render_inline f _ = emit_lit "—" >> return f Actually, the latter instance describes rendering of longdash in any |MonadRender m| -- any monad that defines morphisms |emit|, |emit_elem| and |emit_attr|. Anchor is an inline element with an inline content > data Anchor a b = Anchor a b deriving Show > a attrs body = > build (as_inline . HW . Anchor (as_block attrs) . rev'apppend HNil) > nil_inline body > > instance (Render a, RenderInline b) =>RenderInline (HW ct (Anchor a b)) where > render_inline f (HW (Anchor attrs body)) = > emit_elem "a" [] (Just (render attrs)) (render_ib body) > >> return False Title can be either - a block-level element whose content is CT_inline - an attribute (whose content is, therefore, CT_attr) > newtype Title a = Title a deriving Show > title x = build ((`as_ctx` co) . HW . Title . rev'apppend HNil) nil_ab x > where nil_ab = HW HNil `as_ctx` ci > (ci,co) = title_ctx > class Check_ia (Title ()) i => TitleCtx i o | i -> o, o -> i where > title_ctx :: (HW i a, HW o a) ; title_ctx = undefined > instance TitleCtx CT_attr CT_battr > instance TitleCtx CT_inline CT_block It can be rendered context-sensitively: > instance RenderInline a => Render (HW CT_battr (Title a)) where > render (HW (Title x)) = emit_attr "title" > ((render_inline False x) >> return ()) > instance RenderInline a => Render (HW CT_block (Title a)) where > render (HW (Title x)) = emit_elem "title" [Hint_nl] Nothing > (render_ib x) It seems many of the SXML transformations (cf. the `examples' directory of the SSAX distribution or CVS repository, ssax.sf.net) can be rendered in Haskell. More examples are forthcoming.

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CFP2: Mathematically Structured Functional Programming
by Conor McBride 21 Mar '06

21 Mar '06

SECOND CALL FOR PAPERS Workshop on Mathematically Structured Functional Programming MSFP 2006 Kuressaare, Estonia, 2 July 2006 http://cs.ioc.ee/mpc-amast06/msfp/ a satellite workshop of MPC 2006 a "small workshop" of the TYPES project Background Something wonderful happened when monads arrived in Haskell: some human mathematics explaining the structure of certain computational phenomena became a mechanical means to implement those phenomena. It's a good way to go about functional programming - to dig out the mathematical structure underlying a problem and set it to work! There's more where monads came from, and we want it. This new workshop is about getting it. In recent years, a diverse array of mathematical structures has appeared in our programs: monads dualise to comonads and generalise to Freyd categories aka 'arrows'; 'container' types have a generalised polynomial structure supporting generic programming, not to mention a differential calculus; isomorphisms from 'high school algebra' are used to search libraries and repair type errors; coalgebras give structure to recursion; the list goes on... MSFP is broad in scope, covering the extraction of functionality from structure wherever it can be found. It complements the remit of its host conference, Mathematics of Program Construction, by seeking to enrich the language and toolset available for specifications and programs alike. It is also a "small workshop" of the FP6 IST coordination action TYPES. Invited speakers Andrzej Filinski, Kbenhavns Universitet John Power, University of Edinburgh Important dates * Submission of papers: 10 April 2006 * Notification of authors: 8 May 2006 * Camera-ready version: 5 June 2006 Topics Submissions are welcome on, but by no means restricted to, topics from the following partially computed coinductive list: * structured effectful computation * structured recursion * structured tree and graph operations * structured syntax with variable binding * structures for datatype-genericity * structures for search * structured representations of functions * structured manipulation of mathematical structure * structured <thunk> in functional programming Authors concerned about the suitability of a topic are very welcome to contact Conor McBride, ctm(at)cs.nott.ac.uk. Submission and publication Papers in pdf not exceeding 15 pages and adhering to the eWiC style must be submitted by 10 April 2006 via an online submission webpage. Papers must report previously unpublished work and not be submitted concurrently to another conference with refereed proceedings. Accepted papers must be presented at the workshop by one of the authors. The proceedings of MSFP 2006 will be published in the Electronic Workshops in Computing (eWiC) series of the British Computer Society, http://ewic.bcs.org/. After the workshop, the authors of the best papers will be invited to submit revised and expanded versions to a special issue of the Journal of Functional Programming from Cambridge University Press. Programme committee Yves Bertot, INRIA Sophia Antipolis Marcelo Fiore, University of Cambridge Masahito Hasegawa, Kyoto University Graham Hutton, University of Nottingham Paul Levy, University of Birmingham Andres Lh, Universitt Bonn Christoph Lth, Universitt Bremen Conor McBride, University of Nottingham (co-chair) Marino Miculan, Universit degli Studi di Udine Randy Pollack, University of Edinburgh Amr Sabry, Indiana University Tarmo Uustalu, Institute of Cybernetics (co-chair) Main conferences MSFP 2006 is a satellite workshop of the 8th International Conference on Mathematics on Program Construction, MPC 2006, to take place 3-5 July. Co-located with MPC 2006, the 11th International Conference on Algebraic Methodology and Software Technology, AMAST 2006, will follow 5-8 July. Venue Kuressaare (pop. 16000) is the main town on Saaremaa, the second-largest island of the Baltic Sea. Kuressaare is a charming seaside resort on the shores of the Gulf of Riga highly popular with Estonians as well as visitors to Estonia. The scientific sessions of MPC/AMAST 2006 will take place at Saaremaa Spa Hotel Meri, one among the several new spa hotels in the town. The social events will involve a number of sites, including the 14th-century episcopal castle. Accommodation will be at Saaremaa Spa Hotels Meri and Rtli. To get to Kuressaare and away, one must pass through Tallinn (pop. 402000), Estonia's capital city. Tallinn is famous for its picturesque medieval Old Town, inscribed on UNESCO's World Heritage List. TYPES support MSFP 2006 is an official workshop of the EU FP6 IST coordination action TYPES. Participants from TYPES sites/subsites may use project funds to cover their travel and participation. Local organizers MPC/AMAST 2006 is organized by Institute of Cybernetics, a research institute of Tallinn University of Technology. The local organizers are Tarmo Uustalu (chair), Monika Perkmann, Juhan Ernits, Ando Saabas, Olha Shkaravska, Kristi Uustalu. Contact email address of the local organizers: mpc06(at)cs.ioc.ee. This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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ANN: monadLib 2.0
by Iavor Diatchki 21 Mar '06

21 Mar '06

Hello everyone, There is now a new version of 'monadLib': a library of monad transformers for Haskell. 'monadLib' is a descendent of 'mtl', the monad template library that is distributed with most Haskell implementations. The library web page is at: http://www.csee.ogi.edu/~diatchki/monadLib Comments and feedback are very welcome! -Iavor

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Compile error in GHC HEAD revision - nobody responding to bug report
by Asfand Yar Qazi 21 Mar '06

21 Mar '06

Hi, I filed a bug report for a compile error in the latest GHC build, but nobody has responded to it for 4 days. I might as well try to fix it myself, but I'm just a functional programming and Haskell beginner. Here's the bug I filed: http://hackage.haskell.org/trac/ghc/ticket/715 Here's what the output of GHC says: ------------------------------------------------------------------------ ==fptools== make all -wr -f Makefile; in /home/ayqazi/src/packages/ghc/ghc-build/libraries/OpenAL ------------------------------------------------------------------------ ../../ghc/compiler/ghc-inplace -H32m -O -W -fno-warn-unused-matches -fwarn-unused-imports -Wall -fffi -Iinclude '-#include "HsOpenAL.h"' -cpp -DCALLCONV=ccall -ignore-package OpenAL -package base -package OpenGL -fgenerics -split-objs -c Sound/OpenAL/ALC/Capture.hs -o Sound/OpenAL/ALC/Capture.o -ohi Sound/OpenAL/ALC/Capture.hi Sound/OpenAL/ALC/Capture.hs:85:3: Couldn't match expected type `NumSamples' against inferred type `Sound.OpenAL.Config.ALCint' Expected type: GettableStateVar NumSamples Inferred type: GettableStateVar Sound.OpenAL.Config.ALCint In the expression: makeGettableStateVar $ (getInteger (Just device) CaptureSamples) In the definition of `captureNumSamples': captureNumSamples device = makeGettableStateVar $ (getInteger (Just device) CaptureSamples) make[2]: *** [Sound/OpenAL/ALC/Capture.o] Error 1 make[1]: *** [all] Error 1 make[1]: Leaving directory `/home/ayqazi/src/packages/ghc/ghc-build/libraries' make: *** [build] Error 1 make: Leaving directory `/home/ayqazi/src/packages/ghc/ghc-build' Here is where (I think) the problem lies (I added the line numbers): File Capture.hs: 42: type NumSamples = ALCsizei 83: captureNumSamples :: Device -> GettableStateVar NumSamples 84: captureNumSamples device = 85: makeGettableStateVar $ getInteger (Just device) CaptureSamples ALCsizei is defined in a file Config.hs two directories below this point: 108: -- | Non-negatitve 32-bit binary integer size 109: type ALCsizei = HTYPE_ALCSIZEI A C header file has the entry '#define HTYPE_ALCSIZEI Word32'. Know what's happening? Thanks

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Haskell Weekly News: March 20, 2006
by dons＠cse.unsw.edu.au 20 Mar '06

20 Mar '06

Haskell Weekly News: March 20, 2006 Greetings, and thanks for reading issue 29 of HWN, a weekly newsletter covering developments in the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list and to [2]The Haskell Sequence. [3]RSS is also available. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://sequence.complete.org/node/feed Announcements * lhs2TeX version 1.11. Andres Loeh [4]announced lhs2TeX version 1.11, a preprocessor to generate LaTeX code from literate Haskell sources. lhs2TeX includes the following features: + Highly customized output. + Liberal parser -- no restriction to Haskell 98. + Generate multiple versions of a program or document from a single source. + Active documents: call Haskell to generate parts of the document (useful for papers on Haskell). + A manual explaining all the important aspects of lhs2TeX. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/13414 Haskell' This section covers activity on [5]Haskell'. * [6]Dropping implicit universal quantification * [7]Refine overlap handling for instance declarations * [8]Ranges and the Enum class * [9]Strict tuples * [10]Time library * [11]Associated types 5. http://hackage.haskell.org/trac/haskell-prime 6. http://thread.gmane.org/gmane.comp.lang.haskell.prime/914 7. http://thread.gmane.org/gmane.comp.lang.haskell.prime/918 8. http://thread.gmane.org/gmane.comp.lang.haskell.prime/937 9. http://thread.gmane.org/gmane.comp.lang.haskell.prime/948 10. http://thread.gmane.org/gmane.comp.lang.haskell.prime/949 11. http://article.gmane.org/gmane.comp.lang.haskell.prime/944 Discussion * Deep Functors. Oleg Kiselyov [12]described an fmap over arbitrarily deep `collections': lists of maybes of maps of IOs, etc. -- arbitrarily nested fmappable things. 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/11951 * GHC 6.4.2. Simon Marlow [13]put out a heads up for the forthcoming 6.4.2 release of GHC. The rough timescale is to go into release candidate testing in about a week, and have two weeks of release candidates before the final release. 13. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13935 * Hexdump. Dominic Steinitz [14]mentioned a "hexdump" function he'd written, posing a question about where it would live in the module hierarchy.. 14. http://news.gmane.org/gmane.comp.lang.haskell.libraries Quote of the Week ihope :: My factorial function uses GADTs. Contributing to HWN You can help us create new editions of this newsletter. Please see the [15]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 15. http://haskell.org/haskellwiki/HWN

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Haskell Weekly News: March 13, 2006
by dons＠cse.unsw.edu.au 18 Mar '06

18 Mar '06

Haskell Weekly News: March 13, 2006 Greetings, and thanks for reading issue 28 of HWN, a weekly newsletter covering developments in the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list and to [2]The Haskell Sequence. [3]RSS is also available. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://sequence.complete.org/node/feed Announcements * Alternative to Text.Regex. Chris Kuklewicz [4]announced an alternative to Text.Regex. While working on the [5]language shootout, Chris implemented a new efficient regex engine, using parsec. It contructs a parser from a string representation of a regular expression. 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/11825 5. http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=all * pass.net. S. Alexander Jacobson [6]launched Pass.net. Written in Haskell, using HAppS, Pass.net lets websites replace registration, confirmation mails, and multiple passwords with a single login, authenticating via their email domain. 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/11824 Haskell' This section covers activity on [7]Haskell'. * [8]Partial application syntax * [9]Extending the `...` notation * [10]The dreaded offside rule * [11]Strictness standardization 7. http://hackage.haskell.org/trac/haskell-prime 8. http://thread.gmane.org/gmane.comp.lang.haskell.prime/874 9. http://thread.gmane.org/gmane.comp.lang.haskell.prime/881 10. http://thread.gmane.org/gmane.comp.lang.haskell.prime/883 11. http://thread.gmane.org/gmane.comp.lang.haskell.prime/901 Discussion * Non-trivial markup transformations. Further on last week's article on encoding markup in Haskell, Oleg Kiselyov [12]demonstrates non-trivial transformations of marked-up data, markup transformations by successive rewriting (aka, `higher-order tags') and the easy definition of new tags. 12. http://article.gmane.org/gmane.comp.lang.haskell.general/13393 * Popular libraries and tools. John Hughes [13]posted (and [14]here) some interesting figures on the most important libraries and tools, based on the results of his survey of users earlier this year. 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/11829 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/11875 * haskell-prime fun. Just for fun, Ross Paterson [15]posted, some thought-provoking [16]statistics on haskell-prime traffic. 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/11831 16. http://www.soi.city.ac.uk/~ross/haskell-prime-stats/ * New collections package. Jean-Philippe Bernardy [17]hinted that his new collections package is almost done. 17. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13880 * Is notMember not member? John Meacham [18]sparked a bit of a discussion on whether negated boolean functions are useful with a patch adding Data.Set and Data.Map.notMember. 18. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/4411 * Namespace games. In a similar vein, Don Stewart [19]triggered discussion on how to sort the hierarchical namespace, when proposing alternatives to the longish Text.ParserCombinators module name. 19. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/4383 Darcs Corner * Darcs-server. Unsatisified with the current techniques for centralised development with darcs, Daan Leijen went ahead and [20]wrote darcs-server. With darcs-server you can: + push changes remotely via a CGI script + or push changes via a single SSH account that serves many users + use cryptographic verification and authorization of users for reading and writing + use gpg encryption (for CGI) + use non-public repositories that can only be accessed by authorized users. 20. http://thread.gmane.org/gmane.comp.version-control.darcs.user/9686 * darcsweb 0.15, by Alberto Bertogli, has been [21]released. 21. http://article.gmane.org/gmane.comp.version-control.darcs.user/9664 Contributing to HWN You can help us create new editions of this newsletter. Please see the [22]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 22. http://haskell.org/haskellwiki/HWN

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Re: Haskell Digest, Vol 31, Issue 15
by Paul Johnson 17 Mar '06

17 Mar '06

"minh thu" <noteed(a)gmail.com> wrote: >2006/3/15, Duncan Coutts <duncan.coutts(a)worc.ox.ac.uk>: > > >>On Wed, 2006-03-15 at 17:21 +0100, Sebastian Sylvan wrote: >> >> >>>You can also use laziness (untested!): >>> >>>data DLink a = (DLink a) a (DLink a) | Nil >>> >>>test = d1 >>> where d1 = Nil 5 d2 >>> d2 = d1 6 Nil >>> >>>test here is a linked list containing 5 and the next node containing >>>6. Both nodes have references to the next and previous links (wich is >>>Nil at the ends). The magic here is laziness. You reference d2 in the >>>definition for d1 and d1 in the definition for d2. It gets sort of >>>clumsy to work with, though. You're probably better off using STRefs >>>(for example) if you really need that type of data structures... >>> >>> >>I wrote a talk once on this topic: >>http://web.comlab.ox.ac.uk/oucl/work/duncan.coutts/papers/recursive_data_st… >> >>Duncan >> >> >thanks, but I cannot construct the whole sturcture in one time (i need >incremental update). > > You might also go back and think about why you needed that double linked list in the first place. Many things that require complicated list structures in C are better represented as compositions of functions. The simplest example is StringS in the Standard Prelude, which avoids O(n^2) behaviour in list concatenation by composing functions instead. Similarly you might find that by representing your data structure as the composition of the functions needed to build it you can defer creation of the actual structure to the point at which it gets read. Then all the closures get evaluated, but the evaluated stuff stays around and acts as the foundation for subsequent updates. It all depends on what you want to do. I suggest reading Chris Okasaki (sp?) on the subject. Paul.

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The Cell processor and Haskell
by Mads Lindstrøm 16 Mar '06

16 Mar '06

Hi all It is often claimed that Haskell's referential transparency would make it an excellent choice for a high-level parallel language. Furthermore, IBM, Sony, and Toshiba's Cell processor is in great need of a high-level parallel language. Thus, they seem to be a perfect match. See http://www.research.ibm.com/cell/ and http://en.wikipedia.org/wiki/Cell_processor for more about the Cell processor. My knowledge of parallel programming is limited, but I would still like to know, what the wiser amongst of us, thinks of making a Haskell compiler for the Cell processor. It is not that I consider implementing one. It is just that I am curious. Is the Cell processor better suited, as a target for a parallel Haskell compiler than Intel, AMD, and Sun's multicore approaches? What I am asking here is, if it is easier to make use of the Cell's closely coupled but limited SPEs or it is easier to make use of the loosely couple but full-featured parallelism of multicore approaches. Is it realistic to think that a Haskell compiler targeting the Cell processor, could make use of it's parallelism without requiring huge changes to the source code of ones already existing meant-for-GHC programs? /Mads Lindstrøm

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strange ghc behaviour?
by Christopher Brown 15 Mar '06

15 Mar '06

Hi, I use ghc 6.4.1 on Mac OS X 10.4.5 and recently I have been getting some very strange errors. It has happened when I have been trying to compile DrIFT, and also today when I was compiling Haddock. The errors seem to change each time, and they always complain about an undefined symbol. For example, when compiling Haddock I got: /tmp/ghc24547.s:22969:Invalid mnemonic 'mtcts' /tmp/ghc24547.s:103127:Invalid mnemonic 'mtcur' /tmp/ghc24547.s:103430:Invalid mnemonic 'mtcur' /tmp/ghc24547.s:108482:Invalid mnemonic 'mtcts' I flushed out /tmp and ran make again, and this time I get: /tmp/ghc24804.s:unknown:Undefined local symbol L___DISCARE__$stub make[3]: *** [HsSyn.o] Error 1 make[2]: *** [all] Error 2 make[1]: *** [all] Error 1 make: *** [build] Error 1 Eventually Haddock will compile if I keep typing make every time ghc fails, but is there any reason why ghc is doing this? and how can I correct it? Thanks for your help. Chris Brown. Christopher Brown Ph.D. Student University of Kent. UK. http://www.cs.kent.ac.uk/people/rpg/cmb21/index.html

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implementing pointers-based data structure
by minh thu 15 Mar '06

15 Mar '06

hi everybody, i have to implement some data structure which is usually implemented with pointers in imperative languages (can think of it as a double linked list). i'd like to know how i have to do that. is there any standard way of converting pointer-based data structure into an inductively-defined data type (like standard haskell list) ? is-it possible ? or would it be good to define the data structure in c and write a haskell wrapper around the c code ? thank you a lot, bye, vo minh thu

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