March 2008 - Haskell-Cafe

2nd CFP: PLMMS 2008
by Jacques Carette 05 Mar '08

05 Mar '08

SECOND CALL FOR PAPERS * UPDATE: Post-workshop proceedings in Journal of Automated Reasoning * UPDATE: Invited talk by Conor McBride Second Workshop on Programming Languages for Mechanized Mathematics (PLMMS 2008) http://events.cs.bham.ac.uk/cicm08/workshops/plmms/ As part of CICM / Calculemus 2008 Birmingham, UK, 28-29 July 2008 This workshop is focused on the intersection of programming languages (PL) and mechanized mathematics systems (MMS). The latter category subsumes present-day computer algebra systems (CAS), interactive proof assistants (PA), and automated theorem provers (ATP), all heading towards fully integrated mechanized mathematical assistants that are expected to emerge eventually (cf. the objective of Calculemus). The two subjects of PL and MMS meet in the following topics, which are of particular interest to this workshop: * Dedicated input languages for MMS: covers all aspects of languages intended for the user to deploy or extend the system, both algorithmic and declarative ones. Typical examples are tactic definition languages such as Ltac in Coq, mathematical proof languages as in Mizar or Isar, or specialized programming languages built into CA systems. Of particular interest are the semantics of those languages, especially when current ones are untyped. * Mathematical modeling languages used for programming: covers the relation of logical descriptions vs. algorithmic content. For instance the logic of ACL2 extends a version of Lisp, that of Coq is close to Haskell, and some portions of HOL are similar to ML and Haskell, while Maple tries to do both simultaneously. Such mathematical languages offer rich specification capabilities, which are rarely available in regular programming languages. How can programming benefit from mathematical concepts, without limiting mathematics to the computational worldview? * Programming languages with mathematical specifications: covers advanced "mathematical" concepts in programming languages that improve the expressive power of functional specifications, type systems, module systems etc. Programming languages with dependent types are of particular interest here, as is intentionality vs extensionality. * Language elements for program verification: covers specific means built into a language to facilitate correctness proofs using MMS. For example, logical annotations within programs may be turned into verification conditions to be solved in a proof assistant eventually. How need MMS and PL to be improved to make this work conveniently and in a mathematically appealing way? These issues have a very colorful history. Many PL innovations first appeared in either CA or proof systems first, before migrating into more mainstream programming languages. Some examples include type inference, dependent types, generics, term-rewriting, first-class types, first-class expressions, first-class modules, code extraction etc. However, such innovations were never aggressively pursued by builders of MMS, but often reconstructed by programming language researchers. This workshop is an opportunity to present the latest innovations in MMS design that may be relevant to future programming languages, or conversely novel PL principles that improve upon implementation and deployment of MMS. We also want to critically examine what has worked, and what has not. Why are all the languages of mainstream CA systems untyped? Why are the (strongly typed) proof assistants so much harder to use than a typical CAS? What forms of polymorphism exist in mathematics? What forms of dependent types may be used in mathematical modeling? How can MMS regain the upper hand on issues of "genericity" and "modularity"? What are the biggest barriers to using a more mainstream language as a host language for a CAS or PA/ATP? Invited Talk ------------ Conor McBride (Alta Systems, Northern Ireland) will give an invited talk. Submission ---------- Submission works through EasyChair http://www.easychair.org/conferences/?conf=plmms2008 Two kinds of papers will be considered: * Full research papers may be up to 12 pages long. Authors of accepted papers are expected to present their work on the workshop in a regular talk. * Position papers may be up to 4 pages long. The workshop presentation of accepted position papers consists of two parts: a stimulating statement of certain issues or challenges by the author, followed by a discussion in the plenum. Papers should use the usual ENTCS style http://www.entcs.org/prelim.html (11 point version), and will be reviewed by the program committee. Informal workshop proceedings will be circulated as a technical report. Moreover there will be post-workshop proceedings of improved research papers, or position papers that have been completed into full papers, to appear in a special issue of the Journal of Automated Reasoning. There will be a separate submission and review phase for this, where papers from both PLMMS 2007 and 2008 will be considered. Programme Committee ------------------- Jacques Carette (Co-Chair) (McMaster University, Canada) John Harrison (Intel Corporation, USA) Hugo Herbelin (INRIA, Ecole polytechnique, France) James McKinna (Radboud University Nijmegen, Netherlands) Ulf Norell (Chalmers University, Sweden) Bill Page Christophe Raffalli (Universite de Savoie, France) Josef Urban (Charles University, Czech Republic) Stephen Watt (ORCCA, University of Western Ontario, Canada) Makarius Wenzel (Co-Chair) (Technische Universitaet Muenchen, Germany) Freek Wiedijk (Radboud University Nijmegen, Netherlands) Important Dates --------------- * Submission deadline - 5 May 2008 * Notification of acceptance - 6 June 2008 * Final version - 7 July 2008 (approximately) * Workshop - 28-29 July 2008

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Job opening: Use Haskell to save the environment!
by Ketil Malde 05 Mar '08

05 Mar '08

Well - maybe¹. I'm not sure how relevant this is for this list, but I thought I should mention that there is an open position for a 3-year Ph.D. scolarship at IMR where I work. The work is in bioinformatics, and as I'm a happy Haskell user, I'd be happy to see qualified applicants who know Haskell as well. If you are interested, and posess a Master's degree (or equivalent education), a rough translation of the announcement is attached - the official one (in Norwegian) can be found at: http://www.imr.no/aktuelt/ledige_stillinger/stipendiat_bioinformatikk, Please contact me with any questions! -k ¹) The target of the project is the sea louse, which is a large ecological and economical problem. -- If I haven't seen further, it is by standing in the footprints of giants

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Orphan instances
by Henning Thielemann 05 Mar '08

05 Mar '08

Consider the following modules module A class A t module T import A data T a module B import A import T class A t => B t instance B t => A (T t) GHC emits warning about orphan instance A (T t), since neither A nor T are defined in B. However I can't move the instance to A or T since it depends on B. Would it be fine to lift the restriction, such that it is accepted to declare the instance in a module where the type or the class or a superclass (this is new) is defined? In my example class B provides conversion toInteger (that is Integral), class A provides conversion toRational (that is Real) and T is Ratio.

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Re: Exporting Haskell Libraries to C Programmers
by Bruce, Joseph R (Joe) 05 Mar '08

05 Mar '08

Don Stewart <dons <at> galois.com> writes: > > joseph.bruce: > > Hi, > > > > I have a Haskell library that I want to make available via FFI to C > > programmers on my project team. I read this thread > > (http://thread.gmane.org/gmane.comp.lang.haskell.cafe/21447) which had > > some interesting ideas, but they seemed unresolved. Or maybe it answers > > my question but I don't understand it. > > > > Is there a way I can package (ghc-)compiled Haskell code into a > > statically-linked library and not force the C programmers to include > > headers and libraries that they have no knowledge of and undefine a > > seemingly endless list of preprocessor symbols (run ghc with the verbose > > flag and look at the calls to gcc)? Can this process be automated? > > Yes, check the FFI documentation for the main story. > > In short, build the Haskell code with cabal, with your foreign export > Haskell functions in the cbits. That bundle can then be linked against > C code. > > You do need to link your app against libHSrts.a and libHSbase.a (and > other libs you use), but assuming you foreign export, the code > to call will look just like normal C stuff. > Thanks Don. I finally got back to this. I hadn't looked at CABAL before. It's a very useful tool and met all my library-forming needs. That's only half my problem though. I'm trying to make the use of this Haskell code as transparent as possible to the C programmers on the team. Telling them about the Haskell base libraries dependency or distributing those libraries with my code is not too bad, but the list of -u flags that the linker needs is brutal. Is there a way to avoid it, or embed it in the package? Ex (using ghc-6.8.2 -v): ... gcc -v -o primes Primes.o ./Primes_stub.o hs_primes_wrapper.o cprimes.c -Bc:\ghc\ghc-6.8.2\gcc-lib/ -DDONT_WANT_WIN32_DLL_SUPPORT -Lc:/ghc/ghc-6.8.2/lib\base-3.0.1.0 -Lc:/ghc/ghc-6.8.2 -Lc:/ghc/ghc-6.8.2/gcc-lib -lHSbase-3.0.1.0 -lwsock32 -lmsvcrt -lkernel32 -luser32 -lshell32 -lHSrts -lm -lgmp -lwsock32 -u _base_GHCziBase_Izh_static_info -u _base_GHCziBase_Czh_static_info -u _base_GHCziFloat_Fzh_static_info -u _base_GHCziFloat_Dzh_static_info -u _base_GHCziPtr_Ptr_static_info -u _base_GHCziWord_Wzh_static_info -u _base_GHCziInt_I8zh_static_info -u _base_GHCziInt_I16zh_static_info -u _base_GHCziInt_I32zh_static_info -u _base_GHCziInt_I64zh_static_info -u _base_GHCziWord_W8zh_static_info -u _base_GHCziWord_W16zh_static_info -u _base_GHCziWord_W32zh_static_info -u _base_GHCziWord_W64zh_static_info -u _base_GHCziStable_StablePtr_static_info -u _base_GHCziBase_Izh_con_info -u _base_GHCziBase_Czh_con_info -u _base_GHCziFloat_Fzh_con_info -u _base_GHCziFloat_Dzh_con_info -u _base_GHCziPtr_Ptr_con_info -u _base_GHCziPtr_FunPtr_con_info -u _base_GHCziStable_StablePtr_con_info -u _base_GHCziBase_False_closure -u _base_GHCziBase_True_closure -u _base_GHCziPack_unpackCString_closure -u _base_GHCziIOBase_stackOverflow_closure -u _base_GHCziIOBase_heapOverflow_closure -u _base_GHCziIOBase_NonTermination_closure -u _base_GHCziIOBase_BlockedOnDeadMVar_closure -u _base_GHCziIOBase_BlockedIndefinitely_closure -u _base_GHCziIOBase_Deadlock_closure -u _base_GHCziIOBase_NestedAtomically_closure -u _base_GHCziWeak_runFinalizzerBatch_closure -u _base_GHCziConc_ensureIOManagerIsRunning_closure ... This particular example is a build on a windows system and makes use of the .o's directly and not the .a I create, but those are of no consequence as this is ultimately a linking issue, not a compilation issue. I don't know what these -u's are for, but I know that if I take them out, the linker fails. They do change from one system to another (this list fails with the linker on RHEL 5). But right now my solution for the C programmers is a make file with $haskell_undefine_flags = <that mess up there>, and I'd prefer something more elegant and less system dependent. I am willing to accept that there is no good way around it, but perhaps someone has dealt with this issue before. Any help? Thanks. Joe

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ANN: Takusen 0.8
by Alistair Bayley 05 Mar '08

05 Mar '08

Oleg and I are pleased to announce the release of Takusen 0.8. (Don Stewart did an interim 0.7 release for us a few weeks ago, and added us to Hackage. This release is a tidy-up of some loose ends, and some bug fixes. Hence, I've summarise the changes since the 0.6 release.) Changes since 0.6: - ODBC support. This still has a few gaps (and probably bugs and rough edges) but should be fairly usable. - support for reusable/persistent sessions, so you can hang onto the connection object between invocations of withSession (this was in release 0.6 but omitted from the release notes). - improvements to the Cabal Setup scripts, which should give better experiences for ghc-6.4, ghc-6.6, and ghc-6.8. The (eventual) 1.4 release of Cabal should be able to build our haddock docs, too. - improved UTF8 decoder (marshals directly from buffer). The release bundle: http://hackage.haskell.org/packages/archive/Takusen/0.8/Takusen-0.8.tar.gz The latest code: darcs get http://darcs.haskell.org/takusen Docs: http://darcs.haskell.org/takusen/doc/html/index.html A comprehensive description of API usage can be found in the documentation for module Database.Enumerator (look for the Usage section): http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html Future plans: - FreeTDS backend (Sybase and MS Sql Server) - support for Blobs and Clobs For those of you unfamiliar with Takusen, here is our HCAR blurb: Takusen is a library for accessing DBMS's. Like HSQL, we support arbitrary SQL statements (currently strings, extensible to anything that can be converted to a string). Takusen's `unique-selling-point' is safety and efficiency. We statically ensure all acquired database resources - such as cursors, connection and statement handles - are released, exactly once, at predictable times. Takusen can avoid loading the whole result set in memory, and so can handle queries returning millions of rows in constant space. Takusen also supports automatic marshalling and unmarshalling of results and query parameters. These benefits come from the design of query result processing around a left-fold enumerator. Currently we fully support ODBC, Oracle, Sqlite, and PostgreSQL.

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problem in using wash
by Vikrant 04 Mar '08

04 Mar '08

Hi, I was trying to use wash to learn it. I am using ubuntu and I have ghc6.6.1 installed on my system. I have also installed the package libghc6-wash-dev but in my code when i write "import WASH.CGI" it gives me following error firstCGI.hs:5:7: Could not find module `WASH.CGI': locations searched: WASH/CGI.hs WASH/CGI.lhs Failed, modules loaded: none. can somebody help me in this? Regards, Vikrant

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Haskell & Perl architecture question
by Marty Landman 04 Mar '08

04 Mar '08

I'm looking at a production system running Perl & Haskell in an Apache environment and trying to get a handle on the system architecture. Are there online resources anyone could recommend I start with? Thanks in advance, Marty -- Marty Landman, Face 2 Interface Inc. 845-679-9387 Drupal Development Blog: http://drupal.face2interface.com/ Free Database Search App: http://face2interface.com/Products/FormATable.shtml

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Markup bug in HaskellWiki
by Henning Thielemann 04 Mar '08

04 Mar '08

In the Wiki article http://haskell.org/haskellwiki/Comparison_chain there is the piece unzip">unzip which is improperly formatted.

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Annotating GHC assembler output?
by Justin Bailey 04 Mar '08

04 Mar '08

I'm interested in seeing what kind of assembler my functions turn into. Is there a means of annotating assembler output, similar to the {#- CORE -#} pragma? Is there a trickier way of doing it? Justin

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ID3 tagging
by adekoba 03 Mar '08

03 Mar '08

I was wondering if there are any haskell packages for tagging ID3 frames in mp3 files. Or perhaps if there were any plans for developing them...

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