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ANN: HDBC 0.6.0
by John Goerzen 22 Dec '05

22 Dec '05

Hello, [ sorry, I accidentally posted an early draft of this on -cafe ] Version 0.6.0 of HDBC and the Sqlite3 bindings are now available. New features since Tuesday's 0.5.0 announcement include: * New type system for marshalling different Haskell types back and forth * New support for querying meta-information about the server * Much improved documentation * Fix for a race condition in the Sqlite3 binding * New fetchAllRows function that returns a lazy list of result rows (think hGetContents for database queries) I will shortly begin work on a PostgreSQL binding. Also, I plan to write a MissingH interface module. The main idea of that is to provide a SQL backend for the MissingH AnyDBM interface (which uses *dbm databases for persistent hashes). Combined with Sqlite, this provides a very interesting and easy to use persistent hash interface. Where to get stuff: API docs, quick link: http://darcs.complete.org/hdbc/doc/index.html HDBC general layer: darcs get --partial --tag=hdbc-0.6.0 http://darcs.complete.org/hdbc Sqlite3 driver: darcs get --partial --tag=hdbc-sqlite3-0.6.0 \ http://darcs.complete.org/hdbc-sqlite3 -- John

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A question about fundeps <-> GADT interaction
by Tomasz Zielonka 22 Dec '05

22 Dec '05

Hello! (This message is a literate Haskell module) > {-# OPTIONS -fglasgow-exts -fno-warn-missing-methods #-} > module Term where The papers on GADTs have an example showing how you can transform, traverse and evaluate ASTs (or terms) with more type safety. I've used such an approach in one of my applications and it works remarkably well. However, I would like to be able to "turn off" that type-safety in some parts of code, for example to separate parsing from typing. I thought I found a way to do this, because I was able to create Typed (with all consistency checking) and Untyped (without consistency checking) terms. Unfortunately I seem to be unable to write any useful function on such terms - GHC complains that there are type errors. I think this is because of the known problem with current GADT implementation in GHC, namely - bad GADT / type-classes interaction. I would be very happy to hear that it will be solved in GHC 6.6. I use an additional type parameter for Term that determines whether the Term is used as Typed or Untyped. Typed terms will have types (Term Typed Int), (Term Typed Bool), ..., but Untyped terms only one type: (Term Untyped ()) I use a multiparameter type-class with fundeps to describe a relation between the Typed/Untyped tag used, the types actually used in data constructors and the resulting "phantom" type. > class F f a b | f a -> b where > -- these methods are just for experiments in GHCi > a2b :: f -> a -> b > b2a :: f -> b -> a > data Typed = Typed > instance F Typed a a where > data Untyped = Untyped > instance F Untyped a () where > data Term f a where > Lit :: (F f Int int) => > Int -> Term f int > Succ :: (F f Int int) => > Term f int -> Term f int > IsZero :: (F f Int int, F f Bool bool) => > Term f int -> Term f bool > If :: (F f Bool bool, F f a a') => > Term f bool -> Term f a' -> Term f a' -> Term f a' Some examples: a typeable term > ex1 :: Term Untyped () > ex1 = > If (IsZero (Succ (Lit 0))) > (Lit 1) > (Lit 2) the same as ex1, but Typed > ex1' :: Term Typed Int > ex1' = > If (IsZero (Succ (Lit 0))) > (Lit 1) > (Lit 2) a term that has type bug, but will be accepted as Untyped > ex2 :: Term Untyped () > ex2 = > If (IsZero (Succ (Lit 0))) > (Lit 1) > (IsZero (Lit 2)) Here is the function that doesn't type check (you can comment it out to get the rest of code to compile). > -- A simple cast from typed terms to untyped terms > untype :: Term Typed a -> Term Untyped () > untype (Lit x) = Lit x > untype (IsZero t) = IsZero (untype t) > untype (Succ t) = Succ (untype t) > untype (If c t e) = If (untype c) (untype t) (untype e) The error given by GHC (for the commented "untype" function) is: T.hs:52:8: Couldn't match the rigid variable `a' against `Int' `a' is bound by the type signature for `untype' Expected type: Int Inferred type: a When using functional dependencies to combine F Typed a a, arising from the instance declaration at T.hs:13:0 F Typed Int a, arising from the pattern for `Lit' at T.hs:52:8-12 at T.hs:52:8-12 In the definition of `untype': untype (Lit x) = Lit x Failed, modules loaded: none. So it seems it can't infer that the 'a' in (F Typed Int a) is Int. At the same time... *T> :t a2b a2b :: (F f a b) => f -> a -> b *T> :t a2b Untyped a2b Untyped :: a -> () *T> :t a2b Typed a2b Typed :: b -> b -- see? it knows a and b are equal! *T> :t b2a Typed b2a Typed :: b -> b If there is another way to do this right now (conveniently, Oleg! ;-), I would be more than happy to hear about it. If this worked, it would be a cool trick and a nice example for GADT use. Let me know if it was proposed before. Best regards Tomasz -- I am searching for a programmer who is good at least in some of [Haskell, ML, C++, Linux, FreeBSD, math] for work in Warsaw, Poland

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Design guidance sought for Ranged Sets
by Paul Johnson 21 Dec '05

21 Dec '05

When I started the Ranged Sets library "infinite" sets (i.e. sets based on infinite lists of ranges) looked easy. The set primitives of union and intersection are simple merge algorithms, so they would work fine on infinite lists of ranges. Set difference is implemented as a combination of intersection and negation, and negation is just a simple rearrangement of the range end points, so that works too. However there are cases where this reasoning doesn't work. Suppose I have two ranged sets based on Range (BoundaryBelow n) (BoundaryBelow (n+1)) Set X contains these ranges for all even values of n>0 Set Y contains these ranges for all odd values of n>0 The union of these sets should be the single range Range (BoundaryBelow 1) BoundaryAboveAll In practice however the naive merge algorithm will never terminate because it has to merge an infinite number of ranges into the single range above. A similar problem occurs with intersection. The intersection of these sets should be empty, but again the merge algorithm will iterate forever looking for the first range in the set. As a workaround in 0.0.2 I've put a counter in. The intersection routine adds a null empty range after 10 empty iterations, and the union routine puts a break between touching ranges after 10 full iterations. Hence set membership tests are guaranteed to terminate in the presence of infinite lists. However the same cannot be said of all the functions. Set equality in particular has to evaluate the entire set in order to return True (although it does terminate at the first counter-example). The question of whether a particular expression is guaranteed to terminate is not trivial if it contains even one infinite list. So my question is this: are infinite sets worth bothering about? Should I continue to put in fixes to ensure termination in at least some cases? Or should I just declare that infinite lists of ranges are unsupported? Thanks, Paul.

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[ANNOUNCE] Ranged Sets 0.0.2
by Paul Johnson 21 Dec '05

21 Dec '05

Version 0.0.2 of the Ranged Sets library is now available at http://sourceforge.net/projects/ranged-sets/ The new release features infix operators, improved ability to handle infinite lists, and lots of QuickCheck properties for added confidence. Paul.

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ANNOUNCE: Lambda Shell 0.1
by Robert Dockins 20 Dec '05

20 Dec '05

Fellow Haskellers, I am pleased to announce the first alpha release of Lambda Shell, a shell environment for evaluating terms of the pure, untyped lambda calculus. The Lambda Shell -==================- == What is it? It is a feature-rich shell environment and command-line tool for evaluating terms of the pure, untyped lambda calculus. The Lambda Shell builds on the shell creation framework Shellac, and showcases most of Shellac's features. Features: -- evaluate lambda terms directly from the shell prompt using normal or applicative order. In normal order, one can evaluate to normal form, head normal form, or weak head normal form. -- define aliases for lambda terms using a top level, non-recursive 'let' construct. -- Show traces of term evaluation, or dump the trace to a file -- Count the number of reductions when evaluating terms -- test two lambda terms for confluence (that is; if two terms, when evaluated to normal form, are alpha equivalent) -- programs can be entered from the command line (using the -e option) or piped into stdin (using the -s option) An example session: ------------------------------- $ labmdaShell The Lambda Shell, version 0.1 Copyright 2005, Robert Dockins The Lambda Shell comes with ABSOLUTELY NO WARRANTY; for details type ':nowarranty'. This is free software, and you are welcome to redistribute it under certain conditions; type ':gpl' for details > (\x y. x) (\a. a) (\b. b) \a. a > :load prelude.lam > :show four four = succ three > four \f. \x. f (f (f (f x))) > mul two three \f. \x. f (f (f (f (f (f x))))) > let x = plus six two > x == eight equal > x == nine not equal > :hnf using reduction strategy: head normal form > :showCount show count on > let l = insertSort (cons two (cons three (cons one nil))) > index zero l one 463 reductions > index one l two 2135 reductions > index two l three 5720 reductions > :quit $ ----------------------------------------------- == Why do I care? Because you are a lambda calculus nut, and you just can't get enough. Or, the lambda shell could be a worthwhile teaching tool. The command line features (especially confluence testing) could lend themselves to automatic grading. Also, the lambda shell is a good example of how to write a shell using Shellac. == How is it licensed? The Lambda Shell is licensed under the GNU GPL version 2. See the LICENSE file for details. == How can I get it? darcs get http://www.eecs.tufts.edu/~rdocki01/lambda/ All feedback, suggestions, patches and bug reports are welcome, Robert Dockins

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A simple server (or how to do io).
by Pupeno 20 Dec '05

20 Dec '05

Hello, I have written a simple Daytime sever using network-alt[1] (I am sorry if this is off topic, is it ?) The server is: server port = do runStreamServer (nullStreamServer {handlerSS = sendDaytime, servSS = port}) sendDaytime = handlerWithHandle $ \hs sa -> do putStrLn (show sa) hSetBuffering hs LineBuffering time <- Time.getClockTime hPutStrLn hs (show time) hClose hs It works, but I have the following problems: When I run server "10013" from ghci, the prompt returns immediately and if I do a query to that port I don't get anything, until I go and press enter on ghci and the daytime is sent to the client. Like if the prompt was blocking all IO or something like that. The other problem is that I tried to make a program, so I made DaytimeServer.hs: main = do server "10013" I compile it and run it. It returns immediately and the server of course, is not running. I think what I am missing is that server, after running runStreamServer should block and be able to reply to all the queries (in the final version I'll also have runDgramServer as well) and be able to receive a signal, upon which it should close the socket and finish. How can do that ? Any help will be appreciated. Thank you. -- Pupeno <pupeno(a)pupeno.com> (http://pupeno.com) [1] http://www.cs.helsinki.fi/u/ekarttun/network-alt/ I am currently using the select mode.

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ANNOUNCE: Shellac 0.1
by Robert Dockins 20 Dec '05

20 Dec '05

Fellow Haskellers, I am pleased to announce the first alpha release of Shellac, a shell building library. == What is it? Shellac is a framework for building read-eval-print style shells. Shells are created by declaratively defining a set of shell commands and an evaluation function. Shellac builds on the Haskell readline bindings found in the standard libraries. These bindings reflect the low-level nature of readline and are not very Haskellish. This library attempts to allow users to write shells in at a high-level and still enjoy the advanced features readline provides, like command completion, command history and user-defineable keybindings. == Why do I care? Shellac takes care of much the muckety-muck of writing robust, feature-full shells so you don't have to. == How is it licensed? Shellac is avaliable under a BSD3 license. See the LICENSE file for details. Be aware, however, that the GNU readline library itself is licensed under the GPL. This library will only be useful to you if your project is GPL compatible. == How can I get it? darcs get http://www.eecs.tufts.edu/~rdocki01/shell/ Feedback, suggestions, patches and bug reports are all welcome, Robert Dockins

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New HWN editor sought
by John Goerzen 20 Dec '05

20 Dec '05

Hello everyone, Thanks for the support and encouragement for Haskell Weekly News. However, it's become apparent that HWN is something that I don't really have time for right now. So, I'd like to solicit anybody that would like to take over as HWN editor/maintainer. The job basically requires reading mailing lists and writing summaries of what you see. If nobody steps up, HWN will go on hiatus for an indefinite amount of time. -- John

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TFP2006: Second Call for Papers
by Henrik Nilsson 19 Dec '05

19 Dec '05

Dear Colleague, Please find enclosed the second call for papers for Trends in Functional Programming (TFP) 2006. My apologies for duplicate copies. Best regards, /Henrik -- Henrik Nilsson School of Computer Science and Information Technology The University of Nottingham nhn(a)cs.nott.ac.uk 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. TFP 2006 Seventh Symposium on Trends in Functional Programming Nottingham, UK, 19 - 21 April, 2006 http://www.cs.nott.ac.uk/~nhn/TFP2006 Co-located with Types 2006 and Spring School on Datatype-Generic Programming CALL FOR PAPERS The Symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results through acceptance by extended abstracts. A formal post-symposium refereeing process then selects the best papers presented at the symposium for publication in a high-profile volume. TFP 2006 is going to be held in Nottingham, UK, 19 - 21 April. Note that this is significantly earlier in the year than past TFPs that generally were held in August - September. TFP 2006 is co-located with Types 2006 (18 - 21 April). The TFP symposium is the successor to the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh, Scotland in 2003, in Munich, Germany in 2004, and in Tallinn, Estonia in 2005 (co-located with ICFP and GPCE). For further general information about TFP, see http://www.tifp.org/. SCOPE OF THE SYMPOSIUM The Symposium recognises that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five categories of paper. High-quality papers are solicited in any of these categories: Research Papers: leading-edge, previously unpublished research work Position Papers: on what new trends should or should not be Project Papers: descriptions of recently started new projects Evaluation Papers: what lessons can be drawn from a finished project Overview Papers: summarising work with respect to a trendy subject Papers must be original, and not submitted for simultaneous publication in any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Also applications of functional programming techniques to other languages may be considered. Papers on the following subject areas are particularly welcome: o dependently typed functional programming o validation and verification of functional programs o debugging for functional languages o functional programming and security o functional programming and mobility o functional programming and formally motivated computing o functional languages for telecommunications applications o functional languages for embedded systems o functional programming applied to global computing o functional GRIDs o functional languages for reasoning about imperative/object- oriented programs o interoperability with imperative programming languages o any new emerging trend in the functional programming area If you are in doubt on whether your paper is within the scope of TFP, please contact the TFP 2006 programme chair, Henrik Nilsson, nhn(a)cs.nott.ac.uk. BEST STUDENT PAPER AWARD TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. To acknowledge this, a prize for the best student paper is awarded each year. CO-LOCATION WITH TYPES 2006 AND DATATYPE-GENERIC PROGRAMMING 2006 TFP 2006 is co-located with Types 2006 (to be held 18 - 21 April). To take advantage of the synergies offered by these two complementary events, we will invite a number of joint keynote speakers, hold joint sessions on topics of mutual interest, such as dependently typed functional programming, and run common social events. The schedule will be arranged so that participants may freely move between parallel sessions of the two events. See http://www.cs.nott.ac.uk/types06/ for further details. TFP 2006 and Types 2006 are immediately followed by the Spring School on Datatype-Generic Programming 2006 (24 - 27 April), which should be of direct interest to many of the TFP and Types Participants. See http://www.cs.nott.ac.uk/ssdgp2006/ for further details. SUBMISSION AND LOCAL PROCEEDINGS Acceptance to the symposium is by extended abstracts of between 6 and 10 pages. Accepted abstracts are to be completed to full papers before the symposium for publication in the local symposium proceedings and on-line. Important dates: Deadline for abstract submission: 17 February, 2006 Notification of acceptance: 27 February, 2006 Registration deadline: 17 March, 2006 Camera-ready copy of full paper: 24 March, 2006 The submission must clearly indicate to which category it belongs: research, position, project, evaluation or overview paper. It should also indicate whether the main author or authors are research students. Abstracts and full papers must be written in English. Papers for the symposium proceedings must adhere to the formatting instructions provided on the TFP 2006 site. Papers must not exceed 16 pages; papers in some categories may comprise considerably fewer pages. The papers of the local proceedings will also be made available on-line under the following conditions, with which all authors are asked to agree: The documents distributed by this server have been provided by the contributing authors as a means to ensure timely dissemination of scholarly and technical work on a noncommercial basis. Copyright and all rights therein are maintained by the authors or by other copyright holders, notwithstanding that they have offered their works here electronically. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each author's copyright. These works may not be reposted without the explicit permission of the copyright holder. See the TFP 2006 website for further instructions to authors and details on how to submit. POST SYMPOSIUM REFEREEING AND PUBLICATION In addition to the local symposium proceedings, we intend to continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming (see http://www.intellectbooks.co.uk/series.php?series=1) All TFP authors will be invited to submit revised papers after the symposium. These will will be refereed to normal conference standards, and a subset of the best papers over all categories will be selected for publication. Papers will be judged on their contribution to the research area, with appropriate criteria applied to each category of paper. Papers submitted for publication by Intellect must follow formatting and any other instructions provided by the Programme Chair. For TFP 2005, in order to enhance the quality of student submissions, a process where student papers were given extra feedback was tried out. A similar process might be put in place for this TFP, contingent on the outcome of that trial. ORGANISATION Symposium Chair: Marko van Eekelen, Radboud University Nijmegen, NL Programme Chair: Henrik Nilsson, University of Nottingham, UK Treasurer: Greg Michaelson, Heriot-Watt University, UK Local Arrangements: Joel Wright, University of Nottingham, UK PROGRAMME COMMITTEE: o Kenichi Asai, Ochanomizu University o Gilles Barthes, INRIA, Sophia Antipolis o Olaf Chitil, University of Kent at Canterbury o Catherine Dubois, IIE, Evry o Marko van Eekelen, Radboud Universiteit Nijmegen o Jeremy Gibbons, Oxford University o Kevin Hammond, University of St Andrews o Zoltán Horváth, Eötvös Loránd University o Frank Huch, Christian-Albrechts-University of Kiel o Johan Jeuring, Universiteit Utrecht o Greg Michaelson, Heriot-Watt University o Henrik Nilsson, University of Nottingham o Ricardo Peña, Universidad Complutense de Madrid o Morten Rhiger, Roskilde University o Colin Runciman, University of York o Carsten Schürmann, IT University of Copenhagen o Zhong Shao, Yale University o Phil Trinder, Heriot-Watt University SPONSORS We are actively looking for additional TFP sponsors, who may help to subsidise attendance by research students, for example. If you or your organisation might be willing to sponsor TFP, or if you know someone who might be willing to do so, please do not hesitate to contact the Symposium chair: Marko van Eekelen. Your students will be grateful!

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CFP: International Workshop on Hybrid Logic 2005 (HyLo 2006)
by Carlos Areces 19 Dec '05

19 Dec '05

******************************************************************* FIRST CALL FOR PAPERS International Workshop on Hybrid Logic 2006 (HyLo 2006) Affiliated with LICS 2006 August 11, 2006, Seattle, USA ******************************************************************* AIMS AND SCOPE: Hybrid logic is a branch of modal logic in which it is possible to directly refer to worlds/times/states or whatever the elements of the (Kripke) model are meant to represent. Although they date back to the late 1960s, and have been sporadically investigated ever since, it is only in the 1990s that work on them really got into its stride. It is easy to justify interest in hybrid logic on applied grounds, because of the usefulness of the additional expressive power. For example, when reasoning about time one often wants to build up a series of assertions about what happens at a particular instant,and standard modal formalisms do not allow this. What is less obvious is that the route hybrid logic takes to overcome this problem (the basic mechanism being to add nominals --- atomic symbols true at a unique point --- together with extra modalities to exploit them) often actually improves the behavior of the underlying modal formalism. For example, it becomes far simpler to formulate modal tableau, resolution, and natural deduction in hybrid logic, and completeness and interpolation results can be proved of a generality that is not available in orthodox modal logic. Hybrid logic is now a mature field, therefore a theme of special interest at this HyLo workshop will be the combination of hybrid logic with other logics, the basic methodological question being "what is the best way of hybridizing a given logic?" However, submissions in all areas of hybrid logic are welcome. The workshop HyLo 2006 is likely to be relevant to a wide range of people, including those interested in description logic, feature logic, applied modal logics, temporal logic, and labelled deduction. The workshop continues a series of previous workshops on hybrid logic, for example the LICS-affiliated HyLo 2002 (http://floc02.diku.dk/HYLO) which was held as part of FLoC 2002, Copenhagen, Denmark. If you are unsure whether your work is of relevance to the workshop, please do not hesitate to contact the workshop organizers for more information. Contact details are given below. For more general background on hybrid logic, and many of the key papers, see the Hybrid Logics homepage (http://hylo.loria.fr/) PROGRAM COMMITTEE: Carlos Areces (INRIA Lorraine, France) Patrick Blackburn (INRIA Lorraine, France) Thomas Bolander (Technical University of Denmark) Torben Braüner (Roskilde University, Denmark) --- Chair Valeria de Paiva (PARC, USA) Melvin Fitting (Lehman College, New York, USA) Balder ten Cate (University of Amsterdam, The Netherlands) Jørgen Villadsen (Roskilde University, Denmark) SUBMISSIONS: We invite the contribution of papers reporting new work from researchers interested in hybrid logic. Details about the submission procedure will be announced in the second call for papers (note that the dates below are tentative). The workshop proceedings have been accepted for publication in ENTCS (http://www.elsevier.com/locate/entcs/) A preliminary version of the proceedings will also be distributed at the workshop. One author for each accepted paper must attend the workshop in order to present the paper. IMPORTANT DATES (TENTATIVE): Deadline for submissions: May 26, 2006 Notification of acceptance: June 23, 2006 Deadline for final versions: July 21, 2006 CONTACT DETAILS: See the workshop homepage (http://hylomol.ruc.dk/HyLo2006) for further information. Please send all correspondence regarding the workshop to the organizers: Patrick Blackburn http://www.loria.fr/~blackbur/ Thomas Bolander http://www.imm.dtu.dk/~tb/ Torben Braüner --- Chair http://www.ruc.dk/~torben/ Valeria de Paiva http://www.cs.bham.ac.uk/~vdp/ Jørgen Villadsen http://www.ruc.dk/~jv/

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