- Haskell - Haskell.org

type class problem
by Dean Herington 01 Oct '03

01 Oct '03

Can someone explain why the following doesn't work? Is there some other way to achieve the same effect (declaring a set of instances for pair-like types in one go)? Thanks. Dean swan(108)% cat Test1.hs {-# OPTIONS -fglasgow-exts #-} class R r where rId :: r -> String class (R r) => RT r t where rtId :: r -> t -> String data (R r1, R r2) => RPair r1 r2 = RPair r1 r2 instance (R r1, R r2) => R (RPair r1 r2) where rId (RPair r1 r2) = "RPair " ++ rId r1 ++ " " ++ rId r2 class TPair t t1 t2 where prj :: t -> (t1,t2) inj :: (t1,t2) -> t instance (RT r1 t1, RT r2 t2, TPair t t1 t2) => RT (RPair r1 r2) t where rtId (RPair r1 r2) t = "RT (RPair " ++ rtId r1 t1 ++ " " ++ rtId r2 t2 ++ ")" where (t1,t2) = prj t main = return () swan(109)% ghci Test1.hs ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 5.04.3, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Compiling Main ( Test1.hs, interpreted ) Test1.hs:19: Could not deduce (RT r2 t21, RT r1 t11) from the context (RT (RPair r1 r2) t, RT r1 t1, RT r2 t2, TPair t t1 t2, R (RPair r1 r2)) Probable fix: Add (RT r2 t21, RT r1 t11) to the class or instance method `rtId' arising from use of `rtId' at Test1.hs:19 In the first argument of `(++)', namely `rtId r2 t2' In the second argument of `(++)', namely `(rtId r2 t2) ++ ")"' Test1.hs:20: Could not deduce (TPair t t11 t21) from the context (RT (RPair r1 r2) t, RT r1 t1, RT r2 t2, TPair t t1 t2, R (RPair r1 r2)) Probable fix: Add (TPair t t11 t21) to the class or instance method `rtId' arising from use of `prj' at Test1.hs:20 In a pattern binding: prj t Failed, modules loaded: none. Prelude>

3 2

Re: Interfaces Greencard // Postgres DB
by Gottfried F. Zojer 30 Sep '03

30 Sep '03

Thanks fro the reply Well the installment fails . He more infos : Thats the error : error: failed dependencies: haskell is needed by greencard-2.05-1 Thats in my /etc/profile.local : PATH=$PATH:/home/hugs98-Dec2001/bin/export PATH Thats when I type hugs in a bash : Hugs session for: /home/hugs98-Dec2001/share/hugs/lib/Prelude.hs Type :? for help Prelude> :version -- Hugs Version December 2001 Alastair Reid <alastair(a)reid-consulting-uk.ltd.uk> schrieb am 29.09.03 19:11:42: > > > > Maybe I have a OT question .All is running fine with Hugs98 but I have > > headache to work with Greencard . It will not run (binary and also source > > .rpm fails )on SUSE 8.2 Pro > > Can you give me a bit more information about what is going wrong? > Does the install fail? > Does the install succeed but the binary won't run? > Does the binary run but the generated code won't compile? > > Also, what error messages are produced or, if none, what does happen? > > -- > Alastair Reid >

1 0

Call for Papers: ICFP 2004
by Kathleen Fisher 29 Sep '03

29 Sep '03

Ninth Annual ACM SIGPLAN International Conference on Functional Programming Call for Papers ICFP 2004 September 20-22, 2004 Snowbird, Utah * Important Dates ----------------- Submission deadline 23:00 01 April, 2004 Apia, Samoan time (Thursday) Author review period 23:00 17 May to 23:00 19 May, 2004, Apia, Samoan time Author notification 26 May, 2004 Final paper due 07 July, 2004 Conference 20-22 September, 2004 * Scope ------- ICFP 2004 seeks original papers on the full spectrum of the art, science, and practice of functional programming. The conference invites submissions on all topics ranging from principles to practice, from foundations to features, and from abstraction to application. The scope covers all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages that support objects and concurrency. Topics of interest include, but are not limited to, the following: Foundations Formal semantics, lambda calculus, type theory, monads, continuations, control, state, effects. Design Algorithms and data structures, modules and type systems, concurrency and distribution, components and composition, relations to object-oriented and logic programming, multiparadigm programming. Implementation Abstract machines, compile-time and run-time optimization, just-in-time compilers, memory management. Interfaces to foreign functions, services, components and low-level machine resources. Transformation and analysis Abstract interpretation, partial evaluation, program transformation, theorem proving, specification and verification. Software development techniques for functional programming Design patterns, specification, verification and validation, debugging, test generation, tracing and profiling. Applications and domain-specific languages Systems programming, scientific and numerical computing, symbolic computing and artificial intelligence, systems programming, databases, graphical user interfaces, multimedia programming, application scripting, system administration, distributed-systems construction, web programming, XML and related languages. Practice and experience Functional programming in education and industry, ramifications on other paradigms and computing disciplines. Functional pearls Elegant, instructive examples of functional programming. Papers in the latter three categories need not necessarily report original research results; they may instead, for example, report practical experience that will be useful to others, re-usable programming idioms, or elegant new ways of approaching a problem. The key criterion for such a paper is that it makes a contribution from which other practitioners can benefit. It is not enough simply to describe a program! * Submission guidelines ----------------------- Due date & time: Submissions must be filed at the web site by 23:00 Thursday, 01 April, Apia, Samoa time. Some equivalents to this time are: * New York: 5:00 AM = 5h00 (02 April) * San Francisco: 2:00 AM = 2h00 (02 April) * Chicago: 4:00 AM = 4h00 (02 April) * Paris: Noon (02 April) * Hong Kong: 6:00 PM = 18h00 (02 April) * UTC: 10:00 AM (02 April) Submission URL: http://icfp.acm.org (Available after March 1, 2004). Authors should submit a 100-200 word abstract and a full paper by 23:00 Apia, Samoa Time on Thursday, 01 April, 2004. Submissions should be no more than 12 pages (including bibliography) in standard ACM conference format: two columns, nine-point font on a ten-point baseline, with pages 20pc (3.33in) wide and 54pc (9in) tall, with a column gutter of 2pc (0.33in). Detailed formatting guidelines are available at http://www.acm.org/sigs/pubs/proceed/template.html, along with formatting templates or style files for LaTeX, Word Perfect, and Word. You don't need to include categories, keywords, etc., though you are welcome to do so. Also, note that the ACM copyright notice is not required of submissions, only of accepted papers. Authors wishing to supply additional material to the reviewers beyond the 12-page limit can do so in clearly marked appendices, on the understanding that reviewers are not required to read the appendices. Submissions that do not meet these guidelines will not be considered. The submission deadline and length limitations are firm. Submissions will be carried out electronically via the Web, at the URL given above. Papers must be submitted in either PDF format or as PostScript documents that are interpretable by Ghostscript. They must be printable on US Letter sized paper. Individuals for which this requirement is a hardship should contact the program chair at least one week before the deadline. Submitted papers must adhere to SIGPLAN's republication policy. Each paper should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. Authors should strive to make the technical content of their papers understandable to a broad audience. Authors will be given a 48-hour period (23:00 17 May to 23:00 19 May 2004 Apia, Samoa time) to read and respond to the reviews for their papers before the PC meeting. Authors of submitted papers will receive more details from the submission site. Authors of accepted papers will be required to sign the ACM copyright form. Proceedings will be published by ACM Press. * Conference Chair ------------------ Chris Okasaki U.S. Military Academy, West Point * Program Chair --------------- Kathleen Fisher AT&T Labs Shannon Laboratory 189 Park Ave., E244 Florham Park, NJ, USA kfisher at research.att.com Phone: +1 973 360.8675 Fax: +1 973 360.8077 Program Committee ----------------- * Lennart Augustsson (Sandburst Inc.) * Hans-J. Boehm (HP Laboratories) * Koen Claessen (Chalmers University) * Adriana Compagnoni (Stevens Institute of Technology) * Matthias Felleisen (Northeastern) * Zhenjiang Hu (University of Tokyo) * Erik Meijer (Microsoft SQLServer/WebData) * Manuel Serrano (INRIA Sophia Antipolis) * Peter Sewell (University of Cambridge) * Jérôme Siméon (Bell Laboratories) * Christopher A. Stone (Harvey Mudd College) * Martin Sulzmann (National University of Singapore) * David Walker (Princeton University) * Elena Zucca (Università di Genova) This document can be obtained in the following formats: HTML http://www.cs.indiana.edu/icfp04/cfp.html PostScript http://www.cs.indiana.edu/icfp04/cfp.ps PDF http://www.cs.indiana.edu/icfp04/cfp.pdf Plain text http://www.cs.indiana.edu/icfp04/cfp.txt

1 0

Interfaces Greencard // Postgres DB
by Gottfried F. Zojer 29 Sep '03

29 Sep '03

Hello to all, I m new to Haskell but not to functional programming . Maybe I have a OT question .All is running fine with Hugs98 but I have headache to work with Greencard . It will not run (binary and also source .rpm fails )on SUSE 8.2 Pro Any hint is welcomed . Gottried F. Zojer P.s. Is somebody using Haskell in combination with PostgreSQL via C/or C++ interface.

3 2

RE: Syntax extensions: mdo and do...rec
by Simon Peyton-Jones 29 Sep '03

29 Sep '03

I agree with this. We'll move GHC to implement any consensus. My own opinion is that expr :: = ... | do { stmts } stmts :: = .. | rec { stmts } is the cleanest story. I guess that we should ensure that do rec { stmts } means what it looks like. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of | nilsson(a)cs.yale.edu | Sent: 16 September 2003 18:09 | To: haskell(a)haskell.org | Subject: Syntax extensions: mdo and do...rec | | Dear Haskellers, | | A questions. | | The do-notation has been extended to support recursive bindings by using | the "mdo" keyword. The do-notation has also been extended (through Ross | Patterson's preprocessor, and now also GHC) to support programming | with arrows. In that context, a different syntax, using the keyword "rec", | is used to enable recursive bindings. | | It seems somewhat confusing to have distinct syntax for what appears | to be very closely related purposes. Would it be possible have just a | single syntactic extension to enable recursive bindings in either context? | (Presumably the "rec" version is a bit more flexible in that it can be | applied to a subset of the bindings in a do-construct.) | | Best regards, | | /Henrik | | -- | Henrik Nilsson | Yale University | Department of Computer Science | nilsson(a)cs.yale.edu | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

5 9

Re: Syntax extensions: mdo and do...rec
by Amr A Sabry 29 Sep '03

29 Sep '03

> Another approach to value recursion was recently given by Sabry and Moggi > in their latest FICS paper: They have an mfix-like operator for > continuations there, but it doesn't satisfy left-shrinking either. The paper in question is available at: http://www.cs.indiana.edu/~sabry/papers/valuerecursion_extended.ps > (Their treatment of value recursion is rather different than ours as > well.) See Amr Sabry's papers for details. The typing of mfix given in our paper is: (m a -> m a) -> m a; by changing the (ret e) to e in rule M.2 you get exactly the same mfix of Erkok/Launchbury. The paper also shows why left-shrinking cannot hold in general and gives an example for the continuation monad. --Amr

1 0

GHC allow-overlapping-instances
by H X 29 Sep '03

29 Sep '03

Hi, Does anyone have ever used this option? I see no difference when I present this program to ghc with -fallow-overlapping-instances on/off: module Test where data T = T data F = F data OR a b = OR a b data AND a b = AND a b class C a b | a -> b instance C (OR T r) T instance C (OR r T) T instance C (AND F r) F instance C (AND r F) F -Kenny __________________________________________________ Do You Yahoo!? A free party for the most "shiok" photo! http://sg.yahoo.com/shiok

1 0

CFP: IEEE Int. Conference on Complex Computer Sys, ICECCS 2004, Florence
by ICECCS 2004 27 Sep '03

27 Sep '03

Sorry for any multiple reception of this message, Send an email with REMOVE on the subject Cheers, Pierfrancesco Bellini, Bernhard Steffen, Shawn Bohner _°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_°_° CALL FOR PAPERS IEEE International Conference on Engineering of Complex Computer Systems, IEEE ICECCS, Florence, Italy, 14-16 April, 2004 http://www.dsi.unifi.it/iceccs04 ICECCS-2004 Theme: Navigating Complexity in the e-Engineering Age As society increasingly depends on software, the size and complexity of software systems continues to grow making them more difficult to understand and evolve. Manifold dependencies between critical elements of software now drive software architectures and increasingly influence the system architecture Complexity of software systems has grown significantly, pervading several key application areas including Manufacturing, Communications, Transportation, Internet, Mobile, Healthcare, Aerospace, and Energy. These systems are frequently distributed over heterogeneous networks, recently involving Internet and Intranet technologies. Inundated by temporal constraints, boundless functionalities, complex algorithms, distributed and mobile architectures, security constraints, reliability, high performance, interoperability, and the like, these complexities are further weighing down development and evolution of today's software systems and ultimately the organizations they serve. To cope with complexity, software systems are modeled or specified using multi-paradigm approaches and require instruments and tools to visualize and understand. Whether traditional, formal models or more innovative approaches are employed; these solutions are at the frontier of the software engineering. The goal of this conference is to bring together industrial, academic and government experts, from a variety of user domain and software disciplines, to examine key complexity problems and effective solution techniques. Researchers, practitioners, tool developers and users, and technology transition experts are all welcome. The scope of the interest includes long-term research, near-term complex system requirements and promising tools, existing systems, and commercially available tools. Topic Areas: Papers are solicited in all areas related to complex computer-based systems, including the causes of complexity and means of avoiding, controlling, or coping with complexity. Topic areas includes, but are not limited to: * System and software architecture and system engineering * Tools, environments, and languages for complex systems * Formal methods and approaches to manage and control complex systems * Integration of heterogeneous technologies * Software and system development and control processes for complex systems * Human factors and collaborative aspects * Interoperability and standardization * Systems and software safety and security * Industrial automation, embedded and/or real time systems * Content production and distribution systems, mobile and multi-channel systems * Software complexity visualization * Virtual environments for managing complexity Research papers, case studies, lessons learned, status reports, and discussions of practical problems faced by industry and user domains are all welcome submissions. For review, submissions are divided into two categories: Technical Papers and Experience Reports. All submissions will be reviewed by program committee members on the basis of technical quality, relevance, significance, and clarity; and those accepted will be published in the conference proceedings. Technical papers should describe original research, and industrial experience should include practical projects or lessons learned emphasizing outcomes, insights gained, and lessons learned. ICECCS 2004 will also feature Panels and Special Sections. Proposals of 1 page length for their organization, should come with the list of involved people as well as their agreement of cooperation. SUBMISSION: Papers, panels and special sections should be submitted electronically via the Conference Service http://sttt.cs.uni-dortmund.de:80/iceccs04/servlet/Conference by November 1, 2003. Full submission details will be published on the conference web site. General Co-Chairs Paolo Nesi, Alessandro Fantechi Dep of Systems and Informatics University of Florence, Italy {nesi,fantechi}@dsi.unifi.it Program Co-Chairs Bernhard Steffen Dep. of Computer Science, University of Dortmund, Germany steffen(a)cs.uni-dortmund.de Pierfrancesco Bellini Dep of Systems and Informatics University of Florence, Italy pbellini(a)dsi.unifi.it Shawn Bohner Dep. of Computer Science, Virginia Tech, USA sbohner(a)vt.edu Local Arrangement Chair Davide Cerrai, Boehringer Ingelheim, Italy Sponsored by: IEEE Computer Society IEEE Technical Committee on Complexity in Computing In Cooperation with: University of Florence Boehringer Ingelheim - Italy Important Dates Paper Submission: 1 November 2003 Notification of acceptance: 5 January 2004 Camera ready submission: 20 January 2004 Conference: 14-16 April 2004 WWW pages http://www.dsi.unifi.it/iceccs04 Secretariat: Simonetta Ceglia ceglia@dsi.unifi.it+39-055-4796567

1 0

learning to love laziness
by nr＠eecs.harvard.edu 26 Sep '03

26 Sep '03

Consider the following Haskell function: > asPair x = (fst x, snd x) This function has type forall a b. (a, b) -> (a, b) and is almost equivalent to the identity function, except it can be used to make programs terminate that might otherwise fall into a black hole. My students are extremely mystified by such functions---and I can hardly blame them! Is there a good place to read about programming with lazy evaluation that will cover such functions and when to use them? Norman

6 5

GHC 6.2
by Simon Peyton-Jones 26 Sep '03

26 Sep '03

| > BTW, in GHC 6.2 with the -fglasgow-exts -farrows flags, you will be able | > to use either mdo or do...rec for monads and for arrows, as an experiment. | > (Maybe "rec" wasn't such a great keyword to take from the identifier | > space.) | | When can we expect 6.2? [Widening to GHC users.] Here's the GHC release situation. We've forked the tree for 6.2. Simon M is doing a bunch of house-cleaning on it (principally eliminating "casm", "ccall" and all their dirty cousins); there's still an open question of how much of the "bound threads" stuff goes into it; and we really have to fix the "errno bug", but there's some debate about exactly how. So the long and short of it is that if times were normal we'd release 6.2 in two or three weeks. But times are not entirely normal. Simon M is about to become a father (a second child, human this time, to add to GHC), and this event may distract him without warning. So far we have not been regarding 6.2 as ultra-urgent because we don't know of anyone who is really stuck with 6.0. Please let us know if you are in fact stuck. Simon

2 1