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RE: [Haskell] multiple occurence of the same type variable in instancehead
by Simon Peyton-Jones 26 Oct '05

26 Oct '05

Quite right. I've fixed the documentation (in CVS). Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Wolfgang | Jeltsch | Sent: 17 October 2005 14:04 | To: Haskell ML | Subject: [Haskell] multiple occurence of the same type variable in instancehead | | Hello, | | the following is not Haskell 98: | | class C a | | instance C (a,a) | | Well, GHC allows this with the -fglasgow-exts flag. Surprisingly, I cannot | find a section in the GHC User's Guide which states that -fglasgow-exts can | be used to allow this kind of instance declarations. Well, in the section on | undecidable instances (7.4.4.3), one can read: | | Note that instance heads may contain repeated type variables. For example, | this is OK: | | instance Stateful (ST s) (MutVar s) where ... | | But one has to note that in this expample, the different occurences of s | aren't in the same type. Furthermore, multiple occurences of the same type | variable cannot result in undecidability (as far as I understand). The | above-mentioned statement talks about the things that are allowed *without* | -fallow-undecidable-instances, and premises that multiple occurences of a | type variable are okay. | | So am I missing something? | | Best wishes, | Wolfgang | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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logic problem
by michael＠schmong.org 26 Oct '05

26 Oct '05

Hi, My name is Michael. I'm new to Haskell. I'm working through The Craft of Functional Programming by Simon Thompson. I'm having problems with a few exercises from chapter 4. I will present one per post. This one is from 4.9 Given a function f of type Int -> Int give a recursive definition of a function of type Int -> Int which on input n returns the maximum values f 0, f 1, ... , f n I defined f as follows f 0 = 0 f 1 = 44 f 2 = 5 f 9 = 8 this works except when f n > n. In that case I get an "illegal instruction" error and hugs exits. I'm pretty sure this is a logic problem. Could someone point me in the right direction so I can think about this problem correctly. Here is my code maxOverf :: Int -> Int maxOverf m | f m > m = (f m) | otherwise = (maxOverf m-1) Any hints/help/flames welcome. Thanks Michael Litchard

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[mini-announce] Attribute grammars in happy
by Robert Dockins 26 Oct '05

26 Oct '05

Fellow Haskellers, I have hacked up Happy (http://www.haskell.org/happy/) to support attribute grammars. Attribute grammars are a way of annotating context-free grammars to support syntax directed translation and the checking of context-sensitive properties. What we have: * Support for attribute grammars using a slight modification to the Happy grammar syntax * Haskell 98! No language extensions required. * Support for all well-defined attribute grammars (conjecture, but I'm pretty sure) What we don't have: * Support for GLR parsing (mostly because I don't completely understand it) * Checks for proper attribute usage There is a darcs repo at based on the Happy 1.15 source distribution at: http://www.eecs.tufts.edu/~rdocki01/happy-ag/ And documentation for the extension can be found at: http://www.eecs.tufts.edu/~rdocki01/happy-ag-docs/sec-AttributeGrammar.html If there is sufficient interest I can clean up the code and write test cases and submit an official patch to Happy. Let me know what you think. Comments and suggestions are welcome. Thanks, Robert Dockins P.S. Discussion should probably move to haskell-cafe.

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REMINDER: Contributions to the HC&A Report (November 2005 edition)
by Andres Loeh 25 Oct '05

25 Oct '05

Dear Haskellers, the deadline for the November 2006 edition of the Haskell Communities and Activities Report is only a few days away -- but this is still enough time to make sure that the report contains a section on *your* project, on the interesting stuff that you've been doing; using or affecting Haskell in some way. Many projects that have been included in former reports have not yet updated their entries. Please have a look at http://haskell.org/communities/topics.html and at the May 2005 edition for reference. * Has your project been listed in previous Reports, but is not yet updated? Please write a short update! * Are you no longer working on a project that was included in the Report? Write up what you are working on instead, and tell me if someone else has picked up the project. * Is some project you have heard about not included in any previous Report? Please let me know ... There is still time to write a completely new entry, on a new compiler, tool, library, company, user group, idea, ... -- as long as there is a connection to the Haskell language, there is a place for it in the Report! Submissions are due by next Tuesday, that is Tuesday, 01 November 2005. Please mail your entries to <hcar at haskell dot org>, in plain text or pseudo-(La)TeX format. More information can be found in the original Call for Contributions at http://www.haskell.org/pipermail/haskell/2005-October/016575.html I look forward to receiving your contributions. Thanks a lot, Andres (current editor) -- Haskell Communities and Activities Report (http://haskell.org/communities) 11/2005 edition submission deadline: 01 November 2005 <hcar(a)haskell.org>

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getArgs, maxBound, float division: pure functions?
by oleg＠pobox.com 24 Oct '05

24 Oct '05

The question of getArgs as a pure function has already been debated on this list back in January: http://www.haskell.org/pipermail/haskell/2005-January/015184.html The topic seems worth revisiting as it expands to a bigger, and perhaps, a bleaker picture. To recap, there were two arguments for getArgs to remain with the IO [String] type: 1. getArgs is the function of the environment and does not have a clear denotation. The value of getArgs may change from one program run to another. 2. The existence of System.Environment.withArgs Regarding argument 1: the value of |maxBound :: Int| is also the function of the environment. Haskell98 Report says [p82, Section 6.4] The finite-precision integer type Int covers at least the range [ - 2^29 , 2^29 - 1 ]. As Int is an instance of the Bounded class, maxBound and minBound can be used to determine the exact Int range defined by an implementation. Thus, the value of |maxBound :: Int| may conceivably change from on program run (under runhugs32 on an AMD64 platform) to another (under runghc64 on the same platform). The Haskell98 Report, in section 6.4.6 defines other implementation-dependent functions: floatRadix, floatDigits, and floatRange. The GHC documentation [ghc6/libraries/base/Prelude.html#t%3ARealFloat] is particularly revealing: floatRadix :: a -> Integer a constant function, returning the radix of the representation (often 2) Some may find the phrase ``constant function that often [sic!] has the value 2'' to be incompatible with the notion of a pure function. Regarding argument 2: the existence of System.Environment.withArgs seems to doom getArgs to remain with the IO type. It cannot be a pure function. The simple extension of the argument points however to inconsistency with the floating-point facility. Haskell98 Report permits an implementation to use IEEE FP for Haskell Floats and Doubles. The Report specifically provides the class RealFrac to give a program access to some aspects of the IEEE FP system. IEEE FP computations are sensitive to the rounding mode, which is observable in pure code. The rounding mode can be changed. The following simple program shows > {-# OPTIONS -fglasgow-exts #-} > -- Tested on GHC 6.4 on on i686/Linux > > module FP where > import Foreign.C > > eps ::Float = 2^^(1-24) > > -- from /usr/include/bits/fenv.h > > type FP_RND_T = CInt -- fenv.h > > eFE_TONEAREST = 0 > eFE_DOWNWARD = 0x400 > eFE_UPWARD = 0x800 > eFE_TOWARDZERO = 0xc00 > > foreign import ccall "fenv.h fegetround" fegetround > :: IO FP_RND_T > > foreign import ccall "fenv.h fesetround" fesetround > :: FP_RND_T -> IO FP_RND_T > > test1 = do > let tf () = 1 + eps/2 > let tfe = tf () > putStrLn "Rounding mode and the result" > fegetround >>= print > print $ tf () > print $ tfe > > old <- fesetround eFE_UPWARD > putStrLn "Rounding mode and the result" > fegetround >>= print > print $ tf () > print $ tfe > > fesetround old > putStrLn "Rounding mode and the result" > fegetround >>= print > print $ tf () > print $ tfe > print "Done" that the supposedly pure computation "1 + eps/2" is not, in fact, referentially transparent. Should all floating-point computations be put in the IO monad? Granted, FP addition, among other operations, is not associative; so one may even wonder if FP can be done in any monad at all. OTH, when it comes to IO, the monad laws are usually stretched.

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Read Instances for Data.Map and Data.Set
by Georg Martius 22 Oct '05

22 Oct '05

Hi folks, I was really annoyed by the fact that for Data.Map and Data.Set are no Read instances declared, but Show instances are! I believe there should be some kind of unwritten rule that in the standart lib the Show and Read instances come pairwise and are fully compatible. Anyway since there was no response to S. Alexander Jacobson post [1], I decided to write these instances at least for GHC in the style of the other instances in GHC.Read. For the {a,b,...} syntax I have used a modified version of @list@ from GHC.Read Is there a chance of having this in the libs? Cheers, Georg [1] http://www.haskell.org//pipermail/haskell/2005-February/015380.html import qualified Data.Map as Map import qualified Data.Set as Set import Text.Read import qualified Text.Read.Lex as L import GHC.Read instance (Ord k, Read k, Read e) => Read (Map.Map k e) where readPrec = do elements <- set (readPair readPrec readPrec) return $ Map.fromList elements -- ^ @(readPrec p1 p2)@ parses a pair of things with the syntax @a:=b@ -- where @a@ is parsed by @p1@, -- and @b@ is parsed by @p2@ readPair :: ReadPrec a -> ReadPrec b -> ReadPrec (a,b) readPair reada readb = do a <- reset reada L.Symbol ":=" <- lexP b <- reset readb return (a,b) instance (Ord a, Read a) => Read (Set.Set a) where readPrec = do elements <- set (readPrec) return $ Set.fromList elements set :: ReadPrec a -> ReadPrec [a] -- ^ @(set p)@ parses a list of things parsed by @p@, -- using the curly-braces syntax. set readx = parens ( do L.Punc "{" <- lexP (setRest False +++ setNext) ) where setRest started = do L.Punc c <- lexP case c of "}" -> return [] "," | started -> setNext _ -> pfail setNext = do x <- reset readx xs <- setRest True return (x:xs) -- ---- Georg Martius, Tel: (+49 34297) 89434 ---- ------- http://www.flexman.homeip.net ---------

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TFP2006: call for papers
by Henrik Nilsson 21 Oct '05

21 Oct '05

Apologies for multiple copies. /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 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). Previous TFP symposia were held in Scotland in 2002 and 2003, as successors to the successful series of Scottish Functional Programming Workshops, 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 program 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 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. SUBMISSION Acceptance to the symposium will be based upon 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. 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 using the provided on the TFP 2006 site. Papers must not exceed 16 pages; papers in some categories may comprise considerably fewer pages. 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. Revised papers will be refereed after the symposium to the 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: The programme committee is currently being assembled. The current members of the TFP Advisory Committee are: o Sharon Curtis, Oxford Brookes University o Gaetan Hains, Université d'Orléans o John Hughes, Chalmers University o Kevin Hammond, University of St Andrews o Hans-Wolfgang Loidl, Ludwig-Maximilians-Universität München o Rita Loogen, Philipps-Universität Marburg o Greg Michaelson, Heriot-Watt University o John O'Donnell, University of Glasgow o Ricardo Pena, Universidad Complutense de Madrid, o Phil Trinder, Heriot-Watt University o Marko van Eekelen, University of Nijmegen 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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FM'06: CFP
by event＠mail.in.tu-clausthal.de 21 Oct '05

21 Oct '05

========================================================================= FM'06: 14TH INTERNATIONAL SYMPOSIUM ON FORMAL METHODS 21 - 27 August 2006 McMaster University, Hamilton, Ontario, Canada http://fm06.mcmaster.ca/ ANNOUNCEMENT AND CALL FOR SUBMISSIONS FM'06 is the fourteenth in a series of symposia organized by Formal Methods Europe, http://www.fmeurope.org, an independent association whose aim is to stimulate the use of, and research on, formal methods for software development. The symposia have been notably successful in bringing together innovators and practitioners in precise mathematical methods for software development, industrial users as well as researchers. Submissions are welcomed in the form of original papers on research and industrial experience, proposals for workshops and tutorials, entries for the exhibition of software tools and projects, and reports on ongoing doctoral work. FM'06 welcomes all aspects of formal methods research, both theoretical and practical. We are particularly interested in the experience of applying formal methods in practice. The broad topics of interest of this conference are: * Tools for formal methods: tool support and software engineering, environments for formal methods. * Theoretical foundations: specification and modelling, refining, static analysis, model-checking, verification, calculation, reusable domain theories. * Formal methods in practice: experience with introducing formal methods in industry, case studies. * Role of formal methods: formal methods in hardware and system design, method integration, development process. TECHNICAL PAPERS Full papers should be submitted via the web site. Papers will be evaluated by the Program Committee according to their originality, significance, soundness, quality of presentation and relevance with respect to the main issues of the symposium. Accepted papers will be published in the Symposium Proceedings, to appear in Springer's Lecture Notes in Computer Science series, http://www.springeronline.com/lncs . Submitted papers should have not been submitted elsewhere for publication, should be in Springer's format, (see Springer's web site), and should not exceed 16 pages including appendices. A prize for the best technical paper will be awarded at the symposium. INDUSTRIAL USAGE REPORTS One day will be dedicated to sharing the experience -- both positive and negative -- with using formal methods in industrial environments. The Industry Day is organized by ForTIA, the Formal Techniques Industry Association, http://www.fortia.org . This year's Industry Day investigates the use of formal methods in security and trust. Invited papers on organizational and technical issues will be presented. Inquiries should be directed to the Industry Day Chairs; see the web site for details. WORKSHOPS We welcome proposals for one-day or one-and-a-half-day workshops related to FM'06. In particular, but not exclusively, we encourage proposals for workshops on various application domains. Proposals should be directed to the Workshop Chair. TUTORIALS We are soliciting proposals for full-day or half-day tutorials. The tutorial contents can be selected from a wide range of topics that reflect the conference themes and provide clear utility to practitioners. Each proposal will be evaluated on importance, relevance, timeliness, audience appeal and past experience and qualification of the instructors. Proposals should be directed to the Tutorial Chair. POSTER AND TOOL EXHIBITION An exhibition of both research projects and commercial tools will accompany the technical symposium, with the opportunity of holding scheduled presentations of commercial tools. Proposals should be directed to the Poster and Tools Exhibition Chair. DOCTORAL SYMPOSIUM For the first time, FM'06 will feature a doctoral symposium. Students are invited to submit work in progress and to defend it in front of "friendly examiners". Participation for students who are accepted will be subsidized. Submissions should be directed to the Doctoral Symposium Chair. SUBMISSION DATES Technical Papers, Workshops, Tutorials: Friday, February 24, 2006 Posters and Tools, Doctoral Symposium: Friday, May 26, 2006 NOTIFICATION DATES Technical Papers: Friday, April 28, 2006 Workshops, Tutorials: Friday, March 10, 2006 Posters and Tools, Doctoral Symposium: Friday, June 9, 2006 ORGANIZATION General Chair: Emil Sekerinski (McMaster) Program Chairs: Jayadev Misra (U. Texas, Austin), Tobias Nipkow (TU Munich) Workshop Chair: Tom Maibaum (McMaster) Tutorial Chair: Jin Song Dong (NUS) Tools and Poster Exhibition Chair: Marsha Chechik (U. Toronto) Industry Day Chairs: Volkmar Lotz (SAP France), Asuman Suenbuel (SAP US) Doctoral Symposium Chair: Augusto Sampaio (U. Pernambuco) Sponsorship Chair: Juergen Dingel (Queens U.) PROGRAM COMMITTEE Jean-Raymond Abrial (ETH Zurich) Alex Aiken (Stanford U.) Keijiro Araki (Kyushu U.) Ralph Back (Abo Akademi) Gilles Barthe (INRIA) David Basin (ETH Zurich) Ed Brinksma (U. Twente) Michael Butler (U. Southampton) Rance Cleaveland (U. Stony Brook) Jorge Cuellar (Siemens) Werner Damm (U. Oldenburg) Frank de Boer (U. Utrecht) Javier Esparza (U. Stuttgart) Jose Fiadeiro (U. Leicester) Susanne Graf (VERIMAG) Ian Hayes (U. Queensland) Gerard Holzmann (JPL) Cliff Jones (U. Newcastle) Gary T. Leavens (Iowa State U.) Rustan Leino (Microsoft) Xavier Leroy (INRIA) Dominique Mery (LORIA) Carroll Morgan (UNSW) David Naumann (Stevens) E.-R. Olderog (U. Oldenburg) Paritosh Pandya (TIFR) Sriram Rajamani (Microsoft) John Rushby (SRI) Steve Schneider (U. Surrey) Vitaly Shmatikov (U. Texas, Austin) Bernhard Steffen (U. Dortmund) P.S. Thiagarajan (NUS) Axel van Lamsweerde (U. Louvain) Martin Wirsing (LMU Munich) Pierre Wolper (U. Liege) LOCAL ORGANIZATION Publicity: Wolfram Kahl, Alan Wassyng, Jeff Zucker Tools, Posters, Book Exhibition: Spencer Smith Social Events: Ridha Khedri Local Arrangements:: William Farmer, Mark Lawford Events Co-ordinator: Ryszard Janicki ------------------------------------------------------------------------ This e-mail was delivered to you by event(a)in.tu-clausthal.de, what is a moderated list runned by Computational Intelligence Group of Clausthal University of Technology, Germany. All event announcements sent through this list are also listed in our conference planner at http://cig.in.tu-clausthal.de/index.php?id=planner. In the case of any requests, questions, or comments, do not hesitate and contact event-owner(a)in.tu-clausthal.de ASAP. ****************************************************** * CIG does not take any responsibility for validity * * of content of messages sent through this list. * ****************************************************** Computational Intelligence Group Department of Computer Science Clausthal University of Technology Germany http://cig.in.tu-clausthal.de/

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CFP: CICLing-2006 -- Computational Linguistics, Springer LNCS, February, Mexico -- one week reminder
by Alexander Gelbukh 19 Oct '05

19 Oct '05

CICLing-2006 7th International Conference on Intelligent Text Processing and Computational Linguistics February 19-25, 2006 Mexico City, Mexico Endorsed by the ACL www.CICLing.org/2006 PUBLICATION: LNCS: Springer Lecture Notes in Computer Science. SUBMISSION DEADLINE: Abstract: October 17, late submissions can be considered; Main text: October 24, 2005 (for registered abstracts). MODALITIES: Full paper: 12 pages, short paper: 4 pages. KEYNOTE SPEAKERS: Nancy Ide, Rada Mihalcea, 2 more to be announced, see website. EXCURSIONS: Ancient pyramids, Monarch butterflies, great cave and colonial city, and more. All tentative. See photos on www.CICLing.org. AWARDS: Best paper, best presentation, best poster, best demo. +------------------------------------------------------- | Topics +------------------------------------------------------- Computational linguistics research: Comp. Linguistics theories and formalisms, Knowledge representation, Comp. morphology, syntax, semantics, Discourse models, Machine translation, text generation, Statistical methods, corpus linguistics, Lexical resources; Intelligent text processing and applications: Information retrieval, question answering, Information extraction, Text mining, Document categorization and clustering, Automatic summarization, Natural language interfaces, Spell-checking; and all related topics. +------------------------------------------------------- | Schedule (tentative) +------------------------------------------------------- Sunday, Wednesday, Saturday: full-day excursions; Monday, Tuesday, Thursday, Friday: talks; Monday: Welcome party & poster session. See website. ==================================================== See complete CFP and contact on www.CICLing.org/2006 ==================================================== We send you this CFP in good faith of its usefulness for you. If you do not want to receive any new messages, please let us know replying to this message. We deeply apologize for any inconvenience.

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RE: [Haskell] Excessive sharing and GHC
by Simon Peyton-Jones 19 Oct '05

19 Oct '05

| > >I was thinking it would be nice if one could put a pragma on CAFs that | > >basically made ghc treat them as WHNF so it would float them inward as | > >far as possible including inside lambdas. in particular, constant | > >strings that are created (cheaply) from efficient internal | > >representations should not be held onto in their inefficient form. I think the way to do this is to explain to GHC that unpackCString :: String# -> [Char] is a "cheap" function; that is, applications of it can safely be duplicated. There's no pragma to do this to an arbitrary at present, but it'd be a sensible sort of pragma to have. I wonder if it would make any difference in practice. Simon

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