October 2000 - Haskell

tuple component functions
by trb＠eastpac.com.au 03 Jan '03

03 Jan '03

S.D.Mechveliani writes: > As Haskell has the standard functions fst, snd to decompose (a,b), > maybe, it worths to provide also > tuple31, tuple31, tuple31, > ... > tuple51, tuple52, tuple53, tuple54, tuple55 > > for the tuples of n = 3,4,5 ? I've found some of these useful, except I named them differently: > fst3 :: (a,b,c) -> a > fst3 (x,_,_) = x > snd3 :: (a,b,c) -> b > snd3 (_,x,_) = x > thd3 :: (a,b,c) -> c > thd3 (_,_,x) = x .... never got around to quadruples etc. I also defined (some of these may be untested): > tripl :: a -> (a,a,a) > tripl x = (x,x,x) > curry3 :: ((a, b, c) -> d) -> a -> b -> c -> d > curry3 f x y z = f (x, y, z) > uncurry3 :: (a -> b -> c -> d) -> ((a, b, c) -> d) > uncurry3 f t = f (fst3 t) (snd3 t) (thd3 t) > applyTriple :: (a -> b, a -> c, a -> d) -> a -> (b,c,d) > applyTriple (f,g,h) x = (f x, g x, h x) > cross3 :: (a -> b, c -> d, e -> f) -> (a,c,e) -> (b,d,f) > cross3 (f,g,h) (x,y,z) = (f x, g y, h z) > mapTriple :: (a -> b) -> (a, a, a) -> (b, b, b) > mapTriple = cross3 . tripl > applyFst3 :: (a -> b) -> (a, c, d) -> (b, c, d) > applyFst3 f = applyTriple (f . fst3, snd3, thd3) > applySnd3 :: (a -> b) -> (c, a, d) -> (c, b, d) > applySnd3 f = applyTriple (fst3, f . snd3, thd3) > applyThd3 :: (a -> b) -> (c, d, a) -> (c, d, b) > applyThd3 f = applyTriple (fst3, snd3, f . thd3) > applyArgs3 :: (a -> b) -> (c -> d) -> (e -> f) -> (b -> d -> f -> g) -> (a -> c -> e -> g) > applyArgs3 af1 af2 af3 f = \x y z -> f (af1 x) (af2 y) (af3 z) > rotl :: (a -> b -> c -> d) -> (b -> c -> a -> d) > rotl f y z x = f x y z > rotr :: (a -> b -> c -> d) -> (c -> a -> b -> d) > rotr f z x y = f x y z > rotl4 :: (a -> b -> c -> d -> e) -> (b -> c -> d -> a -> e) > rotl4 f y z t x = f x y z t > rotr4 :: (a -> b -> c -> d -> e) -> (d -> a -> b -> c -> e) > rotr4 f t x y z = f x y z t Some more combinators (only for pairs so far): > twin :: a -> (a,a) > twin x = (x,x) > swap :: (a,b) -> (b,a) > swap (x,y) = (y,x) -- apply a pair of functions to one argument > applyPair :: (a -> b, a -> c) -> a -> (b, c) > applyPair (f, g) x = (f x, g x) -- apply a pair of functions to a pair > cross :: (a -> b, c -> d) -> (a, c) -> (b, d) > cross (f, g) = applyPair (f . fst, g . snd) -- compose a pair of functions onto one function > dotPair :: (a -> b, a -> c) -> (d -> a) -> (d -> b, d -> c) > dotPair (f, g) h = (f . h, g . h) -- compose a pair of functions onto a pair of functions > dotCross :: (a -> b, c -> d) -> (e -> a, f -> c) -> (e -> b, f -> d) > dotCross (f, g) (h, i) = (f . h, g . i) > mapPair :: (a -> b) -> (a, a) -> (b, b) > mapPair = cross . twin > applyFst :: (a -> b) -> (a, c) -> (b, c) > applyFst f = applyPair (f . fst, snd) > applySnd :: (a -> b) -> (c, a) -> (c, b) > applySnd f = applyPair (fst, f . snd) > applyArgs :: (a -> b) -> (c -> d) -> (b -> d -> e) -> (a -> c -> e) > applyArgs af1 af2 f = \x y -> f (af1 x) (af2 y) > betweenFst :: (a -> b -> c) -> (a, d) -> (b, e) -> c > betweenFst = applyArgs fst fst > betweenSnd :: (a -> b -> c) -> (d, a) -> (e, b) -> c > betweenSnd = applyArgs snd snd I find these combinators useful, and probably other people have their own versions - it would be nice to get them standardised, so we all speak the same language. By standardised, I mean a prominent version that will be adopted by users, not necessarily a committee process. Tim

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ICFP programming contest
by trb＠eastpac.com.au 03 Jan '03

03 Jan '03

Michael Hobbs writes: > Just took a look at the results for the ICFP contest. Am I correct in > assuming that "LA" stands for Lennart Augustsson and that "Si^3" stands > for Simon Marlow, Simon Peyton-Jones, Sigbjorn Finne? Is there a URL for the results ? Tim

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Disjoint type classes
by Jose Emilio Labra Gayo 05 Mar '01

05 Mar '01

I have a large program where I would like to include disjoint type classes into a new type class. My problem can be reduced to the following example (taken from [1]): > class Num a => Dividable a > where dividedBy :: a -> a -> a > instance Fractional a => Dividable a where > dividedBy = (/) > instance Integral a => Dividable a where > dividedBy = div Which doesn't work because Haskell doesn't detect that "Integral" and "Fractional" are disjoint. Is there a way to implement these type classes with current Haskell implementations? [1] K. Glynn, M. Sulzmann, P.J. Stuckey Type Classes and Constraint Handling Rules http://www.cs.mu.oz.au/tr_submit/test/cover_db/mu_TR_2000_7.html Best regards, Jose Labra

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Re: Passing an environment around
by José Romildo Malaquias 08 Nov '00

08 Nov '00

On Fri, Oct 27, 2000 at 09:07:24AM -0700, Jeffrey R. Lewis wrote: > José Romildo Malaquias wrote: > > > On Thu, Oct 19, 2000 at 09:08:16AM -0700, Conal Elliott wrote: > > > Indeed Fran behaviors are like your alternative #1 (function passing), and > > > hence sharing loss is a concern. Simon PJ is right that I have a paper > > > discussing this issue and some others. See "Functional Implementations of > > > Continuous Modeled Animation" on my pubs page > > > (http://research.microsoft.com/~conal/papers) > > > > > > About alternative #2 (implicit arguments), would it help? Does it eliminate > > > the non-memoized redundant function applications, or just hide them? For > > > Fran, Erik Meijer suggested implicit functions to me a couple of years ago. > > > I hadn't thought of it, and it did indeed seem to be attractive at first as > > > a way to eliminate the need for overloading in Fran. However, the (Time -> > > > a) representation of Fran behaviors is not really viable, so I wouldn't > > > merely want to hide that representation behind implicit arguments. > > > > It seems that implicit parameters does not eliminate redundant function > > applications, as Conal Elliott has commented. Reading the paper > > > > Implicit Parameters: Dynamic Scoping with Static Types > > Jefrrey Lewis, Mark Shields, Erik Meijer, John Launchbury > > http://www.cse.ogi.edu/~jlewis/ > > > > (especially section 5.1) I got this impression. I would like to hear > > from others as well, as I had some difficulties with the paper. > > I am sorry you had difficulties! The difficulties I had is basicaly due to my lack of solid knowledge on type theory and semantic formalisms. Not that the paper was badly written. > Yes, as implemented using the dictionary > translation, implicit parameterization can lead to loss of sharing, exactly in > the same way that overloading (and HOF in general) can lead to loss of sharing. > > However, I can imagine that a compiler might chose to implement implicit > parameters more like dynamic variables in lisp. Each implicit param essentially > becomes a global variable, implemented as a stack of values - the top of the > stack is the value currently in scope. This would avoid the sharing problem > nicely. > > --Jeff I suppose your implementation of implicit parameterization in GHC and Hugs uses the dictionary translation, right? Would an alternative implementation based on a stack of values be viable and even done? Does it have serious drawbacks when compared with the dictionary translation technique? Thanks. Romildo -- Prof. José Romildo Malaquias <romildo(a)iceb.ufop.br> Departamento de Computação Universidade Federal de Ouro Preto Brasil

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<no subject>
by S Dublin 29 Oct '00

29 Oct '00

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MBR'01 Conference
by Lorenzo Magnani 29 Oct '00

29 Oct '00

Please accept our apologies if you receive multiple copies of this call If you want to receive updated information please send your complete address Last updated October 29, 2000 ********************************************************************** MODEL-BASED REASONING: SCIENTIFIC DISCOVERY, TECHNOLOGICAL INNOVATION, VALUES (MBR'01), Pavia, Italy, May 17-19, 2001. ********************************************************************** Up-to date information on the conference will be found at http://philos.unipv.it/courses/progra1.html or http://www.unipv.it/webphilos_lab/courses/progra1.html ********************************************************************** GENERAL INFORMATION >From Thursday 17 to Saturday 19 May 2001 (three days) the International Conference "MODEL-BASED REASONING. SCIENTIFIC DISCOVERY, TECNOLOGICAL INNOVATION, VALUES" will be held at the University of Pavia (near Milan, Italy). PROGRAM The conference will deal with the logical, epistemological, and cognitive aspects of modeling practices employed in scientific discovery and technological innovation, including computational models of such practices. Abduction is widely recognized as a significant reasoning process in discovery whose features are in need of explication. We will solicit papers that examine various forms of model-based reasoning, such as analogical and visual modeling, from philosophical, historical, sociological, psychological, or computational perspectives. We also plan to address the problem of model-based reasoning in ethics reasoning, especially pertaining to science and technology. RELEVANT RESEARCH AREAS We shall call for papers that cover topics from the following list: - abduction - analogical reasoning - causal and counterfactual reasoning in model construction - computational models of model-based reasoning and scientific reasoning - conceptual combination and theory formation - hypothetical and explanatory reasoning - logical analyses that may contribute to our understanding of the issues in model-based reasoning - model-based reasoning in ethics - models and manipulative reasoning - models and technological innovation - thought experimenting - visual, spatial, imagistic modeling, reasoning, and simulation SUBMISSIONS OF PAPERS All submitted papers will be carefully refereed. The precise format of the conference will be fixed after we have an idea of the number of accepted papers. We are thinking in terms of presentations of 40 and 20 minutes. The funding is Italian and US, but we are also looking elsewhere for further financing (and would appreciate any suggestions). A selected subset will be invited for inclusion (subject to refereeing) in a book which will constitute an advanced handbook for scientists and researchers. The book will be published by an international publishing house. Moreover another selected subset will be invited for inclusion (subject to refereeing) in special issues of suitable international Journals. FORMAT Authors must submit three printed copies and an electronic version - formatted in Microsoft Word, RTF, PDF, or Postcript format - of an extended abstract (about 1000 words) not later than November 30, 2000. Please send electronically the extended abstract to the program chair at the address lmagnani(a)cc.gatech.edu in case of problem with the above address please use lorenzo(a)philos.unipv.it or lmagnaniusa(a)netscape.net REGISTRATION AND FURTHER INFORMATION Registration Fees: Before 15 March 2001: Normal: ITL. 300.000 = appr. US$ 155 (EUR 154.93) (to participate in all the activities of the Conference) Students: Free After 15 March 2001: Normal: ITL. 350.000 = appr. US$ 175 (EUR 180.75) (to participate in all the activities of the Conference) Students: Free METHOD OF PAYMENT AND REGISTRATION DEADLINE: Bank (Swift) Transfer to BANCA REGIONALE EUROPEA S.p.A BRANCH PAVIA - Sede SWIFT BREUITM2 301 Bank Code 06906.11301 Acc. n. 520 Dipartimento di Filosofia indicating CONVEGNO INTERNAZIONALE MBR'01 PLEASE REGISTER by email, fax or air mail (before March 15, 2001) by sending PROGRAM CHAIR first and last name, function, institution, full address, phone, fax and email. For information about paper submission and the program that is not available on the web site, please contact the program chair. IMPORTANT DATES Registration deadline............................15 March 2001 Submission deadline..............................30 Nov 2000 Notification of acceptance.....................28 Feb 2001 Final papers (from those selected for publication) due........30 June 2001 Conference....................................17-19 May 2001 PROGRAM CHAIR Lorenzo MAGNANI School of Public Policy and College of Computing Program in Philosophy, Science, & Technology Georgia Institute of Technology, 685 Cherry Street Atlanta, GA, 30332 - 0345, USA Office: 404-894-0950 & 404-385-0884, Home: 404-875-3566 Fax: 404-385-0504 & 404-894-2970 Email: lorenzo.magnani(a)cc.gatech.edu Address in Italy: Department of Philosophy and Computational Philosophy Laboratory University of Pavia, Piazza Botta 6, 27100 Pavia, Italy Office: +39-0382-506283, Home: +39-0383-371067 Fax: +39-0382-23215 Email: lorenzo(a)philos.unipv.it PROGRAM CO-CHAIR Nancy J. NERSESSIAN (Program Co-Chair) Program in Cognitive Science School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, USA Email: nancyn(a)cc.gatech.edu PROGRAM CO-CHAIR Kenneth J. KNOESPEL (Program Co-Chair) School of History, Technology, and Society, and Program in Cognitive Science Georgia Institute of Technology, Atlanta, USA Email: kenneth.knoespel(a)hts.gatech.edu PROGRAM COMMITTEE - Ann Bostrom, School of Public Policy, Georgia Institute of Technology, Atlanta, GA, USA - Elena Gagliasso, Department of Philosophical and Epistemological Studies, University of Rome La Sapienza, Rome, ITALY - Dedre Gentner, Psychology Department, Northwestern University, Evanston, IL 60208, USA - Ronald N. Giere, Department of Philosophy, University of Minnesota, MN, USA - Mark L. Johnson, Department of Philosophy, 1295 University of Oregon, Eugene, OR, USA - Kenneth Knoespel, School of History, Technology, and Society, Georgia Institute of Technology, Atlanta, GA, USA - Lorenzo Magnani, Department of Philosophy, University of Pavia, Pavia, ITALY and School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, GA, USA - Pat Langley, Adaptive Systems Group, DaimlerChrysler Research & Technology Center, Palo Alto, CA, USA - Nancy J. Nersessian, School of Public Policy and College of Computing, Georgia Institute of Technology, Atlanta, GA, USA - Brian Norton, School of Public Policy, Georgia Institute of Technology, Atlanta, GA, USA - Claudio Pizzi, Department of Philosophy and Social Sciences, University of Siena, Siena, ITALY - Mario Stefanelli, Department of Computer Science, University of Pavia, Pavia, ITALY - Paul Thagard, Department of Philosophy, University of Waterloo, Waterloo, CANADA - Ryan D. Tweney, Bowling Green State University, Bowling Green, OH, USA - Stella Vosniadou, Department of Philosophy and History of Science, Brain and Cognitive Science Division, National and Capodistrian University of Athens, Athens, GREECE. LOCAL ORGANIZING COMMITTEE Riccardo Dossena (riki.dox@libero), Elena Gandini (elegand(a)yahoo.com) Rosella Gennari (gennari(a)hum.uva.nl) Lorenzo Magnani (lmagnani(a)cc.gatech.edu) Massimo Manganaro (triskel(a)worldonline.it) Stefania Pernice (stepernice(a)libero.it) Matteo Piazza (pimat(a)yahoo.com) Giulio Poletti (philosophia(a)libero.it) Stefano Rini (s.rini(a)philos.unipv.it) Andrea Venturi (aventuri@philos.unipv.,it) (Department of Philosophy, University of Pavia, Pavia, Italy), Mario Stefanelli (mstefa(a)ipvstefa.unipv.it) (Department of Computer Science, University of Pavia, Pavia, Italy). IMPORTANT ADDRESSES LORENZO MAGNANI (Conference Chair) School of Public Policy and College of Computing Program in Philosophy, Science, & Technology Georgia Institute of Technology, 685 Cherry Street Atlanta, GA, 30332 - 0345, USA Office: 404-894-9050 & 404-385-0884, Home: 404-875-3566 Fax: 404-385-0504 & 404-894-2970 Email: lorenzo.magnani(a)cc.gatech.edu Address in Italy: Department of Philosophy and Computational Philosophy Laboratory University of Pavia, Piazza Botta 6, 27100 Pavia, Italy Office: +39-0382-506283, Home: +39-0383-371067 Fax: +39-0382-23215 Email: lorenzo(a)philos.unipv.it CONFERENCE SITE: Collegio Ghislieri, Piazza Ghislieri, 27100 PAVIA, Italy, phone +39 0382 22044. The Conference is sponsored by UNIVERSITY OF PAVIA, ITALY GEORGIA INSTITUTE OF TECHNOLOGY, ATLANTA, GA, USA UNIVERSITY OF SIENA, ITALY UNIVERSITY OF ROME "LA SAPIENZA", ITALY, MURST (Ministero dell'Università e della Ricerca Scientifica e Tecnologica), ITALY, CARIPLO (CASSA DI RISPARMIO DELLE PROVINCIE LOMBARDE, MILAN, ITALY) HOW TO REACH PAVIA LINATE Airport: People arriving by plane at LINATE should take the bus to the CENTRAL STATION of Milan (cf below fron this Station to Pavia). In LINATE it could be convenient to take a Taxi because the airport is close to the center of Milan. Moreover, The bus company SGEA offers six runs from LINATE to Pavia at 9.00, 10.00, 12.00 AM and 2.00, 5.00, 8.30 PM. The last stop is Pavia, near the station (see again our updated web page for possible alterations of this time-table) (from Pavia to LINATE six runs at 5,00, 7.45, 10.00 AM, 1.00, 4.00, 6.00 PM) (one hour trip). In Pavia there is only one station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. MALPENSA 2000 and OLD MALPENSA Airports (usually people arrive to Malpensa 2000 and not to OLD MALPENSA): People arriving by plane at MALPENSA 2000 (also called MALPENSA 2000 Terminal 1) or at "old" MALPENSA (now called MALPENSA NORTH but also called Malpensa 2000 Terminal 2) should take the bus to the CENTRAL STATION of Milan. There is also a bus AND A TRAIN from Malpensa 2000 to the NORTH STATION (Piazzale Cadorna) of Milan, in this case from NORTH Station you will have to take the underground MM1 to the Central Station: trains to Pavia leave from Central station). Moreover, the bus company SGEA offers four runs from MALPENSA 2000 to Pavia at 9.00 AM, 1:30 PM, 5.00 PM, and 9:30 PM - from Malpensa North (OLD Malpensa or Malpensa 2000 Terminal 2 5 munutes later) (from Pavia to MALPENSA 2000 and to OLD MALPENSA four runs at 7.00 AM, 11:00 AM, 3.15 PM, and 7:00 PM) (one hour and half trip). The last stop is Pavia, near the station (see again our updated web page for possible alterations of this time-table) In Pavia there is only one station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. There are trains from MILAN (Central Station) to PAVIA and vice Versa about every an hour (routes: MILAN-GENOVA; MILAN-VENTIMIGLIA; MILAN-LA SPEZIA; MILAN-SAVONA; MILAN-SESTRI LEVANTE; MILAN-IMPERIA; MILAN-ALBENGA; Pavia is the first stop only if the train is not slow, that is, if it is not, in ITALIAN, "L", locale). In Pavia there is only one rail station. The easiest way to reach the center of the town is to get off at the station and than take the bus n. 3. ACCOMMODATION The WEB site of the Tourist Office is http://www.systemy.it/pavia/home.html (new! sorry, only in Italian). The email address is info(a)apt.pv.it. When available you will find the whole list of hotels and other information concerning Pavia and its history. See also http://www.itwg.com/ct_00036.asp. In case of accommodation problems remember we will have at our disposal some rooms at special "conference rates" in the Colleges of the University. For further information please contact the Program Chair. As the the conferences dates are very close to summer holidays we recommend making your reservations as early as possible and before March 31, 2000 at the latest. ALL ACCOMMODATIONS (EXCEPT FOR INVITED SPEAKERS) WILL BE PROCESSED BY: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy Phone: +39-0382-539565 Fax: +39-0382-539572 +39-0382-539504 email (only to request information): aloha(a)buonviaggio.it (cut here) ********************************************************************** ACCOMMODATION FORM - MBR'01 ---------------------------------------------------------------------- TO BE FAXED: +39-0382-539572 +39-0382-539504 OR MAILED: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy email (only to request information): aloha(a)buonviaggio.it ---------------------------------------------------------------------- FILL IN CAPITAL LETTERS, PLEASE LAST NAME:___________________FIRST NAME:_____________Prof./Dr./Mr./Ms. AFFILIATION/UNIVERSITY/DEPT.__________________________________________ STREET:_______________________________________________________________ TOWN:___________________________CODE:_____________COUNTRY:____________ PHONE:__________________FAX:__________________E-MAIL:_________________ TYPE OF TRAVELLING:__________________DATE OF ARRIVAL:_________________ DATE OF DEPARTURE:___________________NUMBER OF NIGHTS:________________ CREDIT CARD NUMBER AND TYPE__________________________ EXPIRATION_____________ (you can also pay by bank transfer and postal order, please see below) ACCOMMODATION INCL. BREAKFAST SINGLE ROOM+BATH. / DOUBLE ROOM+BATH. ***HOTEL EXCELSIOR, Piazza Stazione, PAVIA LIT. 100.000 / LIT. 150.000 ______________ (EUR. 51.64 / EUR. 77.46) ****HOTEL ARISTON, Via Scopoli, PAVIA LIT. 130.000 / LIT. 190.000 +_____________ (EUR. 67.13 / EUR. 98.12) ****HOTEL MODERNO, Viale V. Emanuele, PAVIA LIT. 170.000 / LIT. 230.000 +_____________ (EUR. 87.79 / EUR. 118.78) RESERVATION CHARGE LIT. 25.000 +_______ (EUR. 12.91) TOTAL AMOUNT: =_____________ ACCOMMODATION DEPOSIT: ONE NIGHT LIT......... - _____________ (EUR) ACCOMMODATION BALANCE: LIT......... =_____________ (EUR)........ Hotel Excelsior (from the station walk east) Hotel Moderno (from the station walk north) To reach Hotel Ariston take the bus n. 3 or taxi. ____________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *CREDIT CARD* BEFORE *15 MARCH 2001* TO: FAX: +39-0382-539572 +39-0382-539504 MAIL ADDRESS: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy email (only to request information): aloha(a)buonviaggio.it DATE OF PAYMENT____________YOUR SIGNATURE____________________ ________________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *BANK TRANSFER* BEFORE *15 MARCH 2001* (fax or mail also a copy of the bank transfer) TO: BANCA REGIONALE EUROPEA S.p.A.BRANCH PAVIA - SedeSWIFT BREUITM2 301Bank Code 6906.11301 Agenzia Viaggi ALOHATOUR S.r.l. Acc.n 19952/4 DATE OF PAYMENT____________YOUR SIGNATURE___________________ ________________________________________________________________________ PLEASE FAX OR MAIL THIS FORM AND PAY BY *POSTAL ORDER* BEFORE* 15 MARCH 2001* (fax or mail also a copy of the postal receipt) TO: Agenzia Viaggi ALOHATOUR Corso Cairoli 11 I - 27100 PAVIA Italy DATE OF PAYMENT______________________YOUR SIGNATURE______________________ _________________________________________________________________________ ALHOATOUR WILL MAIL OR FAX YOU THE RESERVATION VOUCHER ALOHATOUR WILL SATISFY THE REQUESTS AS FAR AS POSSIBLE. IF NOT POSSIBLE, ANOTHER SIMILAR ACCOMMODATION WILL BE ARRANGED.

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Overloaded function and implicit parameter passing
by José Romildo Malaquias 27 Oct '00

27 Oct '00

Hi. While experimenting with the implicit parameter extension to Haskell 98, implemented in GHC 4.08.1 and latest Hugs, I came accross a difference among those implementations regarding overloading functions with implicit parameters. As a test consider the program ------------------------- cut here module Main where class C a where f :: (?env :: Integer) => a -> Integer instance C Integer where f x = ?env + x main = putStrLn (show (f (45::Integer) with ?env = 100)) ------------------------- cut here Hugs accepts this program and outputs 145, as expected. But GHC 4.08.1 refuses to compile it, emitting the message $ ghc -fglasgow-exts Test1.hs -o test1 Test1.hs:7: Unbound implicit parameter `env_rJX :: Integer' arising from use of `env_rJX' at Test1.hs:7 In the first argument of `+', namely `env_rJX' In the right-hand side of an equation for `f': env_rJX + x Compilation had errors Would anybody comment on what is going on with GHC? I am willing to use implicit parameters in the software I am developing, but I have the need to overload functions with implicit parameters. While Hugs is good for development, its performance may rule it out when the final product is ready. So I will need a good Haskell compiler to compile my system. Any comments? Romildo -- Prof. José Romildo Malaquias <romildo(a)iceb.ufop.br> Departamento de Computação Universidade Federal de Ouro Preto Brasil

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class instance with nested types
by Matthias Höchsmann 27 Oct '00

27 Oct '00

Hello, I have the following problem: basic datatypes > type Sequence a = [a] > data Tree a = N a (Forest a) deriving (Ord,Eq,Show) > type Forest a = Sequence (Tree a) i want to construct a class Xy > class Xy s a where > test :: s a -> a and make an instance for list of characters > instance Xy [] Char where > test [a] = a this works, and an instance for a forest and tried something like this > instance ([] Tree) Char where > test x@(N a xs):txs = a I get illegal type errors. Is it possible to use nested types in a class ? Hope you can help me Matthias

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RE: .net and haskell
by Nigel Perry 27 Oct '00

27 Oct '00

At 10:27 am -0700 26/10/00, Simon Peyton-Jones wrote: >| I was reading some .net stuff (ducks) on microsoft, and they >| mentioned haskell as one of the languages someone was >| targetting for it. >| Anyone know anything about this project? > >I know of several stabs in this direction, none completed. > >- There is most of a Java back end for GHC > >- There are various pieces of a C# back end for GHC, > compiling via in intermediate generic OO language > called GOO. Nigel Perry is working on this (actively > I think) This is indeed being worked on. Currently user code compiles (as far as it has been tested) but there is no prelude yet so it doesn't run too well ;-) The code generator was designed for research and supporting scripting, which is a kind way of saying it doesn't produce blazingly fast code. > >- Don Syme and Reuben Thomas are working on a back end for > GHC that compiles to a polymorphically-typed IL for .NET > that is Don's baby. A lot of this works, but it's not complete. > >Maybe others are doing stuff too? It's a pity that there's nothing >that's usable yet, but I hope that'll change. Cheers, Nigel

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RE: .net and haskell
by Simon Peyton-Jones 26 Oct '00

26 Oct '00

| I was reading some .net stuff (ducks) on microsoft, and they | mentioned haskell as one of the languages someone was | targetting for it. | Anyone know anything about this project? I know of several stabs in this direction, none completed. - There is most of a Java back end for GHC - There are various pieces of a C# back end for GHC, compiling via in intermediate generic OO language called GOO. Nigel Perry is working on this (actively I think) - Don Syme and Reuben Thomas are working on a back end for GHC that compiles to a polymorphically-typed IL for .NET that is Don's baby. A lot of this works, but it's not complete. Maybe others are doing stuff too? It's a pity that there's nothing that's usable yet, but I hope that'll change. Simon

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