November 2003 - Haskell

Announce: wxHaskell 0.4
by Daan Leijen 07 Nov '03

07 Nov '03

Announcement: wxHaskell version 0.4 ---------------------------------------------------------------------- <http://wxhaskell.sourceforge.net> The main addition of this new release is extensive support for ODBC database access. This is currently only tested on windows and not yet supported on MacOS X. Further additions: many GUI improvements for MacOS X, resize issues have been fixed, new functionality to manipulate pixel buffers, and support for OpenGL windows (untested yet with HOpenGL... we are looking for volunteers :-). ---------------------------------------------------------------------- wxHaskell is a portable GUI library for Haskell. The goal of the project is to provide an industrial strength portable GUI library, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore build on top of wxWindows -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with native look-and-feel, and it has a very active community (ranked among the top 25 most active projects on sourceforge). Since most of the interface is automatically generated from the wxEiffel binding, the current release of wxHaskell supports about 85% of the wxWindows functionality -- 2878 methods in 513 classes with 1347 constant definitions. wxHaskell has been build with GHC 6.01 on Windows, MacOS X and Unix systems with GTK. A binary distribution is available for Windows and MacOS X. And even if you don't intend to write GUI's yourself, it will be fun to check out the screenshots at <http://wxhaskell.sourceforge.net>. All the best, dr. :-) Daan Leijen.

1 0

RE: automaticly create the ana, cata, hylomorphisms
by Marta Isabel Oliveira 07 Nov '03

07 Nov '03

Thanks and sorry. Beside new in Haskell i'm also new in this archive lists. So, i was not aware i had sent with sucess the mail to the first list. lesina > -----Original Message----- > From: Keith Wansbrough [SMTP:Keith.Wansbrough@cl.cam.ac.uk] > Sent: Friday, November 07, 2003 3:00 PM > To: Marta Isabel Oliveira > Cc: haskell(a)haskell.org; haskell-cafe(a)haskell.org > Subject: Re: automaticly create the ana, cata, hylomorphisms > > > Hello programmers, > > > > I have a problem to solve and don't have a clue where to start. > > This is a homework question. Please read > > http://www.haskell.org/hawiki/HomeworkHelp > > for some helpful hints. > > By the way, you shouldn't post the same message to multiple lists - you should choose the right one (haskell-cafe in this case), or if you must, cross-post one message to both. This means people who subscribe to both won't see your message twice. > > --KW 8-) > -- > Keith Wansbrough <kw217(a)cl.cam.ac.uk> > http://www.cl.cam.ac.uk/users/kw217/ > University of Cambridge Computer Laboratory. >

1 0

automaticly create the ana, cata, hylomorphisms
by Marta Isabel Oliveira 07 Nov '03

07 Nov '03

Hello programmers, I have a problem to solve and don't have a clue where to start. I need to do a program in haskell that creates automaticly the ana, cata and hylomorphisms to arbitraty types. It's sort of a pre-processer. How can i start? I have the HaPar.hs that has uses Haskell parser to extract the type declarations from a file containing a Haskell module. I also have the TDec1.hs that has some dataTypes defined(TDec1, CDec1, Type) and some Show instances. Can anyone help me? I'm totally new to Haskell :(

2 1

Doing weird things with types.
by David Sankel 07 Nov '03

07 Nov '03

Hello All, I'm trying to create a generic function (*) using classes. I've been playing with ghc extensions but haven't found what I need yet. class HasTimes a b c where (*) :: a -> b -> c This doesn't work because it can't figure out what the return types are for a general expression a*(b*c). This kinda makes sense since someone could overload HasTimes Float Float Int and HasTimes Float Float Float. What about: class HasTimes a b where (*) :: a -> b -> c This would sort of imply that c is the only possible result of a (*) for types a and b. But I'm pretty sure this functionality hasn't been implemented. Why is this important? I'm trying to reduce ugliness of code using the following library: data Matrix = Matrix ((Float,Float),(Float,Float)) data HVec = HVec Float Float data VVec = VVec Float Float idMatrix = Matrix ((1.0,0.0),(0.0,1.0)) vhVecMult (VVec a b) (HVec c d) = Matrix ((a*c,a*d),(b*c,b*d)) matMult (Matrix ((a,b),(c,d))) (Matrix ((e,f),(g,h))) = Matrix (((a*e+b*g),(a*f+b*h)),((c*e+d*g),(c*f+d*h))) matVVecMult (Matrix ((c,d),(e,f))) (VVec a b) = VVec (a*c + b*d) (a*e + b*f) hVecMatMult (HVec a b) (Matrix ((c,d),(e,f))) = HVec (c*c+b*e) (a*d+b*f) vVecMinus (VVec a b) (VVec c d) = VVec (a-c) (b-d) vVecPlus (VVec a b) (VVec c d) = VVec (a+c) (b+d) matMinus (Matrix ((a,b),(c,d))) (Matrix ((e,f),(g,h))) = Matrix ((a-e,b-f),(c-g,d-h)) hvVecMult (HVec a b) (VVec c d) = a*c + b*d scalHVecMult :: Float -> HVec -> HVec scalHVecMult i (HVec a b ) = HVec (i*a) (i*b) Thanks, David J. Sankel

2 1

Call E-CAP2004_Italy
by Lorenzo Magnani 07 Nov '03

07 Nov '03

CALL FOR PAPERS NEW REGISTRATION/SUBMISSION POLICY!!! cf. below. ********************************************************************** COMPUTING AND PHILOSOPHY E-CAP2004_ITALY Pavia, Italy, Collegio Ghislieri, June 3-5, 2004 Chair: Lorenzo Magnani ********************************************************************** Up-to date information on the conference will be found at http://www.unipv.it/webphilos_lab/courses/progra2.html ********************************************************************** ALSO NEW !! Conference MODEL-BASED REASONING IN SCIENCE AND ENGINEERING Pavia, December 2004 http://www.unipv.it/webphilos_lab/courses/progra1.html ********************************************************************** GENERAL INFORMATION From Thursday 3 to Saturday 5 June 2004 (three days) the International European Conference ``COMPUTING AND PHILOSOPHY'' will be held at the University of Pavia (near Milan, Italy). GENERAL INFORMATION The Computational Philosophy Laboratory and the Department of Philosophy of the University of Pavia will be hosting the European Computing and Philosophy (CAP) conference from the 3rd to the 5th of June. PROGRAM The conference will deal with all aspects of the "computational turn" that is occurring within the discipline of Philosophy. We solicit papers that examine topics pertaining to computing and philosophy from the following list. RELEVANT RESEARCH AREAS We call for papers that cover topics pertaining to computing and philosophy from the following list: * Cognitive Science, Epistemology, and Metaphysics * Abductive reasoning, Scientific discovery, Creative processes * Internal and External Representations in Cognitive Science * Simulation, Embodiment, and Distributed Reasoning in Computational Models of Cognitive * Problem of Consciousness in Philosophy * New Models of Logic Software * Computer-based Learning and Teaching Strategies and Resources * Ethics and Computers * The Impact of Distance Learning on the Teaching of Philosophy * The Role of Computers as Tools for Philosophical Research SUBMISSIONS OF PAPERS The deadline for submission is 19th December 2003 - though late submissions will be considered. Authors must submit an electronic version - formatted in Microsoft Word or RTF, but also in PDF or POSTSCRIPT ( in this last case please include source - DOC, TEX, etc., file) - of an extended abstract (total word count aproximately 3500). The file must also contain a 300 WORD abstract that will be used for the conference web site/booklet. PPT files are also accepted. not later than December 19, 2003 Please send electronically the extended abstract to the Prof. Magnani at the address lmagnani(a)cc.gatech.edu (if the previous address does not work please use lorenzo.magnani(a)unipv.it) A RIGID LAW ON PRIVACY IN ITALY DOES NOT FAVOR MORE COMFORTABLE COMPUTATIONAL METHODS OF PAYMENTS (CONFERENCE AND ACCOMODATION FEES), SORRY. PLEASE FOLLOW THE INSTRUCTIONS INDICATED BELOW. REGISTRATION AND FURTHER INFORMATION PLEASE REGISTER by email lmagnani(a)cc.gatech.edu (or lorenzo.magnani(a)unipv.it) fax or air mail by sending the 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. Registration Fees: Before 15 April 2004: Standard: EURO 150,00 (to participate in all the activities of the Conference Reception Included) Phd Students: EURO 90,00 Students: Free After 15 April 2004: Standard: EURO 180,00 (to participate in all the activities of the Conference Reception Included) Phd Students: EURO 110,00 Students: Free One day only: EURO 80,00 No refunds will be granted after May 12th, 2004 Terms & Conditions: an administration fee of EURO 75,00 will be charged for cancellations confirmed in writing by 12th May. We regret that no refund can be made after that date, for whatever reason, although substitutions will be acceptable if notified in writing before the event. METHOD OF PAYMENT: SWIFT TRANSFER Bank (Swift) Transfer to BANCA REGIONALE EUROPEA S.p.A BRANCH PAVIA - Sede SWIFT BREUITM2 301 Bank Code 06906.11301 Acc. n. 42113 COMITATO CONVEGNI E. W. I. C. IBAN: IT32O0690611301000000042113 (attention: the fifth symbol is the letter O and not zero). Please indicate CONVEGNO INTERNAZIONALE E-CAP2004_ITALY Please ask your BANK to clearly indicate in the order of payment your first and last NAME. In case of problems please contact Elena Gandini Local Organizer elena(a)acrossevents.com) If you prefer, you can mail an international check to CONVEGNO INTERNAZIONALE E-CAP2004_ITALY, Dipartimento di Filosofia, Piazza Botta 6, 27100 Pavia, Italy . ACCOMMODATION To book a reservation please fill and fax to +39-0382-23215 the ACCOMMODATION FORM you will find in the Conference Web Site http://www.unipv.it/webphilos_lab/courses/progra1.html (to dr. Elena Gandini Local Organizer). POSSIBLY BEFORE APRIL 15, 2003. For information please email Elena Gandini, Local Organizer elena(a)acrossevents.com. Please do not send email messages containing your credit card data. All accommodation is hotel-based with en-suite facilities (the prices are per room per day). Hotel Moderno ****Euro 103,00 (single b&b) Euro138,00 (double b&b) Hotel Ariston *** Euro 80,00(single) Euro 110,00 (double), Breakfast Euro 10,00 Hotel Excelsior *** Euro 50,00(single) Euro 73,00(double) Euro 62,00(D/S) breakfast Euro 6,00 Hotel Ritz*** Euro 65,00 (single b&b) Euro 87,00 (double b&b) Hotel Excelsior (from the station walk east) Hotel Moderno (from the station walk north) Hotel Ritz (San Genesio-PV); an Hotel bus service is available. To reach Hotel Ariston take the bus n. 3 or taxi. If the Hotels above will be completely booked other Hotels are available, in this last case please email dr. Elena Gandini Local Organizer e-mail: elena(a)acrossevents.com PENALTY In case of no show the Hotels will charged you their own penalty. For further information, please contact our local organiser Elena Gandini elena(a)acrossevents.com. IMPORTANT DATES Submission deadline...........................19 December 2003 Notification of acceptance................... 19 March 2004 Conference................................... 3-5 June 2004 Final papers............................due.. 15 July 2004 PROGRAM CHAIR Lorenzo MAGNANI Professor of Logic and Epistemology 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 & Weissman Distinguished Visiting Professor Department of Philosophy, Baruch College, 1 Bernard Baruch Way, New York , NY 10010 Office: +646-312-4367, Fax: +646- 312-4361, Home: 646-432-9309 Email: lmagnani(a)unipv.it, lmagnani(a)cc.gatech.edu PROGRAM COMMITTEE - Atocha Aliseda, Instituto de Investigaciones Filosoficas Universidad Nacional Autonoma de Mexico (UNAM), Mexico City, MEXICO - Diderik Batens, Centre for Logic and Philosophy of Science, Universiteit Gent, Ghent, Belgium - Robert Cavalier, Department of Philosophy, Carnegie Mellon, Pittsburgh, PA, USA - Simon Colton, Department of Computing, Imperial College London, London, UK - Roberto Cordeschi, Department of Philosophy, University of Salerno, Salerno , ITALY - Chris Dobbyn, Faculty of Maths and Computing,The Open University,Walton Hall, Milton Keynes MK7 6AA - Roy Dyckhoff, School of Computer Science,University of St Andrews,North Haugh, St Andrews,Fife, KY16 9SS, Scotland - Luciano Floridi, Wolfson College, University of Oxford, Oxford, UK and University of Bari,Bari, ITALY - Theo Kuypers, Dept. of Philosophy, University of Groningen, Groningen, The Netherlands - Lorenzo Magnani, Department of Philosophy, University of Pavia, Pavia, ITALY and Baruch College, The City University of New York, New York, USA - Nancy J. Nersessian, College of Computing, Georgia Institute of Technology, Atlanta, GA, USA - Claudio Pizzi, Department of Philosophy and Social Sciences, University of Siena, Siena, ITALY - Susan Stuart, Humanities Advanced Technology and Information Institute, University of Glasgow, Glasgow, UK - Guglielmo Tamburrini, Department of Philosophy, University of Pisa, Pisa, ITALY - Riccardo Viale, Fondazione Rosselli,Via San Quintino, 18/c, 10121 Torino, Italy LOCAL ORGANIZER dr. Elena Gandini Across Events s.r.l. Via A. Moro, 12 27021 Bereguardo (PV) Italy mobile +39 349 55 41 915 e-mail: elena(a)acrossevents.com www.acrossevents.com LOCAL ORGANIZING COMMITTEE Elena Gandini (elena(a)acrossevents.com) Alberto Gatti (gatti_alberto(a)hotmail.com) Riccardo Dossena (riki.dox(a)libero.it) Lorenzo Magnani (lmagnani(a)cc.gatech.edu) Matteo Piazza (pimat(a)yahoo.com) (Department of Philosophy, University of Pavia, Pavia, Italy) Stefanelli Mario (mstefa(a)aim.unipv.it) (Dipartimento di Informatica e Sistemistica, Università di Pavia, Pavia, Italy) IMPORTANT ADDRESSES PROGRAM CHAIR Lorenzo MAGNANI 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: lmagnani(a)unipv.it also Department of Philosophy, Baruch College, The City University of New York 1 Bernard Baruch Way, New York , NY 10010 Office: +646-312-4364 Fax: +646- 312-4361 CONFERENCE SITE: Collegio Ghislieri, Piazza Ghislieri, 27100 PAVIA, Italy, phone +39 0382 37861. http://www.ghislieri.it/ The Conference is sponsored by UNIVERSITY OF PAVIA, ITALY UNIVERSITY OF SIENA, ITALY MIUR (Ministero dell'Università e della Ricerca Scientifica e Tecnologica), ITALY HOW TO REACH PAVIA LINATE Airport: www.sea-aeroportimilano.it/linate People arriving by plane at LINATE should take the bus to the CENTRAL STATION of Milan (cf. below from 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 SILA ( www.sila.it ) 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, 7.30, 10.00 AM, 1.00, 4.00, 6.00 PM) (one hour trip; _13,00 return ticket, _8,00 one way ticket). 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: www.sea-aeroportimilano.it/malpensa (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 shuttle TRAIN (Malpensa Express) from Malpensa 2000 to the NORTH STATION (Piazzale Cadorna) of Milan, in this case from NORTH Station you will have to take the underground MM2 (green line) to the Central Raylway Station: trains to Pavia leave from Central station. Moreover, the bus company SILA offers various runs from MALPENSA 2000 to Pavia at 9.00, 11:00 AM, 1:30 3:00, 5:00, 7:00, 9:30, PM (from Pavia to MALPENSA 2000 and to OLD MALPENSA various runs at 7.00, 9:00, 11:00 AM, 1:00, 3:15, 5:00, 7:00 PM) (one hour and half trip; _18,00 retourn ticket, _12,00 one way ticket). The last stop is Pavia, near the rail station 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. There are trains from MILAN (Central Raylway Station) to PAVIA and vice versa about every an hour www.trenitalia.it (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). (see again our updated web page for possible alterations of this time-table) For any further information do not hesitate to contact our local organizer, Elena Gandini at elena(a)acrossevents.com

1 0

RE: How overload operator in Haskell?
by Hal Daume 06 Nov '03

06 Nov '03

What you want to do is make your Vector an instance of the Num(eric) type class. For instance: instance Num Vector where (+) v1 v2 = zipWith (+) v1 v2 (-) v1 v2 = zipWith (-) v1 v2 negate v1 = map negate v1 abs v1 = map abs v1 (*) v1 v2 = ... fromInteger i = ... signum v1 = ... I've left the last three blank because it's unclear what should go there. Since (*) has type Vector->Vector->Vector (in this instance), you can't use dot product or something like that. signum :: Vector->Vector could be written and just return [-1], [0] or [1], I suppose. fromInteger :: Integer->Vector is a little harder. Perhaps just 'fromInteger i = [fromInteger i]' would be acceptable. Or you could leave these undefined. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-admin(a)haskell.org > [mailto:haskell-admin@haskell.org] On Behalf Of Liu Junfeng > Sent: Wednesday, July 09, 2003 7:25 AM > To: haskell(a)haskell.org > Subject: How overload operator in Haskell? > > > I've learned haskell months, but I still can't understand the > type system very well. > I can only write: > ----------------------------------- > type Vector = [Double] > vadd,vsub :: Vector->Vector->Vector > v1 `vadd` v2 = zipWith (+) v1 v2 > v1 `vsub` v2 = zipWith (-) v1 v2 > svmul :: Double->Vector->Vector > s `svmul` v = map (s*) v > ------------------------------------ > Tough it works, it is not convenient to use. How to create a > Vector type and overload > mathematical operators? > Thanks for your help. > > Liu Junfeng > liujf(a)softhome.net > > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

12 14

Expiring cached data?
by andrew cooke 05 Nov '03

05 Nov '03

I have a Haskell program that caches data in a tree. Unfortunately, the tree grows to exceed the available memory over time. In a different language, where I might be handling the caching myself, rather than relying on laziness within the language, I might work round this by keeping track of which leaves in the tree were more recently used, and, when memory run slow, deleting those that have not been used for some time (by the nature of the problem, access to particular caches tend to be grouped, so a long-unused cache can be deleted without much performance penalty). What options do I have in Haskell? I'm interested both in general solutions (maybe some compilers do this anyway?) and in approaches to structuring the program so that I can control caching in more detail. Thanks, Andrew -- http://www.acooke.org/andrew

6 10

RE: access to fields in nested records
by Tim Docker 05 Nov '03

05 Nov '03

(Apologies for previous incomplete post: Here's the whole thing) One thing that bugs me about the named record syntax, is that with a datatype: data T = T { t_f1 :: X, t_f2 :: X }; the function t_f1 has the type of an "accessor", ie t_f1 :: T -> X but there doesn't any tidy way to get at the "mutator" function t_f1' :: X -> T -> T without actually having to write the following t_f1' x t = t{t_f1=x} or is there? Actually mutators of the more general form t_f1' :: (X->X) -> T -> T t_f1' f t = t{t_f1=f (t_f1 t)} would seem to be quite useful, (even though they are tedious to write) as you can compose them for nested structures, ie if data X = X { x_f1 :: Int, x_f2 :: Int }; Then... (t_f1'.x_f2') (const 5) would be the functional equivalent of the imperative t.f1.f2 = 5 Tim

1 0

RE: access to fields in nested records
by Tim Docker 05 Nov '03

05 Nov '03

One thing that bugs me about the named record syntax, is that with a datatype: data T = T { t_f1 :: X, t_f2 :: X }; the function t_f1 has the type of an "accessor", ie t_f1 :: T -> X but there doesn't any tidy way to get at the "mutator" function t_f1' :: X -> T -> T without actually having to write the following t_f1' x t = t{t_f1=x} Or is there? Actually mutators of the general form t_f1' :: (X->X) -> T -> T t_f1_ f t = t{t_f1=f (t_f1 t)}

3 2

AW: access to fields in nested records
by Markus.Schnell＠infineon.com 05 Nov '03

05 Nov '03

There is updateable syntax. You can write > setSquare :: DiningRoom -> Int -> DiningRoom > setSquare r n = r { square = n } HTH, Markus > -----Ursprüngliche Nachricht----- > Von: haskell-bounces(a)haskell.org > [mailto:haskell-bounces@haskell.org] Im Auftrag von Serge D. > Mechveliani > Gesendet: Mittwoch, 5. November 2003 13:27 > An: haskell(a)haskell.org > Betreff: access to fields in nested records > > > Dear Haskellers, > > My question is about a nice way to provide a getting/setting > access to the nested record fields. > > Example: > --------------------------------------------------------------- > data House = House {houseNo :: Int, > diningRoom :: DiningRoom > } deriving (Show) > data DiningRoom = DRoom {square :: Int, > height :: Int, > numOfWindows :: Int, > diningTable :: DTable > > } deriving (Show) > data DTable = DTable {tableSquare :: Int, > diningPlaces :: Int > } deriving (Show) > -- example: > r1 = DRoom {square = 50, > height = 300, > numOfWindows = 1, > diningTable = dt > } > where dt = DTable {tableSquare = 16, > diningPlaces = 12 > } > --------------------------------------------------------------- > > Question 1: how to change a field in a record? > > I see the following way. For example, > > setSquare :: DiningRoom -> Int -> DiningRoom > setSquare r n = > DRoom {square = n, > height = height r, > numOfWindows = numOfWindows r, > diningTable = diningTable r > } > Example of usage: setSquare r1 (square r2) > for > r1, r2 :: DiningRoom > > Has indeed one to program the above functions, like setSquare, > for all the records, > or there exist some Haskell annotations, or standard library > function for such purpose, which allow to skip extra remaining > fields in the data, like these three fields in DiningRoom ? > > > Question 2: how to get/update a field in a nested record? > > For example, > dtableSquareFromRoom :: DiningRoom -> Int > dtableSquareFromHouse :: House -> Int > > dtableSquareFromRoom = tableSquare . diningTable > dtableSquareFromHouse = dtableSquareFromRoom . diningRoom > > setDTableSquareToHouse :: House -> Int -> House > setDTableSquareToHouse h n = > House { > houseNo = houseNo h, > diningRoom = setDTableSquareToRoom (diningRoom h) n > } > where setDTableSquareToRoom r n = ... > > Has indeed one to program such functions for each path to a > field in the record nesting hierarchy? > I see the main difficulty in a great number of functions to use > for the same field access from different structures. > > I try to improve this by adding classes with get_ and set_ > versions of operations for the record fields: > > class HouseLike a where get_houseNo :: a -> Int > get_diningRoom :: a -> DiningRoom > > set_houseNo :: a -> Int -> a > set_diningRoom :: a -> DiningRoom -> a > ... > > Now, defining the instances, say, for get_dtableSquare, > set_dtableSquare, > > makes it a unique function pair to use for getting/setting of the > corresponding field starting from > House or DiningRoom or DiningTable. > > Is this all a reasonable design for a Haskell user program? > > Thank you in advance for the respond. > > Please, add mechvel(a)botik.ru > to the reply list. > > ------------------ > Serge Mechhveliani > mechvel(a)botik.ru > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

1 0