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drawing costumized squared boxes
by Nuno Silva 12 Dec '01

12 Dec '01

hello I'm new to Haskell and I'm having trouble drawing squares in the screen... it's like the game minesweeper, we will have to define how many squares we want the game to have and automatically draw them. if anyone could help me I'd be gratefull __________________________________________________ Do You Yahoo!? Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com

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Re: haxml
by Christopher Milton 11 Dec '01

11 Dec '01

--- David Smallwood <drs(a)dmu.ac.uk> wrote: > Does anyone know of a mirror site where I can download the latest > version of HaXml. (Connection to York is - and has been for a > while - apparently down: > ftp://ftp.cs.york.ac.uk/pub/haskell/HaXml/HaXml-1.02.tar.gz, that is) It's up now, unlike Hypatia, which needs a new maintainer. [ http://hypatia.dcs.qmul.ac.uk/ ] And, no, I don't have the server space to do it. Chris Milton just noticing Google has Usenet going back to 1981... http://groups.google.com/groups?q=clock+functional+programming&hl=en&rnum=2… __________________________________________________ Do You Yahoo!? Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com

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Re: (no subject)
by Ashley Yakeley 11 Dec '01

11 Dec '01

At 2001-12-10 16:07, uma kompella wrote: >i am new to haskell and am having a problem to write >function which takes a boolean expression and returns >a truthvalue stating whether or not it is a tautology. If you really want to impress your tutor, see if you can find a function that does this in polynomial time. -- Ashley Yakeley, Seattle WA

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(no subject)
by uma kompella 11 Dec '01

11 Dec '01

hi i am new to haskell and am having a problem to write function which takes a boolean expression and returns a truthvalue stating whether or not it is a tautology. Can anyone please help me?? Thanks a lot uma __________________________________________________ Do You Yahoo!? Send your FREE holiday greetings online! http://greetings.yahoo.com

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Re: cond and match
by Marcin 'Qrczak' Kowalczyk 10 Dec '01

10 Dec '01

Fri, 7 Dec 2001 17:12:52 -0500 (EST), David Feuer <dfeuer(a)cs.brown.edu> pisze: > I'm wondering why Haskell doesn't support Scheme-like cond statements > or a pattern matching predicate. I agree that both constructs make sense. The main objective is probably that the syntax is already quite rich and this would be another thing to learn and implement. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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RE: Pointers in Haskell??
by Simon Peyton-Jones 10 Dec '01

10 Dec '01

| > Simon Peyton-Jones. The implementation of functional | > programming languages. Prentice-Hall, 1987 | | is this book could be made available online ? cos on amazon | it seems out of print. I'm planning to scan it in and make the copy available online. In the next month or two. Simon

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Re: instance declarations
by Ketil Z Malde 10 Dec '01

10 Dec '01

David Feuer <dfeuer(a)cs.brown.edu> writes: > 1. Why can't [instances] be hidden in module imports/exports? The way I see it, an instance declaration is an assertion that a certain data type supports a certain set of operations. Thus, if the data type and the operations on it are in scope, it makes sense for the class instance to be, too. (This leads to the question of why we need to have instance declarations at all :-) (My guesses would be: compiler implementation issues, code clarity, error detection, partially implemented classes)) Problems arise when a data type needs to be instantiated twice in the same class, but with different operator implementations. (I.e. you have a data type which prints differently according to which module you're in) This would, I think, be a problem in most languages, think of deriving a C++ class twice from the same base class while providing different overrides for the functions. I'm not entirely convinced it's an issue that needs a better resolution than the language provides today. (There's a diminishing returns effect when adding language features, and at some point, the increased complexity of the language doesn't make it worth it, IMHO.) > 2. Why can't you simultaneously declare a type to be an instance of > multiple classes? Why does it matter? > class C1 t where a::t->t > class C1 t => C2 t where b::t->t > instance C1 T, C2 T where > a=... > b=... To me, it'd make more sense to provide class C1 t where a :: t -> t class (C1 t) => C2 t where b :: t -> t instance C2 T where a = ... -- implicitly instantiating C1 b = ... and avoid long instantiation chains. But that too is IMHO a minor issue. -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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Re: instance declarations
by Marcin 'Qrczak' Kowalczyk 10 Dec '01

10 Dec '01

Fri, 7 Dec 2001 11:38:14 -0800, Mark P Jones <mpj(a)cse.ogi.edu> pisze: > There's no solid technical reason for this, but Haskell doesn't allow > it at the moment because there isn't an easy way to name an instance > declaration. There is another problem: even if we created a syntax to name them, if they would not be exported by default then current programs would have to be changed. An instance is usually meant to be exported, so even not considering compatibility it would be tedious to list all those instances in the export list (unless you want to export every named thing as well and omit the export list). It's easy to overlook some and the point when somebody tries to use a particular instance might be far in the future. Each instance is often a "small" part of an interface. I agree that the ability to selectively export instances would be good. Only it's hard to combine with the current policy of exporting all instances by default. Perhaps in the future it will be possible to specify the interface of a Haskell module more formally, with types of exported values for example. Then we should remember about instances and solve both problems simultaneously. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ QRCZAK

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Re: instance declarations
by David Feuer 10 Dec '01

10 Dec '01

(sorry to mess up mail threading, but I couldn't properly reply to the message the way I'm using email right now--broken mail clients) >Recently, however, there has been some interest in using named instance >declarations in other ways, so perhaps we will see features like this >creeping into future versions of the language. In what kinds of ways? Sounds interesting. >[Of course, there is a way of naming instance declarations with the >current Haskell syntax, although it is a little verbose, and would >require more work on the implementers part than simple matching of >strings. The syntax I'm thinking of would look something like the >following: > > module M(C(..), instance C Int, instance C a => C [a]) where ... This is the sort of thing I was thinking too. But I would probably want to extend that to classes and types. For instance module M (class Eq a=>C a (...), type A, instance C A, instance C a => C [a]) where ... If I am not mistaken, this would allow separation of the type namespace from the typeclass namespace, and would make it obvious whether the thing being exported is a type or a class. It could also potentially allow the context(s) for class and instance declarations to be more restrictive in the header or in imports than in the module body. The latter could perhaps allow resolution of overlapping instances at import time, by restricting the instances to the point of non-overlap. I'm not sure that the former would actually be useful. Hmmm.... speaking of overlapping instances... Would there be a practical way to add negation (of classes and possibly even types) to the context syntax? This would let you say instance (Integral a) => C (T a) where ... instance (not Integral a, Real a) => C (T a) where ... instance (not Num a) => C (T a) where ... .... It would also seem nice to be able to say instance (Integral a, not a Int) => C a where .... and instance C Int where ..... but this seems even more questionable.

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Re: Pointers in Haskell??
by Yoann Padioleau 10 Dec '01

10 Dec '01

Jan Kort <kort(a)science.uva.nl> writes: > > Simon Peyton-Jones. The implementation of functional > programming languages. Prentice-Hall, 1987 is this book could be made available online ? cos on amazon it seems out of print. > > Jan > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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