December 2001 - Haskell-Cafe

drawing grids
by Nuno Silva 14 Dec '01

14 Dec '01

hello can anyone tell me how to draw grids?? it's like this: Imagine that I say that I want the grid to be 5X6, it will compute the distbetween the limits and then draw them. if I want a 6X10, it will do the same. thanks __________________________________________________ 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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overloading efficiency
by David Feuer 14 Dec '01

14 Dec '01

I have read that using overloaded functions is expensive because overloading is implemented by passing dictionaries around. These various sources seem to agree that this in necessary to allow separate compilation. I don't understand why this is... Couldn't the functions be specialized at link time? -- /Times-Bold 40 selectfont/n{moveto}def/m{gsave true charpath clip 72 400 n 300 -4 1{dup 160 300 3 -1 roll 0 360 arc 300 div 1 1 sethsbcolor fill}for grestore 0 -60 rmoveto}def 72 500 n(This message has been)m (brought to you by the)m(letter alpha and the number pi.)m(David Feuer) m(David_Feuer(a)brown.edu)m showpage

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Re: drawing costumized squared boxes
by Yoann Padioleau 12 Dec '01

12 Dec '01

Nuno Silva <nunopedrosilva(a)yahoo.com> writes: > 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 borrow the book The Haskell School of Expression: Learning Functional Programming through Multimedia : Paul Hudak Cambridge university press to your library, and read it. > > __________________________________________________ > 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 > > _______________________________________________ > 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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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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