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Re: Question about typing
by Yoann Padioleau 10 Apr '01

10 Apr '01

Matt Harden <matth(a)mindspring.com> writes: > > zip :: ZipFunctor f => f a -> f b -> f (a,b) > zip = zipWith (,) > zip3 :: ZipFunctor f => f a -> f b -> f c -> f (a,b,c) > zip3 = zipWith3 (,,) > > One can easily create ZipFunctor instances for trees and other data > structures. I can provide examples if you like. With multiple > parameter type classes (MPTCs, they are not in Haskell 98) as well as > functional dependencies (also not in h98), one can also create a > "Zippable" class to generalize the zip function over multiple tuple > types and eliminate zip3, zip4, etc. can you explain how you do that ?? (i dont know what is functional dependencies, but i think i understand multiple parameter type classes and i dont see how do make something that avoid to define a zip3 zip4 ....

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Question about typing
by Toby Watson 09 Apr '01

09 Apr '01

Intuitively the following scenarios seem to be related, can anyone point my in the direction of formal work on this, or give me the formal terms I need to search around? 1. Adding two integers together: Int -> Int -> Int 2. Adding two lists of Integers together: [Int] -> [Int] -> [Int] 3. Adding two lazy streams of integers together, possibly in seperate (parallel) processes for example. cheers, Toby

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Visual Haskell
by Jason J. Libsch 06 Apr '01

06 Apr '01

I recently ran across a paper, Visual Haskell- a First Attempt, and was tremendously impressed. Has anybody here played with this language or read the paper? I would be interested to hear other's opinion on such a language. http://ptolemy.eecs.berkeley.edu/~johnr/papers/visual.html /jason

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Re: "Lambda Dance", Haskell polemic, etc. on O'Reilly site
by Dejan Jelovic 04 Apr '01

04 Apr '01

Jerzy Karczmarczuk wrote: > Over and over again the same silly song, by a person who - visibly - > had never anything to do with functional languages, who thinks now > about hiring some C and java programmers living in Belgrade I don't understand how you deduced I "never had anything to do with functional languages"? Any how is it relevant to the subject at hand that I'm hiring Java and C++ (not C) programmers in Belgrade? > but who > writes such silly, incompetent things as: > > > And there is an air of staleness: where new versions of these other > > languages appear frequently, the Haskell community is offering you > > Hugs98. I don't see why what I said is silly or incompetent? The Haskell Compiler and Interpreters page at haskell.org suggests Hugs98 for newcomers. While you and I know that the latest version of Hugs has been released two weeks ago, a curious visitor will wonder why there isn't Hugs 2001. And the Haskell website is updated rarely in contrast with, say, the Python website. > Delovic points out that some languages became "immensely" popular, > as e.g. Ruby, and that Haskell is marginal. Hm. this extremely > orthodox Japanese essence of O-O programming may have some practical > merits, especially those which come from shameless borrowing from > Eiffel, Sather, Clu and Common Lisp, but calling Haskell "marginal" > or "obscure" informs us not what is Haskell, but who is Jelovic. Compared to the usage of C++, Java or Python, the usage of Haskell is _marginal_. Visit the computer section of your local bookstore if you need to be reminded of that. BTW, you seem to be well-informed about who this Jelovic is. Why don't you share that knowledge with us? :) > He accuses the Haskell community of not providing libraries... Two errors here: 1. I didn't accuse anybody of anything. I was just curious about why people aren't using Haskell and started to think about it. There's a saying among Program Managers at Microsoft that "thinking is writing". I subscribe to that. I often write about things I think about in order to explore the issues. If I think other people might be interested in the end result, I post it. 2. I didn't say that the Haskell community has not provided the libraries. I said the Haskell community hasn't provided the libraries together with the compiler in one standard distribution. I think that's needed in order to lower the barrier to entry. > Perhaps there is *one* point worth mentioning: the necessity to > publish papers about Haskell far from such journals as JFP or HOSC, > but to try to reach DrDobbs etc. Funny. You said at the beginning of your message that there is "NOTHING" serious there. :) Dejan http://www.jelovic.com

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Re: "Lambda Dance", Haskell polemic,... (Jerzy Karczmarczuk)
by Dejan Jelovic 03 Apr '01

03 Apr '01

Jerzy Karczmarczuk wrote: > 1. I didn't find ANYTHING about FP on your pages, > only that accusations. I already explained that was not an accusation. How does it follow that since there's nothing else about FP on my website that I "never had anything to do with functional languages"? Do you really think that the 10 pages or so on my website describe the composite of everything I ever did? > 2. I don't remember any of your eventual contribution to discussion > lists, newsgroups, etc. I might be wrong. Please give some references, > publications, functional software, etc. I will apologize then > immediately, with regret, but also with satisfaction that the Truth won. I have never before posted anything on FP to any list or newsgroups. In fact I subscribed to this list only when I saw your message in the list archives. But that's irrelevant. Do you think that everybody that has ever used a functional laguage has contributed to discussion lists and newsgroups? > 3. Personally you don't care about Haskell. Your page *explicitly* > discourages local people from touching functional languages, the > category of people you want to hire is a very strong signal. > A potential employer who does what you did serves the devil, don't > try to suggest that this isn't relevant. Nonsense. I'm hiring C++ and Java programmers because I need help with the C++ and Java projects I do. I don't see how that would discourage anybody from learning about other languages? And why would you assume that I personally don't care about Haskell? You seem to be piling these assumptions about me at random. > 1. Saying that the Haskell community offers Hugs98, and not > mentioning neither GHC, nor NHC is either incompetent or > provocative. Hugs is the distribution that's suggested to newcommers. It didn't seem relevant to talk about other distributions if we are talking about people migrating to Haskell. > 2. A decent programming language *must* be stable. If the main > criterion of the "quality" you attribute to programming languages > is the speed of its modifications, I wonder what don't you accuse > of staleness your favourite languages: Java and C++. Again, wrong assumptions. Neither C++ nor Java are not my favourite language. I don't have a favourite language. The fact that Java has not grown for a number of years is a horror. The language lacks support for types with value semantics, generic types and other useful facilities. Those have all been proposed but Sun has not moved to implement them. C++ is more expressive. The only addition I can think of right now that would be worth the added complexity would be Java-like inner classes and anonymous classes and functions. I was actually contemplating writing about the above things. But it just so happened that I wrote about Haskell first. I don't understand why the order in which I write things is bothering you? Or did you expect to come and find a complete 200-page analysis of all popular programming languages? But again, this is irrelevant. I was not talking about the language. In fact I said that Haskell is superior to Python, Perl and Ruby at the very beginning of my article. But the Haskell website and the _distributions_ seem to be moving at a slower pace. > Hugs 2001???? Are you sure that you really know what does it mean > a STANDARD? Yes. Haskell 98 is a standard. Hugs is a product. It doesn't have to be called Hugs 98. It can be called Hugs 2001, Hugs XP, Hugs ME, Visual Hugs :) or any other attractive name. Anybody programming in Haskell will benefit from other users migrating to it. More users means more vendors and more libraries. Perception is one of the factors that influences the number of users. Commercial world knows this. Microsoft incremented the version of Word from 2.0 to 6.0 in order to avoid having Word perceived as less mature than WordPerfect. The incremented the Visual C++ version from 2.0 to 4.0 in order to match Borland C++. Sun called Java 1.2 "Java 2". Etc. The examples above are extreme and, IMO, slightly dishonest. I just brought them up to illustrate the point vividly. Calling the Hugs February 2001 distribution "Hugs 2001" is not dishonest, it's just good marketing. > 1. Oh yes. Thousands of books about Ruby. Actually one, in Japanese. > Have you looked here: > http://www.haskell.org/bookshelf/ > This is comparable with Python. Of course, Python IS more popular, > but - - I included Ruby in the trio because it fits the scripting language phenomenon. Python is the one to compare against due to similar starting positions. Go to a bookstore. The fact that many books on Haskell have been published doesn't mean that many people are buying them. The bookstores I visit in the States have a number of books on Perl and Python. If they carry books on Haskell at all that's usually one title hidden somewhere on the shelf. Also, it is a known fact that books on specific products ("Teach Yourself Visual C++ in 21 Days") greatly outsell books on programming languages ("The C++ Programming Language"). Guess of which kind are Haskell books? > 2. You neglect, and I suspect that you do it on purpose, that the main > driving force behind the evolution of Haskell is *RESEARCH*. An issue > absent from many "popular" languages which are meant to be > immediately exploitable with very flat learning curve. Flat learning curve is ideal. Since that's not possible, the smallest possible barrier to entry is the next best thing. Why does that bother you? >The documentation on line is sufficiently good that e.g. - > my students won't even think about going and trying to buy a book. No doubt. Ditto for Python and Java. But that's besides the point. If Haskell was more popular the publishing industry would be on the bandwagon. No? Remember, I brought up the number of books sold as a way to gauge the popularity of Haskell in relation to Python. > Still, there are more publications on FP every month that I can > digest. What about Python? Java? Do you have _any_ idea what the average programmer is reading these days? _Nothing_. Not one trade publication, not one book. (See "Rapid Development" for statistics on this.) DDJ is probably one of the most popular trade magazines. Its circulation is 155,000. What percentage of the working programmers is that? How big is the membership in IEEE or ACM? How many practicing programmers read IEEE Software, let alone any of the Journals? All those publications on FP are _not_ reaching the average programmer. > > BTW, you seem to be well-informed about who this Jelovic is. Why don't you > > share that knowledge with us? :) > > Oh, but I did. > You seem to be a self-appointed specialist on functional languages, who > expresses in public some very dubious truths, which I find harmful. I never said I was a specialist. Do only specialists get a voice? > > 1. I didn't accuse anybody of anything. I was just curious about why people > > aren't using Haskell and started to think about it. > > I understood this in such a way. You seem to be the only one. On this list and off. Doesn't this tell you anything? > You are explicitly negative in your *judgement*. I said that the language is good, but that the distributions are not good enough to facilliate widespead use. A number of people on this list agreed. Why is this giving you an ulcer? > There are hundreds of libraries of Java classes and C++ classes > and procedures which are distributed separately. The "standard" > GNU distribution of C++ is quite limited, there is no point in > overloading the standard environment by things whose usage > is limited. The ease of installation is also important. The standard Java library is actually quite comprehensive. I'd go so far to say that it's one of the main reasons why Java has spread so quickly. The standard C++ library is too small. That's a problem with C++. But the language spread before GUIs and before the Web when people required less. If Haskell is to have a chance its distribution(s) must have a comprehensive library. > BTW. the GHC "standard" distribution has an adequate amount of runtime > support for normal tasks. It worked for me without any problem. You underestimate the value of a large community and lots of vendors. In my last project I had to manipulate some graphic files in various formats. For C++ and Java I had turnkey solutions. (Java being better as it has a standard Image class while for C++ no standard exists.) The closest thing I found for Haskell is a GD wrapper with limited functionality. > RRight. I found one point worth mentioning. Wonderful, splendid, and > original. Hereby I declare that you are the winner of this discussion, > and I am the loser. Relax. I was just nitpicking in order to get a rise out of you. So far you have used "silly", "incompetent", "accuse", "Truth", "serve the devil", "moral", "nasty", "dubious" and "harmful". Funny how people are eager to use such qualifications over the Internet but avoid saying them when they have to look the other person in the eyes, don't you think? You also didn't have the common courtesy and courage to CC: me on your initial posting to this list. Dejan http://www.jelovic.com

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RE: "Lambda Dance", Haskell polemic, etc. on O'Reilly site
by Julian Seward (Intl Vendor) 03 Apr '01

03 Apr '01

S. Alexander Jacobsen wrote: | Although I think Haskell is a beautiful language, Jelovic is right on his | core points, Haskell implementations don't meet the needs of | the working programmer. [...] I also largely agree with Jelovic, and I take what he says as constructive criticism. One observation at least as regards Perl and Python is that Haskell has a very much more academically-intense heritage, whereas Perl and (guessing here) Python were motivated more by end-user need. GHC and Hugs suffer from tensions between being research vehicles and being practical implementations suitable for end-users. I'd guess that Perl and Python don't suffer from such tensions, so their implementors can concentrate more directly on providing excellent implementations suitable for widespread use. I say nothing about Ruby because I know nothing about it. A second observation is that Perl and Python are both single -implementation languages, which makes it easier to have a coherent set of libraries. Haskell, by contrast, isn't -- there are at least 4 available implementations (hbc, hugs, nhc, ghc). The core language (Haskell98) is supported by all of these, but there isn't a coherent story on the libraries. We are working on that. This plurality of implementations has worked well for the diverse research interests centered around Haskell. I think there is now a growing feeling that we need to standardise the libraries more and put more emphasis on end-user issues -- the kind of things Jelovic mentions -- if Haskell is to have a long-term future. Here at GHC HQ we are trying hard to make GHC into a suitable vehicle for widespread use. The upcoming GHC version 5 should go some way to addressing issues of installability, library coverage and speed of compilation. As Simon Marlow pointed out, if you feel motivated to help us work on the libraries, that would be excellent. I think it's worth clarifying a couple of potential misunderstandings with the original posting: -- The current version of Hugs is called hugs98 not because the implementation was last revised in 1998 but because it implements the language as standardised in 1998. Hugs is actively maintained. -- Hugs is not the only Haskell implementation. Ours, GHC, strives hard to provide a coherent, complete set of libraries in the standard distribution. NHC is also moving in that direction. We are not yet there, but are, at least, proceeding. J

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Re: "Lambda Dance", Haskell polemic, etc. on O'Reilly site
by Bill Halchin 02 Apr '01

02 Apr '01

Hello, I think Dejan has written in a good spirit and has many cogent points, especially for example with regard to Python. I guess the bottom line is don't be too think-skinned about what seems to me to be constructive criticism. In the FPL community, it is easy to maintain a siege mentality. Before I worked at Microsoft Hotmail. I asked one person (well known) who does research at Microsoft Research on Haskell. I asked him if any projects inside Microsoft were implemented using Haskell and he said no. Of course, this is not his fault. Management has to see that they are not going "out on a limb" to use FPLs. I know that Sun wrote at least one tool in Scheme (albeit it doesn't have ref. transparency). Regards, Bill Halchin >From: "Dejan Jelovic" <djelovic(a)sezampro.yu> >To: <haskell-cafe(a)haskell.org> >CC: <karczma(a)info.unicaen.fr> >Subject: Re: "Lambda Dance", Haskell polemic, etc. on O'Reilly site >Date: Sun, 1 Apr 2001 22:02:29 +0200 > >Jerzy Karczmarczuk wrote: > > > Over and over again the same silly song, by a person who - visibly - > > had never anything to do with functional languages, who thinks now > > about hiring some C and java programmers living in Belgrade > >I don't understand how you deduced I "never had anything to do with >functional languages"? Any how is it relevant to the subject at hand that >I'm hiring Java and C++ (not C) programmers in Belgrade? > > > but who > > writes such silly, incompetent things as: > > > > > And there is an air of staleness: where new versions of these other > > > languages appear frequently, the Haskell community is offering you > > > Hugs98. > >I don't see why what I said is silly or incompetent? The Haskell Compiler >and Interpreters page at haskell.org suggests Hugs98 for newcomers. While >you and I know that the latest version of Hugs has been released two weeks >ago, a curious visitor will wonder why there isn't Hugs 2001. > >And the Haskell website is updated rarely in contrast with, say, the Python >website. > > > Delovic points out that some languages became "immensely" popular, > > as e.g. Ruby, and that Haskell is marginal. Hm. this extremely > > orthodox Japanese essence of O-O programming may have some practical > > merits, especially those which come from shameless borrowing from > > Eiffel, Sather, Clu and Common Lisp, but calling Haskell "marginal" > > or "obscure" informs us not what is Haskell, but who is Jelovic. > >Compared to the usage of C++, Java or Python, the usage of Haskell is >_marginal_. Visit the computer section of your local bookstore if you need >to be reminded of that. > >BTW, you seem to be well-informed about who this Jelovic is. Why don't you >share that knowledge with us? :) > > > He accuses the Haskell community of not providing libraries... > >Two errors here: > >1. I didn't accuse anybody of anything. I was just curious about why people >aren't using Haskell and started to think about it. There's a saying among >Program Managers at Microsoft that "thinking is writing". I subscribe to >that. I often write about things I think about in order to explore the >issues. If I think other people might be interested in the end result, I >post it. > >2. I didn't say that the Haskell community has not provided the libraries. >I >said the Haskell community hasn't provided the libraries together with the >compiler in one standard distribution. I think that's needed in order to >lower the barrier to entry. > > > Perhaps there is *one* point worth mentioning: the necessity to > > publish papers about Haskell far from such journals as JFP or HOSC, > > but to try to reach DrDobbs etc. > >Funny. You said at the beginning of your message that there is "NOTHING" >serious there. :) > >Dejan >http://www.jelovic.com > > > >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com

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Re: constants and functions without arguments
by Tom Pledger 31 Mar '01

31 Mar '01

Andreas Leitner writes: : | The classic examlple for this is class POINT, which has an interface | like that: | -- | POINT | -- group 1 | x: DOUBLE | y: DOUBLE | -- group 2 | rho: DOUBLE | abs: DOUBLE | -- | Now, you can choose to either implement group 1 as attributes, or | group 2 and calculate the other one. With the uniform access | principle, which says that accessing attributes and functions with no | arguments happen in the same syntactic way, you can change the | implementaion without notice. No user of this class needs to know. | | I am to new to FP to say whether this is equaly important in | FP-languages, since the semantics are different (constants vs. | attributes and immutable values vs. objects), but for now I am just | currious wether it is possible theoretically. That uniformity of access can certainly be achieved in Haskell. Here's the Point example. I've done it with two constructors so as to get fewer floating point imprecisions, but some other possible representations (e.g. one with only the Polar constructor) would look identical outside the module. module Point(Point, cartesian, polar, x, y, r, theta) where -- data type with hidden constructors data Point = Cartesian Double Double -- corresponds to group 1 | Polar Double Double -- corresponds to group 2 -- proxy constructor functions cartesian x y = Cartesian x y polar r theta = Polar r theta -- attribute extraction functions x (Cartesian x y) = x x (Polar r theta) = r * cos theta y (Cartesian x y) = y y (Polar r theta) = r * sin theta r (Cartesian x y) = sqrt (x*x + y*y) r (Polar r theta) = r theta (Cartesian x y) = atan2 y x theta (Polar r theta) = theta

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Instances of Read and Show
by Ingo Sander 30 Mar '01

30 Mar '01

I have a question concerning the Read and Show classes. I have read the Haskell 98 report (section 6.3.3 The Read and Show Classes), but I still do not figure out how to make instances. I have a simple data type: data TVal a = Abst | Prst a I managed to define the function show, so that I can use it with the data type TVal instance (Show a) => Show (TVal a) where show Abst = "_" show (Prst x) = show x Signals> [Prst 1, Abst, Prst 2] [1,_,2] :: [TVal Integer] which is what I want to have. But how do I make a Read instance? I still do not understand the meaning of 'readsPrec' and 'readList' (and not of 'showPrec' and 'showList') either. Can somebody explain to me or give me a good reference so that I can make TVal an instance of the classes Read and Show. Thanks in advance for your help! Ingo Sander

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RE: "Lambda Dance", Haskell polemic, etc. on O'Reilly site
by Simon Marlow 30 Mar '01

30 Mar '01

> There are, perhaps good reasons for all these failures, but please > recognize them for what they are: failures to meet the needs of the > working programmer who just wants to get something done > (whether he/she > lives in YU, FR, JP, or US) > > I would love to be using Haskell for day to day programming work but I > can't at this time. Unless the community recognizes what is > required and > gets it done, I never will. There is one good reason that Haskell fails in these areas, and that's shortage of effort. We in the GHC team are actively trying to encourage our users to contribute: with an open CVS source tree, open development mailing lists, etc. We've had some good results (thanks to our developers!), but we need more. GHC is a large and complex system, and with trying to be all things to all people - a research vehicle / experimentation platform / production compiler, our developer resources are stretched a bit thin. I'm sure this goes for the other Haskell systems too. I see libraries as the biggest missing piece in the Haskell language. Let's face it, Joe Programmer isn't going to pass Haskell by just because it doesn't support a particular flavour of overlapping instance declarations. But he might if it doesn't have a networking library, or unicode support, or an XML parser. Please, join libraries(a)haskell.org. </rant> Cheers, Simon

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