- Haskell - Haskell.org

Re: "Job Adverts" on haskell.org
by C.Reinke 08 Feb '01

08 Feb '01

> Haskell.org has a page "Job Adverts". > http://www.haskell.org/jobs.html I like the new scope. But to minimise confusion of people looking for paid jobs (which now exist), why not reflect the explanations in the first paragraph in the page structure? Two main sections should be sufficient, with the current sections falling naturally into one of the two: A Adverts for positions involving Haskell - Positions in Academia - Positions in Industry B Descriptions of jobs that need doing - new libraries/tools needed - medium-level GUI library needed - new caretakers for existing libraries/tools needed -.. - calls for contributions - donate your programs for testing and benchmarking -.. - calls for cooperations - project X.. (change order if necessary;-) > If you are working on some Haskell project and could > do with some help, then advertise here (and on the Haskell mailing > list). Even more importantly: If you built some Haskell software and > unfortunately no longer feel able to maintain it, then please advertise > here (and on the Haskell mailing list) for new people to take it over > and give it a home. Thus we may alleviate the problem of the large > number of Haskell tools and libraries that are half complete and no > longer maintained. Excellent ideas, especially the focus on keeping existing things in good working order by passing them on to new caretakers! Some aspects of the Haskell wish list might overlap with aspects of the suggested section B? I would suggest to keep the two linked to each other, with the wish list focusing on would-be-nice-to-have, and the task list focusing on needs-to-be-done and is-going-to-be-done. So that ideas might start on the wish list, but move to the task list when they become more concrete (either there exists a concrete customer, or a project is forming with the first names of contributors already written down or work having started, or a current maintainer is looking for someone to take over). Cheers, Claus

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ANNOUNCE: hmake-2.02
by Malcolm Wallace 08 Feb '01

08 Feb '01

We are pleased to announce the release of version 2.02 of 'hmake', the intelligent compilation manager for Haskell compilers. http://www.cs.york.ac.uk/fp/hmake/ ftp://ftp.cs.york.ac.uk/pub/haskell/hmake/ What's new in 2.02? ------------------- This is mainly a bugfix release. * Improved error-reporting. When a module cannot be found, it now shows where the demand for the module arose, and which directories were searched. * Added knowledge of extended file suffixes like .p.o, .T.o, and .T.hi. * Fixed a bug in the generation of Makefile dependencies in the presence of a -I option. * Ghc's options "-syslib n" and "-package n" no longer need to be enclosed in double quotes to protect them from hmake. Regards, Malcolm

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please help me
by FAIZAN RAZA 08 Feb '01

08 Feb '01

Hello Please help me to solve this questions Question Cartesian Product of three sets, written as X x Y x Z is defined as the set of all ordered triples such that the first element is a member of X, the second is member of Y, and the thrid member of set Z. write a Haskell function cartesianProduct which when given three lists (to represent three sets) of integers returns a list of lists of ordered triples. For examples, cartesianProduct [1,3][2,4][5,6] returns [[1,2,5],[1,2,6],[1,4,5],[1,4,6],[3,2,5],[3,2,6],[3,4,5],[3,4,6]] Please send me reply as soon as possible Ok I wish you all the best of luck

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Re: Revamping the numeric classes
by Ketil Malde 08 Feb '01

08 Feb '01

Bjorn Lisper <lisper(a)it.kth.se> writes: >> Two interpretations of a code are "correct", but one is "more correct" >> than the other. > It is quite similar in spirit to the concept of principal type in > Hindley-Milner type systems. An expression can have many types but > only one "best" (most general) type in that system. Now, I'm not any kind of expert on this, but isn't the most general HM type one that encompasses the others, and *not* one out of a set of ambigous (and mutually exclusive) types? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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Re: Fundeps and quantified constructors
by anatoli 08 Feb '01

08 Feb '01

--- Tom Pledger <Tom.Pledger(a)peace.com> wrote: > anatoli writes: > : > | The same error message is given for > | > | > data Foo a = (Eq b) => MkFoo b > > Since the type variable a is orphaned, how about reducing it to this? > > > data Foo = forall b . Eq b => MkFoo b This is possible (the semantics is different of course). What I want to do is, given a multi-parameter context, orphan one type variable leaving the other intact, and that's not possible now. I can only orphan all or preserve all. > > so that MkFoo :: Eq b => b -> Foo > > | I don't know whether this is intended behaviour; IMHO > | it should be treated identically to > | > | > data Foo a = MkFoo (Eq a => a) > > Isn't the Foo-ed a hidden by the Eq-ed a in this example too? i.e. > > > data Foo = MkFoo (forall a . Eq a => a) It appears that both examples are wrong, or at least Hugs thinks so. The first MkFoo happily accepts any type, not just of class Eq: Main> :t MkFoo head MkFoo head :: Foo ([a] -> a) The second accepts nothing of interest: Main> :t MkFoo 'a' ERROR: Inferred type is not general enough *** Expression : 'a' *** Expected type : Eq a => a *** Inferred type : Eq Char => Char Hm... The more I experiment with this, the less I understand. It seems that the only correct place to put the quantifier is before the data constructor, and the context may go either before the type constructor or after the quantifier. This is very unfortunate. How can I correctly write something to this effect: > data Quick a = Eq a => Unsorted [a] > | Ord a => Sorted (Tree a) ??? Regards -- anatoli __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail - only $35 a year! http://personal.mail.yahoo.com/

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FME 2001--Register Now!
by Pamela Zave 08 Feb '01

08 Feb '01

*************************************************************************** * FORMAL METHODS EUROPE 2001 * * "Formal Methods for Increasing Software Productivity" * * * * 12-16 March, Berlin, Germany * * * * Come to the world's leading conference on application of formal methods * * in the software industry! * *************************************************************************** The programme of tutorials, workshops, invited lectures, papers, and tool exhibitions is available on the symposium website: www.informatik.hu-berlin.de/top/fme2001 Please hurry -- 9 February is the deadline for early registration and guaranteed reservations at the conference hotel! Registration and hotel reservation forms are also available on the symposium website. *************************************************************************** * Early Registration Deadline is 9 February * ***************************************************************************

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'Convertible' class?
by Dylan Thurston 08 Feb '01

08 Feb '01

In thinking about various issues with the numeric classes, I came up with the following question: Is there a problem with having a class 'Convertible' as follows? class Convertible a b where convert :: a -> b So, e.g., fromInteger and fromRational could be replaced with convert. (But if you did the same thing with toInteger and toRational as well, you run into problems of overlapping instances. I think there are good semantic reasons for this: fromInteger and fromRational can be defined in terms of the basic +,*,zero,one, while toInteger and toRational rely on details of the representation.) What do people think of this idea in general? Perhaps a better name would be 'Subtype'? Note that "convert . convert" would be up there with "show . read" as an ambiguous term. Best, Dylan Thurston

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Re: Fundeps and quantified constructors
by nubie nubie 07 Feb '01

07 Feb '01

--- Tom Pledger <Tom.Pledger(a)peace.com> wrote: > That line of reasoning establishes that e is constrained on the right > hand side of the "=". However, it's still bound (by an implicit > "forall e") on the left hand side of the "=". The problem is that e > can leak details about c to parts of the program outside the "forall > c". It's still a problem if you remove the "| c -> e" fundep. (1) How can it leak? (2) Why is this a problem? > A more common use of a "Collection c e | c -> e" class is: > > data SomeCollection e = --some data structure involving e > > instance SomeContext e => Collection (SomeCollection e) e where > --implementations of empty and put, for the aforementioned > --data structure, and entitled to assume SomeContext > > Is that collection type polymorphic enough for your purposes? You mean, like instance Collection [a] a where empty = [] put = flip (:) ? Yes, of course this usage is intended. But then I want a type that can hold any collection of a, for given a. Collection is a class, not a type, and I need a type. -- anatoli __________________________________________________ Get personalized email addresses from Yahoo! Mail - only $35 a year! http://personal.mail.yahoo.com/

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GHC 4.08.2: the release dribbles on
by Reuben Thomas 07 Feb '01

07 Feb '01

As of now, several things have been corrected: 1. Sparc HC files are available. 2. The Windows link actually points to the 4.08.2 release, not the 4.08.1 release. 3. RedHat 6 i386 RPMs are available. -- http://sc3d.org/rrt/ | computation, n. automated pedantry

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New PhD Positions in Computing Science, Gothenburg, Sweden
by Reiner Haehnle 07 Feb '01

07 Feb '01

Please pass on to interested students. Apologies for multiple copies. --------------------------------------------------------------------- New PhD Positions (DEADLINE 1 March 2001! See "How to apply" below.) Department of Computing Science, Chalmers University of Technology & University of Gothenburg Sweden The Department has about 70 researchers, half being faculty members and half PhD students. Our focus is on programming logic, type theory, functional programming, formal methods, distributed and concurrent systems, security, algorithms, bioinformatics, human computer interaction, and computational linguistics, but research is not restricted to these topics. For more information, see http://www.cs.chalmers.se/Cs/Research. PhD positions are for 5 years. There is no tuition fee. A PhD position is a regular job with social benefits; the salary amounts currently to about 16700 SEK per month in the first year (the exact amount depends on teaching duties, usually 20% of your time). Knowledge of Swedish is not a prerequisite for application. English is our working language for research. Both Swedish and English are used in undergraduate courses. Half of our researchers and PhD students are native Swedes; the rest come from more than 20 different countries. Applicants must have a very good undergraduate degree in Computing Science or in a related subject with a strong Computing Science component. They must also have a strong interest in doing research. You may also apply if you have not yet completed your degree, but expect to do so by September 2001. You are also invited to apply for our new International Master's Programme in Dependable Computer Systems, which can help you to obtain the necessary qualification (see http://www.cs.chalmers.se/Cs/Education/dcs/) The School especially welcomes female applicants. How to apply ------------ First, immediately register your intention to apply using the electronic application form on the WWW via http://www.md.chalmers.se/Jobs/PhD/phd-01-en.thtml The full application should contain 1 A letter of application, listing specific research interests 2 A curriculum vitae 3 Attested copies of degrees and other certificates 4 Copies of relevant work, for example dissertations or articles, that you have authored or co-authored 5 A description of: a previous teaching experience, documented, if any b previous PhD studies, also in other subjects. State financial support for these, if any c previous work experience 6 Letters of recommendation from your teachers or employers If you have financial support of your own (industry job, grant, etc.), please state this fact clearly. It will increase your chances to be accepted considerably, because you need not compete for the limited number of fully financed positions. Send your application (paper mail) to Section for Mathematics and Computer Science Chalmers University of Technology 412 96 Gothenburg Sweden to arrive by 1 March 2000. You will know the result of your application by 1 May 2000.

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