- Haskell-Cafe - Haskell.org

Could not build win32 dll..
by Yakov ZAYTSEV 13 Oct '08

13 Oct '08

Hello, Sadly, I've found --mk-dll option unrecognized by latest stable GHC 6.8.3.. I'm new to win32 development How one can make win32 dll at the moment? I've successfully compiled Adder sources from example from section 11.5.4 of user guide I need to build dll to be called from foreign application The only way I see is to use MinGW's gcc which is shipped with GHC distrib to manually link everything GHC runtime needs Did I missed something? TIA -- Best wishes, Y

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Still stacking monad transformers
by Andrew Coppin 13 Oct '08

13 Oct '08

I am becoming extremely frustrated now. The task I want to perform is simple, yet I simply cannot make Haskell do what I want. I've given up hope of ever getting my program to handle infinite result sets. That means I can make do with just ListT. So I have the following monad: type MyMonad x = StateT MyState (ListT Identity) x Now I'm trying to run two computations, starting from _the same state_, and combine the two resulting lists. The trouble is, I am literally losing the will to live trying to comprehend the whinings of the type checker. The operation I'm trying to perform is perfectly simple; I don't understand why this has to be so damned *difficult*! >_< Any suggestions? I found that by using the brief and easily memorable construction "runIdentity $ runListT $ runStateT foo state" I can get at the result set for each action, and combine them. But nothing in hell seems to transform this from [((), MyState)] back into MyMonad ().

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Overlapping/Incoherent instances
by J. Garrett Morris 13 Oct '08

13 Oct '08

Hello everyone, As part of a project to formalize the theory of overlapping instances, I'm looking for examples of overlapping and incoherent instances and their usage. One such example would be the old version of the Monad Transformer Library, which used overlapping instances together with MonadTrans. Any other examples or suggestions would be greatly appreciated! Thanks, /g

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ANNOUNCE: Graphalyze-0.4 and SourceGraph-0.2
by Ivan Lazar Miljenovic 13 Oct '08

13 Oct '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I'd like to announce version 0.4 of my Graphalyze library [1] and 0.2 of my SourceGraph programme [2]. [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/SourceGraph This should fix the bugs reported by Gwern Branwen, Magnus Therning (thanks to Niklas Broberg for stating the correct version for Haskell-Src-Exts) and Christopher Hinson. No really new features are included in this release. I was planning on fixing this and releasing it sooner but - to utilise what seems to be a current meme [3] - "I accidentally my Gentoo" on Tuesday night and only fixed it yesterday. [3] http://encyclopediadramatica.com/I_accidentally_X Since I'm more awake now than I was when I made the initial release, here's a run-down of what SourceGraph is: SourceGraph is a programme designed to help you analyse the static complexity of your Haskell code when represented as a graph. At the moment, it does the following (M == for each module, I = for imports, C = the whole codebase): * Visualise it {M,I,C} * See a "collapsed" visualisation {M} * Proposed module/directory layout using two different algorithms {I,C} * See the "core" visualisation (recursively strip off roots/leaves) {M} * Calculate the Cyclomatic complexity [4] {M,I,C} * Root analysis (compare what's exported to what actually is a root) {M,I,C} * Determine how many components you have, to see if you should split {M,I,C} * Clique Analysis (find co-recursive functions) {M,C} * Cycle analysis (non-cliques) {M,I,C} * Chain detection (e.g. "straight-line" functions/imports) {M,I,C} [4] http://en.wikipedia.org/wiki/Cyclomatic_complexity Current limitations: * An automatic refactoring tool: SourceGraph gives *you* information on how you might want to possibly refactor your code. It's not smart: it can't tell that you've clumped functions foo and bar in the same module because they do similar things or because it's a utility module, even though they're not related. For automatic refactoring, see something like HaRe [5]. * SourceGraph ignore's "data-based" functions, i.e. record-functions and class/instance declarations, as it's too confusing (IMHO) which actual function you mean (if you see "show" being called, is it for Int, Double, or something else?). * Despite using Haskell-Src-Exts, some extensions (e.g. TH) are ignored, mainly because I have no idea how they work and nothing to test it on. GHC extensions should be supported (read the parser won't choke on them) though. * Reporting output is currently rather limited: - The report will be generated in a subdirectory called "SourceGraph" of the codebase directory; this is currently hardwired in. - It will produce an all-in-one html file report, with no fancy CSS magic to make it look pretty. Ideally, it would produce a split-file, and allow you to choose output format. - Large graphs are shrunk down to being a maximum of 15"x10". Ideally, I'd like to extend this later so that large graphs will have a shrunk version in the graph, which link to a larger version (note though that these graphs get very large very fast). - The output of individual function names, etc. could be improved. [5] http://www.cs.kent.ac.uk/projects/refactor-fp/hare.html SourceGraph can be installed with cabal-install. Once you've done so, you can analyse a cabalized library/application Foo as follows: $ SourceGraph /path/to/codebase/Foo.cabal Report generated at: /path/to/codebase/SourceGraph/Foo.html This has been written as part of my mathematics Honours Thesis, "Graph-Theoretic Analysis of the Relationships in Discrete Data". Since I've actually got to write the thesis up now, I won't be making any more releases for a while. After uni is over for the semester though, I hope to tidy it up and extend it. If you want to check the code out yourselves, there's also darcs repositories for Graphalyze [6] and SourceGraph [7]. [6] http://code.haskell.org/Graphalyze [7] http://code.haskell.org/SourceGraph/ Note that whilst Graphalyze is fully documented, etc., the internals of SourceGraph are a bit fugly (mainly due to time constraints). Enjoy! - -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) iEYEARECAAYFAkjyAacACgkQfEfFJ9JhvyiHEACfVVuRk2FR3ZQiJ6H18FFK/de/ sukAn0tuCLwqxmzlQvWicQKQ3qEJKC1K =HRUK -----END PGP SIGNATURE-----

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Re: [Haskell-cafe] Haskell in Artificial Intelligence
by Martin Hofmann 13 Oct '08

13 Oct '08

Hi Christos, We and a colleague from Japan use Haskell for Inductive Functional Programming, i.e. learn programs from examples. However, we just have started to port our program to Haskell: http://www.cogsys.wiai.uni-bamberg.de/effalip/ Susumu Katayama has already a Haskell library: http://nautilus.cs.miyazaki-u.ac.jp/~skata/MagicHaskeller.html More information about IP can be found here: http://www.inductive-programming.org/ What kind of survey are you doing? Do you have a pointer, too? Greetings, Martin

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Haskell on mobile platforms
by Janis Voigtlaender 13 Oct '08

13 Oct '08

Hi all, there were several discussions on this list about different implementations of Haskell running on the iPhone and other mobile platforms over the last three months or so. I would very much like to see the current state of what is and is not yet possible here reflected in the "Platforms" section of the upcoming edition of the Haskell Communities and Activities report. So please, if you have been working on getting Haskell to run on your phone, and even more so if you were successful, write a short HCAR entry about it. For further details, see: http://article.gmane.org/gmane.comp.lang.haskell.cafe/45967 Thanks, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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the ghc "reflection" thing?
by Galchin, Vasili 13 Oct '08

13 Oct '08

hello, Several months ago I saw on the wiki or maybe it was a discussion on mechanism to get the ghc compiler's state. I can't remember enough to ask even well. I know there is a wiki entry. Sorry ... I can only "hint" at this ... ?? Thanks, Vasili

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Constraints at construction
by Iain Barnett 12 Oct '08

12 Oct '08

If I were to create an object in C#, for instance, I could add code to the constructor that might limit the type further e.g. public class Car { string model; int wheels; public Car ( string model, int no_of_wheels ) { if ( no_of_wheels <= 2 ) { throw new Exception( "a car must have at least 3 wheels"); } this.model = model; this.no_of_wheels = no_of_wheels; } } or I could specify all sorts of things, like the size of an array could only be a certain length, or whatever. Similarly, when creating a column with SQL I'd be able to specify further constraints on the column than just it's type. I don't see how to do this with Haskell and the data keyword. Is there a tutorial someone could point me to, or an explanation of this? Or is it that I have to wrap the creation in an accessor function that checks the inputs first? type Model = String type Wheels = Int data Car = Car Model Wheels car_maker model wheels = if wheels <= 2 then error ... else Car model wheels ? Most of my programming career (if you can call it that:) has been primarily with C# and SQL, and perhaps this heady mixture of OOP and hacked-functional is confusing me! Iain

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Re: [Haskell] Abusing quickcheck to check existential properties
by Sterling Clover 12 Oct '08

12 Oct '08

My understanding is that SmallCheck and lazy SmallCheck[1] are much better suited to handle existential properties, and indeed have combinators especially for that task. --Sterl. [1] http://www-users.cs.york.ac.uk/~mfn/lazysmallcheck/ smallcheck.pdf, http://hackage.haskell.org/cgi-bin/hackage-scripts/ package/smallcheck, http://hackage.haskell.org/cgi-bin/hackage- scripts/package/lazysmallcheck On Oct 12, 2008, at 1:38 PM, Norman Ramsey wrote: > I recently used QuickCheck to check on some calculations for image > compression. > (I love exact rational arithmetic!) But I thought only to check for > inverse properties, and I realized afterward I had failed to check for > ranges. For example I should have checked that > > boundedB block = -1 <= b && b <= 1 > where Cos a b c d = cos_of_block block > > which turns out to be correct. But actually my calculations were > wrong, and the real bounds on b are not +/- 1 but rather +/- 0.5, so I > might equally well have passed a more stringent test. It's quite > embarrassing as I have only 5 bits of precision to represent b, and > throwing away a bit on values that don't exist is not the best idea I > have had recently. > > What I would really like to do is write some combinators for interval > checking that say > > * It is a *universal* property that for *every* input, the output > lies within the stated interval. > > * It is an *existential* property of *some* input that the output > lies close to the ends of the stated interval. > > But how do I use QuickCheck to check an existential? > I realize I could run > > boundsNotAchieved block = -0.9 <= b && b <= 0.9 > where Cos a b c d = cos_of_block block > > and then if the test of boundsNotAcheived fails, my test passes > (by exists x : P(x) iff not forall(x) : not P(x)). > > But if I set up a test suite in which some tests are supposed to fail > and others are supposed to succeed, I will never keep track of which > is which. I would like to build an existential test. Is it > sufficient for me to write > > boundsAchieved block = expectFailure (-0.9 <= b && b <= 0.9) > where Cos a b c d = cos_of_block block > > and then run 'quickCheck boundsAchieved'? > > In the long run I'd love something like > > fillsIntervalWithin :: (Num a, Ord a, Arbitrary a) => (a, a) -> a > -> a -> Property > > with the idea that I want to test the partial application > > fillsIntervalWithin (lo, hi) epsilon > > and have the test succeed if every input x satisfies lo <= x <= hi > and if some input x satisfies not (lo + epsilon <= x <= hi - epsilon). > > I'm betting someone on this list has already thought about similar > problems and can advise me. (Because I have yet to write the > specialized instance declaration for Arbitrary that guarantees the > numerical invariants of the inputs, I have yet to test any of the > examples in this email.) > > > Norman > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

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Arch Haskell News: Oct 12 2008
by Don Stewart 12 Oct '08

12 Oct '08

News about Haskell on Arch Linux http://archhaskell.wordpress.com/2008/10/12/arch-haskell-news-oct-12-2008/ Arch now has 624 Haskell packages in AUR. That’s an increase of 15 new packages in the last 7 days. Planning is also underway for the GHC 6.10 release, and the 6.10 release candidate is in testing. Noteworthy * cabal-install-0.6.0: “The command-line interface for Cabal and Hackage.” * haskell-cabal-1.6.0.1: “A framework for packaging Haskell software” * haskell-bytestring-0.9.1.3: “Fast, packed, strict and lazy byte arrays with a list interface” * haskell-transactional-events-0.1.0.0: “Transactional events, based on Concurrent ML semantics” Full details on the site.

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