November 2009 - Haskell-Cafe

virus/trojan in bamse package?
by Daniel van den Eijkel 08 Nov '09

08 Nov '09

hi, my Avira antivirus program says that there is a trojan in the bamse-0.9.5 package. I downloaded the hackage-torrent a week ago, and Avira says "TR/Crypt.CFI.Gen" is in bamse. To be sure, I downloaded bamse-0.9.5 from hackage today, and now avira says less specificly that there are "some viruses and/or unwanted programs" inside. Since I have some trojan trouble for a few days now, bamse might be the reason for that, but I am not sure. Maybe it is a false alarm, I can't determine this. (bamse is a framework for building Windows Installer, so it might contain code that looks like a virus or alike wrongly?) Does anybody know if this is really a virus/trojan? Best regards, Daniel

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Small Japi binding for GHC
by Philippos Apolinarius 08 Nov '09

08 Nov '09

JAPI is by far my favorite GUI library. Since every machine has Java RE installed, JAPI offers GUI with a very small footprint. Besides this, it is very easy to code, and delivers GUI programs that are hardly larger than console applications. I use Jorlano's version of JAPI, coded for Java 2, which is very cool. I study Computer Science in a small college, and I always handle my homework in JAPI. When I took functional programming one year ago, the language chosen by Professor Lopes was Clean, that has a GUI. However, I feel that JAPI is much easier than ObjectIO; therefore, I used JAPI for my homework. So, I searched for JAPI bindings for Haskell. The only library I found was something called Small Japi binding for GHC. The package is incomplete, and bug ridden. I wonder whether the author fixed the bugs, completed the package, and added more examples. I would appreciate if people could send me links to a complete Japi binding for GHC. In the mean time, I fixed the bugs of Small Japi Binding, and added a few important components (j_textfield, j_settext, j_gettext, j_button, etc.) Of course, a link to a more recent version of the official binding will save me a lot of work. __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/

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Re: [Haskell-cafe] Haskell image libraries
by Andrew Coppin 08 Nov '09

08 Nov '09

Max Rabkin wrote: > On Sun, Nov 8, 2009 at 5:09 PM, Max Rabkin <max.rabkin(a)gmail.com> wrote: > >> On Sun, Nov 8, 2009 at 4:58 PM, Andrew Coppin >> <andrewcoppin(a)btinternet.com> wrote: >> >>> Try AC-EasyRaster-GTK. >>> >> Thanks, I'll give that a try >> > > Having downloaded it, I must admit I was a bit put off by seeing things like > init_system :: IO () > process_event :: IO () > wait_event :: IO () > main_loop :: IO () > in an image library. > > But it's the best we've got right now, so I've got a couple questions: > is it safe to call init_system more than once? And what do I need the > event-handling functions for, if anything? > If all you want to do is load/save images and do pixel I/O on them, you can completely ignore process_event, wait_event, main_loop, etc. All you need to do is make sure you call init_system at the start of your program. (You see the ib_display function? If you want *that* to work properly, you need to run the GTK event loop, which is what these event-related functions are all about. If you're not trying to display the image on screen, you can ignore all that.) I should probably make the documentation clearer...

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Memoizing in parallel
by Pierre-Etienne Meunier 08 Nov '09

08 Nov '09

Hi, I'm designing an algorithm that uses dynamic programming. I've written it with an array, and it works, but it is still very slow and needs way too much memory. Then I realized that the array was very sparse (at most a O(\sqrt(n)) of its size is actually used). Now I want to rewrite it with a Data.Map, but since I do not know a priori what the keys are, I need a mutable ref somewhere. Which is fine, but... the array solution allowed me to explore the subsolutions in parallel with Control.Parallel, and use items already evaluated by other threads in the array, while an STRef forbids it. Can someone know how to do it (outside IO, and without using unsafePerformIO, of course) ? Thanks Pierre-Etienne Meunier

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Names for properties of operators
by Neil Brown 08 Nov '09

08 Nov '09

Hi, We have names for properties of operators/functions. For example, if this holds: a % b = b % a for some operator %, we say that % is commutative. Similarly, if this holds: (a % b) % c = a % (b % c) we say that % is associative. Is there a name for this property, which I'm numbering 1, (where (%) :: a -> b -> b; i.e. the operator is potentially, but not necessarily, asymmetrically typed): 1: a % (b % c) = b % (a % c) For example, `Set.insert` obeys 1 for any values of a, b and c. (Any operator that is both associative and commutative automatically satisfies this property, but this property can be satisfied without the operator being either of those.) Given this property, we could prove useful follow-on results, such as: foldr (%) x ys = foldr (%) x (reverse ys) foldr (%) x ys = foldl (flip (%)) x ys The property 1 effectively states that the far-right hand element in a chain of such operators is special, but the ordering of everything to the left of it doesn't matter. One could conceive of a mirror property (where (%) :: a -> b -> a): 2: (a % b) % c = (a % c) % b If (%) obeys 1, flip (%) obeys 2 (and vice versa). I think these properties are useful -- I'd like to know if they have names already to describe them by. A similar property of two relations (where ((%), (~)) :: (a -> b -> b, c -> b -> b) ) would be: 3: a % (b ~ c) = b ~ (a % c) with mirror version (and adjusted types): 4: (a % b) ~ c = (a ~ c) % b Do these have a name? As an example, `Set.insert` and `Set.union` obey property 3 for all values of a, b and c. There are also symmetrically-typed examples of these operators, but the Set operations are easy and familiar. Thanks, Neil.

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Fwd: [Haskell-cafe] Is () a 0-length tuple?
by Pasqualino "Titto" Assini 08 Nov '09

08 Nov '09

The syntax is similar, but what else is? In JavaScript there is a "null" value, that is the only value of the null type. Isn't () the same thing? The only value of the unary type? Best, titto 2009/11/6 John Dorsey <haskell(a)colquitt.org>: >> In what sense () is a 0-length tuple? > > In what sense isn't it? > > Data.Tuple is much to narrow to be of any use here. () is in at least most, > if not all, of the type classes that tuples are in. The syntax is > strikingly similar. > > If you ask me, it walks/quacks/smells like a duck, so it's a duck. > > Regards, > John > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Pasqualino "Titto" Assini, Ph.D. http://quicquid.org/

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Nice addition to Foreign: castAny
by Maurício CA 07 Nov '09

07 Nov '09

This could be beside castPtr, castCharToCChar etc. ---- castAny :: (Storable a, Storable b) => a -> b castAny = unsafePerformIO . genericCast where genericCast :: (Storable a, Storable b) => a -> IO b genericCast v = return undefined >>= \r -> allocaBytes (max (sizeOf v) (sizeOf r)) $ \p -> poke p v >> if False then return r else peek (castPtr p) ---- GHCi: > let a = -1000 :: Int16 > castAny a :: Word16 --> 64536 > castAny a :: Ptr () 0xb4c2fc18 > castAny (castAny a :: Ptr ()) :: Int16 -1000 > let b = pi :: CLDouble > b 3.141592653589793 > castAny b :: CInt 1413754136 > castAny b :: Ptr () 0x54442d18 > castAny b :: CFloat 3.3702806e12 > castAny b :: Int8 24 At minimum, this is safer than 'unsafeCoerce'. What do you think? Best, Maurício

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Master's thesis topic sought
by Matus Tejiscak 07 Nov '09

07 Nov '09

Hello, -Cafe, I'm looking for an interesting topic to hack on in my thesis. The thesis should be rather "theoretical"/abstract (writing a mail client in Haskell is not, for example), dealing with FP or related fields. I've had a few (blurry) ideas, ranging from investigating (possibilities for) Haskell extensions, to zygohistomorphic prepromorphisms, but nothing concrete, possibly because I'm not familiar with these areas enough to see what could be done -- which brings up a question whether it is a good idea to even try hacking on a topic like this. However, I'm eager to learn so if you have a topic you'd need somebody to work on, or just an interesting (or maybe even an uninteresting) idea, i'd be grateful for suggestions. :) Thanks, Matus

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RE: Haskell as a first language?
by Simon Peyton-Jones 07 Nov '09

07 Nov '09

Haskell is a great language! Check out haskell.org. I'm ccing the Haskell Cafe which is read by many people better qualified to answer your question than me. (Since I've been working on Haskell for many years, I am not well qualified to say how it seems to a beginner.) S | -----Original Message----- | From: Charles Turner [mailto:charlie.h.turner@googlemail.com] | Sent: 11 July 2009 22:52 | To: Simon Peyton-Jones | Subject: Haskell as a first language? | | I'll make this short! Do you think Haskell is a good language to start | with? I am brand new to programming and have been using Scheme, some of | my peers suggest I should use Haskell. It seems "professional" to me. | Has features that a beginner should not worry about. What would you | suggest. (I'm not worried about bias) | | Thank you very much for your time. | | Charles Turner.

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Re: [Haskell-cafe] Monad Comprehensions
by Günther Schmidt 07 Nov '09

07 Nov '09

Hello Ryan, thank you for your email, it's much appreciated. In summary I'd like to say that in the 2 years that I have been using Haskell I have managed to get a good working knowledge of the language which allows me to construct programs that are concise, correct and without greater redundancy. However I also realize more and more that in order to harness the full power of Haskell I need to gain a greater understanding of the underlying math and go beyond mechanical application. It is only lately that I am recognizing the significance of the often used term "abstraction". Certainly this is pointed out in the Haskell world often enough, but hey I'm a noob. For someone like me this is not immediately apparent. I mean there seems to be almost no end of what I still have to learn, barely scratching the surface, tip of the iceberg, that sort of thing. DSLs are apparently *the* way to go in the abstraction department. Oleg & Co's "Finally Tagless" style is my favorite when it comes to implementation. It bears this simplicity and elegance that I have come to recognize and what to me *is* "mathematical". Not all of my dealings in Haskell are goal-oriented. Well there is that of course, but mostly there are all these shiny beautiful things. I get distracted quite a lot too. Trying to dig deeper on the subject of Dan Piponis video for instance. BTW I found Phil Wadlers paper "Comprehending Monads" quite helpful here. I also find my focus of interest on the topics of articles on haskell-cafe shift. Before I would basically skip "deep stuff", ie. theoretical / abstract topics, and focus on technical details. Now I focus much more on "mathematical" issues despite the fact that I can barely understand them, it'll come to me eventually. Because now I consider the mathematical discussions far more fundamental and more "lasting". Technical details I can look up as the need arises and they will likely change over time, so no need to bother with them beforehand, they may be out-dated when you need them. Mathematical ones won't, they'll be good forever. Well that's my 2 cents for now. Günther Am 07.11.2009, 09:37 Uhr, schrieb Ryan Grant <rgrant(a)rgrant.org>: > 2009/11/1 Günther Schmidt <gue.schmidt(a)web.de>: >> In short, I'm truly lost. If anyone else, with roughly the same starting >> point as me, has found their way through this jungle I'd certainly >> appreciate some tips. In particular I wonder if someone has been able to >> follow what Dan demonstrates in this video, or was it a jaw-dropping >> experience for everyone else just as me? > > Günther, i have been lurking in H-cafe, and enjoying your pace of > exploration. AFAIK, you are trying to understand how to make > excellent languages using Haskell. you are asking some practical > questions that i find relevant to my own journey into Haskell. > > "best practices" for specifying a DSL are not well agreed upon, > partly due to recent advances. i sense this problem in your > question and in the newsworthiness of Dan's talk, (which i also > enjoyed with a jaw-drop). > > i encourage you to say exactly what you want from your DSL (do it > again, if you have already). > > i hope to follow your footsteps, maybe not in exact DSL needs, > but in path of discovery. >

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