Re: [Haskell-cafe] circular imports
That definitely makes more sense On 07/09/2010 3:06 PM, Daniel Peebles pumpkin...@gmail.com wrote: I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had the time or inclination to make it resolve circular dependencies automatically, and not an intentional design decision to encourage good design. On Tue, Sep 7, 2010 at 6:51 AM, Mathew de Detrich dete...@gmail.com wrote: I had the same is... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] circular imports
On 7 September 2010 16:09, Mathew de Detrich dete...@gmail.com wrote: That definitely makes more sense Well, the report (section 5.7) says you're allowed to request extra info for mutually recursive modules... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] circular imports
I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had the time or inclination to make it resolve circular dependencies automatically, and not an intentional design decision to encourage good design. Indeed. I’ve added some notes here http://hackage.haskell.org/trac/ghc/ticket/1409#comment:37 Simon From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Daniel Peebles Sent: 07 September 2010 06:06 To: Mathew de Detrich Cc: Ivan Lazar Miljenovic; haskell Subject: Re: [Haskell-cafe] circular imports I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had the time or inclination to make it resolve circular dependencies automatically, and not an intentional design decision to encourage good design. On Tue, Sep 7, 2010 at 6:51 AM, Mathew de Detrich dete...@gmail.commailto:dete...@gmail.com wrote: I had the same issue zonks ago, and I resorted to using the hs-boot file method as well (which worked fine) Which I guess brings me to my second point, is this something that GHC should do automatically when it sees circular dependencies? When I asked about it earlier on #haskell, I was told that its better that way because it discourages making bad design through circular dependencies (yet in my case and I assume the other cases as well, not using the hs-boot method would have made the design much worse). Are there any cases in particular where people would be encouraged to make interface design with circular dependencies (and that design be deemed as horrible) as opposed to what seems to be more realistic case where circular dependencies rarely crop up, and when they do they actually make the design better? On Tue, Sep 7, 2010 at 1:48 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.commailto:ivan.miljeno...@gmail.com wrote: On 7 September 2010 03:44, Edward Z. Yang ezy...@mit.edumailto:ezy...@mit.edu wrote: Excerpts from Evan Laforge's message of Mon Sep 06 13:30:43 -0400 2010: I feel like the circular imports problem is worse in haskell than other languages. Maybe because there is a tendency to centralize all state, since you need to define it along with your state monad. But the state monad module must be one of the lower level ones, since all modules that use it must import it. However, the tendency for bits of typed data to migrate into the state means it's easy for it to eventually want to import one of its importers. And the state monad module gets larger and larger (the largest modules in my system are those that define state monads: 1186 lines, 706 lines, 1156 lines---the rest tend to be 100--300 lines). I have used hs-boot files to this effect. I separated data and functionality, and typeclasses, which must be in the same module as data or are considered orphaned, get definitions via a circular import. I'm just getting to the point where I have a similar problem. I was thinking about splitting instances off from the classes (and telling GHC to not worry about orphaned instances for the instance-only modules) but then realised that some instance declarations would be circular as well, so I have to either use hs-boot files, define everything in one big module and then re-export them in ways that make sense or define all instances in one big module (at least for those types which have circular deps among instances) and re-export accordingly. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.commailto:ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.comhttp://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.orgmailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.orgmailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Paralelism and Distribution in Haskell
Mathew de Detrich deteego at gmail.com writes: Haskell is still by far one of the best languages to deal with concurrency/parallelism. Sure, I fully agree. I am using concurrency (with explicit forkIO, communication via Chan) a lot (my Haskell application controls several external constraint solvers). For parallelism, I'm just missing some benchmark code that I can run on my machine (i7 CPU, GTX 295 GPU, ghc-6.12.3) more or less out-of-the-box and that will impress my students and myself. (That is, get a speed-up of 8, or 480, without the program looking 8 times (or 480 times) more ugly...) - Johannes. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: RE: [Haskell-cafe] circular imports
Thanks for the clarification On 07/09/2010 5:30 PM, Simon Peyton-Jones simo...@microsoft.com wrote: I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had t... Indeed. I’ve added some notes here http://hackage.haskell.org/trac/ghc/ticket/1409#comment:37 Simon *From:* haskell-cafe-boun...@haskell.org [mailto: haskell-cafe-boun...@haskell.org] *On Behalf Of *Daniel Peebles *Sent:* 07 September 2010 06:06 *To:* Mathew de Detrich *Cc:* Ivan Lazar Miljenovic; haskell *Subject:* Re: [Haskell-cafe] circular imports I was under the impression that the main reason GHC requires .hs-boot files is that nobody has ... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Restricted type classes
On Tuesday 07 September 2010 05:22:55, David Menendez wrote: On Mon, Sep 6, 2010 at 10:22 PM, wren ng thornton w...@freegeek.org wrote: On 9/6/10 1:33 PM, David Menendez wrote: For that matter, can you even describe what pure is intended to do without reference to* or join? As already stated: fmap f . pure = pure . f That's pretty general. For lists, the functions having that property include const [], \x - [x,x], and repeat. In fact, I think *every* appropriately-typed function satisfies that law. Does anyone know of a counter-example? class Functor f = Pointed f where point :: a - f a -- satisfying fmap f . point = point . f notQuitePure :: Pointed f = a - f a notQuitePure _ = point undefined fmap (const True) . notQuitePure = point . const True But I don't see how to violate that law without introducing undefined on the RHS. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Grempa 0.1.0, Embedded grammar DSL and LALR parser generator
Looks like Applicative style. This is good, even while I don't really know why we are seeing @ and # instead of $ and *. How does Grempa compare with other parsing libraries/tools, such as Parsec, Attoparsec and Happy, with regard to ease of use and performance? Cheers! =) -- Felipe. Yes, it is indeed in applicative style. The reason for @ and # is that the functions have slightly different constraints to them, compared to the Applicative equivalents. The arguments passed to the function have to be instances of the ToSym class, which converts terminals and non-terminals to symbols. This allows writing the grammars in the way seen above (Plus @ e # '+' # t) instead of something like Plus @ nont e # tok '+' # nont t. I have yet to do any library comparisons on performance, but it should be faster than monadic combinator style libraries, as it does not have the exponential corner-cases that those parsers can have. It is also easier to write the grammars in Grempa's BNF-like syntax where left-recursion is permitted. Some comparison benchmarks would be interesting though, and I will look into it in the future. I have already done some profiling to eliminate the worst deficiencies of Grempa, but there is definitely room for improvements still. The library does not do lexing for you, which some of the other libraries have support for, which can make it harder to use. A plus for me (compared to Happy) is that you do not have to run an external program every time your grammar has changed, but can instead just recompile your project. I'm glad to see some interest in the project! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Paralelism and Distribution in Haskell
On 07/09/2010, at 6:11 PM, Johannes Waldmann wrote: Mathew de Detrich deteego at gmail.com writes: Haskell is still by far one of the best languages to deal with concurrency/parallelism. Sure, I fully agree. I am using concurrency (with explicit forkIO, communication via Chan) a lot (my Haskell application controls several external constraint solvers). For parallelism, I'm just missing some benchmark code that I can run on my machine (i7 CPU, GTX 295 GPU, ghc-6.12.3) more or less out-of-the-box and that will impress my students and myself. (That is, get a speed-up of 8, or 480, without the program looking 8 times (or 480 times) more ugly...) The matrix-matrix multiplication benchmark from the Repa library does this. Check out http://www.cse.unsw.edu.au/~benl/papers/repa/repa-icfp2010.pdf http://hackage.haskell.org/package/repa http://hackage.haskell.org/package/repa-examples Though be warned you must use a recent GHC head build to get good performance. After GHC 7.0 is out (in a few weeks) we'll be able to release a properly stable version. Note that speedup is an important consideration, but not the end of the story. It's harder to find a benchmark that displays all of nice code + speedup + good absolute performance. The first and last of these tend not to be friends. Ben. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Paralelism and Distribution in Haskell
2010/9/7 Ben Lippmeier b...@ouroborus.net: Though be warned you must use a recent GHC head build to get good performance. After GHC 7.0 is out (in a few weeks) we'll be able to release a properly stable version. Pardon a probably stupid question, but did I miss something ? http://hackage.haskell.org/trac/ghc/roadmap David. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Paralelism and Distribution in Haskell
2010/9/7 David Virebayre dav.vire+hask...@gmail.com: 2010/9/7 Ben Lippmeier b...@ouroborus.net: Though be warned you must use a recent GHC head build to get good performance. After GHC 7.0 is out (in a few weeks) we'll be able to release a properly stable version. Pardon a probably stupid question, but did I miss something ? http://hackage.haskell.org/trac/ghc/roadmap This is not stupid, but yes you missed something :) http://www.reddit.com/r/haskell/comments/dad6j/unless_theres_a_major_hiccup_itll_be_in_ghc_70/ Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Paralelism and Distribution in Haskell
This is not stupid, but yes you missed something :) http://www.reddit.com/r/haskell/comments/dad6j/unless_theres_a_major_hiccup_itll_be_in_ghc_70/ Oh, I saw that thread, but at the time it had vrey few comments, so I definately missed something ! Thanks ! David. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Restricted type classes
2010/9/7 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com 2010/9/7 Gábor Lehel illiss...@gmail.com: *That said*, I actually have nothing at all against splitting the 'a - f a' method out into a separate class if you think it's useful, whether you call it Pointed or something else. (And `class (Pointed f, Functor f) = PointedFunctor f` is sort of cute.) It might be cute, but until we get class aliases [1] this results in yet another class to make your data type an instance of, and what's more it's one that doesnt' even give you anything. I think it makes much more sense to have Functor, Pointed and (Functor f, Pointed f) = Applicative f rather than a useless intermediary class. If, however, we could get class aliases _for free_ (i.e. something like class alias PointedFunctor f = (Functor f, Pointed f) for which all instances of Functor and Pointed are automatically instanced of PointedFunctor), then I can see that as being something nice to have. I agree completely. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Oracle stored procedures
Are there any Haskell libraries that can call stored procedures in Oracle? I've been looking at Takusen which I like, but I can't find a way to call a stored procedure. Thanks Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Oracle stored procedures
2010/9/7 Peter Marks pe...@indigomail.net: Are there any Haskell libraries that can call stored procedures in Oracle? I've been looking at Takusen which I like, but I can't find a way to call a stored procedure. Don't you need to execute a SELECT query that calls the procedure, as in select my_procedure(parameter) Not sure though, I've never used stored procedures. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Restricted type classes
From: Stephen Tetley stephen.tet...@gmail.com On 6 September 2010 20:18, John Lato jwl...@gmail.com wrote: Can you give an example of a Functor that doesn't have pure? I think it's Pointed Functors which are useful; not Functor by itself. Strictly speaking is Pair one? The current implementation tacks on monoid. Interesting example. I tend not to like implementations which rely on bottoms, so I think I'd agree. In a similar spirit, I would propose Data.Vector.Unboxed.Vector as a Pointed Functor (modulo element restrictions) which is not Applicative, since the necessary element restrictions mean * can't be defined. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Restricted type classes
On 07/09/10 05:24, wren ng thornton wrote: that other class would (most likely) be a subclass of pointed functors. In any case, it does mean there's something of a mismatch between singleton vs return/pure/point/unit. Not quite sure what you mean by a mis-match Of course, I'd expect singleton to obey the pointed law as well, so Just that they're not the same thing. For example, ZipList supports pure but it has no meaningful instance of singleton since every ZipList is infinite. I don't believe that every ZipList is infinite (if this should be the case, the constructor shouldn't be exposed!), just that ZipLists created by pure are infinite -- that's the obvious definition to meet the Applicative laws. You can quite happily use: (+) $ ZipList [1,2,3] * ZipList [4,5] == ZipList [5,7] So ZipList does have a meaningful definition of singleton (singleton x = ZipList [x]; I'm sure there are other pointed functors that don't have a good definition for singleton), and a meaningful definition of pure, but they're not the same definition. Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Fwd: Semantics of iteratees, enumerators, enumeratees?
At first I regarded this as simply a bug in the Iteratee.map definition, but like Ben, it's started to bother me a lot. I think this is precisely the sort of issue a proper denotational semantics would fix. Unfortunately the only general solution I see is to abandon chunking and work strictly element-wise. I say unfortunately because my current best implementation is about 5 times slower than the main tree. I'm open to ideas. John From: Ben midfi...@gmail.com Sorry to be late coming into this conversation. Something that has bothered me (which I have mentioned to John Lato privately) is that it is very easy to write non-compositional code due to the chunking. For example, there is a standard function map :: (a - b) - Enumeratee a b c whose meaning I hope is clear : use the function to transform the type of a stream and pass it to an iteratee. However last I checked the versions provided in both the iteratee and enumerator packages fail to satisfy the equation map f (it1 it2) == (map f it1) (map f it 2) because of chunking, essentially. You can check this with f == id and it1 and it2 are head: let r = runIdentity . runIteratee runIdentity $ run $ enumList 10 [1..100] $ r $ joinI $ map id $ r (head head) -- Right (Just 2) runIdentity $ run $ enumList 10 [1..100] $ r $ joinI $ (map id $ r head) (map id $ r head) -- Right (Just 11) It is possible to fix this behavior, but it complicates the obvious definitions a lot. B On Wed, Sep 1, 2010 at 5:10 AM, Heinrich Apfelmus apfel...@quantentunnel.de wrote: Tilo Wiklund wrote: Daniel Fischer wrote: [...] Well, I just gave an example where one would want chunking for reasons other than performance. That iteratees don't provide the desired functionality is a different matter. [...] In the case of hashing, wouldn't it be more reasonable to consider iterators over streams of fixed (or at least predictable) sized chunks (where a set of chunks can themselves be chunked), with the chunking behaviour being given by another iteratee over the original stream? It seems to me that one of the major points of iteratees is to provide an abstraction from the kind of chunking irrelevant to the parsing logic, otherwise I fail to see any difference (at least relevant to chunking) to plain strict IO. I thought so, too, but I was informed[1] that iteratees are just a small step up the abstraction ladder. The difference compared to an ordinary file Handle is that you can now reuse one and the same iteratee for reading from a String , for instance, without changing the source code of the iteratee. Furthermore, iteratees can be suspended, which facilities resource management like closing files handles after they've been read. [1]: http://www.reddit.com/r/haskell/comments/ar4wb/understanding_iteratees/c0j0f3r Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] circular imports
Hello, I had recently a really hard time splitting up my program into parts! The natural, business-oriented split up drove me into a deadly circular dependency. I tried to solve it with: - .hs-boot: It adds a lot of duplicated code and unecessary files, so I gave up - type variables: that too complifies the code with no obvious reasons Finally, i ended up with putting all my types into a file names Types.hs. It's not very satisfatory, since I like to keep the types next to their related code and functions (like it is in the libraries). But I founded this is the way that adds the less burden to the code. Cheers, Corentin Mathew de Detrich dete...@gmail.c Pour om Ivan Lazar Miljenovic Envoyé par : ivan.miljeno...@gmail.com haskell-cafe-bou cc n...@haskell.org haskell haskell-cafe@haskell.org Objet Re: [Haskell-cafe] circular imports 07/09/2010 06:52 I had the same issue zonks ago, and I resorted to using the hs-boot file method as well (which worked fine) Which I guess brings me to my second point, is this something that GHC should do automatically when it sees circular dependencies? When I asked about it earlier on #haskell, I was told that its better that way because it discourages making bad design through circular dependencies (yet in my case and I assume the other cases as well, not using the hs-boot method would have made the design much worse). Are there any cases in particular where people would be encouraged to make interface design with circular dependencies (and that design be deemed as horrible) as opposed to what seems to be more realistic case where circular dependencies rarely crop up, and when they do they actually make the design better? On Tue, Sep 7, 2010 at 1:48 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 7 September 2010 03:44, Edward Z. Yang ezy...@mit.edu wrote: Excerpts from Evan Laforge's message of Mon Sep 06 13:30:43 -0400 2010: I feel like the circular imports problem is worse in haskell than other languages. Maybe because there is a tendency to centralize all state, since you need to define it along with your state monad. But the state monad module must be one of the lower level ones, since all modules that use it must import it. However, the tendency for bits of typed data to migrate into the state means it's easy for it to eventually want to import one of its importers. And the state monad module gets larger and larger (the largest modules in my system are those that define state monads: 1186 lines, 706 lines, 1156 lines---the rest tend to be 100--300 lines). I have used hs-boot files to this effect. I separated data and functionality, and typeclasses, which must be in the same module as data or are considered orphaned, get definitions via a circular import. I'm just getting to the point where I have a similar problem. I was thinking about splitting instances off from the classes (and telling GHC to not worry about orphaned instances for the instance-only modules) but then realised that some instance declarations would be circular as well, so I have to either use hs-boot files, define everything in one big module and then re-export them in ways that make sense or define all instances in one big module (at least for those types which have circular deps among instances) and re-export accordingly. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list
[Haskell-cafe] Re: circular imports
corentin.dupont at ext.mpsa.com writes: I had recently a really hard time splitting up my program into parts! The natural, business-oriented split up drove me into a deadly circular dependency. perhaps you could post your code (enough of it to understand the problem)? J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] generating foreign Code (Java, C++, PHP)?
Hi list, I noticed that there are some libs / packages like atom and HJscript which allow you to write a program in a haskell EDSL and that then actually generates valid source code in another language. In the above example that would be JavaScript and C. I sure would love to be able to write PHP for instance like that but I cannot even fathom how a EDSL would have to be designed for it. Could someone here point me to literature on the topic? Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] random-fu confusion
A PureMT generator is immutable, so must be threaded through the monad in which you are sampling. There are RandomSource instances provided for a few special cases, including IORef PureMT in the IO monad. For example: main = do mt - newPureMT src - newIORef mt flips - runRVar (replicateM 20 flipCoin) src print flips Alternatively, the functions in the module you mentioned can be used to define additional instances, such as: instance MonadRandom (State PureMT) where supportedPrims _ _ = True getSupportedRandomPrim = getRandomPrimFromPureMTState And RandomSource instances look almost the same. See the Data.Random.Source.PureMT source for examples. (I thought I had included this particular instance in the distribution but I apparently missed it. The next release will probably include this as well as corresponding instances for the 'transformers' package, possibly separated out into 'random-fu-mtl' and 'random-fu-transformers' packages). The StdRandom type is a convenient RandomSource designating this instance in the State PureMT monad. Personally, I prefer to use the sample function for this purpose, as well as the sampleFrom function in place of runRVar/runRVarT. GHCi does not display the sample functions' types properly - they are defined for RVarT as well as for all Distribution instances. Sorry it took so long responding. -- James On Sep 2, 2010, at 10:01 AM, Alex Rozenshteyn wrote: I seem to be having confusion at the runRVar level of random-fu. I can't figure out how to use the Data.Random.Source.PureMT module to get a meaningful random source (I can't get my code to type-check). I wrote a [trivial] flipCoin function flipCoin = uniform False True and am trying to fill in the final place of runRVar :t runRVar (replicateM 20 flipCoin) runRVar (replicateM 20 flipCoin) :: (RandomSource m s) = s - m [Bool] -- Alex R ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generating foreign Code (Java, C++, PHP)?
2010/9/7 Günther Schmidt gue.schm...@web.de: Hi list, I noticed that there are some libs / packages like atom and HJscript which allow you to write a program in a haskell EDSL and that then actually generates valid source code in another language. In the above example that would be JavaScript and C. I sure would love to be able to write PHP for instance like that but I cannot even fathom how a EDSL would have to be designed for it. Hi, Probably, the very first thing is to know what purpose the EDSL would serve. For instance, Atom is not meant as a general purpose replacement for C. Do you have something specific in mind? Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] circular imports
Mathew de Detrich schrieb: I had the same issue zonks ago, and I resorted to using the hs-boot file method as well (which worked fine) Which I guess brings me to my second point, is this something that GHC should do automatically when it sees circular dependencies? When I asked about it earlier on #haskell, I was told that its better that way because it discourages making bad design through circular dependencies (yet in my case and I assume the other cases as well, not using the hs-boot method would have made the design much worse). Are there any cases in particular where people would be encouraged to make interface design with circular dependencies (and that design be deemed as horrible) as opposed to what seems to be more realistic case where circular dependencies rarely crop up, and when they do they actually make the design better? I like to compare it with Modula-3 where cyclic imports are strictly forbidden. There it is solved by dividing a module into an interface file and an implementation file. The interface can be compared with .hs-boot files: You can define types there, but you can also simply declare a type without its precise structure. Two mutually depending types in distinct modules could be defined as follows: A.i3: INTERFACE A; TYPE T : REFANY; (* declare T to be a subtype of a general pointer *) END A. A.m3: MODULE A; (* the implementation part automatically imports the corresponding interface A without qualification *) IMPORT B; (* import the interface of module B *) REVEAL T = POINTER TO RECORD b : B.T END; END A. B.i3: INTERFACE B; TYPE T : REFANY; END B. B.m3: MODULE B; IMPORT A; REVEAL T = POINTER TO RECORD a : A.T END; END B. Thus the circular dependency graph A - B, B - A is split into the non-circular dependency graph Ai - Am, Ai - Bm, Bi - Am, Bi - Bm Obviously this only works for pointers, but this is no problem since embedding a record in itself is not possible. Haskell cannot embed a record in another one, it uses pointers by default. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Réf. : [Haskell-cafe] Re: circular imports
That sort of code (stripped out):
In Game.hs:
data Game = Game { ...
activeRules :: [Rule]}
applyTo :: Rule - Game - Game
applyTo r gs = ...
In Rule.hs:
data Rule = Cond (Obs) Rule Rule
| many others..
deriving (Read, Show, Eq, Typeable)
data NamedRule = NamedRule { ...,
rule :: Rule }
isRuleLegal :: Rule - NamedRule - Game - Bool
isRuleLegal = ...
In Obs.hs:
data Obs a where
ProposedBy :: Obs Int -- The player that proposed the tested rule
...
evalObs :: Obs - NamedRule - Game - EvalObsType
evalObs = ...
Corentin
Johannes
Waldmann
waldm...@imn.ht Pour
wk-leipzig.dehaskell-cafe@haskell.org
Envoyé par : cc
haskell-cafe-bou
n...@haskell.orgObjet
[Haskell-cafe] Re: circular imports
07/09/2010 14:00
corentin.dupont at ext.mpsa.com writes:
I had recently a really hard time splitting up my program into parts!
The natural, business-oriented split up drove me into a deadly circular
dependency.
perhaps you could post your code (enough of it to understand the problem)?
J.W.
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Re: [Haskell-cafe] circular imports
Simon Peyton-Jones schrieb: I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had the time or inclination to make it resolve circular dependencies automatically, and not an intentional design decision to encourage good design. Indeed. I’ve added some notes here http://hackage.haskell.org/trac/ghc/ticket/1409#comment:37 When reading this, I'm afraid adding this feature will cause more bugs than features. For me, generally working hs-boot-files would be enough, that is, hs-boot files that support all situations of mutually depending classes and instances. I still prefer non-circular modules, because I understand their relationship more easily. I prefer to explicitly state when I want cyclic imports, as I currently do with hs-boot files. As time went by, I become familiar with the discussed methods of avoiding import cycles and actually, all packages I have written so far do not contain any circular import and thus no hs-boot file. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Hi, Thanks to everybody who replied. I see another solution: are there any hidden problems? I found an interesting package, ChasingBottoms which contains a function testing a value to be bottom and returning a Boolean (of course it cannot be done without unsafePerformIO). I borrowed the idea from that package, and wrote two functions: unThrow :: (Exception e) = a - Either e a unThrow a = unsafePerformIO $ (E.evaluate a = return . Right) `E.catch` (\e - return $ Left e) -- or perhaps the right argument of catch could be just (return . Left)? bm2mb :: a - Maybe a bm2mb a = case unThrow a of Left (e::SomeException) - Nothing Right a - Just a So, if there is a value inside the lazy list which is a bottom (binary parse failure of the last received object in this case, catching any possible exception) then the value can be converted to Nothing within pure code, and then excluded from the result using catMaybes. This solution seems to be working for me. PS Maybe the way I am using the serialized data needs to be changed by implementing some kind of an iterator over the binary stream, and then by taking one object at a time and consuming it right there the problem might be eliminated entirely... Thanks again. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc HEAD
I was compiling ghc-6.13.20100831 from source (*) and then compiling repa-examples with that, and the generated executable says (when called with +RTS -N2): Most RTS options are disabled. Link with -rtsopts to enable them. Where? How? When? (Did I make some error earlier?) (*) that's the latest available src snapshot? (Sadly, it does not contain containers-0.4) How come there are binaries without sources at: http://www.haskell.org/ghc/dist/current/dist/ While cabal install repa-examples works nicely, it is still way too easy to break the system, since cabal install will happily (and silently) destroy ghc's libraries. (e.g. happens for me after installing syb) unfortunately, this means I cannot easily test ghc HEAD and/or containers-0.4 on my sources. J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Réf. : [Haskell-cafe] Re: circular imports
corentin.dup...@ext.mpsa.com schrieb:
That sort of code (stripped out):
In Game.hs:
data Game = Game { ...
activeRules :: [Rule]}
applyTo :: Rule - Game - Game
applyTo r gs = ...
In Rule.hs:
data Rule = Cond (Obs) Rule Rule
| many others..
deriving (Read, Show, Eq, Typeable)
data NamedRule = NamedRule { ...,
rule :: Rule }
isRuleLegal :: Rule - NamedRule - Game - Bool
isRuleLegal = ...
In Obs.hs:
data Obs a where
ProposedBy :: Obs Int -- The player that proposed the tested rule
...
evalObs :: Obs - NamedRule - Game - EvalObsType
evalObs = ...
As I see there is no cycle in the types. How about defining Game, Rule,
Obs in private modules, like Private.Game, Private.Rule, Private.Obs,
and implementing the functions in public modules like Game, Rule, Obs ?
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Re: [Haskell-cafe] ghc HEAD
2010/9/7 Johannes Waldmann waldm...@imn.htwk-leipzig.de: I was compiling ghc-6.13.20100831 from source (*) and then compiling repa-examples with that, and the generated executable says (when called with +RTS -N2): Most RTS options are disabled. Link with -rtsopts to enable them. Where? How? When? (Did I make some error earlier?) AFAIK RTS options are disabled by default now due to security problems. see http://hackage.haskell.org/trac/ghc/ticket/3910 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] random-fu confusion
Okay, I figured the immutability bit out and I got the IORef example working, but I can't get it to work with state. put (pureMT 0) = runRVar flipCoin gives me two type errors: No instance for (MonadState PureMT m) and No instance for (RandomSource m ()) runState $ put (pureMT 0) = runRVar flipCoin runState $ put (pureMT 0) get = runRVar flipCoin put (pureMT 0) get = runRVar flipCoin and other desperate attempts, some of which in hindsight are too embarrassing to list give me similar errors. I'm trying to do figure out how to do this without going to the IO monad (so I can run it with the same seed to replicate results). On Tue, Sep 7, 2010 at 3:14 PM, James Andrew Cook mo...@deepbondi.netwrote: A PureMT generator is immutable, so must be threaded through the monad in which you are sampling. There are RandomSource instances provided for a few special cases, including IORef PureMT in the IO monad. For example: main = do mt - newPureMT src - newIORef mt flips - runRVar (replicateM 20 flipCoin) src print flips Alternatively, the functions in the module you mentioned can be used to define additional instances, such as: instance MonadRandom (State PureMT) where supportedPrims _ _ = True getSupportedRandomPrim = getRandomPrimFromPureMTState And RandomSource instances look almost the same. See the Data.Random.Source.PureMT source for examples. (I thought I had included this particular instance in the distribution but I apparently missed it. The next release will probably include this as well as corresponding instances for the 'transformers' package, possibly separated out into 'random-fu-mtl' and 'random-fu-transformers' packages). The StdRandom type is a convenient RandomSource designating this instance in the State PureMT monad. Personally, I prefer to use the sample function for this purpose, as well as the sampleFrom function in place of runRVar/runRVarT. GHCi does not display the sample functions' types properly - they are defined for RVarT as well as for all Distribution instances. Sorry it took so long responding. -- James On Sep 2, 2010, at 10:01 AM, Alex Rozenshteyn wrote: I seem to be having confusion at the runRVar level of random-fu. I can't figure out how to use the Data.Random.Source.PureMT module to get a meaningful random source (I can't get my code to type-check). I wrote a [trivial] flipCoin function flipCoin = uniform False True and am trying to fill in the final place of runRVar :t runRVar (replicateM 20 flipCoin) runRVar (replicateM 20 flipCoin) :: (RandomSource m s) = s - m [Bool] -- Alex R ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alex R ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Réf. : [Haskell-cafe] Re: circular imports
Henning Thielemann schlepptop at henning-thielemann.de writes: As I see there is no cycle in the types. How about defining Game, Rule, Obs in private modules, like Private.Game, Private.Rule, Private.Obs, and implementing the functions in public modules like Game, Rule, Obs ? I guess that conflicts with the advice of putting the functions (behaviour) close to the data that it concerns. But if a function mentions two types (and the types are separate), it requires a decision - in OO as well: you would (arbitrarily) make them a method of one class or the other. J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ghc HEAD
Yuras Shumovich shumovichy at gmail.com writes: http://hackage.haskell.org/trac/ghc/ticket/3910 So what is the magic link-time flag to en/disable the RTS options? It seems it would be needed for all things multi-core, since you'd want to modify +RTS -Nx J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Réf. : [Haskell-cafe] Re: circular imports
On Tue, 7 Sep 2010, Johannes Waldmann wrote: Henning Thielemann schlepptop at henning-thielemann.de writes: As I see there is no cycle in the types. How about defining Game, Rule, Obs in private modules, like Private.Game, Private.Rule, Private.Obs, and implementing the functions in public modules like Game, Rule, Obs ? I guess that conflicts with the advice of putting the functions (behaviour) close to the data that it concerns. Of course, the public module Game shall export the Game type from Private.Game and so on. That is from the perspective of the Game package user, the Game type and related functions can be imported from the same module. The inconvenience of defining the Game type and its functions in distinct modules exists only for corentin.dupont but not for the user of his library. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ghc HEAD
Excerpts from Johannes Waldmann's message of Tue Sep 07 10:38:47 -0400 2010: Yuras Shumovich shumovichy at gmail.com writes: http://hackage.haskell.org/trac/ghc/ticket/3910 So what is the magic link-time flag to en/disable the RTS options? As you mentioned earlier, -rtsopts. It seems it would be needed for all things multi-core, since you'd want to modify +RTS -Nx This is a good point: if RTS options are disabled, there should probably be a mechanism for specifying what RTS options should be baked in. Cheers, Edward ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Searching for Haskell (was: [Haskell-cafe] Slightly humorous: Headhunters toolbox (example for Germany))
On Aug 31, 2010, at 1:57 PM, Alberto G. Corona wrote: What happened in the first half of 2006? monads were high there!. Wasn't that about the time Microsoft was previewing the Power Shell, codenamed Monad? -- James___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] local-search
I was recently at IFL2010, where I gave a short presentation on my the attempts to put together a local search library for Haskell. This was reasonably well received, and I had a couple of requests for a library. After a couple of days sanitizing the code, and learning a bit about how to package libraries for Hackage I am now announcing that the library has been uploaded, version 0.0.1. Of course I managed to make an error in the summary so it start AA first rather than just A first. I hope that people find this interesting and I look forward to feedback. http://hackage.haskell.org/package/local-search RS ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Paralelism and Distribution in Haskell
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 9/7/10 05:08 , David Virebayre wrote: 2010/9/7 Ben Lippmeier b...@ouroborus.net: Though be warned you must use a recent GHC head build to get good performance. After GHC 7.0 is out (in a few weeks) we'll be able to release a properly stable version. Pardon a probably stupid question, but did I miss something ? http://hackage.haskell.org/trac/ghc/roadmap I think the change is because there's a new type inference engine coming, which justifies the major version bump. - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkyGYi4ACgkQIn7hlCsL25UwXgCdHCeZezzttZe+RHJxeQCDQ3Gx JFcAoMeQcbnaQWoGutTcpAH8EnnxVZ2V =O6U3 -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ghc HEAD
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 9/7/10 10:51 , Edward Z. Yang wrote: Excerpts from Johannes Waldmann's message of Tue Sep 07 10:38:47 -0400 2010: It seems it would be needed for all things multi-core, since you'd want to modify +RTS -Nx This is a good point: if RTS options are disabled, there should probably be a mechanism for specifying what RTS options should be baked in. I'd call this incomplete because programs compiled with RTS options enabled are still insecure. The correct fix is to ignore GHCRTS and die on +RTS *when setuid*. Since this isn't something that can be changed in a running process (well, not without some fairly evil kernel memory poking) there are no race conditions to watch out for; just ignore the RTS options when getuid() != geteuid() and getuid() != 0 (and similar for setgid/setegid, although those are less critical because gid is really only useful for filesystem permissions). A better fix would be to identify safe settings and only allow those (and only via +RTS) when setuid. OTOH that's pretty much the system configuration version of the Halting Problem :) - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkyGakwACgkQIn7hlCsL25UjmgCghMw4kmTsTxcCTYKYYLxGU8Yl 6HQAoIGA9axL8zqCwDpaR2PL/BGTEnpk =XlOo -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Dimitry Golubovsky schrieb: Hi, Thanks to everybody who replied. I see another solution: are there any hidden problems? I found an interesting package, ChasingBottoms which contains a function testing a value to be bottom and returning a Boolean (of course it cannot be done without unsafePerformIO). I borrowed the idea from that package, and wrote two functions: unThrow :: (Exception e) = a - Either e a unThrow a = unsafePerformIO $ (E.evaluate a = return . Right) `E.catch` (\e - return $ Left e) -- or perhaps the right argument of catch could be just (return . Left)? bm2mb :: a - Maybe a bm2mb a = case unThrow a of Left (e::SomeException) - Nothing Right a - Just a So, if there is a value inside the lazy list which is a bottom (binary parse failure of the last received object in this case, catching any possible exception) then the value can be converted to Nothing within pure code, and then excluded from the result using catMaybes. This solution seems to be working for me. This solution looks very ugly to me. Catching 'error's is debugging, but parser failure is kind of exception handling. I guess, the errors you want to catch are caused by non-supported fail method, right? Can't you use a monad transformer like explicit-exception:Synchronous.Exception or transformers:ErrorT around the Binary parser? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: ghc HEAD
Hello Brandon, Tuesday, September 7, 2010, 8:37:32 PM, you wrote: I'd call this incomplete because programs compiled with RTS options enabled are still insecure. The correct fix is to ignore GHCRTS and die on +RTS *when setuid*. Since i strongly agree -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] random-fu confusion
On Sep 7, 2010, at 10:21 AM, Alex Rozenshteyn wrote: Okay, I figured the immutability bit out and I got the IORef example working, but I can't get it to work with state. put (pureMT 0) = runRVar flipCoin gives me two type errors: No instance for (MonadState PureMT m) and No instance for (RandomSource m ()) The first error is because put has the general type: put :: (MonadState s m) = s - m () and GHC doesn't know what monad you want to evaluate it in. Just off the bat there are 2 possibilities provided by Control.Monad.State: State and StateT. The second is because runRVar requires an additional argument specifying the source from which to sample. In your case, you want to sample from the standard source, the MonadRandom instance. The type StdRandom with a single constructor of the same name designates the MonadRandom instance. So for your example, a working incantation would be: put (pureMT 0) = runRVar flipCoin StdRandom :: State PureMT Bool To actually run this action you would then use runState or evalState, in which case the type annotation would no longer be necessary because the use of runState or evalState would give the compiler enough information to know what you want. These functions both also accept an initial state as an argument, so you don't actually need put either: evalState (runRVar flipCoin StdRandom) (pureMT 0) Using the sample function I mentioned earlier you can leave off the mention of StdRandom: evalState (sample flipCoin) (pureMT 0) I'm trying to do figure out how to do this without going to the IO monad (so I can run it with the same seed to replicate results). Incidentally, you can use the 'pureMT' function to seed your generator in the IO monad just as easily: newIORef (pureMT 0) = \src - runRVar flipCoin src or do src - newIORef (pureMT 0); runRVar flipCoin src A large part of the point of the RVar monad as its own independent construct is to allow you to use random variables such as flipCoin in any monad that can support them while at the same time guaranteeing all the same purity / safety as if you had used something obviously pure such as State. -- James___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Réf. : [Haskell-cafe] Re: circular imports
That sort of code (stripped out):
In Game.hs:
data Game = Game { ...
activeRules :: [Rule]}
applyTo :: Rule - Game - Game
applyTo r gs = ...
Often, it helps to parameterize the types/functions (instead
of using recursive modules to hardcode the parameters).
Would something like this work for your case (taking the
Game module out of the loop)?
data Game rule = Game { ...
activeRules :: [rule]}
applyTo :: rule - Game rule - Game rule
applyTo r gs = ...
In Rule.hs:
..
isRuleLegal :: Rule - NamedRule - Game Rule - Bool
isRuleLegal = ...
In Obs.hs:
evalObs :: Obs - NamedRule - Game Rule - EvalObsType
evalObs = ...
For the record, I'd like to have recursive modules without
having to go outside the language (some standardized
notion of Haskell module interfaces would be nicer than
implementation-specific boot files).
But I'd like to have parameterized modules even more,
as that would allow me to avoid many use cases of
recursive modules (again, that would seem to require
module interfaces).
Claus
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Re: [Haskell-cafe] Pointed (was: Re: Restricted type classes)
On Sep 7, 2010, at 5:23 AM, wren ng thornton wrote: In particular, one of the primary complaints against the Monad class is precisely the fact that it *fails* to mention the Functor class as a (transitive) dependency. Why should we believe that making unit independent from fmap will fare any better? A noteworthy difference is that fmap can be defined in terms of return and = but not in terms of point. IMHO, this is a good reason why fmap should be defined for every Monad and may be missing for some Pointed. Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] help me evangelize haskell.
Hi Dan, This presentation is really nice. I went over it a couple of times and I think this ppt will help me try to use Haskell for things that I usually use Perl for :) A quick question - import Process bombs on my GHCI(The Glorious Glasgow Haskell Compilation System, version 6.12.3) -what do I need to do for that? On Sun, Sep 5, 2010 at 11:12 PM, Don Stewart d...@galois.com wrote: Gaius: My usual rhetoric is that one-off, throwaway scripts never are, and not only do they tend to stay around but they take on a life of their own. Today's 10-line file munger is tomorrow's thousand-line ETL batch job on which the business depends for some crucial data - yet the original author is long gone and no-one dares modify in case it breaks. So it is just good sense to use sound practices from the very beginning. I gave a tech talk recently on using Haskell for scripting -- and it is built on the idea that today's throw away script is tomorrow's key piece of infrastructure -- so you better get the maintainance and safety story right: http://donsbot.wordpress.com/2010/08/17/practical-haskell/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] help me evangelize haskell.
That's a separate module, based on System.Process -- http://code.haskell.org/~dons/code/cpuperf/Process.hs ckkashyap: Hi Dan, This presentation is really nice. I went over it a couple of times and I think this ppt will help me try to use Haskell for things that I usually use Perl for :) A quick question - import Process bombs on my GHCI(The Glorious Glasgow Haskell Compilation System, version 6.12.3) -what do I need to do for that? On Sun, Sep 5, 2010 at 11:12 PM, Don Stewart d...@galois.com wrote: Gaius: My usual rhetoric is that one-off, throwaway scripts never are, and not only do they tend to stay around but they take on a life of their own. Today's 10-line file munger is tomorrow's thousand-line ETL batch job on which the business depends for some crucial data - yet the original author is long gone and no-one dares modify in case it breaks. So it is just good sense to use sound practices from the very beginning. I gave a tech talk recently on using Haskell for scripting -- and it is built on the idea that today's throw away script is tomorrow's key piece of infrastructure -- so you better get the maintainance and safety story right: http://donsbot.wordpress.com/2010/08/17/practical-haskell/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] PSA: using MySQL from Haskell programs
If you are using HDBC-mysql or HDBC-odbc to access MySQL databases, you may have run into problems with your programs failing due to connection errors. In this blog posting, I describe what's happening and how to work around it: http://www.serpentine.com/blog/2010/09/04/dealing-with-fragile-c-libraries-e-g-mysql-from-haskell/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: Form a haskell.org committee
On Sun, Sep 5, 2010 at 9:34 PM, Jason Dagit da...@codersbase.com wrote: The darcs project uses the Software Freedom Conservancy as a sort of legal entity to hold on to funds and also to help in case anyone takes legal action against darcs or darcs needs to take legal action. I have only the highest praise for the Software Freedom Conservancy folks. They are smart, capabale, and very accommodating. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Fwd: Semantics of iteratees, enumerators, enumeratees?
On Mon, Sep 6, 2010 at 22:49, Ben midfi...@gmail.com wrote: Sorry to be late coming into this conversation. Something that has bothered me (which I have mentioned to John Lato privately) is that it is very easy to write non-compositional code due to the chunking. For example, there is a standard function map :: (a - b) - Enumeratee a b c whose meaning I hope is clear : use the function to transform the type of a stream and pass it to an iteratee. However last I checked the versions provided in both the iteratee and enumerator packages fail to satisfy the equation map f (it1 it2) == (map f it1) (map f it 2) because of chunking, essentially. You can check this with f == id and it1 and it2 are head: let r = runIdentity . runIteratee runIdentity $ run $ enumList 10 [1..100] $ r $ joinI $ map id $ r (head head) -- Right (Just 2) runIdentity $ run $ enumList 10 [1..100] $ r $ joinI $ (map id $ r head) (map id $ r head) -- Right (Just 11) It is possible to fix this behavior, but it complicates the obvious definitions a lot. Chunking doesn't have anything to do with this, and an iteratee encoding without input chunking would exhibit the same problem. You're running into an (annoying? dangerous?) subtlety in enumeratees. In the particular case of map/head, it's possible to construct an iteratee with the expected behavior by altering the definition of 'map'. However, if the composition is more complicated (like map/parse-json), this alteration becomes impossible. Remember than an enumeratee's return value contains two levels of extra input. The outer layer is from the enumeratee (map), while the inner is from the iteratee (head). The iteratee is allowed to consume an arbitrary amount of input before yielding, and depending on its purpose it might yield extra input from a previous stream. Perhaps the problem is that 'map' is the wrong name? It might make users expect that it composes horizontally rather than vertically. Normally this incorrect interpretation would be caught by the type checker, but using () allows the code to compile. Anyway, the correct way to encode @(map f it1) (map f it 2)@, using above style is: (map id (r head) = returnI) (map id (r head) = returnI) so the full expression becomes: runIdentity $ run $ enumList 10 [1..100] $ r $ (map id (r head) = returnI) (map id (r head) = returnI) which ought to return the correct value (untested; I have no Haskell compiler on this computer). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANNOUNCE: reference 0.1
On Tue, 2010-09-07 at 02:15 +0200, Bas van Dijk wrote:
On Mon, Sep 6, 2010 at 11:55 PM, Maciej Piechotka uzytkown...@gmail.com
wrote:
Reference is class which generalizes references and monads they exists
in. It means that IORef, STRef and others can be accessed by common
interface.
Currently it is of form:
class Reference r m where
1. There was a proposal to rename the class to MonadRef or
MonadReference. IMHO it would imply m - r functional dependency and
therefore disallow the instances for both MVar IO and IORef IO
2. Should the functional dependencies or type famillies be introduced?
Personally I don't think so as I would like to allow all of the
following:
- IORef IO
- MVar IO
- IORef (ContT IO)
- MVar (ContT IO)
Any feedback mostly welcome.
Regards
PS. Darcs repository will be available soon
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First I'd like to say sorry for error in cafe mailing list address. The
whole e-mail is included above.
I've played with a somewhat similar idea:
darcs get http://code.haskell.org/~basvandijk/code/only-read-or-write-vars
API Docs + Hyperlinked source:
http://code.haskell.org/~basvandijk/code/only-read-or-write-vars/doc/html/only-read-or-write-vars/
This is not released (yet) because I'm unsure about the design.
Especially, I'm unsure whether parameterizing Readable with α is a good idea:
class Readable v m α | v → m where read v → m α
and whether parameterizing Writable with α and β is a good idea:
class Writable v α m β | v → m where write v → α → m β
They do allow some some nice instances like:
instance Readable (TMVar α) STM (Maybe α) where
read = TMVar.tryTakeTMVar
instance Writable (TMVar α) α STM Bool where
write = TMVar.tryPutTMVar
instance Writable (Chan α) (End α) IO () where
write t = Chan.unGetChan t unEnd
-- | Writing @End x@ to a 'Chan' or 'TChan' writes @x@ to the end of
the channel
-- instead of to the front. Also see 'unGetChan' and 'unGetTChan'.
newtype End α = End {unEnd α}
Regards,
Bas
I guess they are to some extend like Foldable to FoldableLL and possibly
describing different aspects. Yours seems to be a bit like StateVar[1]
generalized for different monads. Support for ptr others is additional
bonus.
I wanted clear 1-1 mapping with references - i.e. basic 2 operations
with added third for 'atomic' support.
For example one of unmentioned law is that:
write r x read r === write r x return r -- If it's only thread
write r x write r y === write r y -- If it's only thread
read r read r === read r
read r = write r === id -- If it's only thread
read r = const f === f -- If it's only thread?
In fact I guess each on them could be used as RULES as IMHO each case in
which it is not necessary true it is undeterministic anyway.
While Chan is clearly writable and readable it cannot be considered a
reference - it do have it purposes but they are usually different then
references.
To sum up - I would not be willing to use Readable/Writable in place of
Reference but I don't say they don't have their purposes.
PS. I took the liberty of continuing sentence.
[1] http://hackage.haskell.org/package/StateVar-1.0.0.0
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Re: [Haskell-cafe] Re: [Haskell] ANNOUNCE: reference 0.1
Why not to define it for any monad, for example STM (TVars) and whatever?
2010/9/7 Maciej Piechotka uzytkown...@gmail.com
On Tue, 2010-09-07 at 02:15 +0200, Bas van Dijk wrote:
On Mon, Sep 6, 2010 at 11:55 PM, Maciej Piechotka uzytkown...@gmail.com
wrote:
Reference is class which generalizes references and monads they exists
in. It means that IORef, STRef and others can be accessed by common
interface.
Currently it is of form:
class Reference r m where
1. There was a proposal to rename the class to MonadRef or
MonadReference. IMHO it would imply m - r functional dependency and
therefore disallow the instances for both MVar IO and IORef IO
2. Should the functional dependencies or type famillies be introduced?
Personally I don't think so as I would like to allow all of the
following:
- IORef IO
- MVar IO
- IORef (ContT IO)
- MVar (ContT IO)
Any feedback mostly welcome.
Regards
PS. Darcs repository will be available soon
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First I'd like to say sorry for error in cafe mailing list address. The
whole e-mail is included above.
I've played with a somewhat similar idea:
darcs get
http://code.haskell.org/~basvandijk/code/only-read-or-write-vars
API Docs + Hyperlinked source:
http://code.haskell.org/~basvandijk/code/only-read-or-write-vars/doc/html/only-read-or-write-vars/
This is not released (yet) because I'm unsure about the design.
Especially, I'm unsure whether parameterizing Readable with α is a good
idea:
class Readable v m α | v → m where read v → m α
and whether parameterizing Writable with α and β is a good idea:
class Writable v α m β | v → m where write v → α → m β
They do allow some some nice instances like:
instance Readable (TMVar α) STM (Maybe α) where
read = TMVar.tryTakeTMVar
instance Writable (TMVar α) α STM Bool where
write = TMVar.tryPutTMVar
instance Writable (Chan α) (End α) IO () where
write t = Chan.unGetChan t unEnd
-- | Writing @End x@ to a 'Chan' or 'TChan' writes @x@ to the end of
the channel
-- instead of to the front. Also see 'unGetChan' and 'unGetTChan'.
newtype End α = End {unEnd α}
Regards,
Bas
I guess they are to some extend like Foldable to FoldableLL and possibly
describing different aspects. Yours seems to be a bit like StateVar[1]
generalized for different monads. Support for ptr others is additional
bonus.
I wanted clear 1-1 mapping with references - i.e. basic 2 operations
with added third for 'atomic' support.
For example one of unmentioned law is that:
write r x read r === write r x return r -- If it's only thread
write r x write r y === write r y -- If it's only thread
read r read r === read r
read r = write r === id -- If it's only thread
read r = const f === f -- If it's only thread?
In fact I guess each on them could be used as RULES as IMHO each case in
which it is not necessary true it is undeterministic anyway.
While Chan is clearly writable and readable it cannot be considered a
reference - it do have it purposes but they are usually different then
references.
To sum up - I would not be willing to use Readable/Writable in place of
Reference but I don't say they don't have their purposes.
PS. I took the liberty of continuing sentence.
[1] http://hackage.haskell.org/package/StateVar-1.0.0.0
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[Haskell-cafe] Handling platform- or configuration-specific code (or, my CPP complaints)
Good evening, cafe, Having recently taken on maintenance of a package that depends on template-haskell, I've been in some discussion with users and dependencies of my package about how best to write a library that works with multiple incompatible versions of a dependency. The two main approaches that I'm aware of are: 1. Use CPP and the macros defined by Cabal to conditionally include or exclude code for each version. 2. Use Cabal file conditionals to select hs-source-dirs containing those parts of the code (or even TH to help generate those parts of the code) that are specific to each configuration. In my discussion with others and examination of existing libraries, it seems to me that 1. is the preferred option, but I personally can think of a number of reasons to prefer the second option: * CPP was not designed for Haskell, and even cpphs still shows symptoms of it, so we have to worry about things like its handling of string gaps or single quotes. * CPP is primarily a textual manipulation tool, rather than a symbolic one, which makes it even more easy to produce malformed code with it than with TH or similar. * On that note, it's difficult to statically analyse a file using CPP: parser tools like haskell-src-exts don't support it and it's not at all obvious how or if they ever could. With Cabal choosing source files based on configuration, all the source is valid, normal Haskell and is easy for computers and humans to understand. * It may require some significant digging into each source file to establish what configurations must be tested, or to add a new supported configuration or remove an old one, if they are chosen based on CPP conditional compilation. When Cabal chooses what is compiled it is fairly explicit what is chosen and what could be, and adding a new configuration is - at least in theory - as simple as adding a new file and conditional. * It's just not very pretty! Haskell code has a sort of aesthetic that I don't think CPP macros share - different function application syntax, for example. Of course the trouble is that when your conditional compilation is on the module level there are some things which just can't be done without code duplication, and there's a tendency for small and often quite incidental bits of a function definition to suddenly be in another module instead of where they're used. So I wonder what people think of the use of CPP in Haskell code, what alternatives people can propose, or what people hope to see in future to make conditional compilation of Haskell code more elegant and simple? I once pondered whether it would be a good idea to somehow make available to TH splices information from Cabal or GHC's configuration, so that one could do something like this: myFunctionDecl = if packageVersion template-haskell = Version [2, 4] [] then [d| unTyVarBndr (PlainTV n) = n; unTyVarBndr (KindedTV n _) = n |] else [d| unTyVarBndr = id |] This exactly wouldn't make sense because KindedTV wouldn't exist in the earlier version so the quotation would object, but one could imagine something similar being useful. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Re: [Haskell] ANNOUNCE: reference 0.1
On Tue, 2010-09-07 at 20:36 +0200, Alberto G. Corona wrote: Why not to define it for any monad, for example STM (TVars) and whatever? I'm really sorry but I fail to see what does 'it' refers to. reference 0.1 contains at this moment definitions for: - Reference TVar STM - Reference IORef IO - Reference MVar IO - Reference (STRef s) (ST s) (http://hackage.haskell.org/packages/archive/reference/0.1/doc/html/Data-Reference.html#t:Reference) So in fact there is already support for STM/TVar pair. Regards signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PSA: using MySQL from Haskell programs
On 7 Sep 2010, at 18:46, Bryan O'Sullivan wrote: If you are using HDBC-mysql or HDBC-odbc to access MySQL databases, you may have run into problems with your programs failing due to connection errors. In this blog posting, I describe what's happening and how to work around it: http://www.serpentine.com/blog/2010/09/04/dealing-with-fragile-c-libraries-e-g-mysql-from-haskell/ ___ Interestingly a similar issue was posted recently on Hacker News: http://news.ycombinator.com/item?id=1661986 Cheers, G ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskell-Cafe Digest, Vol 85, Issue 20
Do U like combinatory logic - or lambda calculus? It still matters, or something. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (theBinary package)
Quoth Dimitry Golubovsky golubov...@gmail.com, I see another solution: are there any hidden problems? I found an interesting package, ChasingBottoms which contains a function testing a value to be bottom and returning a Boolean (of course it cannot be done without unsafePerformIO). I borrowed the idea from that package, and wrote two functions: unThrow :: (Exception e) = a - Either e a unThrow a = unsafePerformIO $ (E.evaluate a = return . Right) `E.catch` (\e - return $ Left e) Like Henning, I'm not going to try to predict a specific problem with it, but I don't like it. Have you had a chance to look at cereal (Data.Serialize)? I frankly couldn't make it do what you need, as written, but I could make it work if I modify Serialize.Get to export Get(..) instead of Get. From there I wrote a variant of the Get (=) function with an additional end-value-on-failure parameter, [] in your program: ebind m g e = Get (\ s0 f k - unGet m s0 (\ _ _ - k B.empty e) (\ s a - unGet (g a) s f k)) ... so to get your error bounded array of Int, getx = ebind get (\ a - getx = return . (:) a) [] I think it's very likely there's a simpler way to do this with Data.Serial as written, I am just a little backwards with state monads and that kind of thing. Donn Cave, d...@avvanta.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANN] Crypto-API 0.0.0.1 Released
At long last and after much fruitful discussion on librar...@haskell.org, Crypto-API is having its first release, version 0.0.0.1! Crypto-API is a generic interface for cryptographic operations, platform independent quality entropy acquisition, property tests and known-answer tests (KATs) for common algorithms, and a basic benchmark infrastructure. Maintainers of hash and cipher implementations are encouraged to add instances for the classes defined in Crypto.Classes. Crypto users are similarly encouraged to use the interfaces provided. Any concepts or functions of general use to more than one cryptographic algorithm (ex: padding) is within scope of this package. Hackage: http://hackage.haskell.org/package/crypto-api Haddock: http://web.cecs.pdx.edu/~dubuisst/crypto-api-0.0.0.1/html/index.html Blog: http://tommd.wordpress.com/2010/09/07/crypto-api-released/ At it's heart, Crypto-API is an interface to cryptographic algorithms allowing crypto developers to provide a minimal, low level interface and reuse generic higher-level functions while freeing crypto users from specifying a particular algorithm or implementation. Highlights * Five type classes of Hash, BlockCipher, AsymCipher, StreamCipher, and CryptoRandomGen * Generic algorithms implemented using these class interfaces (ex: block cipher modes of operation, hashing and HMAC) * Platform independent acquisition of entropy for cryptographic use (using /dev/urandom on *nix and the CryptoAPI on windows) * Test suite and parsing of NIST KAT files * Rudimentary benchmarking for BlockCipher, Hash, and RNGs Hash Example The hash developer defines a class instances: instance Hash MD5Context MD5Digest where outputLength = Tagged 128 blockLength = Tagged 512 initialCtx = md5InitialContext updateCtx= md5Update finalize = md5Finalize The hash user can remain agnostic about which type of hash is used: authMessage :: Hash ctx dgst = B.ByteString - MacKey - dgst - Bool authMessage msg k = (==) (hmac' k msg) More examples can be found on the blog post. Versioning I don't intend to bump the version number for API changes in modules that aren't built by default (Test.Crypto, Benchmark.Crypto). Otherwise the PVP is in effect. Let me know if this isn't appreciated. Changes Since Release Candidate * Haddock documentation * Crypto.HMAC uses MacKey to help users keep the key and message separate Remaining TODO * Optimize block cipher modes and add new ones * Migrate Crypto.Random to the random package, pending conversation and agreement. * a signature class is planned for signature-only algorithms (DSA) class (Binary k, Serialize k) = Signing k where sign :: ... verify :: ... * Verify Crypto.Random works on Windows (more likely: fix it) once a Windows dev shows interest. * Build and test Crypto.Padding * Expand test suite. Include other hashes, modes, block algorithms, cipher properties. * Improve benchmarks, use CryptoRandomGen class in benchmark. * More Haddock documentation * Consider adding buildIV :: (CryptoRandomGen g) = g - Either GenError iv routine to StreamCipher interface Cheers, Thomas M. DuBuisson ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
On 07.09.2010 20:51, Henning Thielemann wrote: This solution looks very ugly to me. Catching 'error's is debugging, but parser failure is kind of exception handling. I guess, the errors you want to catch are caused by non-supported fail method, right? Can't you use a monad transformer like explicit-exception:Synchronous.Exception or transformers:ErrorT around the Binary parser? ErrorT is useless here since it cannot intercept calls to 'error'. Same should be the case with ExcepcionalT. There is also performance penalty ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 85, Issue 20
Very! On Sep 8, 2010 4:45 AM, Jeff Rubard jeffrub...@gmail.com wrote: Do U like combinatory logic - or lambda calculus? It still matters, or something. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
On Tue, Sep 7, 2010 at 2:45 PM, Dimitry Golubovsky golubov...@gmail.com wrote: unThrow a = unsafePerformIO $ (E.evaluate a = return . Right) `E.catch` (\e - return $ Left e) -- or perhaps the right argument of catch could be just (return . Left)? bm2mb :: a - Maybe a bm2mb a = case unThrow a of Left (e::SomeException) - Nothing Right a - Just a Philosophically these functions are Nasty because they violate referential transparency. In particular it's possible for the same expression to throw different exceptions each time it's run depending on how it's optimised, what other threads are doing, if the user presses ctrl-C, etc. etc. See the spoon package: http://hackage.haskell.org/package/spoon which alleviates this a little by only catching some kinds of exception, and not telling you which it caught. It still violates monotonicity (I believe), so purists will be upset, but practically it can be useful for when editing the source code to provide explicit exceptions (which is ideally what you'd do) is not an option. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad(theBinary package)
Quoth Donn Cave d...@avvanta.com, ... I think it's very likely there's a simpler way to do this with Data.Serial as written, I am just a little backwards with state monads and that kind of thing. OK, another look at it reveals that mplus can be used for this application, so much more simply, import Control.Monad (mplus) getx = do a - get x - getn `mplus` return [] return (a:x) Donn Cave, d...@avvanta.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PSA: using MySQL from Haskell programs
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 9/7/10 14:43 , Gaius Hammond wrote: On 7 Sep 2010, at 18:46, Bryan O'Sullivan wrote: If you are using HDBC-mysql or HDBC-odbc to access MySQL databases, you may have run into problems with your programs failing due to connection errors. In this blog posting, I describe what's happening and how to work around it: http://www.serpentine.com/blog/2010/09/04/dealing-with-fragile-c-libraries-e-g-mysql-from-haskell/ Interestingly a similar issue was posted recently on Hacker News: http://news.ycombinator.com/item?id=1661986 BSD (CSRG) UNIX had restartable system calls (no EINTR except from select(), which you had to use if you wanted to be interruptible under some circumstances which I'm not recalling off the top of my head right now; more than a few programs that didn't follow the rules turned out to not support any kind of interruptibility until rewritten to use select()). ATT commercial UNIX kept the original Research Edition UNIX EINTR semantics. POSIX had to reconcile them; the decision was to go with EINTR (you can simulate restartable system calls by looping on EINTR, but if restartable system calls are the default the only way to escape them is to rewire the program to use select() as above) but systems could offer sigaction() flag SA_RESTARTHAND to enable system call restarting on a signal-by-signal basis. (Note that SA_RESTARTHAND is not required for compliance, but a compliant system with SA_RESTARTHAND must have compliant semantics for it or call it something else.) - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkyGz6wACgkQIn7hlCsL25WargCeKQp4iEMO6y036eFCleertO10 KeEAoK3B9kpVinNWlSnUprAwcAAPtCAI =Yd6E -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] help me evangelize haskell.
Thanks Don! On Tue, Sep 7, 2010 at 10:51 PM, Don Stewart d...@galois.com wrote: That's a separate module, based on System.Process -- http://code.haskell.org/~dons/code/cpuperf/Process.hs ckkashyap: Hi Dan, This presentation is really nice. I went over it a couple of times and I think this ppt will help me try to use Haskell for things that I usually use Perl for :) A quick question - import Process bombs on my GHCI(The Glorious Glasgow Haskell Compilation System, version 6.12.3) -what do I need to do for that? On Sun, Sep 5, 2010 at 11:12 PM, Don Stewart d...@galois.com wrote: Gaius: My usual rhetoric is that one-off, throwaway scripts never are, and not only do they tend to stay around but they take on a life of their own. Today's 10-line file munger is tomorrow's thousand-line ETL batch job on which the business depends for some crucial data - yet the original author is long gone and no-one dares modify in case it breaks. So it is just good sense to use sound practices from the very beginning. I gave a tech talk recently on using Haskell for scripting -- and it is built on the idea that today's throw away script is tomorrow's key piece of infrastructure -- so you better get the maintainance and safety story right: http://donsbot.wordpress.com/2010/08/17/practical-haskell/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Regards, Kashyap -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ghc HEAD
On 8 September 2010 02:37, Brandon S Allbery KF8NH allb...@ece.cmu.edu wrote: A better fix would be to identify safe settings and only allow those (and only via +RTS) when setuid. OTOH that's pretty much the system configuration version of the Halting Problem :) Or optionally, allow the developer to specify which flags are safe (e.g. users are allowed to specify -N). -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to catch exception within the Get monad (the Binary package)
Henning, On Tue, Sep 7, 2010 at 12:51 PM, Henning Thielemann schlepp...@henning-thielemann.de wrote: This solution looks very ugly to me. Catching 'error's is debugging, but parser failure is kind of exception handling. I guess, the errors you want to catch are caused by non-supported fail method, right? Can't you use a monad transformer like explicit-exception:Synchronous.Exception or transformers:ErrorT around the Binary parser? Alexey already replied, but after looking at the way Binary processes parser errors I came to the same conclusion: it is by design that it falls hard when data cannot be deserialized (btw makes sense in many cases, but not in mine). I am beginning to realize that probably (de)serializing lazy structures is not a good idea at all since such structure may be consumed in pure code, and such parser errors are hidden inside, and may fire at any moment. Any complications to the binary parser will bring performance penalty. Or weird solutions like mine are needed. Thanks. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Grempa 0.1.0, Embedded grammar DSL and LALR parser generator
Hi Olle, On Mon, Sep 6, 2010 at 12:45 PM, Olle Fredriksson fredriksson.o...@gmail.com wrote: There are a few other examples in the examples directory of the package, most notably a grammar and parser for a simple functional language similar to Haskell. It is possible to generate random input strings and their expected outputs for grammars written using Grempa which makes it possible to test the generated parsers with QuickCheck. The package and documentation (should be up soon) can be found here: http://hackage.haskell.org/package/Grempa-0.1.0 Very nice job, I'm interested in using it. I wonder why the documentation hasn't been generated on Hackage yet. (I generated it for myself locally.) Do you plan to set up a repository somewhere? Thanks! Paulo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] CnC Haskell
Hi Ryan, I see the generated C++ but where is the CnC front-end code? Regards, Vasili On Thu, Sep 2, 2010 at 7:23 PM, Ryan Newton new...@mit.edu wrote: Belated update: The haskell-cnc distribution (if you grab it from darcs) now has a front-end that parses the graph description files. http://hackage.haskell.org/package/haskell-cnc For any readers who haven't seen this before -- CnC is a parallel programming model that includes both a library and a small DSL for graph specification. The specification file describes the structure of an application and captures various invariants about data access. The CnC front-end in the haskell-cnc distro is meant to replace existing CnC spec translators and generate code for all host languages that support the programming model (currently C++, Java, .NET, Haskell). Also the graph specification language is getting a refresh in the process (new features/syntax). The parser is done with Happy. What's there right now only generates C++ code, but the Haskell codegen is straightforward and should come along shortly (anyone want to help?). The purpose of such a front-end is to generate code that: (1) saves boilerplate in graph construction (more of a problem in non-haskell languages) (2) correctness: enforces invariants expressed in the specification (3) performance: generate code that embodies graph analysis and optimizations (based also on profiling data) Cheers, -Ryan On Fri, Jun 25, 2010 at 11:02 AM, David Peixotto d...@rice.edu wrote: There is a reference for the CnC grammar in the repository for the .NET implementation. http://github.com/dmpots/CnC.NET/blob/master/CnC.NET/CnC.NET/cnc.grammar The parser specification for fsyacc (the F# YACC implementation) is here: http://github.com/dmpots/CnC.NET/blob/master/CnC.NET/CnC.NET/Parser.fsy The textual representation is still in flux a bit, but this grammar should be enough of a guide for implementing a parser in Haskell. The grammar is left recursive, so using a parser generator like Happy would be a good choice. The textual representation will actually be a bit different depending on the underlying language since the types of items stored in a collection is part of the description. For example in C, an item collection that stores an array of ints would be declared like: [int* A]; but in Haskell we would want to write something like [Array Int Int A]; I think dealing with type declarations would in the textual representation would be the main difference in implementing the parser in Haskell. Once the textual representation has been parsed to an AST it should be possible to generate the Haskell code that builds the graph using the haskell-cnc package. -David On Jun 23, 2010, at 3:56 PM, Vasili I. Galchin wrote: On Wed, Jun 23, 2010 at 3:47 PM, Don Stewart d...@galois.com wrote: vigalchin: Hello, I have been reading work done at Rice University: http:// habanero.rice.edu/cnc. Some work has been done by http://www.cs.rice.edu/ ~dmp4866/ on CnC for .Net. One component that David wrote a CnC translator that translates CnC textual form to the underlying language, e.g. F#. Is anybody working on a CnC textual form translator for Haskell so a Haskell user of CnC Haskell can write in a higher level?? Ah, so by a translator from high level CnC form to this: http://hackage.haskell.org/packages/archive/haskell-cnc/latest/doc/hml/Intel-Cnc.htmlhttp://hackage.haskell.org/packages/archive/haskell-cnc/latest/doc/html/Intel-Cnc.html ^^ exactly what I mean ? Do you have a reference for the CnC textual form? ^^ if you mean something like a context-free grammatical definition of the CnC textual form ,,, the answer is I haven't seen such a reference. V. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: text 0.8.0.0, fast Unicode text support
On Wed, Sep 1, 2010 at 12:29 PM, Daniel Fischer daniel.is.fisc...@web.dewrote: I'm on Linux. I guess that's another point in favour of it:) Do you happen to know why it's slower on a Mac? I'd guess because of something to do with the system iconv. So I tentatively believe most of the difference is spent doing the replacements. I have a Replace.hs benchmark in the main text repo, just to be sure we're talking about the same thing. Factoring out the time spent on I/O, with GHC HEAD, my replace code takes twice the space and time of that in the stringsearch package. Given that the space involved is just 121KB maximum residency while processing a 124MB file, I'm not concerned about it. And the time required isn't a bad place to start from, I think. By the way, as this implies, I can't reproduce your space behaviour at all. I can now say more. Looking at Data.Text.Lazy.replace, replace s d = intercalate d . split s , I also got a space leak with that for BS.Lazy's intercalate and stringsearch's split. How did you observe the space leak? Looking at -hT charted with hp2ps shows me nothing, and the program executes in constant space regardless of input size. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
