[Haskell-cafe] Re: Getting my feet wet - small browser game
Marc A. Ziegert schrieb: software upgrades: use Read/Show classes instead of Foreign.Marshal, I'm having second thoughts here. Wouldn't Show evaluate all thunks of the data Shown? That would mean I couldn't use infinite data structures in data that goes out to disk. I don't think this would be a strong restriction for the communication between simulation and satellites, but I'm pretty sure it would be for doing backups of the simulation. Unfortunately, doing simulation backups is also the area where versioning is probably the harder problem. But I think I can work around that. I'd simply have to write a small upgrade program whenever data structures change, which unmarshalls using the old code and marshalls using the new code. Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Low-level Haskell profiling [Was: Re: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project]
Hi, The GHC head can currently build against PAPI[1], a library for gathering CPU statistics. I did not know that. I know PAPI, though I prefer using perfctr directly, at least for what I'm doing (stuff in a JVM) [1], [2], [3]. At the moment you can only gather such statistics for AMD Opteron but it shouldn't be difficult to port it to other CPUs after a bit of browsing around the PAPI docs. Installing PAPI requires installing a linux kernel driver though, so it is not for the faint hearted. Well, AFAIK, PAPI abstracts away the platform dependencies quite well, so I guess your code can be run straightforward on all IA-32 platforms (depending on the events you wish to measure, which may or may not be present on all platforms). PowerPC, Itanium, Mips, Alpha should work as well, IIRC. If the GHC backend can generate code there, that is. We have used this library to find bottlenecks in the current code generation and we have implemented ways of correcting them, so expect some good news about this in the future. Have you published anything about that? I should get around to start a wiki page about using PAPI these days, but meanwhile feel free to contact me if you need further information or help. I've been toying with this idea for a while [4], but never had the time to do something with it. If you have some cool stuff, let us know. I'm very interested. -- Andy [1] Eeckhout, L.; Georges, A.; De Bosschere, K. How Java Programs Interact with Virtual Machines at the Microarchitectural Level. Proceedings of the 18th Annual ACM SIGPLAN Conference on Object- Oriented Programming, Systems, Languages and Applications (OOPSLA 2003). ACM. 2003. pp. 169-186 [2] Georges, A.; Buytaert, D.; Eeckhout, L.; De Bosschere, K. Method- Level Phase Behavior in Java Workloads. Proceedings of the 19th ACM SIGPLAN Conference on Object-Oriented Programming Systems, Languages and Applications. ACM Press. 2004. pp. 270-287 [3] Georges, A.; Eeckhout, L.; De Bosschere, K. Comparing Low-Level Behavior of SPEC CPU and Java Workloads. Proceedings of the Advances in Computer Systems Architecture: 10th Asia-Pacific Conference, ACSAC 2005. Springer-Verlag GmbH. Lecture Notes in Computer Science. Vol. 3740. 2005. pp. 669-679 [4] http://sequence.complete.org/node/68 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Versioning
As written in my other post, I will need to update data structures that were marshalled to disk. Now I'm wondering how to best prepare for the situation. E.g. one of the common situations is that a single data item gets replaced by a list of items. Now assume that there's a SomeData type that's used across the game, and which gets incompatibly updated SomeData1 (say, instead of containing just a string it turns into a list of strings). The update code would now have to unmarshall a blob of game data, traverse it to find all instances of SomeData, wrap them in a one-element list to turn them into SomeData1s, reconstruct the blob of game data with the SomeData1 items, and marshall the result back out to disk. This sounds as if I'd have to write code for every single data type in the update program just to update a single data type. Is that true, or is there a way around this? Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Getting my feet wet - small browser game
jo: Marc A. Ziegert schrieb: software upgrades: use Read/Show classes instead of Foreign.Marshal, I'm having second thoughts here. Wouldn't Show evaluate all thunks of the data Shown? That would mean I couldn't use infinite data structures in data that goes out to disk. Btw, if you're dumping large structures to disk, using Read/Show is a bad idea :) Use NewBinary, at a minimum, or one of the other serialisation modules (possibly the one used in HAppS based on bytestrings) would be a better option. Read/Show is good for testing that the serialising code works, though. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project
Hello ls-haskell-developer-2006, Tuesday, December 19, 2006, 9:32:13 PM, you wrote: why you (and Donald) don't want to understand me. i say that imperative Haskell code is more efficient Second: Bulat, I think your generalization is, that performance matters so much and all the time i don't say so. please don't make me a root of all evil :) -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shrinking the Prelude: The categorical approach
Hello Imam, Wednesday, December 20, 2006, 6:53:35 AM, you wrote: * clean categorical hierarchy of type classes i've tried to write alternative Base library. one caveat is that you can't redefine standard classes, such as Num, without changing ghc itself -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Showing the 1 element tuple
On Tue, 19 Dec 2006, Neil Mitchell wrote: () -- 0 element tuple (,) a b -- 2 element tuple (,,) a b c -- 3 element tuple The problem is that the separator approach (comma) doesn't scale well: http://haskell.org/haskellwiki/Terminator_vs._separator ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A suggestion for the next high profile Haskell project
On Mon, 18 Dec 2006, Bulat Ziganshin wrote: Monday, December 18, 2006, 4:46:16 PM, Henning Thielemann wrote: Very true. I really like to know some more clean tricks for speedup. use C. seriously :) I followed the thread, hoping for a reference to an existing tutorial or an announcement of an article on efficient but idiomatic Haskell programming. But it seems, there is no such tutorial so far. It seems that the tips on http://www.haskell.org/ghc/docs/6.6/html/users_guide/faster.html are not complete. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shrinking the Prelude: The categorical approach
On Tue, 19 Dec 2006, Imam Tashdid ul Alam wrote: hi guys, I was just wondering if anyone is interested is a quasi-project of rewriting the Prelude (only shrinking it as measured by the total number of names imported, read along...) There is a hybrid Java-Haskell language which also contains a Prelude with renamed functions: http://labs.businessobjects.com/cal/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Versioning
Hi Jo, You seem to be describing SYB and not knowing it: http://homepages.cwi.nl/~ralf/syb1/ That basically does exactly what you've requested, in terms of traversing all items when only one matters. That said, serialisation is still a hard problem - think long and hard before picking a data format. With Yhc.Core I used Drift to derve Binary instances, keep a version tag, and if the version tags mismatch refuse to load the data. Thanks Neil On 12/20/06, Joachim Durchholz [EMAIL PROTECTED] wrote: As written in my other post, I will need to update data structures that were marshalled to disk. Now I'm wondering how to best prepare for the situation. E.g. one of the common situations is that a single data item gets replaced by a list of items. Now assume that there's a SomeData type that's used across the game, and which gets incompatibly updated SomeData1 (say, instead of containing just a string it turns into a list of strings). The update code would now have to unmarshall a blob of game data, traverse it to find all instances of SomeData, wrap them in a one-element list to turn them into SomeData1s, reconstruct the blob of game data with the SomeData1 items, and marshall the result back out to disk. This sounds as if I'd have to write code for every single data type in the update program just to update a single data type. Is that true, or is there a way around this? Regards, Jo ___ 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] Re: Getting my feet wet - small browser game
Hi Btw, if you're dumping large structures to disk, using Read/Show is a bad idea :) Just as a mention how bad it is, maybe 30 times at Show and 50 times at Read. I used to use this approach, moving away from it and learning how to use Drift was a good idea. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] RE: New Layout Rule take 2
[EMAIL PROTECTED] wrote: I have made some improvements to the algorithm, and I am happy to say that with some minor tweaks, it correctly lays out the programs in the nofib suite. the algorithm is not much more complicated than the current one in the report, but doesn't have the parse-error rule. it does require a single token of lookahead to look for an in. darcs get http://repetae.net/repos/getlaid/ I have also added a mode so it can work as a ghc preprocesor, allowing very easy testing. just compile with. ghc -pgmF /path/to/getlaid -F --make Main.hs and it will automatically process all your files. Nice! I ran the GHC parser tests using your preprocessor, and get 9 failures out of 27 in the should_compile class. Some of these are bogus (problems with the lexer you're using rather than the layout preprocessor). The should_fail class all failed, but that's because column numbers are different in the preprocessed result, so the error messages changed, I'll need to look at these individually. I've attached a patch that corrects a couple of the failures in the should_compile class. Cheers, Simon simonmar.patches Description: simonmar.patches ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] Haskell Weekly News: December 20, 2006
On 20-dec-2006, at 2:17, Donald Bruce Stewart wrote: -- - Haskell Weekly News http://sequence.complete.org/hwn/20061220 Issue 54 - December 20, 2006 -- - Announcements Haskell Vim plugin. Arthur van Leeuwen [15]announced a new [16]vim plugin for Haskell providing some preliminary folding support, easy insertion of type signatures into programs, and support for handling .hi files. 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/17675 16. http://www.cs.uu.nl/~arthurvl/haskell.vba Read that as 'support for automatically ignoring .hi files' (which really helps when editing large programs consisting of multiple files... it makes tab Do The Right Thing). Doei, Arthur. -- /\/ | [EMAIL PROTECTED] | Work like you don't need the money /__\ / | A friend is someone with whom | Love like you have never been hurt /\/__ | you can dare to be yourself | Dance like there's nobody watching ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Success with Takusen (was: Type problem with simpletakusen code)
To build a program, you need to do ghc --make db.hs -o db D:\Oracle\Ora92\bin\oci.dll (put the path to your oci.dll here). This compiles your program, and links it with oci.dll to get the Oracle externals resolved. I've been working with Paul on his linking problems, and there's a gotcha for Oracle 10 users. Apparently the folder that contains oci.dll, typically $ORACLE_HOME/bin, can also include hsbase.dll, which has something to do with Heterogeneous Services. Obviously (this being Windows, where filenames are not case sensitive) this clashes with GHC's HSbase.dll; hence linker errors. I'm not sure exactly what the solution should be; one obvious one is to not include Heterogeneous Services in your installation. I'm also not sure if this affects Oracle clients; Paul hinted that he was pointing at a server installation folder, so a standard client installation is likely to be OK. Alistair * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FD problem in GHC 6.6
On Dec 19, 2006, at 10:11 PM, Dan Weston wrote: instance CommandFunction (Sh st ()) st where ^ I think your first argument (on which the second has a functional dependence) does not determine the second argument, since it makes use of st in the first argument. This strikes me as a likely place to begin. No, I'm pretty sure this isn't a problem. The second argument is determined _because_ it is mentioned in the first. The functional dependencies and instance declarations work, as long as I can make the compiler accept them. They are only being rejected by the termination-checking part of the algorithm. That said, I'm open to the idea of reformulating these instances. In fact, I don't really like the fact that I need FDs. It seems to me that I should somehow be able to eliminate the second argument altogether and thus the FD, but I can't seem to figure it out. Dan Robert wrote: Fellow Haskellers, I have a package that uses some light typeclass hackery to automaticly build parsing algorithms based on the type of a function. I was recently informed that my package doesn't compile on GHC 6.6 due to the new restrictions on FD resolution; in particular I have instance declarations which fail the coverage condition. I can use undecidable instances to make the package compile again, but I'd prefer not to if I can avoid it. class CommandFunction f st | f - st where parseCommand :: String - f - CommandParser st commandSyntax :: f - [Doc] instance CommandFunction (Sh st ()) st where parseCommand wbc m str = -- list monad do (x,[]) - runRegex (maybeSpaceBefore (Epsilon (CompleteParse m))) str return x commandSyntax _ = [] instance CommandFunction r st = CommandFunction (Int - r) st where parseCommand = doParseCommand Nothing intRegex id commandSyntax f = text (show intRegex) : commandSyntax (f undefined) instance CommandFunction r st = CommandFunction (Integer - r) st where parseCommand = doParseCommand Nothing intRegex id commandSyntax f = text (show intRegex) : commandSyntax (f undefined) Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shrinking the Prelude: The categorical approach
Imam Tashdid ul Alam wrote: hi guys, I was just wondering if anyone is interested is a quasi-project of rewriting the Prelude (only shrinking it as measured by the total number of names imported, read along...) the idea is (just to be substantially different in approach) to develop an alternate history of Haskell. take map for example, and fmap, I don't think they should be named different (fmap is ugly, not suggestive, and conceptually the same). mplus could be renamed (++) (they are conceptually the same I suggest that all functions in classes be given actual names and ASCII symbolic names could be defined outside the class as an additional convenience eg: class Monad m = MonadPlus m where mzero :: m a mplus :: m a - m a - m a (++) = mplus-- 'convenience' name I think people forget that ASCII symbol names which look intuitive to them when they are writing a library or paper, can be very confusing for people who need to use many libraries (with consequent explosion of obfuscatory symbols) in a project, look terrible when qualified, and make code difficult to read because of the need to find/remember precedences and associativity. (Note that Haddock does *not* supply this info, you need to look at the actual source code of the library to find it out.) , mzero looks odd, name it empty, or simply zero) What about (mempty) from Monoid or (empty) from Data.Sequence or Control.Applicative? Either these are in some way the same thing as mzero, or else they are different in which case either qualified imports would be needed everywhere (not necessarily a bad thing) or different names like the ones we already have, are needed. although I think concat should be replaced by msum (or the other way around preferably :) ? msum is a bad name) I am somewhat confused by join. concat seems to match join's type but I don't think the ideas coincide. and so on. in particular, we would want: * no backwards compatibility. the Prelude as is it, is good enough. we are defining a new module. Starting with a clean slate seems a good idea, especially to get rid of lispy names like (cons), (snoc), (null) and replace them with something self-explanatory like (pushL), (pushR), (isEmpty). * clean categorical hierarchy of type classes (category theorists wanted!) promoting uniformity. This would be great. However it is a question to me whether it is even possible to organize everything in a single hierarchy. Eg look at the problems with trying to reorganize Num, or standard OOP problems with hierarchies in general. Since there are multiple ways of looking at a domain, it is likely there will need to be multiple hierarchies which will probably not interact so well. * cleaner names. foldl1 means nothing. absolutely nothing. what's the 1 for? A while back I suggested using capital letters for suffix to distinguish the functionality (fold) from the variant (L == left). Perhaps (foldl1) could be renamed (foldLN) ie fold + left + non-empty or (foldLO) for fold + left + occupied. * our Prelude only contains typeclasses, datatypes, and functions of utmost conceptual (and semantic, such as error, undefined and seq) importance, everything else goes to other modules. our Prelude is not going to be a place for convenient declarations. * the suffix method of naming (liftM2) is considered messy. we would prefer a seperate module (promoting qualified import). In the particular case of *M functions, I quite like the existing naming since it's clear that it's a monadic function. However I'd agree that names like (newIORef) are an abomination, that should be replaced by (Ref.new). this is a fun project. we will not rewrite the Prelude, we'll merely rename it. I would suggest the name TheOtherPrelude to make our intentions clear. the conveniences (like concatMap) goes to TheOtherPrelude.Extension. I suggest we do it on the wiki. anyone interested just open a page with your name of choice. I am not doing it only because there's no point doing it if no one's interested. Good luck with this. For my own project, I re-implemented FingerTree's so I could use my preferred naming style (and also as an exercise following the excellent tutorial-style FingerTree paper), and wrote some trivial wrappers for a few other modules eg Data.IORef, Data.Unique so that I could use Ref.new, Unique.new etc.I think it would be quite a big task to refactor the entire code base according to a clean hierarchy of type classes, and also a task I can't really help with since I'm not familiar enough with category theory at present, but certainly it would be a worthwhile endeavour imho, Brian. -- http://www.metamilk.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Success with Takusen (was: Type problem with simpletakusen code)
On 12/20/06, Bayley, Alistair [EMAIL PROTECTED] wrote: To build a program, you need to do ghc --make db.hs -o db D:\Oracle\Ora92\bin\oci.dll (put the path to your oci.dll here). This compiles your program, and links it with oci.dll to get the Oracle externals resolved. I've been working with Paul on his linking problems, and there's a gotcha for Oracle 10 users. Apparently the folder that contains oci.dll, typically $ORACLE_HOME/bin, can also include hsbase.dll, which has something to do with Heterogeneous Services. Obviously (this being Windows, where filenames are not case sensitive) this clashes with GHC's HSbase.dll; hence linker errors. To clarify a little - I believe the issue exists on Oracle 8i, 9i and 10g. It's not so much the version as the options you choose when you install the software. As far as I am able to confirm, a default enterprise edition install includes hsbase.dll. A default client install does not. If you do a custom install, then the relevant option is Heterogeneous Services - but the simplest way to check is just to look for hsbase.dll in the oracle home\bin directory. Alistair - maybe you could add a check in Setup.hs, to see if hsbase.dll is present, and if so, to display a warning? I can sort of see where such a check would occur (in configOracle), but I don't know enough about Cabal to suggest code... Paul. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] multi parameter type classes for NP problems
Hi all,
For my own study, I've been playing around with various NP complete
problems. Previuosly I was doing so in Java, but because I want to
learn Haskell, I'm trying to port the algorithms. In Java, I had an
abstract class called AbstractNPProblem which looked like this:
public abstract class AbstractNPProblem implements NPProblem {
public abstract boolean validates(Certificate c);
public abstract ListCertificate certificates();
public boolean decide() {
for (Certificate c : certificates()) {
if (validates(c)) {
return true;
}
}
return false;
}
}
This has one problem, however: it is slightly dynamically typed.
Anybody that implements the verify method must cast the object c to a
particular type (could be a bitmask, a list of integers, a subgraph,
etc.) I'd like to get rid of this problem in porting to Haskell. Here
is how I am trying to solve the problem, using multi-parameter type
classes.
class NPProblem inst cert where
validates :: cert - inst - Bool
certificates :: inst - [cert]
decide :: inst - Bool
decide i = any (\x - x `validates` i) $ certificates i
Unfortunately, ghc throws the following type error:
NPProblem.hs:5:45
Could not deduce (NPProblem inst a)
from the context (NPProblem inst cert)
arising from use of `certificates' at NPProblem.hs:5:45-58
Possible fix:
add (NPProblem inst a) to the class or instance method `decide'
In the second argument of `($)', namely `certificates i'
In the expression:
(any (\ x - x `validates` i)) $ (certificates i)
In the definition of `decide':
decide i = (any (\ x - x `validates` i)) $ (certificates i)
Could somebody explain what is wrong with my intuitive approach? Also,
is multi parameter type classes the way to go, or is there a better
way?
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Re: [Haskell-cafe] FD problem in GHC 6.6
Hi, I don't have a solution for you problem (besides using undecidable instances) but I can explain the coverage condition. On 12/19/06, Robert [EMAIL PROTECTED] wrote: class CommandFunction f st | f - st where parseCommand :: String - f - CommandParser st commandSyntax :: f - [Doc] The functional dependency on this class adds the following axiom (improvement rule) : improve (CommandFunction f st1, CommandFunction f st2) using st1 = st2 Before accepting an instance, an implementation needs to check that the instance will not violate this rule (i.e., the functional dependency is satisfied). In general, this may be difficult to check. The coverage condition (CC) is a (conservative) rule that guarantees that the functional dependency is satisfied. It states that an instance is accepted if all type variables in the determined types are mentioned in the determining types. The rule is conservative because (as you have noticed) there are cases when the FD axiom is not violated but the rule rejects an instance.Examples: instance CommandFunction (Sh st ()) st where parseCommand wbc m str = ... This instance satisfies the CC because st is mentioned in Sh st (). instance CommandFunction r st = CommandFunction (Int - r) st where ... This instance does not satisfy the CC because st is not mentioned in Int - r. instance CommandFunction r st = CommandFunction (Integer - r) st where ... This instance does not satisfy the CC because st is not mentioned in Integer - r. Hope this helps. -Iavor ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Versioning
Neil Mitchell schrieb: You seem to be describing SYB and not knowing it: http://homepages.cwi.nl/~ralf/syb1/ That basically does exactly what you've requested, in terms of traversing all items when only one matters. Yup, that's exactly what I was looking for. Actually I had seen it a while ago, but didn't remember it now. Thanks. One thing that might become a problem is that the Scrap your boilerplate approach seems to work only in GHC. There's nothing wrong with GHC, but it sounds like I'm committing to a specific compiler right from the start. I'd like to keep the number of choices as high as possible... and besides, if the compiler gives me an error message, or the generated code does unexpected things, I'd like to have the possibility to cross-check with a different compiler. So have other compilers picked up SYB support yet? It might be not feasible though. The papers mention that you can't serialize (well, actually unserialize) function values with it. For the envisioned update-through-marshalling process, this would prevent me from ever using function values in data that needs to be persistent, and that's quite a harsh restriction. That said, serialisation is still a hard problem - think long and hard before picking a data format. What would be the problems of choosing the wrong one? With Yhc.Core I used Drift to derve Binary instances, keep a version tag, and if the version tags mismatch refuse to load the data. Links? Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] multi parameter type classes for NP problems
Joshua Ball wrote: Here is how I am trying to solve the problem, using multi-parameter type classes. class NPProblem inst cert where validates :: cert - inst - Bool certificates :: inst - [cert] decide :: inst - Bool decide i = any (\x - x `validates` i) $ certificates i Unfortunately, ghc throws the following type error: NPProblem.hs:5:45 Could not deduce (NPProblem inst a) from the context (NPProblem inst cert) arising from use of `certificates' at NPProblem.hs:5:45-58 Possible fix: add (NPProblem inst a) to the class or instance method `decide' In the second argument of `($)', namely `certificates i' In the expression: (any (\ x - x `validates` i)) $ (certificates i) In the definition of `decide': decide i = (any (\ x - x `validates` i)) $ (certificates i) Maybe something like?... class NPProblem inst cert where validates :: cert - inst - Bool certificates :: inst - [cert] decide :: inst - Bool decide i = any (\x - x `validates` i) $ (certificates i :: [cert]) ...or a functional dependency of some sort... class NPProblem inst cert | inst - cert where ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
On Wed, Dec 20, 2006 at 07:30:02PM +0100, Joachim Durchholz wrote: Neil Mitchell schrieb: You seem to be describing SYB and not knowing it: http://homepages.cwi.nl/~ralf/syb1/ That basically does exactly what you've requested, in terms of traversing all items when only one matters. Yup, that's exactly what I was looking for. Actually I had seen it a while ago, but didn't remember it now. Thanks. You spoke of changing each element to something of a different type. I don't think SYB can do that. A solution (and a portable one too) might be to parameterize all these types, and make them instances of Functor, Foldable and Traversable (see Data.Foldable and Data.Traversable in the GHC 6.6 documentation). You'd have the labour or writing all those instances (though the trivial instances of Functor and Foldable would suffice). But once you've done that, a range of different traversals would be available. It might be not feasible though. The papers mention that you can't serialize (well, actually unserialize) function values with it. For the envisioned update-through-marshalling process, this would prevent me from ever using function values in data that needs to be persistent, and that's quite a harsh restriction. That's hard to avoid, unless you have a data representation of the functions you're interested in. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] #haskell irc channel reaches 300 users
Nice to know! Can anybody tell me, how many people have subscribed to the Haskell Cafe mailing list? What is the growth? How many people visit haskell.org? On Tue, 19 Dec 2006 03:04:43 +0100, Donald Bruce Stewart [EMAIL PROTECTED] wrote: A small announcement :) 5 years after its inception, under the guiding hand of Shae Erisson (aka shapr), the #haskell IRC channel[1] on freenode has finally reached 300 users! -- Met vriendelijke groet, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ -- Using Opera's revolutionary e-mail client: https://secure.bmtmicro.com/opera/buy-opera.html?AID=789433 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Versioning
Ross Paterson schrieb: It might be not feasible though. The papers mention that you can't serialize (well, actually unserialize) function values with it. For the envisioned update-through-marshalling process, this would prevent me from ever using function values in data that needs to be persistent, and that's quite a harsh restriction. That's hard to avoid, unless you have a data representation of the functions you're interested in. I could encode functions by their name. I don't think that would scale to a large application with multiple developers, but it's not this kind of project anyway. I'd be reluctant to accept that way if it means adding boilerplate code for every function that might ever be serialized. Since I'm planning to serialize an entire application, I fear that I'd need that boilerplate code for 90% of all functions, so even a single line of boilerplate might be too much. Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] YAHT bug
Hi, The page says this was corrected in the wikibook, but it seems not to have been fixed in the darcs repository at haskell.org. Sorry for that. I still haven't worked out a smart way to update the darcs repository from the wikibook. I'm thinking of versioning a copy of the wiki pages with darcs, and using mvs to synch with the wiki. This will help me keep track of changes, which I can then manually transfer to the latex version. It is on my projects list; I just haven't gotten around to it yet. The intention is for the wikibook version to be the unstable YAHT and the latex version to be stable. I found no mentioning on the YAHT page of ways to change this, so sending a mail to this list seemed simplest to me. One way to do it would be to 1) retrieve with: darcs get http://darcs.haskell.org/yaht 2) edit the latex files in question 3) darcs record 4) darcs send I will then review the changes and push them in. Best, -- Eric Kow http://www.loria.fr/~kow PGP Key ID: 08AC04F9 Merci de corriger mon français. pgplOFAd65tAr.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
On Dec 20, 2006, at 2:37 PM, Joachim Durchholz wrote: Ross Paterson schrieb: It might be not feasible though. The papers mention that you can't serialize (well, actually unserialize) function values with it. For the envisioned update-through-marshalling process, this would prevent me from ever using function values in data that needs to be persistent, and that's quite a harsh restriction. That's hard to avoid, unless you have a data representation of the functions you're interested in. I could encode functions by their name. I don't think that would scale to a large application with multiple developers, but it's not this kind of project anyway. I'd be reluctant to accept that way if it means adding boilerplate code for every function that might ever be serialized. Since I'm planning to serialize an entire application, I fear that I'd need that boilerplate code for 90% of all functions, so even a single line of boilerplate might be too much. Let me just say here that what you are attempting to do sounds very difficult. As I understand, you want to be able to serialize an entire application at some (predetermined / arbitrary?) point, change some of its code and/or data structures, de-serialize and run the thing afterwards. Doing something like this without explicit language support is going to be hard, especially in a fairly static language like Haskell. I would think Smalltalk, Erlang, or something from the Lisp/Scheme family would be more suitable for this sort of work (caveat, I have little experience with any of these languages). Also, take a look here (http://lambda-the-ultimate.org/node/526) for some related discussion. Regards, Jo Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Versioning
Robert Dockins schrieb: Let me just say here that what you are attempting to do sounds very difficult. As I understand, you want to be able to serialize an entire application at some (predetermined / arbitrary?) point, change some of its code and/or data structures, de-serialize and run the thing afterwards. Right. Though it's not too far out of the ordinary. Haskell being a rather orthogonal language, I had hoped that I can simply serialize any data structure. Doing something like this without explicit language support is going to be hard, especially in a fairly static language like Haskell. Exactly. I was intrigued when I found that libraries can do quite a lot serialization in Haskell - that gives Haskell an excellent rating in what could be called aspect-orientedness. It doesn't help to serialize functions values or thunks, though. I would think Smalltalk, Erlang, or something from the Lisp/Scheme family would be more suitable for this sort of work (caveat, I have little experience with any of these languages). Erlang is actually on my list of potential alternatives. It has different advantages than Haskell, though, and right now, I'm willing to try Haskell. Also, take a look here (http://lambda-the-ultimate.org/node/526) for some related discussion. I'm not sure whether that relates to my project. I let network connections be handled by Apache and FastCGI, so I'm leaving out a whole lot of library issues that hit that reported project really hard. Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to serialize thunks?
I have skimmed the serialization libraries on haskell.org (NewBinary, SerTH, AltBinary, HsSyck, GenericSerialize). I'm under the impression that these all force the data that they serialize. Is that correct? If yes: are there workarounds? I'd really like to be able to use infinite data structures in the data that I serialize. Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shrinking the Prelude: The categorical approach
take map for example, and fmap, I don't think they should be named different (fmap is ugly, not suggestive, and conceptually the same). mplus could be renamed (++) (they are conceptually the same Wouldn't this raise the same problems monad comprehensions raise? Worse yet, beginners can't start off with lists -- and understand error messages -- without knowing about monads first! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Origins of (x:xs)?
Paul Hudak [EMAIL PROTECTED] writes: As for x:xs, the xs is meant to be the plural of x, and is pronounced exs (I guess...). Similarly, n:ns is one n followed by many more ens. Make sense? I think this convention is often used in the Prolog community as well, as in X|Xs. -- Doug Quale ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] multi parameter type classes for NP problems
That works. Thanks. I didn't realize you could put types in the expression itself. On 12/20/06, Greg Buchholz [EMAIL PROTECTED] wrote: Joshua Ball wrote: Here is how I am trying to solve the problem, using multi-parameter type classes. class NPProblem inst cert where validates :: cert - inst - Bool certificates :: inst - [cert] decide :: inst - Bool decide i = any (\x - x `validates` i) $ certificates i Unfortunately, ghc throws the following type error: NPProblem.hs:5:45 Could not deduce (NPProblem inst a) from the context (NPProblem inst cert) arising from use of `certificates' at NPProblem.hs:5:45-58 Possible fix: add (NPProblem inst a) to the class or instance method `decide' In the second argument of `($)', namely `certificates i' In the expression: (any (\ x - x `validates` i)) $ (certificates i) In the definition of `decide': decide i = (any (\ x - x `validates` i)) $ (certificates i) Maybe something like?... class NPProblem inst cert where validates :: cert - inst - Bool certificates :: inst - [cert] decide :: inst - Bool decide i = any (\x - x `validates` i) $ (certificates i :: [cert]) ...or a functional dependency of some sort... class NPProblem inst cert | inst - cert where ___ 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] Shrinking the Prelude: The categorical approach
Wouldn't this raise the same problems monad comprehensions raise? The do-notation isn't specific to IO, yet it is the only thing beginners use it for. Do beginners have noticeably more trouble with the do-notation errors than list comprehension errors? As someone who learned Haskell fairly recently, I never really read the compiler errors. I looked for the line number, and whether it was a type error or syntax error. The rest might as well have been Greek, and I was fine with that. Thanks, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Side Effect
Since learning Haskell, I can now count in Spanish! See: one in Spanish, two in Spanish, three in Spanish, four in Spanish.. -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
I thought this email might be interesting for the Spanish speaking part of the Haskell community, so I have written it in Spanish for them: (Since learning Haskell, I can now count in Spanish! See: one in Spanish, two in Spanish, three in Spanish, four in Spanish.. -- Ashley Yakeley) in Spanish ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi With Yhc.Core I used Drift to derve Binary instances, keep a version tag, and if the version tags mismatch refuse to load the data. Links? http://repetae.net/~john/computer/haskell/DrIFT/ http://darcs.haskell.org/yhc/src/libraries/general/Yhc/General/Binary.hs Thats Drift which can derive binary instances (pick GhcBinary), and then a module which can work with the derived classes. Warning, mild hacking was required to get it going on Windows. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
Bernie Pope writes: I thought this email might be interesting for the Spanish speaking part of the Haskell community, so I have written it in Spanish for them: (Since learning Haskell, I can now count in Spanish! See: one in Spanish, two in Spanish, three in Spanish, four in Spanish.. Ashley Yakeley) in Spanish = You have proven once more how powerful is the Haskell genericity. It is straightforward to extend the algorithm to Polski and Türkçe. ...werbeH neve dna a n d C h i n e s e == Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
Am I the only one that doesn't get it? Jason On 12/20/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: Bernie Pope writes: I thought this email might be interesting for the Spanish speaking part of the Haskell community, so I have written it in Spanish for them: (Since learning Haskell, I can now count in Spanish! See: one in Spanish, two in Spanish, three in Spanish, four in Spanish.. Ashley Yakeley) in Spanish = You have proven once more how powerful is the Haskell genericity. It is straightforward to extend the algorithm to Polski and Türkçe. ...werbeH neve dna a n d C h i n e s e == Jerzy Karczmarczuk ___ 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] Haskell Side Effect
On 12/20/06, Bernie Pope [EMAIL PROTECTED] wrote: (Since learning Haskell, I can now count in Spanish! See: one in Spanish, ... Ashley Yakeley) in Spanish I notice you're using the assumption that Spanish is a Monad so that Double Spanish can be mapped back into Spanish. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Shrinking the Prelude: The categorical approach
On 12/20/06, Diego Navarro [EMAIL PROTECTED] wrote: take map for example, and fmap, I don't think they should be named different (fmap is ugly, not suggestive, and conceptually the same). mplus could be renamed (++) (they are conceptually the same Wouldn't this raise the same problems monad comprehensions raise? Worse yet, beginners can't start off with lists -- and understand error messages -- without knowing about monads first! I may be in the distinct minority here, but I greatly miss monad comprehensions. Since the objection to monad comprehensions (as well as more general types for (++) etc) seems to be difficulty for beginners, has anyone considered providing either language levels as a command line switch - ala Dr. Scheme - or specifying the meaning of comprehensions et. al. in regard to whatever operations are in scope and then having different versions of the Prelude for educational purpose? (As a side note, when I was first learning Haskell and learned about MonadPlus - with the comment that (++) was the monadic plus operator for lists, I gleefully assumed that (++) :: MonadPlus m = m a - m a - m a, and was quite happily surprised that something I'd been using for a while was actually more general than I'd realized. When I found out that it wasn't really, I was quite disappointed.) /g -- It is myself I have never met, whose face is pasted on the underside of my mind. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Showing the 1 element tuple
have it be ( ) 1 with a space between the parens to denote that it is a single tuple rather than a nullary one. John -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
On 12/20/06, Jason Dagit [EMAIL PROTECTED] wrote: Am I the only one that doesn't get it? Jason No, you are not the only one that doesn't get it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
Ashley Yakeley wrote: Since learning Haskell, I can now count in Spanish! See: one in Spanish, two in Spanish, three in Spanish, four in Spanish.. Is there a solution ie some concept C such that C Haskell C Spanish, somewhere? Thanks, Brian. -- http://www.metamilk.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Shrinking the Prelude: The categorical approach
so the main issues are these: Bulat Ziganshin raised: Num is intrinsically bound to the compiler. sad. so let's leave Num out. this basically means we will avoid abstract algebra in general. that is, forget groups, rings, for now, the principle focus will be functor, monad... Henning Thielemann provided links to CAL: hi Henning, would you mind if we steal some of the good looking names in your Prelude? Brian Hulley raised one serious issue: even if we were to define a newbie friendly Prelude, which should be preferred, alphanumeric names or operators? I have a thing for operators, they look good! but Brian's issue is solid, the precedence isn't documented by Haddock. any Haddock developer reading this? so mplus stays. I would still suggest plus/zero over mplus/zero but Haskell's scoping is rather liberal. I suggest the convention that Control.Monad is always imported as M. this would mean we use M.plus, M.zero, M.lift and so on. Diego Navarro said: this will confuse beginners. I disagree. I think type classes and monads are the basics of Haskell (before that, it's just commonsense ;)... ) so if the error message successfully conveys the message that there's a problem, that should be enough to inspire the beginner to start on the basics. besides, people will ultimately use the standard Prelude. what I am trying to do is to prove that with a good choice of names programs written in Haskell can look more comprehensible to beginners. like Gosling said about Java, the language syntax has one very good property: it's easy to read it. Garrett Morris seems to agree with me on this. Greg Fitzgerald raised the further issue of monads being overlooked by the beginners. I think do notation considered harmful blog was at least partially right: it's better to expose the concept rather than hiding it. so with enough people interested (I assume) it's time to move this discussion to the wiki. the wiki code is not to be taken seriously, it's a proof-of-concept, a guideline. cheers! Imam __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Side Effect
On Wed, 20 Dec 2006, Bryan Burgers wrote: On 12/20/06, Jason Dagit [EMAIL PROTECTED] wrote: Am I the only one that doesn't get it? Jason But your question on it clearly implies that you did get it. Murray Gross ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
