- Haskell-Cafe - Haskell.org

[Haskell] AJAX applications in Haskell
by Dimitry Golubovsky 10 Aug '06

10 Aug '06

Looks like the discussion is continuing in the Cafe, so I am reposting it here. Hi, Pasqualino 'Titto' Assini wrote: =================== Assuming that the balance is positive, this naturally raises the question: why not doing the same <generate Javascript/Ajax application code to run in browser - DMG> with our favourite language? This would require to: - Retarget one of the existing Haskell compilers to generate JavaScript (other possible targets would be Flash or higher level UI languages such as OpenLaszlo that in turn compiles down to either Flash or JavaScript/HTML) =================== Joel Björnson wrote: =================== I am currently working on a Google Summer of Code project relating to some of this... The project is more or less bound to Haskell Server Pages ( http://www.cs.chalmers.se/~d00nibro/hsp/) enabling JavaScript code generation. The main difference compared to the Google Web Toolkit approach is that there are no special compiler magic added for compiling directly into JavaScript. =================== Looks like the idea is picked up by more and more people ;) I saw some notes on this (generation of Javascript from Haskell source) in Jared Updike's blog, and I got this idea myself independently from Jared in about the same time. I am trying to add some code to nhc98 (contrary to GHC its code is much smaller and better observable) to generate Javascript at the same time when STG tree is converted into bytecodes*. I am in the very beginning though, so I cannot show any results. OTOH I do not feel like I have a lot of time to dedicate to this, so if someone else is working on this, could we team up (possibly for a different (if shown better) approach because one I chose is still questionable optimization-wise, but generation of Javascript from bytecodes does not seem better to me at the time)? -------------- * Work in progress may be observed at http://www.golubovsky.org/repos/nhc98/ in particular in http://www.golubovsky.org/repos/nhc98/src/compiler98/STGJcode.hs but at the moment there is virtually nothing done. -- Dimitry Golubovsky Anywhere on the Web

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Flags
by Maduser 10 Aug '06

10 Aug '06

I have started to program in Haskell. Now I want programm something like flags. It's a set of flags. It sould be possible to convert the Flag as Int/String (the bit combination). I have written this: import Data.Set as Set type Flags = Set Flag data Flag = Flag1 | Flag2 | Flag3 deriving(Eq, Ord, Enum, Show) flagToInt :: Flags -> Int flagToInt flags = flag1 + flag2 + flag3 where flag1 = if member Flag1 flags then 1 else 0 flag2 = if member Flag2 flags then 2 else 0 flag3 = if member Flag3 flags then 4 else 0 but this seems to me to be inelegant. Can somebody help me making it better, please. -- View this message in context: http://www.nabble.com/Flags-tf2083897.html#a5741741 Sent from the Haskell - Haskell-Cafe forum at Nabble.com.

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Strictness, order of IO operations: NewCGI & HDBC
by Tim Smith 10 Aug '06

10 Aug '06

Hello! I'm having a problem with using NewCGI & HDBC together. NewCGI: http://www.cs.chalmers.se/~bringert/darcs/haskell-cgi/doc/ HDBC: http://quux.org/devel/hdbc http://darcs.complete.org/hdbc/ I've distilled it down to a small test case: \begin{code} module Main where import Data.List (intersperse) import qualified Database.HDBC as DB import Database.HDBC.ODBC (connectODBC) import Network.NewCGI main :: IO () main = runCGI (handleErrors cgiMain) cgiMain :: CGI CGIResult cgiMain = do dbh <- liftIO $ connectODBC "DSN=test" res <- liftIO (DB.getTables dbh) -- Remove the disconnect call, and all works liftIO (DB.disconnect dbh) output ((concat . intersperse ", ") res) \end{code} 2:46 ~/m/tmp/hs$ ./cgidb Content-type: text/html; charset=ISO-8859-1 cgidb: unknown exception If I comment out the DB.disconnect call, then it works fine. I tried to work around it with the DeepSeq module, but couldn't find an application of $!! or deepSeq which would make it function. I made a similar test which uses file IO instead of HDBC, and it behaves the way I want: \begin{code} module Main where import Network.NewCGI import System.IO main :: IO () main = runCGI (handleErrors cgiMain) cgiMain :: CGI CGIResult cgiMain = do h <- liftIO $ openFile "t.hs" ReadMode res <- liftIO (hGetLine h) liftIO (hClose h) output res \end{code} 2:55 ~/m/tmp/hs$ ./t Content-type: text/html; charset=ISO-8859-1 module Main My guess is that I'm doing something wrong, but I'm not sure what it is. Or, is this a bug in HDBC, somehow? Thanks for any ideas you might have, Tim -- If you're not part of the solution, you're part of the precipitate.

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IA64 porting: spill code in the mangler
by C Rodrigues 10 Aug '06

10 Aug '06

Hi folks, I've been trying to compile a new ia64 port. I've cross-compiled an unregisterised compiler that generated working binaries the first time it was built, which was a pleasant experience. But I ran into issues with the registerised build. The mangler is choking on floating-point spill code: Prologue junk?: .global __divdf3# .global GHCziFloat_zdwlogBase_entry# .proc GHCziFloat_zdwlogBase_entry# GHCziFloat_zdwlogBase_entry: mov r16 = r12 .save.f 0x1 stf.spill [r16] = f2 .body This saves floating-point register 2 on the stack; it's loaded again later. I could change the mangler to remove this code, if that's the right approach. What should the mangler do about it?

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beginner's haskell question
by Jens Theisen 09 Aug '06

09 Aug '06

Hello, as a haskell newbie I'm wondering about the following question. Are there options to popular haskell implementations or other means (haskell lint?) to check for incomplete patterns at compile time for some? I can't see a reason why this shouldn't be possible or even a relatively simple thing to implement. Cheers, Jens

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Re: Haskell-Cafe Digest, Vol 36, Issue 29
by Mark Haniford 09 Aug '06

09 Aug '06

It seems irony gets lost so easily in these conversations. You have no > way of knowing what the state of haskell would have been had certain > key contributors to GHC and Haskell not taken jobs at Microsoft. > Therefore you statement is meaningless and only good for producing > approving nods among people who already agree with what you say. What's meaningless are GPL jihadists who are bitter that not everybody is joining their religion. Yeah...that's personal.

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Why Not Haskell?
by Hans van Thiel 09 Aug '06

09 Aug '06

Hello All, I'm wondering why I can't find any commercial Haskell applications on the Internet. Is there any reason for this? I can think of the following possibilities only: 1) Haskell is too slow for practical use, but the benchmarks I found appear to contradict this. 2) Input and output are not good enough, in particular for graphical user interfacing and/or data base interaction. But it seems there are several user interfaces and SQL and other data base interfaces for Haskell, even though the tutorials don't seem to cover this. 3) Haskell is not scaleable for commercial use. This looks unlikely to me, but could this be a factor? 4) Haskell is open source and licensing restrictions forbid commercial applications. I haven't seen any such restrictions, but is this a problem for the standard modules? Are there other reasons why there seem to be just a few thousand (hundred?) Haskell programmers in the world, compared to the 3 million Java programmers and x million C/C++ programmers? The reason I ask is that in the early nineties I wrote a data mining /machine learning program. This was not a commercial success and since then I've been working as a free lance IT journalist. As such I covered the O'Reilly European Open Source Convention in Amsterdam last year and there I heard of Haskell. I became interested and started learning from the available free tutorials and Hugs. As an aside, I'd like to thank all those people. I really appreciate their work and I'd like to single out Hal Daume III's 'Yet Another Haskell Tutorial', while not diminishing the other authors in any way. Meanwhile I kept working on a data mining algorithm in my spare time and finally I came up with something that appears to work. While I was learning Haskell, I thought, why not try this part of the algorithm as a Haskell exercise. I could easily test it in Hugs. To my own surprise, after only a few weeks of this, I had a working prototype of my algorithm, printed out on less than 3 pages, using only standard functions in the Prelude. So, I'm really impressed by the power of Haskell, and I'm just a beginner. Now I'm trying to come up with a business model for my algorithm and to avoid the mistakes I made 10 years ago. There is a lot of difference between a prototype and a working tool, and then there is a lot of difference between a working tool and a successful commercial application. Probably it doesn't make much sense to try and develop a tool in C++ or even Java, but if I have to go on my own on this, maybe Haskell could be feasible, both for fun and profit. So, that's the background of my question (while introducing myself to the Cafe at the same time). Why hasn't Haskell made it into the business world (yet), after being available for 15 years, or is this the wrong question? Many thanks for your comments, Hans van Thiel

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HWS - With Plugins
by Johan Tibell 09 Aug '06

09 Aug '06

The HWS - With Plugins tarball is unavailable at the author's website (http://www.mdstud.chalmers.se/~md9ms/hws-wp/) and his email address doesn't work so this is desperate attempt to reach him. So, Martin Sjögren, are you here somewhere? P.S. If someone else knows where I could get hold of the source or at least the source of the original HWS I would be greatful. Cheers, Johan

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Abstract Data Types
by Johan Grönqvist 09 Aug '06

09 Aug '06

Hi, I have a question: Short version: If I want to hide the implementation of a data-type "Stack a" from the rest of the program, do I need to put its definition in a separate file? Long version: I want to use a stack, and I might implement it as a list, but I want to hide the implementation from the rest of the program. This is how I understand abstract data type. In "The Craft of Functional Programming", this seems to be implemented by putting each data type into a separate module and only exporting parts of the definitions. In "The Haskell School of Expression", this seems not to be used at all. In the lecture notes at (http://www.dcs.shef.ac.uk/~mps/courses/com2020/adts.pdf) type classes are used for abstract data types. It seems to me that this approach does not hide any parts of any definition, but only requires that all instances of class stack have functions pop and push of the correct types. I am interested in hiding parts of definitions. In the report, I did not find any mention of a requirement to have different modules in separate files, but I have not managed to put several modules in the same file using ghci. I would like to keep my small program in one literate-haskell tex-file and still be able to hide some definitions from others. Is this possible? One option would of course be to write a script that separates the code into different and then compiles the entire program. Thanks in advance! / johan grönqvist

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AJAX applications in Haskell
by tittoassini＠gmail.com 09 Aug '06

09 Aug '06

Hi, Those among you who have an interest in AJAX-style web development - that is to say the development of web applications that run entirely into the browser environment, calling back to the server back-end only to get raw data -- will probably have noticed the recent appearance of the Google Web Toolkit (http://code.google.com/webtoolkit) The main idea behind it is very simple: you write your Ajax application in Java and your code is compiled down to JavaScript/HTML (rather then to Java Virtual Machine bytecode) so that it can be executed in any browser. The main advantages of this solution are: - Development using a typed language with good compile-time checks and debugger support - No plugins (e.g. a Java VM) required on the user machine The disadvantages are: - An additional compilation step - Probably, a significant loss of performance with respect to hand-written code Assuming that the balance is positive, this naturally raises the question: why not doing the same with our favourite language? This would require to: - Retarget one of the existing Haskell compilers to generate JavaScript (other possible targets would be Flash or higher level UI languages such as OpenLaszlo that in turn compiles down to either Flash or JavaScript/HTML) - Write a suitable runtime library (including support for native JavaScript or Flash UI components, remote method invocations, multi-threading, etc.) - Port a usable subset of the Haskell Libraries - Select an approach to write user interfaces in Haskell. There have been many attempts in this direction but I am unsure if any of them has proven particularly successful. All considered, quite a significant amount of work -- that would require a concerted group effort -- with a rather uncertain pay-off. Is anyone working on anything similar or that might be interested in such a project? And has anyone any thoughts to offer on what compilers/libraries/UI frameworks would be more suitable for the task? Regards, titto assini

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Re: [Haskell-cafe] creating tree with level subnodes and incrementing number?
by Marc Weber 08 Aug '06

08 Aug '06

Thanks to you all! I think I've learned a lot. Marc

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IO Monad/ haskelldb strange error?
by Marc Weber 08 Aug '06

08 Aug '06

line << 39 works fine line 56 doesn't. Why? Isn't both a IO monad (because of the print statements) After commenting out 56 it compiles fine Any suggestion appreciated.. I'm struggling for some hours now.. module Modules.ObjectTree where import Debug.Trace import Data.FunctorM import DBUtils import qualified DB.VT.Ezcontentobject_tree as EOT import qualified DB.VT.Ezcontentobject as CO import Database.HaskellDB.HDBRec import Database.HaskellDB import Database.HaskellDB.Query as Q import Data.Tree import Monad import Control.Monad.Trans import Maybe import qualified List instance FunctorM Tree where fmapM f (Node a forest) = do a' <- f a forest' <- mapM (fmapM f) forest return $ Node a' forest' type ObjectTree a = Tree (Record a) truncTree 1 (Node a _) = Node a [] truncTree x (Node a forest) = Node a $ map (truncTree (x-1)) forest oT con = do print "blah" -- because of this we should have a simple IO Monad ? lookupField con (CO.name) (CO.ezcontentobject) (CO.xid) (constant (1 :: Int)) >>= print :: IO () -- <<<<<<<<<<<<<<<<<<<<<<<<< 39 return "blah" -- printObjectsAsTree :: MonadIO m => ((Database -> m a) -> m a) -> Int -> IO () printObjectsAsTree con startid= do print "test" root <- liftM head $ lRS (EOT.parent_node_id) (constant (startid :: Int)) print root --showRS root >>= putStrLn node <- po root node_show <- fmapM showRS node return $ drawTree node_show -- return "end" where lRS = lookupFieldRS con (EOT.ezcontentobject_tree) po root = let root_id = (root!(EOT.node_id) :: Int) in do print "dumm" -- IO Monad too ? print (root!(EOT.node_id)) lookupField con (CO.name) (CO.ezcontentobject) (CO.xid) (constant (1 :: Int)) >>= print -- <<<<<<<<<<<<<< 56 return $ Node root [] --childs <- lRS (EOT.parent_node_id) (constant root_id) --mapM_ (\r -> r!(EOT.node_id)) childs >>= print showRS r = do -- name <- lookupField con (CO.name) (CO.ezcontentobject) (CO.xid) (constant 1) >>= print return "ab" :: IO String --return $ (show $ r!node_id) ++ " (" ++ (fromJust name) ++ " )" ----------------------------------------------- || Preprocessing executables for dbez-0.0... || Building dbez-0.0... || Chasing modules from: db_ez.hs || [1 of 6] Skipping DBUtils ( DBUtils.hs, dist/build/db_ez/db_ez-tmp/DBUtils.o ) || [2 of 6] Skipping DB.VT.Ezcontentobject_tree ( DB/VT/Ezcontentobject_tree.hs, dist/build/db_ez/db_ez-tmp/DB/VT/Ezcontentobject_tree.o ) || [3 of 6] Skipping DB.VT.Ezcontentobject ( DB/VT/Ezcontentobject.hs, dist/build/db_ez/db_ez-tmp/DB/VT/Ezcontentobject.o ) || [4 of 6] Compiling Modules.ObjectTree ( Modules/ObjectTree.hs, dist/build/db_ez/db_ez-tmp/Modules/ObjectTree.o ) || Modules/ObjectTree.hs|43| 0: || Couldn't match `DB.VT.Ezcontentobject_tree.Contentobject_id' || against `DB.VT.Ezcontentobject.Contentclass_id' || Expected type: RecCons DB.VT.Ezcontentobject_tree.Contentobject_id || (Maybe Int) || vr || Inferred type: RecCons DB.VT.Ezcontentobject.Contentclass_id || Int || vr1 || When using functional dependencies to combine || Database.HaskellDB.Database.GetRec (RecCons f (Expr a) er) || (RecCons f a vr), || arising from the instance declaration at Imported from Database.HaskellDB.Database || Database.HaskellDB.Database.GetRec (RecCons DB.VT.Ezcontentobject_tree.Contentobject_id || (Expr (Maybe Int)) [...] || (RecCons DB.VT.Ezcontentobject_tree.Sort_order || (Expr (Maybe Int)) || RecNil)))))))))))))))) || (RecCons DB.VT.Ezcontentobject.Contentclass_id Int vr), arising from use of `lookupFieldRS' at Modules/ObjectTree.hs|52| 14-26 || When generalising the type(s) for `printObjectsAsTree'

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RE: [Haskell] thread-local variables
by Simon Peyton-Jones 08 Aug '06

08 Aug '06

| I have initialized a wiki page: | | http://haskell.org/haskellwiki/Thread_local_storage Great | I have put a page on the wiki summarizing the thread. However, I want | to say that I think that email is a better medium for most ongoing | discussions. I agree. Discussion by email Outcomes on Wiki (including outcomes recording differences of viewpoint) The goal is that the outcome is a comprehensible summary of the outcome of the discussion, for the benefit of the many who will not follow the evolving debate. Furthermore, can we move this thread from the Haskell mailing list (which should not have heavy traffic) to either Haskell-Café, or the libraries list? Simon

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How can we detect and fix memory leak due to lazyness?
by Ahn, Ki Yung 08 Aug '06

08 Aug '06

Recently, I'm facing the dark side of laziness -- the memory leak because of laziness. Typical pattern that I encounter the problem is like this. My code was working fine and I was happy. I just wanted to inspect some properties of my code so I made a slight chage go the code such as adding counter argument or attaching auxiliary data filed to original data for tracing how the data has been constructed. All of a sudden the program runs out of memory or overflows the stack. One problem is that it comes up unexpectedly. Another even worse problem is that sometimes I get no idea for the exact location causing the leak! It really panics facing such darkness of lazy evaluation. Just a small innocent looking fix for inspection or tracing blow things up, sometime with no clue for its reason. When we implement a debugging or tracing option in the software and let the user toggle those features, how could we be sure that turning on those features won't crash the software written in Haskell? Are there standardized approaches for detecting and fixing these kind of problems? Haskell may be type safe but not safe at all from unexpanded diversion, which is not because of the programmers' mistake but just because of the laziness. I have posted an wiki article including one example of adding a counter to count the number of basic operations in sorting algorithm. http://www.haskell.org/haskellwiki/Physical_equality This was a rather simple situation and we figured out how to cure this by self equality check ( x==x ) forcing evaluation. There are worse cases not being able to figure out the cure. I wrote a function for analyzing some property of a graph, which worked fine. fixOnBy t p f x = if t x' `p` t x then x else fixOnBy t p f x' where x' = f x fixSize f x = fixOnBy Set.size (==) f x sctAnal gs = null cgs || all (not . null) dcs where gs' = fixSize compose $ Set.fromList [(x,y,cs) | To _ x y cs<-Set.toList gs] cgs = [z | z@(x,y,cs)<-Set.toList gs', x==y] dcs = [ [c| c@(a,D,b)<-Set.toList cs , a==b] | (_,_,cs)<-cgs] compose gs = trace ("## "++show (Set.size gs)) $ foldr Set.insert gs $ do (x1,y1,cs1) <- Set.toList gs (_,y2,cs2) <- takeWhileFst y1 $ Set.toList $ setGT (y1,Al""(-1),Set.empty) gs return (x1,y2,cs1 `comp` cs2) takeWhileFst y = takeWhile (\(y',_,_) -> y==y') This function makes a transitive closure of the given set of relations by fixpoint iteration on the size of the set of weighted edges. Sample output is like this. *Main> main ## 170 ## 400 ## 1167 ## 2249 ## 2314 False When I add an extra data field for tracing how the new relation was constructed, (e.g. tag [a,b,c] on a->c if it came from a->b and b->c) it suddenly overflows the stack even before printing out the trace. The following is the code that leaks memory. sctAnal gs = null cgs || all (not . null) dcs where gs' = fixSize compose $ Set.fromList [TT (x,y,cs) [] | To _ x y cs<-Set.toList gs] cgs = [z | z@(TT (x,y,cs) _)<-Set.toList gs', x==y] dcs = [[c| c@(a,D,b)<-Set.toList cs , a==b] | TT (_,_,cs) _<-cgs] compose gs = trace ("## "++show (Set.size gs)) $ foldr checkInsert gs $ do TT (x1,y1,cs1) l1 <- Set.toList gs TT (_,y2,cs2) l2 <- takeWhileTTfrom y1 . Set.toList $ setGT (TT (y1,Al""(-1),Set.empty) []) gs return $ TT (x1,y2,cs1 `comp` cs2) (l1++y1:l2) takeWhileTTfrom y = takeWhile (\(TT (y',_,_) _) -> y==y') checkInsert x s | Set.member x s = s | otherwise = Set.insert x s data TT a b = TT a b deriving (Show) instance (Eq a, Eq b) => Eq (TT a b) where (TT x lx) == (TT y ly) = lx==lx && ly==ly && x == y instance (Ord a, Ord b) => Ord (TT a b) where (TT x lx) < (TT y ly) = lx==lx && ly==ly && x < y The really intersting thing happens when I just make the Ord derived the stack does not overflow and starts to print out the trace. (It is not the result that I want though. My intention is to ignore the tags in the set operation) data TT a b = TT a b deriving (Show,Eq,Ord) I believe my Eq and Ord instances defined above are even more stricter than the derived ones. Is there some magic in "deriving" that prevents memory leak? I've even followed the instance declaration like the following that would be the same as deriving but still leaks memory. data TT a b = TT a b deriving (Show) instance (Eq a, Eq b) => Eq (TT a b) where (TT x lx) == (TT y ly) = x == y && lx == ly instance (Ord a, Ord b) => Ord (TT a b) where (TT x lx) < (TT y ly) = x < y || x == y && lx < ly This is really a panic. -- Ahn, Ki Yung

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Re:Re: Why Haskell
by Hans van Thiel 08 Aug '06

08 Aug '06

From: Hans van Thiel <hthiel.char(a)zonnet.nl> Reply-To: hthiel.char(a)zonnet.nl To: Johan Tibell <johan.tibell(a)gmail.com> Subject: Re: [Haskell-cafe] Re: Why Haskell? Date: Mon, 07 Aug 2006 17:21:17 +0200 On Mon, 2006-08-07 at 15:23 +0200, Johan Tibell wrote: > For me library support, for networking in particular, has been the > major hurdle. It gets problematic when too many libraries are still > marked as experimental and only partially implements the specification > (e.g. protocol) that they are supposed to handle. Also after a quick > look at the source for some common (networking) libraries I found a > few too many calls to error to feel comfortable. It's not okay for a > library to bring down my application behind my back, error should be > reported even if this uglifies the code and interfaces. Furthermore I > think that Haskell would benefit from moving some commonly used > functionality such as HTTP, SQL and XML support into the standard > libraries. I haven't seen any news about the progress of HaskellNet > but I guess it could solve my problems. > That's good to know, thanks! > I really don't have much problems with tool support, speed and the > like. I'm convinced it's a library (and library documentation!) thing. > Likewise. > > > Having someone pay a group of people to hack on Haskell > implementations would indeed be desirable. Without knowing the details > Ubuntu looks like a promising model. If we could just find a willing > billionaire out there.. Candidates would be companies that have an interest in promoting Haskell and/or fp, large and small. Ericsson comes to mind, if they are still active in fp. Or maybe one of the rising Indian, Chinese or or other 'globalization' firms could be the principal here? Personally, I'd love to see a Brazilian company like, for example, PetroBras pick this up. And just from a PR point of view, Haskell does project a cutting edge image. Anyway... Regards, Hans > Cheers, > > Johan

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Need a good book on Haskell
by Johan Tibell 08 Aug '06

08 Aug '06

I've read Haskell: The Craft of Functional Programming on a course on functional programming at Chalmers (I also took the advanced course) and now I'm looking for some more reading material. Are there any other good Haskell books? Is there a Pick Axe, Camel or Dragon Book for Haskell?

3 2

The dark side of lazyness - memory leak
by Ahn, Ki Yung 07 Aug '06

07 Aug '06

I'm facing the dark side of lazyness recently. Typical pattern is like this. My code was working fine and I was happy. I just wanted to inspect some properties of my code so I made a slight chane go the code such as adding counter argument or attaching axulary data filed to original data for tracing how the data has been constructed. All of a sudden the program runs out of memory or overflows the stack. One problem is that it comes up unexptectedly. Another even worse problem is that sometimes I get no idea for the exact loation causing the leak! It really panics facing such darkness of lazy evaluation. Just a small innocent looking fix for inspection or tracing blow things up, sometime with no clue for its reason. When I put a debugging or tracing operating in my software that can be toggled, how could I be sure that turning on those features won't crash my software written in Haskell? Are there appraoches to detect and fix these kind of problem? Haskell may be type safe but not safe at all from unexpteded diversion, not because of the programmers' mistake but just because of the lazyness. I have posted an wiki article including one example of this dark side of lazyness I encountered when I tried to count the number of basic operations in sorting algorithm. This was a rather simple situation and we figured out how to cure this by self equality check ( x==x ) forcing evaluation. There are wose cases not being able to figure out the cure. I wrote a fucntion for analyzing some property of a graph, which worked fine. fixOnBy t p f x = if t x' `p` t x then x else fixOnBy t p f x' where x' = f x fixSize f x = fixOnBy Set.size (==) f x sctAnal gs = null cgs || all (not . null) dcs where gs' = fixSize compose $ Set.fromList [(x,y,cs) | To _ x y cs<-Set.toList gs] cgs = [z | z@(x,y,cs)<-Set.toList gs', x==y] dcs = [ [c| c@(a,D,b)<-Set.toList cs , a==b] | (_,_,cs)<-cgs] compose gs = trace ("## "++show (Set.size gs)) $ foldr Set.insert gs $ do (x1,y1,cs1) <- Set.toList gs (_,y2,cs2) <- takeWhileFst y1 $ Set.toList $ setGT (y1,Al""(-1),Set.empty) gs return (x1,y2,cs1 `comp` cs2) takeWhileFst y = takeWhile (\(y',_,_) -> y==y') This fucntion makes a transitive closure of the given set of relations by fixpoint iteration on the size of the set of weighted edegs. Sample output is like this. *Main> main ## 170 ## 400 ## 1167 ## 2249 ## 2314 False When I add an extra data field for tracing how the new item was made (e.g. tag [a,b,c] on a->c if it was generated by a->b and b->c) It suddenly overflows the stack even before printing out the trace. The following is the code that leaks memory. sctAnal gs = null cgs || all (not . null) dcs where gs' = fixSize compose $ Set.fromList [TT (x,y,cs) [] | To _ x y cs<-Set.toList gs] cgs = [z | z@(TT (x,y,cs) _)<-Set.toList gs', x==y] dcs = [[c| c@(a,D,b)<-Set.toList cs , a==b] | TT (_,_,cs) _<-cgs] compose gs = trace ("## "++show (Set.size gs)) $ foldr checkInsert gs $ do TT (x1,y1,cs1) l1 <- Set.toList gs TT (_,y2,cs2) l2 <- takeWhileTTfrom y1 . Set.toList $ setGT (TT (y1,Al""(-1),Set.empty) []) gs return $ TT (x1,y2,cs1 `comp` cs2) (l1++y1:l2) takeWhileTTfrom y = takeWhile (\(TT (y',_,_) _) -> y==y') checkInsert x s | Set.member x s = s | otherwise = Set.insert x s data TT a b = TT a b deriving (Show) instance (Eq a, Eq b) => Eq (TT a b) where (TT x lx) == (TT y ly) = lx==lx && ly==ly && x == y instance (Ord a, Ord b) => Ord (TT a b) where (TT x lx) < (TT y ly) = lx==lx && ly==ly && x < y The really intersting thing happens when I just make the Ord derived the stack does not overflow and starts to print out the trace. (It is not the result that I want though. My intention is to ignore the tags in the set operation) data TT a b = TT a b deriving (Show,Eq,Ord) I believe my Eq and Ord instances are even more stricter than the derived ones. Is there some magic in "deriving" that prevents memory leak? I've even followed the instance declaration that would be the same as deriving but the that leaks memory. data TT a b = TT a b deriving (Show) instance (Eq a, Eq b) => Eq (TT a b) where (TT x lx) == (TT y ly) = x == y && lx == ly instance (Ord a, Ord b) => Ord (TT a b) where (TT x lx) < (TT y ly) = x < y || x == y && lx < ly This is really a panic. -- Ahn, Ki Yung

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Re: Why Haskell?
by Hans van Thiel 07 Aug '06

07 Aug '06

Hello All, Thanks for the many helpful replies to my question about the suitability of Haskell for industrial/commercial application. >From those I gather there are no licensing problems regarding the use of the standard functions and modules. Use of proprietary modules may or not be restricted by the authors, but of course this is to be expected and fair. Performance and size of Haskell programs don't seem to be problematic either, at least for small and medium size applications. Tool support, however, is less than for the more established languages. But maybe the Eclipse support which is under development will be a boost. Also, there are good interfaces with open source gui widgets etc. So, the summary conclusion would be that Haskell can be used (and is being used) provided the developers are aware that unexpected problems may arise in practice. Advantages of Haskell seem to be short size of code (and all the advantages that implies) and the high abstraction level and mathematical rigour (which makes for less programming errors). As for the 'popularity' of Haskell, someone made the very common sense remark that all successful languages have been promoted by some large corporation. (Please note 'successful' stands for 'spread of use', not 'quality' here.) If fp is to reach the mainstream, it will probably be because of some centralized support from outside the academic world. Maybe something like a 'Haskell Consortium' or 'Haskell Initiative' to promote Haskell should be set up. An example could be the promotion of SystemC for hardware and software co-design by the Open SystemC Initiative www.systemc.org . Availability of an IEEE standard for Haskell would also be a good thing for its acceptance, I think. That is, assuming 'mainstream' is the goal, of course. Regards, Hans van Thiel

1 0

Variants of a recursive data structure
by tpledger＠ihug.co.nz 07 Aug '06

07 Aug '06

Klaus Ostermann wrote: [...] > data Exp e = Num Int | Add e e > > data Labelled a = L String a > > newtype Mu f = Mu (f (Mu f)) > > type SimpleExp = Mu Exp > > type LabelledExp = Mu Labelled Exp > > The "SimpleExp" definition works fine, > but the LabeledExp definition doesn't > because I would need something like > "Mu (\a -> Labeled (Exp a))" where "\" > is a type-level lambda. > > However, I don't know how to do this in > Haskell. I'd need something like the > "." operator on the type-level. One way, that I haven't spotted in any of the replies so far, is to declare a composition type data BComp m n a = BC (m (n a)) as seen in http://web.cecs.pdx.edu/~mpj/pubs/springschool.html , so that type LabelledExp = Mu (BComp Labelled Exp) See http://haskell.cs.yale.edu/pipermail/haskell/2001-May/003942.html for more crafty tricks, including making Eq instances for such Mu-based recursive structures. Regards, Tom

1 0

Type inference problem
by Joel Björnson 07 Aug '06

07 Aug '06

Hi. I have a type inference related problem which causes me some confusion. The following is a simplified example capturing the key aspects. First of all, consider a data type (here called) Elem and a type class IsElem. data Elem = E class IsElem a where toElem :: a -> Elem instance IsElem Elem where toElem = id instance Show a => IsElem a where toElem _ = E Values of type Elem along with all instances of Show, instansitates the IsElem class. What I want to achieve is the enabling of definitions of classes/member functions corresponding to the following. class SetId t v r | t -> r where setId :: t -> v -> r And to instantiate the class, allowing 'setId' to produce values of type Elem as in instance SetId Elem String Elem where setId x _ = x Note that the fundep (t -> r) enables the type checker to uniquely determine the return type of setId, depending on it's first argument. It is now possible to write function definitions according to myElem = E `setId` "id" Checking the type of 'myElem' using ghci confirms that it has type 'Elem'. (Because of the E and the fundep) So far, so good... However, problems arises trying to define the function : test = toElem myElem Yielding the error message : 'No instance for (Show Elem) arising use of `toElem` at ...' For some reason it seems like the type checker picks the *wrong* 'toElem', and that the type of 'myElem' can't be properly determined (without adding explicit type signatures). It seems strange though the the type of myElem really can be determined and that the instance (IsElem Elem) is more specific then the instance for Show types. Anyway, I just realised that turning off the 'monomorphism-restriction' solves the problem. (Don't know why though). Is this *the* recommended solution here and is there any general policy regarding the flag ? Help/explanations are appreciated! Thanks a lot /Joel

1 1

Variants of a recursive data structure
by Klaus Ostermann 07 Aug '06

07 Aug '06

Hi all, I have a problem which is probably not a problem at all for Haskell experts, but I am struggling with it nevertheless. I want to model the following situation. I have ASTs for a language in two variatns: A "simple" form and a "labelled" form, e.g. data SimpleExp = Num Int | Add SimpleExp SimpleExp data LabelledExp = LNum Int String | LAdd LabelledExp LabelledExp String I wonder what would be the best way to model this situation without repeating the structure of the AST. I tried it using a fixed point operator for types like this: data Exp e = Num Int | Add e e data Labelled a = L String a newtype Mu f = Mu (f (Mu f)) type SimpleExp = Mu Exp type LabelledExp = Mu Labelled Exp The "SimpleExp" definition works fine, but the LabeledExp definition doesn't because I would need something like "Mu (\a -> Labeled (Exp a))" where "\" is a type-level lambda. However, I don't know how to do this in Haskell. I'd need something like the "." operator on the type-level. I also wonder whether it is possible to curry type constructors. The icing on the cake would be if it would also be possible to have a function unlabel :: LabeledExp -> Exp that does *not* need to know about the full structure of expressions. So, what options do I have to address this problem in Haskell? Klaus

10 18

Compiling To C And Why Not Compiling To Java Or C#?
by Kaveh Shahbazian 06 Aug '06

06 Aug '06

1 & 2 - Maybe this is not a proper question but I think It has a point. Why Not Compiling To Java Or C#? What is the need of implementing a class interoperability between Haskell and other plateforms? Maybe we donot need that. Haskell can be the big infrastructure and code snippets in Java or C# can serve in a monadic wrapper. It looks like that we can scripting Haskell in that languages. For example F# 's target code is ILX (an extension of MSIL for functional languages). But I think interoperablity between languages - like what .NET claims - is totaly pointless. Again think of an infrastructure that has a Haskell core which defines and controls very high level processes. Then there will be a running machine that Haskell is sitting on top of it. This running machine implement haskell in the plateform language. This is what I mean. 3 - And for an OOP style interoperability between languages, I think most usefull is to have a robust standard for Object-Broking. Something like IEC 61850 in new power systems in industry. A tool from siemens can understand what a hitachi high voltage key commands and all of these devices are from different providers with different internal implementations that meets the standard.

2 1

fast image processing in haskell?
by Jeff Briggs 06 Aug '06

06 Aug '06

Hello, I am attempting to process images captured from a webcam. My aim is to do so, in real time, at the frame rate of the camera. I'm using GHC 6.4.2 with -O3. A frame consists of ~100k 24bit colour values. The webcam is interfaced through FFI bindings to some C++ -- these are all labelled 'unsafe'. The image is passed to Haskell as a Ptr Word8. To blit this to the screen (via Gtk2Hs) I do the following: data Cam = Cam { snap_width :: !Int , snap_height :: !Int , snap_bytespp :: !Int , snap_size :: !Int , cam_img :: Ptr Word8 , cam_obj :: ForeignPtr () } do (PixbufData _ dst _) <- (pixbufGetPixels pixbuf :: IO (PixbufData Int Word8)) copyBytes dst (cam_img cam) This achieves the desired throughput (25-29fps.) However, I am at a bit of a loss how to do something similar for preprocessing the data in Haskell before blitting the data (whilst also retaining some semblance of functional programming...) Currently, I have: cam_snap cam f x = do let loop (r:g:b:rest) n x = f r g b n x >>= loop rest (n+3) loop _ _ x = return x px <- peekArray (snap_size cam) (cam_img cam) loop px 0 x cam_snap2 cam f x = let loop ptr n x | n >= snap_size cam = return x | otherwise = do let ptrs = scanl plusPtr ptr [1,1] [r,g,b] <- mapM peek ptrs f r g b n x >>= loop (ptr `plusPtr` 3) (n+3) in loop (cam_img cam) 0 x do ... let sum_px r g b _ (sr,sg,sb) = return (sr+r,sg+g,sb+b) sum <- cam_snap (cam ui) sum_px (0.0,0.0,0.0) print sum cam_snap only processes at 5 fps, whereas cam_snap2 operates at 6fps. Any suggestions? Thanks.

4 6

Exercise in YAHT
by algorithms＠gmx.de 06 Aug '06

06 Aug '06

Dear Hugs users, could you answer the following question from a Haskell novice? In "Yet another Haskell Tutorial" by Hal Daumé III there is the following exercise: Exercise 4.8 Write functions listHead, listTail, listFoldl and listFoldr which are equivalent to their Prelude twins, but function on our List datatype. Don’t worry about exceptional conditions on the first two. My question is solely on listfoldr, in fact I only want to ask whether the solution provided in the tutorial is really so obviously wrong as I perceive it to be: (What follows uses the definition data List a = Nil | Cons a (List a) ) listFoldr f y Nil = y listFoldr f y (Cons x xs) = f x (foldr f z xs) This IS wrong, isn't it? The y does not even appear after all. And what can you say about my attempt for listFoldr? listFoldr f y Nil = y listFoldr f y (Cons x xs) = f y (listFoldr f (f y x) xs) My attempt yields a similar, albeit not identical result compared with the Prelude function foldr when :t-ing it under Hugs: Hugs> :t foldr foldr :: (a -> b -> b) -> b -> [a] -> b Hugs> :t listFoldr listFoldr :: (a -> a -> a) -> a -> List a -> a Thank you very much. Christian -- Echte DSL-Flatrate dauerhaft für 0,- Euro*. Nur noch kurze Zeit! "Feel free" mit GMX DSL: http://www.gmx.net/de/go/dsl

3 2

A problem with Show
by zdenes＠seznam.cz 06 Aug '06

06 Aug '06

Hello, I made a simple datatype called Pair and I'd like to make it an instance of Show class. But when I try to do that I run into troubles: data Pair a b = Pair a b instance Show a b => Show (Pair a b) where show (Pair a b) = show a ++ "_" ++ show b In Hugs I get this error: "Haskell does not support multiple parameter classes" When I run it in ghci I get a kind error "Show is applied to too many type arguments in the instance declaration for Show (Pair a b)" Am I jsut using wrong syntax or is it not possible to do? Thanks in advance Zdenes

2 1

REALLY simple STRef examples
by Chad Scherrer 06 Aug '06

06 Aug '06

I've looked around at the various STRef examples out there, but still nothing I write myself using this will work. I'm trying to figure out how the s is escaping in really simple examples like x = runST $ return 1 y = runST $ do {r <- newSTRef 1; readSTRef r} Neither of these works in ghci - they both say <interactive>:1:0: Inferred type is less polymorphic than expected Quantified type variable `s' escapes Expected type: ST s a -> b Inferred type: (forall s1. ST s1 a) -> a In the first argument of `($)', namely `runST' In the definition of `it': ... I thought maybe I needed to replace 1 with (1 :: Int) so the state representation didn't force the type, but it still gives the same result. Can someone point me to the simplest possible runST example that actually works? Thanks! -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

2 2

Monad Imparative Usage Example
by Kaveh Shahbazian 05 Aug '06

05 Aug '06

Haskell is the most powerfull and interesting "thing" I'v ever encountered in IT world. But with an imparative background and lack of understanding (because of any thing include that maybe I am not that smart) has brought me problems. I know this is an old issue. But please help it. Question : Could anyone show me a sample of using a monad as a statefull variable? For example see this code in C# : // public class Test { int var; static void Fun1() { var = 0; Console.Write(var); } static void Fun2() { var = var + 4; Console.Write(var); } static void Main() { Fun1(); Fun2(); var = 10; Console.Write("var = " + var.ToString()); } } // I want to see this code in haskell. Thankyou

8 12

Monad Imparative Usage Example
by Kaveh Shahbazian 05 Aug '06

05 Aug '06

Monad Imparative Usage Example Thanks for your replies. I have not haskell on this computer and I will try this solutions tonight. I must notice that IO computations is not the point here. My target is to have this code for mutable variable 'var'. ############################################################################# Haskell is the most powerfull and interesting "thing" I'v ever encountered in IT world. But with an imparative background and lack of understanding (because of any thing include that maybe I am not that smart) has brought me problems. I know this is an old issue. But please help it. Question : Could anyone show me a sample of using a monad as a statefull variable? For example see this code in C# : // public class Test { int var; static void Fun1() { var = 0; Console.Write(var); } static void Fun2() { var = var + 4; Console.Write(var); } static void Main() { Fun1(); Fun2(); var = 10; Console.Write("var = " + var.ToString()); } } // I want to see this code in haskell. Thankyou #############################################################################

3 3

Why shouldn't variable names be capitalized?
by Martin Percossi 05 Aug '06

05 Aug '06

Hi, I'm wondering what the rationale was for not allowing capitalized variable names (and uncapitalized type names and constructors). I can only think of two arguments, and IMHO both of them are bad: 1. Enforces a naming convention. Fine - but my view is that this doesn't belong in the language definition (it belongs in the user's coding standards). I get annoyed, for example, that when I write code that manipulates matrices and vectors, I can't refer to the matrices with capital letters as is common in the literature. And to anyone who says that it's good to enforce naming consistency, I have this to say: Any language that requires me to learn about category theory in order to write imperative code should treat me like an adult when it comes to the naming of variables as well. ;-) 2. It makes it easier to write the compiler. I don't think I need to explain why this is bad... I imagine that someone is just itching to "sort me out". Do your worst! ;-) Thx Martin

9 9

a bunch of newbie questions
by Imam Tashdid ul Alam 04 Aug '06

04 Aug '06

what's the difference between data and co-data exactly? or between inductive data types and co-inductive data types? can you give me some reference points that explain these? > (read "56")::Integer does it in fact pass the type (Integer) to the function (read)? I guess what we want is for the (Integer) implementation of the (read) function to evaluate, not really to cast the value of (read) function to (Integer). in the regex libraries, (~=) cast this way results in completely different things altogether, should type classes have namespaces associated with them? somewhat like Integer.read "56"? this way of selecting the intended implementation, does it work without trouble with multiparameter type classes as well? theoretically is it possible to do a strictness analysis without any help from the programmer? thanks a bunch in advance. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

6 9

RE: ANN: System.FilePath 0.9
by Brian Smith 04 Aug '06

04 Aug '06

[ I tried to send this through the fa.haskell USENET group but apparently it did not go through] I kind of expect that a Haskell library for file paths will use the type system to ensure some useful properties about the paths. For example, when writing security-conscious software I often want to be able to distinguish between absolute, ascending (paths with leading "../" and similar items), and decending paths (paths that contain no "../"). I want to make sure a filename is valid. For example, "prn" and "con" are not valid path elements for normal files on Windows, certain characters are not allowed in filenames (depending on platform), some platforms may require paths to be escaped in different ways. I see there is a "isValid" function and even a (magical) "makeValid" function, but they do not report what was wrong with the filename in the first place. Furthermore, it isn't clear from the documentation how these functions determine whether a filename is valid. Many people might be familiar with Joel Spolsky's article "Making Wrong Code Look Wrong" at http://www.joelonsoftware.com/articles/Wrong.html . If you read that article, you will see that advocates a variable naming convenctions to distinguish between HTML-escaped "safe" and non-escaped "unsafe" strings. In Haskell, we can do much better than that by using convenient strong static typing to enforce such constraints. We should be able to use type signatures to ensure that we are operating on syntactically valid paths of a certain form. For example, a function's type should indicate that it expects an absolute path, or a relative path that doesn't use "../../.." to decend into parent/sibling directories unexpectedly, which is a common exploit technique. IMO, safety is the most important issue regarding file paths and it is not addressed in this library as far as I can see. Writing code to handle these issues is tedious, error-prone, and boring to write despite being critical. It isn't the kind of code that you want to just download off of some guy's webpage. Basically, it is exactly the type of thing that belongs in a standard library. In this library proposal, there are a bunch of "xxxDrive" functions that many Unix-oriented programmers are sure to ignore because they are no-ops on Unixy systems. Even on Windows, they are not very useful: Windows software almost never cares what drive a directory is on, especially because the directory might not be on a drive at all (for example, a UNC network path "\\foo\bar" has no "drive" component but it is an absolute path). Really, Windows software usually works similarly to Unixy software in this regard--the big difference is that Unixy systems have one root path, whereas Windows systems can have many, many root paths (drives and UNC's). - Brian

20 68

Code review: initial factoring for sequences and other structures
by Brian Hulley 04 Aug '06

04 Aug '06

Hi - I've started work on an initial factoring of sequence ops into classes, and already I've run into some major design issues which stand like a mountain in the way of progress. The classes are below: -- all code below standard BSD3 licence :-) module Duma.Data.Class.Foldable ( Foldable(..) ) where import qualified Data.List as List class Foldable c a | c -> a where foldR :: (a -> b -> b) -> b -> c -> b foldL :: (b -> a -> b) -> b -> c -> b foldL' :: (b -> a -> b) -> b -> c -> b -- arg order from FingerTree paper -- opposite to Edison arg order reduceR :: (a -> b -> b) -> (c -> b -> b) reduceR f xs y = foldR f y xs reduceL :: (b -> a -> b) -> (b -> c -> b) reduceL = foldL reduceL' :: (b -> a -> b) -> (b -> c -> b) reduceL' = foldL' instance Foldable [a] a where foldR = List.foldr foldL = List.foldl foldL' = List.foldl' and module Duma.Data.Class.BasicSeq ( BasicSeq(..) ) where import Prelude hiding(map) import Duma.Data.Class.Foldable import qualified Data.List as List import Control.Monad class Foldable c a => BasicSeq c a where empty :: c isEmpty :: c -> Bool atL :: c -> a atR :: c -> a pushL :: a -> c -> c pushR :: c -> a -> c viewL :: Monad m => c -> m (a, c) viewR :: Monad m => c -> m (c, a) -- (1) Should this be in its own class? convert :: BasicSeq d a => c -> d convert = foldR pushL empty -- (2) Is this too general or not general enough? map :: BasicSeq d b => (a -> b) -> c -> d map f xs = case viewL xs of Just (x, xs') -> pushL (f x) (map f xs') Nothing -> empty instance BasicSeq [a] a where empty = [] isEmpty [] = True isEmpty _ = False atL (x:_) = x atR = List.last pushL = (:) pushR xs x = xs ++ [x] viewL (x:xs) = return (x,xs) viewL _ = fail "viewL" viewR xs@(_:_) = return (List.init xs, List.last xs) viewR _ = fail "viewR" (Indexing ops like take, drop, length, at, split would be provided by a third class and measurements (to access the power of finger trees and similar structures) would be dealt with by a fourth class with analogous ops ie takeWith, splitWith etc) However already with just the above I have some questions about the (convert) and (map) functions: 1) Because (convert) takes BasicSeq d a as a context, it is currently impossible to provide an optimized version for specific combinations of source/dest types eg if both types are the same (convert) should just be (id). Does this mean I should put (convert) into its own class or should I expect the compiler to be able to rewrite (foldR pushL empty) into (id) in this situation? 2) Ditto with (map), but here there is another issue: it is at once too general and too specific compared to the usual definitions of (map): --Prelude - limited to lists only map f (x:xs) = f x : map f xs map _ [] = [] -- Functor - source and dest limited to the same type fmap :: (a->b) -> f a -> f b So even though fmap is constrained to only map between the same type, it is more general than BasicSeq.map because the type doesn't need to be a BasicSeq. However it is less general in the sense that fmap wouldn't allow to map between two different instances of BasicSeq. There is a general problem that when the element type needs to be specified along with the type of the overall collection, there is no way to talk about the functor type at the same time eg I'd like to be able to write something like this: class Functor f a b where fmap :: (a->b) -> f a -> f b instance (BasicSeq (f a) a, BasicSeq (f b) b) => Functor f a b where fmap = map but GHC complains that I'd need to use -fallow-undecidable-instances which I'm reluctant to do because I don't know what the implications of such a decision would be. Why are these instances for such a simple thing (ie just pattern matching against the components of a type) already undecidable? The issues above are the kind of problems I just don't know how to solve or even how to approach, since there seem to be too many conflicting dimensions in the design space. Any ideas? Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

1 1

Filtering a big list into the IO monad
by Gabriel Sztorc 03 Aug '06

03 Aug '06

Hello, I want to filter a list with a predicate that returns a IO value, something that filterM is supposed to do. The problem is, filterM overflows the stack for really big lists and I couldn't come up with a simple replacement for filterM that would work for lists of any size (the truth is, I can't come up with anything at all :). The question is: how to do it? Any help is appreciated.

4 3

Translating C to English Using Haskell
by Shannon -jj Behrens 03 Aug '06

03 Aug '06

I've written a two-part series for "Linux Journal" called "Translating C to English Using Haskell". Here are links to the two parts: http://www.linuxjournal.com/article/9096 http://www.linuxjournal.com/article/9242 The catchline is: Write a program in Haskell that translates C type declarations into English. Manually translate the Haskell into English. I've tried very hard to make it an entertaining article for Haskell newbies, so if your head exploded when you tried to read "A Gentle Introduction to Haskell", give my article a shot! A special thank you goes to all the members of this who helped me when I was writing the article!

1 0

Bits and pieces needed to build a web server
by Johan Tibell 03 Aug '06

03 Aug '06

I've got an idea for a web server model I would like to try and since I'm quite new to Haskell it would be great if someone could enumerate a couple of useful libraries to me. Here's what I need (I've put what I've found so far inside parenthesis): * Parsing of incoming HTTP request and creation of replies (http://www.haskell.org/http/) * XML parsing and generating (http://www.cs.york.ac.uk/fp/HaXml/) * Database support (mainly SQLite but perhaps also MySQL/PostgreSQL) (There seems to be several options for this one. I don't know the names of the table nor the columns at compile time so I need something that doesn't require that.) A big plus if the library is still being developed/maintained. Thanks in advance. Johan

2 1

Edison StandardSet has inefficient function implementation
by Ahn, Ki Yung 03 Aug '06

03 Aug '06

Edision does not yet have all the asymtotic description of its functions. I got the Edision 1.2 source and looked into the code whether the container implementations meet the expected asymtotic bounds. In the module Data.Coll.StandardSet which packages Data.Set, some functions which can be O(log n) is implemented as O(n). Data.Set has a split and splitMember running in O(log n). With those functions we can implement OrdCollX operations like filterLT, filterLE, filterGT, filterGE, partitionLT_GE, partitionLE_GT, partitionLT_GT all in O(log n). However, only partitionLT_GT was O(log n) implemended using split. All other function implmentation just used its axiomaic description using CollX operations like filter and partition, which is O(n). It needs to be fixed. P.S. I haven't checked the darcs version yet. -- Ahn, Ki Yung

2 1

[Fwd: Re: [Haskell-cafe] Variants of a recursive data structure]
by Conor McBride 03 Aug '06

03 Aug '06

Hi folks Sorry, meant to send this around, not just to Klaus Conor

1 0

FW: Reviving wxHaskell (was: Re: [wxhaskell-users] [Haskell-cafe] Troublecompiling wxhaskell)
by Daan Leijen 03 Aug '06

03 Aug '06

Dear wxHaskell users, First of all, I apologize for not being responsive on the wxHaskell users mailing list. I recently changed jobs and countries and didn't properly take care of older email aliases. Anyway, even though I am motivated to support wxHaskell, practice proves that the project is too large for me to do alone. It would be great if someone or a group of people feel motivated enough to take over the project and release new versions that are compatible with the latest Ghc versions. One potential challenge is to find a group of testers that are willing to help compiling wxHaskell on different target systems: Windows, MacOS X, and Unix/GTK variations. I am happy to give volunteers administrator privileges on the sourceforge site and help out with the initial transition and building the initial new release (which is generally a lot of careful work in compiling and packaging correctly). All the best, -- Daan Leijen. Ps. Include me on the reply list as I am not subscribed properly to either mailing list at the moment. From: Simon Peyton-Jones Sent: Tuesday, August 01, 2006 4:46 AM To: Daan Leijen Subject: FW: Reviving wxHaskell (was: Re: [wxhaskell-users] [Haskell-cafe] Troublecompiling wxhaskell) Daan Have you seen this thread? Would you care to respond to it? Simon From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Jeremy O'Donoghue Sent: 01 August 2006 09:37 Cc: haskell-cafe(a)haskell.org; wxhaskell-users(a)lists.sourceforge.net Subject: Reviving wxHaskell (was: Re: [wxhaskell-users] [Haskell-cafe] Troublecompiling wxhaskell) Hi list, Apologies for continuing with the cross-posting, but wxhaskell-users is not exactly active. It seems like there may be enough interest in wxHaskell to justify trying to revive the project. At present, from what I can tell, Daan Leijen, the principal developer of wxHaskell, no longer has much interest in the project - the CVS log shows little activity for about 15 months now - and using wxHaskell with newer wxWidgets versions or on Unicode systems requires the application of various patches (for which the interested potential user must search diligently). Ideally, it would be best Daan for to enable new CVS committers to the project (or even to hand over project administration), but if this is not an option, is there a possibility of hosting a fork on hackage.haskell.org (I think there's a benefit in hosting Haskell-specific projects in a Haskell-friendly location). I don't have the time to nurture huge ambitions for wxHaskell, but I think it is realistic to aim for the following in the short term: * Patches to ensure that wxHaskell compiles against latest wxWidgets versions on Mac, Linux and Windows (exists today) * Add Eric Kow's Unicode patches (exist today) * Produce suitable binary packages for whatever targets we can get maintainers for, compatible with up-to-date versions of both GHC and wxWidgets. * Improve samples and documentation. In the longer term, we could look at: * Fixing operation with sash windows (a personal gripe ;-) - easy * Wrapping some of the more complex widgets - easy. * Subclassing of widgets in Haskell ( i.e. allow C++ virtual methods to be redefined in Haskell) - moderately hard * Move from the Eiffel wxc bindings to wxC project to give better maintained interface to wxWidgets - time consuming, but easy * Porting to other Haskell implementations (Hugs, YHC etc) Taking on a project like this is a very significant commitment, and only makes sense if there are a number of willing contributors. I'm happy to kick this off and try to cover some of the boring 'administrative' bits, as well as contributing on documentation and smaller bug fixes, but I don't have time to save wxHaskell from permanent bit-rot. If there's enough interest, I'll push ahead with trying to organize this. Regards Jeremy On 01/08/06, shelarcy <shelarcy(a)gmail.com> wrote: > On 7/31/06, David F. Place <d(a)vidplace.com> wrote: >> Hi: >> >> I'm having trouble compiling wxhaskell 0.9.4 under both ghc 6.4.2 and >> ghc 6.5. Does anyone know where I should direct my queries? If you use ghc 6,4,2 under Windows platform, you can use my patched version of wxHaskell. And you can get my patch from Kamiariduki's source. http://www.haskell.org/pipermail/haskell/2006-June/018043.html https://sourceforge.net/project/showfiles.php?group_id=168626 I also know Eric Y. Kow's unicode patch doesn't include db problems fix. These problems has not only wxWidgets 2.6.x change, but also unicode change. I try to fix latter case, use attached after unicode patch, this fixes compile problem ... but it has another problem that can't use non-ascii characters correctly. So, if want to accesss DB by wxHaskell's ODBC, data is garbled and cause problems. I don't know how to fix that. Attached is already sent wxhaskell-user's list, but you can't get this file. So I send again. http://sourceforge.net/mailarchive/message.php?msg_id=16222530 My patch where I put Kamiariduki's project page doesn't include unicode support that I noticed above Mailng-List's log. Don't worry about this. You can use both my patch and unicode patch, if you want. These cause conflict message but this is not problem. On Tue, 01 Aug 2006 08:18:27 +0900, Jason Dagit <dagit(a)eecs.oregonstate.edu> wrote: > I've done this recently. I put my notes on the wiki: > http://www.haskell.org/haskellwiki/WxHaskell/Install#Windows I don't know this problem when I made patch. So, my patch doesn't fix this problem. -- shelarcy <shelarcy capella.freemail.ne.jp> http://page.freett.com/shelarcy/ ------------------------------------------------------------------------ - Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDE V _______________________________________________ wxhaskell-users mailing list wxhaskell-users(a)lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wxhaskell-users _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Can Your Programming Language Do This?
by Stephane Bortzmeyer 03 Aug '06

03 Aug '06

>From the excellent programming blog "Joel on software", a very good text if you need to convince Java or C programmers that functional programming is a A Good Thing. Probably all the readers of this list will find it brings nothing new (that's perfectly right) but it is oriented towards ordinary programmers :-) http://www.joelonsoftware.com/items/2006/08/01.html

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ANN: TextRegexLazy-0.56, (=~) and (=~~) are here
by Chris Kuklewicz 02 Aug '06

02 Aug '06

Announcing: TextRegexLazy version 0.56 Where: Tarball from http://sourceforge.net/projects/lazy-regex darcs get --partial [--tag=0.56] http://evenmere.org/~chrisk/trl/stable/ License : BSD, except for DFAEngine.hs which is LGPL (derived from CTK light) Development/unstable version is at: darcs get [--partial] http://evenmere.org/~chrisk/trl/devel/ This is the version that has eaten John Meacham's JRegex library and survived to become strong. Thanks John! It now compiles against the posix regexp provided by the c library and the pcre library, in addition to the "full lazy" and the "DFA" backends. All 4 backends can accept regular expressions given as String and as ByteString. All 4 backends can run regular expressions against String and ByteString. In particular, the PosixRE and PCRE can run very efficiently against ByteString. (Though the input for the PosixRE needs to end in a \NUL character for efficiency). So there are 4*2*2 = 16 ways to use to provide input to this library. And the RegexContext class has at least 11 instances that both (=~) and (=~~) can target. So that is 4*2*2*11*2 = 352 things you can do with this library! Get your copy today! To run with cabal before 1.1.4 you will need to comment out the "Extra-Source-Files:" line in the TextRegexLazy.cabal file. The Example.hs file: > {-# OPTIONS_GHC -fglasgow-exts #-} > import Text.Regex.Lazy > import Text.Regex.Full((=~),(=~~)) -- or DFA or PCRE or PosixRE > > main = let b :: Bool > b = ("abaca" =~ "(.)a") > c :: [MatchArray] > c = ("abaca" =~ "(.)a") > d :: Maybe (String,String,String,[String]) > d = ("abaca" =~~ "(.)a") > in do print b > print c > print d This produces: > True > [array (0,1) [(0,(1,2)),(1,(1,1))],array (0,1) [(0,(3,2)),(1,(3,1))]] > Just ("a","ba","ca",["b"]) You can also use makeRegex and makeRegexOpts to compile and save a regular expression which will be used multiple times. Each of the 4 backends has a separate "Regex" data type with its own option types. For low level access, the WrapPCRE and WrapPosix modules expose a typesafe layer around the c libraries. You can query the "getVersion :: Maybe String" to see if the have been compiled into the library. It may be possible to use WrapPCRE and the UTF8 option flags to do unicode regex matching with PCRE. ( The Full and DFA backends use the Haskell unicode Char already ). Adding new types to String/ByteString is a matter of adding instances to the existing classes. Feedback and comments of any length is welcome. -- Chris Kuklewicz

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Re: [Haskell-cafe] ANN: TextRegexLazy-0.56, (=~) and (=~~) are here
by Chris Kuklewicz 02 Aug '06

02 Aug '06

Bulat Ziganshin wrote: > Hello Chris, > > Wednesday, August 2, 2006, 3:16:58 PM, you wrote: > >> Announcing: TextRegexLazy version 0.56 > > your feature list is really strong! it will be great now to make it > a part of GHC standard distribution > > afaiu, selection of regex engine implemented via import statements? > You can actually choose which backend (=~) uses at runtime: > {-# OPTIONS_GHC -fglasgow-exts #-} > import Text.Regex.Lazy > > import qualified Text.Regex.PCRE as R > import qualified Text.Regex.PosixRE as S > import qualified Text.Regex.Full as F > > -- Choose which library to use depending on presence of PCRE library > > (=~) :: (RegexMaker R.Regex R.CompOption R.ExecOption a,RegexContext R.Regex b t > ,RegexMaker F.Regex F.CompOption F.ExecOption a,RegexContext F.Regex b t > ,RegexMaker S.Regex S.CompOption S.ExecOption a,RegexContext S.Regex b t) > => b -> a -> t > (=~) = case R.getVersion of > Just _ -> (R.=~) > Nothing -> case S.getVersion of > Just _ -> (S.=~) > Nothing -> (F.=~) > > main = print (("ba" =~ "(.)a") :: (String,String,String,[String])) The R.getVersion and S.getVersion detect whether it was compiled against PCRE or PosixRE. The (=~) is then chosen at run time.

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[Parsec] Backtracking with try does not work for me?
by Stephane Bortzmeyer 02 Aug '06

02 Aug '06

I'm trying to write a Parsec parser for a language which authorizes (this is a simplified example) "a" or "a,b,c" or "a,c" or "a,b". (I can change the grammar but not the language.) The first attempt was: ***** CUT HERE **** import Text.ParserCombinators.Parsec import System (getArgs) comma = char ',' minilang = do char 'a' optional (do {comma ; char 'b'}) optional (do {comma ; char 'c'}) eof return "OK" run parser input = case (parse parser "" input) of Left err -> putStr ("parse error at " ++ (show err) ++ "\n") Right x -> putStr (x ++ "\n") main = do args <- getArgs run minilang (head args) ***** CUT HERE **** Of course, it fails for "a,c": parse error at (line 1, column 3): unexpected "c" expecting "b" for a reason explained in Parsec's documentation (the parser "optional (do {comma ; char 'b'})" already consumed the input, do note the column number). What puzzles me is that the solution suggested in Parsec's documentation does not work either: ********* CUT HERE ******************* minilang = do char 'a' try (optional (do {comma ; char 'b'})) optional (do {comma ; char 'c'}) eof return "OK" ********* CUT HERE ******************* parse error at (line 1, column 2): unexpected "c" expecting "b" Apparently, "try" was used (do note that the column number indicates that there was backtracking) but the parser still fails for "a,c". Why?

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Future Edison directions
by Robert Dockins 01 Aug '06

01 Aug '06

Hello all, There has been very recently a thread discussing the design decisions involved in creating a sequence abstraction. This was naturally of interest to me as the current Edison maintainer, and generated a fair bit of interesting discussion. I'd like to kick off a new thread here to talk about future directions for the Edison API in particular. 1) Regarding Sequence, I have become convinced by the discussion that the Edison Sequence class should be broken down into smaller classes. Furthermore, it would be very nice to make these smaller classes shared across the various families of data structure abstractions in Edison (Sequences, Collections and Associative Collections). The formulation of Sequence of kind * -> * may need to be sacrificed to this end. I am not convinced that losing the maps and zips would be a major blow; however there are a couple of strategies for retaining them in some form. 2) The associated collection API is in a similar situation, except there are no zips. 3) I am reluctant to undertake a major overhaul of the Edison API while the future of type classes in Haskell' is so hazy. I haven't heard any news from the Haskell' type classes focus group in quite some time, and last I was aware, discussion was somewhat stalled. I there any hope for a coherent story here in the nearish future? 4) I am on the verge of deciding that nobody wants non-observable collections (ie, collections in which the element values are not available for inspection). Currently Edison has no implementations which are non-observable, and I am not aware of anyone else creating a datastructure implementation in Haskell which is non-observable. Therefore, I am considering removing this feature of the Edison typeclass hierarchy to reduce complexity. Shout if you think this would be a terrible mistake. 5) OTOH, something people DO seem to want is collection "views", or the ability to treat a datastructure as though it were something else. For example, it would be nice to transparently treat the keys of a finite map as a set, or to treat a nested sequence as a single flattened sequence. Such uses require the separation of operations which can create datastructures from those which merely inspect them (or some fancy bidirectional stuff I don't think I want to get into). 6) Edison 1.2 has now been out for a couple of months. If you've used or looked at the new Edison, I'd love to hear what you think. I think the next development cycle will involve pretty substantial changes, and if you want to get your gripes addressed, now is a good time to voice them. Alternately, if you think there are some aspects that are very important to keep, that's also good information. 7) Finally, I somehow feel like there should be a nice categorical formulation of these datastructure abstractions which would help to drive a refactoring of the API typeclasses in a principled way, rather than on an ad-hoc I-sort-of-think-these-go-together sort of way. Unfortunately, my category-fu is quite weak, so all I have is this vague intuition that I can't substantiate. I'm sort of familiar with initial algebras, but I think they may be too concrete. I'm looking for some way to classify algebras that have, eg, the property of having folds, or of being set-like, etc. If anybody can point me in the right direction wrt this, that would be great. Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG

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A program which never crashes (even when a function calls "error")
by Stephane Bortzmeyer 01 Aug '06

01 Aug '06

[It is a philosophical question, not a practical programming problem.] I'm used, in imperative programming languages with exceptions (like Python) to call any function without fear of stopping the program because I can always catch the exceptions with things like (Python): while not over: try: code which may raise an exception... except Exception e: do something clever How to do it in Haskell? How can I call functions like Prelude.head while being sure my program won't stop, even if I call head on an empty list (thus calling "error")?

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Fw: [Haskell-cafe] The difficulty of designing a sequence class
by Brian Hulley 01 Aug '06

01 Aug '06

David Menendez wrote: > Brian Hulley writes: > >> 1) Did Edison choose MonadPlus just because this fitted in with the >> lack of multi-parameter typeclasses in H98? > > Instances of Monoid (and your ISeq) have kind *. Instances of > MonadPlus (and Edison's Sequence) have kind * -> *. > > Functions like map, zip, and their variants are best defined in terms > of type constructors. > > With Sequence, you have > > zipWith :: (Sequence s) => (a -> b -> c) -> s a -> s b -> s c > > With ISeq, you'd have to do something like > > zipWith :: (ISeq s1 a, ISeq s2 b, ISeq s3 c) => > (a -> b -> c) -> s1 -> s2 -> s3 > > which isn't able to make any assumptions about s1, s2, and s3 having > the same structure. On the other hand it's more powerful because they can now have different structures ie was there any reason not to have: zipWith :: (Sequence s1, Sequence s2, Sequence s3) => (a -> b -> c) -> s1 a -> s2 b -> s3 c >> 3) Is it worth bothering to derive ISeq from Monoid (with the >> possible extra inefficiency of the indirection through the >> definitions for append = mappend etc or does the compiler completely >> optimize this out)? > > I would expect the compiler to inline append. Thanks - that's good news. I' probably still too much in C++ mode. >> 4) Would it be worth reconsidering the rules for top level names so >> that class methods could always be local to their class (ditto for >> value constructors and field names being local to their type >> constructor). > > Qualified module imports are the way to go, here. Do you really want > to start writing "if x Eq/== y Num/+ 1 then ... "? I'm beginning to see that qualified module imports are indeed the only way to go, because the methods in a type class are only the "virtual" methods - often there are many other "methods" which are put outside the class to save space in the dictionary but which conceptually belong to the class thus putting the class + these extra functions in a single module wraps everything up into a conceptual unit. eg: module Foldable ( Foldable(..) , reduceR ) where class Foldable c a | c -> a where foldR :: (a -> b -> b) -> b -> [a] -> b -- ... reduceR :: Foldable c a => (a -> b -> b) -> (c -> b -> b) reduceR f xs y = foldR f y xs forms the single conceptual unit to use Foldable.foldR, Foldable.reduceR etc so I'll have to retract my suggestion as regards classes... (Although I'm still concerned about value constructors and field names being in the top level instead of local to their type but changing this would require some changes to type inference (so that the constructors and field names could be used unqualified when the type at the given position is known eg by a top level type signature for the function or value) so that's more of a long term idea.) Regards, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

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The difficulty of designing a sequence class
by Brian Hulley 01 Aug '06

01 Aug '06

Hi - Part 1 of 2 - Monoid versus MonadPlus =========================== I've just run into a troublesome question when trying to design a sequence class: class ISeq c a | c -> a where empty :: c single :: a -> c append :: c -> c -> c However I've noticed that people sometimes separate the empty and append operations out as sequences with these ops form a Monoid therefore: class Monoid c => ISeq c a | c -> a where single :: a -> c -- now outside the class append :: ISeq c a => c -> c -> c append = mappend empty :: ISeq c a => c empty = mempty Another option, is the Edison library which uses: class (Functor s, MonadPlus s) => Sequence s where so here MonadPlus is used instead of Monoid to provide empty and append. So I've got three main questions: 1) Did Edison choose MonadPlus just because this fitted in with the lack of multi-parameter typeclasses in H98? 2) Are there any reasons to prefer the Edison design over the MPTC design (apart from H98 compatibility) or vice versa? 3) Is it worth bothering to derive ISeq from Monoid (with the possible extra inefficiency of the indirection through the definitions for append = mappend etc or does the compiler completely optimize this out)? and a fourth more long term question: 4) Would it be worth reconsidering the rules for top level names so that class methods could always be local to their class (ditto for value constructors and field names being local to their type constructor). For example it would be nice imho to be able to write: class Monoid c => ISeq c a | c -> a where length :: c -> Int f x y = Monoid/append x y -- or ISeq/append x y g x = ISeq/length x instead of having all names collide in the top level of a module, since at the moment it is difficult to think of method names that don't collide with the Prelude, and it's not nice to have to write "mempty" in place of "empty". Part 2 of 2 - Monad versus Ancillary result type ================================ Another issue relates to left and right views of a sequence. If a sequence is non-empty, the left view is just the leftmost element and the rest of the sequence. The problem arises when the sequence is empty. In the Edison library, this is solved by returning a monadic value ie: lview :: Monad m => s a -> m (a, s a) whereas from the paper "Finger trees: a simple general purpose data structure" by Ralf Hinze and Ross Paterson they use an ancillary data type to store the result of a view: data ViewL s a = NilL | ConsL a (s a) viewL :: FingerTree a -> ViewL FingerTree a So my question here is: what's the best choice? I can see that the monadic version has the advantage that it could be used in do notation in cases where you expect the sequence to be non-empty, but has the disadvantage that it treats the empty sequence as something special (resulting in Monad/fail) and an extra indirection to find the components when the sequence is non-empty. Anyway these are my main questions for now - any feedback appreciated ;-) Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com

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Reviving wxHaskell (was: Re: [wxhaskell-users] [Haskell-cafe] Trouble compiling wxhaskell)
by Jeremy O'Donoghue 01 Aug '06

01 Aug '06

Hi list, Apologies for continuing with the cross-posting, but wxhaskell-users is not exactly active. It seems like there may be enough interest in wxHaskell to justify trying to revive the project. At present, from what I can tell, Daan Leijen, the principal developer of wxHaskell, no longer has much interest in the project - the CVS log shows little activity for about 15 months now - and using wxHaskell with newer wxWidgets versions or on Unicode systems requires the application of various patches (for which the interested potential user must search diligently). Ideally, it would be best Daan for to enable new CVS committers to the project (or even to hand over project administration), but if this is not an option, is there a possibility of hosting a fork on hackage.haskell.org (I think there's a benefit in hosting Haskell-specific projects in a Haskell-friendly location). I don't have the time to nurture huge ambitions for wxHaskell, but I think it is realistic to aim for the following in the short term: * Patches to ensure that wxHaskell compiles against latest wxWidgets versions on Mac, Linux and Windows (exists today) * Add Eric Kow's Unicode patches (exist today) * Produce suitable binary packages for whatever targets we can get maintainers for, compatible with up-to-date versions of both GHC and wxWidgets. * Improve samples and documentation. In the longer term, we could look at: * Fixing operation with sash windows (a personal gripe ;-) - easy * Wrapping some of the more complex widgets - easy. * Subclassing of widgets in Haskell (i.e. allow C++ virtual methods to be redefined in Haskell) - moderately hard * Move from the Eiffel wxc bindings to wxC project to give better maintained interface to wxWidgets - time consuming, but easy * Porting to other Haskell implementations (Hugs, YHC etc) Taking on a project like this is a very significant commitment, and only makes sense if there are a number of willing contributors. I'm happy to kick this off and try to cover some of the boring 'administrative' bits, as well as contributing on documentation and smaller bug fixes, but I don't have time to save wxHaskell from permanent bit-rot. If there's enough interest, I'll push ahead with trying to organize this. Regards Jeremy On 01/08/06, shelarcy <shelarcy(a)gmail.com> wrote: > > > On 7/31/06, David F. Place <d(a)vidplace.com> wrote: > >> Hi: > >> > >> I'm having trouble compiling wxhaskell 0.9.4 under both ghc 6.4.2 and > >> ghc 6.5. Does anyone know where I should direct my queries? > > If you use ghc 6,4,2 under Windows platform, you > can use my patched version of wxHaskell. > > And you can get my patch from Kamiariduki's source. > > http://www.haskell.org/pipermail/haskell/2006-June/018043.html > https://sourceforge.net/project/showfiles.php?group_id=168626 > > > I also know Eric Y. Kow's unicode patch doesn't > include db problems fix. These problems has not > only wxWidgets 2.6.x change, but also unicode > change. > > I try to fix latter case, use attached after unicode > patch, this fixes compile problem ... but it has > another problem that can't use non-ascii characters > correctly. So, if want to accesss DB by wxHaskell's > ODBC, data is garbled and cause problems. > > I don't know how to fix that. > > Attached is already sent wxhaskell-user's list, but > you can't get this file. So I send again. > http://sourceforge.net/mailarchive/message.php?msg_id=16222530 > > > My patch where I put Kamiariduki's project page doesn't > include unicode support that I noticed above Mailng-List's > log. > > Don't worry about this. You can use both my patch and > unicode patch, if you want. These cause conflict message > but this is not problem. > > > On Tue, 01 Aug 2006 08:18:27 +0900, Jason Dagit > <dagit(a)eecs.oregonstate.edu> wrote: > > I've done this recently. I put my notes on the wiki: > > http://www.haskell.org/haskellwiki/WxHaskell/Install#Windows > > I don't know this problem when I made patch. > So, my patch doesn't fix this problem. > > > -- > shelarcy <shelarcy capella.freemail.ne.jp> > http://page.freett.com/shelarcy/ > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share > your > opinions on IT & business topics through brief surveys -- and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > > _______________________________________________ > wxhaskell-users mailing list > wxhaskell-users(a)lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/wxhaskell-users > > > >

1 0

Trouble compiling wxhaskell
by David F. Place 31 Jul '06

31 Jul '06

Hi: I'm having trouble compiling wxhaskell 0.9.4 under both ghc 6.4.2 and ghc 6.5. Does anyone know where I should direct my queries? Thanks. -------------------------------- David F. Place mailto:d@vidplace.com

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Re: [Haskell-cafe] The difficulty of designing a sequence class
by David Menendez 31 Jul '06

31 Jul '06

Brian Hulley writes: > 1) Did Edison choose MonadPlus just because this fitted in with the > lack of multi-parameter typeclasses in H98? Instances of Monoid (and your ISeq) have kind *. Instances of MonadPlus (and Edison's Sequence) have kind * -> *. Functions like map, zip, and their variants are best defined in terms of type constructors. With Sequence, you have zipWith :: (Sequence s) => (a -> b -> c) -> s a -> s b -> s c With ISeq, you'd have to do something like zipWith :: (ISeq s1 a, ISeq s2 b, ISeq s3 c) => (a -> b -> c) -> s1 -> s2 -> s3 which isn't able to make any assumptions about s1, s2, and s3 having the same structure. > 3) Is it worth bothering to derive ISeq from Monoid (with the > possible extra inefficiency of the indirection through the > definitions for append = mappend etc or does the compiler completely > optimize this out)? I would expect the compiler to inline append. > 4) Would it be worth reconsidering the rules for top level names so > that class methods could always be local to their class (ditto for > value constructors and field names being local to their type > constructor). Qualified module imports are the way to go, here. Do you really want to start writing "if x Eq/== y Num/+ 1 then ... "? -- David Menendez <zednenem(a)psualum.com> | "In this house, we obey the laws <http://www.eyrie.org/~zednenem> | of thermodynamics!"

1 0

What is the state if Unicode in Haskell implementations?
by Olof Bjarnason 31 Jul '06

31 Jul '06

Hi there! I'm trying to user Haskell as a code-generating language, specifically generating C# code files. The wish list is 1) reading UTF-8 coded text files into unicode-enabled Strings, lets call them UString 2) writing UStrings to UTF-8 coded text files 3) using unicode strings in-code, that is in my .hs files I can live without 3), and with a little good will also 2), but 1) is harder since I cannot really hope my input files (meta-data-files) are coded in anything else than UTF-8. I've searched&browser the web for information on the current state of unicode in GHC/Hugs but the latest discussion I could find on the topic leaves me less than happy. BUT it is from january 2005 so I thought maybe you guys have more up-to-date answers to these questions. The discussion I found: http://groups.google.se/group/fa.haskell/browse_thread/thread/ccf1c6f32dbea… Thanks! /Olof

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