Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
chaddai.fouche: > 2008/3/31, Bruno Carnazzi <[EMAIL PROTECTED]>: > >Dears Haskellers, > > > > As an Haskell newbie, I'm learning Haskell by trying to resolve Euler > > Project problems (http://projecteuler.net/ ). I'm hanging on problem > > 14 (Collatz problem). > > > > I've written the following program... Which does not end in a reasonable > > time :( > > My algorithm seems ok to me but I see that memory consumption is > > gigantic... > > Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) > > In a more general way, how can I troubleshoot these kind of problem ? > > Others have pointed potential source of memory leaks, but I must say > that using Data.Map for the cache in the first place appear to me as a > very bad idea... Data.Map by nature take much more place than > necessary. You have an integer index, why not use an array instead ? > > > import Data.Array > > import Data.List > > import Data.Ord > > > > syrs n = a > > where a = listArray (1,n) $ 0:[ syr n x | x <- [2..n]] > > syr n x = if x' <= n then a ! x' else 1 + syr n x' > > where x' = if even x then x `div` 2 else 3 * x + 1 > > > > main = print $ maximumBy (comparing snd) $ assocs $ syrs 100 > > This solution takes 2 seconds (on my machine) to resolve the problem. > > On the other hand, now that I have read your solution, I see that > using Map was the least of the problem... All those Map.map, while > retaining the original Map... Your solution is too clever (twisted) > for its own good, I suggest you aim for simplicity next time. > and if its got Int indices, Data.IntMap is always a better option than Data.Map and usually outperforms the HashTable type, while being pure. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
2008/3/31, Bruno Carnazzi <[EMAIL PROTECTED]>: >Dears Haskellers, > > As an Haskell newbie, I'm learning Haskell by trying to resolve Euler > Project problems (http://projecteuler.net/ ). I'm hanging on problem > 14 (Collatz problem). > > I've written the following program... Which does not end in a reasonable > time :( > My algorithm seems ok to me but I see that memory consumption is gigantic... > Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) > In a more general way, how can I troubleshoot these kind of problem ? Others have pointed potential source of memory leaks, but I must say that using Data.Map for the cache in the first place appear to me as a very bad idea... Data.Map by nature take much more place than necessary. You have an integer index, why not use an array instead ? > import Data.Array > import Data.List > import Data.Ord > > syrs n = a > where a = listArray (1,n) $ 0:[ syr n x | x <- [2..n]] > syr n x = if x' <= n then a ! x' else 1 + syr n x' > where x' = if even x then x `div` 2 else 3 * x + 1 > > main = print $ maximumBy (comparing snd) $ assocs $ syrs 100 This solution takes 2 seconds (on my machine) to resolve the problem. On the other hand, now that I have read your solution, I see that using Map was the least of the problem... All those Map.map, while retaining the original Map... Your solution is too clever (twisted) for its own good, I suggest you aim for simplicity next time. -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HDBC, character encoding
On 31/03/2008, at 11:42 PM, Bjorn Bringert wrote: 2008/3/26 Adrian Neumann <[EMAIL PROTECTED]>: Hi, I wrote a CGI program to access a Postgres database using HDBC. [...] I think that Peter Gammie (copied) has some code to deal with this. I added some stuff to HSQL (not HDBC) and HaskellDB so that UTF8 can be used to talk to the database. It's not very pretty though, so I haven't tried to get it merged. cheers peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How can I represent 4x4 map in haskell
I mean board but I found the solution to my problem don't worry I really don't want someone to do my Project since I won't learn from that and I really want to learn since that's what is important at the end of the day. Thanks to all that people who understood what I mean and advised me, thanks again! Chris Smith wrote: > > iliali16 wrote: > >> Hi can you please tell me how can I represent 4x4 map in haskell.Should >> I show it as a list of lines and each line to be a list of char or I am >> mistaken? Thanks in advance! > > What do you mean by a 4x4 map? Maybe I'm missing something obvious, but > there are several different meanings for "map", and I don't see which one > you mean. > > -- > Chris Smith > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- View this message in context: http://www.nabble.com/How-can-I-represent-4x4-map-in-haskell-tp16396273p16401807.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] Student applications deadline extended one week
On Mon, Mar 31, 2008 at 12:00 PM, Manlio Perillo <[EMAIL PROTECTED]> wrote: > Since Nginx is asynchronous, how can be solved the producer-consumer > problem (that is, the Haskell program produces more data that Nginx can > send to the client without blocking)? I assume that the Haskell process is connected to nginx over a pipe or socket. In which case, nginx can use flow control to block the sending side of the pipe and the Haskell code will backup on that. If many connections need to be multiplexed over the same flow-controlled entity (i.e. a pipe), without head-of-line blocking then you can just suspend the current thread using an MVar or the STM objects. Alternatively, with Network.MiniHTTP the problem is turned inside out. Request handlers give return a Source object, which can be asked to generate more data on request. This would be similar to generators in Python. AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
On Mon, Mar 31, 2008 at 6:00 PM, Bruno Carnazzi <[EMAIL PROTECTED]> wrote: > I've done this modification with no more success : > > import qualified Data.List as List > import qualified Data.Map as Map > > f :: Integer -> Integer > > f n | even n = n `div` 2 > | otherwise = 3 * n + 1 > > chain m n = > let chain' cn cm | Map.member cn m = Map.map (+ (m Map.! cn)) cm > | otherwise = chain' (f cn) $! Map.insert cn 1 (Map.map > (+1) cm) > in chain' n Map.empty This function raises a red flag for me. The collatz sequence gets _very_ big, with very many distinct numbers. You are saving the length of the resulting chain for each of those numbers, which is going to take a lot of memory. But Map is also lazy in its values, so the values you are storing once chain finishes will look like: 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1 Instead of 22, which is taking quite a lot of memory as well. My impression is that the caching approach is just a bad idea. It is not necessary to solve the problem efficiently; a brute force approach runs in under 1 minute in constant memory for me. Try to simplify your approach. I'd suggest generating a list representing the collatz sequence starting at the number, then just taking its 'length'. Do that for each number and find the maximum. There should be no need for Data.Map. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] X Haskell bindings
Hello Antoine, On Mon, Mar 31, 2008 at 3:23 PM, Antoine Latter <[EMAIL PROTECTED]> wrote: > I've been looking into to this a bit myself, and have had trouble with > the fact that the XML descriptions of the protocol are extremely > C-centric. As in, the union types defined in the XML are C-unions, > and I've seen a struct definition which uses padding-bytes to store > semantically useful data. > > Both of which are fine things to do in C, but a bit tricky to map onto > Haskell. > Maybe this Haskell package libxml [1] will be helpful for this. The package provides bindings for the XML parser and toolkit for Gnome: libxml [2]. Hope this helps. __ Donnie 1. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/libxml-0.1 2. http://xmlsoft.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] X Haskell bindings
I've been looking into to this a bit myself, and have had trouble with the fact that the XML descriptions of the protocol are extremely C-centric. As in, the union types defined in the XML are C-unions, and I've seen a struct definition which uses padding-bytes to store semantically useful data. Both of which are fine things to do in C, but a bit tricky to map onto Haskell. You should still be able to generate a large amount of data-types and serializing/deserializing code automatically. As for code generation, Language.Haskell.Syntax paired with Language.Haskell.Pretty is a pretty good way to do it, from what I can tell. On Mon, Mar 31, 2008 at 1:29 PM, Adam Langley <[EMAIL PROTECTED]> wrote: > 2008/3/31 Roman Cheplyaka <[EMAIL PROTECTED]>: > > > Especially I need help with "Milestones" section. I'm not quite sure how > > it should look like for such project. > > This would seem to be a commendable SoC project. I'm not sure that the > milestones are all that important - no plan ever survives contact with > reality. However, I'd suggest that these would be important aspects: > > * A working parser for the XCB (this involves choosing an XML parser > and getting useful data structures from it) > * A working Haskell code generator which outputs bindings for a > minimal subset of the functions > > (the last two need not be in Haskell, although I suspect that it would > be a good idea for them to be so) > > * The first, minimal, Haskell X client using XCB > * Having sensible bindings for 25%/50%/75% and 100% of the XCB interface. > > > > AGL > > -- > Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org > ___ > 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] [GSoC] X Haskell bindings
* Adam Langley <[EMAIL PROTECTED]> [2008-03-31 11:29:57-0700] > 2008/3/31 Roman Cheplyaka <[EMAIL PROTECTED]>: > > Especially I need help with "Milestones" section. I'm not quite sure how > > it should look like for such project. > > This would seem to be a commendable SoC project. I'm not sure that the > milestones are all that important - no plan ever survives contact with > reality. However, I'd suggest that these would be important aspects: > > * A working parser for the XCB (this involves choosing an XML parser > and getting useful data structures from it) > * A working Haskell code generator which outputs bindings for a > minimal subset of the functions > > (the last two need not be in Haskell, although I suspect that it would > be a good idea for them to be so) > > * The first, minimal, Haskell X client using XCB > * Having sensible bindings for 25%/50%/75% and 100% of the XCB interface. Thanks, Adam! Your suggestions will help me a lot. -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock... signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] Student applications deadline extended one week
Don Stewart ha scritto: Hey all, As you might know, the Google Summer of Code application submission period is open. Google has decided to extend the deadline for initial student applications by one week, http://groups.google.com/group/google-summer-of-code-announce/browse_thread/thread/9fa88f31aa401f70 If you've thought about submitting, and are interested in hacking on Haskell for 3 months this summer, and bootstrapping into the Haskell developer community, check our project wiki, http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 and get your applications into google this week! -- Don Hi. I'm very new to Haskell. From the SoC2008 page I see that there is a project for working on a mod_haskell for Apache. Now, I'm the author of the WSGI (Python Web Server gateway Interface) module for Nginx: http://hg.mperillo.ath.cx/nginx/mod_wsgi/ I'm thinking about writing an Haskell module for Nginx, for learning purpose. I'm not a student, so this is not a SoC2008 proposal, but I'm very interested in related works. As an example, how should be a CGI like interface for Haskell? Since Nginx is asynchronous, how can be solved the producer-consumer problem (that is, the Haskell program produces more data that Nginx can send to the client without blocking)? I have easily solved this in Python, since the WSGI application returns a generator and I can simply suspend the iteration. Is it possible to support asynchronous Haskell applications (as an example an application that needs to do a HTTP request to a server without blocking the worker process)? Here, again, I have solved the problem for Python by making use of generators: http://hg.mperillo.ath.cx/nginx/mod_wsgi/file/tip/examples/nginx-postgres-async.py (but this is very experimental) Thanks and sorry for having used this thread for an unrelated topic (I have removed the Cc to haskell-soc-2008) Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [GSoC] X Haskell bindings
2008/3/31 Roman Cheplyaka <[EMAIL PROTECTED]>: > Especially I need help with "Milestones" section. I'm not quite sure how > it should look like for such project. This would seem to be a commendable SoC project. I'm not sure that the milestones are all that important - no plan ever survives contact with reality. However, I'd suggest that these would be important aspects: * A working parser for the XCB (this involves choosing an XML parser and getting useful data structures from it) * A working Haskell code generator which outputs bindings for a minimal subset of the functions (the last two need not be in Haskell, although I suspect that it would be a good idea for them to be so) * The first, minimal, Haskell X client using XCB * Having sensible bindings for 25%/50%/75% and 100% of the XCB interface. AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
I've done this modification with no more success : import qualified Data.List as List import qualified Data.Map as Map f :: Integer -> Integer f n | even n = n `div` 2 | otherwise = 3 * n + 1 chain m n = let chain' cn cm | Map.member cn m = Map.map (+ (m Map.! cn)) cm | otherwise = chain' (f cn) $! Map.insert cn 1 (Map.map (+1) cm) in chain' n Map.empty chains n = List.foldl' (\m i -> Map.union m (chain m i)) (Map.singleton 1 1) [2..n] maxCollatz c1@(_,l1) c2@(_,l2) | l1 < l2 = c2 | otherwise = c1 maxChain = List.foldl' maxCollatz (0,0) . Map.toList . chains main = let n = 100 in putStrLn $ show $ maxChain n Best regards, Bruno. 2008/3/31, Ketil Malde <[EMAIL PROTECTED]>: > "Bruno Carnazzi" <[EMAIL PROTECTED]> writes: > > > The program ends for values up to 40 : > > > Wild guess here - I know nothing about the problem, and haven't > examined your program in detail - but could it be that you default to > Int, and that it wraps silently at some power of two, thereby making > your algorithm wrap around? Try to stick some 'Integer' type > annotations in there, and see if it helps. > > -k > > (cetera censeo...) > > -- > If I haven't seen further, it is by standing in the footprints of giants > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
"Bruno Carnazzi" <[EMAIL PROTECTED]> writes: > The program ends for values up to 40 : Wild guess here - I know nothing about the problem, and haven't examined your program in detail - but could it be that you default to Int, and that it wraps silently at some power of two, thereby making your algorithm wrap around? Try to stick some 'Integer' type annotations in there, and see if it helps. -k (cetera censeo...) -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [GSoC] Student applications deadline extended one week
Hey all, As you might know, the Google Summer of Code application submission period is open. Google has decided to extend the deadline for initial student applications by one week, http://groups.google.com/group/google-summer-of-code-announce/browse_thread/thread/9fa88f31aa401f70 If you've thought about submitting, and are interested in hacking on Haskell for 3 months this summer, and bootstrapping into the Haskell developer community, check our project wiki, http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 and get your applications into google this week! -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
The program ends for values up to 40 : *Main> :set +s *Main> maxChain 1000 (871,179) (0.09 secs, 3697648 bytes) *Main> maxChain 1 (6171,262) (0.73 secs, 31560008 bytes) *Main> maxChain 10 (77031,351) (9.31 secs, 347122064 bytes) *Main> maxChain 20 (156159,383) (19.32 secs, 709303708 bytes) << This one take about 10 minutes and swap a lot >> *Main> maxChain 30 (230631,443) (38.02 secs, 1083800124 bytes) << This one swap a lot and does not end in less than 10 minutes >> *Main> maxChain 40 The ratio memreq/n seems to be more or less constant : *Main> 3697648/1000 3697.648 *Main> 31560008/1 3156.0008 *Main> 347122064/10 3471.22064 *Main> 709303708/20 3546.51854 *Main> 1083800124/30 3612.66708 Thank you, Bruno. 2008/3/31, Bulat Ziganshin <[EMAIL PROTECTED]>: > Hello Bruno, > > > Monday, March 31, 2008, 7:51:43 PM, you wrote: > > > I've written the following program... Which does not end in a reasonable > time :( > > My algorithm seems ok to me but I see that memory consumption is > gigantic... > > Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) > > In a more general way, how can I troubleshoot these kind of problem ? > > > first step is to reduce n and see whether program will finish and how > memreqs depends on value of n > > > main = > > let n = 100 > > > > -- > Best regards, > Bulatmailto:[EMAIL PROTECTED] > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HDBC, character encoding
2008/3/26 Adrian Neumann <[EMAIL PROTECTED]>: > Hi, > > I wrote a CGI program to access a Postgres database using HDBC. The > database stores books and I want to display those from a certain > author. Everything works fine, unless I search for someone with an > umlaut in his name. Böll, for example. I have a function like this > > > bookByAuthor :: Connection -> AutorName -> IO [[String]] > > bookByAuthor c aName = do > > writeFile "./err.log" ((show aName)++" "++(show $ toSql aName)) > > rows <- quickQuery c "SELECT * FROM buecher WHERE lower > (autor_name) LIKE ? ORDER BY autor_name, buch_name" [toSql $ map > toLower $ '%':aName++"%"] > > return $ map (map fromSql) rows > > It returns me a SqlError. However, doing the same in ghci works > perfectly. I can't understand why. err.log contains > > > "b\195\182ll" SqlString "b\195\182ll" > > which is ok I think. Since > > > quickQuery c "SELECT * FROM buecher WHERE lower(autor_name) LIKE ? > ORDER BY autor_name, buch_name" [toSql "%b\195\182%"] > > works in ghci. I have tried "b\246ll", but that doesn't even work in > ghci, although the database-encoding is utf-8. This all is really > annoying... I think that Peter Gammie (copied) has some code to deal with this. /Björn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [GSoC] X Haskell bindings
Hi! I've written a draft proposal for GSoC on XCB Haskell Bindings[1]. I'd appreciate any feedback. Especially I need help with "Milestones" section. I'm not quite sure how it should look like for such project. 1. http://ro-che.info/docs/xhsb.txt -- Roman I. Cheplyaka :: http://ro-che.info/ ...being in love is totally punk rock... signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking Daan Leijen
On Thu, Mar 27, 2008 at 6:43 PM, John Goerzen <[EMAIL PROTECTED]> wrote: > I tried to email this to Daan, but his mail is bouncing... > > Subject: http://legacy.cs.uu.nl/daan/parsec.html > > Hi Daan, > > I noticed Parsec 3.0.0 on Hackage, and went to your homepage to read about > the new package. But it looks like your homepage still has the old version > put out in 2003. This might cause confusion for some that are looking > for new releases at your website. Daan is now working at Microsoft Research, see http://research.microsoft.com/users/daan/ /Bjorn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: HTTP client libraries
On 2008-03-30, Iavor Diatchki <[EMAIL PROTECTED]> wrote: > Hi, > > On Fri, Mar 28, 2008 at 6:42 AM, John Goerzen <[EMAIL PROTECTED]> wrote: >> On 2008-03-28, Don Stewart <[EMAIL PROTECTED]> wrote: >> > paulrbrown+haskell-cafe: >> >> > And we have a curl binding, already in wide use. >> > >> > http://code.haskell.org/curl.git/ >> > >> > a release to hackage is imminent. >> >> Do you mean this? >> >> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl-1.3.1 >> >> Looks like it's not quite as current as your Git repo. > > Is this surprising? Hackage is not a revision control system. > The curl package on hackage is a fairly recent version of the git repo. No, but I was confirming that the Hackage package corresponds to the given Git repo. -- John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
Hello Bruno, Monday, March 31, 2008, 7:51:43 PM, you wrote: > I've written the following program... Which does not end in a reasonable time > :( > My algorithm seems ok to me but I see that memory consumption is gigantic... > Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) > In a more general way, how can I troubleshoot these kind of problem ? first step is to reduce n and see whether program will finish and how memreqs depends on value of n > main = > let n = 100 -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Newbie] Problem with Data.Map (or something else ?)
Dears Haskellers, As an Haskell newbie, I'm learning Haskell by trying to resolve Euler Project problems (http://projecteuler.net/ ). I'm hanging on problem 14 (Collatz problem). I've written the following program... Which does not end in a reasonable time :( My algorithm seems ok to me but I see that memory consumption is gigantic... Is this a memory problem with Data.Map ? Or an infinite loop ? (Where ?) In a more general way, how can I troubleshoot these kind of problem ? Here's the code : import qualified Data.List as List import qualified Data.Map as Map f n | even n = n `div` 2 | otherwise = 3 * n + 1 chain m n = let chain' cn cm | Map.member cn m = Map.map (+ (m Map.! cn)) cm | otherwise = chain' (f cn) $! Map.insert cn 1 (Map.map (+1) cm) in chain' n Map.empty chains n = List.foldl' (\m i -> Map.union m (chain m i)) (Map.singleton 1 1) [2..n] maxCollatz c1@(_,l1) c2@(_,l2) | l1 < l2 = c2 | otherwise = c1 maxChain = List.foldl' maxCollatz (0,0) . Map.toList . chains main = let n = 100 in putStrLn $ show $ maxChain n Hope someone can help me, I really don't see what is th problem... Best regards, Bruno. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How can I represent 4x4 map in haskell
iliali16 wrote: > type Line = [Char] > type Board = [Line] > > so my question is if this is ok to represent a map. If yes I will try to > write the function which makes it 4 x 4 myself. What I jsut need as an > answer is Yes or No. Just to let you know is that I am trying to build the > Wumpus World A list of lists of cells is a possible representation for a two-dimensional array, yes. for bigger maps, there may be a performance problem, but for such a small world, it should be fine. You may consider using an array, e.g. with import Data.Array type Board = Array (Int, Int) Char Boards will be indexed by coordinate tuples. Another point: maybe you should use an algebraic data type instead of Char to represent the individual cells? e.g. data Cell = Wumpus | Trap | Gold | Nothing type Board = [[Cell]] Be aware of the Wumpus! Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Homework wiki page (was Re: How can I represent 4x4 map in haskell)
Hi Chris, > The Haskell community has a reputation of being helpful and welcoming to > newcomers. I'm having a hard time reconciling that with this wiki page. > In particular. For those who want to follow along, its this one: http://haskell.org/haskellwiki/Homework_help I agree. That page is pretty nasty. It looks like the person summarised Eric Raymond's article, which is also pretty nasty. A rewrite would be very good! > Let me be clear: I am not arguing that we should do people's homework for > them. But I am arguing for changing the tone of the response. I'd have > been rather put off if that wiki page had been my first introduction to > the Haskell community. Yes. I think that we should suggest people ask homework questions to homework authors, as they are based equipped to answer the questions using the techniques and tools the students have been taught. But politely, and saying why they benefit doing it the right way. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How can I represent 4x4 map in haskell
iliali16 wrote: Just to let you know that that is not a homework just for one function representing the map. It is my project wich I subdivided into peaces but since I am not that new to haskell I am not sure if I am on the right track so that is my code till now: type Line = [Char] type Board = [Line] so my question is if this is ok to represent a map. That certainly is one way to represent a map. For example, for any b::Board you will be able to access elements via b !! i !! j for some i,j from 0 to 3. Whether it is the best choice of representation for your application very much depends on what you are going to do with it. For example, which kind of operations on boards you are going to need. Just to mention an alternative: if it is important for your application that you always have exactly 4x4 maps, and you do not want to ensure this invariant "by hand", then you could use something along the lines of: > type Quadruple a = (a,a,a,a) > type Line = Quadruple Char > type Board = Quadruple Line Then, of course, you have to write your own "accessors" to get an element at position i,j. (But there are several ways, differing in their level of complication, of making this more generic, rather than inventing your own Quadruple. Probably they are overkill for your goal.) Ciao, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Homework wiki page (was Re: How can I represent 4x4 map in haskell)
This is a little off-topic, but perhaps we can have some discussion of that Wiki page? The Haskell community has a reputation of being helpful and welcoming to newcomers. I'm having a hard time reconciling that with this wiki page. In particular. 1. The tone is generally threatening, as in: if you step over the line, you could be reported for cheating, so don't ask for too much help. 2. There's a general RTFM attitude. 3. There's a link to Eric Raymond's insulting article at the end, which goes on to inform people that we don't care about them, we are only here for our personal daily fix of mental challenge, and if they can't meet that then they've got no business wasting our time. Let me be clear: I am not arguing that we should do people's homework for them. But I am arguing for changing the tone of the response. I'd have been rather put off if that wiki page had been my first introduction to the Haskell community. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How can I represent 4x4 map in haskell
Just to let you know that that is not a homework just for one function representing the map. It is my project wich I subdivided into peaces but since I am not that new to haskell I am not sure if I am on the right track so that is my code till now: type Line = [Char] type Board = [Line] so my question is if this is ok to represent a map. If yes I will try to write the function which makes it 4 x 4 myself. What I jsut need as an answer is Yes or No. Just to let you know is that I am trying to build the Wumpus World iliali16 wrote: > > Hi can you please tell me how can I represent 4x4 map in haskell.Should I > show it as a list of lines and each line to be a list of char or I am > mistaken? Thanks in advance! > -- View this message in context: http://www.nabble.com/How-can-I-represent-4x4-map-in-haskell-tp16396273p16396290.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How can I represent 4x4 map in haskell
iliali16 wrote: > Hi can you please tell me how can I represent 4x4 map in haskell.Should > I show it as a list of lines and each line to be a list of char or I am > mistaken? Thanks in advance! What do you mean by a 4x4 map? Maybe I'm missing something obvious, but there are several different meanings for "map", and I don't see which one you mean. -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How can I represent 4x4 map in haskell
iliali16 wrote: Hi can you please tell me how can I represent 4x4 map in haskell.Should I show it as a list of lines and each line to be a list of char or I am mistaken? Thanks in advance! Sure this is no homework? If it is, please first consult: http://www.haskell.org/haskellwiki/Homework_help -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How can I represent 4x4 map in haskell
Hi can you please tell me how can I represent 4x4 map in haskell.Should I show it as a list of lines and each line to be a list of char or I am mistaken? Thanks in advance! -- View this message in context: http://www.nabble.com/How-can-I-represent-4x4-map-in-haskell-tp16396273p16396273.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] SYB with class: Bug in Derive.hs module
Hi people (and Ralf and Alex), I found a bug in the SYB with class library when trying to implement generic equality. I am hoping that someone in the Cafe (maybe Ralf) can confirm it is a bug, or maybe show me that I am doing something wrong. I am using the "Scrap your boilerplate with class" library (http:// homepages.cwi.nl/~ralf/syb3/). More precisely, I am using the library distributed by the HAppS project, because it works with GHC 6.8 . You can get the repository as follows: darcs get http://happs.org/HAppS/syb-with-class However, the offending module (Derive.hs) produces broken instances in both distributions. The bug: -- Generic equality needs type safe casting when implemented in SYB3, I have tried both the gzipwith variant and using Pack datatypes (geq*.hs in the first distribution). However, both functions loop when applied to a tree value. This loop occurs when the functions try to cast one of the arguments. I have managed to reduce the error to a smaller source file that I send attached. It does the following: > main = print typeReps > > tree = (Bin (Leaf 1) (Leaf 2))::BinTree Int > > data Pack = forall x. Typeable x => Pack x > > packedChildren = gmapQ geqCtx Pack tree > > typeOfPack (Pack x) = typeOf x > > typeReps = map typeOfPack packedChildren Basically the tree is transformed into a list of Pack-ed values and then to a list of type representations. This program loops at "typeOf" when you call "main". The Data instance that Derive generates is as follows: > instance (Data ctx a, > Data ctx (BinTree a), > Sat (ctx (BinTree a))) => > Data ctx (BinTree a) where Note the recursive |Data ctx (BinTree a)| in the context. If I get rid of it (a correct manual instance is also included in the attachment) the example works. I thought of removing this from the context in the Derive source. But maybe I might break some other use cases. So I am asking for help! Should Derive be fixed? How? Cheers, Alexey BugBinTree.lhs Description: Binary data ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] lexicographic order
2008/3/31, Simeon Mattes <[EMAIL PROTECTED]>: > why I should take as right > > (a,b) <= (a',b') iff (a < a' or (a == a' and b <= b')) > > and not > > (a,b) <= (a',b') iff (a <= a' or (a == a' and b <= b')) > > > The latter seems more logical, doesn't it? No, it doesn't, since in the latter (1,2) <= (1,1) because 1 <= 1 > Though I can't understand why both > (Branch l r) <= (Branch l' r') = l < l' || l == l' && r <= r' > (Branch l r) <= (Branch l' r') = l <= l' || l == l' && r <= r' > give the same results They don't, the second is a mistake, the first is the right one. -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Possible to automatically determine typeclass membership?
Hopefully, accessing the instance environment from Tempalte Haskell
will be possible in next GHC's release:
http://hackage.haskell.org/trac/ghc/ticket/1835
2008/3/31 jeff p <[EMAIL PROTECTED]>:
> Hello,
>
>
> > Is it possible in Haskell + GHC extensions to use reflection
> > techniques to determine typeclass membership? I'm thinking of things
> > like the following:
> >
> I think the short answer is not in general; i.e. I don't think there is any
> way to access the members of an arbitrary typeclass (but I'd love to be
> proved wrong).
>
> However, you could always explicitly list the members of a typeclass you are
> interested in (this is similar to your Idea 2):
>
> {-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances
> -fallow-overlapping-instances #-}
>
> class InEq a b | a -> b where inEq :: a -> Bool
> instance TypeCast b HFalse => InEq a b where inEq _ = False
> instance InEq Int HTrue where inEq _ = True
> instance InEq a b => InEq [a] b where inEq _ = inEq (undefined :: a)
>
> data HTrue
> data HFalse
>
> class TypeCast a b | a -> b, b-> a where typeCast :: a -> b
> class TypeCast' t a b | t a -> b, t b -> a where typeCast' :: t -> a -> b
> class TypeCast'' t a b | t a -> b, t b -> a where typeCast'' :: t -> a -> b
> instance TypeCast' () a b => TypeCast a b where typeCast x = typeCast' ()
> x
> instance TypeCast'' t a b => TypeCast' t a b where typeCast' = typeCast''
> instance TypeCast'' () a a where typeCast'' _ x = x
>
> You can also do an arguably nicer, more flexible version of the previous by
> recreating some of the typeclass machinery yourself; Oleg has several
> examples of this such as: //okmij.org/ftp/Haskell/poly2.txt
>
> -Jeff
>
>
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