[Haskell-cafe] Re: Can somebody give any advice for beginners?
clisper clisper at 163.com writes: haskell is greate but i don't know how to start. Don't! Learning Haskell will change your world! For worse! Really! Don't do that, you still have time to go back! Or be damned like all of us here... Referential transparency will suck up your soul. You'll think about monads as your warm and fuzzy friends. You'll wash your hands after doing IO because you'll feel that your purity suffered. You'll consider unit testing a downgraded form of static typing. When your programs finally compile, they will magically just work. You'll write less and less KLOC, doing more at the same time. Your C#/C++/Java code will look like higher order code after first order transformation done by hand. Your co-workers and friends will not understand what you wrote any more. You'll be like a wizard from another planet for them. You will know the difference between foldl and foldr. All your data structures will be infinite in size. Space leaks will bite you hard. Your functions will be not lazy enough in some arguments and not strict enough in some others at the same time. And even seq will not help you. You'll know what MPTCs and GADTs are. You'll actually understand olegs posts. You'll wonder, what was that OO thing again? You'll take out Java from your CV. Take a friendly advice: go back and forget that you ever heard about Haskell! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Over-allocation
Hi, My program is eating too much memory: copyfile source.txt dest.txt +RTS -sstderr Reading file... Reducing structure... Writting file... Done in 20.277s 1,499,778,352 bytes allocated in the heap 2,299,036,932 bytes copied during GC (scavenged) 1,522,112,856 bytes copied during GC (not scavenged) 17,846,272 bytes maximum residency (198 sample(s)) 2860 collections in generation 0 ( 10.37s) 198 collections in generation 1 ( 8.35s) 50 Mb total memory in use INIT time0.00s ( 0.00s elapsed) MUT time1.26s ( 1.54s elapsed) GCtime 18.72s ( 18.74s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time 19.98s ( 20.28s elapsed) %GC time 93.7% (92.4% elapsed) Alloc rate1,186,898,778 bytes per MUT second Productivity 6.3% of total user, 6.2% of total elapsed The source.txt is 800kb, and I expect files of size 100 times more, say 80MB, so using -H800M will not help here much. The profile -p says: Wed Nov 21 14:23 2007 Time and Allocation Profiling Report (Final) copyfile +RTS -p -RTS source.txt dest.txt total time =4.48 secs (224 ticks @ 20 ms) total alloc = 1,500,359,340 bytes (excludes profiling overheads) COST CENTREMODULE %time %alloc xparse PdfModel 78.1 95.0 followed by a lot of 0.0 numbers. Then the faulty xparse: xparse uniq borders body bin = do parseOperatorEq xref p - P.many (parseXRefSection uniq) parseOperatorEq trailer e - parseDict let entries = IntMap.fromList (map (\(a,b,c) - (a,c)) (concat p)) return (Body e entries) where the P is Text.ParserCombinators.ReadP made to work with [Word8]. How do I know WHAT is making so much allocation in this function? My files are xml-like in structure. The task currently is to read, parse, write the file. I can provide more details for interested souls. How do I make my program make less allocations? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Over-allocation
Stefan O'Rear stefanor at cox.net writes: Note that heap profiling is even more a black art than time profiling; you may need to do a lot of experimentation to find an enlightening profile. Black art indeed... I did -hc, looked at the postscript generated from every angle I could and it looks like this: /|/|/| / | / | / | / | / | / | / | / | / | /|/|/| This is only xparse, other functions are unimportant and aren't even visible on the graph. My xparse allocates a lot of memory which is then almost all freed at the very next occasion by GC. Seems I do not have space leaks. The problem is that my prog allocates a lot just to free it immediatelly after. But what? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Over-allocation
Ketil Malde ketil+haskell at ii.uib.no writes: Gracjan Polak gracjanpolak at gmail.com writes: let entries = IntMap.fromList (map (\(a,b,c) - (a,c)) (concat p)) Gut reaction: Map is lazy in its values (but probably not the key, which are checked for order), so you should force the 'c' before inserting it in the map. (There's probably a strict fromList or IntMap somewhere?) I tried both Map and IntMap and there was no difference in memory total usage or usage pattern. Seems I'm already strict enough. Values are left lazy till the point where they are forced, and that is at write-out in my current excersise. I'd want to leave them lazy as in more involved transformation not all of them will be needed. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Over-allocation
Ketil Malde ketil+haskell at ii.uib.no writes: Then you get the memory behavior you ask for. Unevaluated strings are extremely expensive, something like 12 bytes per char on 32 bit, twice that on 64 bits, and then you need GC overhead, etc. ByteStrings are much better, but you then probably need to implement your own XML parsing. My lazy chunks have type ByteString - Object. Only internally they use ByteString.unpack to get the list of Word8s to parse them. My parser is totally my own so I can do anything I wish. Except it is hard for me to image a parser working on something else than [Word8]. How do I do this? So how do I get rid of those (:) and W8# that are allocated everywhere on my heap? Thanks for the suggestion for -hd, really useful option! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Over-allocation
Don Stewart dons at galois.com writes: ByteStrings have all the same operations as lists though, so you can index, compare and take substrings, with the benefit that he underlying string will be shared, not copied. And only use 1 byte per element. Is there any parser built directly over ByteString that I could look at? Or maybe somebody implemented something like Text.ParserCombinators.ReadP for ByteString? From the first sight it seems doable, so there is light at the end of the tunnel :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Over-allocation
Gracjan Polak gracjanpolak at gmail.com writes: Don Stewart dons at galois.com writes: ByteStrings have all the same operations as lists though, so you can index, compare and take substrings, with the benefit that he underlying string will be shared, not copied. And only use 1 byte per element. Is there any parser built directly over ByteString that I could look at? Or maybe somebody implemented something like Text.ParserCombinators.ReadP for ByteString? From the first sight it seems doable, so there is light at the end of the tunnel :) Just a success report, after 58 min of coding I got kind of ReadP parser over ByteString working and my memory usage went down from 1500MB to... 1.2MB! Over 1000 times better! Incredible! Thanks for the suggestion to do it with ByteStrings! I hope to publish it when I clean it up enough! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: A ReadP style parser for ByteStrings
I'm happy to announce a ReadP style parser for ByteStrings, Text.ParserCombinators.ReadP.ByteString. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bytestringreadp Text.ParserCombinators.ReadP.ByteString is an adaptation of Text.ParserCombinators.ReadP to work over Data.ByteString as input stream representation. This gives enormous improvements in terms of parsing speed but most significantly in memory usage. Features: * ReadP style parser over ByteString input * Drop-in replacement for Text.ParserCombinators.ReadP * Fast * Good memory usage The algorithm is slightly modified to exploit ByteString as random access data input structure. Unlike original ReadP, that stressed garbage collection very much by creating a lot of conses (:), this parser has very good memory allocation behaviour. Package works out of the box with GHC 6.8.1, with slight (cabal) modifications also with GHC 6.6.1. Thanks to everyone for their support! Happy hacking! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Happstack basic question
I'd like to add a warning to this discussion. You might be affected by this issue: http://trac.haskell.org/network/ticket/11 TL;DR: It is kind of random if you bind to IPv4 or IPv6 or both. For example Windows Vista likes to bind to IPv6 only. Watch your ports and protocols! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to set a breakpoint in GHCi
Hi all, Tried to use :break today, without success: guestbook-session-bugghci -DMIN_VERSION_template_haskell(a,b,c)=1 -isrc Main -i../happstack/happstack-ixset/src GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help ... ... [10 of 13] Compiling Happstack.Data.IxSet ( ..\happstack\happstack-ixset\src\Happstack\Data\IxSet.hs, interpreted ) ... ... *Main :m +Happstack.Data.IxSet *Main Happstack.Data.IxSet :bre getOrd No breakpoints found at that location. *Main Happstack.Data.IxSet What now? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Are there any web server framework ?
Recently I started to play with Happstack and I must say I'm amazed how good it works for me! It has server, string templating, type safe html templating, persistence (like a database, only more fun), email stuff. To get a grasp at what goes under Happstack name here is a tutorial: http://tutorial.happstack.com/ -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Are there any female Haskellers?
Alberto G. Corona agocorona at gmail.com writes: Hope that this cold answer don't end this funny thread ;( Those concerned with Haskellers to Haskellinas ration can always employ this technique: http://www.newton.dep.anl.gov/askasci/bio99/bio99128.htm Any volunteers? :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: src/Text/XML/HaXml/Lex.hs:(156, 0)-(160, 22): Non-exhaustive patterns in function white
Antoine Latter aslatter at gmail.com writes: Sending off to the maintainer of haxr, although it looks like it might be in HaXml (from an outside guess). Without some real example to look at it will be quite tough to proceed. Alexander, can you send that stream of packets to me? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: src/Text/XML/HaXml/Lex.hs:(156, 0)-(160, 22): Non-exhaustive patterns in function white
Alexander Kotelnikov sacha at myxomop.com writes: On Wed, 21 Jul 2010 06:46:26 + (UTC) GP == Gracjan Polak gracjanpolak at gmail.com wrote: GP GP Antoine Latter aslatter at gmail.com writes: Sending off to the maintainer of haxr, although it looks like it might be in HaXml (from an outside guess). GP GP Without some real example to look at it will be quite tough to proceed. GP GP Alexander, can you send that stream of packets to me? I attach a stream dump. Attachment (poster.dump): application/octet-stream, 2916 bytes My guess at this point: Your XML contains PNG as binary data. Since this part is interpreted as a string with UTF-8 encoding we have big trouble here. Some of byte combinations in PNG do not constitute correct coding points, are probably converted/normalized and are interpreted as invalid XML. Solution: use text-based encoding for binary data. Base64 seems to be obvius candidate here. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ReadP and MonadFix
Hi all, A question for hot summer day: Text.ParserCombinators.ReadP.ReadP is an instance of Monad. Could it be an instance of MonadFix too? I'm not that sharp in Haskell to write it myself, but it seems I could make use of such a beast. :) Anybody willing to share? This will also present the advantage of Lazy over Eager Parser Combinators, mentioned in some other thread. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ReadP and MonadFix
Thanks for your response! I searched for something more found: An Abstract Monadic Semantics for Value Recursion, Eugenio Moggi, Amr Sabry http://citeseer.ist.psu.edu/moggi03abstract.html Section 4 of this paper says something about References and Continuations. But it will be quite hard to translate this into actual code. Could you please point me to the running examples you were talking about? I'm going to create MonadFix instance for the P monad and then I'll see what can I achieve with that. 2006/6/23, Levent Erkok [EMAIL PROTECTED]: Gracjan: To declare ReadP an instance of MonadFix; you'll first have to make the P monad into a MonadFix instance. That can be done using existing techniques in the literature. ReadP is essentially the continuation monad transformer wrapped around P. It's well known in the value-recursion literature that continuation monad is too strong to have a value-recursion operator. I am not aware of any simple solutions in that space. Hence, ReadP is beyond the realm of current theories of value recursion. Having said that, I'd also like to point out that Amr Sabry and Eugenio Moggi, and independently Magnus Carlsson has done some interesting work to extend value recursion to the world of continuations; which might help with your particular problem. Essentially, you end up adding some extra infrastructure to your monad, and then forgo some of the basic axioms of value recursion. But you can get running examples! Maybe all you'll need is a MonadFix instance of P; which is definitely doable with the current techniques. Anything further would actually make a nice research paper... -Levent. (I could provide references to above work if needed; all is available on the net freely, anyhow.) On 6/23/06, Gracjan Polak [EMAIL PROTECTED] wrote: Hi all, A question for hot summer day: Text.ParserCombinators.ReadP.ReadP is an instance of Monad. Could it be an instance of MonadFix too? I'm not that sharp in Haskell to write it myself, but it seems I could make use of such a beast. :) Anybody willing to share? This will also present the advantage of Lazy over Eager Parser Combinators, mentioned in some other thread. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Network.CGI.Compat.pwrapper
Hi, I wanted to setup really simple http server, found Network.CGI.Compat.pwrapper and decided it suits my needs. Code: module Main where import Network.CGI import Text.XHtml import Network doit vars = do return (body (toHtml (show vars))) main = withSocketsDo (pwrapper (PortNumber ) doit) Pointng any browser to http://127.0.0.1: does not render the page. It seems the response headers are broken. How do I report this bug (trac? something else?). We might want to either fix it, or just get rid of it, as nobody seems to notice the problem :) $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.6 Tested under WinXP and MacOSX 10.4.9. Another question is: how do I do equivalent functionality without pwrapper? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Network.CGI.Compat.pwrapper
Bjorn Bringert bringert at cs.chalmers.se writes: Another question is: how do I do equivalent functionality without pwrapper? You can roll you own web server if you want something very simple. If you don't want to do that, there is a version of Simon Marlow's Haskell Web Server with CGI support [1]. You could also get the original HWS [2] and merge it with your program. You might also be interested In HAppS [3]. Haskell Web Server seems to be the closest match. I don't want fully functional web server. I need more low level thing, as I need to set this up as a testing environment for some other (browser like) application. So I need a way to trigger (atrificial) errors, like protocol errors, garbage and broken connections. Thanks for the response. Is there a description what is a *CGI* protocol? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Network.CGI.Compat.pwrapper
Bjorn Bringert bringert at cs.chalmers.se writes: Is there a description what is a *CGI* protocol? Here you go: http://hoohoo.ncsa.uiuc.edu/cgi/interface.html I should be more clear: what kind of data does pwrapper expect? Somewhere in the middle it needs two handles: one to write and one to read which seem to be equivalent to stdin/stdout. But what about environment? How is it transfered, as someone ale pointed out pwrapper runs on different machine? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Deleting list of elements from Data.Set
My strictness analyser in my brain hurts. Which one (foldl,foldl',foldr) is the best way? Prelude Data.Set Data.List let s = fromList [1,2,3,4,5] Loading package array-0.1.0.0 ... linking ... done. Loading package containers-0.1.0.0 ... linking ... done. Prelude Data.Set Data.List foldl (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Prelude Data.Set Data.List foldl' (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Prelude Data.Set Data.List foldr (.) id (Data.List.map Data.Set.delete [1,3,5]) s fromList [2,4] Which one is best? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Deleting list of elements from Data.Set
Duncan Coutts duncan.coutts at worc.ox.ac.uk writes: Data.List.foldr (Data.Set.delete) s [1,3,5] or Data.List.foldl' (flip Data.Set.delete) s [1,3,5] There will be a day when I finally grasp foldr/foldl :) which is O (n + m * log m) rather than O(m * log n) or if the elements you're deleting are already sorted you can shave off the log m using Data.Set.fromAscList to get just O (n + m). Thanks for advice. My data is sorted so the above applies really well. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: acme-dont
Hello fellow haskellers, While reading reddit in the morning today: http://www.reddit.com/r/programming/comments/a26fe/dont/ I was shocked and surprised to see that Haskell lacks a very important feature present in Perl. It appeared that Haskell cannot not do monadic actions! I decided to act as fast as possible. Luckily, monads enable us to create control flow constructs on enterprise level. I'm proud to present the Acme.Dont module, that implements the indispensable don't monadic action. http://hackage.haskell.org/package/acme-dont-1.0 With special apologies to Luke Palmer that it took the Haskell community 7.5 years to catch up with Perl. Thanks go to Damian Conway. Have fun! Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: acme-dont
Deniz Dogan deniz.a.m.dogan at gmail.com writes: Are you sure you want to license this as BSD? Yes, BSD3 to be more exact. Of course commercial options are available on case by case basis. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Happstack with XML-RPC
Michael Hartl mikehartl at web.de writes: BTW, what's the status of HaXR? Is it being actively developed? Developed not. Maintained yes, by me. And you can argue that 'actively' part. Please send patches against darcs get http://code.haskell.org/haxr -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] The errorCalls and ioErrors in extensible exceptions way
Hi all, I have base==3.* code that uses errorCalls and ioErrors to intercept either ErrorCall or IOError that may arise in deeper code. I'd like to convert this code to base==4.* new exceptions. -- | Evaluate the argument and catch error call exceptions errorToErr :: Monad m = a - Err m a errorToErr x = let e = unsafePerformIO (tryJust errorCalls (evaluate x)) in ErrorT (return e) -- | Catch IO errors in the error monad. ioErrorToErr :: IO a - Err IO a ioErrorToErr = ErrorT . liftM (either (Left . show) Right) . tryJust ioErrors Look here for more context: http://hackage.haskell.org/packages/archive/haxr/3000.5/doc/html/Network-XmlRpc-Internals.html#5 I know that just importing OldException will do the trick for now. But I'd like to know how to do such a trick in extensible exceptions way. Also that unsafePerformIO looks a bit scary. Isn't there a better way to achieve purpose? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List manipulation
Dmitri Pissarenko wrote: Hello! I have two lists of Double with equal length and want to create a third one, in which each element is the sum of the corresponding element of the first list and the second list. If list1 is [1, 2, 100] and list2 is [2, 3, 500], then the result of the operation I desire is [3, 5, 600]. zipWith (+) [1,2,100] [2,3,500] I wrote this function function add2Img :: [Double] - [Double] - [Double] add2Img summand1 summand2 = sum where sum = [ (x+y) | x - summand1, y - summand2 ] /function, This is intepreted as two nestes loops: foreach x in summand1 (foreach y in summand2: x + y). You need zipWith. There is GHC extension: parallel list composition to do what you want. Lookup GHC documentation for extensions. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hFileSize vs length
S. Alexander Jacobson wrote: I am using GHC 6.2 on windows and am finding that when I open a file and use hFileSize I get a different number than I get from reading in the file and calculating the length. I assume this is not a bug, but I don't know why its happening. Isn't that because of line end conversion? EOL on windows is \r\n (2 bytes), when read converted on the fly to \n (1 char). Try to open your file in binary mode. Also, why isn't there getFileSize function in System.Directory? System.Posix.Files has getFileStatus and fileSize. No idea if they work on windows. -Alex- __ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Map
Hi all, As I tried to convert some of my code to newer libraries comming with GHC 6.4, I would like to share two things with you: I noticed that there are two functions missing: deleteList and insertList. The first one is easy with foldl: deleteList list map = foldl (flip Data.Map.delete) map list Second one is even shorter: insertList asclist map = union map (Data.Map.fromList asclist) Still I find both of them useful also execution speed seems to be of some concern here. Why generate temporary map just to join it with second in a moment? Isn't it slower? Also why Data.Map.lookup and Data.Map.findWithDefault? Why not lookupWithDefault? Besides, I really like new library :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Map
Sebastian Sylvan wrote: On Apr 3, 2005 9:38 AM, Gracjan Polak [EMAIL PROTECTED] wrote: insertList asclist map = union map (Data.Map.fromList asclist) How about: insertList :: (Ord a) = Map a b - [(a, b)] - Map a b insertList = foldr (uncurry insert) Is there any reason why foldr is better than foldl here? /S -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Speed comparison?
Daniel Carrera wrote: Hi all, Thank you for all the information on my previous question. I learned a lot, and good pointers to more info. My next question is about speed. How fast would you consider Haskell? (say, for computational work). How would you compare it to C, Python and Ruby? I started a small project in Ruby some time ago. It involved a bit of parsing and moving quite large binary data around. In Ruby speed was real problem so I looked for another language and ended up with... Haskell :) Speed of GHC compiled programs is ok for me, but if you need handling of binaries FFI is your very good friend! I cannot say anything about OCaml or Python, though. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Text search
Hi, Simple question: I need a function that matches string in another string. Something like: find (isSuffixOf needle) (inits haystack) This one is beautiful, but not very practical. Could anybody point me to some haskell library that does some searching, using KMP for example? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Text search
Ketil Malde wrote: Gracjan Polak [EMAIL PROTECTED] writes: find (isSuffixOf needle) (inits haystack) Hmm... While the result isn't exactly the same, I suspect using isPrefixOf and tails would be more efficient. I need the data before and including my needle. Like this: ( ... needle ) ignored Or at least count of the first part. Or, best, pair of: (beforeandincluding,after). String is rather long (potentially infinite), so using reverse and tail could be a problem :) This one is beautiful, but not very practical. Unless you have very repetitive data and/or tiny alphabet, it is actually quite efficient, as the expected length of prefixes that need to be checked before a mismatch can be determined is small. At least, I was unable to beat it with my (feeble attempts at) BM or KMP implementations. -kzm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space questions about intern and sets
Marcin 'Qrczak' Kowalczyk wrote: Gracjan Polak [EMAIL PROTECTED] writes: intern :: Ord a = a - a intern x = unsafePerformIO $ internIO x iorefset :: Ord a = IORef(Map.Map a a) iorefset = unsafePerformIO $ do newIORef $ Map.empty It will not work because you can't put values of different types as keys of the same dictionary, as you can't compare them. I could have as many dictionaries as there are types. The problem is I get one dictionary for each object which defeats the idea. Is there any other way to safe some memory when having many same objects? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space questions about intern and sets
Scott Turner wrote: On 2005 June 02 Thursday 04:38, Gracjan Polak wrote: iorefset :: Ord a = IORef(Map.Map a a) iorefset = unsafePerformIO $ do newIORef $ Map.empty I could have as many dictionaries as there are types. The problem is I get one dictionary for each object which defeats the idea. To avoid unsafe operations and get control over the dictionaries that are created, I would put the desired dictionaries into a state monad. The type of 'intern' becomes Ord a = a - DictionaryState a All the code that uses 'intern' would need some modification to deal more directly with the dictionary state. It may be more complex, but it's also more solid. As intern behaves like id and does not have any side effects, I thought its interface should be purely functional. But I do not see any way to do it :( I'll end up with a monad, probably. In related question: does anybody here have experience/benchmarks/tests how/if is PackedString better (uses less memory) than String in parsing tasks? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space questions about intern and sets
Duncan Coutts wrote: On Fri, 2005-06-03 at 10:53 +0200, Gracjan Polak wrote: As intern behaves like id and does not have any side effects, I thought its interface should be purely functional. But I do not see any way to do it :( I'll end up with a monad, probably. In related question: does anybody here have experience/benchmarks/tests how/if is PackedString better (uses less memory) than String in parsing tasks? GHC itself uses a rather low level thing it calls FastString which is basically a pointer into a character array with a length and a unique id. The unique ids are allocated by entering each FastString into a global hash table which also provides sharing if the same string is seen more than once (like your itern feature). I thought FastString was first incarnation of PackedString, thanks for the hint it could be something more. Does HaXml use any such optimization for XML element name handling? It is all very low level and ghc-specific however and probably only makes sence in a compiler-like application. Exactly my setting. Duncan -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Quest for inheritance
Cédric Paternotte wrote:
Hi. This is my first message here so Hello to everyone.
I'm just starting to learn Haskell and I really think it's a cool
language.
Me too :)
I know OO and inheritance is not really the point of Haskell and that
other mechanisms are provided to somewhat achieve reuse. But it's a
way of programming I've been so used to that I feel lost without it.
You might think I'm heading in the wrong direction. My mistake I have
to agree. Let's take it as a learning exercise then.
Me too :)
5. With this :
http://www.cs.utexas.edu/ftp/pub/techreports/tr01-60/tr01-60.pdf
I've been thinking about slight generalization of this lately. Here are
my semi-backed thoughts as of now.
First of all, in Haskell there will be strict separation between
interfaces and data, so almost every method will be declared twice. This
is not so strange to anybody programing in Java, but for C++ programmers
can be. Inheritance relation is specified after data. There is also
separation between two concepts: what interfaces each piece of data
implements and which intefaces given interface inherits. So:
{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
module Main where
-- general inheritance relation
class Inherits b x where
get_super :: x - b
-- declare interface with one method
class IA a where
get_a :: a - Int
-- define data with one field
data DA = DA { da_field :: Int }
-- say how data DA conforms to interface IA
instance IA DA where
get_a x = da_field x
-- declare some other interface IB
-- note: IB is unrelated to IA
class IB a where
get_b :: a - String
-- data that inherits fields of DA and adds one another field
data DB = DB { db_super :: DA, db_field :: String }
-- DB inherits fields and methods of DA
instance Inherits DA DB where
get_super x = db_super x
-- data DB implements interface IB
instance IB DB where
get_b x = db_field x
-- some other random data
data DC = DC { dc_super :: DA }
-- DC implements interface IB
instance IB DC where
get_b x = show (get_a x)
-- and inherits DA
instance Inherits DA DC where
get_super x = dc_super x
-- now the tricky part: state that every data x inheriting DA
-- implements all interfaces of DA (repeat for each interface)
instance (Inherits DA x) = IA x where
get_a w = da_field (get_super w)
main = do
let db = DB (DA 123) zzz
let dc = DC (DA 123)
putStrLn $ show (get_a db)
putStrLn $ show (get_a dc)
putStrLn $ show (get_b db)
putStrLn $ show (get_b dc)
As you see there is much more writting as in Java. But this gives better
control over inheritance and subsumption because everything must be
stated explicitly. Multiple inheritance is allowed :) Also it is
private inheritance (as in C++) by default.
There are some problems left: how to update a field? or how to make
inheritance transitive. I don't know it yet :)
I guess my question now is this : Are there other ways to achieve
inheritance in Haskell ?
Me too:)
My proposal (above) is about the level of 'OO' things done in procedural
languages (example: C with GTK+ library). There must be a better way.
Any comments?
--
Gracjan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Looking for lost library
Hi, Sorry for stupid question, but... Some time ago I read a beautiful paper about variables that had their dependencies automatically tracked and could trigger recalculation when changed. Prototype was implemented in OCaml, then reimplemented in Haskell (using monads). I would like to read that paper once again, but... I lost it :( I do not remember neither title, nor authors. Google asked about any keywords that come to my mind do not show any interesting results. So I ask here :) Can anybody help me, please? Thanks for any pointers... -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] foldl and space problems
Hello, My space problems continued... I have foldl that produces list, some combining function and quite large source list: let xyz = foldl f state myBigList This setting should lazyli consume myBigList when next elements of xyz are demanded. Except that it seems that myBigList is held by state to the end of computation :( Question: is there any way to see what is holding my source list? I did try to guess, but without results as of now:( How do I debug and/or reason about such situation? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Quest for inheritance
Cédric Paternotte wrote: Hi Gracjan, This is smart. So I understand the point of this part is to forward the function call to the parent (through get_super). All you have to do is to define these forwards in each inheriting data. Yes. I think this is the whole point of inheritance :) Does it also mean that, in each inheriting data, you have to define these forwards to all your parents (meaning not only to the one just above, but all of them) ? In other words if I was to define a data DD which inherits from DB (and thus also from DA), will I have to define forwards for both get_a and get_b ? If not, how would you declare it ? This is exactly what I described as private inheritance. If you have (Inherits DA DB) and (Inherits DB DC) this does not mean that you have automatically (Inherits DA DC). Why? This would require instance: instance (Inherits a b,Inherits b c) = (Inherits a c) where ... but this summons known problem: multiple inheritance. How to chose b? Imagine such situation: data DA; data DB; data DC; data DD instance Inherits DA DB where ... instance Inherits DA DC where ... instance Inherits DB DD where ... instance Inherits DC DD where ... DD inherits DA *twice*. So b in above instance declaration would not be determined uniquely. As you see there is much more writting as in Java. But this gives better control over inheritance and subsumption because everything must be stated explicitly. Multiple inheritance is allowed :) Also it is private inheritance (as in C++) by default. I think I like this way of dealing with inheritance. There's a bit more typing indeed and it's kind of limited but it has the advantage of being relativily simple to put in action. I agree with typing, but compared to Java this is actually not limited but more powerful, because it gives greater control over inheritance. Most important aspect to me is that inheritance can be specified *after* data declaration. Imagine you have some strange library that has DA and DB, that are obviosly in generalization-specialization hierarchy, but some jerk forgot to inherit one from another. In Java you are toast, in Haskell you can specify inheritance relation in your code :) What I really like with this is that you can come up with new data types inheriting DA without having to change anything in the declaration of DA. I guess you'd just better avoid having too many levels of hierarchy as it tends to get more and more verbose ;) If you stick to single inheritance there is other way to simulate OO in Haskell. Look for phantom types. Whole wxHaskell (for example) is based on this concept. Cédric -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Newbie] Quest for inheritance
Ralf Lammel wrote: Cédric Paternotte wrote: ... 5. With this : http://www.cs.utexas.edu/ftp/pub/techreports/tr01-60/tr01-60.pdf Gracjan Polak wrote: I've been thinking about slight generalization of this lately. Here are my semi-backed thoughts as of now. I should have mentioned http://homepages.cwi.nl/~ralf/OOHaskell/src/PoorMens2/ (again *not* using OOHaskell) From the quick skim of code: .?. -- apply function to upcast object .!. -- apply modification function to upcast object and substitute returned value (new object), basically update Is there any description avaliable what is PoorMens2 all about? A more general and preliminary observation: the entire approach is potentially more about object *composition* (and perhaps delegation) rather than inheritance. Many OO evangelists consider inheritance as a concept that was used too much in early OO times, while object composition is often more appropriate and flexible. So one *might* say that this approach does not encode a Java-inheritance solution but it does an inheritance-to-object-composition migration on the fly. So what Gracjan calls Inherits (and I call subtyping or substitution) is perhaps more a delegates. Yes, I agree with this statement. The OP question was: how to simulate inheritance in Haskell? One of the answers: using delegation :) Ralf -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] class Ref...
Hi, I the paper of Magnu Carlsson I noticed small, interesting class: class Monad m = Ref m r | m - r where newRef :: a - m (r a) readRef :: r a - m a writeRef :: r a - a - m () He defined it locally, but it seems to be very useful generalization of IORef and STRef. Is there something like this in standard libraries? I couldn't find it... :( Is there any reason why isn't it included? Another question: priority queue. In libraries bundled with ghc we have Data.Queue, but I couldn't find PriorityQueue. Is there somewhere an implementation that everybody uses, but is not in the library? Thanks! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldl and space problems
Bernard Pope wrote: A more practical solution is to force the compiler to generate more strict code. I tried to put strictness annotation in every place I could think of. Without result :( You might also find GHood useful: http://www.cs.kent.ac.uk/people/staff/cr3/toolbox/haskell/GHood/ Thanks for the pointer. Cheers, Bernie. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] class Ref...
Bulat Ziganshin wrote: Hello Gracjan, Tuesday, June 07, 2005, 2:25:50 PM, you wrote: class Monad m = Ref m r | m - r where GP newRef :: a - m (r a) GP readRef :: r a - m a GP writeRef :: r a - a - m () may be the following will be even more interesting: I like it very much! import Control.Monad import Data.IORef infixl 0 =:, +=, -=, =::, = ref = newIORef val = readIORef a=:b = writeIORef a b Pretty shame := is already reserver :(. There is something alike Graphics.Rendering.OpenGL.GL.StateVar. The use $= for assignment. Generalizing variables (in respect to some monad) seems to be often reinvented idea :) As I see this could be generalized to all Ref-like constructs (IO,ST,others?) a+=b = modifyIORef a (\a- a+b) a-=b = modifyIORef a (\a- a-b) a=::b = ((a=:).b) = val a Is this convoluted modify? Why doesn't it use modifyIORef? Or am I wrong? for :: [a] - (a - IO b) - IO () for = flip mapM_ I like: foreach = flip mapM foreach_ = flip mapM_ newList = ref [] list = x = list =:: (++[x]) Is this append? push list x = list =:: (x:) pop list = do x:xs-val list; list=:xs; return x main = do sum - ref 0 lasti - ref undefined for [1..5] $ \i - do sum += i lasti =: i sum =:: (\sum- 2*sum+1) print = val sum print = val lasti xs - newList for [1..3] (push xs) xs = 10 xs = 20 print = val xs Haskell as ultimate imperative language :) I use this module to simplify working with references in my program. The first inteface can be used for IORef/STRef/MVar/TVar and second for lists and Chan Then we should create classes for those interfaces. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] class Ref...
Tomasz Zielonka wrote: On Tue, Jun 07, 2005 at 12:25:50PM +0200, Gracjan Polak wrote: Another question: priority queue. In libraries bundled with ghc we have Data.Queue, but I couldn't find PriorityQueue. Is there somewhere an implementation that everybody uses, but is not in the library? You can use the new Data.Map module for this (old Data.FiniteMap too, but a bit more clumsily), it has findMin, findMax, deleteFindMin, deleteFindMax, deleteMin, deleteMax. All these operations should have O(log N) cost. Wow, I did not think about this. As far as I remember in imperative world priority queues had special implementation, with very good O() characteristics. Is O(log N) the best thing that can bo done in pure functional setting? To put it another way: is Data.Map only workaround to get something done, or is it The Right Way of doing PQs in Haskell? Best regards Tomasz -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space questions about intern and sets
Bjorn Bringert wrote:
memory. Here is something I wrote, but it doesn't work :(
I must have been doing something really wrong that day, because today it
works smoothly... :)
The code below seems to work for strings, and should be generalizable to
any type for which you have a hash function:
import Data.HashTable as H
import System.IO.Unsafe (unsafePerformIO)
{-# NOINLINE stringPool #-}
stringPool :: HashTable String String
stringPool = unsafePerformIO $ new (==) hashString
{-# NOINLINE shareString #-}
shareString :: String - String
shareString s = unsafePerformIO $ do
mv - H.lookup stringPool s
case mv of
Just s' - return s'
Nothing - do
H.insert stringPool s s
return s
Very interesting, thanks!
It seems very similiar to your code, except that it uses HashTable
instead of Map.
Question is: which one is better? My tupicall file contains 16
tokens, where 95% is taken by about 20 tokens that are used very frequently.
/Björn
--
Gracjan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Space questions about intern and sets
Udo Stenzel wrote: Gracjan Polak wrote: iorefset :: Ord a = IORef(Map.Map a a) iorefset = unsafePerformIO $ do newIORef $ Map.empty I could have as many dictionaries as there are types. The problem is I get one dictionary for each object which defeats the idea. I believe the (Ord a) constraint acts like a function argument. Therefore iorefset is no CAF, cannot be memoized itself and you get one dictionary per invocation. On the other hand, that is what is to be expected when playing games with unsafePerformIO. Seems you are right. Monomorphic type works, polymorphic doesn't. But it probably is not in any way guaranteed to stay like this in future. You might get it working by giving iorefset a monomorphic type or by specializing it for the type(s) you are using it at. Don't forget the NOINLINE pragma. I wouldn't do it this way, though. If you're parsing, chances are that your code is monadic anyway. Put a StateT over the parser monad and everything works without black magic. Even better, if you're using parsec you can just put the Map in the user state. This will create intern-per-parse, which isn't bad and has it's advantages, but I wanted to do something global. Anyway it was interesting experiment :) Udo. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] class Ref...
David Menendez wrote: [many things deleted]... I think the best way to look at MonadRef is as a generalization of MonadState. This could be a way to transliterate (not translate, transliterate) many imperative programs to Haskell. And as such this could be a starting point for many imperative souls into functional liberation :) I do not think that, for beginners, limitation to Hugs or GHC is serious problem. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Garbage collection and finalizer thread priority
Hi, My space problems continued... :) I have some ForeignPtr's, with finalizers (finalizerFree only). And I have lazyly produced list of those (yes, there is some unsafePerformIO magic behind, but I think I got this right). The problem is I get out-of-memory condition because elements get produced faster than those consumed are garbage collected. Example: list = ... mapM_ writeOut list writeOut :: Ptr Word8 writeOut dat = do hPutBuh handle dat 1024 -- Control.Concurrent.threadDelay 1000 Uncommenting this line allows gc thread to run finalizers, memory gets freed, everything runs smoothly... As far as I know finalizers are run in separate thread. How do I increase priority of this thread so it runs faster? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] foldl and space problems
Bernard Pope wrote:
Perhaps you could post the definition of the state type? Or even better,
a small example of code that runs badly.
I still don't know where old code had problems, but after rewriting
everything it seems to run smoothly now :) Thanks for all ideas, btw.
I invented something like this:
type RestAndState = (MyState - [MyData]) - MyState - [MyData]
this is the type of funtions that take current state and continuation as
parameters. Example:
putValues v1 v2 v3 rest state =
[v1,v2,v3] ++ rest state
there is a bit of syntactic ugliness when state chages:
putValueEx v1 rest state =
let newstate = state { ... } in
[v1] ++ rest nstate
good thing is that function can be composed quite easily with ($):
putV v1 v2 v3 v4 rest = -- state skipped here :)
putValue v1 v2 v3 $
putValueEx v4 rest
It works as I want it to. But I have strange feeling that there must be
a better way to compose foldr and state... Does anybody have any idea
how to put monad into this?
--
Gracjan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Garbage collection and finalizer thread priority
Simon Marlow wrote: I presume you're running GHC. There's no way to increase the priority of a thread - GHC's scheduler doesn't have a concept of priorities. Yes, I forgot to state it explicitly. I would look into whether you can use mallocForeignPtr: this is much faster than using newForeignPtr with finalizerFree, because the memory is garbage collected directly and there's no need for a finalizer. I use mallocBytes + reallocBytes + addForeignPtrFinalizer finalizerFree. I wouldn't think this is any different, thanks for your suggestion. May I ask where that difference comes from? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Garbage collection and finalizer thread priority
Sebastian Sylvan wrote: On 6/13/05, Simon Marlow [EMAIL PROTECTED] wrote: I presume you're running GHC. There's no way to increase the priority of a thread - GHC's scheduler doesn't have a concept of priorities. Just out of curiousity, what scheme does GHC use for scheduling threads? As I read somewhere, round robin... -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Garbage collection and finalizer thread priority
Simon Marlow wrote: On 13 June 2005 11:30, Gracjan Polak wrote: My space problems continued... :) Follow up :) I have some ForeignPtr's, with finalizers (finalizerFree only). And I have lazyly produced list of those (yes, there is some unsafePerformIO magic behind, but I think I got this right). The problem is I get out-of-memory condition because elements get produced faster than those consumed are garbage collected. Example: list = ... mapM_ writeOut list writeOut :: Ptr Word8 writeOut dat = do hPutBuh handle dat 1024 -- Control.Concurrent.threadDelay 1000 This sould be: writeOut :: Ptr Word8 writeOut dat = do hPutBuh handle dat 1024 System.Mem.performGC Control.Concurrent.threadDelay 1000 My small experimets show, that gc is not triggered?!?! What are the conditions to trigger gc? As I read the docs, is some % of heap. Is mallocForeinPtrBytes counted into that %? Anyway I ended up triggering GC by hand and giving it time to run finalizers. Frankly speaking this is nonsolution:( Related question: Documentation says: -Msize [Default: unlimited] Set the maximum heap size to size bytes. The heap normally grows and shrinks according to the memory requirements of the program... GHC 6.4 says: Heap exhausted; Current maximum heap size is 268435456 bytes (256 Mb); use `+RTS -Msize' to increase it. What am I missing? PS: I might be mistaken in any of above statements. I'll be thankful for any light... :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Garbage collection and finalizer thread priority
Bulat Ziganshin wrote: Hello Gracjan, Tuesday, June 14, 2005, 1:29:09 PM, you wrote: GP Documentation says: GP -Msize GP [Default: unlimited] Set the maximum heap size to size bytes. The GP heap normally grows and shrinks according to the memory requirements of GP the program... GP GHC 6.4 says: GP Heap exhausted; GP Current maximum heap size is 268435456 bytes (256 Mb); GP use `+RTS -Msize' to increase it. it's an error in GHC 6.4/win32 :) How do I take care of that? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Conversion between MonadPlus instances
Hi all, A simple question for advanced Haskellers, but I still have some problems bending my mind over it. Example: I have some function, that can return multiple results. Currently I need only the first one, but in the spirit of NotJustMaybe, I try to be as general as possible. If I code it like this: reduction :: (MonadPlus m) = [Rule] - Expr - m Expr reduction expr = do rule - rules reduction rule expr Variable m gets unified with []. But I want m to stay as general as possible here. This version works, but I somehow do not like the smell of it reduction expr = do let listmonad = do rule - rules reduction rule expr msum (map return listmonad) Is there a better way how to embed MonadPlus in other MonadPlus? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FFI and callbacks
Duncan Coutts wrote: Most toolkits with a main loop system allow you to setup timers. In the Gtk2Hs bindings we can use this trick: -- 50ms timeout, so GHC will get a chance to scheule about 20 times a second -- which gives reasonable latency without the polling generating too much -- cpu load. timeoutAddFull (yield return True) priorityDefaultIdle 50 Just for the record, above line in wxHaskell is spelled as: timer mainWindow [ interval := 50, on command := return () ] By the way, thanks for this tip! This helped me to work around showstopper bug in my program :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Template Haskell and Types
Hi, Probably very simple question about template haskell: How do I make a type for an argument to splice? Example: data MyData = MyData1 | MyData2 mysplice mytype = [| litE $ stringL $ show mytype |] main = do putStrLn $(mysplice MyData) The above is not accepted, error: Compiling Main ( thtest.hs, thtest.o ) thtest.hs:51:34: Not in scope: data constructor `MyData' So how do I provide type as an argument? Besides: documentation that I found for th is very dated. Could somebody point me to something more up to date about th? Thanks! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell and Types
Tomasz Zielonka wrote: On Mon, Sep 12, 2005 at 12:08:14PM +0200, Gracjan Polak wrote: Probably very simple question about template haskell: How do I make a type for an argument to splice? Example: data MyData = MyData1 | MyData2 mysplice mytype = [| litE $ stringL $ show mytype |] main = do putStrLn $(mysplice MyData) Cale explained how you can quote types in general. In the special case when you simply want the Name of a type-constructor, you can use the '' quoting syntax: putStrLn $(mysplice ''MyData) Thanks for responses. Is there any up-to-date documentation avaliable? Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell and Types
Simon Peyton-Jones wrote: | putStrLn $(mysplice ''MyData) | | | Thanks for responses. Is there any up-to-date documentation avaliable? Template Haskell is, alas, poorly documented. I would really welcome someone to volunteer to help write better documentation. Meanwhile, as the user manual says, the stuff about quoting names is described in a design note http://research.microsoft.com/~simonpj/tmp/notes2.ps Thanks. With haddoc documentation it is quite easy to translate old names to new names and guess the meanning of others. Next quiestion is: how do I debug my macros? When I make some error in my program, I get coredump (or the windows equivalent)? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] TH Q Monad and fail
Hi all, The Q Monad in template haskell has fail method. As I understand it, it throws some kind of exception. How do I catch this exception? Some code I'm trying to create: infoToCode :: Info - Q Exp infoToCode (ClassI dec) = -- ClassI Dec fail ClassI not supported -- this will be implemented infoToCode (ClassOpI name xtype name2 fixity) = -- ClassOpI Name Type Name Fixity fail ClassOpI not supported infoToCode (TyConI dec) = -- TyConI Dec fail TyConI not supported infoToCode (PrimTyConI name int bool) = -- PrimTyConI Name Int Bool fail PrimTyConI not supported infoToCode (DataConI name xtype name2 fixity) = -- DataConI Name Type Name Fixity fail DataConI not supported infoToCode (VarI name xtype maybedec fixity) = -- VarI Name Type (Maybe Dec) Fixity fail TVarI not supported infoToCode (TyVarI name xtype) = -- TyVarI Name Type fail TyVarI not supported nameToCode1 :: Name - Q Exp nameToCode1 name = do info - reify name Code - infoToCode info runIO $ putStrLn $ pprint Code return Code -- Here be dragons... nameToCode name = nameToCode1 name `catch` c where c e = do runIO $ putStrLn $ show e fail refailed -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell and Types
Simon Peyton-Jones wrote: design note http://research.microsoft.com/~simonpj/tmp/notes2.ps In the above paper there is something about 'giveUp'. Seems to quite useful, but there is no such thing in ghc 6.4. Where did my giveUp go? And why? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Template Haskell and Types
Simon Peyton-Jones wrote: Hmm. Q is a monad, so I think fail :: Monad m = String - m a will do the job. 'recover' should catch the exception, and let you try something else. So I think I have bug report :) Haskell-cafe is probably wrong place for this, where do I go now with my failing test cases? -- Gracjan Simon | -Original Message- | From: Gracjan Polak [mailto:[EMAIL PROTECTED] | Sent: 20 September 2005 10:43 | To: Simon Peyton-Jones | Cc: haskell-cafe@haskell.org | Subject: Re: [Haskell-cafe] Template Haskell and Types | | Simon Peyton-Jones wrote: | design note http://research.microsoft.com/~simonpj/tmp/notes2.ps | | | In the above paper there is something about 'giveUp'. Seems to quite | useful, but there is no such thing in ghc 6.4. | | Where did my giveUp go? And why? | | -- | Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Template Haskell -- Bug?
Hi,
Could somebody try to compile these two files *TWICE*? GHC dumps core at
me. I don't know if it is something about me, or something more general
:) I'd like to know a bit more, before I bother anybody from devel team.
Log:
$ ghc --make THTest1.hs
Chasing modules from: THTest1.hs
Compiling THTest1TH( ./THTest1TH.hs, ./THTest1TH.o )
Compiling THTest1 ( THTest1.hs, THTest1.o )
THTest1.hs:10:4: `incrSelf' is not a (visible) method of class `IncrSelf'
$ ghc --make THTest1.hs
Chasing modules from: THTest1.hs
Skipping THTest1TH( ./THTest1TH.hs, ./THTest1TH.o )
Compiling THTest1 ( THTest1.hs, THTest1.o )
Loading package base-1.0 ... linking ... done.
Loading package haskell98-1.0 ... linking ... done.
Loading package template-haskell-1.0 ... linking ... done.
(here core dump, aka 0xc0001)
First of all, I do not understand the error in first compilation.
Second, core dump is not nice :)
My config:
Windows XP Home,
$ ghc -v
Glasgow Haskell Compiler, Version 6.4, for Haskell 98, compiled by GHC
version 6.2.2
Using package config file: c:\ghc\ghc-6.4\package.conf
Using package config file: C:\Documents and Settings\gracjan\Application
Data\ghc/i386-mingw32-6.4/package.conf
Default windows package as taken from www.haskell.org.
--
Gracjan
{-# OPTIONS -fglasgow-exts -fth -fallow-undecidable-instances #-}
module THTest1TH
(
instanceIncrSelfTuple,
IncrSelf(..)
)
where
import Control.Monad
import Data.Maybe
import Language.Haskell.TH
class IncrSelf a where
incrSelf :: a - a
instance Num a = IncrSelf a where
incrSelf x = x + 1
sel' :: Int - Int - ExpQ
sel' i n = lamE [pat] rhs
where pat = tupP (map varP as)
rhs = varE (as !! (i - 1))
as = map mkName [ (a__ ++ show j) | j - [1..n] ]
instanceIncrSelfTuple :: Int - Q [Dec]
instanceIncrSelfTuple n = do
decs - qOfDecs
let listOfDecQ = map return decs
conIncrSelf = conT ''IncrSelf
name_a = mkName a
name_b = mkName b
name_c = mkName c
var_a = varT name_a
var_b = varT name_b
var_c = varT name_c
dec - instanceD (sequence [appT conIncrSelf var_a,appT conIncrSelf var_b])
(appT conIncrSelf
(appT
(appT (tupleT 2)
var_a
)
var_b
)
)
listOfDecQ
return [dec]
where qOfDecs = [d|
incrSelf value =
let
value1 = maybe Nothing (Just . fst) value
value2 = maybe Nothing (Just . snd) value
in error adfasf -- (incrSelf value1, incrSelf value2)
|]
{-# OPTIONS -fglasgow-exts -fth -fallow-undecidable-instances #-}
module THTest1
where
import THTest1TH
instance IncrSelf String where
incrSelf x = x ++ x
$(instanceIncrSelfTuple 2)
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Detecting Cycles in Datastructures
2005/11/19, Benjamin Franksen [You should read some of his papers, for instance the most unreliable techique in the world to compute pi. I was ROTFL when I saw the title and reading it was an eye-opener and fun too.] Care to post a link? Seems interesting, but unknown to google :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hPutStrLn and hFlush
Hi all,A bit strange behaviour with hPutStrLn. Consider following program:main = do handle - openFile output.txt WriteMode hPutStrLn handle (unlines contLines2) -- hFlush houtput where contLines2 = flip map [1..2000] $ \x - show x ++ been there done thatOutputs file which ends with following lines:1989 been there done that1990 been there done that 1991 been there done that1992 been there done that199(END)So the output is truncated. When I uncomment hFlush, file is fully written. Is this expected/documented behaviour?Platform: WinXP, GHC version 6.4.1-- Regards,Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hPutStrLn and hFlush
Thanks for the answers. I can go with hFlush or hClose, no problem here. Anyway this is a bit surprising that default stdout behaves different than file opened with default options. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell to call Microsoft COM (Dispatch)
Hi all,Is there any library to make Haskell call Microsoft COM functions using Dispatch? E.g I don't need the full COM binary functionality, scripting is enough. Google didn't seem to find anything interesting... beside rolling my own using FFI :) Thanks in advance!-- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell to call Microsoft COM (Dispatch)
2006/1/30, Paul Moore [EMAIL PROTECTED]: On 1/30/06, Gracjan Polak [EMAIL PROTECTED] wrote: Is there any library to make Haskell call Microsoft COM functions using Dispatch? E.g I don't need the full COM binary functionality, scripting is enough. Google didn't seem to find anything interesting... beside rolling my own using FFI :)I believe that HDirect allows you to do this. Unfortunately, I don'tknow of a binary build of a recent version, and I have yet to manage to build it myself :-(Latest version is from January 2004, hierarchical library layout has changed a bit since then :( It doesn't compile for me, either.Anyway it seems to be a bit of overkill for what I want to do. I'm not aware of any other libraries to do this.Thanks for the pointer! Paul.-- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Embedded scripting Language for haskell app
Bulat Ziganshin bulat.ziganshin at gmail.com writes: Hello Hemanth, Tuesday, August 17, 2010, 2:05:44 PM, you wrote: btw, i've written unfinished hslua tutorial: http://haskell.org/haskellwiki/HsLua And in related news embedded Lua interpreter recently got upgraded to version 5.1.4. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Error Calling Lua Function
Change this: succ - Lua.loadfile l /Haskell2Lua.lua into succ - Lua.loadfile l Haskell2Lua.lua Note that 0 at the beginning says there was an error loading a script. I should make it an exception I guess... -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Converting Values Between Lua And Haskell
aditya siram aditya.siram at gmail.com writes: I was fooled :). Some indication of that on the page would be very helpful.-deech Bulat was dreaming about better Lua support, but since the thing fulfilled my purpose, Bulat's dreams never got implemented. Aditya, I'm eager to accept patches, if you produce some :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: What's the problem with iota's type signature?
michael rice nowgate at yahoo.com writes: I've been digging into this stuff for months and it's still tripping me up. For exploration use GHCi. It can tell you the type of thing you have written. It has command to tell you type of thing, the :t. See here: Prelude let double x = Just (x + x) Prelude :t double double :: (Num a) = a - Maybe a Prelude let iota n = [1..n] Prelude :t iota iota :: (Num t, Enum t) = t - [t] Prelude [3,4,5] = iota [1,2,3,1,2,3,4,1,2,3,4,5] You don't have to guess then, Haskell compiler can do the guessing for you. It is called type inference. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Don't “accidentallyparallelize”
Hi all, In DEFUN 2009: Multicore Programming in Haskell Now! (http://donsbot.wordpress.com/2009/09/05/defun-2009-multicore-programming-in-haskell-now/), slide 30 I see: Don't “accidentally parallelize”: – f `par` f + e and that the correct way of achieving parallelism is: – f `par` e `pseq` f + e Actually I don't understand the difference between these two forms. Could any brave soul explain it to me, please? As a bonus question: what is the difference between `seq` and `pseq`? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Don't “accidentallyparallelize”
Thanks for great response! Brent Yorgey byorgey at seas.upenn.edu writes: x `pseq` y guarantees to evaluate x before y. There is no such guarantee with x `seq` y; the only guarantee with `seq` is that x `seq` y will be _|_ if x is. I found an old thread here http://www.mail-archive.com/glasgow-haskell-us...@haskell.org/msg11022.html where Simon states [quote] Indeed, if GHC was in the habit of causing the second argument of seq to be evaluated before the first, then a lot of people would probably be surprised. eg. imagine what happens to foldl': foldl' f a [] = a foldl' f a (x:xs) = let a' = f a x in a' `seq` foldl' f a' xs It wouldn't do what you want at all. [/quote] So... seems foldl' relies on `seq` having unstated evaluation order in GHC. So, what guarantees does foldl' have in turn? Semantics only or operational? Shouldn't it be written using `pseq`? Seems I have always used (this `seq` that) when I meant (this `before` that). Is it time to revisit my code and use `pseq` more? What does Haskell' say about this? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Don't “accidentallyparallelize”
Dan Doel dan.doel at gmail.com writes: On Sunday 06 September 2009 2:18:31 am David Menendez wrote: It turns out, pseq limits the effectiveness of strictness analysis, because it forces the order of evaluation. John Meacham described this pretty well last week in the Haskell' list http://www.haskell.org/pipermail/haskell-prime/2009-August/003006.html. Interesting. I hadn't thought of this before, but it certainly makes sense. Thank to all of you! This thread is fascinating! :) I used `seq` to duct tape my space leaks and stack overflow issues. Now looked for `pseq` for parallelism. And I think I understand enough to use both reasonably. Thanks! Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Optimizing 'sequence'
Hi all,
On the other day I noticed that we could optimize 'sequence' more.
I needed it for my monadic parser. Below is my small experiment.
Sequence from standard library needs 2.3s to finish (and additional
stack space), my version uses only 0.65s and default stack.
Is my version better or am I missing something obvious?
-- standard
sequence1 :: Monad m = [m a] - m [a]
sequence1 ms = foldr k (return []) ms
where
k m m' = do { x - m; xs - m'; return (x:xs) }
-- accumulator version
sequence2 :: Monad m = [m a] - m [a]
sequence2 ms = sequence' [] ms
where
sequence' vs [] = return (reverse vs)
sequence' vs (m:ms) = m = (\v - sequence' (v:vs) ms)
main = do
let l = map return [1..100]
w - sequence1 l
print (sum w)
return ()
[EMAIL PROTECTED]:~/some_faster time ./Some1 +RTS -K100M
5050
real0m2.318s
user0m2.284s
sys 0m0.032s
[EMAIL PROTECTED]:~/some_faster time ./Some2
5050
real0m0.652s
user0m0.592s
sys 0m0.052s
--
Gracjan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing 'sequence'
Antoine Latter aslatter at gmail.com writes: The function runIdentity is found in Control.Monad.Identity in the mtl package. Thanks, I see it now! Laziness is not there! But still... Identity is a bit special monad. What other monads need full laziness in sequence? As far as I know IO is strict. What about lazy/strict state monad? Initially I spotted this possible optimization in context of monadic parser. I am not really sure if I need this property there or not. How do I prove this to myself? Thanks to others who responded. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Optimizing 'sequence'
Chaddaï Fouché chaddai.fouche at gmail.com writes: 2008/7/22 Luke Palmer lrpalmer at gmail.com: A little formal reasoning reveals that sequence1 = sequence2 exactly when (=) is strict in its left argument. There are four common monads which are _not_: Identity, Reader, Writer, State (and RWS by extension). Still if that makes that much of a difference, maybe we could envision putting a sequence' in the library ? Yes, in my experiments this is to be or not to be. Stack space is limited. Also processing time goes down by 800%, so it is a big deal sometimes. Incomplete list of functions affected: sequence mapM foldM Text.ParserCombinators.Parsec.Combinator(many1,sepBy,endBy,manyTill) Text.ParserCombinators.ReadP(many,many1,count,sepBy,endBy,manyTill) ... As far as I know sequence could be specialized to IO monad and use my transformation. How do I reason if = for parsers is lazy in its first argument? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: language proposal: ad-hoc overloading
Philippa Cowderoy flippa at flippac.org writes: Haskell already has one method of overloading: type classes. What you propose is a seemingly innocent extension that I now doubt has extremely far-reaching consequences into the language. Such a feature should be properly researched before it is added to the language. http://homepages.dcc.ufmg.br/~camarao/CT/ -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Hugs vs GHC (again)
Marcin 'Qrczak' Kowalczyk wrote: fileRead :: File - FileOffset - Integer - Buffer - IO () This is unimplementable safely if the descriptor is read concurrently by different processes. The current position is shared. UNIX98 defines function: extern ssize_t pread (int __fd, void *__buf, size_t __nbytes, __off_t __offset); Windows has: BOOL ReadFile( HANDLE hFile, LPVOID lpBuffer, DWORD nNumberOfBytesToRead, LPDWORD lpNumberOfBytesRead, LPOVERLAPPED lpOverlapped ); Where that OVERLAPPED structure contains information where to start read. Seems implementable to me, or am I wrong? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Hugs vs GHC (again) was: Re: Somerandomnewbiequestions
Simon Marlow wrote: There's a big lock on File. If you want to do truly concurrent reading, you can make multiple FileInputStreams, each of which has its own file descriptor (the Unix implementation uses dup(2)). Original and descriptor returned by dup or dup2 share file pointer. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Linear shuffle
Hi, I want to implement linear list shuffle in Haskell (http://c2.com/cgi/wiki?LinearShuffle) and I invented code: shuffle :: [a] - IO [a] shuffle [] = return [] shuffle x = do r - randomRIO (0::Int,length x - 1) s - shuffle (take r x ++ drop (r+1) x) return ((x!!r) : s) This algorithm seems not effective, length, take, drop and (!!) are costly. Is there any better way to implement shuffle? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linear shuffle
Henning Thielemann wrote: Is it a good idea to use IO monad for this plain computation? It is needed as random number supply. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linear shuffle
John Meacham wrote: Oleg wrote a great article on implementing the perfect shuffle. with some sample code. http://okmij.org/ftp/Haskell/misc.html#perfect-shuffle Thats the kind of answer I was hoping to get :) Thanks. shuffle could be useful in standard library. At least Python has it. I was translating some small Python program, the hardest part was the missing shuffle function. What do you think? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Control.Monad.State.Strict, mdo and let
Hi,
I stumbled at some interaction of Control.Monad.State.Strict, mdo and let I do
not understand. The following program:
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main where
import Control.Monad.State.Strict
thenumber :: Float
thenumber = flip execState 1.3 $ mdo
c - donothing []
let donothing x = return x
return ()
main = print thenumber
Says (in GHC 6.6.1):
Stack space overflow: current size 8388608 bytes.
Use `+RTS -Ksize' to increase it.
Why is this so?
--
Gracjan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Scripting.Lua 0.1
Hi all, I'm pleased to announce the first public release of Scripting.Lua. The package hslua-0.1 contains Haskell FFI bindings for a Lua interpreter along with some Haskell utility functions simplifying Haskell to Lua and Lua to Haskell calls. Full Lua interpreter is included in the package. Example import qualified Scripting.Lua as Lua main = do l - Lua.newstate Lua.openlibs l Lua.callproc l print Hello from Lua Lua.close l More information http://home.agh.edu.pl/~gpolak/hslua The Lua language http://www.lua.org -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: Scripting.Lua 0.1
Donald Bruce Stewart dons at cse.unsw.edu.au writes: Great work! would you like to upload it to hackage.haskell.org too, so it will be archived for the ages? I surely will, but I'd like to wait a moment and first see what people say :) -- Gracjan\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: Scripting.Lua 0.1
Andrea Rossato mailing_list at istitutocolli.org writes: I quote: this is a really nice news. I'll be trying to use it in project of mine very soon (I'm developing a sort of Ion3 like status bar, which is scriptable through Lua). Exactly such a scenario I had in mind. Calling Lua from Haskell was easy, the hard part was to call Haskell from Lua. Give me a sign how it worked. Please follows Donald's suggestion and upload it on Hackage. Uploaded. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Comments from OCaml Hacker Brian Hurt
Ketil Malde ketil at malde.org writes: On Thu, Jan 15, 2009 at 07:46:02PM +, Andrew Coppin wrote: If we *must* insist on using the most obscure possible name for everything, I don't think anybody even suggests using obscure names. Some people insist on precise names. Ketil, to second your here: Appendable *is* an obscure name! Even more than Monoid. I remember my early CS algebra courses. I met cool animals there: Group, Ring, Vector Space. Those beasts were very strong, but also very calm at the same time. Although I was a bit shy at first, after some work we became friends. When I first saw Monad, Monoid, Functor and others, I wasn't scared. They must be from the same zoo as my old friends! Some work is needed to establish a connection, but it is doable. And it is very rewarding, because then you get very powerful, dependable friends that give you strong guaranties! Now compare ICollecion, IAppendable or the alike. These are warm, and fuzzy, and don't hurt me please, so the guaranties they give depend on mood or something as intuitive as phase of the moon. And don't feed corner cases to them, because they may scratch you! So: Warm, fuzzy: under defined, intuitive, sloppy... Cool, strong: well defined, dependable, concrete... There are plenty of warm, fuzzy languages out there, if you want Java, you know where to find it. And *real programmers* seem to look for something more these days. I need to sleep well knowing my programs work. I need powerful, strong abstraction. I use Haskell wherever possible because it is based on the strongest thing we have: MATHS! Keep it that way! Monads aren't warm, they are COOL! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: GHCi Memory Leak in Windows Vista
Same here: Vista, GHC 6.8.3 Tested a bit changed scenario: instead of 20 separate compilations it is worthwhile to run single, longer build, e.g. ghc --make of same package. Seems like GHCi does not run garbage collection when machine is busy. And then it accumulates memory. This renders Vista totally unresponsive and even can lead to automatic reboot (happened once to me). :) -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell IDE
Alexander Danilov alexander.a.danilov at gmail.com writes: 03.03.2011 16:05, Hauschild, Klaus (EXT) пишет: Hi Haskellers, whats your Haskell IDE of choise? Currently I use leksah. Is the EclipseFP Plugin for Eclipse a real alternative? Thanks Klaus Emacs, look at haskell wiki for details about haskell-mode. Emacs is good as an editor for Haskell. Indentation is problematic. I'd like to have a indent mode that has following bindings: - TAB indents 4 chars more - Shift-TAB indents 4 chars less - RET - indents a line same as previous line unless last line had a block opening keyword Indentation indents mostly too far right in current haskell-mode for my taste. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell IDE
Ivan Lazar Miljenovic ivan.miljenovic at gmail.com writes: Sounds similar to what haskell-indent does, except that it uses 2 spaces rather than 4, backspace does the chars less, and TAB also has a version (albeit not as nice as the one in haskell-indentation) of the tab-cycle. I rejected haskell-indent some time ago, do not remember the reason now. I think I'll give it a second chance. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to keep cabal and ghci package versions in sync?
Hi all, I have a project with a .cabal file listing package dependencies using the usual version constraints ==X.Y.* Z.W or =K.J syntax. Standard route cabal configure; cabal build works correctly as it is able to select working set of package versions. I have also a .ghci file. When I run GHCi it uses all latest installed packages in the system. This prevents the project from loading. I tried to use 'cabal-dev ghci', but this still selects latest global packages. So, how to I load up ghci with the same package versions as selected by cabal? Thanks! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to keep cabal and ghci package versions in sync?
Henning Thielemann schlepptop at henning-thielemann.de writes: You can manually select packages for GHCi with '-package' option. However I do not know a way to automatically syncronise this with the dependencies from the Cabal file. I kind of expected 'cabal-dev ghci' to do this for me. Thanks for help, I'm cleaning my packages for now. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Python is lazier than Haskell
Ketil Malde ketil at malde.org writes: In Haskell, I often need to add stubs of undefined in order to do this. I don't mind, since it is often very useful to say *something* about the particular piece - e.g. I add the type signature, establishing the shape of the missing piece without bothering with the actual implementation just yet. Seconded. Sometimes I wish for a -fphp flag that would turn some type errors into warnings. Example: v.hs:8:6: Couldn't match expected type `[a]' against inferred type `()' In the first argument of `a', namely `y' In the expression: a y In the definition of `c': c = a y GHC could substitute 'y = error Couldn't match expected type `[a]' against inferred type `()'' and compile anyway. Would that bring Haskell closer to Python? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ErrorT vs Either
Hi all, A why question: Why: Control.Monad.Error Prelude runErrorT (fail msg) :: IO (Either String Int) Left msg but Control.Monad.Error Prelude (fail msg) :: (Either String Int) *** Exception: msg ? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ErrorT vs Either
Thanks Daniel, Yves and Edward for explanation. Two things come to my mind now. 1. It should be unified. Why? Because conceptually: runIdentity (runErrorT (fail msg)) :: Either String Int Left msg and fail msg :: Either String Int *** Exception: msg Should be the same as Identity monad should not add structure. 2. I need a Failure monad that works well with pattern match failures (that call fail). I'd like to use it like this: runErrorT $ do Active - getStatus-- ensure proper status Just elm - lookup stuff there -- lookup element when (condition) $ fail wrong! -- check condition return 1234-- return useful value sort of... Any ideas what could be used in place of Either monad? Basically I need working pattern match failures (I guess that means I need working fail method that is not equal to error). -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ErrorT vs Either
Daniel Fischer daniel.is.fischer at googlemail.com writes: On Monday 16 May 2011 23:41:44, Gracjan Polak wrote: Thanks Daniel, Yves and Edward for explanation. Two things come to my mind now. 1. It should be unified. The (Either e) Monad instance was recently changed after people have long complained that there shouldn't be an (Error e) constraint. It's unlikely that that will be reverted soon. I did not request a revert, I asked about consistent behavior. It's the (Error e) Monad which adds the structure [nowadays, Error e = ErrorT e Identity]. I do not understand this part. Can you elaborate? 2. I need a Failure monad that works well with pattern match failures (that call fail). I'd like to use it like this: runErrorT $ do Active - getStatus-- ensure proper status Just elm - lookup stuff there -- lookup element when (condition) $ fail wrong! -- check condition return 1234-- return useful value sort of... That does work, doesn't it? Indeed this does work, but it is fragile wrt refactorings. Suppose we have the code: result - runErrorT $ do lift $ print was here fail msg (result = Left msg) after a while the print statement may be removed: result - runErrorT $ do fail msg (result = Left msg) and then somebody will see that inner 'do' does not depend on outer monad so next refactoring will be: let result = do fail msg (result = error msg) And here code breaks... Roll your own, That is a good idea. I looked also at Attempt. Thanks for responses. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Exclusive mode in openFile
Hi all, It seems I'm not allowed to open same file both for writing and for reading: Prelude System.IO f_out - openFile mylog.log AppendMode Prelude System.IO f_in - openFile mylog.log ReadMode *** Exception: mylog.log: openFile: resource busy (file is locked) Usage scenario: I use hslogger to write to logs, but I'd like to read parts of these logs *from inside same Haskell application*. How do I get around exclusive mode in openFile? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Exclusive mode in openFile
Max Bolingbroke batterseapower at hotmail.com writes: This behaviour is part of the Haskell 98 specification (section 21.2.3, http://www.haskell.org/onlinereport/io.html): Thanks for the explanation. Such sharing behavior should be mentioned in documentation: http://hackage.haskell.org/packages/archive/haskell98/latest/doc/html/IO.html#v:openFile What was the rationale behind such strict non-sharing policy? Anyway, where do I find an 'openFileShared' function? Packages unix/Win32 do not have obvious leads... Implementations should enforce as far as possible, at least locally to the Haskell process, multiple-reader single-writer locking on files. That is, there may either be many handles on the same file which manage input, or just one handle on the file which manages output. If any open or semi-closed handle is managing a file for output, no new handle can be allocated for that file. I've been bitten by this before and don't like it. It would be possible for GHC to enforce Unix semantics instead (there are appropriate flags to CreateFile that get those semantics on Windows), which would support more use cases. This change would have to be carefully thought through, and the report would have to be amended. Cheers, Max -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Exclusive mode in openFile
Max Bolingbroke batterseapower at hotmail.com writes: http://hackage.haskell.org/packages/archive/unix/2.4.2.0/doc/html/System-Posix-IO.html. Thanks for the link. I tried to use it: Prelude System.Posix.IO fd1 - openFd xxx.tmp WriteOnly (Just 0666) defaultFileFlags Loading package unix-2.4.0.2 ... linking ... done. Prelude System.Posix.IO fd2 - openFd xxx.tmp WriteOnly (Just 0666) defaultFileFlags Prelude System.Posix.IO print (fd1,fd2) (5,7) Prelude System.Posix.IO h1 - fdToHandle fd1 Prelude System.Posix.IO h2 - fdToHandle fd2 *** Exception: openFile: resource busy (file is locked) So I can open file twice. So far so good. Then I convert Fds to Handles and second conversion fails. I'm looking for file locking code in GHC.IO.* modules, but cannot find any. How do I convince fdToHandle to create an independent handle to non-locked file? -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
