- Haskell-Cafe - Haskell.org

Re: [web-devel] statically compiled css
by Tim Matthews 11 Aug '10

11 Aug '10

On Thu, Aug 5, 2010 at 11:33 PM, Mark Bradley <barkmadley(a)gmail.com> wrote: but CSS type checking might be possible within hamlet. > I have often wondered "OK haml implemented now what about sass". Michael Snoyman what is your opinions on sass? Would a sass inspired syntax like you did with the haml->hamlet fit in well and if so, as it often best to keep styles separate, could a quasi quoted language live in in a separate haskell module and then at run time it recreates the separate css files on first launch? Thanks Tim Matthews

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[ANNOUNCE] (and request for review): directory-tree v0.9.0
by Brandon Simmons 11 Aug '10

11 Aug '10

Greetings Haskellers! directory-tree is a module providing a directory-tree-like datatype along with Foldable and Traversable instances, along with a simple, high-level IO interface. You can see the package along with some examples here (apologies if the haddock docs haven't been generated yet) : http://hackage.haskell.org/package/directory-tree This primary change in this release is the addition of two experimental "lazy" functions: `readDirectoryWithL` and `buildL`. These functions use `unsafePerformIO` behind the scenes to traverse the filesystem as required by pure computations consuming the returned DirTree data structure. I believe I am doing this safely and sanely but would love if some more experienced folks could comment on the code. These changes (and this whole revamping of this originally very simple module) were inspired by the fact that a few people seemed to really like this API, and this recent reddit post lamenting the perceived difficulty of writing a `du`-like function in haskell. http://www.reddit.com/r/haskell/comments/cs54i/how_would_you_write_du_in_ha… One could write such a function using directory-tree as follows (sorry if the monadic compositional style is foreign): > import System.Directory.Tree > import qualified Data.Foldable as F > import System.IO > import Control.Monad > > du :: FileName -> IO () > du = print . F.sum . free <=< readDirectoryWithL (hFileSize <=< readHs) > where readHs = flip openFile ReadMode Thanks for reading and for any input, especially performance suggestions or opinions on my unsafe function usage. I hope this is useful to someone. SIncerely, Brandon Simmons http://coder.bsimmons.name/

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StablePtr overhead?
by Gregory Collins 11 Aug '10

11 Aug '10

Hi all, Can anyone explain what the overhead of using StablePtrs is? Specifically I am interested in knowing the time/space complexity of the various Foreign.StablePtr operations and how many memory indirections are involved when using deRefStablePtr. G -- Gregory Collins <greg(a)gregorycollins.net>

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Re: [Haskell-cafe] iPhone/Android and Haskell [Was: Embedded funcional programming?]
by Liam O'Connor 11 Aug '10

11 Aug '10

Our best bet is to compile to ARM native code and then use the NDK to talk to the Java APIs. Cheers. ~Liam

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Unused import warnings.
by Lyndon Maydwell 11 Aug '10

11 Aug '10

Hi Cafe. I have written some QuickCheck properties in my source and am using these for testing, however, when I compile my program I get warned about unused imports: > Warning: Module `Test.QuickCheck' is imported, but nothing from it is used Is there a way to suppress these warnings for a particular module by using a pragma directive or something similar? Thanks! - Lyndon

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zip-archive performance/memmory usage
by Pieter Laeremans 10 Aug '10

10 Aug '10

Hello, I'm trying some haskell scripting. I'm writing a script to print some information from a zip archive. The zip-archive library does look nice but the performance of zip-archive/lazy bytestring doesn't seem to scale. Executing : eRelativePath $ head $ zEntries archive on an archive of around 12 MB with around 20 files yields Stack space overflow: current size 8388608 bytes. The script in question can be found at : http://github.com/plaeremans/HaskellSnipplets/blob/master/ZipList.hs I'm using the latest version of haskell platform. Are these libaries not production ready, or am I doing something terribly wrong ? kind regards, Pieter -- Pieter Laeremans <pieter(a)laeremans.org> "The future is here. It's just not evenly distributed yet." W. Gibson

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Couple of questions about *let* within *do*
by michael rice 10 Aug '10

10 Aug '10

From: Learn You a Haskell =================== Remember let bindings? If you don't, refresh your memory on them by reading this section. They have to be in the form of let bindings in expression, where bindings are names to be given to expressions and expression is the expression that is to be evaluated that sees them. We also said that in list comprehensions, the in part isn't needed. Well, you can use them in do blocks pretty much like you use them in list comprehensions. Check this out: import Data.Char main = do putStrLn "What's your first name?" firstName <- getLine putStrLn "What's your last name?" lastName <- getLine let bigFirstName = map toUpper firstName bigLastName = map toUpper lastName putStrLn $ "hey " ++ bigFirstName ++ " " ++ bigLastName ++ ", how are you?" =================== Questions: 1) Is there an implicit *in* before the last line above? 2) Within a do "in" the IO monad (or any other monad), can a *let* do something like this? let x = do -- in a different monad Michael

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QuickCheck and Pairing Heaps
by Matias Eyzaguirre 10 Aug '10

10 Aug '10

Hi, I'm trying to figure out QuickCheck and how to generate arbitrary test data form complex data structures; I thought an interesting experiment would be Pairing Heaps. A pairing heap is essentially just a tree whose nodes obey the heap property (for all nodes A in a pairing whose nodes can be compared, the value of A is greater then the value of any descendants of A). I came with a definition that I think seems reasonable \begin{code} data (Ord a) => Heap a = Heap a [Heap a] \end{code} But I cannot think of a way to generate arbitrary heaps, I see three main issues: 1. Based on the examples I have seen, I understand how you could define arbitrary so that it uses frequency to choose either a leaf or a branch, but how would you generate a variable number of children? 2. That would hardcode the probably size of the heap, how would you define an arbitrary heap that was dependent on some sort of size parameter? 3. The way I see it, you could generate arbitrary heaps of type A (where A is an instance of Arbitrary and Ord), but how would you make sure that each node of the generated tree was heapy (the max of all its descendants)?

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Re: [Haskell-cafe] Couple of questions about *let* within *do*
by Felipe Lessa 10 Aug '10

10 Aug '10

On Tue, Aug 10, 2010 at 2:40 PM, Bill Atkins <batkins57(a)gmail.com> wrote: > They're not really statements, they're just named expressions and are still subject to lazy evaluation. > > In: > > let x = putStrLn "Name" >> getLine > putStrLn "Welcome" > x Yes, 'putStrLn "name" >> getLine' is an expression. However, the whole line 'let x = putStrLn "Name" >> getLine' inside the do-block is an statement. Althought the word 'let' is used in both cases, they are defined in different places of the grammar (see the links of my previous mail). So when you write do ... let ... -- stmt ... you are using a let statement. You can use a let expression in a do-block as well: do ... let ... in ... -- expr ... Note, however, that you must indent the 'in' part, as you would need to indent an if expression inside a do-block. do ... do {... let ... -- expr gets parsed as ;let ... -- stmt in ... -- ;in ... -- ??? ... ;...} Cheers, -- Felipe.

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More Flexible Monad Transformer OR Bad Coding Style
by aditya siram 10 Aug '10

10 Aug '10

Hi all, I was experimenting with monad transformers and realized that the stacking order of the monads can remain unknown until it is used. Take for example the following code: import "mtl" Control.Monad.State import "mtl" Control.Monad.Writer import "mtl" Control.Monad.Identity test :: (MonadWriter [Char] m, Num t, MonadState t m) => m () test = do put 1 tell "hello" main = do x <- return $ runIdentity $ runStateT (runWriterT test) 1 -- test :: WriterT String (StateT Int Identity) y <- return $ runIdentity $ runWriterT $ runStateT test 1 -- test :: StateT Int (WriterT String Identity) z <- runWriterT $ runStateT test 1 -- test :: StateT Int (WriterT String IO) (((), Int), String) print x print y print z *Main> main (((),"hello"),1) (((),1),"hello") (((),1),"hello") Until test is called in 'main' we don't know the order of monads. In fact even the base monad is not know. All we know is that it uses the State and Writer monad. In each call to 'test' in main we can determine the stacking order and the base monad yielding different results. This seems to be a more flexible way of using monad transformers but I haven't seen this in code before so is there anything wrong with this style? -deech

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Some Haskell mode extensions
by Christopher Done 09 Aug '10

09 Aug '10

Hi there, I've written some very simple Emacs modules for making using Haskell in Emacs a little bit nicer: http://github.com/chrisdone/haskell-mode-exts You can download the project with git, or pick and choose individual files: http://github.com/chrisdone/haskell-mode-exts/raw/master/haskell-navigate-m… http://github.com/chrisdone/haskell-mode-exts/raw/master/haskell-align-impo… http://github.com/chrisdone/haskell-mode-exts/raw/master/haskell-sort-impor… http://github.com/chrisdone/haskell-mode-exts/raw/master/haskell-installed-… More documentation about installed module completion here, I need to do another module for syntax-aware import editing, but this module is already quite usable: http://www.chrisdone.com/posts/2010-08-07-emacs-haskell-installed-packages.… I have a few more in the works and more planned, e.g. (some of which may already have been implemented somewhere, but): 1) syntax aware import line editing (think: tabbing between sections, toggling qualified on/off, etc.) 2) controlling cabal through inferior-haskell-mode (already done this, but I need to make it portable) 3) tidying up of inferior-haskell (it wastes a lot of space) 4) more interactiveness with inferior-haskell e.g. "you need -XExtension" should really just prompt me whether I want to add it to the file or enable it in ghci, and then do it. (When you're in the middle of working, adding extensions to the top of the file is laborious.) 5) automatic integration with etags and some improvement to its little issues 6) a high-level .cabal file editing mode 7) unit testing integration And so on. There's loads that can be done. I'm just implementing the stuff I want, and if some of it's useful in general, maybe it can be absorbed into the general haskell-mode distrib. The haskell-emacs mailing list is down at the moment, so I thought I'd post here. Cheers!

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Re: [Haskell] ANNOUNCE: jhc 0.7.4
by Antoine Latter 09 Aug '10

09 Aug '10

On Sat, Jul 10, 2010 at 1:47 AM, John Meacham <john(a)repetae.net> wrote: > Announcing jhc 0.7.4! There have been a few major changes, the main one being > that there is now support for a garbage collector. This drastically increases > the number of programs which are feasable to compile with jhc. > > http://repetae.net/computer/jhc/ > Hi John, This looks fantastic and fun to play with. A few issues: * running DrIFT on src/E/TypeCheck.hs fails with an illegal bytesequence in hGetContents. I'm guessing that this is only an issue when building DrIFT with GHC 6.12+, and that the file contains bytes illegal in UTF8. I deleted everything funny looking in the file and then it went smooth * The way you use sed doesn't work with the BSD sed that ships with my Mac Book. Installing GNU sed and using it works. Similarly, BSD find doesn't know about '-name', so make hl-clean results in sadness. * jhci works great, but jhc crashes when I try to compile something: >>>>> jhc test1.hs jhc 0.7.4 (tokfekyuvi-27) Finding Dependencies... Using Ho Cache: '/Users/alatter/.jhc/cache' Main [test1.hs] Typechecking... [1 of 1] Main (.............................................) test1.hs:9 - Warning: defaulting: t93 => Jhc.Basics.Integer Compiling... [1 of 1] Main <..................................................> Collected Compilation... -- typeAnalyzeMethods -- BoxifyProgram -- Boxy WorkWrap -- LambdaLift E jhc: <stdout>: hPutChar: invalid argument (Illegal byte sequence) <<<<< Again, this seems like the handle is in UTF8 mode and we're trying to output something non-UTF8. * cabal install has a --jhc flag, but it doesn't seem to work: >>>>> cabal install byteorder --jhc Resolving dependencies... cabal: internal error: impossible <<<<< I have jhc installed in a non-standard location (under ${HOME}/usr) so I may need to have some environment variables set up. This is wil Cabal 1.8.0.4 and cabal-install 0.8.2 Keep up the good work! I have an implementation for STRefs I threw together this afternoon for jhc if you're interested. I can't test it properly, though, with the compiler crash above. Antoine

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Odd parallel haskell observations
by Alexander Kotelnikov 09 Aug '10

09 Aug '10

Hello. I am exploring haskell features for parallel and cocurrent programming and see something difficult to explain. In brief - asking RTS to use more threads results in awfull drop of performance. And according to 'top' test programm consumes up to N CPUs power. Am I doing something wrong? I attached the code, but I am just issuing thousands of HTTP GET requests in 1-4 forkIO threads. And since it looks like local apache is faster than haskell program (which is a pity) I expected that using more OS threads should improve performance. Just in case: ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.1 import Data.List import System.IO import qualified System.IO.UTF8 import System.Environment (getArgs) import Network.HTTP import Network.URI import System.Time import System.IO.Unsafe import Control.Monad import Control.Exception import Control.Concurrent import Control.Concurrent.MVar secDiff :: ClockTime -> ClockTime -> Float secDiff (TOD secs1 psecs1) (TOD secs2 psecs2) = fromInteger (psecs2 - psecs1) / 1e12 + fromInteger (secs2 - secs1) -- single get get :: Int -> IO(String) get id = do res <- simpleHTTP $ getRequest "http://127.0.0.1" case res of Left err -> return(show err) Right rsp -> return(show $ rspCode rsp) -- perform GET per each list element using c threads doList :: [Int] -> Int -> IO() doList ids 0 = return() doList [] c = return() doList ids c = do forkChild $ forM_ todo get doList later (c-1) where (todo, later) = splitAt (length ids `div` c) ids {- Copied from http://haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control-Conc… Terminating the program -} children :: MVar [MVar ()] children = unsafePerformIO (newMVar []) waitForChildren :: IO () waitForChildren = do cs <- takeMVar children case cs of [] -> return () m:ms -> do putMVar children ms takeMVar m waitForChildren forkChild :: IO () -> IO ThreadId forkChild io = do mvar <- newEmptyMVar childs <- takeMVar children putMVar children (mvar:childs) forkIO (io `finally` putMVar mvar ()) -- end of copied code main = do [c', n'] <- getArgs let c = read c' :: Int n = read n' :: Int start <- getClockTime doList [1..n] c waitForChildren end <- getClockTime putStrLn $ show(c) ++ " " ++ show(secDiff start end) ++ "s" 20:31 sacha@loft4633:/tmp 21> ghc --make -threaded get.hs [1 of 1] Compiling Main ( get.hs, get.o ) Linking get ... 20:31 sacha@loft4633:/tmp 22> ./get 1 10000 1 3.242352s 20:31 sacha@loft4633:/tmp 23> ./get 2 10000 2 3.08306s 20:31 sacha@loft4633:/tmp 24> ./get 2 10000 +RTS -N2 2 6.898871s 20:32 sacha@loft4633:/tmp 25> ./get 3 10000 3 2.950677s 20:32 sacha@loft4633:/tmp 26> ./get 3 10000 +RTS -N2 3 7.381678s 20:32 sacha@loft4633:/tmp 27> ./get 3 10000 +RTS -N3 3 14.683548s 20:32 sacha@loft4633:/tmp 28> ./get 4 10000 4 3.332165s 20:33 sacha@loft4633:/tmp 29> ./get 4 10000 +RTS -N4 -s ./get 4 10000 +RTS -N4 -s 4 57.17923s 2,147,969,912 bytes allocated in the heap 49,059,288 bytes copied during GC 736,656 bytes maximum residency (98 sample(s)) 486,744 bytes maximum slop 5 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 949 collections, 948 parallel, 76.73s, 25.67s elapsed Generation 1: 98 collections, 98 parallel, 7.70s, 2.56s elapsed Parallel GC work balance: 2.17 (6115428 / 2822692, ideal 4) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 1.43s ( 27.76s) 6.31s ( 2.12s) Task 1 (worker) : 0.00s ( 28.13s) 10.62s ( 3.56s) Task 2 (worker) : 0.37s ( 28.63s) 11.06s ( 3.69s) Task 3 (worker) : 0.00s ( 28.95s) 6.29s ( 2.10s) Task 4 (worker) : 20.73s ( 28.95s) 9.68s ( 3.24s) Task 5 (worker) : 0.00s ( 28.95s) 0.60s ( 0.20s) Task 6 (worker) : 21.81s ( 28.95s) 11.91s ( 3.97s) Task 7 (worker) : 18.59s ( 28.95s) 13.04s ( 4.36s) Task 8 (worker) : 17.24s ( 28.96s) 14.92s ( 4.99s) SPARKS: 0 (0 converted, 0 pruned) INIT time 0.00s ( 0.00s elapsed) MUT time 79.23s ( 28.95s elapsed) GC time 84.43s ( 28.23s elapsed) EXIT time 0.00s ( 0.01s elapsed) Total time 162.49s ( 57.19s elapsed) %GC time 52.0% (49.4% elapsed) Alloc rate 27,513,782 bytes per MUT second Productivity 48.0% of total user, 136.5% of total elapsed gc_alloc_block_sync: 15006 whitehole_spin: 0 gen[0].steps[0].sync_large_objects: 7617 gen[0].steps[1].sync_large_objects: 35 gen[1].steps[0].sync_large_objects: 1400

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Suggestions For An Intro To Monads Talk.
by aditya siram 09 Aug '10

09 Aug '10

Hi all, I am doing an "Intro To Monads" talk in September [1]. The audience consists of experienced non-Haskell developers but they will be familiar with basic functional concepts (closures, first-class functions etc.). I am looking for suggestions on how to introduce the concept and its implications. I'd also like to include a section on why monads exist and why we don't really see them outside of Haskell. Has anyone here done a talk like this? And if so what parts of your presentation were successful and what would you stay away from. Thanks for the feedback. -deech [1] It's in St.Louis, Missouri at the St.Louis Perl Mongers meeting<http://St.Louis%20Perl%20Mongers%20meeting>so come on by if you're around!

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preparing for Haskell 2011
by Malcolm Wallace 09 Aug '10

09 Aug '10

Dear all, Although the Haskell 2010 Language Report has only been published recently, it will soon be time for the Committee to make decisions on the next version, Haskell 2011. I am aiming for the committee to make decisions around the end of Sept or beginning of October 2010. Can I therefore encourage any people who have made proposals, either informally on mailing lists, or formally in the Haskell-prime ticket system, to consider what they need to do to bring those proposals to a state where the committee can vote on them. Perhaps you have not made such a proposal yourself, but are very keen that someone else's proposal be adopted. Work with the proposer to polish it! Here is what you need to know about the proposal process: http://hackage.haskell.org/trac/haskell-prime/wiki/Process Please note especially that the key requirement that will bring your proposal to the attention of the committee for a decision is the "Report delta", which describes the changes with exact precision. Regards, Malcolm

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Socket not released
by Jonathan Geddes 09 Aug '10

09 Aug '10

Cafe, I'm writing a network application that uses static configuration a la xmonad and yi. When the app receives a certain command it recompiles its source, closes the socket it is using and runs its newly compiled "predecessor" as a new process. The problem I'm having is that the port that the parent process was using is not available to the child process. Even though the parent process has terminated, the port is unusable until the child process also terminates. Can anyone give me a clue about what's going on here? I'm using Network and System.Process modules and ruining on Ubuntu linux. I'm using the sClose function to close the socket. Thanks for any tips. --Jonathan

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Re: [Haskell] ANNOUNCE: jhc 0.7.4
by Simon Marlow 09 Aug '10

09 Aug '10

On 27/07/2010 01:54, John Meacham wrote: > For each type I can statically generate an "optimal" layout based on its > structure. For instance, maybe benefits from two of these optimizations, > first of all, nullary constructors (Nothing) need never appear in the > heap, so they are given values that pack directly into a word, this > happens for all nullay constructors in general. Then, since there is > only one constructor left (Just) we can discard the tag field, because > if something of type Maybe, is in WHNF, and is not Nothing then in must be > a Just. so the Just is a single heap allocated word (which are packed > end to end in a page with no overhead) > > I am refining the optimization algorithm, on 64 bit machines I have > another few bits to play with for instance that I can take advantage of. > > A particularly nice case is that characters can be fully integreated > into the word, so the entire space usage of > > "Hello" is 10 words as lists benefit from the same packing benefits as > Maybe. I should point out that in GHC "Hello" requires 15 words: 3 for each list cell, and the Chars are free because they're statically allocated in the RTS. A Just requires 2 words (one more than JHC, I guess). Tantalisingly, it's almost possible to represent a Just with zero words - the pointer to the Just points directly to the element - but there's nowhere to put the tag bits for the element pointer (the tag bits are for the Just). A Nothing in GHC takes zero words, as do all nullary constructors. I wrote up a summary of the GHC heap representation on Stack Overflow recently: http://stackoverflow.com/questions/3254758/memory-footprint-of-haskell-data… Cheers, Simon > compare this to 30 or so words used in a traditional "everything is on > the heap and tagged" model. > > > The manual has a section describing the RTS, it doesn't describe the GC > though, but talks about how I pack things in the pointers. > > http://repetae.net/computer/jhc/manual.html#the-run-time-system > > John >

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Typo or on purpose? http://haskell.org/ghc/docs/6.12.2/html/users_guide/lang-parallel.html
by Alexander Kotelnikov 09 Aug '10

09 Aug '10

This + 1 in (n1 + n2 + 1) what is it doing there? import Control.Parallel nfib :: Int -> Int nfib n | n <= 1 = 1 | otherwise = par n1 (pseq n2 (n1 + n2 + 1)) where n1 = nfib (n-1) n2 = nfib (n-2) BTW, same code can be found in "Seq no more: Better Strategies for Parallel Haskell" article.

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a random numbers generator with a good 'split'
by deb＠pudlak.name 09 Aug '10

09 Aug '10

Hi cafe. recently I was looking at various possibilities of generating random numbers in Haskell. Apparently, the main problem is the 'split' function in the System.Random.RandomGen class. Since it is rarely needed in imperative programs, not much is known how to implement it safely. It's documentation says: > The split operation allows one to obtain two distinct random number > generators. This is very useful in functional programs (for example, > when passing a random number generator down to recursive calls), but > very little work has been done on statistically robust implementations > of split ([System.Random, System.Random] are the only examples we know > of). I consulted it with a friend, who has done much work in the area of random number generators. He suggested that this might be implemented using a random number generator with a very large period, such as Mersene Twister (MT19937 has a period of 2^19937-1). A pair of splitted generators states could be positioned sufficiently far enough from each other so that in practice they never reach each other, and in such a way that successive splits (in practice) never meet. I searched Hackage, where I found a few implementations of Mersene Twister, but AFAIK no one actually implements neither RandomGen nor 'split' alone. I wonder why -- is RandomGen inconvenient or obsolete in some way? Or just nobody tried? With best regards, Petr Pudlak PS: Sorry if you get multiple copies, I had problems sending the mail.

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Please take the State of Haskell, 2010 survey
by Johan Tibell 09 Aug '10

09 Aug '10

Hi all, I've put together a quick, 9-question State of Haskell, 2010 survey: http://blog.johantibell.com/2010/08/state-of-haskell-2010-survey.html The survey will hopefully give us some insight into how people use Haskell and perhaps also some ideas on how Haskell tools and libraries could be improved. P.S. Please direct replies to this email to haskell-cafe(a)haskell.org. Cheers, Johan

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gkt2hs seg fault issue
by briand＠aracnet.com 09 Aug '10

09 Aug '10

I reported a seg-fault in chart a while back. so I was experimenting with cairo and rendering to to the screen, which if my understanding is correct, uses gtk. Certainly looks like it. So I compiled the cairo example Drawing.hs and that worked fine. I then tried running the example from ghci, i.e. loading it and typing main. I get a seg-fault when it exits: Ok, modules loaded: Main. *Main> main Loading package array-0.3.0.0 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package unix-2.4.0.0 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package process-1.0.1.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package haskell98 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package cairo-0.11.0 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package glib-0.11.0 ... linking ... done. Loading package gio-0.11.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package pango-0.11.0 ... linking ... done. Loading package gtk-0.11.0 ... linking ... done. *Main> Segmentation fault I included all the messages in case someone knows that one of the libraries is out of date and could be the source of the problem. Is it to be expected that it would seg-fault under ghci ??

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Preview the new haddock look and take a short survey
by Mark Lentczner 09 Aug '10

09 Aug '10

The Haddock team has spent the last few months revamping the look of the generated output. We're pretty close to done, but we'd like to get the community's input before we put it in the main release. Please take a look, and then give us your feedback through a short survey Sample pages: http://www.ozonehouse.com/mark/snap-xhtml/index.html Frame version: http://www.ozonehouse.com/mark/snap-xhtml/frames.html Survey: http://spreadsheets.google.com/viewform?formkey=dHcwYzdMNkl5WER1aVBXdV9HX1l… Short link to same survey: http://bit.ly/9Zvs9B Thanks! - Mark Mark Lentczner http://www.ozonehouse.com/mark/ irc: MtnViewMark

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Re: [Haskell-cafe] cairo rendered to screen examples
by Herng Yi Cheng 09 Aug '10

09 Aug '10

<original> Date: Sun, 8 Aug 2010 11:13:33 -0700 From: <briand(a)aracnet.com> Subject: [Haskell-cafe] cairo rendered to screen examples To: haskell-cafe(a)haskell.org Message-ID: <20100808111333.44b5f14a(a)windy.deldotd.com> Content-Type: text/plain; charset=US-ASCII I've been running around the gtk2hs web site and can't seem to find the actual code (I did find the cairo blog, with examples but no code). Can some kind soul post a link ? Thanks <\original> If you've installed gtk2hs on your computer, go to gtk2hs/0.10.1/share/demo/cairo or some similar folder (using your own gtk2hs version). There are some cairo examples there with source code. regards, Herng Yi

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Spivak's "Databases are Categories" video/slides at www.galois.com
by Vasili I. Galchin 09 Aug '10

09 Aug '10

Hello, I'm sorry if this has already been posted. http://www.galois.com/blog/2010/05/27/tech-talk-categories-are-databases/ Vasili

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Re: [Haskell-cafe] Is there any experience using Software Transactional Memory in substantial applications?
by Johnny Morrice 09 Aug '10

09 Aug '10

> My opponent gave me that link: http://logicaloptimizer.blogspot.com/2010/06/so-microsofts-experiments-with… I enjoy the article you linked but I sort of skimmed it because it was a little boring, however its main point seem to be: 1. Ghostbusters. 2. Artificial intelligence is useless [1] 3. Listen to Anders! [2] An interesting sample: "Anders Hejlsberg: Well, the best Software Transactional Memory implementations are still sitting at around 200% to 400% and that's even in best cases actually and still with Software Transactional Memory it's still, in a sense, it's still a problem of synchronization and shared state which... Carl Franklin: It's just under the lower level. Anders Hejlsberg: Some would argue it's t h e wrong way to look at the problem in the beginning. We shouldn't have the shared state to begin with. Richard Campbell: Right. Hat guy from xkcd (Enter stage left): But don't you see that Haskell has no shared state. That's exactly why STM is so great for doing concurrency in Haskell!" (I maybe edited that a little there.) Ta ta, Johnny [1] Artificial intelligence is pointless http://www.youtube.com/watch?v=nvZBtJ-ncEM [2] The internet audio talkshow http://www.dotnetrocks.com/default.aspx?showNum=541 I found this transcript on google. Server seems to give of fake 404 pages, so have to hotlink :( http://perseus.franklins.net/dotnetrocks_0541_anders_hejlsberg.pdf

3 2

cairo rendered to screen examples
by briand＠aracnet.com 09 Aug '10

09 Aug '10

I've been running around the gtk2hs web site and can't seem to find the actual code (I did find the cairo blog, with examples but no code). Can some kind soul post a link ? Thanks

1 1

Fwd: [Haskell-cafe] Is there any experience using Software Transactional Memory in substantial applications?
by Alberto G. Corona 09 Aug '10

09 Aug '10

---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2010/8/8 Subject: Re: [Haskell-cafe] Is there any experience using Software Transactional Memory in substantial applications? To: Serguey Zefirov <sergueyz(a)gmail.com> This first papers is the first that describes the preliminary haskell implementation and the performance data says that STM scales well with the number of CPU cores Blocking does not scale, as expected. http://research.microsoft.com/en-us/um/people/simonpj/papers/stm/lock-free-… In this other study, also for microsoft: <http://research.microsoft.com/en-us/um/people/simonpj/papers/stm/lock-free-…> Dissecting Transactional Executions in Haskell<http://www.cs.rochester.edu/meetings/TRANSACT07/papers/perfumo.pdf> . The worst performance in the study is from an extreme case example form my package TCache described here<http://haskell-web.blogspot.com/2006/11/transactional-cache-for-haskell.html>. In that example, a set of treads update the same two objects all the time. Since STM is non blocking, all threads tries to perform the task and rollback at the very end if things have been changed by other thread in the meantime. Just like databases. The bad thing is that the more CPU cores are executing the example, the more work being rolled back is done. That is more or less the history. I heard (The Monad Reader -mplementing STM in pure Haskell<http://themonadreader.files.wordpress.com/2010/01/issue15.pdf>) about other tentative implementation that do not wait for the end of the atomic task to test the atomicity of the transaction, but instead, any update of a TVar inmediately invalidates (and kill) all atomic transactions that uses that TVar. This could potentially improve the performance a lot. However I don´t know the strategy of the current haskell implementation nor the strasategy of the Microsoft runtime(s) either. Anyway, it is waranteed 100% that 1) the slowest in memory transaction is way faster than the transaction delegated to the fastest external database. 2) in memory transactions with blocking is a nightmare. For me these are enough arguments for STM usage in many ordinary (I mean Web) applications. 2010/8/8 Serguey Zefirov <sergueyz(a)gmail.com> Recently we discussed Haskell and especially types in Russian part of > LiveJournal and of course we talk about STM. > > My opponent gave me that link: > > http://logicaloptimizer.blogspot.com/2010/06/so-microsofts-experiments-with… > > It says that performance with STM in Microsoft Research was more than > horrible. > > I failed to find convincing counter-evidence on the web. Not for > Haskell, even for Java/C#/C++. > > So I asking Haskell-cafe for clarification. Do anyone here have an > experience with STM in computing-intensive tasks? Did it help there? > What are the possible reasons for STM failure in MR? > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

2 1

using shared libs on the windows version
by Axel Huizinga 09 Aug '10

09 Aug '10

Hi to all from a haskell newbie! I run into problems using shared libs on windows. The error messages I get looks like: Could not find module `Data.List': Perhaps you haven't installed the "dyn" libraries for package `base'? Any ideas how to enable shared libs system-wide? Cordially, Axel

2 1

hdbc-mysql broken on snow-leopard?
by Carter Schonwald 08 Aug '10

08 Aug '10

Hey All, when i build hdbc-mysql and then try to run some example code, i get the following error message: Loading package HDBC-mysql-0.6.3 ... can't load .so/.DLL for: mysqlclient (dlopen(libmysqlclient.dylib, 9): no suitable image found. Did find: /usr/local/lib/libmysqlclient.dylib: mach-o, but wrong architecture) does this mean that it won't build on OS X snow leopard? (and yes, I am aware of hdbc-odbc, but i was curious if I could use hdbc-mysql thanks -Carter

3 2

Re: [Haskell-cafe] What is <-
by michael rice 08 Aug '10

08 Aug '10

That was my suspicion. So, you can't change horses (monads) in mid-stream. A parallel question: main = do ... -- in the IO monad I know I can have other *do*s in main, if foo then do . . else do . . but must all these other *do*s also be in the same IO monad? What determines what monad a *do* is "in"? The first line after the *do*? Thanks for your patience. Michael --- On Sun, 8/8/10, Henning Thielemann <lemming(a)henning-thielemann.de> wrote: From: Henning Thielemann <lemming(a)henning-thielemann.de> Subject: Re: [Haskell-cafe] What is <- To: "michael rice" <nowgate(a)yahoo.com> Date: Sunday, August 8, 2010, 11:01 AM On Sun, 8 Aug 2010, michael rice wrote: > How would I print each of these integers, one per line? > > [1,2,3,4,5] >>= \x -> ? You can't do this from inside the List monad, but you can easily do it from outside, since the result of a 'do' block in List monad is just a list. mapM_ print [1..5] or mapM_ print $ do x <- [1..] ... return (x+y+z)

3 2

setting gcc during the ghc-build phase
by Günther Schmidt 08 Aug '10

08 Aug '10

Hi all, for build ghc from source, how can I set which c-compiler to use? ./configure --with-gcc= .... does not seem to work for ghc-6.12.3 nor does setting the CC-environment variable. Günther

1 0

What is <-
by michael rice 08 Aug '10

08 Aug '10

What is <- ? Couldn't find anything on Hoogle. 1) main = do x <- getLine -- get the value from the IO monad putStrLn $ "You typed: " ++ x 2) pythags = do z <- [1..] --get the value from the List monad? x <- [1..z] y <- [x..z] guard (x^2 + y^2 == z^2) return (x, y, z) From: http://en.wikibooks.org/wiki/Haskell/Syntactic_sugar Do and proc notation Sweet Unsweet Monadic binding do x <- getLIne getLine >>= \x -> putStrLn $ "You typed: " ++ x putStrLn $ "You typed: " ++ x So, Example 2 desugared becomes... [1..] >== \z -> ? Michael

7 9

Combining Gtk2hs and Fieldtrip
by Herng Yi Cheng 08 Aug '10

08 Aug '10

Recently I wrote a 3D graphics viewer using Gtk2hs and Cairo, and it works ok, aside from the fact that it got quite slow when it got to displaying about 1000 polygons. It works something like this: The three-dimensional coordinates of polygons are given, and the program sorts the polygons using a BSP Tree (following the Painter's Algorithm), then it projects the polygons onto the plane of vision and renders each polygon to the screen using Cairo. After some investigation, I realised that my bottleneck was the rendering of polygons, but I could not speed up the rendering using parallel programming since the rendering order is crucial in the Painter's Algorithm. Even if I switched to an algorithm based on Hidden Surface Removal so I could render all my "obscured" polygons at once, Gtk2hs "is single threaded and its functions cannot be called from other threads". Then I heard about FieldTrip, which uses the GPU to process rendering efficiently. I decided to switch to using FieldTrip in conjunction with Gtk2hs to write applications, but it doesn't seem that easy because (i) there doesn't seem to be any version of GHC where Gtk2hs, Glade and Fieldtrip can work together on Windows and (ii) unlike Cairo, there is no Gtk2hs support for Fieldtrip in the sense that there are no Gtk2hs functions that render FieldTrip output to a Gtk2hs widget, like the DrawWindow. The latter would mean that Gtk2hs can't interact easily with FieldTrip. I really like Gtk2hs because it is very comprehensive and its interface can be designed using Glade. Does anyone know if there is a project linking Gtk2hs and FieldTrip? Otherwise, does anyone know if user interfaces can be written using Reactive (since it's linked to FieldTrip) with the usual functionality (e.g. menus, buttons, FieldTrip display reacting to mouseclicks etc)? If that is possible then I might have to switch to Reactive, but I'd miss Glade a lot :) regards, Herng Yi

3 3

lambdacats
by Tony Morris 08 Aug '10

08 Aug '10

Hello, does anyone happen to have the lambdacats page cached? The domain ( arcanux.org) and server have disappeared and the wayback machine doesn't have the images. -- Tony Morris http://tmorris.net/

10 16

Music-related
by Johann Bach 08 Aug '10

08 Aug '10

Midi files or music exported by the typical music editor is "expressionless." A *human* would play that music with slight tempo variations, subtle accents... some notes would be overlapped in time slightly, some separated in time. I want a program that starts with a plain midi file, then via a domain-specific language lets me describe nuances of expression. (Aside: this is mostly an experiment done for curiosity and an excuse to write Haskell code. As a practical matter, since I already play some piano and I am working on improving my music imagination, it makes more sense to put time into music practice and not programming. But hey, I don't always make sense.) Nuances include - stretching or shrinking small units of time, for example single beats within a measure - inserting pauses before or after a beat, or half-beat, or other small unit of time - changing how much sequential notes overlap (in time) or are separated. Be able to do this over a range of time - similar to previous: over a range of time, make notes overlap in time, and vary that overlap from a larger amount to a smaller amount - accenting (making slightly louder) notes at a specific time - put in a crescendo (gradually louder) or decrescendo (gradually softer) over a span of time Examples: stretch time between beats 3 and 4, measure 7: m7 [ 3 --> 4 time:+105% ] Change overlap of beat 3 to following beat by increasing it 100 ms: m7 [ 3 overlap:+100] Over the range of beats 1 to 4, stepping by 1/2 beat, gradually increase the overlap from 100 ms to 200ms: m7 [3 --> 4 (step 1/2) overlap:+100 --> +200] It would be useful to define patterns that are used repetitively. define patternFoo [ 3 --> 4 time:+105% 3 overlap: +100 3 --> 4 (step 1/2) overlap:+100 --> +200 ] Then, m7 [ patternFoo ] Often music has a hierarchy of expressive elements: there is some larger, basic expressive pattern, while individual measures deviate slightly from that. So it is useful to invoke a pattern, then use the language to describe additional changes: m7 [ patternFoo 1 --> 2 overlap:+50 ] In this case, patternFoo already defines an "overlap value" for beat 1, so the additional mention of overlap here is *summed* with the existing value. I want to solicit suggests for the basic data structure to represent the expression descriptors. First, note the job of the software in translating a "flat" midi file into an expressive one can be expressed like this: - For every note in the midi file - find out what overlap applies to that note - find out what dynamic changes apply to that note - find out what time the note occurs at - etc. - finally compute the note's actually begin time, end time, and dynamic So the basic problem to solve is: given a list of expressive element descriptors, and the begin time of a note (specified as a measure and beat), figure out which descriptors are "in effect" at the given time, and sum them. Let's look just at descriptors that stretch or shrink time. Let's say that for measure 7, we have the following two descriptors present: - 1 --> 2 1/2 time:+110% - 2 --> 2 2/3 time:+120% Note: 2 1/2 is "two and a half", 2 2/3 is "two and two-thirds." They overlap in time. I wonder what is the best form to store this information in order to facilitate translating a note? I'm thinking of this: each descriptor becomes a pair of elements: an "on" element and an "off" element. - beat 1: time: +110 ON - beat 2: time: +120 ON - beat 2 1/2: time: +110 OFF - beat 2 2/3: time: +120 OFF For a note at beat X, you run though this list of on/off elements, tracking the total changes to elements like 'time', until you reach beat X.

2 1

Trying to statically link Gtk2Hs application (Windows XP, network drive)
by Peter Schmitz 08 Aug '10

08 Aug '10

In [Haskell-beginners], please see: http://www.haskell.org/pipermail/beginners/2010-August/004949.html Please reply to [Haskell-beginners]; thanks much. -- Peter

1 0

finding out which gcc is hard-coded into a ghc?
by Günther Schmidt 07 Aug '10

07 Aug '10

Hello, how can I find out which gcc a ghc is hard-coded to use and is it possible to override it? Günther

4 3

Haddock New Look Survey results
by Mark Lentczner 07 Aug '10

07 Aug '10

Thank you to all who took the Haddock New Look Survey. We got a 161 responses. Some graphs of the results can be found here: http://www.ozonehouse.com/mark/snap-xhtml/Haddock-Survey-Summary.pdf I've read through all of the comments, and I'd like to share some initial thoughts with you: • Source links are indeed still supported in Haddock, I just happened to generate those sample pages with it turned off. Sorry for any confusion. The functionality remains exactly like it is in Haddock today. • I also failed to turn off all the "alternate style" bits on the index page, and many of you found it, explored the other styles, and then wondered why it failed on the module pages. I had intended for the survey to just give pages in the new style, and missed updating the index page. In the new Haddock, you can specify which "themes" you want to render your documentation with. If you include more than one, the pages have a "style switcher" menu added. The default themes that will come with Haddock include "Classic" which is a pretty faithful recreation of the current look. • Many great suggestions were made about ways to improve the UI experience of Synopsis drawer. Of course, the web is hardly a full featured UI framework, and to implement many of them we would have to decide to move to a much larger JavaScript framework. At present, Haddock attempts to use JavaScript very lightly, and only needs one small .js file. I think we are planning on keeping it that way for now. • Several people mentioned that perhaps we should have "user preferences" for things like where the Synopsis section goes. This is possible (the "style switcher" menu above uses such a preference), but know that a page can only set a cookie for a site. So if we do such things, they will stick per site, and users will have to choose their preference for each new site of Haddock docs they browse to. Fortunately, all of Hackage would count as one site, as does your local machine, and those two settings probably cover the bulk one's use. There were many many good suggestions, reported problems, and observations among the comments. I'm pulling together a short of list with the Haddock team of high priority changes based on these to be completed before the first release. To be sure, this will include: - fixing the layout issues on Firefox & Chrome - improving the expanding/collapsing behavior in module lists The most difficult issue is how to handle the Synopsis. As evident both from the multiple choice question in the survey, and from the comments, there is no clear consensus. While 2/3rds of you like the Synopsis drawer, there is a wide range of how it should look and operate. Another 1/5th want it back where it was, in-line with the page. There were many other suggestions as well. I'm going to go have to spend some time mulling what to do. Finally, thanks for the huge amount of positive feedback. When working on open source, often on speculation that it is what the community will want, it is really great to hear that you've done good! I realize that there is no way that such a change as this can please everyone 100%, but I'm glad to see that we are, on the whole, people are really happy with the work. - Mark Mark Lentczner http://www.ozonehouse.com/mark/ mark(a)glyphic.com irc: mtnviewmark

1 0

Re: using Network.CGI
by Anders Kaseorg 07 Aug '10

07 Aug '10

On Fri, 6 Aug 2010, Andrew U. Frank wrote: > i think this limits what network.cgi can be used for: it will work only > on systems, where the output from the ghc can execute. That’s not a limitation of Network.CGI; it’s just the way CGI always works, no matter what language you use. http://en.wikipedia.org/wiki/Server-side_scripting > specifically, this means, i cannot move the executable to an android > mobile phone and use it there (assuming that there is a web server, e.g. > i-jetty, which understands cgi (does it?)). is this correct? You’d need a Haskell compiler that targets Android; I don’t know whether such a thing exists yet. (Of course, keep in mind that if the CGI script is running on another computer, such as <http://andersk.mit.edu/greet.cgi> , you will still be able to visit it and use it from a browser running on Android. That’s the point of CGI; only the server needs to know how to run the code.) Anders

1 0

Does Hackage have a connection to some SFT package (Significant FFT coefficients) ...
by caseyh＠istar.ca 06 Aug '10

06 Aug '10

Does Hackage have a connection to some SFT package (Significant FFT coefficients) and/or can one get the SFT from FFTW without generating all the coefficients?

1 0

real-time audio processing [Was: can Haskell do everyting as we want?]
by Stephen Sinclair 06 Aug '10

06 Aug '10

On Aug 3, 8:31 pm, Jeremy Shaw <jer...(a)n-heptane.com> wrote: > The only area I have had any trouble with Haskell is doing realtime > music synthesis. And only because the garbage collector is not > realtime friendly. That is not unfixable though. However, I am > thinking that the best way to do realtime synthesis with Haskell is to > use it to create a DSL that uses LLVM to create code at runtime so > that the realtime code is outside the scope of the normal RTS and > garbage collector. I'm also very interested in this topic---how to apply a general- purpose functional language to real-time needs, even if it is in a domain-specific way. Indeed, it mostly comes down to memory management and the fact that functional concepts like closures and laziness require a lot of dynamic allocation and garbage collection. Certainly, one solution is to provide a real-time-friendly memory manager. However, it's interesting to notice that, as proven by FAUST [1], a huge amount of DSP algorithms can be expressed functionally in a real- time-compatible way by describing them as static diagrams of connected blocks. These can be efficiently compiled to imperative code with no dynamic memory allocation required. So yes, if such a language were available as an embedded DSL in Haskell (one effort can be found here [2]), it could be generated at run-time using LLVM and called out to. Alternatively, it would be very cool if it were possible to generate code statically at compile time, just like in FAUST. I can imagine this being very useful, especially if it could be generalized to operate on datatypes other than floating points, and had easy access to data structures provided by non-RT portions of the code. If there are mutability requirements, it could be made to run in the ST monad with a pre-allocated workspace. Of course _modifying_ such structures at run-time is always a dynamic thing by definition, although there is the possibility of dynamically generating a replacement block diagram while an one existing one runs, and using an atomic pointer swap to switch them without causing interruptions. In any case, as far as I know the only thing in the way is that it's impossible to tell GHC to compile a section of code in such as way as to guarantee avoidance of memory management. Compilers and runtime- systems always seem to be either RT- or non-RT-friendly, but never seem to support the idea of code *portions* that have differing requirements. My point is, RT code _can_ be expressed functionally, even if the RT-ness imposes certain expressivity restrictions. It would be very cool to be able to mark sections of code as following such a "sub-language" and be guaranteed that the compiler will generate GC-free code for a particular function, if possible, or otherwise fail. Even if such a sub-language were no more expressive than C, it would be nice to be able to write it in Haskell instead of dropping down to C, so that data can be easily shared with non-RT parts, and Haskell's type checker could be exploited. It seems strange to me that with technology like Haskell and GHC we still depend on using C to express these last remaining droplets of real-time determinism requirements--- strange, since I think of higher-level languages like Haskell to be supersets of the capabilities of C---and annoying, because it means having to deal with the complexities of language interoperability, just for a few low-level components of an application. I realize some of this has probably been discussed in conjunction with FRP. I'm aware of one paper on RT-FRP that talks about requiring an RT-friendly sub-language [3], but I don't pretend to follow it completely. I'm almost sure it also has something to do with arrows, but I have very little idea what they are, since I'm still just "getting" monads at this point in my personal Haskell understanding. I hope someone more knowledgeable about these things on this list might be able to comment on their relation to real-time determinism. [1] http://faust.grame.fr/ [2] http://claudiusmaximus.goto10.org/cm/2009-12-04_heist_dataflow_algebra.html [3] http://www.haskell.org/frp/rt-frp.pdf

7 8

Question about rpc design
by lysgaard 06 Aug '10

06 Aug '10

Hi, I'm tinkering with making a DHT im my spare time this summer. For this i need to do some unusual rpc calls. You see in a dht a query (rpc) is first sent from you (node "a") to a node "b" which probably doesn't know the answer. If it still does know the answer it returns the value of the query to node "a". This gives the latency: 2*latency(a,b) On the other hand, if i t doesn't it sends a new rpc to a node "c" more probable to know the ansver. Then the latency is: latency(a,b) + 2*latency(b,c) + latency(b,a) While what I would like is this: latency(a,b) + latency(b,c) + latency(c,a) you see that for many forwards this adds considerable latency and also many more calls than nessesary. Is this way of sending messages already known? Does it have a name? And if not, how hard do you think it would be to hack some rpc library to implement this? -- View this message in context: http://old.nabble.com/Question-about-rpc-design-tp29356441p29356441.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 1

Wildly off-topic: de Boor's algorithm
by Andrew Coppin 06 Aug '10

06 Aug '10

Given a suitable definition for Vector2 (i.e., a 2D vector with the appropriate classes), it is delightfully trivial to implement de Casteljau's algorithm: de_Casteljau :: Scalar -> [Vector2] -> [[Vector2]] de_Casteljau t [p] = [[p]] de_Casteljau t ps = ps : de_Casteljau t (zipWith (line t) ps (tail ps)) line :: Scalar -> Vector2 -> Vector2 -> Vector2 line t a b = (1-t) *| a + t *| b Now if you want to compute a given point along a Bezier spline, you can do bezier :: Scalar -> [Vector2] -> Vector2 bezier t ps = head $ last $ de_Casteljau t ps You can chop one in half with split :: Scalar -> [Vector2] -> ([Vector2], [Vector2]) split t ps = let pss = de_Casteljau t ps in (map head pss, map last pss) And any other beautiful incantations. Now, de Boor's algorithm is a generalisation of de Casteljau's algorithm. It draws B-splines instead of Bezier-splines (since B-splines generalise Bezier-splines). But I think I may have ACTUALLY MELTED MY BRAIN attempting to comprehend it. Can anybody supply a straightforward Haskell implementation?

3 5

what's the best environment for haskell work?
by Rustom Mody 06 Aug '10

06 Aug '10

Do most people who work with haskell use emacs/vi/eclipse or something else?? Personal Note: I used gofer some 15 years ago. At that time I hacked up a emacs mode (I did not know of any then) along with some changes to gofer to have gofer inside emacs rather than vi inside gofer. Things have got more exciting now -- just trying to catch up!! [Note: My preferrred/default OS is debian-squeeze]

14 21

Re: using Network.CGI
by Anders Kaseorg 06 Aug '10

06 Aug '10

On Thu, 5 Aug 2010, Andrew U. Frank wrote: > which is clearly not producing the second part of the code, namely > output a greeting. That’s what it’s supposed to output. Have you considered typing in a name and submitting the form? It works fine for me: <http://andersk.mit.edu/greet.cgi>. > i try to use the Network.CGI package from darcs. (Note also that the current version is maintained in Git, not Darcs, but that’s a minor detail. See http://hackage.haskell.org/package/cgi .) Anders

2 1

Re: [Haskell-cafe] subversion with haskell
by Yuras Shumovich 06 Aug '10

06 Aug '10

Hi, Try the next: % env EXTRA_CPPFLAGS="-I/usr/local/include/subversion-1" \ EXTRA_LDFLAGS="-L/usr/local/lib" \ runhaskell Setup.hs configure % runhaskell Setup.hs build % runhaskell Setup.hs install (and read the installation instructions included into the tarball :) ) 2010/8/5 Andrew U. Frank <frank22(a)geoinfo.tuwien.ac.at>: > i found the file in usr/include/subversion-1 (i use an ubuntu (debian) > installation form). but the cabal installer (i.e. the configure script) > does not find the file. > > can you give me a hint where it could search and where i could copy the > file to. i tried to read the configure script, but cannot see, where it > searches. i am not familiar with cpp and do not understand what the hint > 'extra cpp flags' could mean. > > thanks for your help! > > andrew >

1 0

Why do "unsafe" foreign calls block other threads?
by Gregory Crosswhite 06 Aug '10

06 Aug '10

Hey everyone, Could someone explain to me the logic behind having "unsafe" calls block other threads from executing? It seems to me that if anything it would make more sense for "safe" calls to block other threads since the call can call back into the Haskell runtime, as opposed to "unsafe" calls which (by assertion) will never call back into Haskell and therefore should be safer to run in parallel with other threads. What am I missing here? Cheers, Greg

8 16

network.cgi - incomplete translation of code to javascript
by Andrew U. Frank 06 Aug '10

06 Aug '10

i try to use the Network.CGI package from darcs. my testing uses the example code from the webpage 'practical web programming in haskell' http://www.haskell.org/haskellwiki/Practical_web_programming_in_Haskell#Get… specifically the example with code: import Network.CGI import Text.XHtml inputForm = form << [paragraph << ("My name is " +++ textfield "name"), submit "" "Submit"] greet n = paragraph << ("Hello " ++ n ++ "!") page t b = header << thetitle << t +++ body << b cgiMain = do mn <- getInput "name" let x = maybe inputForm greet mn output $ renderHtml $ page "Input example" x main = runCGI $ handleErrors cgiMain -- Get the value of an input variable, for example from a form. -- If the variable has multiple values, the first one is returned. -- getInput :: String -> CGI (Maybe String) this runs (runghc) and produces the output: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" ><head ><title >Input example</title ></head ><body ><form ><p >My name is <input type="text" name="name" id="name" /></p ><input type="submit" value="Submit" /></form ></body ></html > which is clearly not producing the second part of the code, namely output a greeting. the same happens with the next example, using cookies, where from two options for pattern matching only the first is include in the javascript. i assume that i do something wrong - but what? any help is appreciated! andrew

1 0

jswm - how to manipulate strings?
by Andrew U. Frank 06 Aug '10

06 Aug '10

i try to use jswm to build some web applications, but i got quickly stuck. I used the example programs provided and tried to change them. starting with the calculator, i would like to use the string that the user puts in and apply a function to it (say transform it to capitals, later i want to do more complex operations). now i cannot find a way to apply a function to the type returned from the input: get'value :: (Monad mn, CHTMLTextAreaElement this) => Expression this -> mn (Expression String) how can i apply some function to the string in the input : mn (Expression String) ? or how can i get the string out such that i can change it and later put it back into an expression? help is appreciated - there seems to be only a small piece missing.. andrew

1 0

Haskell Platform OPENGL dependencies
by aditya siram 06 Aug '10

06 Aug '10

Hi folks, I just installed the latest Haskell Platform on a fresh Ubuntu Lucid machine and I had to install the following packages to satisfy Open GL: libgmp3-dev,libgl1-mesa-dev, libglu1-mesa-dev, freeglut3-dev Just thought you might want to document that on the Haskell Platform page. -deech

2 1