Re: [Haskell-cafe] Loading bitmap with xlib
Conrad Parker conrad at metadecks.org writes: On 31 January 2011 21:40, Francesco Mazzoli f at mazzo.li wrote: Francesco Mazzoli f at mazzo.li writes: At the end I gave up and I wrote the function myself: http://hpaste.org/43464/readbitmapfile cool ... the listed maintainer for the Xlib bindings is libraries at haskell.org. Perhaps you could prepare a patch and send it there? (does anyone know if there is an actual maintainer?) Conrad. I will send a patch, but I'm sure there must be a reason behind the fact that those functions were not included, even if I can't see it. Francesco. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Instancing Typeable for monad transformers?
One can do something a bit shorter instance (Typeable a, Typeable1 m) = Typeable1 (Iteratee a m) where typeOf1 i = mkTyConApp (mkTyCon Data.Enumerator.Iteratee) [typeOf a, typeOf1 m] where (a,m) = peel i peel :: Iteratee a m w - (a, m ()) peel = undefined still a bother to write every time one needs it, but tolerable. Only the signature of 'peel' matters. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: HackageOneFive: Reverse dependency lookup for all packages on Hackage
Hello, I wrote a tiny Snap app that provides reverse dependency lookup for all packages on Hackage. A git repository is at: https://github.com/sol/HackageOneFive Setup instructions are provide in the README[1] file. It uses a PostgreSQL database for storage but it should be trivial to port this to e.g. SQLite. As always feedback and patches are gladly welcome! btw: Is there still progress on Hackage 2.0? Cheers, Simon [1] https://github.com/sol/HackageOneFive#readme ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: HackageOneFive: Reverse dependency lookup for all packages on Hackage
On 2 February 2011 11:57, Simon Hengel simon.hen...@wiktory.org wrote: Hello, I wrote a tiny Snap app that provides reverse dependency lookup for all packages on Hackage. Are you familiar with Roel van Djik's revdep Hackage? http://bifunctor.homelinux.net/~roel/hackage/packages/hackage.html It's usually quite up to date, and very useful. btw: Is there still progress on Hackage 2.0? Last I heard was that Matt Gruen had done quite a lot of work on it in the last Summer of Code (see http://cogracenotes.wordpress.com/), but they haven't got around to actually deploying the new version - but that was a few months ago. Cheers, Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] http-enumerator: redirects, streaming and keep-alive
Hi all, There are a number of new feature requests for http-enumerator, and I wanted to discuss some possible API changes with everyone: * Allow keep-alive requests, which will reuse the same connection. * Allow client code to determine whether it accepts a server's SSL certificate. * Allow the request body to be an Enumerator so we can send large request bodies without using lazy IO. This is already implemented via streamingHttp, but it would make more sense to modify the Request datatype to replace L.ByteString with (Int, Enumerator ByteString IO ()). * Fix redirect behavior. It seems that the right thing to do is change a POST into a GET and remove the request body for a 303, and resend the same request for all other 3xx codes. However, when using an Enumerator for the request body, it is not guaranteed that we can resend an Enumerator. For addressing the last two, my plan is to: * Change the Request datatype as mentioned, but provide a convenience method for converting a lazy ByteString into a (Int, Enumerator ByteString IO ()). * Implement redirecting as I have described, and explain in the documentation that automatic redirecting can only work with Enumerators that can be run multiple times. AFAIK, this works with most standard Enumerators, such as enumFile, and with the helper function I will provide to convert lazy ByteStrings to Enumerators. * Remove streamingHttp, as it will no longer be necessary. As far as keep-alive goes, I still need to do a bit more research, but my basic idea (with credit to Bryan O'Sullivan): * http (and family) will all take an extra argument, Maybe Manager. * Manager will be an abstract type that will keep an MVar (Map (Host, Port, IsSecure) Socket). * If http is provided with a Manager, then it uses the Socket available in the Manager. If none is available, it creates a new Socket and places it in the Manager. * If http is *not* provided with a Manager, then it creates a new socket and closes it before returning. * There will be a newManager :: IO Manager, and a closeManager :: Manager - IO (), which closes all Sockets in the Manager and empties out the inner Map. Some open questions are: * Who is responsible to recover if a server is no longer responding on a Socket from the Manager: http or the client code? I would assume http. * I haven't fully thought through how this will work with secure connections: most likely in addition to storing the Socket in the Manager I will need to store some certificate data. And speaking of certificates, the main concern I have here is data types: since http-enumerator can use either tls or OpenSSL, there isn't a single certificate datatype I can use. If someone wants to help out and write some code to convert an OpenSSL X509 datatype into a Certificate from the certificate package (which tls uses), I will be very grateful. Assuming we had such a unified datatype, I would recommend changing Request's secure record to be Certificate - IO Bool, where returning True means the certificate is accepted and False means it is rejected. To get the current functionality of trusting any certificate, we would use (const $ return True). Any thoughts? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell function help
*can't -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-function-help-tp3365994p3368001.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell function help
I didn't write it like that...because since I'm using the dot notation I can specify aguments for the function...I rectified that...sorry I forgot to mention -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-function-help-tp3365994p3368000.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Gedit Haskell mode plugin indentation
Update. Current version: v0.8 Changelog: * Fixed some issues with nested lists --- ftp://neverb.net/soft/mine/gedit_haskell_mode/haskell_indentation-latest.tar.gz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell DPLL
One :Thank you Carsten Schultz,Daniel Fischer and all the other for your help. Two:After my last post I wrote some function that should help me in the future,but I need some help with the followint as I'm tired and have to fit in a schedule.I know it is long so I'll try and explain it as short and consice as I can. The DPLL procedure has two main stages: a simplification stage and a search stage. In the simplification stage, functions are applied to the formula to assign truth values to certain propositional variables. The simplifications are made because if there is a satisfying assignment for the simplified formula then it is also a satisfying assignment for the original formula. This reduces the need for search which can take a long time. The search stage is performed when no more simplifications can be made. In this stage a literal is chosen and is assigned true or false leading to two new branches in the search space. I wrote some function wich should be helpfull,but I have to fit in a schedule and I'm getting tired I need some additional help if possible. module Algorithm where import System.Random import Data.Maybe import Data.List type Atom = String type Literal = (Bool,Atom) type Clause = [Literal] type Formula = [Clause] type Model = [(Atom, Bool)] type Node = (Formula, ([Atom], Model)) -- This function takess a Clause and return the set of Atoms of that Clause. atomsClause :: Clause - [Atom] -- This function takes a Formula returns the set of Atoms of a Formula atoms :: Formula - [Atom] -- This function returns True if the given Literal can be found within -- the Clause. isLiteral :: Literal - Clause - Bool -- this function takes a Model and an Atom and flip the truthvalue of -- the atom in the model flipSymbol :: Model - Atom - Model -- is this ok? Additional functions that I wrote: remove :: (Eq a) )a -[a] -[a] -This function removes an item from a list. neg :: Literal-Literal -This function flips a literal (ie. from P to :P and from :P to P). falseClause :: Model - Clause - Bool -This function takes a Model and a Clause and returns True if the clause is unsatisfied by the model or False otherwise. falseClauses :: Formula - Model - [Clause] -This function takes a Formula and a Model and returns the list of clauses of the formula that are not satisfied. assignModel :: Model - Formula - Formula -This function applies the assign function for all the assignments of a given model. checkFormula :: Formula - Maybe Bool This function checks whether a formula can be decided to be satisfiable or unsatisfiable based on the effects of the assign function. satisfies :: Model - Formula -. Bool This function checks whether a model satisfies a formula. This is done with the combination of the assignModel and checkFormula functions. --Where do I need help: removeTautologies :: Formula-Formula This function should output a simplified formula if tautologies can be found in one or more clauses in the input Notes: If in a clause, a literal and its negation are found, it means that the clause will be true, regardless of the value finally assigned to that propositional variable. Consider the following example: (A v B v -A) ^ (B v C v A) The first clause contains the literals A and -A. This means that the clause will always be true, in which case it can be simplify the whole set to simply (B v C v A) (the second clause alone) pureLiteralDeletion :: Formula-Formula This function is suppose to implement a simplification step that assumes as true any atom in a formula that appears exclusively in a positive or negative form (not both). Consider the formula: (P v Q v R) ^ (P v Q v -R) ^ (-Q v R) Note that in this formula P is present but -P is not. Using Pure Literal Deletion it can be assumed that the value of P will be True thus simplifying the formula to (-Q v R). If the literal were false then the literal would simply be deleted from the clauses it appears in. In that case any satisfying model for the resulting formula would also be a satisfying model for the formula when we assume that the literal is true. Hence this simplification is sound in that if there is a solution to the simplified formula then there is a solution to the original formula. propagateUnits :: Formula-Formula If a clause in a propositional formula contains only one literal, then that literal must be true (so that the particular clause can be satisfied). When this happens,we can remove the unit clauses (the ones that contain only one literal), all the clauses where the literal appears and also, from the remaining clauses, we can delete the negation of the literal (because if P is true, -P will be false).For example, in the formula (P v Q v R) ^ (-P v Q v -R) ^ (P) we have one unit clause (the third clause(P) ). Because this
Re: [Haskell-cafe] Haskell DPLL
I didn't upload the code for the funtion I wrote because of the space...I ca do so If you require. -- View this message in context: http://haskell.1045720.n5.nabble.com/Haskell-DPLL-tp3368123p3368130.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Loading bitmap with xlib
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On 2/2/11 04:03 , Francesco Mazzoli wrote: Conrad Parker conrad at metadecks.org writes: On 31 January 2011 21:40, Francesco Mazzoli f at mazzo.li wrote: Francesco Mazzoli f at mazzo.li writes: At the end I gave up and I wrote the function myself: http://hpaste.org/43464/readbitmapfile cool ... the listed maintainer for the Xlib bindings is libraries at haskell.org. Perhaps you could prepare a patch and send it there? (does anyone know if there is an actual maintainer?) I will send a patch, but I'm sure there must be a reason behind the fact that those functions were not included, even if I can't see it. Pretty much what the comment says. Graphics.X11 was never really a complete set of bindings, just what people needed at the time. The Extras stuff in there was driven by xmonad development, for example (and named so because originally it was a separate library before it got folded in, so the module names were difficult to change while maintaining compatibility). Dealing with structs in the FFI is painful enough that I can easily imagine someone saying we don't need those, let someone else figure it out --- which you have done. Patch away. - -- brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.11 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk1Jq9cACgkQIn7hlCsL25XaJgCfc+CCngSmZlL9JOeZ21vZwkBO BHkAn128z1dH2entJKEfH6pKJ2Y7qW4w =LOMj -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] SYB: extending a generic reader with a type class
Dear -cafe, Is it possible to extend a generic reader (extR / ext1R from syb) with a type class? For example, let foo :: (Integral a) = SomeMonad a I could write: reader = ... `extR` (foo :: SomeMonad Int) `extR` (foo :: SomeMonad Integer) However, that is tedious. Could I do something like reader = ... `extR` foo and have it apply to all instances of Integral? I hope I am being clear. Thank you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] SYB: extending a generic reader with a type class
Hi, I don't think you can do that, since `ext` relies on Typeable and Typeable only works for monomorphic types. Cheers, Pedro On Wed, Feb 2, 2011 at 20:31, Sugar Bzzz sugarbz...@gmail.com wrote: Dear -cafe, Is it possible to extend a generic reader (extR / ext1R from syb) with a type class? For example, let foo :: (Integral a) = SomeMonad a I could write: reader = ... `extR` (foo :: SomeMonad Int) `extR` (foo :: SomeMonad Integer) However, that is tedious. Could I do something like reader = ... `extR` foo and have it apply to all instances of Integral? I hope I am being clear. Thank you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 11:57 AM, Michael Snoyman mich...@snoyman.com wrote: As far as keep-alive goes, I still need to do a bit more research, but my basic idea (with credit to Bryan O'Sullivan): * http (and family) will all take an extra argument, Maybe Manager. * Manager will be an abstract type that will keep an MVar (Map (Host, Port, IsSecure) Socket). * If http is provided with a Manager, then it uses the Socket available in the Manager. If none is available, it creates a new Socket and places it in the Manager. * If http is *not* provided with a Manager, then it creates a new socket and closes it before returning. * There will be a newManager :: IO Manager, and a closeManager :: Manager - IO (), which closes all Sockets in the Manager and empties out the inner Map. How about concurrent use of Manager? Should we do A) do m - newManager forM xs $ forkIO $ doSomething m B) forM xs $ forkIO $ do m - newManager doSomething m While B) should work with any sane Manager implementation, it is not optimal. If all your connections are to the same host, than both approaches are the same. But if access hosts O and P, for example, than it is possible that Manager m1 has an open connection to O, but you try connect to O using another Manager m2. That means that ideally we should support approach A) as well. However, to support A a simple Map inside an MVar isn't sufficient. Cheers! =) -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 10:15 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Wed, Feb 2, 2011 at 11:57 AM, Michael Snoyman mich...@snoyman.com wrote: As far as keep-alive goes, I still need to do a bit more research, but my basic idea (with credit to Bryan O'Sullivan): * http (and family) will all take an extra argument, Maybe Manager. * Manager will be an abstract type that will keep an MVar (Map (Host, Port, IsSecure) Socket). * If http is provided with a Manager, then it uses the Socket available in the Manager. If none is available, it creates a new Socket and places it in the Manager. * If http is *not* provided with a Manager, then it creates a new socket and closes it before returning. * There will be a newManager :: IO Manager, and a closeManager :: Manager - IO (), which closes all Sockets in the Manager and empties out the inner Map. How about concurrent use of Manager? Should we do A) do m - newManager forM xs $ forkIO $ doSomething m B) forM xs $ forkIO $ do m - newManager doSomething m While B) should work with any sane Manager implementation, it is not optimal. If all your connections are to the same host, than both approaches are the same. But if access hosts O and P, for example, than it is possible that Manager m1 has an open connection to O, but you try connect to O using another Manager m2. That means that ideally we should support approach A) as well. However, to support A a simple Map inside an MVar isn't sufficient. Good point: it should be a MVar (Map HostInfo (MVar Socket)) I think* Thanks, Michael * It's late here, just make sure I'm not saying something stupid ;). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 2:28 PM, Michael Snoyman mich...@snoyman.com wrote: On Wed, Feb 2, 2011 at 10:15 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Wed, Feb 2, 2011 at 11:57 AM, Michael Snoyman mich...@snoyman.com wrote: As far as keep-alive goes, I still need to do a bit more research, but my basic idea (with credit to Bryan O'Sullivan): * http (and family) will all take an extra argument, Maybe Manager. * Manager will be an abstract type that will keep an MVar (Map (Host, Port, IsSecure) Socket). * If http is provided with a Manager, then it uses the Socket available in the Manager. If none is available, it creates a new Socket and places it in the Manager. * If http is *not* provided with a Manager, then it creates a new socket and closes it before returning. * There will be a newManager :: IO Manager, and a closeManager :: Manager - IO (), which closes all Sockets in the Manager and empties out the inner Map. How about concurrent use of Manager? Should we do A) do m - newManager forM xs $ forkIO $ doSomething m B) forM xs $ forkIO $ do m - newManager doSomething m While B) should work with any sane Manager implementation, it is not optimal. If all your connections are to the same host, than both approaches are the same. But if access hosts O and P, for example, than it is possible that Manager m1 has an open connection to O, but you try connect to O using another Manager m2. That means that ideally we should support approach A) as well. However, to support A a simple Map inside an MVar isn't sufficient. Good point: it should be a MVar (Map HostInfo (MVar Socket)) I think* Or you could remove the socket from the map while it's in use. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 6:30 PM, Antoine Latter aslat...@gmail.com wrote: Or you could remove the socket from the map while it's in use. And what about connection limits? We shouldn't create a thousand connections to the same host =). -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] timely shutdown of timer threads
Interesting. I hadn't thought of this solution. You're forking the timer to yet a third thread so that if it continues waiting beyond the checkpoint thread shutdown it doesn't really matter. I guess that works as long as the main thread doesn't wait for all other threads to terminate before terminating the app. It still seems to me that haskell is lacking when it comes to operations that can wait for multiple conditions. Warren On Feb 1, 2011, at 6:25 PM, Albert Y. C. Lai wrote: On 11-02-01 02:58 PM, Warren Harris wrote: I have an application that forks a thread to run an activity on a timer. (The activity happens to be Berkeley DB checkpointing, but that's actually beside the point here.) The problem is that when the application wants to quit, I would like my main thread to be able to tell the timer thread to shut down in a timely way. However, I don't see a primitive in haskell that allows me to both wait for a timeout, or a notification. (If I were to do this in java, I would use wait/notify.) Use an MVar for signalling; use a two-valued data type to represent time-to-work or time-to-die. For extra correctness, use a second MVar to be notified that the child thread is really done --- because otherwise there would be the race condition of the child thread still in the middle of critical I/O when the program quits. import Control.Concurrent import Control.Exception(finally) data DoOrDie = Do | Die main = do v - newEmptyMVar finale - newEmptyMVar forkIO (timeloop v `finally` putMVar finale ()) putStrLn press enter to quit getLine putMVar v Die takeMVar finale timeloop v = run where run = do forkIO (threadDelay 1500 putMVar v Do) m - takeMVar v case m of Do - putStrLn checkpoint run Die - putStrLn checkmate ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 3:01 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Wed, Feb 2, 2011 at 6:30 PM, Antoine Latter aslat...@gmail.com wrote: Or you could remove the socket from the map while it's in use. And what about connection limits? We shouldn't create a thousand connections to the same host =). Not a bad idea, but that may be creeping outside the scope of the bug as reported. If you're writing a web-scraper/spider, it is true you might need some sort of higher-level manager to handle concurrent access. I'm not sure what that would look like, though -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] timely shutdown of timer threads
On Wed, Feb 2, 2011 at 10:42 PM, Warren Harris warrensomeb...@gmail.com wrote: Interesting. I hadn't thought of this solution. You're forking the timer to yet a third thread so that if it continues waiting beyond the checkpoint thread shutdown it doesn't really matter. I guess that works as long as the main thread doesn't wait for all other threads to terminate before terminating the app. It still seems to me that haskell is lacking when it comes to operations that can wait for multiple conditions. I think we can make waiting for both I/O activity and timers at the same time using the I/O manager. I will need to do this for my planned timeout support in the network package. Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] timely shutdown of timer threads
On Feb 2, 2011, at 2:02 PM, Johan Tibell wrote: On Wed, Feb 2, 2011 at 10:42 PM, Warren Harris warrensomeb...@gmail.com wrote: Interesting. I hadn't thought of this solution. You're forking the timer to yet a third thread so that if it continues waiting beyond the checkpoint thread shutdown it doesn't really matter. I guess that works as long as the main thread doesn't wait for all other threads to terminate before terminating the app. It still seems to me that haskell is lacking when it comes to operations that can wait for multiple conditions. I think we can make waiting for both I/O activity and timers at the same time using the I/O manager. I will need to do this for my planned timeout support in the network package. I could see wanting to wait for an MVar, timeout, IO activity, STM channels (anything that could block), all in the same event handler. (Rather like the old WaitForMultipleObjects on Windows.) This would also require a way to test each condition without blocking (MVar has this with tryTakeMVar, but it doesn't look like they all support it.) Warren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 167 - February 02, 2011
Welcome to issue 167 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of January 23 to 29, 2011. This week I've added a section which compiles a list of the top answers given in StackOverflow during the week. These seem to be of more interest to more experienced Haskell users than the newbie questions usually posted on the site. See what you think. Announcements R. Emre Basar [2]annouced the release of follower, a tool that allows you to follow people's tweets without having an account with Twitter. Alberto Ruiz [3]announced hmatrix version 0.11, a package for numerical computation based on LAPACK and SGL. Michael Snoyman [4]made some point updates for WAI and Warp. They fix some documentation issues, add some status aliases, make it possible to handle exceptions more easily, and make things more responsive on Windows. Antoine Latter [5]announced a minor point release for Parsec 3.1.0. John Meacham [6]announced version 0.7.7 of jhc is out! This release fixes a large number of bugs that cropped up when compiling haskell out in the wild as well as adds some more features. A major one being the garbage collector is enabled by default. Quotes of the Week * Twey: Maybe Bool: the Haskell equivalent to True/False/FileNotFound * elliott: Only two things in the universe are certain: Death, and two of the libraries you've decided to use taking different types of ByteString. * shapr: my personal heuristics judge Haskell as totally practical, perhaps too practical. * monochrom: the guys that I see when I look into the irc window believe that I'm just a bunch of text. * bernardh: Refactoring: spend a week to get where you were * Question: How do I use fix, and how does it work? Answer (by TomMD): The prank answer is fix has no real use, it's just there so you can type 'fix error' in ghci and feel good about yourself. Top Reddit Stories * Haskell at Bump Domain: devblog.bu.mp, Score: 44, Comments: 9 On Reddit: http://www.reddit.com/r/haskell/comments/f8cr8/haskell_at_bump/ Original: http://devblog.bu.mp/haskell-at-bump * How to write a simple TCP Server in Haskell Domain: catonmat.net, Score: 35, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/faa80/how_to_write_a_simple_tcp_server_in_haskell/ Original: http://catonmat.net/blog/simple-haskell-tcp-server * Snap Framework article in IEEE Internet Computing Domain: steve.vinoski.net, Score: 32, Comments: 1 On Reddit: http://www.reddit.com/r/haskell/comments/fa0e0/snap_framework_article_in_ieee_internet_computing/ Original: http://steve.vinoski.net/blog/2011/01/21/column-on-the-snap-framework/ * My Dream GHCi Session, Take 2 Domain: cdsmith.wordpress.com, Score: 23, Comments: 5 On Reddit: http://www.reddit.com/r/haskell/comments/f8im5/my_dream_ghci_session_take_2/ Original: http://cdsmith.wordpress.com/2011/01/24/my-dream-ghci-session-take-2/ * Text: a visual programming language based on Haskell, demo Domain: vimeo.com, Score: 20, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/fbgxd/text_a_visual_programming_language_based_on/ Original: http://vimeo.com/19273744 * Hoogle Embed Domain: neilmitchell.blogspot.com, Score: 16, Comments: 3 On Reddit: http://www.reddit.com/r/haskell/comments/f7iqa/hoogle_embed/ Original: http://neilmitchell.blogspot.com/2011/01/hoogle-embed.html * What does this mean for Haskell on Android? Domain: reddit.com, Score: 15, Comments: 12 On Reddit: http://www.reddit.com/r/haskell/comments/f9o67/what_does_this_mean_for_haskell_on_android/ Original: http://www.reddit.com/r/Android/comments/f97zh/google_not_happy_with_number_of_android_app/c1ebkji * Evolving a computer with Genprog (exercises from the TECS book) Domain: jpmoresmau.blogspot.com, Score: 13, Comments: On Reddit: http://www.reddit.com/r/haskell/comments/f7y6a/evolving_a_computer_with_genprog_exercises_from/ Original: http://jpmoresmau.blogspot.com/2011/01/evolving-computer-with-tecs-and-genprog.html * All about MVars : Inside T5 Domain: blog.ezyang.com, Score: 13, Comments: 4 On Reddit: http://www.reddit.com/r/haskell/comments/fduxb/all_about_mvars_inside_t5/ Original: http://blog.ezyang.com/2011/02/all-about-mvars/ * What textbooks would be useful to start approaching the low-hanging fruit on the ghc project? Domain: self.haskell, Score: 12, Comments: 8 On Reddit: http://www.reddit.com/r/haskell/comments/f8dm5/what_textbooks_would_be_useful_to_start/ Original: /r/haskell/comments/f8dm5/what_textbooks_would_be_useful_to_start/ Top StackOverflow Answers * What is an idiomatic way to add lists in Haskell? Votes: 14 Read on SO:
Re: [Haskell-cafe] timely shutdown of timer threads
On 11-02-02 04:42 PM, Warren Harris wrote: It still seems to me that haskell is lacking when it comes to operations that can wait for multiple conditions. STM opens the avenue to waiting for multiple conditions. import Control.Concurrent import Control.Concurrent.STM import Control.Exception(finally) data DoOrDie = Do | Die main = do die - atomically newEmptyTMVar finale - atomically newEmptyTMVar forkIO (timeloop die `finally` atomically (putTMVar finale ())) putStrLn press enter to quit getLine atomically (putTMVar die Die) atomically (takeTMVar finale) timeloop die = run where run = do w - atomically newEmptyTMVar i - forkIO (threadDelay 1500 atomically (putTMVar w Do)) r - atomically (takeTMVar w `orElse` takeTMVar die) case r of Do - putStrLn checkpoint run Die - killThread i putStrLn checkmate ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problems with iteratees
I'm working on a project that's using John Lato's old implementation of
iteratees (iteratee = 0.3.5 0.4; I'm hoping to migrate to 0.7
soon, but that's a ways off yet) and I'm running into some issues I
haven't been able to untangle. Maybe a new set of eyes can help...
The overarching program brings three things together for doing some
interprocess communication: the medium is Posix FIFOs, the messages
themselves are encoded with Google's Protocol Buffers[1], and the
control flow for getting and processing the messages is handled by
iteratees. The error message indicates iteratees are at fault, though it
could be an error elsewhere instead.
First, some boilerplate.
-- For messageWithLengthEnumeratee only
{-# LANGUAGE ScopedTypeVariables #-}
import qualified Text.ProtocolBuffers.Reflections as R
import qualified Text.ProtocolBuffers.WireMessage as W
import qualified Text.ProtocolBuffers.Get as G
import qualified Data.ByteString as S
import qualified Data.ByteString.Lazy as L
import qualified Data.Iterateeas I
import Data.Iteratee.WrappedByteString
import Data.Word(Word8)
import Control.Monad(liftM)
-- | Return a final value, and the remainder of the stream.
idone :: a - c el - I.IterGV c el m a
idone a xs = I.Done a (I.Chunk xs)
{-# INLINE idone #-}
-- | Convert a continuation into 'I.IterGV'.
icontinue
:: (I.StreamG c el - m (I.IterGV c el m a))
- I.IterGV c el m a
icontinue k = I.Cont (I.IterateeG k) Nothing
{-# INLINE icontinue #-}
-- | Throw an error message.
ifail :: (Monad m) = String - I.IterGV c el m a
ifail msg = ierror (I.Err msg)
{-# INLINE ifail #-}
-- | An 'I.IterGV' variant of 'I.throwErr'.
ierror :: (Monad m) = I.ErrMsg - I.IterGV c el m a
ierror err = I.Cont (I.throwErr err) (Just err)
{-# INLINE ierror #-}
toLazyBS :: S.ByteString - L.ByteString
toLazyBS = L.fromChunks . (:[])
{-# INLINE toLazyBS #-}
toStrictBS :: L.ByteString - S.ByteString
toStrictBS = S.concat . L.toChunks
{-# INLINE toStrictBS #-}
Now we have the code for converting the Get monad used by protocol
buffers into an iteratee. This should be correct, and it's pretty
straightforward.
-- | Convert a 'G.Result' iteratee state into a 'I.IterGV'
-- iteratee state.
result2iterv
:: (Monad m)
= G.Result a
- I.IterGV WrappedByteString Word8 m a
result2iterv (G.Finished rest _ a) = idone a (WrapBS $ toStrictBS rest)
result2iterv (G.Failed _ msg) = ifail msg
result2iterv (G.Partial k) = I.Cont (iterify k) Nothing
-- | Convert a protobuf-style continuation into an
-- iteratee-style continuation.
iterify
:: (Monad m)
= (Maybe L.ByteString - G.Result a)
- I.IterateeG WrappedByteString Word8 m a
iterify k =
I.IterateeG $ \s - return $!
case s of
I.Chunk (WrapBS xs) - result2iterv $ k (Just $ toLazyBS xs)
I.EOF Nothing - result2iterv $ k Nothing
I.EOF (Just err)- ierror err
-- | A variant of 'G.runGet' as an iteratee.
runGetIteratee
:: (Monad m, R.ReflectDescriptor a, W.Wire a)
= G.Get a
- I.IterateeG WrappedByteString Word8 m a
runGetIteratee g =
I.IterateeG $ \s - return $!
case s of
I.Chunk (WrapBS xs) - result2iterv $ G.runGet g (toLazyBS xs)
I.EOF Nothing - result2iterv $ G.runGet g L.empty
I.EOF (Just err)- ierror err
Okay, now we have an iteratee which consumes a stream of bytestrings and
will render a protocol buffer message. But what we really want is an
enumeratee to do this repeatedly so we can use an iteratee to consume
the stream of messages. I have the following definition which
typechecks, but doesn't seem to work. The call to convStream seems like
it always hangs:
-- | A variant of 'G.runGet' as an enumeratee.
runGetEnumeratee
:: (Monad m, R.ReflectDescriptor a, W.Wire a)
= G.Get a
- I.EnumeratorN WrappedByteString Word8 [] a m b
runGetEnumeratee =
I.convStream . liftM (Just . (:[])) . runGetIteratee
Once we have a working definition of runGetEnumeratee, then we can
define the specific enumeratee we need:
-- | An enumeratee for converting bytestrings into protocol
-- buffer messages.
messageWithLengthEnumeratee
:: forall m msg a
. (Monad m, R.ReflectDescriptor msg, W.Wire msg)
= I.EnumeratorN WrappedByteString Word8 [] msg m a
messageWithLengthEnumeratee =
runGetEnumeratee (W.messageWithLengthGetM :: G.Get msg)
And then at the use site we have the following:
let processRequest = ... :: msg - IO ()
I.run -- run
Re: [Haskell-cafe] Inheritance and Wrappers
OK, what about this as a use case then. I want to create a type class 'Term' with only one function in it. The function returns a 'termTag' which labels the kind of a value in a DSL. class Term a where termTag :: a - String A user of this type-class can happily provide an instance without any other type class requirement. However, I want those types which are instances of Data to be an instance of Term automatically. On top of that, I don't want to stop the user from creating a special instance for their data type. I want to be able to write the following instance to accomplish that: instance Data t = Term t where termTag = show . toConstr A much more predictable option is to provide this default implementation as a function termTagData :: (Data t) = (t - String) and let the library clients use it in their instances if the behavior is fine: instance Term MyT where termTag = termTagData And if the user wants to write a more specific instance, they should be welcome to do so: instance Term UserDT where termTag (...) = ... I am not very much interested in the technical details about how things currently are, I am more interested in a discussion about why (if?) this would be considered a design flaw? Here's one thing to consider: Can you write a function f :: (Data a) = a - String f x = termTag x It would seem the Data a = Term a instance justifies this function, and it will always use the default instance. Now, what happens if f is applied to a value of some type T which is an instance of Data, but has a custom Term instance? Brandon. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with iteratees
I think the problem is that the iteratee you give to I.convStream
always returns Just [something] while you should return Nothing on
EOF.
Suppose you want to have an enumeratee that adds 1 to each integer in
the stream and then use stream2list to get an iteratee that consumes
the result stream and returns it as a list:
let iter = joinI $ (convStream (head = return . Just . (:[]) . (+1)))
stream2list :: IterateeG [] Int IO [Int]
run iter
*** Exception: control message: Just (Err EOF)
Note that run simply passes EOF to iter and extracts the result.
Instead of throwing an error the code above should produce an [] (i.e.
no stream to consume, no elements in the list). This can be fixed by
checking whether the stream is empty:
let iter = joinI $ (convStream (isFinished = maybe (head = return . Just
. (:[]) . (+1)) (\_ - return Nothing))) stream2list :: IterateeG [] Int IO
[Int]
run iter
[]
I think you should do the same in your code:
runGetEnumeratee get =
I.convStream $ isFinished = maybe convIter (\_ - return Nothing)
where
convIter = (Just . return) `liftM` (runGetIteratee get)
When the stream is not empty, it runs (runGetIteratee get) and returns
its result wrapped in Just . (:[]). When the stream is empty, it
returns Nothing so convStream knows it is done.
-- Maciej
On Thu, Feb 3, 2011 at 10:06 AM, wren ng thornton w...@freegeek.org wrote:
I'm working on a project that's using John Lato's old implementation of
iteratees (iteratee = 0.3.5 0.4; I'm hoping to migrate to 0.7 soon,
but that's a ways off yet) and I'm running into some issues I haven't been
able to untangle. Maybe a new set of eyes can help...
The overarching program brings three things together for doing some
interprocess communication: the medium is Posix FIFOs, the messages
themselves are encoded with Google's Protocol Buffers[1], and the control
flow for getting and processing the messages is handled by iteratees. The
error message indicates iteratees are at fault, though it could be an error
elsewhere instead.
First, some boilerplate.
-- For messageWithLengthEnumeratee only
{-# LANGUAGE ScopedTypeVariables #-}
import qualified Text.ProtocolBuffers.Reflections as R
import qualified Text.ProtocolBuffers.WireMessage as W
import qualified Text.ProtocolBuffers.Get as G
import qualified Data.ByteString as S
import qualified Data.ByteString.Lazy as L
import qualified Data.Iteratee as I
import Data.Iteratee.WrappedByteString
import Data.Word (Word8)
import Control.Monad (liftM)
-- | Return a final value, and the remainder of the stream.
idone :: a - c el - I.IterGV c el m a
idone a xs = I.Done a (I.Chunk xs)
{-# INLINE idone #-}
-- | Convert a continuation into 'I.IterGV'.
icontinue
:: (I.StreamG c el - m (I.IterGV c el m a))
- I.IterGV c el m a
icontinue k = I.Cont (I.IterateeG k) Nothing
{-# INLINE icontinue #-}
-- | Throw an error message.
ifail :: (Monad m) = String - I.IterGV c el m a
ifail msg = ierror (I.Err msg)
{-# INLINE ifail #-}
-- | An 'I.IterGV' variant of 'I.throwErr'.
ierror :: (Monad m) = I.ErrMsg - I.IterGV c el m a
ierror err = I.Cont (I.throwErr err) (Just err)
{-# INLINE ierror #-}
toLazyBS :: S.ByteString - L.ByteString
toLazyBS = L.fromChunks . (:[])
{-# INLINE toLazyBS #-}
toStrictBS :: L.ByteString - S.ByteString
toStrictBS = S.concat . L.toChunks
{-# INLINE toStrictBS #-}
Now we have the code for converting the Get monad used by protocol buffers
into an iteratee. This should be correct, and it's pretty straightforward.
-- | Convert a 'G.Result' iteratee state into a 'I.IterGV'
-- iteratee state.
result2iterv
:: (Monad m)
= G.Result a
- I.IterGV WrappedByteString Word8 m a
result2iterv (G.Finished rest _ a) = idone a (WrapBS $ toStrictBS rest)
result2iterv (G.Failed _ msg) = ifail msg
result2iterv (G.Partial k) = I.Cont (iterify k) Nothing
-- | Convert a protobuf-style continuation into an
-- iteratee-style continuation.
iterify
:: (Monad m)
= (Maybe L.ByteString - G.Result a)
- I.IterateeG WrappedByteString Word8 m a
iterify k =
I.IterateeG $ \s - return $!
case s of
I.Chunk (WrapBS xs) - result2iterv $ k (Just $ toLazyBS xs)
I.EOF Nothing - result2iterv $ k Nothing
I.EOF (Just err) - ierror err
-- | A variant of 'G.runGet' as an iteratee.
runGetIteratee
:: (Monad m, R.ReflectDescriptor a, W.Wire a)
= G.Get a
- I.IterateeG WrappedByteString Word8 m a
runGetIteratee g =
I.IterateeG $ \s - return $!
case s of
I.Chunk (WrapBS xs) - result2iterv $ G.runGet
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Thu, Feb 3, 2011 at 12:00 AM, Antoine Latter aslat...@gmail.com wrote: On Wed, Feb 2, 2011 at 3:01 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Wed, Feb 2, 2011 at 6:30 PM, Antoine Latter aslat...@gmail.com wrote: Or you could remove the socket from the map while it's in use. And what about connection limits? We shouldn't create a thousand connections to the same host =). Not a bad idea, but that may be creeping outside the scope of the bug as reported. If you're writing a web-scraper/spider, it is true you might need some sort of higher-level manager to handle concurrent access. I'm not sure what that would look like, though -- Felipe. I think Felipe's point is that using the approach I outlined, we will never spawn more than one connection to a single host. By simply taking the socket out of the map, there's no limit to the number of sockets that will be created. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] http-enumerator: redirects, streaming and keep-alive
On Wed, Feb 2, 2011 at 11:06 PM, Michael Snoyman mich...@snoyman.com wrote: On Thu, Feb 3, 2011 at 12:00 AM, Antoine Latter aslat...@gmail.com wrote: On Wed, Feb 2, 2011 at 3:01 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Wed, Feb 2, 2011 at 6:30 PM, Antoine Latter aslat...@gmail.com wrote: Or you could remove the socket from the map while it's in use. And what about connection limits? We shouldn't create a thousand connections to the same host =). Not a bad idea, but that may be creeping outside the scope of the bug as reported. If you're writing a web-scraper/spider, it is true you might need some sort of higher-level manager to handle concurrent access. I'm not sure what that would look like, though -- Felipe. I think Felipe's point is that using the approach I outlined, we will never spawn more than one connection to a single host. By simply taking the socket out of the map, there's no limit to the number of sockets that will be created. Ah, then you would block one thread on another if the host info is in the map? I get it. Strictly one socket per host might be a tricky invariant to maintain - you'd have to insert an empty socket MVar in the map on lookup failure, and the shuffling of the nested MVars seems tricky off the top of my head. But even without all of that I don't think you'd be flooding the host any more than without any keepalive support, which was what I was getting at. This is just speculation on my part - I don't have a stake in this, it just sounded like an interesting problem. I'd hate to be steering this into a design black hole. Antoine Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Another Question
hi , I am stuck in the following problem. I am maintaining a list of tuples of the form ([Char],Int,Int, Int,Int) . The purpose of maintaining the tuples is that the program reads from a file line by line , Matches the contents with the first element of the tuple and updates the tuple respectively. The precise function I am using is as follows tupup::Bool-[Char]-Int-Int-Int-Int-Char-([Char],Int,Int,Int,Int) tupup val elf els elr ell elx ys= if val then case ys of 'A' - (elf, els+1,elr,ell,elx) 'G' - (elf,els, elr +1,ell,elx) 'C' - (elf,els,elr, ell +1,elx) 'T' - (elf,els,elr,ell, elx +1) else (elf,els,elr,ell,elx) uptable::[[Char]]-[([Char],Int,Int,Int,Int)]-[([Char],Int,Int,Int,Int)] uptable (xf:xs) main_array = map (\(x,y,z,r,t)- tupup (x==xf) x y z r t (secvalue xs) ) main_array It gives the error ERROR - Control stack overflow. I assume it is because of the lazy evaluation . Is there a way to enforce strict evaluation only for the function tupup. Thanks, Navin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
