Re: [Haskell-cafe] how to implement daemon start and stop directives?
You can abstract this pattern: -- runs its argument in an infinite loop, and returns an action that stops the loop daemon :: IO () - IO (IO ()) daemon action = do stopvar - atomically $ newTVar False let run = do stop - atomically $ readTVar stopvar if stop then return () else (action run) forkIO run return (atomically $ writeTVar stopvar True) TVars are overkill here, actually, an IORef would be just fine, I think. Luke Thanks, Luke! Why do you write return (atomically $ writeTVar stopvar True) in the end? Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe... Belka -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp21598690p21599567.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] A pattern type signature cannot bind scoped type variables `t'
On Mon, 2009-01-12 at 20:24 -0200, rodrigo.bonifacio wrote: Hi all, I'm trying to build a library that has the following code: hasTypeOf (TermRep (dx,_,_)) (x::t) = ((fromDynamic dx)::Maybe t) Could you do something like this? Enforce the types with a signature: hasTypeOf :: (Typeable t) = Dynamic - t - Maybe t hasTypeOf x _ = fromDynamic x hasTypeOf (toDyn (2::Int)) (undefined::Integer) Nothing hasTypeOf (toDyn (2::Int)) (undefined::Int) Just 2 Or if you just want boolean result: hasTypeOf x y = typeOf y == dynTypeRep x rcmAttmntN3MDzg Description: micalg/pgp-sha1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to implement daemon start and stop directives?
Although I am not Luke, I will answer :) The code creates a TVar 'stopvar', whose truth means to the 'run' loop that it's time to return (). So, if we're going to return an action that stops the loop, we're going to return an action that sets stopvar to True. That's precisely what return (atomically $ writeTVar stopvar True) does. In case you're wondering about the atomically, it's because writeTVar has type STM () and whereas we need to 'return' an IO (). For precisely the same reason is atomically present in the run loop, since the loop is also in the IO monad. 2009/1/22 Belka lambda-be...@yandex.ru: You can abstract this pattern: -- runs its argument in an infinite loop, and returns an action that stops the loop daemon :: IO () - IO (IO ()) daemon action = do stopvar - atomically $ newTVar False let run = do stop - atomically $ readTVar stopvar if stop then return () else (action run) forkIO run return (atomically $ writeTVar stopvar True) TVars are overkill here, actually, an IORef would be just fine, I think. Luke Thanks, Luke! Why do you write return (atomically $ writeTVar stopvar True) in the end? Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe... Belka -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp21598690p21599567.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 -- Евгений Кирпичев Разработчик Яндекс.Маркета ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: tensor product of dynamic-sized bits
* Ahn, Ki Yung wrote: This is why I am looking for existing work, because I am not yet very sure about my code I'm using. http://www.galois.com/technology/communications_security ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal.exe is available from http://haskell.org/~duncan/cabal/, but is not included in the latest cabal-install tool (version 0.6.0).
I just tried to install the cabal-install tool (version 0.6.0) (see http://www.haskell.org/cabal/download.html) on Windows XP, Service Pack 2, but when I followed the instructions on the download page and downloaded cabal-install-0.6.0.tar.gz, the gunzipped untarred cabal-install-0.6.0 directory did not include cabal.exe. Further, according to the bundled README file: Quickstart on Windows systems - For Windows users we hope to provide a pre-compiled `cabal.exe` program shortly. In the mean time you have to build the three dependencies in [the standard way]. [the standard way]: http://haskell.org/haskellwiki/Cabal/How_to_install_a_Cabal_package Running the bundled bootstrap.sh file in Cygwin resulted in an installation error. However, when I then visited the above-mentioned HaskellWiki page, I discovered that cabal.exe, in fact, already existed: ... Windows users can download a binary (cabal.exe) from here. (Here currently references http://haskell.org/~duncan/cabal/.) Apparently, this cabal.exe file is in fact the complete cabal-install tool (version 0.6.0) itself: (After adding the cabal.exe installation directory to the path:) C:\Documents and Settings\Benjamincabal --version cabal-install version 0.6.0 using version 1.6.0.1 of the Cabal library To facilitate installation for Windows users, perhaps cabal.exe should be bundled with cabal-install-0.6.0.tar.gz, and the README file updated? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] GLUT (glutGet undefined reference)
Thanks Kazuya, that link is perfect. Basically, I have to explicitly add -lglut : ghc -package GLUT -lglut HelloWorld.hs -o HelloWorld Great. GLUT (and now FreeGLUT) remains the simplest and most reliable standard cross-platform OpenGL windowing API. (It seems from the link that the information used by ghc-pkg is wrong, and stems from the GLUT package's relationship to libraries known as Xmu and Xi.) Cheers, Paul -Original Message- From: Kazuya Sakakihara [mailto:kaz...@gmail.com] Sent: Thu 22/01/2009 02:14 To: Paul Keir Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] GLUT (glutGet undefined reference)[MESSAGE NOT SCANNED] Check this thread: http://groups.google.com/group/fa.haskell/browse_thread/thread/1716fa5e5643541e/38373ec65e2537fd?lnk=gst Kazuya 2009/1/20 Paul Keir pk...@dcs.gla.ac.uk: Hi all, I was hoping to introduce my old pal OpenGL with my new chum, Haskell. I used cabal to install GLUT on my 64-bit Ubuntu machine with GHC 6.8.2 (installed via apt-get/synaptic). I followed the wiki OpenGLTutorial1 until: ghc -package GLUT HelloWorld.hs -o HelloWorld at which point my screen is filled with errors. The errors begin with: /home/paul/.cabal/lib/GLUT-2.1.1.2/ghc-6.8.2/libHSGLUT-2.1.1.2.a(Begin.o): In function `szEn_info': (.text+0x26c): undefined reference to `glutGet' This surprised me a little because I've already seen these same errors recently on two separate Windows boxes. Somehow I'd got the idea it was (on Windows) due to installing from a binary; though I guess the story is the same with apt-get. Should I look for an apt-get switch to reinstall GHC from source instead? Regards, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: how to implement daemon start and stop directives?
Luke Palmer lrpal...@gmail.com wrote: TVars are overkill here, actually, an IORef would be just fine, I think. Using IORefs is generally a sign of bad style. But MVars would perfectly suffice here. They would be essentially the same, but without 'atomically'. Greets, Ertugrul. -- nightmare = unsafePerformIO (getWrongWife = sex) http://blog.ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to implement daemon start and stop directives?
On Thu, Jan 22, 2009 at 8:11 AM, Belka lambda-be...@yandex.ru wrote: You can abstract this pattern: -- runs its argument in an infinite loop, and returns an action that stops the loop daemon :: IO () - IO (IO ()) daemon action = do stopvar - atomically $ newTVar False let run = do stop - atomically $ readTVar stopvar if stop then return () else (action run) forkIO run return (atomically $ writeTVar stopvar True) TVars are overkill here, actually, an IORef would be just fine, I think. Luke Thanks, Luke! Why do you write return (atomically $ writeTVar stopvar True) in the end? Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe... I think you should follow Unix standards in this case. So depending on what you kind of communication you are looking for you have different options (this is based on my understanding of the Unix way): * Signals - for simple control, such as getting the daemon to stop, reread its configuration, or restart * Pipe/Socket - for more complex control such as job control /M -- Magnus Therning(OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: how to implement daemon start and stop directives?
On Thu, Jan 22, 2009 at 5:48 AM, Ertugrul Soeylemez e...@ertes.de wrote: Luke Palmer lrpal...@gmail.com wrote: TVars are overkill here, actually, an IORef would be just fine, I think. Using IORefs is generally a sign of bad style. I totally disagree. The disadvantage of IORefs is that they do not work together very nicely. If you have more than one, it is very hard (impossible) to keep multithreaded invariants between them. But in this case, the IORef is completely encapsulated: it does not leave the scope in which it was created. You will never have to use it with any other IORef, because nobody else even knows it exists. The pattern is self-contained and threadsafe with just an IORef. A program that needs only IORefs and is threadsafe is *good* style to me, because it means all the state is well-encapsulated (if it escaped, it would fail to be threadsafe). Luke But MVars would perfectly suffice here. They would be essentially the same, but without 'atomically'. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Big endian vs little endian in Haskell land?
Sure, I've had to deal with this frequently. Luckily, Data.Binary has functions like getWord32be, putWord64le, etc. I've never had any problems and typically don't worry about the wire format after making the Binary instances. Or, if your question was what types of programs might be concerned you can include any program that writes data to a file where the file might be read on a different system and networking programs, obviously. Tom 2009/1/22 Galchin, Vasili vigalc...@gmail.com: Hello, Are there applications that have to deal with both(!!!) big endian and little endian on persistent store?? I.e. when marshalling out and unmarshalling in endian-ness has to be considered?? Regards, Vasili ___ 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] Cabal.exe is available from http://haskell.org/~duncan/cabal/, but is not included in the latest cabal-install tool (version 0.6.0).
On Thu, 2009-01-22 at 18:38 +0900, Benjamin L.Russell wrote: To facilitate installation for Windows users, perhaps cabal.exe should be bundled with cabal-install-0.6.0.tar.gz, and the README file updated? I will mention it in the README for the next release. As it happens the new bootstrap.sh also works if you've got mingw/cygwin and wget/curl. I did not have access to a Windows machine at the time I made the previous release, so the cabal.exe was not available at the time. Also it was a bit experimental at the time, not many people had tested it on Windows. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re: [Haskell-cafe] How to make code least strict?
Thomas Davie wrote: Further to all the playing with unamb to get some very cool behaviors, you might want to look at Olaf Chitil's paper here: http://www.cs.kent.ac.uk/pubs/2006/2477/index.html It outlines a tool for checking if your programs are as non-strict as they can be. We have discussed StrictCheck on the thread Maintaining Laziness which also covered the topic least strictness but wasn't as popular as this one. I have put up a page with functions from Data.List which are not least strict. I want to extend this with other examples from standard libraries. The page can be found at http://www.informatik.uni-kiel.de/~jac/strictcheck/. Jan -- View this message in context: http://www.nabble.com/How-to-make-code-least-strict--tp21546891p21604665.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] Why monoids will abide...
On Wed, Jan 21, 2009 at 11:12 PM, Eugene Kirpichov ekirpic...@gmail.com wrote: To my mind, in the map-reduce case you generally need a commutative monoid. Or, you need an extra infrastructure that mappend's only results from adjacent machines, or something like that. This is a good paper on the stuff I'm talking about: http://citeseer.ist.psu.edu/blelloch90prefix.html It doesn't explicitly mention monoids but it's all about associative operations with identity. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why monoids will abide...
See, that's the kind of name we need! StructureWithAssociativeOperationAndIdentity -- make both the mathematicians AND the non-mathematicians mad! On Thu, Jan 22, 2009 at 9:53 AM, Dan Piponi dpip...@gmail.com wrote: On Wed, Jan 21, 2009 at 11:12 PM, Eugene Kirpichov ekirpic...@gmail.com wrote: To my mind, in the map-reduce case you generally need a commutative monoid. Or, you need an extra infrastructure that mappend's only results from adjacent machines, or something like that. This is a good paper on the stuff I'm talking about: http://citeseer.ist.psu.edu/blelloch90prefix.html It doesn't explicitly mention monoids but it's all about associative operations with identity. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monoids and newtypes
One wart that was briefly mentioned during the Great Monoid Naming
Thread of 2009 is the need to wrap types in newtypes to provide multiple
instances of the same class with different semantics -- the archetypical
example being Integer as a monoid over addition as well as
multiplication.
I was just wondering if not phantom types might serve here as an
alternative way to go about that. Here's a small example illustrating
it:
{-# LANGUAGE EmptyDataDecls #-}
{-# LANGUAGE FlexibleInstances #-}
module Monoids where
import Data.Monoid
data Foo a = Foo Integer deriving (Show, Eq)
data Additive
data Multiplicative
instance Monoid (Foo Additive) where
mappend (Foo x) (Foo y) = Foo (x+y)
mempty = Foo 0
instance Monoid (Foo Multiplicative) where
mappend (Foo x) (Foo y) = Foo (x*y)
mempty = Foo 1
instance Num (Foo a) where
fromInteger x = Foo x
Foo x + Foo y = Foo (x+y)
Foo x * Foo y = Foo (x*y)
signum (Foo x) = Foo (signum x)
Loading this into ghci, you get:
*Monoids mconcat [1,2]
interactive:1:0:
Ambiguous type variable `t' in the constraints:
`Monoid t' arising from a use of `mconcat' at interactive:1:0-12
`Num t' arising from the literal `2' at interactive:1:11
Probable fix: add a type signature that fixes these type variable(s)
*Monoids mconcat [1,2::Foo Additive]
Foo 3
*Monoids mconcat [1,2::Foo Multiplicative]
Foo 2
(This can of course be prettified a bit by omitting the constructor
from the Show instance).
Any thought about this, pro/contra the newtype method?
-k
--
If I haven't seen further, it is by standing in the footprints of giants
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why monoids will abide...
On Thu, Jan 22, 2009 at 06:53:24AM -0800, Dan Piponi wrote: On Wed, Jan 21, 2009 at 11:12 PM, Eugene Kirpichov ekirpic...@gmail.com wrote: To my mind, in the map-reduce case you generally need a commutative monoid. Or, you need an extra infrastructure that mappend's only results from adjacent machines, or something like that. This is a good paper on the stuff I'm talking about: http://citeseer.ist.psu.edu/blelloch90prefix.html It doesn't explicitly mention monoids but it's all about associative operations with identity. Indeed, the parallel scan algorithm over an arbitrary monoid (originally due to Ladner and Fischer) was one of the inspirations for the use of monoids in the fingertree paper. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why monoids will abide...
Thanks; I saw you mention the paper before, but now I finally started reading it :) By the way, the paper *does* arrange an extra infrastructure for mappending only adjacent results. Looks like with a commutative monoid, a fold could be done in a fully distributed fashion, however it would no more be a scan. 2009/1/22 Dan Piponi dpip...@gmail.com: On Wed, Jan 21, 2009 at 11:12 PM, Eugene Kirpichov ekirpic...@gmail.com wrote: To my mind, in the map-reduce case you generally need a commutative monoid. Or, you need an extra infrastructure that mappend's only results from adjacent machines, or something like that. This is a good paper on the stuff I'm talking about: http://citeseer.ist.psu.edu/blelloch90prefix.html It doesn't explicitly mention monoids but it's all about associative operations with identity. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: how to implement daemon start and stop directives?
Luke Palmer lrpal...@gmail.com wrote: On Thu, Jan 22, 2009 at 5:48 AM, Ertugrul Soeylemez e...@ertes.de wrote: Luke Palmer lrpal...@gmail.com wrote: TVars are overkill here, actually, an IORef would be just fine, I think. Using IORefs is generally a sign of bad style. I totally disagree. The disadvantage of IORefs is that they do not work together very nicely. If you have more than one, it is very hard (impossible) to keep multithreaded invariants between them. But in this case, the IORef is completely encapsulated: it does not leave the scope in which it was created. You will never have to use it with any other IORef, because nobody else even knows it exists. The pattern is self-contained and threadsafe with just an IORef. A program that needs only IORefs and is threadsafe is *good* style to me, because it means all the state is well-encapsulated (if it escaped, it would fail to be threadsafe). That's not my point. The use of IORefs indicates an imperative programming style. Sometimes this is inevitable, but I've never seen a case, where IORefs couldn't be replaced by a more elegant State/StateT-based solution. And if you need to do multi-threading, Chans, MVars and semaphores are better anyway. There is no reason to prefer an IORef over an MVar to signal something to another thread. By the way, IORefs are by themselves not thread-safe. You need to use a special function, when using it in a multi-threaded manner. Greets, Ertugrul. -- nightmare = unsafePerformIO (getWrongWife = sex) http://blog.ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: how to implement daemon start and stop directives?
On Thu, Jan 22, 2009 at 9:04 AM, Ertugrul Soeylemez e...@ertes.de wrote: A program that needs only IORefs and is threadsafe is *good* style to me, because it means all the state is well-encapsulated (if it escaped, it would fail to be threadsafe). That's not my point. The use of IORefs indicates an imperative programming style. Um, we were talking about IORefs vs. MVars or TVars. I thought we were already firmly in the imperative world. Nobody on this list will argue against a pure solution always being preferable. Sometimes this is inevitable, but I've never seen a case, where IORefs couldn't be replaced by a more elegant State/StateT-based solution. And if you need to do multi-threading, Chans, MVars and semaphores are better anyway. Please define better. For the function in question, what advantages do they give us? Just to be clear, I wouldn't dare argue that IORefs can do everything MVars and TVars can do. I'm just perplexed why you say MVars and TVars are better, when an IORef does the trick just fine for our function. There is no reason to prefer an IORef over an MVar to signal something to another thread. Well, I usually don't go here, but benchmarks show that IORefs are the fastest of any of the mutable variable primitives, by at least a factor of 2. I wish I remembered where I saw that. By the way, IORefs are by themselves not thread-safe. You need to use a special function, when using it in a multi-threaded manner. You mean atomicModifyIORef? IORefs *are* thread-safe by themselves: you will not make your program segfault by using them in a multithreaded program. So it all comes down to invariants. IORefs have no synchronization concepts, so code like: x - readIORef ref writeIORef ref (x+1) Is not threadsafe by most standards. That doesn't mean IORefs themselves are not threadsafe, just that you have to be careful how you use them. And I will reiterate: *in this case* the use of IORef is fully encapsulated in this function and *is threadsafe!* Which is the basis of my argument: in imperative code, when you can limit the scope of an IORef to a small abstraction that is threadsafe, there is no advantage of TVars or MVars over them. I don't think they deserve bad style sledgehammer. (An instance of use the right tool for the job) daemon :: IO () - IO (IO ()) daemon action = do stopvar - newIORef False let run = do stop - readIORef stopvar if stop then return () else (action run) forkIO run return (writeIORef stopvar True) Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pure Haskell implementation of Float type?
Lennart Augustsson schrieb: There's the numbers package which contains BigFloat. You can pick your own precision, but it's not IEEE. It's actually base 10 floats which makes it more fun (actually, the iEEE standard will cover base 10 floats in the future). Actually, all of the arbitrary precision real number implementations may be of interest for you: http://haskell.org/haskellwiki/Applications_and_libraries/Mathematics#Number_representations The NumericPrelude implementation by me, however, sometimes uses the Double implementation for speedup. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Does readFile /proc/mounts hang for you?
On Wed, Jan 21, 2009 at 9:20 AM, David Fox dds...@gmail.com wrote: I posted a bug about this (http://hackage.haskell.org/trac/ghc/ticket/2971) but its so odd I had to ask here. Using ghc 6.10.1, both readFile /proc/mounts and Data.ByteString.Lazy.Char8.readFile /proc/mounts hang on an amd64 machine running Linux. Also, Data.ByteString.readFile /proc/mounts returns the empty string. Is this behavior present for others? On i386? I can now confirm that this bug also affects the i386 architecture. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Elegant external sorting
Hello haskell-cafe, SPJ asked us a few years ago about examples of simple and elegant haskell programs. i want to propose this external sorting program: it reads stdin in chunks of 5000 lines, writes sorted chunks into files and then merges files together: import Data.List import Control.Monad import Control.Arrow main = do -- (Lazily) create sorted sublists sublists - fmap chop_and_sort getContents -- Write the sublists into files named 1..n n - fmap length $ zipWithM writeFile (map show [1..]) sublists -- Read (again lazily) contents of these files sublists - mapM (fmap lines.readFile.show) [1..n] -- Merge them and write result to stdout putStr (unlines (merge_lists compare sublists)) -- Split input list into 5000-line chunks and sort them chop_and_sort = lines recursive (splitAt 5000) map (sortunlines) -- unfoldr variant that stops on empty list recursive splitFunc = unfoldr (\xs - guard (xs[]) Just (splitFunc xs)) -- Merging sorted lists (kidnapped from Data.List) merge_lists :: (a - a - Ordering) - [[a]] - [a] merge_lists cmp [] = [] merge_lists cmp [xs] = xs merge_lists cmp xss = merge_lists cmp (merge_pairs cmp xss) merge_pairs :: (a - a - Ordering) - [[a]] - [[a]] merge_pairs cmp [] = [] merge_pairs cmp [xs] = [xs] merge_pairs cmp (xs:ys:xss) = merge cmp xs ys : merge_pairs cmp xss merge :: (a - a - Ordering) - [a] - [a] - [a] merge cmp xs [] = xs merge cmp [] ys = ys merge cmp (x:xs) (y:ys) = case x `cmp` y of GT - y : merge cmp (x:xs) ys _ - x : merge cmpxs (y:ys) -- Best regards, Bulat mailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ 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: Re[2]: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt
Hello, Just some minor suggestions and comments: The description might read better as two sentences: A class for monoids with various general-purpose instances. Monoids are types with an associative binary operation that has an identity. One thing that I think is a bit unclear from that description is the fact that it does not matter *what* the binary operation does, as long as the laws are followed. That is the whole point of the monoid class -- you use it when you only care about the laws, not the specific operation... For the laws, it would be nice to label each rule, something like * mappend mempty x = x -- Left Identity * mappend x empty = x -- Right Identity * mappend x (mappend y z) = mappend (mappend x y) z-- Associative * mconcat = foldr mappend mempty -- Not sure what to call this. Perhaps it an axiom? See the Applicative class for a formatting example: http://www.haskell.org/ghc/dist/current/docs/libraries/base/Control-Applicative.html As an expert, seeing the name is faster than reverse engineering the meaning of each law. I also suspect many people have never heard of the concept of an identity element (I am pretty sure I hadn't when I first started Haskell). So, I think it would be nice to tie together the concepts mentioned in the description with the actual laws so that the link is explicit. j. At Sun, 18 Jan 2009 13:57:07 +, Duncan Coutts wrote: On Sat, 2009-01-17 at 13:36 -0800, David Leimbach wrote: On Sat, Jan 17, 2009 at 9:16 AM, david48 dav.vire+hask...@gmail.com wrote: On Sat, Jan 17, 2009 at 4:08 PM, David Leimbach leim...@gmail.com wrote: So you're saying it should be better documented in Haskell what a Monoid is. Did you say you searched for C++ class why not Haskell Monoid then? The first correct google hit that didn't think I meant Monads, takes you straight to the GHC documentation for Data.Monoid. Read my first post on the thread, that's exactly what I did ( and then complained that the doc for Data.Monoid was close to useless ) Sorry missed it! This is an exceptionally long thread! :-) I agree Data.Monoid's docs don't give you much to work with. Do you think they look better now: http://www.haskell.org/ghc/dist/current/docs/libraries/base/Data-Monoid.html Any other improvements you'd make? Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell mode for Emacs question
I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
On my Mac I've had the same problem. Commenting out lines (unless (equal default-directory root) (setq default-directory root) (inferior-haskell-send-command proc (concat :cd default-directory))) solved it for me. On 22 Jan 2009, at 20:23, Andrew Wagner wrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
mmm, it seems that the code is searching for the location of a cabal file and uses that as the current directory, assuming all source code is relative to that directory, instead of using the source directive in that cabal file. On Thu, Jan 22, 2009 at 6:23 PM, Andrew Wagner wagner.and...@gmail.comwrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ 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] Haskell mode for Emacs question
Oops, sorry, forgot to mention that lines worth commenting were in inf-haskell.el file. On 22 Jan 2009, at 20:23, Andrew Wagner wrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
indeed, that works! the comment above those lines is: ;; Not sure if it's useful/needed and if it actually works. :-) On Thu, Jan 22, 2009 at 6:41 PM, Miguel Mitrofanov miguelim...@yandex.ruwrote: On my Mac I've had the same problem. Commenting out lines (unless (equal default-directory root) (setq default-directory root) (inferior-haskell-send-command proc (concat :cd default-directory))) solved it for me. On 22 Jan 2009, at 20:23, Andrew Wagner wrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monoids and newtypes
On Thu, 2009-01-22 at 16:11 +0100, Ketil Malde wrote:
One wart that was briefly mentioned during the Great Monoid Naming
Thread of 2009 is the need to wrap types in newtypes to provide multiple
instances of the same class with different semantics -- the archetypical
example being Integer as a monoid over addition as well as
multiplication.
I was just wondering if not phantom types might serve here as an
alternative way to go about that. Here's a small example illustrating
it:
{-# LANGUAGE EmptyDataDecls #-}
{-# LANGUAGE FlexibleInstances #-}
module Monoids where
import Data.Monoid
data Foo a = Foo Integer deriving (Show, Eq)
data Additive
data Multiplicative
instance Monoid (Foo Additive) where
mappend (Foo x) (Foo y) = Foo (x+y)
mempty = Foo 0
instance Monoid (Foo Multiplicative) where
mappend (Foo x) (Foo y) = Foo (x*y)
mempty = Foo 1
instance Num (Foo a) where
fromInteger x = Foo x
Foo x + Foo y = Foo (x+y)
Foo x * Foo y = Foo (x*y)
signum (Foo x) = Foo (signum x)
Loading this into ghci, you get:
*Monoids mconcat [1,2]
interactive:1:0:
Ambiguous type variable `t' in the constraints:
`Monoid t' arising from a use of `mconcat' at interactive:1:0-12
`Num t' arising from the literal `2' at interactive:1:11
Probable fix: add a type signature that fixes these type variable(s)
*Monoids mconcat [1,2::Foo Additive]
Foo 3
*Monoids mconcat [1,2::Foo Multiplicative]
Foo 2
(This can of course be prettified a bit by omitting the constructor
from the Show instance).
Any thought about this, pro/contra the newtype method?
The old wiki had an excellent page that has not been replicated either
verbatim or in spirit in the new wiki.
http://web.archive.org/web/20060831090007/http://www.haskell.org/hawiki/CommonHaskellIdioms
This lists many small tips and tricks that Haskell programmers have
discovered/used throughout the years.
This particular example is an example of using wrapper types to attach a
phantom type as described here:
http://web.archive.org/web/20070614230306/http://haskell.org/hawiki/WrapperTypes
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Comments from OCaml Hacker Brian Hurt
On Thu, 2009-01-22 at 11:32 -0600, Jeremy Shaw wrote: Hello, Just some minor suggestions and comments: The description might read better as two sentences: A class for monoids with various general-purpose instances. Monoids are types with an associative binary operation that has an identity. One thing that I think is a bit unclear from that description is the fact that it does not matter *what* the binary operation does, as long as the laws are followed. That is the whole point of the monoid class -- you use it when you only care about the laws, not the specific operation... For the laws, it would be nice to label each rule, something like * mappend mempty x = x -- Left Identity * mappend x empty = x -- Right Identity * mappend x (mappend y z) = mappend (mappend x y) z-- Associative * mconcat = foldr mappend mempty -- Not sure what to call this. Perhaps it an axiom? This is just a definition, both actually and nominally. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
Not that you're looking to switch editors, but if you want something a little more hassle-free: http://www.n-brain.net/unashots/Haskell/ErrorHighlighting.png Regards, John On Jan 22, 2009, at 10:17 AM, Peter Verswyvelen wrote: I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ 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] Why monoids will abide...
On Thu, 22 Jan 2009, Eugene Kirpichov wrote: To my mind, in the map-reduce case you generally need a commutative monoid. Or, you need an extra infrastructure that mappend's only results from adjacent machines, or something like that. The paper http://www.cs.vu.nl/~ralf/MapReduce/ analyzes the model of Google's MapReduce and Sawzall. quick haskell summaries at: http://www.thenewsh.com/~newsham/x/machine/MapReduce.hs http://www.thenewsh.com/~newsham/x/machine/Sawzall.hs The MapReduce model isn't based directly on a monoid, but the Sawzall model is. Tim Newsham http://www.thenewsh.com/~newsham/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Does readFile /proc/mounts hang for you?
Thomas DuBuisson thomas.dubuis...@gmail.com writes:
open(/proc/mounts, O_RDONLY|O_NOCTTY|O_NONBLOCK) = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0x77470b70) = -1 ENOTTY
(Inappropriate ioctl for device)
This is to test whether the file is a terminal.
select(4, [3], [], NULL, {0, 0})= 0 (Timeout)
select(4, [3], [], NULL, {134, 217727} unfinished ...
Here's the real issue: select() doesn't work on /proc entries (or at
least not that one). Here's a small C program to illustrate the
behaviour:
#include sys/select.h
#include sys/types.h
#include fcntl.h
#include stdio.h
int
main(int argc, char** argv)
{
char* filename;
intfd;
struct timeval tv;
fd_set read_fds, write_fds;
intretval;
if (argc 2) return 1;
filename = argv[1];
fd = open(filename, O_RDONLY | O_NOCTTY | O_NONBLOCK);
FD_ZERO(read_fds);
FD_SET(fd, read_fds);
FD_ZERO(write_fds);
tv.tv_sec = 0;
tv.tv_usec = 0;
retval = select(fd+1, read_fds, write_fds, NULL, tv);
printf(select() returned %d\n, retval);
printf(FD_ISSET returns %d\n, FD_ISSET(fd, read_fds));
}
Running this program on /proc/mounts shows that select() will never
report it as readable:
~/tmp/select $ gcc -o test_select test_select.c
~/tmp/select $ ./test_select /bin/ls
select() returned 1
FD_ISSET returns 1
~/tmp/select $ ./test_select /proc/mounts
select() returned 0
FD_ISSET returns 0
~/tmp/select $
G.
--
Gregory Collins g...@gregorycollins.net
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] Haskell mode for Emacs question
Hello John, Thursday, January 22, 2009, 8:50:39 PM, you wrote: thanks, support of over-internet and intranet collaboration looks very promising these days (even if not saying about ability to highlight error place ;) btw, i was unable to download mp4 video from http://vimeo.com/1653402 (online players doesn't work in my browser) Not that you're looking to switch editors, but if you want something a little more hassle-free: http://www.n-brain.net/unashots/Haskell/ErrorHighlighting.png Regards, John On Jan 22, 2009, at 10:17 AM, Peter Verswyvelen wrote: I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ 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 -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[2]: [Haskell-cafe] Haskell mode for Emacs question
http://depositfiles.com/files/4565hs7vl On 22 Jan 2009, at 21:14, Bulat Ziganshin wrote: Hello John, Thursday, January 22, 2009, 8:50:39 PM, you wrote: thanks, support of over-internet and intranet collaboration looks very promising these days (even if not saying about ability to highlight error place ;) btw, i was unable to download mp4 video from http://vimeo.com/1653402 (online players doesn't work in my browser) Not that you're looking to switch editors, but if you want something a little more hassle-free: http://www.n-brain.net/unashots/Haskell/ErrorHighlighting.png Regards, John On Jan 22, 2009, at 10:17 AM, Peter Verswyvelen wrote: I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ 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 -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Error in HTTP 4.004 + CouchDB?
Hello
(i sent this message to the mail of author, specified at hackage, but it
returned to me, so i decided to resend it here)
I found strange thing during work with latest versions of CouchDB HTTP
module on my Mac OS X 10.4. The problem is, that when i send document to
the couchdb server, it name was cut to the 2 characters.
After some investigation i found, that this is problem in combination of
the CouchDB + HTTP usage. CouchDB module fills out the Request structure,
and specify scheme authority fields. This lead that i see (in network
dumps) following data:
PUT http://127.0.0.1:5984/test1/Users_ott_tmp_1_tst HTTP/1.1
Content-Type: ...
...
Host: 127.0.0.1:5984
...
instead of proper
PUT /test1/Users_ott_tmp_1_tst HTTP/1.1
I can eliminate this by explicitly setting of the scheme authority into
empty values, but this lead to improper creation of the Host header in
request:
PUT /test1/Users_ott_tmp_1_tst HTTP/1.1
Content-Type: ...
...
Host:
...
I tried to fix this problem myself, but I'm novice in the industrial
Haskell programming ;-)
P.S. this code from (CouchDB/HTTP.hs) will restore proper behaviour of the
code, but break Host header
makeURL path query = CouchMonad $ \conn - do
return ( (ccURI conn) { uriPath = '/':path
, uriQuery = if null query then else
'?':(urlEncodeVars query)
, uriScheme =
, uriAuthority = Nothing
}
,conn )
--
With best wishes, Alex Ott, MBA
http://alexott.blogspot.com/http://xtalk.msk.su/~ott/
http://alexott-ru.blogspot.com/
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: STM-IO-Hooks-0.0.1
This library provides an STM monad with commit and retry IO hooks. A retry-action is run (once) in a separate thread if the transaction retries, while commit-actions are executed iff the transaction commits. The code is based on the AdvSTM Monad [1] by Chris Kuklewicz, but in addition also ensures some atomicity guarantees for commit-actions, see documentation for details. Cheers, Peter [1] http://www.haskell.org/haskellwiki/New_monads/MonadAdvSTM ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monoids and newtypes
On Thu, Jan 22, 2009 at 10:11 AM, Ketil Malde ke...@malde.org wrote: I was just wondering if not phantom types might serve here as an alternative way to go about that. Here's a small example illustrating it: ... *Monoids mconcat [1,2::Foo Additive] Foo 3 *Monoids mconcat [1,2::Foo Multiplicative] Foo 2 (This can of course be prettified a bit by omitting the constructor from the Show instance). Any thought about this, pro/contra the newtype method? I'm not sure that requiring type annotations is less intrusive than using a wrapper or an explicit dictionary. But there may be types where this sort of thing makes sense to do. My favorite alternative to Monoid uses labeled instances. data Proxy l -- empty, to ensure that labels are never examined class LMonoid label where type Carrier label :: * unit :: Proxy label - Carrier label mult :: Proxy label - Carrier label - Carrier label - Carrier label data Sum a sum_ :: Proxy (Sum a) sum_ = undefined instance Num a = LMonoid (Sum a) where type Carrier (Sum a) = a unit _ = 0 mult _ = (+) -- this works nicely with the writer monad data Writer l a = W (Carrier l) a instance (LMonoid l) = Monad (Writer l) where return a = W (unit (undefined :: Proxy l)) a (W o1 a) = f = let W o2 b = f a in W (mult (undefined :: Proxy l) o1 o2) b tell :: Carrier l - Writer l () tell x = W x () -- and with Foldable class Foldable f where fold :: (LMonoid l) = Proxy l - f (Carrier l) - Carrier l -- e.g., fold sum_ [1,2,3] -- and it works well with Monoid data Std a instance (Monoid a) = LMonoid (Std a) where unit _ = mempty mult _ = mappend newtype WrapL l = WrapL (Carrier l) instance LMonoid l = Monoid (WrapL l) where mempty = WrapL (unit (undefined :: Proxy l)) mappend (Wrap x) (Wrap y) = WrapL (mult (undefined::l) x y) -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Factoring into type classes
Hello again, I think that I have done all of the above in different situations, and so I don't think that there is a single correct answer. I usually avoid using the newtype trick as I find it inconvenient: usually the newtype does not have the same operations as the underlying type and so it cannot be used directly, and if you are going to wrap thing just when you use the class methods, then you may as well use the non-overloaded operations. Yes, I had the same thought. If I have to explicitly convert between various wrappers, that's basically the same as defining separate functions from the start. The newtype trick is certainly nice when you don't want to mix the different uses on the same piece of data, but that was exactly my problem. I'd say your posts as well as wren ng thornton's answer my question as thoroughly as possible at this point, although wren's lengthy letter could probably even be extended and turned into a tutorial on the topic. Of course type classes are not only important just for making dictionary passing implicit, but also because of their interactions, which is nicely demonstrated by the sigfpe blog entry that someone also linked from this thread. That's probably why I feel kind of uncomfortable when not taking advantage of standard classes wherever possible. Thanks for the answers, Gergely -- http://www.fastmail.fm - Access all of your messages and folders wherever you are ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Processor availability
How might I go about finding out how many processors are available in a concurrent GHC program? I have some code I'd like to parallelize, but I don't want to spawn a separate (even lightweight) thread for each of thousands of minor tasks. Louis Wasserman wasserman.lo...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Processor availability
wasserman.louis: How might I go about finding out how many processors are available in a concurrent GHC program? I have some code I'd like to parallelize, but I don't want to spawn a separate (even lightweight) thread for each of thousands of minor tasks. Louis Wasserman [1]wasserman.lo...@gmail.com You set the number of OS threads with +RTS -N at runtime. This value is accessible from Haskell via: GHC.Conc: -- | the value passed to the @+RTS -N@ flag. This is the number of -- Haskell threads that can run truly simultaneously at any given -- time, and is typically set to the number of physical CPU cores on -- the machine. numCapabilities :: Int -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Processor availability
2009/1/22 Louis Wasserman wasserman.lo...@gmail.com: How might I go about finding out how many processors are available in a concurrent GHC program? I have some code I'd like to parallelize, but I don't want to spawn a separate (even lightweight) thread for each of thousands of minor tasks. Use a thread pool and feed it tasks. Control.Concurrent.Chan makes a good queue. Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
It's too bad Visual Haskell was not continued, since a free version of the Visual Studio platform is available now. I felt Visual Haskell was very promising, like on the fly type inference with tool tips, code completion, built in Cabal support, etc... On Thu, Jan 22, 2009 at 6:50 PM, John A. De Goes j...@n-brain.net wrote: Not that you're looking to switch editors, but if you want something a little more hassle-free: http://www.n-brain.net/unashots/Haskell/ErrorHighlighting.png Regards, John On Jan 22, 2009, at 10:17 AM, Peter Verswyvelen wrote: I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Question about allocaArray and friends
In C, if you try to alloca too much memory, then the stack gets overwritten and bad things happen. Does GHC exhibit the same behavior with allocaArray and the like? Is there a way to find out how much is safe to allocate? Thanks in advance for the help, Patrick ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Question about allocaArray and friends
Hello Patrick, Friday, January 23, 2009, 1:22:21 AM, you wrote: In C, if you try to alloca too much memory, then the stack gets overwritten and bad things happen. Does GHC exhibit the same behavior with allocaArray and the like? Is there a way to find out how much is safe to allocate? alloca allocs memory in heap, so it should be safe if you are not going to allocate lots of megabytes. you can use usual binary division algorithm to find how much you can allocate -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GHCi Memory Leak in Windows Vista
On Tue, 2009-01-20 at 10:22 +, Gracjan Polak wrote: Same here: Vista, GHC 6.8.3 Tested a bit changed scenario: instead of 20 separate compilations it is worthwhile to run single, longer build, e.g. ghc --make of same package. Seems like GHCi does not run garbage collection when machine is busy. And then it accumulates memory. This renders Vista totally unresponsive and even can lead to automatic reboot (happened once to me). Did either of you file a ghc ticket about this issue? Does the same happen with 6.10 ? Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Big endian vs little endian in Haskell land?
Hi Tom, What is an example of some software in Hackage that reads/writes things like integers to persistent store ... i.e. where endian-ness is an issue? Regards, Vasili On Thu, Jan 22, 2009 at 7:24 AM, Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Sure, I've had to deal with this frequently. Luckily, Data.Binary has functions like getWord32be, putWord64le, etc. I've never had any problems and typically don't worry about the wire format after making the Binary instances. Or, if your question was what types of programs might be concerned you can include any program that writes data to a file where the file might be read on a different system and networking programs, obviously. Tom 2009/1/22 Galchin, Vasili vigalc...@gmail.com: Hello, Are there applications that have to deal with both(!!!) big endian and little endian on persistent store?? I.e. when marshalling out and unmarshalling in endian-ness has to be considered?? Regards, Vasili ___ 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] Processor availability
2009/1/22 Louis Wasserman wasserman.lo...@gmail.com How might I go about finding out how many processors are available in a concurrent GHC program? I have some code I'd like to parallelize, but I don't want to spawn a separate (even lightweight) thread for each of thousands of minor tasks. Consider using Contorl.Parallel.Strategies which allows you to spark of lightweight jobs that get run on a pool of threads. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: how to implement daemon start and stop directives?
Luke Palmer lrpal...@gmail.com wrote: On Thu, Jan 22, 2009 at 9:04 AM, Ertugrul Soeylemez e...@ertes.de wrote: Sometimes this is inevitable, but I've never seen a case, where IORefs couldn't be replaced by a more elegant State/StateT-based solution. And if you need to do multi-threading, Chans, MVars and semaphores are better anyway. Please define better. For the function in question, what advantages do they give us? It gives you thread-safety for free, which IORefs don't give you. It's the same purpose, the same amount of code, but threadsafe by concept. Of course, for simple variables, IORefs will likely be thread-safe as well, but there is no guarantee here. With MVars you have that guarantee. Just to be clear, I wouldn't dare argue that IORefs can do everything MVars and TVars can do. I'm just perplexed why you say MVars and TVars are better, when an IORef does the trick just fine for our function. What I'm saying is: Even if IORefs suffice, why would you want to use them, if MVar does the job as well and likely better? There is no reason to prefer an IORef over an MVar to signal something to another thread. Well, I usually don't go here, but benchmarks show that IORefs are the fastest of any of the mutable variable primitives, by at least a factor of 2. I wish I remembered where I saw that. Yes, that's a good point, but I think, you can safely disregard that for signalling a thread to quit. By the way, IORefs are by themselves not thread-safe. You need to use a special function, when using it in a multi-threaded manner. You mean atomicModifyIORef? Yes. IORefs *are* thread-safe by themselves: you will not make your program segfault by using them in a multithreaded program. So it all comes down to invariants. IORefs have no synchronization concepts, so code like: x - readIORef ref writeIORef ref (x+1) Is not threadsafe by most standards. That doesn't mean IORefs themselves are not threadsafe, just that you have to be careful how you use them. That's exactly my point. In the above case they do just the same, but need more care. And I will reiterate: *in this case* the use of IORef is fully encapsulated in this function and *is threadsafe!* Which is the basis of my argument: in imperative code, when you can limit the scope of an IORef to a small abstraction that is threadsafe, there is no advantage of TVars or MVars over them. I don't think they deserve bad style sledgehammer. (An instance of use the right tool for the job) daemon :: IO () - IO (IO ()) daemon action = do stopvar - newIORef False let run = do stop - readIORef stopvar if stop then return () else (action run) forkIO run return (writeIORef stopvar True) In this case, it's simply a coincidence that it's safe. It's because you're using an IORef Bool, and because writes to a Bool variable are atomic on virtually all platforms. An Integer may already fail to be thread-safe. You need more care and the payoff is zero. If you still insist on using IORefs, at least use the atomic function above, but that destroys the little performance benefit of using IORefs, unless GHC does some intelligent optimization here, which I doubt. Greets, Ertugrul. -- nightmare = unsafePerformIO (getWrongWife = sex) http://blog.ertes.de/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
Hmm, strange. This doesn't appear to fix my problem. Perhaps I have something bigger broken locally :( On Thu, Jan 22, 2009 at 12:44 PM, Peter Verswyvelen bugf...@gmail.comwrote: indeed, that works! the comment above those lines is: ;; Not sure if it's useful/needed and if it actually works. :-) On Thu, Jan 22, 2009 at 6:41 PM, Miguel Mitrofanov miguelim...@yandex.ruwrote: On my Mac I've had the same problem. Commenting out lines (unless (equal default-directory root) (setq default-directory root) (inferior-haskell-send-command proc (concat :cd default-directory))) solved it for me. On 22 Jan 2009, at 20:23, Andrew Wagner wrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell mode for Emacs question
After emacs started your GHCi session, when you manually type :cd the full path of the directory of your Main.hs :load Main.hs Does it work then? Can you use GHCi from outside Emacs? On Fri, Jan 23, 2009 at 1:09 AM, Andrew Wagner wagner.and...@gmail.comwrote: Hmm, strange. This doesn't appear to fix my problem. Perhaps I have something bigger broken locally :( On Thu, Jan 22, 2009 at 12:44 PM, Peter Verswyvelen bugf...@gmail.comwrote: indeed, that works! the comment above those lines is: ;; Not sure if it's useful/needed and if it actually works. :-) On Thu, Jan 22, 2009 at 6:41 PM, Miguel Mitrofanov miguelim...@yandex.ru wrote: On my Mac I've had the same problem. Commenting out lines (unless (equal default-directory root) (setq default-directory root) (inferior-haskell-send-command proc (concat :cd default-directory))) solved it for me. On 22 Jan 2009, at 20:23, Andrew Wagner wrote: Interesting. I have a similar, but worse problem. For me, ':load'ing main.hs would fail to find the imported files. The only thing I appear to be able to :load is files that don't import from local directories. 2009/1/22 Peter Verswyvelen bugf...@gmail.com I have a silly problem. I'm using Emacs with the Haskell mode extension on Windows I have a source file in say c:/foo/src/main.hs main.hs is importing some other modules in that same src directory When I invoke GHCi from within Emacs, the first thing it does is :cd c:/foo and then :load src/main.hs But of course GHCi won't find the imported modules now, since the current directory is wrong. If I type in GHCi :cd src :load main.hs then it compiles fine. Does anyone have an idea why Emacs or the Haskell mode is switching to the parent directory of src instead of src itself, and how to fix this? Thanks a lot, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
Jonathan Cast wrote: On Mon, 2009-01-19 at 21:04 +, Andrew Coppin wrote: I mean, heck, *I* use Haskell at work - and I'm not even supposed to be coding things! /me feels slightly relieved, if you'll forgive my saying so :) Damn... I didn't think I was *that* bad at using Haskell? o_O Also, if you don't mind my asking, what *is* your job title? Technically, system administrator. An equally valid description might be the whole computer department. But in reality, my job involves swapping the backup tapes each day, and rebooting people's computers when Word crashes. Obviously, I'd like to be doing something a *tad* more interesting. (Not to mention better paid...!) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
Paul Johnson wrote: So next time I hear the you can't get the programmers line I'm going to respond with something like this: If you post an advert for a Haskell developer you will get 20 applicants. All of those people will be the kind of developer who learns new programming languages to improve their own abilities and stretch themselves, because nobody yet learns Haskell just to get a job. If you post an advert for a Java developer you will get 200 applicants. Most of them will be the kind of developer who learned Java because there are lots of Java jobs out there, and as long as they know enough to hold down a job then they see no reason to learn anything. If this isn't an elevator pitch for using Haskell then I don't know what the hell *is*! Seriously, this is a pretty damned persuasive argument... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Elevator pitch for functional programming
Jim Burton wrote: Parallelism! Something based on dons' blog http://cgi.cse.unsw.edu.au/~dons/blog/2007/11/29#smoking-4core will be a good start. +3 Ever tried to do anything like this in Java? Even Smalltalk makes it relatively hard compared to Haskell's parallelism primitives. (I do *mean* parallelism, not concurrency - although Haskell does that pretty damned impressively too...) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
On Tue, 2009-01-20 at 21:01 +, Andrew Coppin wrote: Paul Johnson wrote: So next time I hear the you can't get the programmers line I'm going to respond with something like this: If you post an advert for a Haskell developer you will get 20 applicants. All of those people will be the kind of developer who learns new programming languages to improve their own abilities and stretch themselves, because nobody yet learns Haskell just to get a job. If you post an advert for a Java developer you will get 200 applicants. Most of them will be the kind of developer who learned Java because there are lots of Java jobs out there, and as long as they know enough to hold down a job then they see no reason to learn anything. If this isn't an elevator pitch for using Haskell then I don't know what the hell *is*! Seriously, this is a pretty damned persuasive argument... Not really. My company *advertises* for Haskell developers, and then when they come in to interview, informs them that the code base is actually written in Perl. Works, too --- we have several Haskellers working here. If all you care about is the quality of the developers, and not their productivity once you've got them, you don't actually need to let them use Haskell after the interview is over... jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
On Tue, 2009-01-20 at 19:14 +, Andrew Coppin wrote: Jonathan Cast wrote: On Mon, 2009-01-19 at 21:04 +, Andrew Coppin wrote: I mean, heck, *I* use Haskell at work - and I'm not even supposed to be coding things! /me feels slightly relieved, if you'll forgive my saying so :) Damn... I didn't think I was *that* bad at using Haskell? o_O You have expressed continued bafflement on any number of subjects that have been repeatedly explained to you, so yes. Also, if you don't mind my asking, what *is* your job title? Technically, system administrator. An equally valid description might be the whole computer department. But in reality, my job involves swapping the backup tapes each day, and rebooting people's computers when Word crashes. Obviously, I'd like to be doing something a *tad* more interesting. (Not to mention better paid...!) Ah, you poor thing. No *wonder* you're driven to coding! jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
That's..evil On Thu, Jan 22, 2009 at 7:56 PM, Jonathan Cast jonathancc...@fastmail.fmwrote: On Tue, 2009-01-20 at 21:01 +, Andrew Coppin wrote: Paul Johnson wrote: So next time I hear the you can't get the programmers line I'm going to respond with something like this: If you post an advert for a Haskell developer you will get 20 applicants. All of those people will be the kind of developer who learns new programming languages to improve their own abilities and stretch themselves, because nobody yet learns Haskell just to get a job. If you post an advert for a Java developer you will get 200 applicants. Most of them will be the kind of developer who learned Java because there are lots of Java jobs out there, and as long as they know enough to hold down a job then they see no reason to learn anything. If this isn't an elevator pitch for using Haskell then I don't know what the hell *is*! Seriously, this is a pretty damned persuasive argument... Not really. My company *advertises* for Haskell developers, and then when they come in to interview, informs them that the code base is actually written in Perl. Works, too --- we have several Haskellers working here. If all you care about is the quality of the developers, and not their productivity once you've got them, you don't actually need to let them use Haskell after the interview is over... jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Moving nobench towards HaBench
Hello, A while back, we had a discussion on #haskell about assembling a Haskell benchmark suite, that is suitable for doing performance tests. A preliminary page was erected athttp://www.haskell.org/haskellwiki/HaBench . In the meantime, Donald Steward extended the original nofib suite with some shootout benchmarks afaik, resulting in nobench. The code base for the latter currently resides at http://code.haskell.org/nobench/ . I have been trying to get it running on GHC 6.10.1. For now, I added a number of type definitions to the code, causing the build/runtime system to compile. The same probably ought to be done for the benchmarks themselves, unless there is a cheat around this using some language extension. Anyhow, I'll post a patch against the current repository as soon as I have a number of benchmarks running. The main issue that still remains is the availability of real life benchmarks. I agree with the fact that micro-benchmarks can be useful for testing purposes or measures the efficacy and effectiveness of certain optimisations, yet I firmly believe any community has need of a set of benchmarks that actually reflects the real life usage of the language. I am think along the lines of something alike to the DaCapo projects, which assembled a number of very good benchmarks for the Java language and its VM. So the question basically boils down to this. Is there anybody interested in making the move toward HaBench, and if so, do you know of real life benchmarks that can serve for this exact purpose? The benchmarks should preferably execute for 10s on modern machines, using a decent amount of RAM (say somewhere between 50 and 500MB), thus exercising all parts of a modern computing system. The code should not be trivial and the set of benchmarks should eventually cover the most uses of Haskell in the industry. Of course, the benchmarks themselves should be open source. If possible, they should come with multiple inputs, allowing a short (test) run as well as longer measurement runs. If you are able and willing to help out, drop by at the HaBench page and drop a line, -- Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
On Thu, 2009-01-22 at 20:02 -0500, Andrew Wagner wrote: That's..evil I know. I'm evil too, though. So it's cool. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Employment
On Fri, Jan 23, 2009 at 11:56 AM, Jonathan Cast jonathancc...@fastmail.fm wrote: Not really. My company *advertises* for Haskell developers, and then when they come in to interview, informs them that the code base is actually written in Perl. Works, too --- we have several Haskellers working here. If all you care about is the quality of the developers, and not their productivity once you've got them, you don't actually need to let them use Haskell after the interview is over... I saw this trick recently for a job advertised locally to me, in Melbourne. I was initially pretty excited that someone in this city was actually advertising for Haskell programmers, until I realised they needed to be good at Javascript and Perl so they could work on their web apps. Argh, I didn't bother applying. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] MySQL and HDBC?
Hello, Real World Haskell seems to say that the abstraction layer HDBC doesn't support MySQL. If so, in what sense doesn't HDBC support MySQL?? Thanks, Vasili ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: GHCi Memory Leak in Windows Vista
Duncan Coutts wrote: Does the same happen with 6.10 ? Yes. In 6.10.1 also leak. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is it possible to model eventually consistent side effects?
I am trying to figure out if there is a way to model cloud computing computations in Haskell. My specific problems is that in cloud computing, as in Amazon WebServices, side effects (writes to storage, simple database, queue) follow the eventually consistent model. Which means even if your writes succeeds, it may or may not be immediately available for reads. Each call to the services may also temporarily experience network errors or end-system unavailability. Virtual machines can mount a local disk that does offers consistent storage, but the storage wont survive a reboot (after a crash). I am trying to find out if I can model computation (and its compositions) where I can hide reliability and consistency issues. And also be able to reason about a computation to make sure no combination of errors and inconsistencies would break my logic. Is it possible? If so is there a good starting point? -- Daryoush ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error in HTTP 4.004 + CouchDB?
Thanks Alex,
contacting the maintainer of a package rather than author is probably
the best course of action in general. They may both be out of date,
but the former maybe less so. :)
As verified offline, you issue this request via sendHTTP when experiencing
this misbehavior.
A couple of suggestions on what to do:
* Use Network.Browser instead and send it via (browse $ request req),
which will normalize the path and Host: headers as you expect for
(non-proxy)
use.
* pull down the latest bits from the repository and normalize your request
prior to calling sendHTTP by using
(Network.HTTP.Base.normalizeRequest False{-no proxy-} req)
(we're in a tight spot wrt. backwards compatibility for sendHTTP, so
having
it perform this normalization step by default would break code that
now interacts
with proxies via sendHTTP.)
The repository version also has support for custom request verbs, which
might be
of interestuse to some.
Let me know how it goes -- git repository URL available via
http://projects.haskell.org/http/
hth
--sigbjorn
On 1/22/2009 11:32, Alex Ott wrote:
Hello
(i sent this message to the mail of author, specified at hackage, but it
returned to me, so i decided to resend it here)
I found strange thing during work with latest versions of CouchDB HTTP
module on my Mac OS X 10.4. The problem is, that when i send document to
the couchdb server, it name was cut to the 2 characters.
After some investigation i found, that this is problem in combination of
the CouchDB + HTTP usage. CouchDB module fills out the Request structure,
and specify scheme authority fields. This lead that i see (in network
dumps) following data:
I tried to fix this problem myself, but I'm novice in the industrial
Haskell programming ;-)
P.S. this code from (CouchDB/HTTP.hs) will restore proper behaviour of the
code, but break Host header
makeURL path query = CouchMonad $ \conn - do
return ( (ccURI conn) { uriPath = '/':path
, uriQuery = if null query then else
'?':(urlEncodeVars query)
, uriScheme =
, uriAuthority = Nothing
}
,conn )
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
