Re: [Haskell-cafe] How many Haskell Engineer I/II/IIIs are there?
On Wed, Feb 10, 2010 at 16:59, Jason Dusek jason.du...@gmail.com wrote: I wonder how many people actually write Haskell, principally or exclusively, at work? We (typLAB) use Haskell. There's four of us, but only two actually program Haskell, and not exclusively. We also use Javascript in the browser (though we use functional programming techniques there as well). Erik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Dungeons of Wor - a largish FRP example and a fun game, all in one!
Hello all, I just uploaded the first public version of Dungeons of Wor [1], a homage to the renowned three-decade-old arcade game, Wizard of Wor. While it makes a fine time killer if you have a few minutes to spare, it might be of special interest to the lost souls who are trying to figure out FRP. The game was programmed using the Simple version of the experimental branch of Elerea [2], which provides first-class discrete streams to describe time-varying quantities, and the main game logic is described as a composition of streams instead of a world state transformer. Developing in this manner was an interesting experience, and I'll write about it in more detail over the weekend. All the best, Gergely [1] http://hackage.haskell.org/package/dow [2] http://hackage.haskell.org/packages/archive/elerea/1.2.3/doc/html/FRP-Elerea-Experimental-Simple.html -- http://www.fastmail.fm - The professional email service ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Seen on reddit: or, foldl and foldr considered slightly harmful
In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he considers foldl and foldr harmful as they hinder parallelism because of Process first element, then the rest Instead he proposes a divide and merge aproach, especially in the light of going parallel. The slides at http://docs.google.com/viewer?url=http%3A%2F%2Fresearch.sun.com%2Fprojects%2Fplrg%2FPublications%2FICFPAugust2009Steele.pdf [Bware: Google docs] are somewhat geared towards Fortress, but I wonder what Haskellers have to say about his position. Greetings, Johann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
On 02/10/2010 04:59 PM, Jason Dusek wrote: I wonder how many people actually write Haskell, principally or exclusively, at work? Well, my main language at work in the moment is C++, we also use Java, a lot of Tcl and Python. I use Haskell for my own programs and test utilities / converters. The biggest achievement at work was an Installer program, which was quite complicated and had to be safe and of course we had time pressure, so I quickly coded it in Haskell. It is now used in the installation procedure of a part from a big mission control system for satellites. lg, Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HDBC convert [SqlValue] without muchos boilerplate
Hi, I'm trying to get to grips with HDBC and have the following problem. When I run a query that returns a result set, each row comes back as a [SqlValue]. Naively, I thought the following function would convert a [SqlValue] into a string, but instead I get the error below. convrow2 :: [SqlValue] - String convrow2 (x:xs) = foldl (\i j - i ++ | ++ show j ) (show (fromSql x)) xs Prelude :l TasksSimple.lhs [1 of 1] Compiling Main ( TasksSimple.lhs, interpreted ) TasksSimple.lhs:126:65: No instance for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) arising from a use of `fromSql' at TasksSimple.lhs:126:65-73 Possible fix: add an instance declaration for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) In the first argument of `show', namely `(fromSql x)' In the second argument of `foldl', namely `(show (fromSql x))' In the expression: foldl (\ i j - i ++ | ++ show j) (show (fromSql x)) xs Failed, modules loaded: none. I tried looking at how to add an instance declaration for convertible, but was stumped. This code, however, works in GHCi. Would anyone know how to convert from [SqlValue] in a straightforward way without having to specify every field by hand ? I don't fancy doing this for each sql statement I need to run. convrow1 :: [SqlValue] - String convrow1 [tasksid,title,added] = show ( (fromSql tasksid)::Integer ) ++ | ++ fromSql title ++ | ++ show ((fromSql added)::LocalTime) Any help is much appreciated, especially as I haven't looked at any Haskell in a while and wasn't any good with it before! Regards, Iain This is my set up: GHC is 6.10.4 HDBC is HDBC-2.1.1, HDBC-2.2.2, HDBC-postgresql-2.1.0.0,HDBC-postgresql-2.2.0.0 Convertible is convertible-1.0.5, convertible-1.0.8 OSX 10.6___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seen on reddit: or, foldl and foldr considered slightly harmful
Johann Höchtl johann.hoec...@gmail.com writes: In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he considers foldl and foldr harmful as they hinder parallelism because of Process first element, then the rest Instead he proposes a divide and merge aproach, especially in the light of going parallel. In Haskell foldl/foldr apply to linked lists (or lazy streams, if you prefer) which are already inherently sequential, and gets a rather harsh treatment. I notice he points to finger trees, which I though was implemented in Data.Sequence. are somewhat geared towards Fortress, but I wonder what Haskellers have to say about his position. Can we (easily) parallelize operations on Data.Sequence? Often, the devil is in the details, and there's a lot of ground to cover between 'trees are easier to parallelize' to an efficient and effective high level interface. (E.g. non-strict semantics allowing speculative evalutaion - you still need to insert manual `par`s, right?) -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] Seen on reddit: or, foldl and foldr considered slightly harmful
Isn't it the kind of things Data Parallel Haskell is achieving ? I'm in no way an expert of the field, but from what I've read on the subject it looked like : I have a list of N elements and I want to map the function F on it. technically, I could spawn N processes and build the result from that, but it would be highly inefficient. So the really hard part is to guess how I should split my data to get the best performances. Well, I guess it's pretty easy for a flat structure if you have access to it's length, but for a recursive one it is complicated as you don't know if a branch of the tree will lead to a leaf or a huge subtree ... the evil detail ! Tom On Thu, Feb 11, 2010 at 11:00:51AM +0100, Ketil Malde wrote: Johann Höchtl johann.hoec...@gmail.com writes: In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he considers foldl and foldr harmful as they hinder parallelism because of Process first element, then the rest Instead he proposes a divide and merge aproach, especially in the light of going parallel. In Haskell foldl/foldr apply to linked lists (or lazy streams, if you prefer) which are already inherently sequential, and gets a rather harsh treatment. I notice he points to finger trees, which I though was implemented in Data.Sequence. are somewhat geared towards Fortress, but I wonder what Haskellers have to say about his position. Can we (easily) parallelize operations on Data.Sequence? Often, the devil is in the details, and there's a lot of ground to cover between 'trees are easier to parallelize' to an efficient and effective high level interface. (E.g. non-strict semantics allowing speculative evalutaion - you still need to insert manual `par`s, right?) -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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HDBC convert [SqlValue] without muchos boilerplate
The problem is, fromSql x doesn't know that type it should return. It's sure that it has to be of class Convertible SqlValue, but nothing more. Could be String, or Int32, or something else. What if you just omit the show function? fromSql seems to be able to convert almost anything to String. Iain Barnett wrote: Hi, I'm trying to get to grips with HDBC and have the following problem. When I run a query that returns a result set, each row comes back as a [SqlValue]. Naively, I thought the following function would convert a [SqlValue] into a string, but instead I get the error below. convrow2 :: [SqlValue] - String convrow2 (x:xs) = foldl (\i j - i ++ | ++ show j ) (show (fromSql x)) xs Prelude :l TasksSimple.lhs [1 of 1] Compiling Main ( TasksSimple.lhs, interpreted ) TasksSimple.lhs:126:65: No instance for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) arising from a use of `fromSql' at TasksSimple.lhs:126:65-73 Possible fix: add an instance declaration for (convertible-1.0.5:Data.Convertible.Base.Convertible SqlValue a) In the first argument of `show', namely `(fromSql x)' In the second argument of `foldl', namely `(show (fromSql x))' In the expression: foldl (\ i j - i ++ | ++ show j) (show (fromSql x)) xs Failed, modules loaded: none. I tried looking at how to add an instance declaration for convertible, but was stumped. This code, however, works in GHCi. Would anyone know how to convert from [SqlValue] in a straightforward way without having to specify every field by hand ? I don't fancy doing this for each sql statement I need to run. convrow1 :: [SqlValue] - String convrow1 [tasksid,title,added] = show ( (fromSql tasksid)::Integer ) ++ | ++ fromSql title ++ | ++ show ((fromSql added)::LocalTime) Any help is much appreciated, especially as I haven't looked at any Haskell in a while and wasn't any good with it before! Regards, Iain This is my set up: GHC is 6.10.4 HDBC is HDBC-2.1.1, HDBC-2.2.2, HDBC-postgresql-2.1.0.0,HDBC-postgresql-2.2.0.0 Convertible is convertible-1.0.5, convertible-1.0.8 OSX 10.6___ 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: Haskell-Cafe Digest, Vol 78, Issue 14
On Tue, 2010-02-09 at 16:41 +, John Lato wrote:
See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a valid
Stream instance using iteratee. Also Gregory Collins recently posted
an iteratee wrapper for Attoparsec to haskell-cafe. To my knowledge
these are not yet in any packages, but hackage is vast.
Hmm. Am I correct that his implementation caches everything?
I tried to rewrite the implementation using... well imperative linked
list. For trivial benchmark it have large improvement (althought it may
be due to error in test such as using ByteString) and, I believe, that
it allows to free memory before finish.
Results of test on Core 2 Duo 2.8 GHz:
10: 0.000455s 0.000181s
100:0.000669s 0.001104s
1000: 0.005209s 0.023704s
1: 0.053292s 1.423443s
10: 0.508093s 132.208597s
After I broke the running as it was taking too long.
Is my implementation correct (when I try to write less trivial benchmark
I probably find out but I hope for comment on the idea).
Regards
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
import Control.Applicative
import Control.Concurrent.MVar
import Data.Maybe
import Control.Monad
import Control.Monad.ST
import Data.Iteratee
import Data.Iteratee.Base.StreamChunk (StreamChunk)
import Data.Iteratee.WrappedByteString
import Data.IORef
import qualified Data.ListLike as LL
import Data.STRef
import Data.Time
import Data.Word
import System.Mem.Weak
import Text.Parsec
import Text.Parsec.Pos
import ParsecIteratee
class Monad m = Reference r m where
newRef :: a - m (r a)
readRef :: r a - m a
writeRef :: r a - a - m ()
modifyRef :: r a - (a - m (a, b)) - m b
modifyRef r f = readRef r = f = \(a, b) - writeRef r a return b
instance Reference IORef IO where
newRef = newIORef
readRef = readIORef
writeRef = writeIORef
instance Reference (STRef s) (ST s) where
newRef = newSTRef
readRef = readSTRef
writeRef = writeSTRef
instance Reference MVar IO where
newRef = newMVar
readRef = readMVar
writeRef = putMVar
data (Monad m, Reference r m, StreamChunk c el) = NextCursor r m c el =
NextCursor (Cursor r m c el) | None | Uneval
data (Monad m, Reference r m, StreamChunk c el) = Cursor r m c el =
Cursor (r (NextCursor r m c el)) (c el)
mkCursor :: (Monad m, Reference r m, StreamChunk c el) = m (Cursor r m c el)
mkCursor = newRef Uneval = \r - (return $! Cursor r LL.empty)
instance (Monad m, Reference r m, StreamChunk c el) =
Stream (Cursor r m c el) (IterateeG c el m) el where
uncons = unconsStream
unconsStream :: (Monad m, Reference r m, StreamChunk c el)
= Cursor r m c el
- IterateeG c el m (Maybe (el, Cursor r m c el))
unconsStream p@(Cursor r c)
| LL.null c = IterateeG $ \st - join $ modifyRef r $ unconsCursor st p
| otherwise = return $! justUnconsCursor p
unconsCursor :: forall r m c el. (Monad m, Reference r m, StreamChunk c el)
= StreamG c el
- Cursor r m c el
- NextCursor r m c el
- m (NextCursor r m c el,
m (IterGV c el m (Maybe (el, Cursor r m c el
unconsCursor st_ rv@(NextCursor p@(Cursor r c))
| LL.null c = return $! (rv, join $ modifyRef r $ unconsCursor st p)
| otherwise = return $! (rv, return $! Done (justUnconsCursor p) st)
unconsCursor st_ rv@(None)
= return $! (rv, return $! Done Nothing st)
unconsCursor st@(Chunk c) p rv@(Uneval)
| LL.null c = return $! (rv, return $! Cont (unconsStream p) Nothing)
| otherwise = do r - newRef Uneval :: m (r (NextCursor r m c el))
let p' = Cursor r c
ra = Done (justUnconsCursor p') (Chunk LL.empty)
return $! (NextCursor p', return $! ra)
unconsCursor st@(EOF Nothing) _ rv@(Uneval)
= return $! (None, return $! Done Nothing st)
unconsCursor st@(EOF (Just e)) _ rv@(Uneval)
= return $! (rv, return $! Cont (throwErr e) (Just e))
justUnconsCursor :: (Monad m, Reference r m, StreamChunk c el) =
Cursor r m c el - Maybe (el, Cursor r m c el)
justUnconsCursor (Cursor r c) = Just $! (LL.head c, Cursor r $ LL.tail c)
benchmarkParser :: (Stream s m Char) = Int - ParsecT s () m ()
benchmarkParser i | i 5 = try $ sequence_ $ replicate i $ char '\0'
| i = 5 = (try $ sequence_ $ replicate 5 $ char '\0')
benchmarkParser (i - 5)
mkBenchmark :: Int - IO (NominalDiffTime, NominalDiffTime)
mkBenchmark i = do start - getCurrentTime
c - mkCursor :: IO (Cursor IORef IO WrappedByteString Char)
let bp :: ParsecT (Cursor IORef IO WrappedByteString Char)
()
(IterateeG WrappedByteString Char IO)
Re: [Haskell-cafe] Using Cabal during development
Eventually, I think using cabal during development may be convenient. The
only drawback is that you have to specify each dependency and -- above all
-- every module each time you add one.
Nevertheless, I'm not convinced regarding the use of Makefiles with Cabal. I
happen to think it's a bit outsize.
A shell script is enough.
By the way, I've found another way to develop simultaneously a (or many)
library(ies) and an executable.
It would be to use a local ghc package database.
In my project directory, I do:
ghc-pky init pkg.conf.d
It create a directory pkg.conf.d which will contain my local database.
Then all the libs must be configured with:
cabal configure --package-db pkg.conf.d
(or 'runhaskell Setup.hs configure --package-db pkg.conf.d' if you don't use
cabal-install)
Then build normally ('cabal build')
Then, the little trouble is that you have to register you newly-built
manually with a:
cabal register --inplace
(Anyone knows how to tell cabal to register automatically to the local pkg
database?)
Then, to compile you executable with ghc (because Cabal is definitely not
convient when you have a lib and an executable in the same package):
ghc --make --package-conf pkg.conf.d main.hs
Again, should you have better/simpler ways to achieve this, I would be glad
to know them.
Simon Michael wrote:
Another great thread. I'm another who uses both make and cabal. I try to
automate a lot of things and find a makefile
easier for quick scripting. Perhaps at some point I'll get by with just
cabal. Here's an example:
http://joyful.com/repos/hledger/Makefile
An unusual feature, I think, is the use of the little-known sp tool for
auto-recompiling (see ci rule). Typically I
leave make ci running in an emacs shell window, where I can watch the
errors as I edit and save source. I don't have
clickable errors currently, I get by with linum-mode. When I need to
explore I'll run ghci in another shell window.
After reading this thread, I'm going to try using C-c C-l more.
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[Haskell-cafe] Re: Using Cabal during development
Eventually, I think using cabal during development may be convenient. The only drawback is that you have to specify each dependency and -- above all -- every module each time you add one. When writing bindings-posix, bindings-glib etc., which have lots of modules, I used a shell script to take all modules under ./src to .cabal. What it did was: 1) for each subdirectory, create a .hs file that reimport all modules under that subdirectory; 2) list all .hs (and, in my case, also .hsc) under ./src and insert then into .cabal. I've found that scripts of this kind have been very usefull. They require you to follow some rules (like, say, all modules with name mapping to directories are always a reimport of submodules). Then, to compile you executable with ghc (because Cabal is definitely not convient when you have a lib and an executable in the same package): ghc --make --package-conf pkg.conf.d main.hs Again, should you have better/simpler ways to achieve this, I would be glad to know them. I usually find useful, at first, to build only the executable and leave the library. When modules get stable enough, I separate both. Other scripts have been also usefull: one to check uncommited changes in all packages I'm working in, other to sync all my local packages with their repos. You could have a single 'b' script you could run like: b l # build and install your library in local database b t # build and run your test package executable b m # update module list in .cabal file for all your packages etc. Best, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seen on reddit: or, foldl and foldr considered slightly harmful
On Thu, Feb 11, 2010 at 11:00:51AM +0100, Ketil Malde wrote: Johann Höchtl johann.hoec...@gmail.com writes: In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he considers foldl and foldr harmful as they hinder parallelism because of Process first element, then the rest Instead he proposes a divide and merge aproach, especially in the light of going parallel. In Haskell foldl/foldr apply to linked lists (or lazy streams, if you prefer) which are already inherently sequential, and gets a rather harsh treatment. I notice he points to finger trees, which I though was implemented in Data.Sequence. Direct URL for the slides: http://research.sun.com/projects/plrg/Publications/ICFPAugust2009Steele.pdf As he says, associativity is the key to parallelism -- an old observation, but still underappreciated. Even without parallelism, associativity also gives us greater freedom in structuring our solutions. The moral is that our datatypes need associative binary operations more than asymmetric ones. We use lists too much (because they're so convenient) and apart from the loss of parallelism it constrains our thinking to the sequential style criticised by Backus back in 1978. Regarding finger trees, he's just referring to the idea of caching the results of monoidal folds in nodes of a tree. That's crucial to the applications of finger trees, but it can be applied to any kind of tree. As he mentions, it's related to the Ladner-Fischer parallel prefix algorithm, which has an upward pass accumulating sums for each subtree followed by a downward accumulation passing each sum into the subtree to the right. But it's not just for parallelism: when you have these cached values in a balanced tree, you can compute the sum of any prefix in O(log n) steps. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] If monads are single/linearly threaded, doesn't that reduce parallelism?
Perhaps if you search for Abelian Monad or so, you will find interesting things in the category theory literature. Some of them may be transplantable to Haskell --- but you probably don't want a completely commutative structure. Arrows seem to express the dependencies between operations more fine-grained than the sequencing that Monads require. (I meant to look into arrows for ages..) Matthias. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using Cabal during development
On Thu, Feb 11, 2010 at 5:28 AM, Limestraël limestr...@gmail.com wrote: Eventually, I think using cabal during development may be convenient. The only drawback is that you have to specify each dependency... I actually think this is a benefit, not a drawback. In one of my projects where I used makefiles, I was depending on a variety of hackage projects. I was using development code from one of these that had not yet made it onto hackage. There was a period of time where I didn't do much development, and when I came back, I updated to the most recent development code and discovered that it broke my build. Since I didn't have all my dependencies specified and didn't know which devel version I had been using, I was unable to build the project until I fixed all the places where the update to the other package broke my code. If you are on a tight time schedule, this could be very problematic, whereas if you had specified the dependencies, cabal would easily be able to get the right versions for you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
I am working on an analytics server with a web front end. Being a personal endeavor at this time, I can choose any language that I fancy. I love Haskell and have achieved a modicum of proficiency with many years of following along. I spent a few weeks of serious Haskell prototyping and came to the realization that Haskell has a very steep learning curve to become truly proficient in it. The basics are easy, the various typeclasses can be understood with some study. But, there are thousands of packages on Hackage and not much documentation on most them. Another issue for me is the lack of a cohesive infrastructure for working with web services. Now my work has shifted to Clojure. I like it so far but I miss the elegance of Haskell. Whether Haskell becomes an easy choice for commercial work or remains a boutique language depends on how easy it is to build today's applications. But, I still love Haskell :) Praki On Thu, Feb 11, 2010 at 1:39 AM, Michael Oswald muell...@gmx.net wrote: On 02/10/2010 04:59 PM, Jason Dusek wrote: I wonder how many people actually write Haskell, principally or exclusively, at work? Well, my main language at work in the moment is C++, we also use Java, a lot of Tcl and Python. I use Haskell for my own programs and test utilities / converters. The biggest achievement at work was an Installer program, which was quite complicated and had to be safe and of course we had time pressure, so I quickly coded it in Haskell. It is now used in the installation procedure of a part from a big mission control system for satellites. lg, Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.google.com/profiles/praki.prakash ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Hello, elegance of Haskell. Whether Haskell becomes an easy choice for commercial work or remains a boutique language depends on how easy it is to build today's applications. Do you (or anyone reading this thread) know of some kind of wishlist of missing features and/or libraries? Would be nice to see what's still missing. - Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seen on reddit: or, foldl and foldr considered slightly harmful
On Feb 11, 2010, at 3:41 AM, Johann Höchtl wrote: In a presentation of Guy Steele for ICFP 2009 in Edinburgh: http://www.vimeo.com/6624203 he considers foldl and foldr harmful as they hinder parallelism because of Process first element, then the rest Instead he proposes a divide and merge aproach, especially in the light of going parallel. The slides at http://docs.google.com/viewer?url=http%3A%2F%2Fresearch.sun.com%2Fprojects%2Fplrg%2FPublications%2FICFPAugust2009Steele.pdf [Bware: Google docs] There's no need to use Google docs. A direct url for the pdf: http://research.sun.com/projects/plrg/Publications/ICFPAugust2009Steele.pdf I recently gave a followup talk at Portland State, arguing that notation matters, and that even with better notation programmer mindset is also going to be hard to change: http://research.sun.com/projects/plrg/Publications/PSUJan2010-Maessen.pdf The key thing here isn't *just* the handedness of lists, but the handedness of foldl/foldr *irrespective of the underlying data structure*. So switching to tree-structured data a la fingertrees is a necessary step, but not a sufficient one. The use of monoidal reductions has always been an important part of parallel programming. are somewhat geared towards Fortress, but I wonder what Haskellers have to say about his position. Now, what if list comprehensions were really shorthand for construction of Applicative or Monoid structures by traversing a mixture of data types with a common interface (something like this one)? class Generator t e | t - e mapReduce :: (Monoid m) = t - (e - m) - m -Jan-Willem Maessen Another Fortress/Haskell crossover Greetings, Johann ___ 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] Re: How many Haskell Engineer I/II/IIIs are there?
I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? /jve On Thu, Feb 11, 2010 at 10:12 AM, Michael Lesniak mlesn...@uni-kassel.dewrote: Hello, elegance of Haskell. Whether Haskell becomes an easy choice for commercial work or remains a boutique language depends on how easy it is to build today's applications. Do you (or anyone reading this thread) know of some kind of wishlist of missing features and/or libraries? Would be nice to see what's still missing. - Michael ___ 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] Re: Haskell-Cafe Digest, Vol 78, Issue 14
Maciej Piechotka uzytkown...@gmail.com writes: On Tue, 2010-02-09 at 16:41 +, John Lato wrote: See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a valid Stream instance using iteratee. Also Gregory Collins recently posted an iteratee wrapper for Attoparsec to haskell-cafe. To my knowledge these are not yet in any packages, but hackage is vast. Hmm. Am I correct that his implementation caches everything? The one that John posted (iteratees on top of parsec) has to keep a copy of the entire input, because parsec wants to be able to do arbitrary backtracking on the stream. Attoparsec provides an *incremental* parser. You feed it bite-sized chunks of an input stream, and it either says ok, I'm done, here's your value, and the rest of the stream I didn't use or I couldn't finish, here's a parser continuation you can feed more chunks to. This, of course, is a perfect conceptual match for iteratees -- with a little bit of plumbing you should be able to parse a stream in O(1) space. I tried to rewrite the implementation using... well imperative linked list. For trivial benchmark it have large improvement (althought it may be due to error in test such as using ByteString) and, I believe, that it allows to free memory before finish. Results of test on Core 2 Duo 2.8 GHz: 10: 0.000455s 0.000181s 100: 0.000669s 0.001104s 1000: 0.005209s 0.023704s 1:0.053292s 1.423443s 10: 0.508093s 132.208597s Which column corresponds to which module here, and which module are you benchmarking against, John's or mine? G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
On Thu, Feb 11, 2010 at 6:30 PM, John Van Enk vane...@gmail.com wrote: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? Could you be a bit more precise about your RTS needs? For example, if you want to run Haskell on raw hardware you might be interested with House project, http://programatica.cs.pdx.edu/House/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
I'm not specifically interested in raw hardware, but I am interested in, say, making the garbage collection deterministic and altering the scheduler to fit some other needs. I'll try and find a link to the paper describing the GC i want to implement On Thu, Feb 11, 2010 at 11:10 AM, Ivan Panachev ivan.panac...@gmail.comwrote: On Thu, Feb 11, 2010 at 6:30 PM, John Van Enk vane...@gmail.com wrote: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? Could you be a bit more precise about your RTS needs? For example, if you want to run Haskell on raw hardware you might be interested with House project, http://programatica.cs.pdx.edu/House/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell and the Job Market, e.g. with Google
Hello, Somewhat in response to the original post about Haskell engineers I, II and III. This confirms the remark that Haskell experience is now being appreciated, though not (yet) used (very much). Steven Grant, recruiter from Google, asked me to bring to his attention anyone who might be suitable, so that's what I'm doing. start quote We are currently aggressively recruiting for a large number of engineers in EMEA. I spotted your extensive open source experience and was particularily interested to see you have worked with Haskell. I am not looking for a Haskell developer but more interested in people that have worked in exotic languages such as Haskell or Erlang or Scheme. The roles we have are heavily open sourced based and will be mainly working with Python, C, Linux, shell etc and are based in Dublin, London or Zurich. If you have any interest in discussing these further, drop me an email to stevengr...@google.com and we can discuss. end quote From a second email: start quote The job specs are below. http://www.google.ie/support/jobs/bin/answer.py?answer=34884 http://www.google.ie/support/jobs/bin/answer.py?answer=34883 The roles are within a very specialist team within Google. They are a hybrid type role and are responsible for making our products reliable scalable and more efficient. end quote Get in touch with Steven: Steven Grant European IT Staffing Phone: +353 1 543 5083 Google Ireland Ltd., Barrow Street, Dublin 4, Ireland Registered in Dublin, Ireland Registration Number: 368047 I think this is interesting even to those who are not looking for a job right now, since it shows the current mind-set regarding Haskell, at a major and leading IT company. Best Regards, Hans van Thiel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Here's the paper: http://comjnl.oxfordjournals.org/cgi/content/abstract/33/5/466 On Thu, Feb 11, 2010 at 11:45 AM, John Van Enk vane...@gmail.com wrote: I'm not specifically interested in raw hardware, but I am interested in, say, making the garbage collection deterministic and altering the scheduler to fit some other needs. I'll try and find a link to the paper describing the GC i want to implement On Thu, Feb 11, 2010 at 11:10 AM, Ivan Panachev ivan.panac...@gmail.comwrote: On Thu, Feb 11, 2010 at 6:30 PM, John Van Enk vane...@gmail.com wrote: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? Could you be a bit more precise about your RTS needs? For example, if you want to run Haskell on raw hardware you might be interested with House project, http://programatica.cs.pdx.edu/House/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Is JHC not suitable in this case? It won't compile all of Haskell but it does some to be doing the right things as regards a pluggable RTS. I think it's fair to say at this point that GHC can compile all the Haskell we want and that new Haskell pieces will come to GHC before anything else gets them. So going with a totally new system, front-to-back, is not really desirable when all you want is a new RTS; however, I don't think GHC was designed to be a Haskell compiler superserver. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Streamed creation of STArray from list?
Hello, I was wondering if there is a trick for generating a new STArray from a list in such a way that you do not have to hold both the list and array in memory? http://www.haskell.org/ghc/docs/latest/html/libraries/array-0.3.0.0/Data-Array-MArray.html As far as I can tell, that is the interface for creating ST Arrays. For example, newListArray looks almost perfect: *newListArray* :: (MArrayhttp://www.haskell.org/ghc/docs/latest/html/libraries/array-0.3.0.0/Data-Array-MArray.html#t%3AMArraya e m, Ixhttp://www.haskell.org/ghc/docs/latest/html/libraries/base-4.2.0.0/Data-Ix.html#t%3AIxi) = (i, i) - [e] - m (a i e) If I know the length of the list, I might expect newListArray to have the memory behavior I want. In my case, the code calls (length xs) to calculate the length of the list. As I understand it, that will force the spine of the list into memory. Can this be avoided? The only trick that comes into mind is the one used by the C++ vector class where you dynamically resize the array and copy the values to the new array. That's potentially a lot of copying, right? Is some other array better suited for this, such as vector or uvector? Thanks, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Well, my point here is that if we want to see GHC branch into other fields (mine being safety critical), and actually see the code generated by GHC be what's really running (rather than once-removed in the form of an EDSL), some changes will have to be made. Being able to experiment with GHC's RTS and possibly being able to write your own (should the project require it) would go a long way to helping me make the case for GHC in safety critical. Perhaps I'd be better off looking at UHC/LHC/JHC as a starting place. /jve On Thu, Feb 11, 2010 at 12:13 PM, Jason Dusek jason.du...@gmail.com wrote: Is JHC not suitable in this case? It won't compile all of Haskell but it does some to be doing the right things as regards a pluggable RTS. I think it's fair to say at this point that GHC can compile all the Haskell we want and that new Haskell pieces will come to GHC before anything else gets them. So going with a totally new system, front-to-back, is not really desirable when all you want is a new RTS; however, I don't think GHC was designed to be a Haskell compiler superserver. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell-src type inference algorithm?
Anyone know of a type inference utility that can run right on haskell-src types? or one that could be easily adapted? I want to be able to pass in an HsExp and get back an HsQualType. It doesn't have to be fancy, plain Haskell98 types would do. It wouldn't be to hard to make one myself, but I figured there might be one floating around already and it'd be a shame to write it twice :) Thanks, - Job ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell-src type inference algorithm?
Hello Job For Haskell 98 would the code from 'Typing Haskell in Haskell' paper suffice? A web search should find the code... Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell-src type inference algorithm?
http://web.cecs.pdx.edu/~mpj/thih/ Looks like its a type _checker_ though... On 11 February 2010 17:39, Stephen Tetley stephen.tet...@gmail.com wrote: Hello Job For Haskell 98 would the code from 'Typing Haskell in Haskell' paper suffice? A web search should find the code... Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and the Job Market, e.g. with Google
On Thu, Feb 11, 2010 at 11:49 AM, Hans van Thiel hthiel.c...@zonnet.nl wrote: Hello, Somewhat in response to the original post about Haskell engineers I, II and III. This confirms the remark that Haskell experience is now being appreciated, though not (yet) used (very much). Steven Grant, recruiter from Google, asked me to bring to his attention anyone who might be suitable, so that's what I'm doing. start quote We are currently aggressively recruiting for a large number of engineers in EMEA. I spotted your extensive open source experience and was particularily interested to see you have worked with Haskell. I am not looking for a Haskell developer but more interested in people that have worked in exotic languages such as Haskell or Erlang or Scheme. The roles we have are heavily open sourced based and will be mainly working with Python, C, Linux, shell etc and are based in Dublin, London or Zurich. If you have any interest in discussing these further, drop me an email to stevengr...@google.com and we can discuss. end quote From a second email: start quote The job specs are below. http://www.google.ie/support/jobs/bin/answer.py?answer=34884 http://www.google.ie/support/jobs/bin/answer.py?answer=34883 The roles are within a very specialist team within Google. They are a hybrid type role and are responsible for making our products reliable scalable and more efficient. end quote Get in touch with Steven: Steven Grant European IT Staffing Phone: +353 1 543 5083 Google Ireland Ltd., Barrow Street, Dublin 4, Ireland Registered in Dublin, Ireland Registration Number: 368047 I think this is interesting even to those who are not looking for a job right now, since it shows the current mind-set regarding Haskell, at a major and leading IT company. Best Regards, Hans van Thiel I would be far from the first to remark that the 'Python Paradox' (http://www.paulgraham.com/pypar.html) has moved on and become the Scala/Haskell Paradox. -- gwern ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On 10.02.10 19:03, Bryan O'Sullivan wrote: I'm thinking of switching the statistics library over to using vector. that would be even better of course! an O(0) solution, at least for me ;) let me know if i can be of any help (e.g. in testing). i suppose uvector-algorithms would also need to be ported to vector, then. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? i've been using the library for wavelet transforms, matching pursuits and the like, and while my implementations are not heavily optimized, they perform reasonably well (no benchmarking done yet, though). the key arguments for using vector instead of uvector were the cleaner interface and Data.Vector.Storable for interfacing with foreign libraries (such as fftw, through the fft package). sk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell-src type inference algorithm?
To do anything interesting you also to process modules, something which I hope to contribute soon to haskell-src-exts. On Thu, Feb 11, 2010 at 6:35 PM, Job Vranish job.vran...@gmail.com wrote: Anyone know of a type inference utility that can run right on haskell-src types? or one that could be easily adapted? I want to be able to pass in an HsExp and get back an HsQualType. It doesn't have to be fancy, plain Haskell98 types would do. It wouldn't be to hard to make one myself, but I figured there might be one floating around already and it'd be a shame to write it twice :) Thanks, - Job ___ 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-src type inference algorithm?
It does type inference, it's just not engineered to be part of a real compiler. On Thu, Feb 11, 2010 at 6:41 PM, Stephen Tetley stephen.tet...@gmail.com wrote: http://web.cecs.pdx.edu/~mpj/thih/ Looks like its a type _checker_ though... On 11 February 2010 17:39, Stephen Tetley stephen.tet...@gmail.com wrote: Hello Job For Haskell 98 would the code from 'Typing Haskell in Haskell' paper suffice? A web search should find the code... Best wishes Stephen ___ 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] vector to uvector and back again
stefan kersten schrieb: uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? i've been using the library for wavelet transforms, matching pursuits and the like, Nice I have also worked on this topics, even with Haskell. However, at that time I used plain lists. and while my implementations are not heavily optimized, they perform reasonably well (no benchmarking done yet, though). the key arguments for using vector instead of uvector were the cleaner interface and Data.Vector.Storable for interfacing with foreign libraries (such as fftw, through the fft package). Btw. Data.StorableVector can also be used for this interfacing, and I would be very interested in an interface to FFTW. Actually, I have already used FFTW on StorableVector http://code.haskell.org/~thielema/morbus-meniere/src/StorableVectorCArray.hs There is also Data.StorableVector.Lazy which is nice for processing stream data. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
John Van Enk schrieb: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? As far as I know JHC is intended to work without an RTS. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Hackage download statistis
Hi, all, Some time ago a download statistic of hackage was made available, and analysed in a few ways. Googling for it still find that at a Galois web page. I though that, since the tools to get that were there, this would be output once in a while, but it seems it hasn't been done since then. Does anyone know if there are plans about that? Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
On Thu, Feb 11, 2010 at 06:57:48PM +0100, Henning Thielemann wrote: John Van Enk schrieb: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? As far as I know JHC is intended to work without an RTS. It is more that the RTS is generated as a part of the normal code generation process, this is done by implementing as much as possible in haskell itself, jhc has a very rich set of unboxed primitives, making it as expressible as c-- for the most part, for the bits of C I do need, I try to make them conditionally compilable, so parts that arn't used will not be included. all in all, the overhead is ~= 1k or so. A side effect is that jhc is very lightly coupled to any particular RTS, so experimenting with alternate ones is pretty straigtforward. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Implementing an alternative RTS for GHC seems like a viable Google Summer of Code project to me. What do you think? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell-src type inference algorithm?
On Thu, Feb 11, 2010 at 9:35 AM, Job Vranish job.vran...@gmail.com wrote: Anyone know of a type inference utility that can run right on haskell-src types? or one that could be easily adapted? I want to be able to pass in an HsExp and get back an HsQualType. It doesn't have to be fancy, plain Haskell98 types would do. It wouldn't be to hard to make one myself, but I figured there might be one floating around already and it'd be a shame to write it twice :) I've never checked to know if this is true, but could you use the GHC API to have GHC do your type inference/checking? http://www.haskell.org/ghc/docs/latest/html/libraries/ghc-6.12.1/index.html If you figure out if this is possible (or not), I'd love to hear what you figure out. Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Streamed creation of STArray from list?
On Thu, Feb 11, 2010 at 9:23 AM, Jason Dagit da...@codersbase.com wrote: If I know the length of the list, I might expect newListArray to have the memory behavior I want. In my case, the code calls (length xs) to calculate the length of the list. As I understand it, that will force the spine of the list into memory. Can this be avoided? The only trick that comes into mind is the one used by the C++ vector class where you dynamically resize the array and copy the values to the new array. That's potentially a lot of copying, right? Not really: as long as you grow the array exponentially the total number of copies is linear in the size of the array. On average you will copy each element twice; the first element gets copied (log n) times but the last half of the elements go directly into the final array. If you want to avoid putting any of the spine into memory you might do a third copy where you shrink the array size at the end (or perhaps there is an array type that has a 'shrink' operation that just reduces the bounds without freeing any memory) -- ryan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: sendfile leaking descriptors on Linux?
On Wed, Feb 10, 2010 at 1:15 PM, Bardur Arantsson s...@scientician.netwrote: I've also been contemplating some solutions, but I cannot see any solutions to this problem which could reasonably be implemented outside of GHC itself. GHC lacks a threadWaitError, so there's no way to detect the problem except by timeout or polling. Solutions involving timeouts and polling are bad in this case because they arbitrarily restrict the client connection rate. Cheers, I believe solutions involving polling and timeouts may be the *only* solution due to the way TCP works. There are two cases to consider here: 1. what happens when the remote client does a proper disconnect by sending a FIN packet, etc 2. what happens when the remote client just drops the connection Case #1 - Proper Disconnect I believe that in case we are ok. select() may not wakeup due to the socket being closed -- but something will eventually cause select() to wakeup, and then next time through the loop, the call to select will fail with EBADF. This will cause everyone to wakeup. We can test this case by writing a client that purposely (and correctly) terminations the connection while threadWaitWrite is blocking and see if that causes it to wakeup. To ensure that the IOManager is eventually waking up, the server can have an IO thread that just does, forever $ threadDelay (1*10^6) Look here for more details: http://darcs.haskell.org/packages/base/GHC/Conc.lhs Case #2 - Sudden Death In this case, there is no way to tell if the client is still there with out trying to send / recv data. A TCP connection is not a 'tangible' link. It is just an agreement to send packets to/from certain ports with certain sequence numbers. It's much closer to snail mail than a telephone call. If you set the keepalive socket option, then the TCP layer will automatically ping the connection to make sure it is still alive. However, I believe the default time between keepalive packets is 2 hours, and can only be changed on a system wide basis? http://www.unixguide.net/network/socketfaq/2.8.shtml The other option is to try to send some data. There are at least two cases that can happen here. 1. the network cable is unplugged -- this is not an 'error'. The write buffer will fill up and it will wait until it can send the data. If the write buffer is full, it will either block or return EAGAIN depending on the mode. Eventually, after 2 hours, it might give up. 2. the remote client has terminated the connection as far as it is concerned but not notified the server -- when you try to send data it will reject it, and send/write/sendfile/etc will raise sigPIPE. Looking at your debug output, we are seeing the sigPIPE / Broken Pipe error most of the time. But then there is the case where we get stuck on the threadWaitWrite. threadWaitWrite is ultimately implemented by passing the file descriptor to the list of write descriptors in a call to select(). It seems, however, that select() is not waking up just because calling write() on a file descriptor *would* cause sigPIPE. The easiest way to confirm this case is probably to write a small, pure C program and see what really happens. If this is the case, then it means the only way to tell if the client has abruptly dropped the connection is to actually try sending the data and see if the sending function calls sigPIPE. And that means doing some sort of polling/timeout? What do you think? I do not have a good explanation as to why the portable version does not fail. Except maybe it is just so slow that it does not ever fill up the buffer, and hence does not get stuck in threadWaitWrite? Any way, the fundamental question is: When your write buffer is full, and you call select() on that file descriptor, will select() return in the case where calling write() again would raise sigPIPE? - jeremy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 78, Issue 14
On Thu, 2010-02-11 at 11:00 -0500, Gregory Collins wrote: Maciej Piechotka uzytkown...@gmail.com writes: On Tue, 2010-02-09 at 16:41 +, John Lato wrote: See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a valid Stream instance using iteratee. Also Gregory Collins recently posted an iteratee wrapper for Attoparsec to haskell-cafe. To my knowledge these are not yet in any packages, but hackage is vast. Hmm. Am I correct that his implementation caches everything? The one that John posted (iteratees on top of parsec) has to keep a copy of the entire input, because parsec wants to be able to do arbitrary backtracking on the stream. Well. Not quite. AFAIU (and ByteString implementation indicate so) the uncons have a type uncons :: s - m (Maybe (t, s)) Where s indicates the position on the stream. Since it is impossible to get back from having s alone the GC should be free to finalize all memory allocated to cache the stream before the first living s. I.e. if input is: text = 'L':'o':'r':'e':'m':' ':'i':'p':'s':'u':'m':[] ^ ^ s1 s2 and s1 and s2 are position in the stream (for stream that is list) GC can free Lor part. It seems that it might be significant in real live as try calls are relatively short comparing with rest of code. By keeping s as 'pointer to' element second uncons have O(1) time instead of O(n). I tried to rewrite the implementation using... well imperative linked list. For trivial benchmark it have large improvement (althought it may be due to error in test such as using ByteString) and, I believe, that it allows to free memory before finish. Results of test on Core 2 Duo 2.8 GHz: 10: 0.000455s 0.000181s 100:0.000669s 0.001104s 1000: 0.005209s 0.023704s 1: 0.053292s 1.423443s 10: 0.508093s 132.208597s Which column corresponds to which module here, and which module are you benchmarking against, John's or mine? G As I'm implementing for parsec (I don't know attoparsec) [as a kind of exercise to get iteratee better] I benchmarked against John's. My results are on the left. I forgot to compile and optimize. Here's result for ByteString: MineJohn's 10: 0.000425s 0.000215s 100:0.000616s 0.001963s 1000: 0.0041s 0.048359s 1: 0.041694s 4.492774s 10: 0.309289s 434.238449s And []: MineJohn's 10: 0.000605s 0.000932s 100:0.001464s 0.008101s 1000: 0.004036s 0.054125s 1: 0.032341s 1.36938s 10: 0.317859s 115.846891s Regards and sorry for confusion PS. Sorry - I know that test is somehow simplistic but I thing it emulates real live situation where you are interested in small amount of elements around current position (short try). I also think that /dev/zero have relatively predictable access time (it does not need to be loaded from slow disk first after which it can be accessed from cache, it does not run out of entropy etc.). signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 78, Issue 14
On Thu, Feb 11, 2010 at 1:27 PM, Maciej Piechotka uzytkown...@gmail.com wrote: On Thu, 2010-02-11 at 11:00 -0500, Gregory Collins wrote: Maciej Piechotka uzytkown...@gmail.com writes: On Tue, 2010-02-09 at 16:41 +, John Lato wrote: See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a valid Stream instance using iteratee. Also Gregory Collins recently posted an iteratee wrapper for Attoparsec to haskell-cafe. To my knowledge these are not yet in any packages, but hackage is vast. Hmm. Am I correct that his implementation caches everything? The one that John posted (iteratees on top of parsec) has to keep a copy of the entire input, because parsec wants to be able to do arbitrary backtracking on the stream. Well. Not quite. AFAIU (and ByteString implementation indicate so) the uncons have a type uncons :: s - m (Maybe (t, s)) Where s indicates the position on the stream. Since it is impossible to get back from having s alone the GC should be free to finalize all memory allocated to cache the stream before the first living s. I'm not sure that this is correct - parsec believes that it is free to call 'uncons' multiple times on the same value and receive an equivalent answer. Maybe I'm misunderstanding what we're talking about, but a simple test is: backtrackTest = (try (string aardvark)) | (string aaple) And then attempt to parse the stream equivalent to aaple with 'backtrackTest'. This should be a successful parse (untested). Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On 11.02.10 18:55, Henning Thielemann wrote: i've been using the library for wavelet transforms, matching pursuits and the like, Nice I have also worked on this topics, even with Haskell. However, at that time I used plain lists. interesting! was performance acceptable for practical work? at the moment i'm not too concerned about performance -- the base line maybe could be to be competitive with matlab. in the long run i hope i'll be able to scale my stuff to larger amounts of data, however ... and while my implementations are not heavily optimized, they perform reasonably well (no benchmarking done yet, though). the key arguments for using vector instead of uvector were the cleaner interface and Data.Vector.Storable for interfacing with foreign libraries (such as fftw, through the fft package). Btw. Data.StorableVector can also be used for this interfacing, and I would be very interested in an interface to FFTW. Actually, I have already used FFTW on StorableVector i'm simply using the fft package and adapted some of it's internals to work on Data.Vector.Storable; nothing fancy though, and only for RC and CR transforms. let me know if you're interested in the code ... There is also Data.StorableVector.Lazy which is nice for processing stream data. yes, i know about storablevector, but i already had some code using uvector, so in the end vector was the easier upgrade. to me the relative merits of storablevector vs. vector are still unclear; the lazy interface could be implemented on top of vector as well, i suppose? sk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Iteratee and parsec (was: Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 78, Issue 14)
On Thu, 2010-02-11 at 13:34 -0600, Antoine Latter wrote:
On Thu, Feb 11, 2010 at 1:27 PM, Maciej Piechotka
uzytkown...@gmail.com wrote:
On Thu, 2010-02-11 at 11:00 -0500, Gregory Collins wrote:
Maciej Piechotka uzytkown...@gmail.com writes:
On Tue, 2010-02-09 at 16:41 +, John Lato wrote:
See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a
valid
Stream instance using iteratee. Also Gregory Collins recently
posted
an iteratee wrapper for Attoparsec to haskell-cafe. To my
knowledge
these are not yet in any packages, but hackage is vast.
Hmm. Am I correct that his implementation caches everything?
The one that John posted (iteratees on top of parsec) has to keep a
copy
of the entire input, because parsec wants to be able to do
arbitrary
backtracking on the stream.
Well. Not quite. AFAIU (and ByteString implementation indicate so)
the
uncons have a type
uncons :: s - m (Maybe (t, s))
Where s indicates the position on the stream. Since it is impossible
to
get back from having s alone the GC should be free to finalize all
memory allocated to cache the stream before the first living s.
I'm not sure that this is correct - parsec believes that it is free
to call 'uncons' multiple times on the same value and receive an
equivalent answer.
That's what I meant. But it have to keep the reference to the first
element.
Consider example with list:
text = 'L':'o':'r':'e':'m':' ':'i':'p':'s':'u':'m':[]
^ ^ ^
s1 s2 s3
uncons s1 == Identity (Just ('e', 'm':' ':'i':'p':'s':'u':'m':[]))
uncons s2 == Identity (Just ('p', 's':'u':'m':[]))
uncons s3 == Identity Nothing
However we will never get (nor we keep reference to):
'L':'o':'r':'e':'m':' ':'i':'p':'s':'u':'m':[],
'o':'r':'e':'m':' ':'i':'p':'s':'u':'m':[]
'r':'e':'m':' ':'i':'p':'s':'u':'m':[]
so those values can be freed as they are before first pointer (namely
s1).
Regards
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[Haskell-cafe] Re: sendfile leaking descriptors on Linux?
Jeremy Shaw wrote: On Wed, Feb 10, 2010 at 1:15 PM, Bardur Arantsson s...@scientician.netwrote: I've also been contemplating some solutions, but I cannot see any solutions to this problem which could reasonably be implemented outside of GHC itself. GHC lacks a threadWaitError, so there's no way to detect the problem except by timeout or polling. Solutions involving timeouts and polling are bad in this case because they arbitrarily restrict the client connection rate. Cheers, I believe solutions involving polling and timeouts may be the *only* solution due to the way TCP works. There are two cases to consider here: True, but my point was rather that a solution in the sendfile libary would incur an _extra_ timeout on top of the timeout which is handled by the OS. It's very hard to come up with a proper timeout here because apps will have different requirements depending on the expected connection rate, etc. This is what I see as unacceptable since it would have to be a completely arbitrary timeout -- there's no way for the application to specify a timeout to the sendfile library since the API doesn't permit it. [--snip--] Case #1 - Proper Disconnect I believe that in case we are ok. select() may not wakeup due to the socket being closed -- but something will eventually cause select() to wakeup, and then next time through the loop, the call to select will fail with EBADF. This will cause everyone to wakeup. We can test this case by writing a client that purposely (and correctly) terminations the connection while threadWaitWrite is blocking and see if that causes it to wakeup. To ensure that the IOManager is eventually waking up, the server can have an IO thread that just does, forever $ threadDelay (1*10^6) Look here for more details: http://darcs.haskell.org/packages/base/GHC/Conc.lhs I don't have time to write a C test program right now. I'm actually not 100% convinced that this case is *not* problematic, but my limited testing with well-behaved clients (wget, curl) hasn't turned up any problems so far. Case #2 - Sudden Death In this case, there is no way to tell if the client is still there with out trying to send / recv data. A TCP connection is not a 'tangible' link. It is just an agreement to send packets to/from certain ports with certain sequence numbers. It's much closer to snail mail than a telephone call. If you set the keepalive socket option, then the TCP layer will automatically ping the connection to make sure it is still alive. However, I believe the default time between keepalive packets is 2 hours, and can only be changed on a system wide basis? http://www.unixguide.net/network/socketfaq/2.8.shtml There are some options you can set via setsockopt(), see man 7 tcp: tcp_keepalive_intvl(default: 75s) tcp_fin_timeout(default: 60s) (The latter is the amount of time to wait for the final FIN before forcing a the socket to close.) These can be set per-socket. The other option is to try to send some data. There are at least two cases that can happen here. This is what I tried. The trouble here is that you have to force the thread doing threadWaitWrite to wake up periodically... and how do you decide how often? Too often and you're burning CPU doing nothing, too seldom and you're letting threads (and by implication used-but-really-disconnected-as-far-as-the-OS-is-concerned file descriptors) pile up. The overhead of mempcy (avoidance of which is sendfile's raison-d'être) is probably much less than the overhead of doing all this administration in userspace instead of just letting the kernel do its thing. Even waking up very seldom (~1/s IIRC) incurred a lot of CPU overhead in my test case... but I suppose I could give it another try to see if I'd made some mistake in my code which caused it to use more CPU than necessary. 1. the network cable is unplugged -- this is not an 'error'. The write buffer will fill up and it will wait until it can send the data. If the write buffer is full, it will either block or return EAGAIN depending on the mode. Eventually, after 2 hours, it might give up. I believe the socket is actually in non-blocking mode in my application. I'm not putting it into non-blocking mode, so I'm guessing that the accept call is doing that -- or maybe it's just the default behavior of accept() on Linux. Converting a socket to a Handle (which is what the portable sendfile does) automatically puts it into blocking mode. Actually, I think this whole issue could be avoided if the socket could just be forced into blocking mode. In that case, there would be no need to call threadWaitWrite: The native sendfile() call could never return EAGAIN (it would block instead), and so there'd be no need to call threadWaitWrite to avoid busy-waiting. 2. the remote client has terminated the connection as far as it is concerned but not notified the server -- when you try to send data it will reject it, and
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
I'd suggested this in an earlier SoC thread. 2010/2/11 Matthias Görgens matthias.goerg...@googlemail.com Implementing an alternative RTS for GHC seems like a viable Google Summer of Code project to me. What do you think? ___ 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] Re: How many Haskell Engineer I/II/IIIs are there?
I'll definitely take a closer look. On Thu, Feb 11, 2010 at 1:09 PM, John Meacham j...@repetae.net wrote: On Thu, Feb 11, 2010 at 06:57:48PM +0100, Henning Thielemann wrote: John Van Enk schrieb: I need to be able to swap out the RTS. The place I want to stick Haskell absolutely needs its own custom RTS, and currently, I don't think it's all that easy or clean to do that. Am I wrong? Are there resources describing how to do this already? As far as I know JHC is intended to work without an RTS. It is more that the RTS is generated as a part of the normal code generation process, this is done by implementing as much as possible in haskell itself, jhc has a very rich set of unboxed primitives, making it as expressible as c-- for the most part, for the bits of C I do need, I try to make them conditionally compilable, so parts that arn't used will not be included. all in all, the overhead is ~= 1k or so. A side effect is that jhc is very lightly coupled to any particular RTS, so experimenting with alternate ones is pretty straigtforward. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ 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] Re: How many Haskell Engineer I/II/IIIs are there?
It seems quite big for a 3 months project made by a student, though. 2010/2/11 Matthias Görgens matthias.goerg...@googlemail.com Implementing an alternative RTS for GHC seems like a viable Google Summer of Code project to me. What do you think? -- Alp Mestanogullari http://alpmestan.wordpress.com/ http://alp.developpez.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Undecidable instances with functional dependencies
I have the following class and instance class Register a r | a - r where instance (Register a ra, Register b rb) = Register (a,b) (ra,rb) where and GHC refuses the instance because of violated Coverage Condition. I have more instances like instance Register Int8 (Reg Int8) where instance Register Word8 (Reg Word8) where and for the set of instances I plan, the instance resolution will always terminate. I remember that the term 'undecidable instance' is not fixed and may be relaxed if a more liberal condition can be found. Is there a place, say a Wiki page, where we can collect examples where we think that the current check of GHC is too restrictive? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Undecidable instances with functional dependencies
-- {-# LANGUAGE FunctionalDependencies#-}
-- {-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}
module Register where
-- class Register a r | a - r
class Register a where
type R a
-- instance Register Int Int
instance Register Int where
type R Int = Int
-- instance Register Float Float
instance Register Float where
type R Float = Float
-- instance (Register a1 r1, Register a2 r2) = Register (a1, a2) (r1,
r2)
instance (Register a, Register b) = Register (a, b) where
type R (a, b) = (R a, R b)
On 12 Feb 2010, at 00:32, Henning Thielemann wrote:
I have the following class and instance
class Register a r | a - r where
instance (Register a ra, Register b rb) =
Register (a,b) (ra,rb) where
and GHC refuses the instance because of violated Coverage Condition.
I have more instances like
instance Register Int8 (Reg Int8) where
instance Register Word8 (Reg Word8) where
and for the set of instances I plan, the instance resolution will
always terminate. I remember that the term 'undecidable instance' is
not fixed and may be relaxed if a more liberal condition can be
found. Is there a place, say a Wiki page, where we can collect
examples where we think that the current check of GHC is too
restrictive?
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Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Perhaps just defining the interface and demonstrating that different RTS's are swappable would be enough? 2010/2/11 Alp Mestanogullari a...@mestan.fr It seems quite big for a 3 months project made by a student, though. 2010/2/11 Matthias Görgens matthias.goerg...@googlemail.com Implementing an alternative RTS for GHC seems like a viable Google Summer of Code project to me. What do you think? -- Alp Mestanogullari http://alpmestan.wordpress.com/ http://alp.developpez.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
Re: [Haskell-cafe] Re: sendfile leaking descriptors on Linux?
Bardur Arantsson s...@scientician.net wrote: ... then do errno - getErrno if errno == eAGAIN then do threadDelay 100 sendfile out_fd in_fd poff bytes else throwErrno Network.Socket.SendFile.Linux else return (fromIntegral sbytes) That is, I removed the threadWaitWrite in favor of just adding a threadDelay 100 when eAGAIN is encountered. With this code, I cannot provoke the leak. Unfortunately this isn't really a solution -- the CPU is pegged at ~50% when I do this and it's not exactly elegant to have a hardcoded 100 ms delay in there. :) I don't think it matters wrt the desired final solution, but this is NOT a 100 ms delay. It is a 0.1 ms delay, which is less than a GHC time slice and as such is basically a tight loop. If you use a reasonable value for the delay you will probably see the CPU being almost completely idle. Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
On Thu, Feb 11, 2010 at 1:49 PM, John Van Enk vane...@gmail.com wrote: Perhaps just defining the interface and demonstrating that different RTS's are swappable would be enough? I read a paper by (I think) a Simon, in which he described a haskell RTS. It would make it easier to experiment with GC, scheduling, and whatever else. I recall a few problems, such as performance, but nothing really intractable. Swappable RTS would be a nice side-effect. Unfortunately I don't remember the title of the paper. Maybe it had to do with the whole GMP thing? It might be big for SoC but perhaps there's some well-defined subset, like fix some blocking issue? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type arithmetic with ATs/TFs
Andrew Coppin wrote: OK, so I sat down today and tried this, but I can't figure out how. There are various examples of type-level arithmetic around the place. For example, http://www.haskell.org/haskellwiki/Type_arithmetic (This is THE first hit on Google, by the way. Haskell is apparently THAT popular!) But this does type arithmetic using functional dependencies; what I'm trying to figure out is how to do that with associated types. Any hints? Several people have now replied to this, both on and off-list. But all the replies use type families, not associated types. Now type families are something I don't yet comprehend. (Perhaps the replies will help... I haven't studied them yet.) What I understand is that ATs allow you to write things like class Container c where type Element c :: * ... And now you can explicitly talk about the kind of element a container can hold, rather than relying on the type constructor having a particular kind or something. So the above works for containers that can hold *anything* (such as lists), containers which can only hold *one* thing (e.g., ByteString), and containers which can hold only certain things (e.g., Set). ...which is great. But I can't see a way to use this for type arithmetic. Possibly because I don't have a dramatically solid mental model of exactly how it works. You'd *think* that something like class Add x y where type Sum x y :: * instance Add x y = Add (Succ x) y where type Sum (Succ x) y = Succ (Sum x y) ought to work, but apparently not. As to what type families - type declarations outside of a class - end up meaning, I haven't the vaguest idea. The Wiki page makes it sound increadibly complicated... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Happstack 0.4.1
I was unable to install happstack-data-0.4.1 on windows with GHC 6.12.1.
Here the log:
Resolving dependencies...
Configuring happstack-data-0.4.1...
Preprocessing library happstack-data-0.4.1...
Preprocessing executables for happstack-data-0.4.1...
Building happstack-data-0.4.1...
src\Happstack\Data\GOps.hs:54:0:
warning: no newline at end of file
src\Happstack\Data\SerializeTH.hs:88:0:
warning: no newline at end of file
[ 1 of 16] Compiling Happstack.Data.GOps ( src\Happstack\Data\GOps.hs,
dist\buil
d\Happstack\Data\GOps.o )
src\Happstack\Data\Serialize.hs:1:85:
Warning: -XPatternSignatures is deprecated: use
-XScopedTypeVariables or pra
gma {-# LANGUAGE ScopedTypeVariables #-} instead
src\Happstack\Data\Xml\Base.hs:6:13:
Warning: -XPatternSignatures is deprecated: use
-XScopedTypeVariables or pra
gma {-# LANGUAGE ScopedTypeVariables #-} instead
[ 2 of 16] Compiling Happstack.Data.Normalize (
src\Happstack\Data\Normalize.hs,
dist\build\Happstack\Data\Normalize.o )
[ 3 of 16] Compiling Happstack.Data.Migrate (
src\Happstack\Data\Migrate.hs, dis
t\build\Happstack\Data\Migrate.o )
[ 4 of 16] Compiling Happstack.Data.Default (
src\Happstack\Data\Default.hs, dis
t\build\Happstack\Data\Default.o )
[ 5 of 16] Compiling Happstack.Data.DeriveAll (
src\Happstack\Data\DeriveAll.hs,
dist\build\Happstack\Data\DeriveAll.o )
[ 6 of 16] Compiling Happstack.Data.Default.Generic (
src\Happstack\Data\Default
\Generic.hs, dist\build\Happstack\Data\Default\Generic.o )
[ 7 of 16] Compiling Happstack.Data.Xml.Base (
src\Happstack\Data\Xml\Base.hs, d
ist\build\Happstack\Data\Xml\Base.o )
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package array-0.3.0.0 ... linking ... done.
Loading package bytestring-0.9.1.5 ... linking ... done.
Loading package containers-0.3.0.0 ... linking ... done.
Loading package pretty-1.0.1.1 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package syb-with-class-0.6.1 ... linking ... done.
Loading package HUnit-1.2.2.1 ... linking ... done.
Loading package syb-0.1.0.2 ... linking ... done.
Loading package base-3.0.3.2 ... linking ... done.
Loading package Win32-2.2.0.1 ... linking ... done.
Loading package old-locale-1.0.0.2 ... linking ... done.
Loading package time-1.1.4 ... linking ... done.
Loading package random-1.0.0.2 ... linking ... done.
Loading package QuickCheck-1.2.0.0 ... linking ... done.
Loading package extensible-exceptions-0.1.1.1 ... linking ... done.
Loading package mtl-1.1.0.2 ... linking ... done.
Loading package old-time-1.0.0.3 ... linking ... done.
Loading package parsec-2.1.0.1 ... linking ... done.
Loading package hsemail-1.3 ... linking ... done.
Loading package network-2.2.1.7 ... linking ... done.
Loading package SMTPClient-1.0.1 ... linking ... done.
Loading package filepath-1.1.0.3 ... linking ... done.
Loading package directory-1.0.1.0 ... linking ... done.
Loading package process-1.0.1.2 ... linking ... done.
Loading package hslogger-1.0.7 ... linking ... done.
Loading package deepseq-1.1.0.0 ... linking ... done.
Loading package parallel-2.2.0.1 ... linking ... done.
Loading package strict-concurrency-0.2.2 ... linking ... done.
Loading package unix-compat-0.1.2.1 ... linking ... done.
Loading package happstack-util-0.4.1 ... linking ... done.
Loading package binary-0.5.0.2 ... linking ... done.
Loading package haskell98 ... linking ... done.
Loading package HaXml-1.13.3 ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
ghc.exe: dist\build\Happstack\Data\Default.o: unknown symbol
`_sybzmwithzmclassz
m0zi6zi1_DataziGenericsziSYBziWithClassziInstances_constrZMacbsZN_closure'
cabal: Error: some packages failed to install:
happstack-data-0.4.1 failed during the building phase. The exception was:
ExitFailure 1
I can create more detailed log if you need.
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Re: [Haskell-cafe] Type arithmetic with ATs/TFs
Actually, at least in GHC, associated types are just syntax sugar for type families. That is, this code: class Container c where type Element c :: * view :: c - Maybe (Element c,c) instance Container [a] where type Element [a] = a view [] = Nothing view (x:xs) = Just (x,xs) is the same as this code: type family Element c :: * class Container c where view :: c - Maybe (Element c, c) type instance Container [a] = a instance Container [a] where view [] = Nothing view (x:xs) = Just (x,xs) -- ryan On Thu, Feb 11, 2010 at 1:10 PM, Andrew Coppin andrewcop...@btinternet.com wrote: Andrew Coppin wrote: OK, so I sat down today and tried this, but I can't figure out how. There are various examples of type-level arithmetic around the place. For example, http://www.haskell.org/haskellwiki/Type_arithmetic (This is THE first hit on Google, by the way. Haskell is apparently THAT popular!) But this does type arithmetic using functional dependencies; what I'm trying to figure out is how to do that with associated types. Any hints? Several people have now replied to this, both on and off-list. But all the replies use type families, not associated types. Now type families are something I don't yet comprehend. (Perhaps the replies will help... I haven't studied them yet.) What I understand is that ATs allow you to write things like class Container c where type Element c :: * ... And now you can explicitly talk about the kind of element a container can hold, rather than relying on the type constructor having a particular kind or something. So the above works for containers that can hold *anything* (such as lists), containers which can only hold *one* thing (e.g., ByteString), and containers which can hold only certain things (e.g., Set). ...which is great. But I can't see a way to use this for type arithmetic. Possibly because I don't have a dramatically solid mental model of exactly how it works. You'd *think* that something like class Add x y where type Sum x y :: * instance Add x y = Add (Succ x) y where type Sum (Succ x) y = Succ (Sum x y) ought to work, but apparently not. As to what type families - type declarations outside of a class - end up meaning, I haven't the vaguest idea. The Wiki page makes it sound increadibly complicated... ___ 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] Examples/docs for simulated annealing bindings
On Thu, Oct 15, 2009 at 02:41:42PM +0100, Dougal Stanton wrote: I found the HsASA library [1] on Hackage, but there's no documentation and it's not particularly intuitive. I can't see any obvious way of choosing initial config or generating new configurations. Google reveals no one using it. Does anyone have ideas? Hi, performing ASA efficiently relies on a very efficient implementation of the algorithm, the actual parameters of the ASA are hard coded as C #defines, see the original C distribution for documentation on them. For using HsASA in projects, it is recommended you directly include the modules into your program and modify them with the specific parameters appropriate to your task. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type arithmetic with ATs/TFs
What Ryan said, and here's an example of addition with ATs, specifically (not thoroughly tested, but tested a little). The translation to TFs sans ATs is straightforward. class Add a b where type SumType a b instance Add Zero Zero where type SumType Zero Zero = Zero instance Add (Succ a) Zero where type SumType (Succ a) Zero = Succ a instance Add Zero (Succ a) where type SumType Zero (Succ a) = Succ a instance Add (Succ a) (Succ b) where type SumType (Succ a) (Succ b) = Succ (Succ (SumType a b)) On Thu, Feb 11, 2010 at 4:10 PM, Andrew Coppin andrewcop...@btinternet.com wrote: Andrew Coppin wrote: OK, so I sat down today and tried this, but I can't figure out how. There are various examples of type-level arithmetic around the place. For example, http://www.haskell.org/haskellwiki/Type_arithmetic (This is THE first hit on Google, by the way. Haskell is apparently THAT popular!) But this does type arithmetic using functional dependencies; what I'm trying to figure out is how to do that with associated types. Any hints? Several people have now replied to this, both on and off-list. But all the replies use type families, not associated types. Now type families are something I don't yet comprehend. (Perhaps the replies will help... I haven't studied them yet.) What I understand is that ATs allow you to write things like class Container c where type Element c :: * ... And now you can explicitly talk about the kind of element a container can hold, rather than relying on the type constructor having a particular kind or something. So the above works for containers that can hold *anything* (such as lists), containers which can only hold *one* thing (e.g., ByteString), and containers which can hold only certain things (e.g., Set). ...which is great. But I can't see a way to use this for type arithmetic. Possibly because I don't have a dramatically solid mental model of exactly how it works. You'd *think* that something like class Add x y where type Sum x y :: * instance Add x y = Add (Succ x) y where type Sum (Succ x) y = Succ (Sum x y) ought to work, but apparently not. As to what type families - type declarations outside of a class - end up meaning, I haven't the vaguest idea. The Wiki page makes it sound increadibly complicated... ___ 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-src type inference algorithm?
Anyone know of a type inference utility that can run right on haskell-src types? or one that could be easily adapted? This is very high on my wish-list for haskell-src-exts, and I'm hoping the stuff Lennart will contribute will go a long way towards making it feasible. I believe I can safely say that no such tool exists (and if it does, why haven't you told me?? ;-)), but if you implement (parts of) one yourself I'd be more than interested to see, and incorporate, the results. Cheers, /Niklas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Michael Lesniak wrote: Hello, elegance of Haskell. Whether Haskell becomes an easy choice for commercial work or remains a boutique language depends on how easy it is to build today's applications. Do you (or anyone reading this thread) know of some kind of wishlist of missing features and/or libraries? Would be nice to see what's still missing. HTTPS support in the HTTP library. One library that JustWorks (tm) for HTTP and HTTPS. Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell-Cafe Digest, Vol 78, Issue 14
On Thu, Feb 11, 2010 at 10:00 AM, Gregory Collins g...@gregorycollins.net wrote: Maciej Piechotka uzytkown...@gmail.com writes: On Tue, 2010-02-09 at 16:41 +, John Lato wrote: See http://inmachina.net/~jwlato/haskell/ParsecIteratee.hs for a valid Stream instance using iteratee. Also Gregory Collins recently posted an iteratee wrapper for Attoparsec to haskell-cafe. To my knowledge these are not yet in any packages, but hackage is vast. Hmm. Am I correct that his implementation caches everything? The one that John posted (iteratees on top of parsec) has to keep a copy of the entire input, because parsec wants to be able to do arbitrary backtracking on the stream. This is true, however I believe this alternative approach is also correct. The Cursor holds the stream state, and parsec holds on to the Cursor for backtracking. Data is only read within the Iteratee monad when it goes beyond the currently available cursors, at which point another cursor is added to the linked list (implemented with IORef or other mutable reference). The downside to this approach is that data is consumed from the iteratee stream for a partial parse, even if the parse fails. I did not want this behavior, so I chose a different approach. I tried to rewrite the implementation using... well imperative linked list. For trivial benchmark it have large improvement (althought it may be due to error in test such as using ByteString) and, I believe, that it allows to free memory before finish. Results of test on Core 2 Duo 2.8 GHz: 10: 0.000455s 0.000181s 100: 0.000669s 0.001104s 1000: 0.005209s 0.023704s 1: 0.053292s 1.423443s 10: 0.508093s 132.208597s I'm surprised your version has better performance for small numbers of elements. I wonder if it's partially due to more aggressive inlining from GHC or something of that nature. Or maybe your version compiles to a tighter loop as elements can be gc'd. I expected poor performance of my code for larger numbers of elements, as demonstrated here. I envisioned the usage scenario where parsers would be relatively short (20 chars), and most of the work would be done directly with iteratees. In this case it would be more important to preserve the stream state in the case of a failed parse, and the performance issues of appending chunks wouldn't arise either. Cheers, John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Happstack 0.4.1
As a work around install happstack-data like this:
cabal install -O0 happstack-data
More details at the end of this thread:
http://groups.google.com/group/happs/browse_thread/thread/c66c74294d8eabf/a4de5e67853925e0?lnk=gstq=happstack-data#a4de5e67853925e0
I am using GHC 6.13, and I believe this problem has been resolved. Not
sure what the best work around is in the meantime though. I guess I
should at least update the download page to mention it..
- jeremy
On Feb 11, 2010, at 4:19 PM, Станислав Черничкин
wrote:
I was unable to install happstack-data-0.4.1 on windows with GHC
6.12.1. Here the log:
Resolving dependencies...
Configuring happstack-data-0.4.1...
Preprocessing library happstack-data-0.4.1...
Preprocessing executables for happstack-data-0.4.1...
Building happstack-data-0.4.1...
src\Happstack\Data\GOps.hs:54:0:
warning: no newline at end of file
src\Happstack\Data\SerializeTH.hs:88:0:
warning: no newline at end of file
[ 1 of 16] Compiling Happstack.Data.GOps ( src\Happstack\Data
\GOps.hs, dist\buil
d\Happstack\Data\GOps.o )
src\Happstack\Data\Serialize.hs:1:85:
Warning: -XPatternSignatures is deprecated: use -
XScopedTypeVariables or pra
gma {-# LANGUAGE ScopedTypeVariables #-} instead
src\Happstack\Data\Xml\Base.hs:6:13:
Warning: -XPatternSignatures is deprecated: use -
XScopedTypeVariables or pra
gma {-# LANGUAGE ScopedTypeVariables #-} instead
[ 2 of 16] Compiling Happstack.Data.Normalize ( src\Happstack\Data
\Normalize.hs,
dist\build\Happstack\Data\Normalize.o )
[ 3 of 16] Compiling Happstack.Data.Migrate ( src\Happstack\Data
\Migrate.hs, dis
t\build\Happstack\Data\Migrate.o )
[ 4 of 16] Compiling Happstack.Data.Default ( src\Happstack\Data
\Default.hs, dis
t\build\Happstack\Data\Default.o )
[ 5 of 16] Compiling Happstack.Data.DeriveAll ( src\Happstack\Data
\DeriveAll.hs,
dist\build\Happstack\Data\DeriveAll.o )
[ 6 of 16] Compiling Happstack.Data.Default.Generic ( src\Happstack
\Data\Default
\Generic.hs, dist\build\Happstack\Data\Default\Generic.o )
[ 7 of 16] Compiling Happstack.Data.Xml.Base ( src\Happstack\Data\Xml
\Base.hs, d
ist\build\Happstack\Data\Xml\Base.o )
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package array-0.3.0.0 ... linking ... done.
Loading package bytestring-0.9.1.5 ... linking ... done.
Loading package containers-0.3.0.0 ... linking ... done.
Loading package pretty-1.0.1.1 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package syb-with-class-0.6.1 ... linking ... done.
Loading package HUnit-1.2.2.1 ... linking ... done.
Loading package syb-0.1.0.2 ... linking ... done.
Loading package base-3.0.3.2 ... linking ... done.
Loading package Win32-2.2.0.1 ... linking ... done.
Loading package old-locale-1.0.0.2 ... linking ... done.
Loading package time-1.1.4 ... linking ... done.
Loading package random-1.0.0.2 ... linking ... done.
Loading package QuickCheck-1.2.0.0 ... linking ... done.
Loading package extensible-exceptions-0.1.1.1 ... linking ... done.
Loading package mtl-1.1.0.2 ... linking ... done.
Loading package old-time-1.0.0.3 ... linking ... done.
Loading package parsec-2.1.0.1 ... linking ... done.
Loading package hsemail-1.3 ... linking ... done.
Loading package network-2.2.1.7 ... linking ... done.
Loading package SMTPClient-1.0.1 ... linking ... done.
Loading package filepath-1.1.0.3 ... linking ... done.
Loading package directory-1.0.1.0 ... linking ... done.
Loading package process-1.0.1.2 ... linking ... done.
Loading package hslogger-1.0.7 ... linking ... done.
Loading package deepseq-1.1.0.0 ... linking ... done.
Loading package parallel-2.2.0.1 ... linking ... done.
Loading package strict-concurrency-0.2.2 ... linking ... done.
Loading package unix-compat-0.1.2.1 ... linking ... done.
Loading package happstack-util-0.4.1 ... linking ... done.
Loading package binary-0.5.0.2 ... linking ... done.
Loading package haskell98 ... linking ... done.
Loading package HaXml-1.13.3 ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
ghc.exe: dist\build\Happstack\Data\Default.o: unknown symbol
`_sybzmwithzmclassz
m0zi6zi1_DataziGenericsziSYBziWithClassziInstances_constrZMacbsZN_closure
'
cabal: Error: some packages failed to install:
happstack-data-0.4.1 failed during the building phase. The exception
was:
ExitFailure 1
I can create more detailed log if you need.
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Re: [Haskell-cafe] Re: sendfile leaking descriptors on Linux?
On Feb 11, 2010, at 1:57 PM, Bardur Arantsson wrote:
2. the remote client has terminated the connection as far as it is
concerned but not notified the server -- when you try to send data
it will
reject it, and send/write/sendfile/etc will raise sigPIPE.
Looking at your debug output, we are seeing the sigPIPE / Broken
Pipe error
most of the time. But then there is the case where we get stuck on
the
threadWaitWrite.
threadWaitWrite is ultimately implemented by passing the file
descriptor to
the list of write descriptors in a call to select(). It seems,
however, that
select() is not waking up just because calling write() on a file
descriptor
*would* cause sigPIPE.
That's what I expect select() with an errfd FDSET would do.
Nope. The expectfds are only trigger in esoteric conditions. For TCP
sockets, I think it only occurs if there is out-of-band data available
to be read via recv() with the MSG_OOB flag.
http://uw714doc.sco.com/en/SDK_netapi/sockC.OoBdata.html
The easiest way to confirm this case is probably to write a small,
pure C
program and see what really happens.
If this is the case, then it means the only way to tell if the
client has
abruptly dropped the connection is to actually try sending the data
and see
if the sending function calls sigPIPE. And that means doing some
sort of
polling/timeout?
Correct, but the trouble is deciding how often to poll and/or how
long the timeout should be.
I don't see any easy answer to that. That's why my suggested
solution is to simply punt it to the OS (by using portable mode)
and suck up the extra overhead of the portable solution. Hopefully
the new GHC I/O manager will make it possible to have a proper
solution.
The whole point of the sendfile library is to use sendfile(), so not
using sendfile() seems like the wrong solution. I am also not
convinced that the new GHC I/O manager will do anything new to make it
possible to have a proper solution. I believe we would be seeing the
same error even in pure C, so we need to know the work around that
works in pure C as well. I am not convinced we are punting to the OS
by using portable mode either (more below).
I do not have a good explanation as to why the portable version
does not
fail. Except maybe it is just so slow that it does not ever fill up
the
buffer, and hence does not get stuck in threadWaitWrite?
The portable version doesn't call threadWaitWrite. It simply turns
the Socket into a handle (which causes it to become blocking) and
so the kernel is tasked with handling all the gritty details.
The portable version does not directly call threadWaitWrite, but it
still calls it.
Data.ByteString.Char8.hPutStr calls
Data.ByteString.hPut which calls
Data.ByteString.hPutBuf which calls
System.IO.hPutBuf which calls
GHC.IO.Handle.Text.hPutBuf which calls
GHC.IO.Handle.bufWrite.Text which calls
GHC.IO.Device.write which calls
GHC.IO.FD.fdWrite which calls
GHC.IO.FD.writeRawBufferPtr which calls
which is defined as:
writeRawBufferPtr :: String - FD - Ptr Word8 - Int - CSize - IO
CInt
writeRawBufferPtr loc !fd buf off len
| isNonBlocking fd = unsafe_write -- unsafe is ok, it can't block
| otherwise = do r - unsafe_fdReady (fdFD fd) 1 0 0
if r /= 0
then write
else do threadWaitWrite (fromIntegral (fdFD
fd)); write
where
do_write call = fromIntegral `fmap`
throwErrnoIfMinus1RetryMayBlock loc call
(threadWaitWrite (fromIntegral (fdFD fd)))
write = if threaded then safe_write else unsafe_write
unsafe_write = do_write (c_write (fdFD fd) (buf `plusPtr` off)
len)
safe_write= do_write (c_safe_write (fdFD fd) (buf `plusPtr`
off) len)
According to the following test program, I expect that 'isNonBlocking
fd' will be 'True'. So it seems like the portable solution should be
vulnerable to the same condition. Perhaps the portable version is just
so slow that the OS buffers never fill up so EAGAIN is never raised?
---
{-# LANGUAGE RecordWildCards #-}
module Main where
import Control.Concurrent (forkIO)
import Control.Monad (forever)
import Network (PortID(PortNumber), Socket, listenOn)
import Network.Socket (accept, socketToHandle)
import System.IO
import qualified GHC.IO.FD as FD
import GHC.IO.Handle.Internals (withHandle, flushWriteBuffer)
import GHC.IO.Handle.Types (Handle__(..), HandleType(..))
import qualified GHC.IO.FD as FD
import System.Posix.Types (Fd(..))
import System.IO.Error
import GHC.IO.Exception
import Data.Typeable (cast)
import GHC.IO.Handle.Internals (wantWritableHandle)
main =
listen (PortNumber (toEnum 2525)) $ \s -
do h - socketToHandle s ReadWriteMode
wantWritableHandle main h $ \h_ - showBlocking h_
showBlocking :: Handle__ - IO ()
[Haskell-cafe] Re: sendfile leaking descriptors on Linux?
Thomas DuBuisson wrote: Bardur Arantsson s...@scientician.net wrote: ... then do errno - getErrno if errno == eAGAIN then do threadDelay 100 sendfile out_fd in_fd poff bytes else throwErrno Network.Socket.SendFile.Linux else return (fromIntegral sbytes) That is, I removed the threadWaitWrite in favor of just adding a threadDelay 100 when eAGAIN is encountered. With this code, I cannot provoke the leak. Unfortunately this isn't really a solution -- the CPU is pegged at ~50% when I do this and it's not exactly elegant to have a hardcoded 100 ms delay in there. :) I don't think it matters wrt the desired final solution, but this is NOT a 100 ms delay. It is a 0.1 ms delay, which is less than a GHC time slice and as such is basically a tight loop. If you use a reasonable value for the delay you will probably see the CPU being almost completely idle. Excellent, thanks. I was probably too tired or annoyed when I wrote that code. I sorta-kinda-knew I must have been doing *something* wrong :). I'll retry with a more reasonable delay tomorrow. Cheers, ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seen on reddit: or, foldl and foldr considered slightly harmful
On Feb 11, 2010, at 9:41 PM, Johann Höchtl wrote:
In a presentation of Guy Steele for ICFP 2009 in Edinburgh:
http://www.vimeo.com/6624203
he considers foldl and foldr harmful as they hinder parallelism
because of Process first element, then the rest Instead he proposes
a divide and merge aproach, especially in the light of going parallel.
I think I first heard about that issue in the 80s.
Let me just take an Erlang perspective on this for a few minutes.
Ignoring types, the classic foldl in Erlang (which is strict) is
foldl(F, A, [X|Xs]) - foldl(F, F(X, A), Xs);
foldl(_, A, []) - A.
In a strict language, you have to wait for F to finish
before you can go on to the next element.
In a non-strict language, you don't. The interesting
question is how far F can get just given X, before it
has to look at A.
Suppose we can factor F(X, A) into G(H(X), A)
where H is rather time-consuming, but G is cheap (maybe it's an add).
So we write
foldl_map(G, H, A, [X|Xs]) - foldl_map(G, H, G(H(X), A), Xs);
foldl_map(_, _, A, []) - A.
Now we can parallelise it. We'll spark off a separate thread
for each call of H.
pfoldl_map(G, H, A, Xs) -
Outer = self(),
Pids = [spawn(fun () - Outer ! {self(),H(X)} end || X - Xs],
foldl(G, A, [receive {Pid,Val} - Val end | Pid - Pids]).
If N is the length of the list and G is O(1)
we have O(N) time to traverse the list
and O(N) time to collect and fold the results.
The H calculations can take place in parallel.
Provided each H calculation is expensive enough, we may not _care_
about the O(N) bits. In fact, if they aren't, we probably shouldn't
be worrying about parallelism here.
The problem exists when we *can't* factor F(X, A) into G(H(X), A)
with a cheap G and costly H. Then divide-and-parallel-conquer
using k-way trees gives us a computation depth of $\log_k N$
calls of G waiting for results to come back.
As I say, I met this stuff in the 80s. It's hardly news.
Indeed, if I remember correctly, back when Occam was hot stuff
people were worried about
PAR i = 0 for n
...
which forks n processes. Doing that one at a time in the parent
process takes O(n) time. I believe something was done about
making this work by recursive bisection.
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[Haskell-cafe] Re: sendfile leaking descriptors on Linux?
Jeremy Shaw wrote: On Feb 11, 2010, at 1:57 PM, Bardur Arantsson wrote: [--snip lots of technical info--] Thanks for digging so much into this. Just a couple of comments: The whole point of the sendfile library is to use sendfile(), so not using sendfile() seems like the wrong solution. Heh, well, presumably it could still use sendfile() only platforms where it can actually guarantee correctness :). There is some evidence that when you are doing select() on a readfds, and the connection is closed, select() will indicate that the fds is ready to be read, but when you read it, you get 0-bytes. That indicates that a disconnect has happened. However, if you are only doing read()/recv(), I expect that only happens in the event of a proper disconnect, because if you are just listening for packets, there is no way to tell the difference between the sender just not saying anything, and the sender dying: True, but the point here is that the OS has a built-in timeout mechanism (via keepalives) and *can* tell the program when that timeout has elapsed. That's the timeout we're trying to get at instead of having to implement a new one. Good point about the the readfds triggering when the client disconnects. I think that's what I've been seeing in all my other network-related code and I just misremembered the details. All my code is extremely likely to have been both reading and writing from (roughly) the same set of FDs at the same time. If this method of detection is correct, then what we need is a threadWaitReadWrite, that will notify us if the socket can be read or written. The IO manager does not currently provide a function like that.. but we could fake it like this: (untested): import Control.Concurrent import Control.Concurrent.MVar import System.Posix.Types data RW = Read | Write threadWaitReadWrite :: Fd - IO RW threadWaitReadWrite fd = do m - newEmptyMVar rid - forkIO $ threadWaitRead fd putMVar m Read wid - forkIO $ threadWaitWrite fd putMVar m Write r - takeMVar m killThread rid killThread wid return r I'll try to get the sendfile code to use this instead. AFAICT it shouldn't actually be necessary to peek on the read end of the socket to detect that something has gone wrong. We're guaranteed that sendfile() to a connection that's died (according to the OS, either due to proper disconnect or a timeout) will fail. I might get a bit tricky to use this if the client is actually expecting to send proper data while the sendfile() is in progress -- if there's actual data to be read from the socket() then the naive replace threadWaitR by threadWaitRW will end up busy-waiting on EAGAIN since the socket() will be readable every time threadWaitReadWrite gets called. HOWEVER, that's not an issue in my particular scenario, so a simple relacement of threadWaitWrite by threadWaitReadWrite should do fine for testing purposes. Of course, in the case where the client disconnects because someone turns off the power or pulls the ethernet cable, we have no way of knowing what is going on -- so there is still the possibility that dead connections will be left open for a long time. True, but then it's (properly) left to the OS to decide and timeouts can be controlled via setsockopt -- as they should IMO. I'll test tomorrow. What I'll expect is that I'll still see a few dead threads lingering around for ~60 seconds (the OS-based timeout), but that I'll not see any threads lingering indefinitely -- something which usually happens after a few hours of persistent use of my media server. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
bos: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? uvector's not seeing much development, but at least in the last round of benchmarks it was still consistently faster -- since it's been micro-optimized. Also, we have uvector-algorithms, so you can sort etc. a uvector. I'm not sure its the long term solution, but its a simpler, faster lib at the moment, with more surrounding support, users and documentation. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
rl: On 11/02/2010, at 05:03, Bryan O'Sullivan wrote: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? Yes, with the caveat that I haven't really used it in production code (I have tested and benchmarked it, though). BTW, I'll release version 0.5 as soon as get a code.haskell.org account and move the repo there. That's the main problem. I think we could move to vector as a whole, if the suite of testing/ performance/documentation stuff from uvector was ported. Maybe this is a good job for the hackathon. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Dungeons of Wor - a largish FRP example and a fun game, all in one!
1) This is missing the obligatory youtube video. 2) AWESOME! :) thomas. 2010/2/11 Patai Gergely patai_gerg...@fastmail.fm: Hello all, I just uploaded the first public version of Dungeons of Wor [1], a homage to the renowned three-decade-old arcade game, Wizard of Wor. While it makes a fine time killer if you have a few minutes to spare, it might be of special interest to the lost souls who are trying to figure out FRP. The game was programmed using the Simple version of the experimental branch of Elerea [2], which provides first-class discrete streams to describe time-varying quantities, and the main game logic is described as a composition of streams instead of a world state transformer. Developing in this manner was an interesting experience, and I'll write about it in more detail over the weekend. All the best, Gergely [1] http://hackage.haskell.org/package/dow [2] http://hackage.haskell.org/packages/archive/elerea/1.2.3/doc/html/FRP-Elerea-Experimental-Simple.html -- http://www.fastmail.fm - The professional email service ___ 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] vector to uvector and back again
On Thursday 11 February 2010 12:43:10 pm stefan kersten wrote: On 10.02.10 19:03, Bryan O'Sullivan wrote: I'm thinking of switching the statistics library over to using vector. that would be even better of course! an O(0) solution, at least for me ;) let me know if i can be of any help (e.g. in testing). i suppose uvector-algorithms would also need to be ported to vector, then. I could do this. I've been occupied with things other than uvector-algorithms for a while, but I've been meaning to get back into it (perhaps finally get timsort in there). How widespread is the consensus on vector over uvector? dons seems to have added to uvector as recently as mid December, so I'm not really sure how bit rotted it is. But vector seems to have a lot more going on in it, including boxed arrays, which I suppose is a gap in using uvector. I also notice that vector seems to have discarded the idea of Vec (A * B) = Vec A * Vec B with associated types. Was this determined to not be worth it? uvector- algorithms actually used the fact for a cute trick (Schwartzian transform can be done for such arrays by computing a new array containing 'f e' for each 'e' in the original array, pairing up the two arrays, and performing an algorithm that only looks at the 'f e' half, and then pulling the 'e' half out of the pair; doing it this way requires no copying of the original array). Anyhow, if vector is the clear way forward, I don't mind porting uvector- algorithms. But I don't relish maintaining two slightly different parallel branches. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hackage download statistis
mauricio.antunes: Hi, all, Some time ago a download statistic of hackage was made available, and analysed in a few ways. Googling for it still find that at a Galois web page. I though that, since the tools to get that were there, this would be output once in a while, but it seems it hasn't been done since then. Does anyone know if there are plans about that? Since we moved Hackage to a new machine, the logs are stored differently. I need to get access to the machine to get the stats again. Hopefully this weekend. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: Dungeons of Wor - a largish FRP example and a fun game, all in one!
Exciting! But on a mac, I can't get the window to become focussed or accept input. Tips ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On 12/02/2010, at 12:39, Don Stewart wrote: bos: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? uvector's not seeing much development, but at least in the last round of benchmarks it was still consistently faster -- since it's been micro-optimized. FWIW, the development version of vector is usually faster the both uvector and dph-prim-seq, at least for the development version of NoSlow. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
rl: On 12/02/2010, at 12:39, Don Stewart wrote: bos: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? uvector's not seeing much development, but at least in the last round of benchmarks it was still consistently faster -- since it's been micro-optimized. FWIW, the development version of vector is usually faster the both uvector and dph-prim-seq, at least for the development version of NoSlow. Ah ha -- that's useful. Public benchmarks soon? In time for the Zurich Hackathon?? (March 20) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On 12/02/2010, at 12:40, Don Stewart wrote: rl: On 11/02/2010, at 05:03, Bryan O'Sullivan wrote: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? Yes, with the caveat that I haven't really used it in production code (I have tested and benchmarked it, though). BTW, I'll release version 0.5 as soon as get a code.haskell.org account and move the repo there. That's the main problem. I think we could move to vector as a whole, if the suite of testing/ performance/documentation stuff from uvector was ported. Hmm, I'm not sure what you mean here. Mostly thanks to Max Bolingbroke's efforts, vector has a fairly extensive testsuite. I benchmark it a lot (with NoSlow) and haven't found any significant performance problems in a while. As to documentation, there are comments for most of the functions :-) Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
rl: On 12/02/2010, at 12:39, Don Stewart wrote: bos: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? uvector's not seeing much development, but at least in the last round of benchmarks it was still consistently faster -- since it's been micro-optimized. FWIW, the development version of vector is usually faster the both uvector and dph-prim-seq, at least for the development version of NoSlow. If Roman declares the vector to be faster -- my main concern here for flat uarrays -- and makes the repo available so we can work on it, I'd be willing to merge uvector's tests and docs and extra array operations in. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On 12/02/2010, at 12:54, Dan Doel wrote: I also notice that vector seems to have discarded the idea of Vec (A * B) = Vec A * Vec B Oh no, it hasn't. In contrast to uvector/DPH, which use a custom strict tuple type for rather outdated reasons, vector uses normal tuples. For instance, Data.Vector.Unboxed.Vector (a,b,c) is internally represented as a triple of unboxed vectors of a, b and c. In general, vector supports 4 kinds of arrays at the moment: Data.Vector.Primitive wrappers around ByteArray#, can store primitive types Data.Vector.Unboxed uses type families, can store everything D.V.Primitive can plus tuples and can be extended for user-defined types Data.Vector.Storable wrappers around ForeignPtr, can store Storable things Data.Vector boxed arrays Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hledger 0.8 released
hledger 0.8 is out! http://hledger.org http://hledger.org/MANUAL.html#installing Bug fixes, refactoring and Hi-Res Graphical Charts. (See Roman Cheplyaka's blog: http://www.reddit.com/r/haskell/comments/b0w0q/using_the_hledger_package_to_track_finances) Best - Simon Release notes: .. * parsing: in date=date2, use first date's year as a default for the second * add: ctrl-d doesn't work on windows, suggest ctrl-c instead * add: --no-new-accounts option disallows new accounts (Roman Cheplyaka) * add: re-use the previous transaction's date as default (Roman Cheplyaka) * add: a command-line argument now filters by account during history matching (Roman Cheplyaka) * chart: new command, generates balances pie chart (requires - fchart flag, gtk2hs) (Roman Cheplyaka, Simon Michael) * register: make reporting intervals honour a display expression (#18) * web: fix help link * web: use today as default when adding with a blank date * web: re-enable account/period fields, they seem to be fixed, along with file re-reading (#16) * web: get static files from the cabal data dir, or the current dir when using make (#13) * web: preserve encoding during add, assuming it's utf-8 (#15) * fix some non-utf8-aware file handling (#15) * filter ledger again for each command, not just once at program start * refactoring, clearer data types Stats: 62 days since last release, 2 contributors, 76 commits, 3464 lines of non-test code, 97 tests, 53% test coverage ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] vector to uvector and back again
On Thursday 11 February 2010 9:57:40 pm Roman Leshchinskiy wrote: Oh no, it hasn't. In contrast to uvector/DPH, which use a custom strict tuple type for rather outdated reasons, vector uses normal tuples. For instance, Data.Vector.Unboxed.Vector (a,b,c) is internally represented as a triple of unboxed vectors of a, b and c. In general, vector supports 4 kinds of arrays at the moment: Ah, all right. I was looking at the (0.4.2) documentation on hackage, which doesn't mention Data.Vector.Unboxed. Never mind about that bit, then. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: hledger 0.8 released
On Feb 11, 2010, at 22:02 , Simon Michael wrote: * add: ctrl-d doesn't work on windows, suggest ctrl-c instead Ctrl-Z would be the usual EOF in the Windows world, fwiw. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How many Haskell Engineer I/II/IIIs are there?
Hear hear. But a few successful happstack private sector startups could change that... 2010/2/10 Jason Dusek jason.du...@gmail.com: 2010/02/10 Roderick Ford develo...@live.com: A U.S. president would probably subsidize such a job-creating endeavor too! The US government generally subsidizes these kinds of things through DoD spending (and a few NSF grants). That is probably hard to get into. -- Jason Dusek ___ 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] vector to uvector and back again
On 12/02/2010, at 13:49, Don Stewart wrote: rl: On 12/02/2010, at 12:39, Don Stewart wrote: bos: I'm thinking of switching the statistics library over to using vector. uvector is pretty bit-rotted in comparison to vector at this point, and it's really seeing no development, while vector is The Shiny Future. Roman, would you call the vector library good enough to use in production at the moment? uvector's not seeing much development, but at least in the last round of benchmarks it was still consistently faster -- since it's been micro-optimized. FWIW, the development version of vector is usually faster the both uvector and dph-prim-seq, at least for the development version of NoSlow. Ah ha -- that's useful. Public benchmarks soon? In time for the Zurich Hackathon?? (March 20) I've been trying to find the time to put the benchmarks on my blog since the beginning of January but, alas, unsuccessfully so far. In any case, vector and NoSlow currently live in http://www.cse.unsw.edu.au/~rl/code/darcs/vector http://www.cse.unsw.edu.au/~rl/code/darcs/NoSlow If Roman declares the vector to be faster -- my main concern here for flat uarrays -- and makes the repo available so we can work on it, I'd be willing to merge uvector's tests and docs and extra array operations in. It is generally faster than dph-prim-seq. Benchmarking against uvector is a bit difficult because it's missing operations necessary for implementing most of the algorithms in NoSlow (in particular, bulk updates). For the ones that uvector supports, vector tends to be faster. BTW, this is for unsafe operations which don't use bounds checking. Bounds checking can make things a little slower but often doesn't cost anything as long as only collective operations are used. Sometimes it makes things faster which means that the simplifier still gets confused in some situations. There are also some significant differences between 6.12 and the HEAD (the HEAD is much more predictable). In general, I find it hard to believe that the performance differences I'm seeing really matter all that much in real-world programs. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
Things are missing but Haskell was certainly fit for practical use two years ago. The big things missing now are trust, mindshare and enough people who think reliability and consistency are a good play for long term productivity. -- Jason Dusek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell-src type inference algorithm?
On 12 February 2010 10:13, Niklas Broberg niklas.brob...@gmail.com wrote: Anyone know of a type inference utility that can run right on haskell-src types? or one that could be easily adapted? This is very high on my wish-list for haskell-src-exts, and I'm hoping the stuff Lennart will contribute will go a long way towards making it feasible. I believe I can safely say that no such tool exists (and if it does, why haven't you told me?? ;-)), but if you implement (parts of) one yourself I'd be more than interested to see, and incorporate, the results. A long time ago I worked on hatchet: http://www.cs.mu.oz.au/~bjpop/hatchet/src/hatchet.tar.gz which I believe was incorporated into JHC. Hatchet was based on thih and haskell-src. I gave up on it when I figured out a way to do what I wanted without type information. If I was going to do it again then I'd consider using Chameleon as a starting point, (I don't know where the most up-to-date sources are). Cheers, Bernie. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Computer Camp for kids 13 - 15 years old in Colorado featuring Functional Reactive Programming
Western State College in Colorado has a computer camp for kids aged 13 - 15. Although we don't use Haskell (it's Python on the inside) the underlying engine is Functional Reactive Programming. We use a 3-D game engine to explore more than just programming - we cover a lot of math and physics. We have a very unique camp - every day includes 3 - 4 hours of recreation in the area: rafting, rock climbing, kayaking, mountain biking. Our website is at http://western.edu/academics/computerscience/computer-camp.html The camp is the last week of June. See the website for further details. We're trying to get the software in releasable form - should be ready to go in a few months. This is the fourth year of our camp and FRP has been an ideal way to introduce novices to computing. John (PS - all recreational activities at our camp are approved by Simon PJ - http://haskell.org/haskellwiki/Simon_Has_Fun) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] parallel and distributed haskell?
On 17 December 2009 06:21, Scott A. Waterman tswater...@gmail.com wrote: I feel there is quite a bit of latent interest in the subject here, but relatively little active development (compared to erlang, clojure, etc.) Can anyone involved give a quick overview (or pointers to one)? It would be good to hear what directions people are taking, and why, and where it's going. I've recently moved into HPC and am now quite interested in using Haskell on large clusters. My first goal was to get hMPI working (HaskellMPI). The original version appears to be from Michael Weber: http://www.foldr.org/~michaelw/hmpi/ which was followed up by Hal Daume III: http://hal3.name/newhmpi.tar.gz It doesn't appear to be cabalised. I wonder if anyone else has been using it? Cheers, Bernie. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Time for a San Francisco Hackathon?
I'm thinking it might be a good idea to organise a Haskell Hackathon for people in (and who'd like to visit) the Bay Area. The tentative date I have in mind is the first weekend in May (conveniently May 1). If you'd be interested in attending or helping to organise, please let me know. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HDBC convert [SqlValue] without muchos boilerplate
On 11 Feb 2010, at 10:05, Vasyl Pasternak wrote: But fromSql function could convert everything to String, so you never need to use `show`, just simply write convrow2 :: [SqlValue] - String convrow2 (x:xs) = foldl (\i j - i ++ | ++ (fromSql j)) (fromSql x) xs But, IMO, this is more readable version of your function: convrow2' :: [SqlValue] - String convrow2' = unwords . intersperse | . map fromSql On 11 Feb 2010, at 10:06, Miguel Mitrofanov wrote: What if you just omit the show function? fromSql seems to be able to convert almost anything to String. Ok, thanks, that's a big help. I'm really glad to get rid off all that extra cruft I had there. I'd forgotten about intersperse, too. The new code works fine. Regards, Iain___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Time for a San Francisco Hackathon?
bos: I'm thinking it might be a good idea to organise a Haskell Hackathon for people in (and who'd like to visit) the Bay Area. The tentative date I have in mind is the first weekend in May (conveniently May 1). If you'd be interested in attending or helping to organise, please let me know. Interesting. We were planning a PDX one for late April. Maybe we can coordinate and have a unified West Coast hackathon... Video + IRC can keep the hackers in sync :) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How many Haskell Engineer I/II/IIIs are there?
I looked at generating C for AVR with JHC. I wanted to see what
this program became:
http://github.com/solidsnack/trippy-waves/blob/99ad424a3ed4a21ff6f6a662293d6d21e92d6611/using-jhc/RGB.hs
The program is relatively simple. It doesn't work, of course (I
never did get the right FFI bindings figured out) but the
generated C is suggestive.
http://github.com/solidsnack/trippy-waves/blob/99ad424a3ed4a21ff6f6a662293d6d21e92d6611/using-jhc/hs.out_code.c
The generated `main' is very plain:
static void A_STD
ftheMain(void)
{
jhc_function_inc();
uintptr_t v10 = ((uintptr_t)DDRB());
*((uint8_t *)(v10)) = 23;
uintptr_t v18 = ((uintptr_t)PORTB());
return *((uint8_t *)(v18)) = 23;
}
This is a simple, literal translation of my foreign calls. To
all appearances, the runtime is entirely bypassed. The
function `jhc_function_inc()' is a performance counter, set to
no-op for non-profiling builds as far as I can tell.
It also doesn't compile but that's because I can't figure out
how to declare pointers in the FFI; and if I could, then I'd
have to go through by hand and pull out includes for things
that aren't available for AVR programming -- locale.h and
such.
--
Jason Dusek
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Re: [Haskell-cafe] ANN: Dungeons of Wor - a largish FRP example and a fun game, all in one!
1) This is missing the obligatory youtube video. That's usually handled by dons. ;) Gergely -- http://www.fastmail.fm - Email service worth paying for. Try it for free ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: Dungeons of Wor - a largish FRP example and a fun game, all in one!
Exciting! But on a mac, I can't get the window to become focussed or accept input. Tips ? I don't have a Mac, but I heard that GLFW is not without problems there, so maybe it's the culprit this time too. Do other GLFW apps work on your machine? Gergely -- http://www.fastmail.fm - IMAP accessible web-mail ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
