[Haskell-cafe] ANNOUNCE xml-conduit-generic
Hello, cafe!
I made a package
xml-conduit-generichttps://github.com/odr/xml-conduit-generic to
provide conversion from ADT to xml and vice versa.
Conversion works as Conduit (ToXml) or Consumer (FromXml).
Example:
data T4 = T4 {v4 :: Int, n4 :: Maybe T4} deriving (Eq, Show, Generic)
instance ToXml T4
instance FromXml T4
runToXml $ T4 5 $ Just $ T4 6 Nothing
T4 v4=\5\n4 v4=\6\//T4
runFromXml $ T4 v4=\5\n4 v4=\6\//T4 :: IO (Either String T4)
Right $ T4 5 $ Just $ T4 6 Nothing
It would be great if someone look to the version on github and give me some
notes. Then I am going to put it on hackage.
Unfortunately, I didn't find a way to avoid OverlappingInstances (for
GFromXml class). Any ideas are welcome.
Best regards,
Dmitry
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Re: [Haskell-cafe] Parser left recursion
Did you see expression parser in parsec packagehttp://hackage.haskell.org/packages/archive/parsec/3.1.3/doc/html/Text-Parsec-Expr.html? Is it not enough? 2013/2/20 Martin Drautzburg martin.drautzb...@web.de Hello all, this was previously asked on haskell-beginners, but only partially answered. As an exercise I am writing a parser roughly following the expamples in Graham Hutton's book. The language contains things like: data Exp = Lit Int -- literal integer | Plus Exp Exp My naive parser enters an infinite recursion, when I try to parse 1+2. I do understand why: hmm, this expression could be a plus, but then it must start with an expression, lets check. and it tries to parse expression again and again considers Plus. Twan van Laarhoven told me that: Left-recursion is always a problem for recursive-descend parsers. and suggested to do something like: parseExp = do lit - parseLit pluses - many (parsePlusToken * parseLit) return (combinePlusesWithLit lit pluses) combinePlusesWithLit = foldr Plus -- or foldl This indeed does the trick, but only when the first token is a Lit (literal integer). I then added the possibility to optionally put things in parentheses. But then I cannot parse (1+2)+3. The original code fails, because (1+2) is not a Lit and when I allow an expression as the first argument to + I get infinite recursion again. I am generally confused, that saying a plus expression is an integer followed by many plus somethings is not what the language says. So this requires a lot of paying attention to get right. I'd much rather say a plus expression is two expressions with a '+' in between. I do know for sure, that it is possible to parse (1+2)+3 (ghci does it just fine). But I seem to be missing a trick. Can anyone shed some light on this? -- Martin ___ 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] I killed performance of my code with Eval and Strategies
Just another definition of calculateSeq:
calculateSeq = zipWith ($) (cycle [sin,cos]) . map sqrt
2012/11/15 Janek S. fremenz...@poczta.onet.pl
Do you really mean to calculate the 'sin . sqrt' of just the head of the
list, or do you mean:
calculateSeq = map (sin . sqrt) ?
Argh.. of course not! That's what you get when you code in the middle of a
night. But in my code I
will not be able to use map because elements will be processed in pairs,
so let's say that my
sequential function looks like this:
calculateSeq :: [Double] - [Double]
calculateSeq [] = []
calculateSeq [x] = [sin . sqrt $ x]
calculateSeq (x:y:xs) = (sin . sqrt $ x) : (cos . sqrt $ y) : calculateSeq
xs
I don't think there's a memory leak. It looks more like you're just
allocating much more than is sane for such a simple function.
On a recent processor, sin . sqrt is two instructions. Meanwhile, you
have
a list of (boxed?) integers being split up, then recombined. That's bound
to hurt the GC.
I am not entirely convinced that my idea of using eval+strategies is bound
to be slow, because
there are functions like parListChunk that do exactly this: split the list
into chunks, process
them in parallel and then concatenate the result. Functions in
Control.Parallel.Strategies were
designed to deal with list so I assume it is possible to process lists in
parallel without GC
problems. However I do not see a way to apply these functions in my
setting where elements of
lists are processed in pairs, not one at a time (parList and parMap will
not do). Also, working
on a list of tuples will not do.
Also, you might want to configure criterion to GC between
runs. That might help.
The -g flag passed to criterion executable does that.
What I'd suggest doing instead, is breaking the input into chucks of,
say,
1024, and representing it with a [Vector]. Then, run your sin.sqrt's on
each vector in parallel. Finally, use Data.Vector.concat to combine your
result.
As stated in my post scriptum I am aware of that solution :) Here I'm
trying to figure what am I
doing wrong with Eval.
Thanks!
Janek
Hope that helps,
- Clark
On Wed, Nov 14, 2012 at 4:43 PM, Janek S. fremenz...@poczta.onet.pl
wrote:
Dear Haskellers,
I am reading Simon Marlow's tutorial on parallelism and I have problems
with correctly using Eval
monad and Strategies. I *thought* I understand them but after writing
some code it turns out that
obviously I don't because parallelized code is about 20 times slower.
Here's a short example
(code + criterion benchmarks):
{-# LANGUAGE BangPatterns #-}
module Main where
import Control.Parallel.Strategies
import Criterion.Main
main :: IO ()
main = defaultMain [
bench Seq $ nf calculateSeq xs
, bench Par $ nf calculatePar xs ]
where xs = [1..16384]
calculateSeq :: [Double] - [Double]
calculateSeq [] = []
calculateSeq (x:xs) = (sin . sqrt $ x) : xs
calculatePar :: [Double] - [Double]
calculatePar xss = runEval $ go xss
where
go :: Strategy [Double]
go [] = return []
go xs = do
lsh - (rpar `dot` rdeepseq) $ calculateSeq as
lst - go bs
return (lsh ++ lst)
where
!(as, bs) = splitAt 8192 xs
Compiling and running with:
ghc -O2 -Wall -threaded -rtsopts -fforce-recomp -eventlog evalleak.hs
./evalleak -oreport.html -g +RTS -N2 -ls -s
I get:
benchmarking Seq
mean: 100.5990 us, lb 100.1937 us, ub 101.1521 us, ci 0.950
std dev: 2.395003 us, lb 1.860923 us, ub 3.169562 us, ci 0.950
benchmarking Par
mean: 2.233127 ms, lb 2.169669 ms, ub 2.296155 ms, ci 0.950
std dev: 323.5201 us, lb 310.2844 us, ub 344.8252 us, ci 0.950
That's a hopeless result. Looking at the spark allocation everything
looks fine:
SPARKS: 202 (202 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)
But analyzing eventlog with ThreadScope I see that parallel function
spends most of the time doing
garbage collection, which suggests that I have a memory leak
somewhere. I
suspected that problem
might be caused by appending two lists together in the parallel
implementation, but replacing
this with difference lists doesn't help. Changing granularity (e.g.
splitAt 512) also brings no
improvement. Can anyone point me to what am I doing wrong?
Janek
PS. This is of course not a real world code - I know that I'd be better
of using unboxed data
structures for doing computations on Doubles.
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Re: [Haskell-cafe] Maximum bipartite matching: 24 lines
I didn't analyze it but anytime I see M.insertWith I am just in doubt - do you know about a strict version M.insertWith' ? 2012/10/24 Stefan Klinger all-li...@stefan-klinger.de On 2012-Oct-22 14:23 (-0700), Eugene Kirpichov wrote with possible deletions: fwd = foldr (\(x,y) - M.insertWith (++) x [y]) M.empty $ S.toList g Use foldl' here, foldr is absolutely useless here and it only consumes the stack space as your operation is strict. Thank you very much for that. I'll review the code under strictness aspects. As for the actual code: I'd prefer the code itself to be more readable, rather than have a lot of literate comments around it; I like comments documenting why something's done, complementing the code which tells what's done. currently, IMO all the uncurry's, flips, eithers, maybes and point-free style hurt readability heavily. I agree. Between babbling bloated and incomprehensible terse, my code is certainly towards the terse extreme. For me, that's a balancing act that I find hard to do right. I'll probably try to write my own version as an exercise :) Cool! I'd like to see that... Cheers! Stefan -- Stefan Klinger o/klettern /\/ bis zum send plaintext only - max size 32kB - no spam \ Abfallen http://stefan-klinger.de ___ 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] Data.Text and quasi quoting
Hello, if you change from test2 = [expr| test |] to test2 = [expr| $test |] then it will be compile. Do you want that or what? 2012/10/2 Jake Wheat jakewheatm...@gmail.com Hello, I have a parser which parses to an ast which contains Text values. I am trying to use this parser with quasiquoting, but the implementation of Data for Text is incomplete. I've attached a smallish test case, when I try to compile Text.hs I get: Text.hs:17:9: Exception when trying to run compile-time code: Data.Text.Text.toConstr Code: Language.Haskell.TH.Quote.quoteExp expr test Is there a way to get this working? Thanks, Jake. ___ 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] not enough fusion?
s1 ~ sum $ map (sum . flip map [0..n] . gcd) [0..n] s2 ~ sum $ concatMap (flip map [0..n] . gcd) [0..n] There are some posts from Joachim Breitner investigated fusion for concatMap: http://www.haskell.org/pipermail/haskell-cafe/2011-December/thread.html#97227 2012/6/25 Johannes Waldmann waldm...@imn.htwk-leipzig.de Dear all, while doing some benchmarking (*) I noticed that function s1 is considerably faster than s2 (but I wanted s2 because it looks more natural) (for n = 1, s1 takes 20 s, s2 takes 13 s; compiled by ghc-7.4.2 -O2) s1 :: Int - Int s1 n = sum $ do x - [ 0 .. n-1 ] return $ sum $ do y - [ 0 .. n-1 ] return $ gcd x y s2 :: Int - Int s2 n = sum $ do x - [ 0 .. n-1 ] y - [ 0 .. n-1 ] return $ gcd x y I was expecting that in both programs, all lists will be fused away (are they?) so the code generator essentially can produce straightforward assembly code (no allocations, no closures, etc.) For reference, I also wrote the equivalent imperative program (two nested loops, one accumulator for the sum) (with the straightforward recursive gcd) and runtimes are (for same input as above) C/gcc: 7.3 s , Java: 7.7 s, C#/Mono: 8.7 s So, they sort of agree with each other, but disagree with ghc. Where does the factor 2 come from? Lists? Laziness? Does ghc turn the tail recursion (in gcd) into a loop? (gcc does). (I am looking at -ddump-asm but can't quite see through it.) (*) benchmarking to show that today's compilers are clever enough such that the choice of paradigm/language does not really matter for this kind of low-level programming. ___ 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] not enough fusion?
In my test it works ~20% faster than s2 and ~20% slower than s1. Did you use -O2 flag? 2012/6/25 Lorenzo Bolla lbo...@gmail.com I wonder why this performs really badly, though (I would expect it to be the same as s2): s3 :: Int - Int s3 n = sum [gcd x y | x - [ 0 .. n-1 ], y - [ 0 .. n-1 ]] From the links posted by Dmitry, it might be that the code generated is made of 2 recursive calls: in fact, what I observe is a stack space overflow error on runtime... L. On Mon, Jun 25, 2012 at 10:09 AM, Dmitry Olshansky olshansk...@gmail.comwrote: s1 ~ sum $ map (sum . flip map [0..n] . gcd) [0..n] s2 ~ sum $ concatMap (flip map [0..n] . gcd) [0..n] There are some posts from Joachim Breitner investigated fusion for concatMap: http://www.haskell.org/pipermail/haskell-cafe/2011-December/thread.html#97227 2012/6/25 Johannes Waldmann waldm...@imn.htwk-leipzig.de Dear all, while doing some benchmarking (*) I noticed that function s1 is considerably faster than s2 (but I wanted s2 because it looks more natural) (for n = 1, s1 takes 20 s, s2 takes 13 s; compiled by ghc-7.4.2 -O2) s1 :: Int - Int s1 n = sum $ do x - [ 0 .. n-1 ] return $ sum $ do y - [ 0 .. n-1 ] return $ gcd x y s2 :: Int - Int s2 n = sum $ do x - [ 0 .. n-1 ] y - [ 0 .. n-1 ] return $ gcd x y I was expecting that in both programs, all lists will be fused away (are they?) so the code generator essentially can produce straightforward assembly code (no allocations, no closures, etc.) For reference, I also wrote the equivalent imperative program (two nested loops, one accumulator for the sum) (with the straightforward recursive gcd) and runtimes are (for same input as above) C/gcc: 7.3 s , Java: 7.7 s, C#/Mono: 8.7 s So, they sort of agree with each other, but disagree with ghc. Where does the factor 2 come from? Lists? Laziness? Does ghc turn the tail recursion (in gcd) into a loop? (gcc does). (I am looking at -ddump-asm but can't quite see through it.) (*) benchmarking to show that today's compilers are clever enough such that the choice of paradigm/language does not really matter for this kind of low-level programming. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Guide for converting existing code to Conduit 0.4?
I transfered my code from 0.3 to 0.4 without any changes. There are type synonyms in Conduit for that. Changes were from 0.2 to 0.3. Michael discribed it here http://www.yesodweb.com/blog/2012/03/announcing-conduit-0-3 Actually, in 0.4 no changes with Control.Monad.Trans.Resource. type Source m a = Pipe Void a m () old Conduit-API use type synonyms and not changed 2012/4/9 Erik de Castro Lopo mle...@mega-nerd.com Hi all, Is there some sort of a guide for converting existing code Conduit 0.4? What happened to Control.Monad.Trans.Resource.with? What happens to stuff that used to to have a type C.Source m a which now seems to need type C.Pipe Void a (ResourceT m) a? Cheers, 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] is the evaluation order deterministic when using applicative with IO
As usual you can check:
Prelude Control.Applicative pure (||) * pure True * undefined
*** Exception: Prelude.undefined
Prelude Control.Applicative (||) True undefined
True
2012/3/16 Rouan van Dalen rvda...@yahoo.co.uk
Hi everyone.
I was wondering if I can make assumptions about the evaluation order of
the following code:
isTrue :: Int - IO Bool
isTrue val = pure (||) * boolTest1 val * boolTest2 val
{- boolTest1 is an inexpensive, quick check -}
boolTest1 :: Int - IO Bool
boolTest1 val = undefined
{- boolTest2 is a very expensive check -}
boolTest2 :: Int - IO Bool
boolTest2 val = undefined
When using Applicative in the isTrue function, I would like to make use of
the short-circuit behaviour of || and rely on the fact that the boolTest1
will be executed first. The reason I am asking is because the boolTest
functions
are in the IO monad, instead of just returning pure Bool values.
Regards
Rouan.
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Re: [Haskell-cafe] Empty Input list
Look also at safe package http://hackage.haskell.org/package/safe 2012/3/13 Chris Wong chrisyco+haskell-c...@gmail.com On Tue, Mar 13, 2012 at 12:24 PM, Chris Smith cdsm...@gmail.com wrote: On Mon, Mar 12, 2012 at 3:14 PM, Kevin Clees k.cl...@web.de wrote: Now my function looks like this: tmp:: [(Int, Int)] - Int - (Int, Int) tmp [] y = (0,0) tmp xs y = xs !! (y-1) Just a warning that this will still crash if the list is non-empty by the index exceeds the length. That's because your function is no longer recursive, so you only catch the case where the top-level list is empty. The drop function doesn't crash when dropping too many elements though, so you can do this and get a non-recursive function that's still total: tmp :: [(Int,Int)] - Int - (Int, Int) tmp xs y = case drop (y-1) xs of [] - (0,0) Just (x:_) - x That last line should be (x:_) - x without the Just. Hopefully that'll save a bit of confusion. Chris -- Chris Smith ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] need help with monad transformers
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print freed2
or I didn't catch something?
2012/3/1 Alexander V Vershilov alexander.vershi...@gmail.com
Hello.
I'm trying to add monad stack into network-conduit, and everything
works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and
inside conduit I want to run writer to gather results of inner computation.
In inner computation I want to use IO, data from outter stack (ReaderT)
so I'm running {-1-}:
(k,t) - lift $ runWriterT $ ask = \x - tell [x] {- 1 -}
and {-2-}
(k,t) - lift $ runWriterT $ do {- 2 -}
x - ask
liftIO $ print $x+1
tell [x]
and that will work (except I've thought I should not lift runWriterT, but
calling functions inside.
And finally in computation that will run once I want to register cleaning
function (for example register $ putStrLn cleaned) ({-3-})
(k,t) - lift $ runWriterT $ do {- 3 -}
x - ask
liftIO $ print $x+1
register $ print freed2
tell [x]
but I've got type error. If I'm running register outside runWriterT
everything
will work.
I would apperated if there will be any suggestions how to make this code
better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151
--
Best regards,
Alexander V Vershilov
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Re: [Haskell-cafe] need help with monad transformers
Did you try to use transformers instead of mtl? I am just in doubt about it
in my work.
I've found that Conduit use it. So you remove extra dependency.
I hope that transformers have more readable messages (without FD) and you
can control what is lift more clear.
I have no experience although.
2012/3/2 Alexander V Vershilov alexander.vershi...@gmail.com
I've found a solution, I should not use lift for runWriterT, and should
explicilty lift all computation of level I need, i.e. (lift.lift) for ask
and lift for register.
Thu, Mar 01, 2012 at 02:19:29PM +0400, Dmitry Olshansky wrote
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print freed2
or I didn't catch something?
2012/3/1 Alexander V Vershilov alexander.vershi...@gmail.com
Hello.
I'm trying to add monad stack into network-conduit, and everything
works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and
inside conduit I want to run writer to gather results of inner
computation.
In inner computation I want to use IO, data from outter stack
(ReaderT)
so I'm running {-1-}:
(k,t) - lift $ runWriterT $ ask = \x - tell [x] {- 1 -}
and {-2-}
(k,t) - lift $ runWriterT $ do {- 2 -}
x - ask
liftIO $ print $x+1
tell [x]
and that will work (except I've thought I should not lift
runWriterT, but
calling functions inside.
And finally in computation that will run once I want to register
cleaning
function (for example register $ putStrLn cleaned) ({-3-})
(k,t) - lift $ runWriterT $ do {- 3 -}
x - ask
liftIO $ print $x+1
register $ print freed2
tell [x]
but I've got type error. If I'm running register outside runWriterT
everything
will work.
I would apperated if there will be any suggestions how to make this
code
better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151
--
Best regards,
Alexander V Vershilov
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[Haskell-cafe] Fwd: XML modification
Personally I prefer xml-enumerator. You can work with xml-stream or with DOM through cursor (like XPath). I think that in your case working with stream is preferrable. You can just make an Enumeratee like import qualified Data.Enumerator.List as EL myEnum = EL.map f where f (EventBeginElement n ats) = ... -- parse attributes f e = e 2011/11/23 Andrew Coppin andrewcop...@btinternet.com Hi guys. I've got a folder with about 80 XML files in it. I want to take each file and make specific modifications to it. (Mostly just finding specific attributes and changing their values to make then all consistent.) Now I guess it wouldn't take me /that/ long to code something from scratch. But does anybody have a better suggestion for tools or libraries that might be useful? __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://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] Is it possible to get the information of instances of a type?
For TH look also at http://www.mail-archive.com/haskell-cafe@haskell.org/msg13057.html 2011/10/27 Magicloud Magiclouds magicloud.magiclo...@gmail.com On Thu, Oct 27, 2011 at 1:57 AM, Brent Yorgey byor...@seas.upenn.edu wrote: On Wed, Oct 26, 2011 at 09:10:23PM +0400, MigMit wrote: Can't be done. Even if this particular module doesn't contain instance Class Type, it's quite possible that the said instance would be defined in another module, about which this one knows nothing about. That doesn't mean it can't be done, only that you would have to be explicit about which modules to look in. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe May I know more about this? Have not used TH on this subject. -- 竹密岂妨流水过 山高哪阻野云飞 ___ 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] Enumerators, Enumeratees and Iterators
Hi, for the first question you can look at combinators in Data.Iteratee.ListLikehttp://hackage.haskell.org/packages/archive/iteratee/0.8.5.0/doc/html/Data-Iteratee-ListLike.html for iteratee package or Data.Enumerator.Listhttp://hackage.haskell.org/packages/archive/enumerator/0.4.10/doc/html/Data-Enumerator-List.html for enumerator package. I doubt that I understand the second question. It seems that Map is more natural here. You can transform list into enumerator for instance by enumListhttp://hackage.haskell.org/packages/archive/enumerator/0.4.10/doc/html/Data-Enumerator.html#g:7. But I wonder what is the reason for that in your case? 2011/6/28 Sævar Berg s.b.saevars...@gmail.com Hey Café. I've been playing with Enumerators, Iteratees and Enumeratees today after having spent a few days writing a server application using lazy IO, then reading slides from Oleg's DEFUN8 talk notes, and I quote: Lazy IO in serious, server-side programming is unprofessional, I can talk a lot how disturbingly, distressingly wrong lazy IO is theoretically, how it breaks all equational reasoning after which my OCD self has been eating me up to take a proper look at this, so here I am. I'm already beginning to see how Iteratees, Enumerators and Enumeratees can be nifty, but I have a couple of questions about a couple of ideas and whether, and if so how they can be implemented. The first question is, I think, to be solved with enumeratees but I can't really grok how. Let's say I have an iteratee that consumes all input. Is it possible to implement an enumeratee or something else to stick between the enumerator and the iteratee to basically modify the input to the iteratee to only be a part of the input? Something like this: enumFile someFile printFileLines -- prints file with prepended line numbers enumFile someFile ?? onlyGet10Lines printFileLines -- print only 10 lines The second question could actually have an application in the server I'm writing. I was wondering if it was possible to write iteratees/enumerators that would only generate/consume when a certain something was the next chunk to be processed? It's a bit hard to explain, but let me try to give you an example. Let's say my application takes input from the network which contains commands that the server reacts to. Let's say I have a list of command handlers that I want to run this command through, but the handlers will only execute when they are passed the command that they are responsible for handling. Can this list of command handlers be enumerators/iteratees/enumeratees? E.g. is it possible to 'concat' them, making them each peek at the next chunk to see if it's theirs to handle and put it back if it isn't? I know this is possible to do differently and I have an idea for how I would do this, but I'm wondering if this is possible. If I can get answers to either or both of the questions it would help me a bit on my way to completely realize the roles that enumerators vs. iteratees vs. enumeratees have, as the lines seem a bit blurred -- sometimes, anyway. Thanks in advance. :) ___ 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] Enumerators, Enumeratees and Iterators
If I've understood it correctly, concurrent is similar to functions discussed here: http://www.haskell.org/pipermail/haskell-cafe/2011-April/091474.html and here http://www.haskell.org/pipermail/haskell-cafe/2011-January/088319.html 2011/6/28 Ertugrul Soeylemez e...@ertes.de Sævar Berg s.b.saevars...@gmail.com wrote: The first question is, I think, to be solved with enumeratees but I can't really grok how. Let's say I have an iteratee that consumes all input. Is it possible to implement an enumeratee or something else to stick between the enumerator and the iteratee to basically modify the input to the iteratee to only be a part of the input? Yes, this is an enumeratee. An enumeratee is neither a data producder nor a consumer. It is an iteratee, which feeds another iteratee with input based on its own input, so it acts like a kind of map operation. enumFile someFile printFileLines -- prints file with prepended line numbers enumFile someFile ?? onlyGet10Lines printFileLines -- print only 10 lines In fact an enumeratee can split the input stream into lines. Another one can zip the stream with a list. A final one can take 10 lines from the stream. The code would look like this (in the 'enumerator' package): enumFile myFile.txt $$ lines =$ zipWithList [1..] =$ take 10 =$ printLines where lines :: Monad m = Enumeratee Text Text m b zipWithList :: Monad m = [a'] - Enumeratee a (a, a') m b take:: Monad m = Int - Enumeratee a a m b printLines :: MonadIO m = Iteratee (Int, Text) m () This is how I would do it. The second question could actually have an application in the server I'm writing. I was wondering if it was possible to write iteratees/enumerators that would only generate/consume when a certain something was the next chunk to be processed? You want concurrent iteratees here. As far as I know in the 'enumerator' package there is no builtin way to do it (you may be luckier in the 'iteratee' package, but I don't know). However, I think it should be possible to write a 'concurrent' function, if the iteratees in question all have the same input type: concurrent :: Monad m = [Step a m b] - Iteratee a m [b] A version, which doesn't collect the results is probably much easier to write: concurrent_ :: Monad m = [Step a m b] - Iteratee a m () Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ ___ 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] GHC 7.0.3 / Win32: Data.Time library?
Could you look at http://hackage.haskell.org/packages/archive/time/1.2.0.5/doc/html/Data-Time-Format.html ? Is it enough? 2011/6/14 Dmitri O.Kondratiev doko...@gmail.com Sorry for typo - I need subtract dates (no 'abstracting') : On Tue, Jun 14, 2011 at 3:49 PM, Dmitri O.Kondratiev doko...@gmail.comwrote: It looks like GHC, 7.0.3 Haskell Hierarchical Libraries documentation generated for Win32, that goes with Haskell Platform installation package, does not have a section on Data.Time module. How can that be? I need to convert a string of the form ,10/11/2009 7:04:28 PM to Haskell type that can be used for comparing and abstracting dates. What is the simplest way to day that? Thanks! ___ 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] Oracle Sessions in Takusen
Hello,
Could anyone explain strange behavior of Takusen with OracleDB (OraClient
11.x)? Several sequential sessions give Seqmentation Fault error. In case
of nested sessions it works well.
{-# LANGUAGE ScopedTypeVariables #-}
module Main where
import Database.Oracle.Enumerator
import Control.Monad(replicateM)
import Control.Monad.Trans(liftIO)
main = do
{-
-- This gives an Segmentation Fault for the second session
replicateM 2 (do
res - withSession (connect x x x) (do
doQuery (sql SELECT dummy FROM dual) (\(d::String)
(_::Maybe String) - result' $ Just d) Nothing
)
print res
)
-}
-- This is works well
withSession (connect x x x) (do
r1 - doQuery (sql SELECT dummy FROM dual) (\(d::String)
(_::Maybe String) - result' $ Just d) Nothing
liftIO $ print r1
liftIO $ withSession (connect x x x) (do
r2 - doQuery (sql SELECT dummy FROM dual)
(\(d::String) (_::Maybe String) - result' $ Just d) Nothing
liftIO $ print r2
)
)
Best regards,
Dmitry
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Re: [Haskell-cafe] Iteratee: manyToOne
Thank you! Working implementation is even more than I've expected. 2011/4/28 Felipe Almeida Lessa felipe.le...@gmail.com On Thu, Apr 28, 2011 at 1:10 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: On Thu, Apr 28, 2011 at 12:09 PM, Felipe Almeida Lessa felipe.le...@gmail.com wrote: I foresee one problem: what is the leftover of 'manyToOne xs' if each x in xs needs different lengths of input? One possible untested-but-compiling solution: [snip] Like I said, that manyToOne implementation isn't very predictable about leftovers. But I guess that if all your iteratees consume the same input OR if you don't care about leftovers, then it should be okay. Sorry for replying to myself again. =) I think you can actually give predictable semantics to manyToOne: namely, the leftovers from the last iteratee are returned. This new implementation should be better: import Data.Monoid (mappend) import qualified Data.Enumerator as E manyToOne :: Monad m = [E.Iteratee a m b] - E.Iteratee a m [b] manyToOne is = E.Iteratee $ mapM E.runIteratee is = E.runIteratee . go where go [step] = fmap (:[]) (E.returnI step) go (E.Yield b _ : xs) = fmap (b:) (go xs) go (E.Error exc : _) = E.returnI (E.Error exc) go (E.Continue f : xs) = E.continue $ go' (E.Continue f : xs) go [] = return [] go' xs stream = manyToOne $ feed xs where feed [E.Yield b s] = [E.yield b (s `mappend` stream)] feed (E.Continue f : ys) = f stream : feed ys feed (step : ys) = E.returnI step : feed ys feed [] = [] With the same test as before: *Main E.run $ E.enumList 1 [5 :: Int, 6, 7] E.$$ manyToOne [return 1, maybe 2 id `fmap` E.head, return 3, maybe 4 id `fmap` (E.head E.head)] = \xs - (,) xs `fmap` E.head Right ([1,5,3,6],Just 7) *Main E.run $ E.enumList 10 [5 :: Int, 6, 7] E.$$ manyToOne [return 1, maybe 2 id `fmap` E.head, return 3, maybe 4 id `fmap` (E.head E.head)] = \xs - (,) xs `fmap` E.head Right ([1,5,3,6],Just 7) When the last iteratee doesn't consume anything: *Main E.run $ E.enumList 1 [5 :: Int, 6, 7] E.$$ manyToOne [return 1, maybe 2 id `fmap` E.head, return 3, maybe 4 id `fmap` (E.head E.head), return 10] = \xs - (,) xs `fmap` E.head Right ([1,5,3,6,10],Just 5) *Main E.run $ E.enumList 10 [5 :: Int, 6, 7] E.$$ manyToOne [return 1, maybe 2 id `fmap` E.head, return 3, maybe 4 id `fmap` (E.head E.head), return 10] = \xs - (,) xs `fmap` E.head Right ([1,5,3,6,10],Just 5) HTH, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Iteratee: manyToOne
In my case leftover is not important. But in common case... Just an idea... What if we provide iterWhile :: Iteratee a m () - Iteratee a m b - Iteratee a m b The first Iteratee only control when the result should be yeilded and feed an input to second Iteratee. Then we can change manyToOne to manyToOne' :: Iteratee a m () - [Iteratee a m b] - Iteratee a m [b] manyToOne' iw = iterWhile iw . manyToOne 2011/4/29 Felipe Almeida Lessa felipe.le...@gmail.com On Fri, Apr 29, 2011 at 6:32 AM, John Lato jwl...@gmail.com wrote: If you do this, the user needs to take care to order the iteratees so that the last iteratee has small leftovers. Consider: manyToOne [consumeALot, return ()] In this case, the entire stream consumed by the first iteratee will need to be retained and passed on by manyToOne. In many cases, the user may not know how much each iteratee will consume, which can make these semantics problematic. Iteratee has 'enumPair', (renamed 'zip' in HEAD) which returns the leftovers from whichever iteratee consumes more. This avoids the problem of retaining extra data, and seems simpler to reason about. Although if you really need to consume a predictable amount of data, the safest is probably to run the whole thing in a 'take'. My motivation is: in general it is difficult (impossible?) to choose the iteratee that consumed more data because you don't know what the data is. For example, if you give 'Chunks [a,b]' to two iteratees and one of them returns 'Chunks [c]' and the other one returns 'Chunks [d]', which one consumed more data? The answer is that it depends on the types. If they are Ints, both consumed the same, if they are ByteStrings, you would need to check if one is prefix of the other. What if one returns 'Chunks [c]' and the other one returns 'Chunks [d,e]'? If they are ByteStrings, should we compare 'c' against 'd ++ e'? So I thought it would be easier to program with an API that is predictable and immune to changes in block sizes. If you don't want leftovers, just use 'manyToOne [..., dropWhile (const True)]', which guarantees that you won't leak. Cheers, -- Felipe. ___ 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] Iteratee: manyToOne
Hello, does somewhere exist function with type like this - manyToOne :: [Iteratee a m b] - Iteratee a m [b] ? I.e. I need to process one input through many Iteratees indepentently in constant space and collect results. It is similar by type with sequenceM but as far as I understand sequenceM won't use the same input for all Iteratees. Dima ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fwd: using IO monad in Iteratee
-- Forwarded message -- From: Dmitry Olshansky olshansk...@gmail.com Date: 2011/4/2 Subject: Re: [Haskell-cafe] using IO monad in Iteratee To: wren ng thornton w...@freegeek.org Well, in my case I can use probably withBinaryFile fn (\h- run $ enumHandle h ...) 2011/4/2 wren ng thornton w...@freegeek.org On 4/1/11 3:59 PM, Dmitry Olshansky wrote: But enumFile use IO monad instead of MonadIO class. [...] Is it possible to change enumFile to using MonadIO class? Unless its changed significantly since I looked at it last (which it may well have), it's not possible. The problem is that what we'd really need is lowerIO :: m a - IO a for the m in question; liftIO goes the wrong way. Of course, getting a lowerIO with the right semantics will be tricky for most monads. -- Live well, ~wren ___ 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] using IO monad in Iteratee
Very interesting, thanks. I didn't feel your classes yet... Do you think that provide these instances for Iteratee is possible? 2011/4/2 Bas van Dijk v.dijk@gmail.com On 1 April 2011 21:59, Dmitry Olshansky olshansk...@gmail.com wrote: Is it possible to change enumFile to using MonadIO class? No because it uses the control operation Control.Exception.finally :: IO a - IO b - IO a internally. You can't lift control operations with liftIO :: MonadIO m = IO a - m a. However if you are able to define a MonadTransControl and MonadControlIO instance (from the monad-control package[1]) for Iteratee and use Control.Exception.Control.finally instead of the regular finally, you can use your MyMonad with the modified enumFile. Good luck, Bas [1] http://hackage.haskell.org/package/monad-control ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] using IO monad in Iteratee
Ertugrul, thanks for information. I've found several decisions for my real problem (using enumHandle and some more special decision). But I'll be have in mind about monad-control. 2011/4/3 Ertugrul Soeylemez e...@ertes.de Bas van Dijk v.dijk@gmail.com wrote: On 1 April 2011 21:59, Dmitry Olshansky olshansk...@gmail.com wrote: Is it possible to change enumFile to using MonadIO class? No because it uses the control operation Control.Exception.finally :: IO a - IO b - IO a internally. You can't lift control operations with liftIO :: MonadIO m = IO a - m a. However if you are able to define a MonadTransControl and MonadControlIO instance (from the monad-control package[1]) for Iteratee and use Control.Exception.Control.finally instead of the regular finally, you can use your MyMonad with the modified enumFile. I don't think that's possible, because Iteratee is based on CPS. I think, so far nobody has come up with an instance definition for monad-peel or monad-control for CPS-based monads like ContT or Iteratee. However, it is easy to write an own handle enumerator, which uses monad-peel or monad-control exception handling to convert errors to iteratee exceptions. On the other hand, as has been noted, there is enumHandle, which does that by itself. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ ___ 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] using IO monad in Iteratee
Dear collegues, I use Iteratee with Monad Transformer stack in this way: type MyMonad a b = Iteratee a (StateT StateType IO) b I've wrote some Enumeratees using this type. Then I want to compose it with standard enumerator like Data.Enumerator.Binary.enumFile. But enumFile use IO monad instead of MonadIO class. I didn't see (maybe I'm blind...) a way to compose my Enumeratees with enumFile. How I can do that? Is it possible to change enumFile to using MonadIO class? Best regards, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] fetching BLOBs
Hello, cafe, Is there a way to get BLOB fields from OracleDB using Takusen? What about other possibilities (through HDBC - ODBC)? Dima ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Takusen and QuickCheck
Hello, I have a problem with using Takusen in my current project because it uses old QuickCheck 1.*. This leads to conflict with other packages which use QuickCheck 2.*. Could someone help me to decide this problem? Best wishes, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Bug with [Double]
Hello all, It seems that I saw something like this in Cafe recevtly. But I am not sure... In GHC 6.12.1 (Platform 2010 on Windows Vista) I have Prelude [1,1+2/3..10] [1.0,1.6665,2.333,2.9996,3.666,4.332,4.998,5.664,6.33,6.9964,7.6625,8.329,8.995,9.66,10.327] -- It is a bug! Prelude [1,5/3..10] [1.0,1.6667,2.3335,3.0,3.6665,4.333,5.0,5.667,6.334,7.001,7.668,8.336,9.004,9.671] -- correct, but... Prelude [1,5/3..4] [1.0,1.6667,2.3335,3.0,3.6665,4.333] -- ... wrong again Prelude [1,1+2/3..10] :: [Float] [1.0,1.667,2.335,3.002,3.67,4.34,5.01,5.68,6.35,7.02,7.69,8.36,9.03,9.7] -- correct Prelude [1,1+2/3..10] :: [Double] [1.0,1.6665,2.333,2.9996,3.666,4.332,4.998,5.664,6.33,6.9964,7.6625,8.329,8.995,9.66,10.327] -- wrong Any comments? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bug with [Double]
But Prelude Data.List [1,1+2/3..4] :: [Double] [1.0,1.6665,2.333,2.9996,3.666,4.332] Prelude Data.List unfoldr (\n - let n'=n+2/3 in if n' = 4 then Just (n',n') else Nothing) 1 :: [Double] [1.6665,2.333,2.9996,3.666] Prelude Data.List takeWhile (=4) $ iterate (+2/3) 1 :: [Double] [1.0,1.6665,2.333,2.9996,3.666] How 'dodgy' it should be to produce different result? How [a,b..c] works in this case? 2010/5/19 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com: Dmitry Olshansky olshansk...@gmail.com writes: Hello all, It seems that I saw something like this in Cafe recevtly. But I am not sure... In GHC 6.12.1 (Platform 2010 on Windows Vista) I have Prelude [1,1+2/3..10] [1.0,1.6665,2.333,2.9996,3.666,4.332,4.998,5.664,6.33,6.9964,7.6625,8.329,8.995,9.66,10.327] -- It is a bug! No it isn't, because of the dodgy Ord instance for Float and Double values. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bug with [Double]
Thanks, it's clear now.
2010/5/19 Serguey Zefirov sergu...@gmail.com:
2010/5/19 Erik de Castro Lopo mle...@mega-nerd.com:
Dmitry Olshansky wrote:
It seems that I saw something like this in Cafe recevtly. But I am not
sure...
In GHC 6.12.1 (Platform 2010 on Windows Vista) I have
snip
Any comments?
The problem you point out is not a problem with Haskell, but a problem
with the whole concept of floating point arithmetic as implemented on
all modern CPUs. See:
http://docs.sun.com/source/806-3568/ncg_goldberg.html
You would have got similar problems with just about any language running
on the same hardware.
This is what used for Double list generation (Haskell Platform 2010):
--
numericEnumFromThenTo :: (Ord a, Fractional a) = a - a - a - [a]
numericEnumFromThenTo e1 e2 e3
= takeWhile predicate (numericEnumFromThen e1 e2)
where
mid = (e2 - e1) / 2
predicate | e2 = e1 = (= e3 + mid)
| otherwise = (= e3 + mid)
--
So normal C loop like for {double i = 1; i = 10; i += 1+2/3) {
insert_list(i); } won't generate the same list, as Haskell does in
[1,1+2/3..10].
PS
Rationals:
Prelude [1,1+2/3..10] :: [Rational]
[1 % 1,5 % 3,7 % 3,3 % 1,11 % 3,13 % 3,5 % 1,17 % 3,19 % 3,7 % 1,23 %
3,25 % 3,9 % 1,29 % 3,31 % 3]
Same result.
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[Haskell-cafe] instance reification in TH
Hello cafe, Could you say can I determine in Template Haskell that datatype X has instance of class Y? Regards, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ErrorT instance of MonadPlus
Hello, ErrorT instance of MonadPlus define that in case of fail both arguments of mplus a value of Error will be the Error of second computation: m `mplus` n = ErrorT $ doa - runErrorT mcase a of Left _ - runErrorT nRight r - return (Right r) Could it be changed in this way: m `mplus` n = ErrorT $ doa - runErrorT mcase a of Left e - do b - runErrorT n case b of Left e' - return $ Left (e `eplus` e') r - return r r - return r where `eplus` could be placed in class Error a: eplus :: a - a - a eplus x y = y -- default implementation In this case we could combine Errors more flexible. Best regards, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell2Xml - Suggest looking at HXT
Hi Max, thanks for your suggestion. I also have a not pretty code which used Text.XML.Light and TH. I am going to rewrite it. HXT by my opinion is too big. The question is a requirements. Which correlations exist between Haskell types and XML-Schema possibilities? How to prepare XML for different Haskell types? How to generate Haskell types from XML-Schema, which restrictions in schema could be authomatically modeled in Haskell? And so on... 2009/8/8 Max Cantor mxcan...@gmail.com Hi Dmitry, I've been using HXT and its XmlPickler class for encoding and decoding between XML - Haskell types. It takes a while to wrap your brain around the arrows based API for HXT (something I'm still working on) but it seems to be quite powerful and well maintained. Also, I've written some Template Haskell code to derive instances for the XmlPickler class (so that types can automatically be encoded and decoded as XML. Its not pretty, has bugs, and is far from perfect but I can send that to you if you'd like a way to get stared. Max On Aug 7, 2009, at 7:04 PM, Dmitry Olshansky wrote: Well, great thanks for interesting links. But definitely at first I need a time to try to understand what Generic Haskell and EMGM are. Does it stronger than Template Haskell? Could it be explained briefly and simplistic for first impression? Could it be compared with SYB or TH? Would it be applied to realisation of translation or to target Haskell code? Regards, Dmitry 2009/8/7 Sean Leather leat...@cs.uu.nl On Fri, Aug 7, 2009 at 12:05, John Lask jvl...@hotmail.com wrote: the paper: Scripting XML with Generic Haskell Frank Atanassow, Dave Clarke and Johan Jeuring October 14, 2003 describes a translation from XML Schema to Haskell data types (like dtd2haskell) in generic haskell, I believe that the code for the tool described may also be available, how hard it would be to migrate over to vanilla haskell+generics is another question It looks like this almost might work in EMGM. They use a Label in addition to all the other representation structure elements. EMGM doesn't have a Label, but it might be useful to add it... With any needed changes such as the Label done, migrating this Generic Haskell code to EMGM would not be difficult. Sean ___ 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] Network.Curl and posting XML data
Hi, Erik, Did you try Network.HTTP? Is it not enough? 2009/8/12 Erik de Castro Lopo mle...@mega-nerd.com mle%2...@mega-nerd.com Hi all, I need to do a HTTP post of XML data (Content-type == text/xml) to a HTTP (eventually HTTPS) server and to retrieve both the response code and some returned XML data. I have had an extensive read of the haskell-curl docs: http://hackage.haskell.org/packages/archive/curl/1.3.5/doc/html/Network-Curl.html as well as playing around with some code, but haskell-curl doesn't seem to support this. I've tried curlPost which along with not returning a response also insists on encoding my XML data as application/x-www-form-urlencoded which simply doesn't work. Anyone ben able to get something like this to work? Are there any alternatives to haskell-curl which will work for my application? Cheers, 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell2Xml
Like in Keith proposal I need it for working with web-services, maybe Xml transformations and so on. And I tried to make it by self with a partial success. To work with xml I only used xml package (Text.XML.Light). Now I am going to work a little (?) on this task to provide more standard and regular tool than I have now. So it is very interesting for me to learn any ideas (if exists) on this thing from community. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell2Xml
Well, great thanks for interesting links. But definitely at first I need a time to try to understand what Generic Haskell and EMGM are. Does it stronger than Template Haskell? Could it be explained briefly and simplistic for first impression? Could it be compared with SYB or TH? Would it be applied to realisation of translation or to target Haskell code? Regards, Dmitry 2009/8/7 Sean Leather leat...@cs.uu.nl On Fri, Aug 7, 2009 at 12:05, John Lask jvl...@hotmail.com wrote: the paper: Scripting XML with Generic Haskell Frank Atanassow, Dave Clarke and Johan Jeuring October 14, 2003 describes a translation from XML Schema to Haskell data types (like dtd2haskell) in generic haskell, I believe that the code for the tool described may also be available, how hard it would be to migrate over to vanilla haskell+generics is another question It looks like this almost might work in EMGM. They use a Label in addition to all the other representation structure elements. EMGM doesn't have a Label, but it might be useful to add it... With any needed changes such as the Label done, migrating this Generic Haskell code to EMGM would not be difficult. Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient functional idiom for histogram
My measurements show that - using strict version of insertWith doesn't improve performance. - in case of compilation with -O2 flag foldl' also is equal to foldl (-O2 gives approx 2 time impovements).- using RandomGen and State monad to generate a list gives at least 4 times improvements (on 1 000 000 items). More complicated improvements (using Array, PRNG and so on) were not tested by me. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient functional idiom for histogram
I got the impression Dmitry was using Haskell's standard RNG, not Mersenne Twister. If so, then we'd get further improvements with MT, but that's still a hit against Haskell, as I'd interpret it as meaning that Haskell supplies as default a PRNG which costs noticeable performance in order to provide guarantees that ordinary programs don't need. Paul. Yes, I used standard RNG just made corrections from the second Daniel Fischer's post. My file is attached. Commented strings are from original version and next lines are from Daniel. (Note that simulation and simulate types depend on type of dice). Just compile with ghc --make -O2 histogram.hs and run histogram +RTS -s As a pre-intermediate ;-) I just check some proposals... histogram.hs Description: Binary data ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell2Xml
Hello all, I need a convenient tool to generate Haskell types from XML W3C Schema Definition (xsd) and vice versa - generate instances for Haskell ADT's to make corresponding XML. It is just the same that HaXml do with DTD. I need - using XSD - support for unicode - using xml-attributes as far as elements are very desirable - by my opinion TemplateHaskell for generate instances is prefferable than using DrIFT (which used in HaXml) - both possibilities is great of course - generation of xsd by Haskell type is a good feature also and so on... Does this tool exist? Do some articles / thoughts / standards / recomendations about correspondence between XML and Haskell ADT's exist? Best wishes, Dmitry ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
