- Haskell-Cafe - Haskell.org

Looking for documentation on Control.Parallel.Strategies
by Jefferson Heard 18 Feb '07

18 Feb '07

Is there anything that documents this further than the Haddock documentation available from Haskell.org or the GHC pages? I've gotten some basic parallelism to work using parMap and using >|| and >|, but I had a fold and a map that I could logically compute at the same time. I found this example for quicksort using GPH: import Strategies main = print (quicksort ([999,998..0]::[Int])) quicksort :: (Ord a, NFData a) => [a] -> [a] quicksort [] = [] quicksort [x] = [x] quicksort (x:xs) = (lo ++ (x:hi)) `using` strategy where lo = quicksort [ y | y <- xs, y < x] hi = quicksort [ y | y <- xs, y >= x] strategy result = rnf lo `par` rnf hi `par` rnf result Is the syntax the same for GHC using Control.Parallel.Strategies? If so, does the following execute the two computations from the where clause in parallel? import Control.Parallel import Control.Parallel.Strategies stats bigList summation mean = (stddev, proportions) `using` strategy where stddev = sqrt (fold ((+) . (^2) . (-mean)) 0 bigList) proportions = map (/summation) bigList strategy result = rnf stddev >|| rnf proportions >|| rnf result Thanks! --Jeff

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Application Level server state in Haskell Web server
by Pieter Laeremans 18 Feb '07

18 Feb '07

Hello, I'm trying to write a simple module for the haskell web server (hws- cgi). And I would like to write a simple module that maintains some kind of state for a session. But I'm I write I cannot do this in pure Haskell ? Without adopting the sources of the Haskell web server ? I'll examplify to make it more concrete : The requestHandler function a module has to implement has this signature. requestHandler :: ServerState -> ServerRequest -> IO (Maybe Response) Let 's assume I have this implementation requestHandler st _ = return $ Just $ mkRequest where mkRequest = okResponse (serverConfig st) mkBody hs True mkBody = HereItIs " This is a test" hs = mkHeaders [contentTypeHeader "text/html"] And I would like the response to include, for example, a number indicating the number of calls that has been handled by the module. I would concider using an Mvar but I can't "remember" the mvar between requests. Am I right to assume that the interface of the requestHandler method has to be adapted ? Or that serverstate has to be adopted so that it can act as a datastore ? kind regards, Pieter

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Re: [Haskell-cafe] How to solve this problem?It's quite easy in PHP.
by Henk-Jan van Tuyl 18 Feb '07

18 Feb '07

On Fri, 16 Feb 2007 22:44:25 +0100, David House <dmhouse(a)gmail.com> wrote: > On 16/02/07, Henk-Jan van Tuyl <hjgtuyl(a)chello.nl> wrote: >> Yet simpler: >> > formatTableItems (a,b) = a : " = " ++ (show b) ++ "\n" > > You can drop the parentheses around 'show b'; infix function > application always binds tighter than pretty much everything else. I missed that one; of course I knew it, but you could say it's in my passive vocabulary. -- Met vriendelijke groet, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ -- Using Opera's revolutionary e-mail client: https://secure.bmtmicro.com/opera/buy-opera.html?AID=789433

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LugRadio talk
by Dougal Stanton 17 Feb '07

17 Feb '07

So which one of you wonderful people volunteered to give a talk on Haskell at the coming LugRadio Live? I'm afraid I didn't catch the name, though it might have been a Magnus something? It might be enough to make me go if I knew there would be some funky Haskelling going on. Cheers, D. -- Dougal Stanton

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Newbie Q: GHCi: Where “List” module is imported from?
by Dmitri O.Kondratiev 16 Feb '07

16 Feb '07

Going through "Haskell. The Craft of Functional Programming" book , in section 16.8 I found a Set module example. Module declarations starts with: import List hiding (union) "Set" module here is built with list and uses among other things list comparison functions such as (==) and (<=). For example: eqSet :: Eq a => Set a -> Set a -> Bool eqSet (SetI xs) (SetI ys) = (xs == ys) Q1: Where "List" module is imported from? GHC "Base" package contains "Data.List" module, not just "List" module. Besides, "Data.List" does not have (<=) function. Q2: Any tutorial on using GHC libraries out there? Thanks! Dima

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How to solve this problem?It's quite easy in PHP.
by keepbal 16 Feb '07

16 Feb '07

For example, ----------------------------------- <?php //test.php require ("tiny.php");//Tiny is a small template engine. $tn=new Tiny(); $arr=new Array(); $arr['a']='1'; $arr['b']='2'; $arr['c']='3'; $tn->set('arr',$arr); $tn->show('_test.php'); ?> ----------------------------------- <?php require('_header.php');?> <?php foreach($arr as $key => $val){ echo "$key = $val <br>"; } ?> <?php require('_footer.php');?> ----------------------------------- a = 1 b = 2 c = 3 -----------------------------------

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new member
by P. R. Stanley 16 Feb '07

16 Feb '07

Hi Paul here - new member - checking to see my account is fully functional. Does the list know of another list where I can post questions on functional programming and the related mathematics? I'm assuming Haskell Cafe is mainly for discussions on Haskell programming and not so much the underlying theory. Any help would be appreciated. Cheers Paul

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Strange memory consumption problems in something that should be tail-recursive
by Jefferson Heard 16 Feb '07

16 Feb '07

Hi, I am running the following code against a 210 MB file in an attempt to determine whether I should use alex or whether, since my needs are very performance oriented, I should write a lexer of my own. I thought that everything I'd written here was tail-recursive, but after compiling this with GHC 2.4.6, and running it, I eat up 2GB of RAM in less than a second. So far, I have tried token and character oriented Parsec parsers and alex and alex is winning by a factor of 2. I would like to be able to tokenize the entirety of a 1TB collection in less than 36 hours on my current machine, which is where alex has gotten me so far. Thanks in advance! -- Jeff --- module Main where import qualified FileReader import qualified Data.Set as Set punct = foldl (flip Set.insert) Set.empty "<,>.?/:;\"'{[}]|\\_-+=) (*&^%$##@!~`" stripTagOrComment [] = [] stripTagOrComment ('>':rest) = rest stripTagOrCOmment (c:rest) = stripTagOrComment rest pass1 :: String -> String -> String pass1 left [] = left pass1 left ('<':right) = pass1 left (stripTagOrComment right) pass1 left (' ':right) = pass1 left right pass1 left (c:right) | Set.member c punct = pass1 (' ':c:' ':left) right | otherwise = pass1 (c:left) right pass2 :: [String] -> String -> Char -> String -> [String] pass2 left word ' ' [] = word:left pass2 left word c [] = (c:word):left pass2 left word ' ' (' ':right) = pass2 left word ' ' right pass2 left word ' ' (c:right) = pass2 (word:left) "" c right pass2 left word l (c:right) = pass2 left (l:word) c right tokenize = (pass2 [] "" ' ') . (pass1 []) main = do file <- do FileReader.trecReadFile "trecfile" print (tokenize (head (tail file))) -- print (length (map (runParser tokenizeDoc [] "") file))

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State of OOP in Haskell
by Alexy Khrabrov 16 Feb '07

16 Feb '07

...In the tradition of the "letters of an ignorant newbie"... What's the consensus on the OOP in Haskell *now*? There're some libraries such as OOHaskell, O'Haskell, and Haskell~98's own qualified type system with inheritance. If I have GHC, which way to do anything OOP-like is considered "right" today? Cheers, Alexy

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SoC: Port Haddock to use GHC
by Nicolas Frisby 16 Feb '07

16 Feb '07

I am very ready for a Haddock that can swallow infix typenames. In dons's recent overview of the last SoC, a darcs repo for Waern's project was listed. I jumped at the link but couldn't find much documentation (i.e. the README file is GHC's, not the SoC project's). Some Google queries followed with no success. My questions for Waern or anyone else who knows where to look: 1) Where to look for more complete documentation? 2) Is the implementation integrated into GHC yet? GHC head? Separate repo? 3) What Haddock features are supported as of yet? 4) Is it still actively developed? Thanks for any hints, Nick

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