May 2007 - Haskell-Cafe

Data.Generics
by mark＠ixod.org 30 May '07

30 May '07

Do we have a simple example somewhere of how to use gzipWithQ ? I can get things like everything and everywhere working with mkQ and mkT, but I can't work out how to make a curried query thing for gzipWithQ - I'm sure I'm missing the obvious. -- Mark

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Efficiency question
by Evil Bro 30 May '07

30 May '07

I'm pretty new to Haskell, so forgive me if my question is due to my non-functional way of thinking... I have the following code: module Main where main = print solution solution = solve 1000000 solve d = countUniqueFractions d 2 1 0 canBeSimplified (a,b) = gcd a b > 1 countUniqueFractions stopD currentD currentN count | currentD > stopD = count | currentN == currentD = countUniqueFractions stopD (currentD + 1) 1 count | canBeSimplified (currentN, currentD) = countUniqueFractions stopD currentD (currentN+1) count | otherwise = countUniqueFractions stopD currentD (currentN+1) (count + 1) When I run this code, I get a stack overflow. I don't understand why. Could anyone explain please? -- View this message in context: http://www.nabble.com/Efficiency-question-tf3823154.html#a10823572 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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System.Timeout problems
by Neil Mitchell 30 May '07

30 May '07

Hi I'm using the System.Timeout module from base, copied into my local repo, so that I can work with GHC 6.6.1. My copy is at: http://www.cs.york.ac.uk/fp/darcs/catch/catch_1/System/TimeoutGHC.hs (but it is identical to the one in base) Sadly, it doesn't seem to work for me. Here are the tests I've been using, the results I get, and what I would have liked. All are GHC 6.6 on Windows. -- TEST 1 import System.TimeoutGHC main :: IO () main = do r <- timeout (5 * 10^6) (putStrLn "here") print r Without -threaded: here >> Just () >> wait 5 seconds Without -threaded: here >> wait 5 seconds >> Just () So, either way, I get a 5 second delay - not something I want. -- TEST 2 import System.TimeoutGHC main :: IO () main = do r <- timeout (length [1..]) (putStrLn "here") print r Now, with either -threaded, or without, it never terminates. Basically I can't get the timeout to do anything I would like with any flags. Can someone come to my rescue? Am I getting timeout wrong? Thanks Neil

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Shared libraries in GHC
by Georg Sauthoff 30 May '07

30 May '07

Hi, while searching, if ghc can create packages as shared libraries I found a ticket with a kind of non-accepted status: http://hackage.haskell.org/trac/summer-of-code/ticket/46 But at the google SoC page it looks like an accepted project: http://code.google.com/soc/haskell/appinfo.html?csaid=D0137F8B637176F1 Well what is the status of the project? Does the student have a blog/webpage where one can track the progress of the project? Btw, the problem I want to solve with shared libraries is the case, where I want to program 2 frontends (==2 executables), which share a lot of Haskell-Code. I am afraid, if both frontends are linked statically, the result will look a bit 'bloated' ... Best regards Georg Sauthoff

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Is there a Template lib like Cheetah in python?
by Albert Lee 30 May '07

30 May '07

I am writing some webpage using haskell, I know Xhtml, but I also need some other persons to write simple htmls so I need a template system like cheetah in python, but I didn't find anything through google. any help? -- http://www.kamang.net

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ffi linking problem
by jeff p 30 May '07

30 May '07

Hello, Can anyone give me some tips concerning the following error: myPrompt> ghc --make -fffi f.hs -l mylib.lib ghc --make -fffi f.hs -l mylib.lib [1 of 1] Compiling Main ( f.hs, f.o ) Linking f.exe ... d:\ghc\ghc6.6\gcc-lib\ld.exe: cannot find -l-Ld:/ghc/ghc6.6 collect2: ld returned 1 exit status thanks, Jeff

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Coding Standards (Coding Conventions)
by Philipp Volgger 30 May '07

30 May '07

I wonder if there are any Coding Standards or Coding Conventions for Haskell. Does anybody know something about it? Kind regards, Philipp Volgger

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Help with terminal IO
by Ryan Ingram 30 May '07

30 May '07

I was hoping that hSetBuffering would turn off the line buffering for stdin, but it doesn't seem to work. ---- module Main where import System.IO main :: IO () main = do hSetBuffering stdin NoBuffering hSetBuffering stdout NoBuffering hPutChar stdout '>' c <- hGetChar stdin hPutChar stdout '<' ---- This program should terminate immediately after the first character is typed into the terminal, but it waits until I type a newline. It also looks like it's using GNU readline (it handles the up & down arrow keys.) How do I turn this off and use raw character-based IO? I'm using GHC6.6 on Win32 if that makes a difference. -- ryan

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teaming up for the IFCP contest
by Tim Docker 29 May '07

29 May '07

I've put aside the weekend of July 20-23 for the ICFP contest (http:// www.icfpcontest.org/) and am looking to form or join a haskell wielding team. Any interest? Geographically I'm in Sydney, but have entered in a previous year with a team of 3 from around the globe which worked fine. Tim

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Control.Monad.State.Strict, mdo and let
by Gracjan Polak 29 May '07

29 May '07

Hi, I stumbled at some interaction of Control.Monad.State.Strict, mdo and let I do not understand. The following program: {-# OPTIONS_GHC -fglasgow-exts #-} module Main where import Control.Monad.State.Strict thenumber :: Float thenumber = flip execState 1.3 $ mdo c <- donothing [] let donothing x = return x return () main = print thenumber Says (in GHC 6.6.1): Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. Why is this so? -- Gracjan

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