- Haskell-Cafe - Haskell.org

TimeZone bug?
by Magicloud Magiclouds 23 Oct '09

23 Oct '09

Hi, As we know, "CST" could mean both +8 or -6 time zone. So I got a problem. In the same envoironment. When a ZonedTime is shown, I got "xxxxx CST". Now it means +8 time zone. Then I read it, stupidly, it turns into -6 time zone. How could I fix this? I am using ghc 6.10.4 in rhel 5. -- 竹密岂妨流水过山高哪阻野云飞

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Lazy problem ?
by zaxis 23 Oct '09

23 Oct '09

"ssqHitNum.txt" contains data as below: 6 7 18 24 30 32 9 4 12 20 25 28 29 16 3 5 11 12 31 32 11 2 9 13 15 19 24 3 5 17 21 25 27 32 14 5 9 15 21 26 31 13 12 16 25 26 27 31 05 ... good_ssq_red:: IO [Int] good_ssq_red = withFile "ssqHitNum.txt" ReadMode (\h -> do { samp <- fmap str2Ints $ hGetContents h; print samp; --without this line, the result will always [1..16] return $ statis samp; }) statis :: [Int] -> [Int] statis samp = take 16 $ map (\(a,b) -> a) $ sortBy (\a b-> if (snd a >= snd b) then LT else GT) $ times4n where times = map (\n -> (foldl (\acc x -> if x==n then acc+1 else acc) 0 samp)) [1..33] times4n = map (\n -> (n,times!!(n-1))) [1..33] Does it mean that the sampe will not be evalued with `print samp` line ? thanks! -- View this message in context: http://www.nabble.com/Lazy-problem---tp26021845p26021845.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Time and space complexity of "take k . sort"
by Paul Johnson 23 Oct '09

23 Oct '09

This question on StackOverflow asked about how to find the largest 100 items in a very long list: http://stackoverflow.com/questions/1602998/fastest-way-to-obtain-the-larges… I replied that you could do it with something like this (but here taking the k smallest to strip out some irrelevant complications): > takeLargest k = take k . sort Because "sort" is lazily evaluated this only does enough sorting to find the first k elements. I guess the complexity is something like O(n*k*log(k)). But of equal practical interest is the space complexity. The optimum algorithm is to take the first k items, sort them, and then iterate through the remaining items by adding each item to the sorted list and then throwing out the highest one. That has space complexity O(k). What does the function above do? Paul.

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why cannot i get the value of a IORef variable ?
by zaxis 23 Oct '09

23 Oct '09

> let aaa = unsafePerformIO $ newIORef [] > writeIORef aaa [1,2,3] > readIORef aaa [(),(),()] sincerely! -- View this message in context: http://www.nabble.com/why-cannot-i-get-the-value-of-a-IORef-variable---tp26… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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NetSnmp problem.
by Magicloud Magiclouds 23 Oct '09

23 Oct '09

Hi, I am trying to use NetSnmp to get some information from my switch. And I met this problem. After initialize, I used snmpWalk to get some information, and dealed with it. Everything is fine. Then I sleep for 5 mins. SnmpWalk again. But this time, all asnValues were unsupported format, which broke my dealing process. Why? I am sure my switch and OID, bluh bluh bluh are correct. They worked in ruby script. -- 竹密岂妨流水过山高哪阻野云飞

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cvs.haskell.org down? haskell-mode abandoned?
by Svein Ove Aas 22 Oct '09

22 Oct '09

Attempting to update haskell-mode, I've been getting authorization failures from the cvs.haskell.org pserver. I thought this might have some connection to the recent disk crash, and as nobody uses cvs anymore, it could have been overlooked. In any case, I need it fixed before I can work on haskell-mode. Preferably by migrating haskell-mode over to cvs. :-) On a different note, I've been unable to contact the apparent current maintainer of haskell-mode, while in a state of having a useful patch. Though it may already have made it to cvs, with me simply being unable to check that.. actually, who *is* the current maintainer? The last release was Dec. 2007. -- Svein Ove Aas

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Is there in Haskell the eval function?
by Waldemar Biernacki 22 Oct '09

22 Oct '09

Hello! I have a very stupid question. Sorry for that! Is there the eval function like in imperative languages? I'd like to write an application which has to be compiled to exec file. It is neccessary to performe some additional procedures which are unknown at the moment of the compilition. Regards wb.

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Simple but interesting (for me) problem
by michael rice 22 Oct '09

22 Oct '09

There's a thread on the plt-scheme list about creating a function of NO arguments named NEXT that just returns the number of times it's been called, a piece of cake in Scheme, but how would one do this in Haskell? Would the best approach be to use a State monad? Michael

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How can i safely change the value of specified key ?
by zaxis 22 Oct '09

22 Oct '09

aaa <- newIORef ([]::[(Int,Int)]) writeIORef aaa [(1,1),(2,2),(3,3)] then if i want to change aaa to [(1,1),(2,222),(3,3)] , what's the best way ? re-write aaa is not permitted. Sincerely! -- View this message in context: http://www.nabble.com/How-can-i-safely-change-the-value-of-specified-key---… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: mecha-0.0.0
by Tom Hawkins 22 Oct '09

22 Oct '09

A few months ago, I started toying with a few alternative pump designs to power our hydraulic hybrids. After not being able to secure a ProE license, I searched for a free solid modeler to sketch out a few ideas. To my surprise, their are practically no open source 3D CAD packages available. So I created Mecha, DSL for constructive solid modeling. Mecha's geometry is based on octrees, which makes it easy to perform set operations on solids, as well as volumetric calculations such as center-of-mass, moments of inertia, and of course, total volume. Drawbacks of octrees include consuming a lot of memory and the loss of some surface information. To address the later, Mecha carries forward surface points and normals to the leaf nodes of the octree to assist in rendering, such that solids don't look like they're made from a bunch of LEGOS. Note this is a very early release. The only thing Mecha can do at the moment is draw a pretty blue ball -- well it can also zoom and pan on a pretty blue ball (mouse wheel). Establishing a primitive API and building a primitive library must be finished before Mecha an do anything useful. Any comments and suggestions are welcome. http://tomahawkins.org/

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