June 2010 - Haskell-Cafe

IORef memory leak
by Jim Snow 15 Oct '10

15 Oct '10

I'm having some trouble with excessive memory use in a program that uses a lot of IORefs. I was able to write a much simpler program which exhibits the same sort of behavior. It appears that "modifyIORef" and "writeIORef" leak memory; perhaps they keep a reference to the old value. I tried both ghc-6.8.3 and ghc-6.10.1. Is this a known limitation, or is this a ghc bug, or am I using IORefs in the wrong way? -jim module Main where import Data.IORef import Control.Monad -- Leaks memory leakcheck1 ior = do go 1000000000 where go 0 = return () go n = do modifyIORef ior (+1) go (n-1) -- Leaks memory leakcheck2 ior = do go 1000000000 where go 0 = return () go n = do x <- readIORef ior writeIORef ior (x+1) go (n-1) -- Runs in constant memory leakcheck3 ior = do go 1000000000 where go 0 = return () go n = do x <- readIORef ior go (n-1) main :: IO () main = do ior <- newIORef 0 leakcheck2 ior compiled with: ghc -O2 --make Leak.hs -o Leak

10 17

cabal problem on OS X
by Bill Atkins 19 Sep '10

19 Sep '10

When I run "cabal update" on my Mac (Snow Leopard, Intel), I get: % cabal update Downloading the latest package list from hackage.haskell.org cabal: Codec.Compression.Zlib: incompatible zlib version Anyone else seeing this? Reinstalling the Haskell Platform hasn't helped. Thanks!

8 7

CnC Haskell
by Vasili I. Galchin 08 Sep '10

08 Sep '10

Hello, I have been reading work done at Rice University: http://habanero.rice.edu/cnc. Some work has been done by http://www.cs.rice.edu/~dmp4866/ on CnC for .Net. One component that David wrote a CnC translator that translates CnC textual form to the underlying language, e.g. F#. Is anybody working on a CnC textual form translator for Haskell so a Haskell user of CnC Haskell can write in a higher level?? Thanks, Vasili

4 5

Re: [Haskell-cafe] iPhone/Android and Haskell [Was: Embedded funcional programming?]
by Liam O'Connor 10 Aug '10

10 Aug '10

Our best bet is to compile to ARM native code and then use the NDK to talk to the Java APIs. Cheers. ~Liam

8 15

design question: decision tree from "Programming Collective Intelligence"
by Daniel Lyons 04 Aug '10

04 Aug '10

Hi, I'm having a little trouble figuring out precisely how to port the decision tree code from the book "Programming Collective Intelligence." You can see the code here: http://code.google.com/p/memothing/source/browse/trunk/PCI/ch7/treepredict.… The design issue is that this code depends on dynamic typing pretty heavily. He has a table of heterogenous data. Each column has the same type, but that's implicit, not explicit. He depends on all of the values supporting "==", which he uses to get a list of distinct values from each column. These values are used by the divide set function which takes a column and a value as parameters. Based on the type of the value, he chooses a different partitioning function; for strings, it's just equality again, but for numeric types he uses >=. The decision tree nodes then collect not just the left and right branches but also the column number and value on which the split was performed. I have thought about this for several days and can't seem to come to a design that I like, so I'm wondering how others would approach the problem. I guess you could implement it as a list of lists of some data type that is either a string or numeric, but this feels a bit like a cop-out. How would you support creating a decision tree with different types of data? I imagine possibilities using existential quantification, SYB, Data.Data and other stuff, but I don't know how to make it work. I wonder if there is an obvious functional design hiding in here that doesn't depend on any fancy stuff, but I'm blinded to it by having read and understood the Python version of the code. Anybody have any suggestions? I'd greatly appreciate any help. Thanks, — Daniel Lyons

4 3

ANN: scan-0.1.0.3, a Haskell style scanner
by Christian Maeder 03 Aug '10

03 Aug '10

Dear Haskell friends, I like to announce a Haskell style scanner at http://hackage.haskell.org/package/scan documented under http://projects.haskell.org/style-scanner/ It's best used in conjunction with hlint http://community.haskell.org/~ndm/hlint/ and gives many suggestions regarding the file format. Feedback is welcome. Thanks Christian (Discussions should only be posted to either haskell-cafe@ or beginners@)

5 10

Fwd: [Haskell-cafe] Bytestrings and [Char]
by Alberto G. Corona 18 Jul '10

18 Jul '10

The question can be generalized via type classes: Is there any common set of primitives encapsulated into a single type class that has instances for Strings (Data.List) ByteStrings, Data.Text, Lazy bytestrings, Arrays, vectors and wathever container that can store an boxed, unboxed, packed unpacked sequence of wathever including chars? All of them have folds, heads, tails and a lot of common functions with the same name, but since there is not a single type class, the library programmer can not abstract his code when it is possible, so the library user can chose the particular instance for his particular problem. 2010/3/23 Johann Höchtl <johann.hoechtl(a)gmail.com> On 22.03.2010 14:15, Ivan Miljenovic wrote: > >> On 23 March 2010 00:10, Johan Tibell<johan.tibell(a)gmail.com> wrote: >> >> >>> A sequence of bytes is not the same thing as a sequence of Unicode >>> code points. If you want to replace String by something more efficient >>> have a look at Data.Text. >>> >>> >> Though Data.Text still has the disadvantage of not being as nice to >> deal with as String, since you can't pattern match on it, etc. >> >> Whilst it may degrade performance, treating String as a list of >> characters rather than an array provides you with greater flexibility >> of how to deal with it. >> >> >> > But doesn't this basically mean sacrifice performance / applicability for > algorithmic beauty? Sure, pattern match comes in handy, but in the case of > strings at a high price > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

3 3

haskell platform questions
by Warren Harris 12 Jul '10

12 Jul '10

I installed haskell platform some time ago, and now I'm wondering what version I have. How do I find out? Also, when the new one comes along on the 21st, is there a way to upgrade? Or if I must first uninstall the one I have now, how do I uninstall it? Is it recommended to periodically upgrade packages that came with the platform (cabal upgrade), or is it recommended that they be left alone to avoid dependency incompatibilities. Similar question for ghc itself -- can/should it be upgraded in the context of haskell platform? (I was hoping to try Leksah, but it dies without ghc 6.12.1. I seem to have 6.10.4.) Apologies in advance if this is all documented somewhere, but I couldn't find it on the haskell platform site/trac. BTW, I'm on Mac/ Leopard -- love the fact that it didn't take hours to build everything! Warren

9 22

haskell on suse?
by gladstein＠gladstein.com 12 Jul '10

12 Jul '10

I've been spoiled by package managers that download and install everything for you, and I've forgotten how RPM works. In particular, I want to install Haskell on suse, and I read that "RPMs are available from openSUSE. " I followed the link, and found a bunch of folders of folders of RPM files. What exactly should I do to install Haskell? Sorry about the newbicity of this request, but I'm totally stumped. If suse isn't a well-supported platform, I'll switch. Thanks in advance.

4 3

What is Haskell unsuitable for?
by aditya siram 08 Jul '10

08 Jul '10

Hi all, Haskell is a great language and in a lot of ways it still hasn't found a niche, but that's part of what is great about it. But I wanted to ask people are more experienced with Haskell - what kinds of problems is it unsuited for? Have you ever regretted using it for something? Meaning if you could write the program over you would do it in another language. thanks ... -deech

26 40