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Haskell good for parallelism/concurrency on manycore?
by Ahn, Ki Yung 07 Jan '09

07 Jan '09

Dear Haskellers, I just got an inquiry from a research department head of a Korean company seriously considering to adopt functional languages because they heard that functional languages can do good at parallel programming on manycore platforms. They want to know what technologies out there implemented in functional languages, such as Erlang or Haskell, that can help them write more maintainable programs that are better at utilizing parallelism and avoiding bugs related to synchronization. They are also very interested in Cilk, as well as Haskell or Erlang. My first thought is that maybe Cilk would work better for them just because it would not be easy to recruit Erlang or Haskell programmers experienced in network, security, or concurrent/parallel programming. I myself can answer basic inquiries such as what libraries to look for to implenent such and so, but not able to give advice on large scale projects such as unified security solution package. So, it wouldn't be practical form them to launch a project without inviting an Erlang or Haskell expert in their domain as a project manager from overseas, which I don't think they are very willing to do. Are there Haskell consultants or Haskell experts on this subject, who believes that Haskell based approach might work better for them, or Haskell can be useful along with other approaches (e.g. DSL, prototyping, formal modeling of policies)? If so, I would like to recommend them trying contact you, and try my best to help communicating with them, if needed. They know English, of course, but may not be familiar with functional programming orlanguage-oriented programming jargons such as DSLs, oops, I mean language middleware :-) For your information: The company is a network security company whose main products are VPN and firewall appliances and their management software. Their research department is in search of better technologies to implement their future UTM (unified threat management) solutions utilizing the manycore platforms. In Korea, there are some research groups and few companies using OCaml, but almost no Erlang or Haskell communities. This company is preferring local researchers or consultants for advice or consulting, but there's no local group using Haskell seriously, as far as I know, even in research yet. That's why this person contacted me, just because I wrote a small tutorial on Haskell Server Programming while ago. P.S. If you happen to be a local Korean expert on this matter, sorry for my ignorance, and I'd be happy to forward their inquiry to you! -- Ahn, Ki Yung

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how out of memory is handled in Haskell
by Manlio Perillo 06 Jan '09

06 Jan '09

Hi. Here: http://damienkatz.net/2008/03/what_sucks_abou.html I found how Erlang (or at least old versions of Erlang) handles out of memory failure: it just calls exit(1). How is this handled in GHC? - exit(1)? - abort()? - IO exception? Thanks Manlio Perillo

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Lack of inlining -> slow parsing with Data.Binary
by Eugene Kirpichov 06 Jan '09

06 Jan '09

Hi, I'm parsing Java classfiles with Data.Binary, the code is here: http://paste.org/index.php?id=4625 The problem is that the resulting code parses rt.jar from JDK6 (about 15K classes, 47Mb zipped) in 15 seconds (run the program with main -mclose rt.jar, for instance), which is 10 times slower than my Java version of the same code. I compile the program with -O2 ; I tried -ddump-inlinings and it turns out that my readByte/readWord16/readWord32 functions don't get inlined, despite being simply aliases for 'get::Get WordXX'; so, in places where my Java version does a pointer access (after being JIT-compiled), the Haskell version does two function calls. What can be the reason of this lack of inlining? Or how do I understand the output of -ddump-inlinings? -- Eugene Kirpichov

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Pattern combinators
by Andrew Wagner 06 Jan '09

06 Jan '09

All, Wadler posted a blog entry the other day about a paper on pattern-matching in Haskell (http://wadler.blogspot.com/) I've taken a first stab at turning it into actual code for hackage (http://hpaste.org/13215) There are two commented-out definitions that don't type-check, though, and the types are too wild for me to grok. Anybody have any suggestions for 1.) How to fix it and/or 2.) How to use data/type/newtype to simplify the types and make it more manageable? Thanks!

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Re: bug in HPDF?
by Roman Cheplyaka 06 Jan '09

06 Jan '09

Thanks for helping! * alpheccar <misc(a)alpheccar.org> [2009-01-06 19:47:21+0100] > Roman, > > Here is the source code to do what you want: > > import Graphics.PDF > import Complex > > main = runPdf "bug.pdf" standardDocInfo (PDFRect 0 0 100 100) pdf > where > pdf = do > p <- addPage Nothing > drawWithPage p $ do > moveto $ 10 :+ 10 > sequence $ replicate 10 $ drawText $ text (PDFFont Helvetica > 10) 0 0 (toPDFString "ABC") > > > It is the Text monad that needs to be replicated. Each copy will start > drawing the text lines at (10,10) as specified by the moveto. > But, inside the text monad, each "text" will create a new line. > > Thanks, > Christophe. > > >> Here is a program which illustrates an unexpected behaviour: >> >> import Graphics.PDF >> >> main = runPdf "bug.pdf" standardDocInfo (PDFRect 0 0 100 100) pdf >> where >> pdf = do >> p <- addPage Nothing >> drawWithPage p $ drawText $ >> sequence $ replicate 10 $ >> text (PDFFont Helvetica 10) 10 10 (toPDFString "ABC") >> >> What I expect here is "ABC" printed 10 times on the same place >> (starting >> at (10,10)). What I see (in Okular) is ABC printed each time in the new >> place like this: >> >> ABC >> ABC >> ABC >> ABC >> >> What's happening here? I'm using HPDF-1.4.1 from Hackage. >> >> -- >> Roman I. Cheplyaka :: http://ro-che.info/ >> "Don't let school get in the way of your education." - Mark Twain > -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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bug in HPDF?
by Roman Cheplyaka 06 Jan '09

06 Jan '09

Here is a program which illustrates an unexpected behaviour: import Graphics.PDF main = runPdf "bug.pdf" standardDocInfo (PDFRect 0 0 100 100) pdf where pdf = do p <- addPage Nothing drawWithPage p $ drawText $ sequence $ replicate 10 $ text (PDFFont Helvetica 10) 10 10 (toPDFString "ABC") What I expect here is "ABC" printed 10 times on the same place (starting at (10,10)). What I see (in Okular) is ABC printed each time in the new place like this: ABC ABC ABC ABC What's happening here? I'm using HPDF-1.4.1 from Hackage. -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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HDBC-Sqlite3 "attaching databases"
by Günther Schmidt 06 Jan '09

06 Jan '09

Hi, has anybody here successfully tried to "attach" another database to an Sqlite database with HDBC-Sqlite3? I keep failing, so I'd be grateful for a hint how to do it. Günther

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Threads with high CPU usage
by Günther Schmidt 06 Jan '09

06 Jan '09

Hi, in an application of mine I start a long-running operation in a thread via forkIO so that the UI process doesn't get blocked. It just so happens, that the long-running process also takes the CPU to nearly 100% while it runs. During that time the run-time system does *not* switch back and forth between the UI-process and the long-running task, it seems that the UI process only gets woken up *after* the high CPU thread finishes completely. To the effect of course that it makes no difference at all to the UIs responsiveness whether I use forkIO or not. The long running process is pretty atomic, it's a single query to the database which takes up to a minute to complete so I don't see a chance to squeeze a "mainIteration" in there. What can I do? Günther

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building HSQL MySQL on windows (Was: FFI imported function names)
by Daniil Elovkov 06 Jan '09

06 Jan '09

Ok, enough talking to myself :) If anybody ever wants to build hsql-mysql on windows and has the same problems as I had, here's how it should be done. The problem I had seemed to be that libmysql.dll uses stdcall, but names its functions without @<n> decoration. Thus, when linking a Haskell program against it, names with @<n> cannot be resolved. The solution is pretty much a hack. Somebody from the Ruby community used to run into the same problem, from the same situation -- namely building ruby mysql bindings. Here is the procedure one person suggests http://rubydotnetproxy.rubyforge.org/mysql_win.html It worked perfectly for me. Of course, with some cabal specifics, which is obviously not described in the above page. The solution was to create a def file listing the names which could not be resolved and creating a .a file based on the dll and this def file. 2008/12/24 Daniil Elovkov <daniil.elovkov(a)googlemail.com>: > Mm, actually I didn't change the calling convention ffi imports when I > thought I did. I tried to do it through defines... > > Well, by explicitly saying ccall I get the names without @<n> > decoration. And it all links well. But I get segault when I run the > code, which should mean that calling conventions didn't match. > > Actually I found some ramblings on the internet that there's something > wrong with libmysql.dll and libmysql.lib in this respect, but they > were from 2004. > > Thus the question: how do I link against a lib file in ghc? When I say > -lmysql on command line it strictly searches for dll and complains if > it's not found. Adding lib exlpicitly on the cmd line doesn't seem to > have any effect. > > Thanks > > > 2008/12/24 Daniil Elovkov <daniil.elovkov(a)googlemail.com>: >> Hello >> >> How is decided whether the name of imported function gets the ending >> of the form @4 in ghc? >> >> I'm having this problem on Windows trying to use HSQL MySQL on windows. >> >> I compile HSQL Oracle backend and I get names without that. It's ok. >> With HSQL MySQL I get names with that stuff. It prevents me from >> further linking to dll. Supplying in the ghc command-line the "lib" >> file where names have those marks doesn't have any effect. >> >> The linker says that fname@NN cannot be resolved. >> >> Can I control that? >> >> The ffi calling convention doesn't (and shouldn't as I understand) >> affect this. The only difference is that in the case of mysql the >> header file itself where functions are described marks it STDCALL. Is >> that the reason? >> >> Also I changed ffi import line from "hsmysql.h func" to just "func", >> to no avail. >> >> ghc 6.8.2 >> >> I'm lost. Please help. >> >> -- >> Daniil Elovkov >> > > > > -- > Daniil Elovkov > -- Daniil Elovkov

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Can I destructive rebind a local variable in haskell?
by Wang, Chunye (NSN - CN/Beijing) 06 Jan '09

06 Jan '09

Dear haskeller, Can I destructive rebind a local variable like this import System.Directory test filename = do is_dir <- doesDirectoryExist filename let filename = if not is_dir then filename else filename putStrLn $ " filename " ++ filename main = test "." in GHCi 6.10.1 on WinXP, the ghci aborts silencely when I executes "main" after compile it into a executable file. c:\USERS\home\learning_haskell\>testDirectory testDirectory C stack overflow in generated code I have some code in scheme which works very well (define (func x) (let ((x x)) x)) By rebinding a formal variable, we can save naming some varaibles. I am not good at naming a variable. Thank you in advance Best Regards Chunye Wang <chunye.wang(a)nsn.com>

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