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Apache HTTP Server And Haskell
by Kaveh Shahbazian 31 Jul '06

31 Jul '06

Is there a mod_haskell (like mod_perl and mod_python) for Apache HTTP server? Does anyone know about it?

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Fwd: [Haskell-cafe] Apache HTTP Server And Haskell
by Kaveh Shahbazian 31 Jul '06

31 Jul '06

Thanks, But it seems to be dead! (Last news on 18 Apr 2002). Is there a more mature one?

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The possibility of a real OS based on Haskell zippers
by Andy Elvey 30 Jul '06

30 Jul '06

Hi everyone - I'm very much a Haskell newbie, but have followed Haskell (and the various Haskell sites) for quite a few months now, and I absolutely *love* the language. One thing that **fascinated** me a while ago was the site which gave Haskell code for a "Haskell-based fileserver/OS" using zippers (the URI follows) - http://okmij.org/ftp/Computation/Continuations.html#zipper That code looks amazing! So, I was thinking - would it *actually be (theoretically) possible* to create a "real" booting OS (a bit like "House") from the above code? By a "real" OS, I mean something that uses (say) GRUB, and at least has a command-line of some kind. ( A GUI could come later ... ). I think that a "Plan 9-ish" OS (with all its "namespace/URL stuff, and its network-centric approach) would seem to be *particularly well suited* to being done using Haskell. ( I have to say that I love Plan 9's elegance, but I just *can't* manage its controls/GUI, they have me flummoxed ... ) If it were possible, I would *love* to see it - I've actually seriously considered even coughing up say $100 to $200 or so for a contest to create such a thing.... Anyway, "first things first" :-) - is such an OS possible? Many thanks for your time - bye for now - - Andy

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Serializing Functions and Actions for Distributed Programming
by Brian Sniffen 30 Jul '06

30 Jul '06

I'm very excited by the ability to pass functions or IO actions between threads of the same program. But I don't see any language or library support for doing so between programs, or between sessions with the same program. OCaml provides a partial solution: <http://caml.inria.fr/pub/docs/manual-ocaml/libref/Marshal.html> Though all it's really sending is an address and a hash of the binary program. Even SerTH doesn't help with functional types. I seek the knowledge of the Haskell Cafe: is there a reasonable way of addressing this problem? -- Brian T. Sniffen bts(a)alum.mit.edu or brian.sniffen(a)gmail.com http://www.evenmere.org/~bts

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Baffled by Disk IO
by Matthew Bromberg 30 Jul '06

30 Jul '06

I have run into a baffling distinction between the behavior of GHCi and the compiled binary from GHC. I suspect it's something pretty stupid on my part. I have the following test program <test.hs> import Matrix main = let f1 = bRgauss 4 3 f2 = bRgauss 3 2 fu = f1 *. f2 in bsave "fumat" fu ---------------------------------- The type signature of bsave is -- | save a matrix to a file bsave :: String -> m -> IO() bsave str z = do k <- matindx z withCString str (\x -> bmsave x k) and bmsave is a C routine that does a simple write to disk using fprintf. If I compile using GHC and run this as test.exe it does absolutely nothing, no file is actually saved. In fact no file is saved even if I try to print components of fu in the IO monad. Whereas if I load it into GHCi and run main, everything works as expected. Well sort of. Apparently everytime I extract something out of fu and use it in an IO monad it executes all the IO actions in fu, so it's easy to get unwanted behavior with incautious use.

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Cabal in ghc 6.4.2
by allan 30 Jul '06

30 Jul '06

Hello all, (before I start I should say I'm relatively new (a few months) to haskell, so I'm not exactly savvy with the use of the compilers) I have a problem using the cabal with version 6.4.2 of ghc, the same thing occurs with two projects which I wish to compile, I'll use the simplest one since the problem seems to be the same in both cases. The program is a very simple printer thing for haskell the source of which you can download at: http://homepages.inf.ed.ac.uk/s9810217/software/haskell_print/haskellprint.… <http://homepages.inf.ed.ac.uk/s9810217/software/haskell_print/haskell_print…> (but you probably won't need to, in order to diagnose this problem) I wish to compile this with the sequence of commands: ./Setup.hs configure --user --prefix=/home/allan/install ./Setup.hs build this works perfectly on version 6.4 of ghc, however with version 6.4.2 I get the following error: haskellprint$ ./Setup.hs build Preprocessing executables for haskellprint-0.1... Building haskellprint-0.1... Chasing modules from: Main.hs Could not find module `Text.ParserCombinators.Parsec': use -v to see a list of the files searched for (imported from ./Parser.hs) haskellprint$ Now if I run haskellprint$ ./Setup.hs build --verbose then I can see the command line used to compile the program which is: /home/allan/install/bin/ghc -Idist/build -o dist/build/haskell_print/haskell_print --make -Wall -hide-all-packages -i -idist/build/autogen -i. -odir dist/build/haskell_print/haskell_print-tmp -hidir dist/build/haskell_print/haskell_print-tmp -package base-1.0 Main.hs If I copy and paste this into the command line and remove the argument [ -hide-all-packages ] then the program compiles fine. So basically my question is: what am I doing wrong? I assume my problem is in the .cabal file, so I include the contents here: name: haskellprint version: 0.1 license: GPL license-file: LICENSE author: Allan Clark maintainer: a.d.clark(a)ed.ac.uk build-depends: base executable: haskell_print main-is: Main.hs include-dirs: c-sources: other-modules: extra-libraries: extensions: ghc-options: -Wall -- ghc-options: -fwarn-incomplete-patterns -fwarn-missing-fields -- ghc-options: -prof -auto-all -Wall -fglasgow-exts -O -funbox-strict-fields -fasm -optl-Wl,-s thanks in advance for any help. allan

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Is id strict?
by David House 30 Jul '06

30 Jul '06

Hi all. I've seen two definitions of a 'strict function', which I'm trying to unite in my mind: 1) f is strict iff f _|_ = _|_. 2) f is strict iff it forces evaluation of its arguments. There is a large sticking point that in my minds seems to fit (1) but not (2): id. Clearly, id undefined is undefined, but I also don't think id forces evaluation of its argument. There was a mini-discussion concerning this topic last night on #haskell, but if there was a consensus conclusion, it passed me by. Thanks in advance. -- -David House, dmhouse(a)gmail.com

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Sending Ctrl-C under Windows
by Neil Mitchell 29 Jul '06

29 Jul '06

Hi, I want to send Ctrl-C to a process opened by runInteractiveCommand, under Windows. I have found System.Posix.Signals, but on Windows none of those methods exist. For further information, the processes I want to send Ctrl-C to are ghci and hugs, so doing something like terminateProcess isn't what i want, because I don't want the process to be terminated, just the current computation. If there is another way to programmatically terminate the computation started by hugs/ghci (but not the process) via runInteractiveCommand, that would be great too. Thanks Neil

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commandline parsing?
by Marc Weber 29 Jul '06

29 Jul '06

I've been using pesco_cmdline for a while now. But I did notice that it doesn't fit my needs.. And it took me quite a while to get to know why I was getting strange typeable errors when specifying the wrong default value or reading the wrong type.. (these errors occur at runtime thus they don't use haskells strength) So I got another crazy idea. Why not see arguments as tokens and use a parser such as parsec? All you would have to do is creating some kind of syntax tree. Consider an example application : mmewcde (my mega executable which can do everything). mmewcde edit <file> mmewcde mv <file> <file> mmewcde mv --target-dir <dest> <folder> <files>> mmewcde cp <file> <file> mmewcde cp --target-dir <dest> <folder> <files>> mmewcde callsox <infile> <options> <outfile> Why not something like tar? mmewcde tar <x|c|f|v>* ..? Of cause I'll have to write the funtions edit :: String -> IO () mv :: String -> String -> IO () mvDest :: String -> [String] -> IO () ... ... which have to be called Now I'd like to do this: optionParser = many $ oneOf [ edit, mv, mvDest, cp, cpDest, callsox, tar] optionParserWithHelp = optionParser <|> printHelp edit = do string "edit" file <- existingFilename launchEditor file mv = [..] mvDest = do string mv string "--target-dir" td <- existingDirectory files <- many existingFilename map (movefile td) files [...] printHelp = do oneOf $ map string ["-h","--help","--usage"] prettyPrint optionParser main = do args <- getArgs parseAndExecute optionParserWithHelp prettyPrint might look like this (this will be unncommon ;) mmewcde --help: many edit <exitingfile> or mv <exitingfile> <file> .... Would this be nice? Does this already exist somehow? perhaps many can even be made nongreedy so that you can specify more than one command at once mmewcde mv --target-dir d f1 f2 cp --target-dir d2 f3 f4 ... Does this make sense? I think this would lead to self documenting well mantainable code. Marc

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StablePtr's and castStablePtrToPtr
by DeeJay-G615 28 Jul '06

28 Jul '06

I have a query which is asked out of interest's sake... I'm essentially looking for an affirmation of what I think I already understand (or some info if I'm deluded ;)). To put this in context... I have some C code... typedef int func(void *); void from_maybe_int(void *val, func *my_func) { int i; i = my_func(val); printf("value within C: %d\n", i); } And some Haskell code... type FromMaybeInt = StablePtr (Maybe Int) -> IO CInt foreign import ccall "wrapper" wrapFromMaybeInt :: FromMaybeInt -> IO (FunPtr FromMaybeInt) foreign import ccall "from_maybe_int" cFromMaybeInt :: StablePtr (Maybe Int) -> FunPtr GetJust -> IO () functionToPass :: FromMaybeInt functionToPass sPtr = do m <- deRefStablePtr sPtr case m of Nothing -> return (-1) Just i -> return (fromIntegral i) main :: IO () main = do sPtr <- newStablePtr (Just 3) -- for example funPtr <- wrapFromMaybeInt functionToPass cFromMaybeInt sPtr funPtr freeStablePtr sPtr The compiled program works fine. However I wanted to check this was correct usage. As in, is perfectly fine to pass a value of type StablePtr a into C? Am I correct in thinking that StablePtr is defined as a void pointer in C? From my very limited understanding of C, it is also the case that you can implicitly cast a void pointer to any other pointer type and vice-versa. Some appear to deem it bad practice if you explictly give the cast. So therefore I am somewhat hazy on the use for castStablePtrToPtr. I found the ghc docs to be quite cryptic for this function. Google dug up a few examples of it's use in PUGS... which has lead me to think that the function is purely for type 'convience' in Haskell. Is this the case or am I missing a use case here? Disclaimer: My knowledge and experience of C is somewhat limited. Ironically I have started playing with C by way of Haskell. (Sick and twisted I know). Thanks, Daniel James P.S. I must say, I really like the Haskell FFI. Very clean and enjoyable to work with.

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