- Haskell-Cafe - Haskell.org

Interactive Haskell and hs-plugins
by Fraser Wilson 01 Nov '05

01 Nov '05

Hi there, I would like to use evaluate arbitrary expressions in the context of a mixed-language (Ada, Haskell and about twelve lines of C glue) applications. Is it possible to use dynload from hs-plugins to load a module that references symbols in the loading program? For example, the application contains a Haskell module that looks a bit like this: > module TestKeys.NamedObject where > tt :: Int > tt = 2 I want the application to be able to offer the following sort of interaction: haskell> tt 2 haskell> But what actually happens is this: haskell> tt test_haskell3: /tmp/MDnum15633.o: unknown symbol `TestKeysziNamedObject_tt_closure' test_haskell3: user error (resolveObjs failed with <<False>>) Compiling Haskell code in advance works (i.e. if I create and compile a module that evalutes tt and link it in, everything runs fine). This is how I try to evaluate the expression: > evaluate :: String -> IO () > evaluate "" = return () > evaluate e = do writeFile "temp.hs" fileContents > status <- makeWith "LeanderStub.hs" "temp.hs" ["-c"] > case status of MakeSuccess code path -> loadAndEval path > MakeFailure error -> print error > where fileContents = "module Temp where\n\ > \ result = " ++ e ++ "\n" > > loadAndEval :: FilePath -> IO () > loadAndEval path = do mv <- dynload path [] [] "result" > case mv of > LoadFailure msg -> print msg > LoadSuccess _ v -> putStrLn v LeanderStub.hs is a module containing the necessary imports for the expression to evaluate in the right context. I was hoping that passing "-c" to makeWith would create an object file whose missing dependencies would be resolved when it was loaded into an application which contained them. Is this a dumb expectation? The alternative -- linking to the entire application for each expression evaluated -- seems a bit over the top, and I can't see how state would be maintained. I originally used unsafeEval_, but this has the same problem. I can't help but think that this must have been done before. Any advice? If you know Guile, then the equivalent of gh_repl is what I'm really after. cheers, Fraser.

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DARCS and case of file name letters
by Dimitry Golubovsky 01 Nov '05

01 Nov '05

I have a file in my repo (HSX11/Xauthority.hs) and I want to rename it changing just case of one letter: bash$ darcs mv HSX11/Xauthority.hs HSX11/XAuthority.hs darcs failed: A file or dir named HSX11/XAuthority.hs already exists in working directory. bash$ ls HSX11/X[aA]*.hs HSX11/Xauthority.hs bash$ darcs --version 1.0.3 (release) DARCS was compiled by GHC 6.2.2. bash$ uname -a Linux dmghome 2.2.16 #9 Mon Sep 16 22:43:25 EDT 2002 i686 unknown Is it DARCS that ignores the case of letters in filenames, or the Haskell runtime? Dimitry Golubovsky Middletown, CT

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Computations that can time out + gathering feedback from threads
by Joel Reymont 31 Oct '05

31 Oct '05

Folks, I need to implement computations that can time out (connecting to a server, reading from socket, etc.), plus gather feedback from a few thousands of threads. What is the best way to implement this? Do I launch a thread to sleep and a thread to connect/read from socket and use something like Shared Transaction Memory to wait for either of the two to finish? Also, my "simple scripting engine" launches a few thousands of scripts that connect to a server, exchange commands and update their internal state. I need to wait for all these to finish and get the results of their execution. My scripts are a combination of monads and I run them with runXXX( ... ) from the IO monad so that I can inspect the resulting state. Is there an elegant solution for waiting for all the threads to complete and then figuring out how many of these are in good share according to their end state? Thanks, Joel -- http://wagerlabs.com/

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Value-weak hash tables for GHC?
by Juliusz Chroboczek 31 Oct '05

31 Oct '05

Hi, Does anyone have an implementation of value-weak hash tables for GHC he'd be willing to share? (Hash tables where an entry is removed when the value, not the key, is collected.) Since GHC has (usable) weak pointers, finalisers and hash tables, I could in principle roll my own, but I'd rather get an efficient implementation off someone competent. Oh, and it needs to be under a license that makes it suitable for inclusion in Darcs. Thanks a lot, Juliusz P.S. I am not subscribed to the list -- I'd be grateful if you could CC me with any replies.

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RE: [Haskell-cafe] Silly question
by Bayley, Alistair 31 Oct '05

31 Oct '05

> From: Joel Reymont [mailto:joelr1@gmail.com] > > I didn't know about "it" in ghci, thanks. Are there multiple levels > of it? > > I wanted z "a" :: Maybe Int which I understand now. > > Thanks, Joel What do you mean by multiple levels? "It" just stores the most recent expression/value. If you type "print it" then the result of the print becomes the most recent value e.g. *Foo> "boo" "boo" *Foo> :t it it :: [Char] *Foo> print it "boo" *Foo> :t it it :: () *Foo> print it () *Foo> The docs probably explain it better: http://www.haskell.org/ghc/docs/latest/html/users_guide/ch03s04.html#id31036 40 Alistair. ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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RE: [Haskell-cafe] Silly question
by Bayley, Alistair 31 Oct '05

31 Oct '05

s> From: Joel Reymont [mailto:joelr1@gmail.com] > > How do I run z "a" from ghci or the IO monad? > > module Foo where > > import qualified Data.Map as M > import Control.Monad > import Control.Monad.List > import Prelude hiding ((!!)) > > (!!) :: (Ord k, MonadPlus m) => [M.Map k v] -> k -> m v > (!!) maps key = msum $ map (M.lookup key) maps > x :: M.Map String Int = M.empty > y :: M.Map String Int = M.fromList [("a", 1)] > z m = [x, y] !! m There are a couple of ways, depending on how you want to run it through MonadPlus, I think (although I don't understand your code much): main = do let a :: [Int]; a = z "a" print a b <- z "a" print b *Foo> main <<- running main from ghci [1] 1 Or directly the the ghci prompt: *Foo> z "a" *Foo> :t it it :: Int *Foo> print it 1 *Foo> z "a" :: [Int] [1] Did you know about the "it" variable in ghci? It holds the last expression typed at the prompt. Alistair. ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Silly question
by Joel Reymont 31 Oct '05

31 Oct '05

How do I run z "a" from ghci or the IO monad? module Foo where import qualified Data.Map as M import Control.Monad import Control.Monad.List import Prelude hiding ((!!)) (!!) :: (Ord k, MonadPlus m) => [M.Map k v] -> k -> m v (!!) maps key = msum $ map (M.lookup key) maps x :: M.Map String Int = M.empty y :: M.Map String Int = M.fromList [("a", 1)] z m = [x, y] !! m Thanks, Joel -- http://wagerlabs.com/

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RE: [Haskell-cafe] FFI and modifying haskell memory
by Simon Marlow 29 Oct '05

29 Oct '05

On 21 October 2005 14:40, Joel Reymont wrote: > I stumbled upon this when binding the Zlib library and want to make > sure I'm doing this right. > > foreign import ccall unsafe "uncompress" uncompress_ :: > Ptr Word8 -> Ptr CULong -> Ptr Word8 -> CULong -> IO CInt > > You give this function the address of your size as second argument > and it updates size for you. basic uncompress(char* buf, unsigned > long *size, ...) for you. > > Is it correct that I need to allocate a chunk of 4 bytes to be passed > into C and updated there and then need to peek my value from that > chunk of memory? yes, something like with $ \pculong -> r <- uncompress_ buf pculong ... size <- peek pculong > I thought StablePtr would give me the address of a Haskell value but > it gives me an offset into some table instead. That's right, the reason being that Haskell values move around when GC happens. Cheers, Simon

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hugs maintenance
by Iavor Diatchki 28 Oct '05

28 Oct '05

hello, i was wondering if anyone is maintaining hugs. in particular is the hugs-bugs list still operational? i tried to post a bug-report, but it seems that it never got there, but it also didn't bounce back... and the last post in the archive is from 10 sept 2005. -iavor

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RE: [Haskell-cafe] lockFile: fd out of range
by Simon Marlow 28 Oct '05

28 Oct '05

Yes, it's hardcoded. FD_SETSIZE should be the maximum number of file descriptors you can ever have open. On my Linux box here, FD_SETSIZE is 1024, and I can't ulimit -n any more than this. Cheers, Simon On 27 October 2005 15:18, Joel Reymont wrote: > Actually, I think I was just hitting the top range of FD_SETSIZE, > about 8000 on that machine. > > Does FD_SETSIZE get hardcoded into ghc-built binaries? That is if I > increase the available descriptors per process with uname -n, will it > be taken into account? > > Thanks, Joel > > On Oct 26, 2005, at 10:04 AM, Simon Marlow wrote: > >> lockFile uses FD_SETSIZE as its idea of the maximum value of a file >> descriptor. If you can get file descriptors outside this range, then >> the above error would ensue. Not sure if this is the case on >> FreeBSD... seems odd if it is. Can you try a truss/ktrace and see >> the values of your file descriptors?

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