October 2008 - Haskell-Cafe

New System.Process
by john lask 07 Oct '08

07 Oct '08

Something that has irked me in the past about System.Process is the inability to obtain an OS system handle from the haskell Process handle. Such a facility would greatly enhance the interoperabity of c and haskell libraries. Provision is made (although not standardised) to obtain OS specific handles from haskell File Handles which is very useful. The same should be provided for Haskell Process handles. The main barrier to such a facility is the variability between OS representations of such a type (aka windows Handles, unix PID). comments anyone. _________________________________________________________________

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announcing darcs 2.1.0pre3
by Eric Kow 07 Oct '08

07 Oct '08

Hi everybody, The third pre-release of darcs 2.1 is now available at http://darcs.net/darcs-2.1.0pre3.tar.gz Since the last pre-release, we have resolved two of the items on our work list and a recently discovered darcs 2 bug. On the other hand, we have discovered a new regression from darcs 2.0.2 and some performance issues in our recent work for issue971. We are confident that we can resolve these within the upcoming week, but since regressions are involved, I think it might be prudent to delay the release so that we at least have one week to test these changes. At the very latest, darcs 2.1 should be released on 17 October, but I hope we will be able to get it out soon after the tenth. We are now very close to the finish line. More news in a week! Upcoming release schedule ------------------------- 2008-10-10: darcs 2.1.0pre4 2008-10-17: darcs 2.1.0 Work remaining -------------- * Backing out http://bugs.darcs.net/issue971 (Petr Ročkai) We have observed a performance regression in the newer, more robust version of the darcs repair code and will be postponing this feature for next release. The work for this week consists of undoing the relevant changes and auditing the undo. * http://bugs.darcs.net/issue1095 Darcs sometimes crashes in darcs send. It is clear to us why the crash happens and how to fix it. The work for this week consists of creating a minimal test case for our regression testing suite and implementing the relevant changes. * http://bugs.darcs.net/issue1026 Improve the error messages for 'bug in get_extra' errors, which can happen if darcs is fooled into thinking that two patches are the same. Changes since the last pre-release ---------------------------------- * Bug Fix: Eliminate an error merging repeated conflicts in darcs-2 repositories (issue1043, David Roundy) * New Feature: Hide 'Ignore-this:' lines which will be generated by future versions of darcs to prevent patch-id collisions. (issue1102, Eric Kow, David Roundy) * Bug Fix: Support darcs repositories which have symbolic links in their paths (issue1078, Dmitry Kurochkin) * Bug Fix: Make ssh connection sharing (darcs transfer-mode) work with old-fashioned repositories (issue1003, David Roundy) -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

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I'll do USB in Haskell - tips?
by Mauricio 07 Oct '08

07 Oct '08

Hi, I'll need to use a lot of USB at work and, after looking around, it seems there's no general USB code done. 'libusb' and 'openusb' do not seem ready enough so that wrapping them would be easier than writing from scratch. (If you think I am wrong until here and have time to write me your opinion, I'll value it a lot.) So: I would like to (try to) write a good implementation of USB access in Haskell. I would like it to be really general, so that we could use all of USB without need to resort to something else; available to all possible environments and operating systems; allow easy testing of USB clients, maybe using "fake" USB devices that could simulate problems; do that using Haskell code to directly access operating system API. I've read the appropriate chapters of USB 2.0 standard reference. I'll greatly appreciate any information you can give me: sugestions on what would be "the Haskell way" of doing USB; good technical information on how USB is implemented in different OSes; warnings on problems I may have; wishes of good luck :) I hope in one year I'll be able to post a message here saying Haskell is the greatest language to interface with USB devices. Thanks, Maurício

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Haskell participating in big science like CERN Hadrian...
by Galchin, Vasili 07 Oct '08

07 Oct '08

Hello, One of my interests based on my education is "grand challenge science". Ok .. let's take the CERN Hadrian Accelerator. Where do you think Haskell can fit into the CERN Hadrian effort currently? Where do you think think Haskell currently is lacking and will have to be improved in order to participate in CERN Hadrian? Kind regards, Vasili

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Re: [Haskell-cafe] newbie questions (read, etc., with Data.ByteString.Lazy.Char8)
by wman 07 Oct '08

07 Oct '08

as usual, i forgot to use the magical "reply to all" and under the impression I'm still talking to the list had bothered dons personally (heresy/sacrilege/deathwish , i know) to rectify it a bit at least, i'm posting a summary, in hopes someone find it useful. ---------------------------- -- this doesn't work - space leak no matter which optimizations you use, with -O2 it crashes in 5 secs instead in 75 ;-) import qualified Data.ByteString.Lazy.Char8 as S main = print . go 0 =<< S.getContents where go n s = case S.readInt s of Nothing -> n Just (k,t) -> go (n+k) (S.tail t) -- slightly stricter version, notice those ! before parameters in go declaration and the fancy -XBangPatterns option to ghc which it requires ;-) -- let dons_bstr.hs = import qualified Data.ByteString.Lazy.Char8 as S main = print . go 0 =<< S.getContents where go !n !s = case S.readInt s of Nothing -> n Just (k,t) -> go (n+k) (S.tail t) ghc -XBangPatterns --make dons_bstr.hs time dons_bstr < nums real 1m8.686s user 0m0.015s sys 0m0.031s ghc -XBangPatterns -Onot -fstrictness --make dons_bstr.hs time dons_bstr.exe < nums real 1m10.607s user 0m0.031s sys 0m0.015s ghc -XBangPatterns -O2 --make dons_bstr.hs time dons_bstr.exe < nums real 0m1.500s user 0m0.015s sys 0m0.031s so althought the -fstrictness still seems to have no effect in this case, using -O2 the dons version is ~2 times faster then the bytestring/readInt version -O2

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After upgrade bytestring to 0.9.1.3, my program cannot run.
by Magicloud 07 Oct '08

07 Oct '08

Just a simple text process program. When I runhaskell it. I got: GHCi runtime linker: fatal error: I found a duplicate definition for symbol fps_minimum whilst processing object file ~/.cabal/lib/bytestring-0.9.1.3/ghc-6.8.3/HSbytestring-0.9.1.3.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry.

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Name for Haskell based VPN Client/Server
by John Van Enk 07 Oct '08

07 Oct '08

Hello All, I'm working on a Haskell based VPN. I can't think of any good names, so I'm crowd sourcing it. A few details that may help in naming it: 1. It's distributed (doesn't need a "master" or "server"). 2. It's secure (duh) 3. It uses TUN/TAP 4. It's written (mostly) in Haskell! The best I can do is HaskVPN. This name is so bad I'm afraid to admit it. A better suggestion would be much appreciated. -- /jve

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a really juvenile question .. hehehehe ;^)
by Galchin, Vasili 06 Oct '08

06 Oct '08

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Re: I want my free (and good looking) parser!
by Slavomir Kaslev 06 Oct '08

06 Oct '08

On Mon, Oct 6, 2008 at 9:36 PM, Christian Maeder <Christian.Maeder(a)dfki.de> wrote: > import Text.ParserCombinators.Parsec > > freeParser :: (Enum a, Bounded a, Show a) => Parser a > freeParser = choice $ map (\ a -> try $ do > string $ show a > notFollowedBy (alphaNum <|> char '_') > return a) [minBound .. maxBound] > This is exactly what I needed. Though I still don't quite understand why this works and mine doesn't. > I see not need for extensions. (And I don't like > Text.ParserCombinators.Parsec.Token) > > Where did you get enumAll from? > Mine definition of enumAll was equivаlent to [minBound .. maxBound]: enumAll :: (Bounded a, Enum a) => [a] еnumAll = enumFromTo minBound maxBound > The type of the Parser must be deducible from the context (or given by a > type annotation). > > Cheers C. > > Slavomir Kaslev wrote: >> On Mon, Oct 6, 2008 at 8:07 PM, Christian Maeder >> <Christian.Maeder(a)dfki.de> wrote: >>> Slavomir Kaslev wrote: >>>>> freeParser = freeParser' minBound >>>>> where enumAll' :: (Bounded a, Enum a) => a -> [a] >>>>> enumAll' _ = enumAll >>>>> freeParser' :: (Enum a, Bounded a, Show a, Read a) => a -> Parser a >>>>> freeParser' x = liftM read $ choice (map (string . show) (enumAll' x)) >>> 1. I would use an explicit function argument instead of "Show" to allow >>> strings starting with lower case. >>> >> >> You are right. But that was not the problem. The problem was that I >> wrestled with Haskell's type system quite a bit to make freeParser >> work. What I want to write is >> >> freeParser :: (Enum a, Bounded a, Show a, Read a) => Parser a >> freeParser = liftM read $ choice (map (string . show) enumAll) >> >> but it doesn't compile. How can I make this piece code work? >> >>> 2. Calling read after parsing looks stupid. Just return the value shown >>> as parser result (within map). >>> >> >> Good point. It is silly =-) >> >>> 3. Instead of the "string" parser, it should be checked if a further >>> alphaNum or '_' follows (for the longest match). And don't forget "try"! >>> >> >> Sure. I actually use Parsec's reserved, which is kind enough to manage >> all this stuff for me. >> >>> Cheers Christian >>> >>>> [Actually, in my code I use reserved' (reserved' x = reserved x >> return x) >>>> instead of string, where reserved is from Parsec's builtin tokenizer (which does >>>> some neat things behind the curtains). Here string is used just to >>>> illustrate the >>>> expamle.] >>>> >>>> The problem is that freeParser, although useful, is far from elegant. It's >>>> something that I came up with by trial and error. In short: it's a hack. >>>> >>>> I would like to hear your suggestions about how it can be beautified. >>>> >>>> Thank you in advance. >>>> >>>> Cheers! >>>> >> >> >> > -- Slavomir Kaslev

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MPFR / FFI - Nefarious (Simple?) bug
by Jared Updike 06 Oct '08

06 Oct '08

In order to create an arbitrary precision floating point / drop in replacement for Double, I'm trying to wrap MPFR (http://www.mpfr.org/) using the FFI but despite all my efforts the simplest bit of code doesn't work. It compiles, it runs, but it crashes mockingly after pretending to work for a while. A simple C version of the code happily prints the number "1" to (640 decimal places) a total of 10,000 times. The Haskell version, when asked to do the same, silently corrupts (?) the data after only 289 print outs of "1.0000...0000" and after 385 print outs, it causes an assertion failure and bombs. I'm at a loss for how to proceed in debugging this since it "should work". The code can be perused at http://hpaste.org/10923 (and attached) and downloaded at http://www.updike.org/mpfr-broken.tar.gz I'm using GHC 6.83 on FreeBSD 6 and GHC 6.8.2 on Mac OS X. Note you will need MPFR (tested with 2.3.2) installed with the correct paths (change the Makefile) for libs and header files (along with those from GMP) to successfully compile this. Why does the C version work, but the Haskell version flake out? What else am I missing when approaching the FFI? I tried StablePtrs and had the exact same results. Can someone else verify if this is a Mac/BSD only problem by compiling and running my code? (Does the C executable"works" work? Does the Haskell executable "noworks" not work?) Can anyone on Linux and Windows attempt to compile/run and see if you can get the same results? Jared. P.S. I actually have much more code, having wrapped dozens of functions from the MPFR library and created instances using unsafePerformIO and foreignPtrs and all that useful high level Haskell/pure stuff--- all of which basically works perfectly except that it doesn't work at all since it crashes mysteriously after pretending to work at first. I had to narrow it down to something simple and the "Print "1.00000..." 10,000 times" was the best I could do. If I can get that working, I will then move on to something like the factorial of 1000 (printing intermediate values), which also works in C, but not Haskell, and after that, maybe everything will "just work" and I can use/publish this library! ----------------- works.c #include <stdio.h> #include <stdlib.h> #include <string.h> #include <gmp.h> #include <mpfr.h> #include "mpfr_ffi.c" int main() { int i; mpfr_ptr one; mpf_set_default_prec_decimal(640); one = mpf_set_signed_int(1); for (i = 0; i < 10000; i++) { printf("%d\n", i); mpf_show(one); } } ---------------- Main.hs --- Doesn't work! module Main where import Foreign.Ptr ( Ptr, FunPtr ) import Foreign.C.Types ( CInt, CLong, CULong, CDouble ) import Foreign.StablePtr ( StablePtr ) data MPFR = MPFR foreign import ccall "mpf_set_default_prec_decimal" c_set_default_prec_decimal :: CInt -> IO () setPrecisionDecimal :: Integer -> IO () setPrecisionDecimal decimal_digits = do c_set_default_prec_decimal (fromInteger decimal_digits) foreign import ccall "mpf_show" c_show :: Ptr MPFR -> IO () foreign import ccall "mpf_set_signed_int" c_set_signed_int :: CLong -> IO (Ptr MPFR) showNums k n = do print n c_show k main = do setPrecisionDecimal 640 one <- c_set_signed_int (fromInteger 1) mapM_ (showNums one) [1..10000] -------------- mpfr_ffi.c // a little bit of wrapper code... this may be where the problem is // but since the (working) C code uses this and has no problems, I don't // understand why the Haskell code appears to be corrupting the limbs (the mantissa) #include <stdio.h> #include <stdlib.h> #include <string.h> #include <gmp.h> #include <mpfr.h> void mpf_show(mpfr_ptr x) { mpfr_out_str(stdout, 10, 0, x, GMP_RNDN); printf("\n"); } #define LOG2_10 3.3219280948873626 #define IEEE_BITS 53 void mpf_set_default_prec_decimal(int dec_digits) { double bits = LOG2_10 * dec_digits; int ibits = (int)bits; double ddec; int dec; //printf("DEC_DIGITS = %d\n", dec_digits); //printf("IBITS = %d\n", ibits); ddec = ibits / LOG2_10; dec = (int)ddec; //printf("DEC = %d\n", dec); while (dec < dec_digits) { ibits++; //printf("IBITS = %d\n", ibits); ddec = ibits / LOG2_10; dec = (int)ddec; //printf("DEC = %d\n", dec); } mpfr_set_default_prec(ibits); } mpfr_ptr mpf_new_mpfr() { return (mpfr_ptr)malloc(sizeof(__mpfr_struct)); } mpfr_ptr mpf_set_signed_int(int x) { mpfr_ptr result = mpf_new_mpfr(); if (result == NULL) return NULL; mpfr_init_set_si(result, x, GMP_RNDN); return result; } --------------- Makefile CC = gcc HC = ghc INCLUDE = -I/home/private/local/include -I/usr/local/include -I/opt/local/include LIBS = -L/opt/local/lib -L/usr/local/lib all: works noworks works: mpfr_ffi.o works.o $(CC) -o works works.o -lgmp -lmpfr $(INCLUDE) $(LIBS) works.o: works.c $(CC) -c works.c $(INCLUDE) mpfr_ffi.o: mpfr_ffi.c $(CC) -c mpfr_ffi.c $(INCLUDE) noworks: Main.hs mpfr_ffi.o $(HC) mpfr_ffi.o -fffi -lgmp -lmpfr $(LIBS) $(INCLUDE) --make Main -o noworks clean: rm *.o *.hi works noworks

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