- Haskell-Cafe - Haskell.org

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.

3 2

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

10 16

a really juvenile question .. hehehehe ;^)
by Galchin, Vasili 07 Oct '08

07 Oct '08

8 15

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

1 0

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

6 7

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

06 Oct '08

I am writing a Parsec parser for a C-like language and I have several datas that look more or less like this one: > import Control.Monad( liftM ) > import Text.ParserCombinators.Parsec > data FooBar = Foo | Bar > deriving (Show,Read,Bounded,Enum) Looking at these, it seems that there should be no need to write a parser for this guy by hand. We already know that it is bounded and enumerable, so we can get a list of all possible FooBars: > enumAll :: (Bounded a, Enum a) => [a] > enumAll = enumFromTo minBound maxBound Also, we know how to show and read each FooBar. Therefore, I should get a free parser! > freeParser :: (Enum a, Bounded a, Show a, Read a) => Parser a Here is one use of freeParser: > paramMod = option Foo freeParser > test = parseTest $ do { x <- paramMod; eof; return x } Not suprisingly: test "Foo" => Foo test "Bar" => Bar test "" => Foo I had a little hard time figuring out how this parser should look. The best I came up with was: > 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)) [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

3 3

editing a Alex and Happy file
by Manlio Perillo 06 Oct '08

06 Oct '08

Hi. There is support for editing an Alex or Happy file? I have seen some files that make use of tabs for layout (even Alex template files, and examples from both Alex and Happy), however tabs seems to be not recommended in Haskell. Thanks Manlio Perillo

1 0

Help me prove macid can scale! (Macid stress tests results for happs-tutorial toy job board disappointing so far.)
by Thomas Hartman 06 Oct '08

06 Oct '08

From: tphyahoo <thomashartm...@googlemail.com> Subject: Help me prove macid can scale! (Macid stress tests results for happs-tutorial toy job board disappointing so far.) To: HAppS HAppS is a new, relatively unproven technology. So I am asking myself this question. Will HAppS allow me to scale the toy job board I created for happs-tutorial into a high-volume, high concurrency, large-user count type job board? You know, the kind that might make money? I have done some preliminary testing to answer this question, and so far the results have been disappointing. I am hoping that I am doing something wrong, and that there is a way of using macid effectively for more than just toy applications. If there are solution for the problems I'm experiencing I will definitely be integrating this knowledge into the tutorial, so stay tuned. I am seeking feedback from HAppS experts and educated users on the following questions: * Is building a heavy duty website like monster.com in HAppS a realistic goal -- say, in the next twelve months? * Are there certain types of web apps that are unlikely to work well with the HAppS web architecture? * Are there changes I can make to my toy app's architecture -- be it data structures, buying new hardware, whatever -- that will enable me to get good performance against the stress test described below and in the demo? * Are there other HAppS stress tests in the public domain, and what are the results so far? A complete description of the stress test I did (basically, insert 200 users with 200 jobs apiece) along with a runnable demo, is in the tutorial preview at http://happstutorial.com:5002/tutorial/macid-stress-test. (The actual stress test is disabled in the online demo because I don't want to zap my server.) But the summary is, it's slow, slow to start, and creates a huge events file -- 356M. For around 40000 records. That's like, 8 megabytes per job, which is a few lines of text. OK, happs isn't a database -- but still. This is all is checked into darcs and tagged: darcs get --tag='stress test'http://code.haskell.org/happs-tutorial Thanks in advance for helping make happs usable in the real world! thomas.

3 3

Hmm, what license to use?
by Magnus Therning 06 Oct '08

06 Oct '08

Recently I received an email with a question regarding the licensing of a module I've written and uploaded to Hackage. I released it under LGPL. The sender wondered if I would consider re-licensing the code under BSD (or something similar) that would remove the need for users to provide linkable object files so that users can re-link programs against newer/modified versions of my library. Now I have fairly strong feelings about freedom of code and I everything I release is either under GPL or LGPL. What I like about those licenses is it protects freedom in a way that I think it should and it forces a sort of reciprocity which resonates very well with my selfishness. Re-licensing code under BSD is not something I'm willing to do without something that compensates for that reciprocity, and I can think of several kinds of compensation here but they all pretty much boil down to either fame or fortune. ;-) Once GHC supports dynamic binding on all platforms (or at least the major ones) this issue will (largely) go away (thanks Andrew for reporting on the state of this), but until then LGPL does create a large burden for users of my module. Until that happens I wouldn't mind re-licensing the code under a license that has the reciprocity attribute of LGPL on the source level, but does allow for static linking without requiring the availability of linkable object files. Is there such a license? I've heard that the OCaml crowd uses a modified LGPL with a static linking exception. Unfortunately I've also heard that their addition to LGPL hasn't gotten much review by lawyers, I'd much rather use something that feels less ad hoc, if you get what I mean. Any suggestions? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

37 96

Re: MPFR / FFI - Nefarious (Simple?) bug
by Michal Konecny 06 Oct '08

06 Oct '08

Jared Updike wrote on 6 Oct 02:25: > In order to create an arbitrary precision floating point / drop in > replacement for Double, I'm trying to wrap MPFR > (http://www.mpfr.org/) Have you looked at: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hmpfr Michal -- |o| Michal Konecny |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aow

1 0