- Haskell-Cafe - Haskell.org

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 07 Oct '08

07 Oct '08

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Re: I want my free (and good looking) parser!
by Slavomir Kaslev 07 Oct '08

07 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 07 Oct '08

07 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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I want my free (and good looking) parser!
by Slavomir Kaslev 07 Oct '08

07 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

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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

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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.

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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

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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

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Health effects
by Andrew Coppin 06 Oct '08

06 Oct '08

The other day, I sat down to eat a 2 Kg block of chocolate - one of those ones that's divided into lots of little squares. I proceeded to recursively subdivide it into smaller and smaller blocks, and then eat the individual squares in depth-first order. It was only after getting through 16 of the things that I stopped to notice that the whole bar just happens to have an exact power of two squares on it. And it was some time after *that* when I thought to myself "...woah, maybe do too much Haskell?" o_O Seriously, who recursively subdivides their food? I think I have something wrong with me...

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Type family oddity
by Florian Weimer 05 Oct '08

05 Oct '08

I can't figure out why the following code doesn't compile with the October 2n GHC 6.10 beta (-XTypeFamilies -XFlexibleContexts) when the type declaration is not commented out. module T where type family RangeTrait c class InputRange r where remaining :: r -> Bool advance :: r -> r class (InputRange (RangeTrait s)) => Sequence s where erase :: RangeTrait s -> IO (RangeTrait s) -- erase_range :: (Sequence s) => RangeTrait s -> IO (RangeTrait s) erase_range r = if remaining r then do r' <- erase r erase_range r' else return r GHCi says the type is precisely as specified in the comment. However, when I activate the type declaration, GHC complains: T.hs:16:22: Couldn't match expected type `RangeTrait s' against inferred type `RangeTrait s2' In the first argument of `erase', namely `r' In a stmt of a 'do' expression: r' <- erase r In the expression: do r' <- erase r erase_range r' T.hs:17:22: Couldn't match expected type `RangeTrait s1' against inferred type `RangeTrait s2' In the first argument of `erase_range', namely `r'' In the expression: erase_range r' In the expression: do r' <- erase r erase_range r' Any suggestions? Is this a bug in GHC?

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Total Functional Programming in Haskell
by Jason Dagit 05 Oct '08

05 Oct '08

Hello, I recently had someone point me to this thread on LtU: http://lambda-the-ultimate.org/node/2003 The main paper in the article is this one: http://www.jucs.org/jucs_10_7/total_functional_programming/jucs_10_07_0751_… It leaves me with several questions: 1) Are there are existing Haskell-ish implementations of the total functional paradigm? 2) Could we restructure Haskell so that it comes in 3 layers, total functional core, lazy pure partial functional middle, and IO outer layer? The idea with #2 is that similar to how we use the type system to separate the purely functional from monadic, and in particular IO actions, can we make the inner most part of Haskell total? Furthermore, could we do this in a way that makes it easy to intermingle the three layers the way we can mingle pure Haskell with IO actions? Maybe instead of using (->) as the function constructor for total functions we use a different symbol, say (|->), and the compiler knows to use the more specialized semantics on those definitions. I'm not sure how make this work for values that are total functional versus values that are just pure (partial) functional. I'm also interested in hearing about the optimizations that would be possible when all your expressions are strongly normalizing. Jason

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Job Opportunity
by Michael Bott 05 Oct '08

05 Oct '08

Afternoon, I have been recommended to use this site from a couple of people I have spoken to. Sorry if this offends anyone but I have an amazing opportunity for a 2 Functional Programmers based in London. Functional Programming - (HASKELL / ERLANG / OCAML) - Financial This is an incredible opportunity for a FUNCTIONAL PROGRAMMER (Haskell / Erlang or Ocaml) to join an expanding London software house who specialise in Asset Management for top financial clients - they specialise in providing algorithmic execution solutions for hedge funds. My client are a leading provider in financial software, they are looking for a top Graduates or 1-2 years experienced Java / Functional Programmers to join the team and really make a difference to the company and work with the biggest clients in the UK. Desirable Skills - * Functional Programming - ( Haskell or Erlang or Ocaml to name 3). * Java * Degree Education - top University - 2:1 and above only. * Experience within the finance and/or banking sector would be highly advantageous. This is an URGENT requirement and my client are keen to get at least 2 exceptional developers into the team ASAP. You will join a relaxed team who work on exciting projects, and use the most up to date technologies........ To learn more about the role and the client please contact Mike at Lawrence Harvey. Please contact me if you are interested. Kind Regards, Mike Michael Bott Java Recruitment Specialist Lawrence Harvey Search & Selection Tel: +44 (0)208 875 4353 Fax: +44 (0)208 870 8116 Mobile: +44 (0)7966 554892 Email: m.bott(a)Lawrenceharvey.com <mailto:m.bott@Lawrenceharvey.com> Web: www.Lawrenceharvey.com <http://www.lawrenceharvey.com/> LinkedIn - http://www.linkedin.com/in/mikebott <http://www.linkedin.com/in/mikebott> The information transmitted contains confidential material and is intended only for the person or organisation to which it is addressed. Any review, retransmission, dissemination or other use of this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer. No liability whatsoever is accepted by Lawrence Harvey Search & Selection in respect of the contents of this email.

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Hackage Build Failures
by Cetin Sert 05 Oct '08

05 Oct '08

Hi, what is the best action to take if a package from hackage fails to build? Is there a recommended/established common way to deal with build failures/runtime bugs etc.? For example: cetin@linux-d312:~/Links/Elite/ac> cabal install wired Resolving dependencies... Downloading Wired-0.1.1... Configuring Wired-0.1.1... Preprocessing library Wired-0.1.1... Building Wired-0.1.1... [ 1 of 21] Compiling Data.Hardware.Internal ( Data/Hardware/Internal.hs, dist/build/Data/Hardware/Internal.o ) Data/Hardware/Internal.hs:198:15: Ambiguous occurrence `><' It could refer to either `Data.Hardware.Internal.><', defined at Data/Hardware/Internal.hs:129:4 or `Test.QuickCheck.><', imported from Test.QuickCheck at Data/Hardware/Internal.hs:11:0-21 cabal: Error: some packages failed to install: Wired-0.1.1 failed during the building phase. The exception was: exit: ExitFailure 1 Regards, CS

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Restricted file reading monad
by George Pollard 05 Oct '08

05 Oct '08

Hello all, I'm currently working on a (toy) ID3 [1] tag reader, which made me think of a library which might be quite useful. The structure of an ID3 tag goes something like this: Header: - total size of tag - other header info A series of frames, each with: - total size of frame - other header info - frame data Since the ID3 tag as a whole has size information, I need to pass that into the frame-reading functions to ensure that I never read past the end of the total header. This exact same requirement is present within the frame-reading function itself; it must read the frame data without reading past the end of the frame. It would be nice to have some kind of monad or similar so that I could do: > readTag = do > size <- -- read size > -- read other header info > withLimit size $ -- read frames then the read-frames function would be able to do its work without having to worry about size-checking all the time, as this would be implicit. (And similarly with the frame-reading functions as well.) This could easily be extended to: > f x = readManyWithLimit size readerFunction where readManyWithLimit would return a list of results of applying the reader function as many times as possible within the size limit (and possibly returning some kind of error if the reader function 'bails early' and doesn't gobble right up to the end of the size limit). The thing is, I've not implemented a monad of any substantial size so I don't have a clue where to start. Calling it FileReader (for want of a better name), I guess it would almost be the same as a parsing monad, so the type would have a reference to the file Handle and the current index into the file, as well as the last point that it's allowed to read up to. So, umm... a rather open-ended question, but how would I go about this? [1]: http://www.id3.org/Developer_Information

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Haddock Feature Proposal
by Jason Dagit 05 Oct '08

05 Oct '08

Hello, I was just thinking about how many devs put "TODO ...", "FIXME ...", or "HACK..." into comments. Do others think this could be nice optional information for Haddock to display? I think it could give people an idea for how mature, stable or clean an api is just by inspecting the above items when they are present. Thoughts? Thanks, Jason

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outdated OpenSPARC webpage
by Wolfgang Jeltsch 05 Oct '08

05 Oct '08

Hello, the webpage under <http://haskell.org/opensparc/> ist outdated. There is still the line saying that students can now apply. Who is responsible for this page? Wouldn’t it be better to move this page to the wiki so that keeping it up to date is easier? Best wishes, Wolfgang

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Haskell Weekly News: Issue 88 - October 4, 2008
by Brent Yorgey 05 Oct '08

05 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081004 Issue 88 - October 04, 2008 --------------------------------------------------------------------------- Welcome to issue 88 of HWN, a newsletter covering developments in the [1]Haskell community. An extra-short HWN this week, so you get an extra ten minutes to do something else during the time you would have normally spent reading the HWN! HWN-editor-approved activities for your ten minutes include eating cookies, playing [2]Fantastic Contraption, and writing a type checker in the type system while eating cookies. Announcements Arch Haskell News: Oct 4 2008. Don Stewart [3]sent out the newest Arch Haskell news --- now with 609 Haskell packages! Announcing OneTuple-0.1.0. John Dorsey [4]announced the release of the ground-breaking [5]OneTuple library, which adds the long neglected one-tuple to Haskell. It also turns out that the denizens of Haskell-cafe are completely unable to refrain from turning jokes into long-winded technical discussions about strictness and lifted types. Haskell protocol-buffers version 0.3.1. Chris Kuklewicz [6]announced the release of [7]protocol-buffers 0.3.1, with some functionality also split off into [8]protocol-buffers-descriptor and [9]hprotoc. The 'hprotoc' compiler for proto files to Haskell source code now takes a "-u" command-line option. When given, this turns on code generation to support loading, storing, and saving unknown fields. Discussion Stacking monads. Andrew Coppin began a long [10]discussion on monads, monad transformers, Applicative, MonadPlus, and related topics. planning for ghc-6.10.1 and hackage. Duncan Coutts began a [11]discussion on how to make the transition to GHC 6.10 as painless as possible, especially as it relates to the new base-4 package and Cabal. Proposal #2629: Data.List: Replace nub; add nubOrd, nubInt, nubWith. Bart Massey [12]proposed refactoring nub into a 'nubWith' function which can be specialized to efficient versions for Int and Ord. Blog noise [13]Haskell news from the [14]blogosphere. * Luke Palmer: [15]Laziness and the monad laws. Luke explains why making a Functor or Monad instance too lazy can be just as bad as making it too strict. * Paul R Brown: [16]The Haskell Platform and Lessons Learned Elsewhere. * Eric Kow (kowey): [17]darcs weekly news #6. * Mads Lindstroem: [18]Overlapping Instances in Haskell. * >>> Bill Six: [19]Dabbling with Haskell. Bill explores palindromic pangrams using Haskell. Quotes of the Week * ozy`: [on RWH] most authors are like "FUNCTIONAL PROGRAMMING IS FUNCTIONAL!!!" whereas these guys are more like "yeah but practical programming is practical. map wash_dish dishes" * BMeph: * wants an "Everything I know about computing I learned from sigfpe" T-shirt * OlegFacts: Oleg can evaluate bottom. With his fists. * quicksilver: my computer starts to play 'Dies Irae' when shapr gets ops, automatically. About the Haskell Weekly News New editions are posted to [20]the Haskell mailing list as well as to [21]the Haskell Sequence and [22]Planet Haskell. [23]RSS is also available, and headlines appear on [24]haskell.org. To help create new editions of this newsletter, please see the information on [25]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [26]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://fantasticcontraption.com/ 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45786 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45586 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OneTuple 6. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10134 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers… 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hprotoc 10. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45634 11. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/15339 12. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/10133 13. http://planet.haskell.org/ 14. http://haskell.org/haskellwiki/Blog_articles 15. http://luqui.org/blog/archives/2008/10/03/laziness-and-the-monad-laws/ 16. http://mult.ifario.us/p/the-haskell-platform-and-lessons-learned-elsewhere 17. http://koweycode.blogspot.com/2008/10/darcs-weekly-news-6.html 18. http://lindstroem.wordpress.com/2008/09/27/inheritance-in-composites-and-ov… 19. http://billsix.blogspot.com/2008/10/dabbling-with-haskell.html 20. http://www.haskell.org/mailman/listinfo/haskell 21. http://sequence.complete.org/ 22. http://planet.haskell.org/ 23. http://sequence.complete.org/node/feed 24. http://haskell.org/ 25. http://haskell.org/haskellwiki/HWN 26. http://code.haskell.org/~byorgey/code/hwn/

1 0

An important question to Simon P. Jones
by Vag 05 Oct '08

05 Oct '08

Dear Simon! Can you please give an authoritative explanation, in the nutshell, what is exact relationship between object-oriented programming and proposed lightweight extensible records? Thanks in advance, sincerely yours, Vag.

1 0

NewLines in string
by Serge D. Mechveliani 05 Oct '08

05 Oct '08

People, Here is a certain naive question about string setting in a Haskell program. I have the functions parseProgram :: String -> Program apply :: Program -> Term -> Term -- interpreter, and try to build the example modules for them as in the following example: ---------------------------------------------------------------- module Main where program = parseProgram " isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo " main = let {data = ... :: Term; res = apply program data} in putStr $ concat ["data = ", shows data "\n", "res = ", shows res "\n"] ---------------------------------------------------------------- -- that is set a string (an object program example), parse it to a program, apply this program and print the result. But in reality, the above string must be set like this: (2) "\ \ isOrdered nil -> true;\ \ isOrdered (X:nil) -> true;\ \ isOrdered (X:Y:Ys) -> \ \ isOrd (X > Y) (isOrdered (Y:Ys));\ \\ \ isOrd true bo -> false;\ \ isOrd false bo -> bo\ \" -- because otherwise Haskell treats the NewLine characters in the above string in an unneeded way. But with (2), the program Main occurs hard to read. One could try to improve this by using readFile. Form the file data.txt -------------------------------- isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo ----------------------------------------- and combine readFile "data.txt", the `do' construct, pearseProgram, apply, putStr. But this needs adding one more file, and this also changes the programming style in defining examples. Now, what is the difference? 1. readFile reads string from file, with treating NewLine as needed. 2. The Haskell compiler reads the expression parseProgram " isOrdered nil > true; ... " from the input Haskell program with treating NewLine in the string in a different way. I wonder: how to remove most of backslashes in the program (2) ? Thank you in advance for your comments. ----------------- Serge Mechveliani mechvel(a)botik.ru

2 1

maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Hello, Here is a site I discovered a while back for another language ... I guess in the back of my mind this more where I was going vis-a-vis scientific computing .... http://www.enthought.com/ Kind regards, Vasili

3 2

Re: [Haskell-cafe] maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Let me recuse myself .... What is the nature of the open source license? Vasili On Fri, Oct 3, 2008 at 8:39 PM, Jeff Wheeler <jeff(a)nokrev.com> wrote: > On Oct 3, 2008, at 8:26 PM, Galchin, Vasili wrote: > > Here is a site I discovered a while back for another language ... I >> guess in the back of my mind this more where >> I was going vis-a-vis scientific computing .... http://www.enthought.com/ >> > > I interned at Enthought over this last summer; it's a very cool place. Many > of the open-source scientific libraries could be rewritten in Haskell > without significant difficulty, and this actually seems like a decent idea. > > SciPy and NumPy are the two most significant libraries worth thinking > about, in my opinion. Some of the other software, e.g. Traits, is less > relevant to scientific software in the context of Haskell. > > Much of their stack, especially Traits, TraitsGUI, and application > libraries are designed to help write applications quickly without much > programming experience. With these tools, it's easy for scientists, without > knowing much Python, to write large programs that work well for most of > their purposes. > > Jeff Wheeler >

1 0

Announcing OneTuple-0.1.0
by John Dorsey 04 Oct '08

04 Oct '08

Fellow Haskellers, Much attention has been paid over the years to the regrettable omission of singleton tuples from Haskell. I am pleased to announce OneTuple, a humble implementation of the singleton tuple for Haskell. Now you can: * Wrap a single value of any type in a OneTuple ! * Pattern match to retrieve your value ! * Solve any of the software problems that cannot be solved without the singleton tuple ! * Enjoy instances for all the classes normal tuples have, plus more ! * Proclaim feature parity with Python ! Note: the singleton tuple does not support tuple syntax. Contributions are welcome. The project could use a tutorial, and a decent test suite. Strict singleton tuples are planned for the next version. Enjoy! Regards, John Dorsey

17 31

pure Haskell database
by Manlio Perillo 04 Oct '08

04 Oct '08

Hi. I need a simple, concurrent safe, database, written in Haskell. A database with the interface of Data.Map would be great, since what I need to to is atomically increment some integer values, and I would like to avoid to use SQLite. Thanks Manlio Perillo

9 21

having fun with GADT's
by Anatoly Yakovenko 04 Oct '08

04 Oct '08

I dont remember where i saw it, but i think someone had an example of a list whose type is the maximum element in the list. I've been trying to reproduce that with GADT's. data One = One data Two = Two data Three = Three data MaxList t where Elem1 :: MaxList One Elem2 :: MaxList Two ML1Cons1 :: MaxList One -> MaxList One -> MaxList One ML1Cons2 :: MaxList One -> MaxList Two -> MaxList Two ML2Cons1 :: MaxList Two -> MaxList One -> MaxList Two ML2Cons2 :: MaxList Two -> MaxList Two -> MaxList Two a = ML2Cons2 Elem2 $ ML2Cons1 Elem2 $ ML1Cons1 Elem1 $ Elem1 so one problem is the tedium of defining a cons for each possible combination. The other problem is that i cant define a usefull tail that makes any sense. mlTail :: MaxList Two -> MaxList t mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b this one doesn't work, and probably because there is nothing that i could do with the return value. mlTail :: MaxList Two -> MaxList Two mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b --wont compile because b is a MaxList One will only work for lists that only contain Two's, which is not what i want either. So is this somehow possible? Thanks

6 13

Building gtkhs, OpenSolaris x86
by Lally Singh 04 Oct '08

04 Oct '08

Hey folks, I know it seems an obtuse OS to build on, but trust me, it's pretty nice despite the hassles. I'm getting these three errors (repeated a few times) while building gtkhs-0.9.13 on ghc 6.8.3, and was hoping for any suggestions on where to go from here: tools/c2hs/base/general/Map.hs:16:7: Could not find module `Data.Map': it is a member of package containers-0.1.0.2, which is hidden tools/c2hs/base/errors/Errors.hs:44:0: Failed to load interface for `Position': Use -v to see a list of the files searched for. glib/System/Glib.hs:13:0: Failed to load interface for `System.Glib.UTFString': Use -v to see a list of the files searched for. What did I screw up? Is there something else I should load? Maybe an older version of gtkhs? ghc? Thanks for any help! -- H. Lally Singh Ph.D. Candidate, Computer Science Virginia Tech

2 1

Alex and Flex
by Manlio Perillo 04 Oct '08

04 Oct '08

Hi. I'm starting to write a CSS parser with Alex and Happy. The grammar is defined here: http://www.w3.org/TR/CSS21/grammar.html However I have noted that there are some difference in the syntax between Alex and Flex? What is the rationale? One more thing. Here: http://www.haskell.org/alex/doc/html/alex-files.html it seems that there is an error with macrodef := @smac '=' set | @rmac '=' regexp it should be macrodef := $smac '=' set | @rmac '=' regexp Thanks Manlio Perillo

2 5

Monoids [Stacking monads]
by Andrew Coppin 04 Oct '08

04 Oct '08

Ryan Ingram wrote: > Newtypes is the general (& sadly unsatisfactory) answer: > Oh dear. Well that _is_ pretty unsatisfactory... Given the constraints of the Haskell type system, could we do better in principle?

1 0

Source of 16x16 Sudokus?
by Murray Gross 04 Oct '08

04 Oct '08

Folks: For research on the behavior of parallel Haskell, does anyone know of a source for graded (easy through evil) 16x16 Sudoku puzzles? Our hardware runs too fast for us to get meaningful timings on 9x9's. I suppose we could insert time wasters, but I think that would also distort the results . . . . Thanks in advance, Murray Gross Brooklyn College

4 3

Kind-agnostic type classes
by Florian Weimer 04 Oct '08

04 Oct '08

I'm trying to encode a well-known, informally-specified type system in Haskell. What causes problems for me is that type classes force types to be of a specific kind. The system I'm targeting however assumes that its equivalent of type classes are kind-agnositic. For instance, I've got class Assignable a where assign :: a -> a -> IO () class Swappable a where swap :: a -> a -> IO () class CopyConstructible a where copy :: a -> IO a class (Assignable a, CopyConstructible a) => ContainerType a class (Swappable c, Assignable c, CopyConstructible c) => Container c where size :: (Num i, ContainerType t) => c t -> IO i I suppose I could address this with creating aliases for the relevant classes, but I wonder if there is a better workaround. I see that the ML module system has a similar restriction on type sharing. Is there a fundamental reasons behind this?

4 5

Re: [Haskell-cafe] Haskell participating in big science like CERN Hadrian...
by Rafael Gustavo da Cunha Pereira Pinto 03 Oct '08

03 Oct '08

> > > > On Fri, Oct 3, 2008 at 07:47, Dougal Stanton <dougal(a)dougalstanton.net>wrote: > >> 2008/10/3 Galchin, Vasili <vigalchin(a)gmail.com>: >> > 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? >> >> Is that the experiment where Picts are accelerated to just short of >> the speed of light in order to smash through to the Roman Empire? ;-) >> > Man, that was almost as good as the Large Hardon Collider<http://largehardoncollider.com/> !!! > >> I don't know what the main computational challenges are to the LHC >> researchers. The stuff in the press has mostly been about >> infrastructure --- how to store the gigabytes of data per second that >> they end up keeping, out of the petabytes that are produced in the >> first place (or something). >> >> > There is a lot of data filtering, looking for the right trigger event... -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

1 0

Is Haskell-Cafe down?
by Benjamin L.Russell 03 Oct '08

03 Oct '08

About two hours ago, I sent two follow-ups to the "Announcing OneTuple-0.1.0" thread on the Haskell-Cafe mailing list, neither of which has appeared in either my newsreader or my Inbox, even though they have both appeared on the Web archive; viz.: [Haskell-cafe] Re: Announcing OneTuple-0.1.0 http://www.haskell.org/pipermail/haskell-cafe/2008-October/048633.html [Haskell-cafe] Re: Announcing OneTuple-0.1.0 http://www.haskell.org/pipermail/haskell-cafe/2008-October/048636.html Is Haskell-Cafe down? -- Benjamin L. Russell

2 1

mysql (hsql-mysql-1.7) on Linux with GHC 8.3 - cabal issues
by Anton Tayanovskyy 03 Oct '08

03 Oct '08

Hello, I had some difficulty building hsql and hsql-mysql (native driver) packages under GHC 8.3 on Fedora 9. Namely, they do not install with cabal install, because of a few API changes. Is this considered all right as GHC 8.3 is still experimental, or should the packages be updated? If so, can somebody please do it. I love when things just work with cabal install! The problem looks very basic -- just some Cabal file incompatibilities. However I am not experienced with the Cabal build process, so I'll just write what I did to get it to work on my platform, maybe it will help someone. == hsql.cabal == name: hsql version: 1.7 license: BSD3 author: Krasimir Angelov <ka2_mail(a)yahoo.com> category: Database description: Simple library for database access from Haskell. exposed-modules: Database.HSQL, Database.HSQL.Types build-depends: base, old-time build-type: Simple ghc-options: -O2 extensions: ForeignFunctionInterface, TypeSynonymInstances, CPP, RankNTypes, DeriveDataTypeable == hsql-mysql.cabal == name: hsql-mysql version: 1.7 license: BSD3 author: Krasimir Angelov <kr.angelov(a)gmail.com> category: Database description: MySQL driver for HSQL. ghc-options: -O2 build-depends: base, hsql, Cabal, old-time extensions: ForeignFunctionInterface, CPP include-dirs: Database/HSQL, /usr/include/mysql build-type: Simple extra-source-files: Database/HSQL/HsMySQL.h extra-libraries: mysqlclient extra-lib-dirs: /usr/lib/mysql exposed-modules: Database.HSQL.MySQL == hsql-mysql*/Setup.lhs == #!/usr/bin/runghc \begin{code} import Distribution.Simple main = defaultMain \end{code} Of course this hsql-mysql.cabal should not mention Fedora-specific locations as /usr/lib/mysql and /usr/include/mysql but I don't know how to make that generic. The original version had a big custom Setup.lhs file which wouldn't compile with the new Cabal and which I couldn't tweak myself. Thanks, --A

3 4

ANN: Haskell-Embedded System Design: ForSyDe 3.0 and Tutorial
by Alfonso Acosta 03 Oct '08

03 Oct '08

Hi everyone, I am glad to announce the 3.0 release of ForSyDe's implementation, now available from HackageDB. The ForSyDe (Formal System Design) methodology has been developed with the objective to move system design (e.g. System on Chip, Hardware and Software systems) to a higher level of abstraction. ForSyDe is implemented as a Haskell-embedded behavioral DSL (Domain Specific Language). >From this release, ForSyDe includes a new deep-embedded DSL and embedded compiler. We have also published tutorial which should be much more user-friendly than the Haddock documentation and the ForSyDe research papers. ForSyDe includes two DSL flavours which offer different features: 1) Deep-embedded DSL (ForSyDe.Signal) Deep-embedded signals, based on the same concepts as Lava, are aware of the system structure. Based on that structural information ForSyDe's embedded compiler, can perform different analysis and transformations. o Thanks to Template Haskell, computations are expressed in Haskell, not needing to specifically design a DSL for that purpose. o Embedded compiler backends: + Simulation + VHDL (with support for Modelsim and Quartus II) + GraphML (with yFiles graphical markup support.) o Synchronous model of computation. o Support for components. o Support for fixed-sized vectors à la VHDL. 2) Shallow-embedded DSL (ForSyDe.Shallow.Signal) Shallow-embedded signals are modeled as streams of data isomorphic to lists. Systems built with them are unfortunately restricted to simulation, however, shallow-embedded signals provide a rapid-prototyping framework with which to experiment with Models of Computation (MoCs). o Synchronous MoC. o Untimed MoC. o Continuous Time MoC. o Domain Interfaces allow connecting various subsystems with different timing (domains) regardless of their MoC. o Deep-embedded models can be integrated through simulation. Links ==== ForSyDe website: http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/ ForSyDe tutorial: http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/files/tutorial/t… HackageDB package page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ForSyDe Darcs repository: darcs get http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/darcs/ForSyDe/

2 2

Re: [Haskell-cafe] A question about constraints
by Luke Palmer 03 Oct '08

03 Oct '08

On Thu, Oct 2, 2008 at 7:51 AM, jean-christophe mincke <jeanchristophe.mincke(a)gmail.com> wrote: > Hello, > > Thank you for your comments. > > Would not it be feasible to add constraints at type definition, something > like, in a somewhat free style syntax > > data String2 = String2 (s::String) with length s <= 5 > > and with a polymorphic type > > data List5 a= List5 (l::[a]) with length l <= 5 Well, yeah, it is possible that to a language. However, it's a question of how far you take it. What do you want that to do? Is it a runtime check on the constructor? Is it a compile-time guarantee? If it's runtime, how lazy is it -- i.e. when does it check? If it's compile-time, how do you enforce it? Basically it dumps the contents of pandora's box all over the design space, so it's easier to leave it out and just let module abstraction take care of the hard questions. There are definitely ways to simulate it: You can simulate the runtime checks as follows: subtype :: (a -> Bool) -> (a -> b) -> a -> b subtype p f x = if p x then f x else error "Subtype constraint failed" string2 :: String -> String2 string2 = subtype (\s -> length s < 5) String2 -- And don't expose String2 from the module, so string2 is the only way to make them But to give an example of why this is not a straightforward thing to answer, here's a different way which might also be correct, depending on what you want: string2 :: String -> String2 string2 s = partial 5 s where partial 0 _ = error "Subtype constraint failed" partial n [] = [] partial n (x:xs) = x:partial (n-1) xs Which lazily checks the constraint; i.e. only errors if a value is demanded beyond the index 5 and exists. Implementing Compile-time checks is typically much harder, and demands a bit more cleverness, since the way you do it is different for each type of constraint you have. For this example, you could create an algebra of lengthed lists: import Prelude hiding (++) -- Type level numbers; Z = 0, S n = n + 1. data Z data S n -- Lists of length exactly n data Listn n a where Nil :: Listn Z a Cons :: a -> Listn n a -> Listn (S n) a -- Type-level addition of numbers type family Plus m n :: * type instance Plus Z n = n type instance Plus (S m) n = S (Plus m n) -- Typed append; appends the lists, adds the lengths. -- The compiler verifies that the implementation actually does this! (++) :: Listn m a -> Listn n a -> Listn (Plus m n) a Nil ++ ys = ys Cons x xs ++ ys = Cons x (xs ++ ys) -- Type-level less than or equal; represents the type of *proofs* that m <= n. data m :<= n where LeN :: n :<= n LeS :: m :<= n -> m :<= S n -- A List5 a is a function which takes a proof than n <= 5, and returns a Listn n a type List5 a = forall n. n :<= S (S (S (S (S Z)))) -> Listn n a So that was a bit of work, wasn't it? But this solution is quite expressive; the compiler will not even compile your code if you try to construct a list with more than 5 elements. Furthermore, you can actually write most things you'd expect to because of Haskell's great GADT typechecking features :-) The downside is that you have to redefine all the standard list operations, because, well, they have different types now. The above is approaching what dependently typed languages do. My favorite is Coq (a lot of haskell folks like Agda 2), and in it you can express directly the constraint you want without all this type boilerplate: Definition List5 a := { l : List a | length l <= 5 }. But internally it is doing something very similar to the above Haskell program. This also has the property that it is impossible to write a well-typed program that constructs a List5 of length > 5. In addition, you can use all the standard list functions, however you have to prove what they do to the constraint: Theorem append_length : forall m n a (xs ys : List a), (length xs <= m) -> (length ys <= n) -> (length (xs ++ ys) <= m+n). (* prove prove prove.... *) Qed. And then you can use that theorem to prove that the parts of your program that use List5 are well-typed. Whew, so now that we're done with that, in summary, it depends on your situation how you want to do it, and there's really no "easy answer". I hope you got something out of seeing these techniques. Adding notation like that you suggest is a challenge for the language, since a runtime constraint changes the strictness properties of the object, and a compile-time constraint written that concisely actually does require full dependent types. Best to leave it to the users. Luke

1 0

SCGI module
by Anton Tayanovskyy 03 Oct '08

03 Oct '08

Hello, SCGI module from Hackage is not working for me with Apache mod_scgi, I think because it uses LazyBytestring to hGetContents on a socket handle and the Apache side does not close the socket. Also, looking at the source I didn't see any fork* calls, so I assume it is not doing concurrency. So I ended up writing a replacement and would like to invite comments. It does forkIO per request and, if asked to, timeouts those threads. So far it works for me on simple examples from http://www.haskell.org/haskellwiki/Practical_web_programming_in_Haskell giving roughly 800 requests a second versus 250 on plain CGI (both through Apache). http://hpaste.org/10842 Thanks! Also, in general, is there any interest in using SCGI, or FastCGI (plain CGI, HappS, you name it) is vastly superior? --Anton

2 1

Alex and Flex
by Manlio Perillo 03 Oct '08

03 Oct '08

Hi. I'm starting to write a CSS parser with Alex and Happy. The grammar is defined here: http://www.w3.org/TR/CSS21/grammar.html However I have noted that there are some difference in the syntax between Alex and Flex? What is the rationale? One more thing. Here: http://www.haskell.org/alex/doc/html/alex-files.html it seems that there is an error with macrodef := @smac '=' set | @rmac '=' regexp it should be macrodef := $smac '=' set | @rmac '=' regexp Thanks Manlio Perillo

1 0

Climbing up the shootout...
by Don Stewart 03 Oct '08

03 Oct '08

Thanks to those guys who've submitted parallel programs to the language benchmarks game, we're climbing up the rankings, now in 3rd, and ahead of C :) http://shootout.alioth.debian.org/u64q/benchmark.php?test=all&lang=all Just one or two more parallel programs required... Submit them here, and we can test on quad core, http://haskell.org/haskellwiki/Shootout/Parallel -- Don

24 73

System.Process
by Andrew Coppin 03 Oct '08

03 Oct '08

Much hair-pulling resulted today when I attempted to perform a small task. The System.Process module provides the runCommand function. This takes a complete command line and returns a ProcessHandle. No problem there. The module also provides the runProcess function, which enables you to set environment variables and so forth. However... this doesn't take a complete command line. It takes a path to an executable and a list of parsed arguments. Herein lies the problem: I have a program that accepts complete commands from a file and executes them. It works perfectly. And now I'd just like to set an environment variable while each command runs... But alas no, the only way to do that is with runProcess, which expects me to parse the command line first. (Before anybody remarks that "words" will do this, consider the "echo" command, which treats whitespace meaningfully.) In the end I resorted to reading the source code for the module. After about 30 minutes of hacking, I got something which typechecks but throws a runtime exception. It appears that runCommand looks for binaries in the system search path, but the code I've concocted doesn't. (Despite being cut and pasted from the definition of runCommand.) The only thing I can think of is that the source code I'm looking at (GHC 6.8.3) is different from the version of the library I have (GHC 6.8.1). Anyway, the point I'm trying to get to is... would it be hard for however maintains this library to add a little more flexibility in what it can do please?

10 15

enumeration I/O and non-sequential access
by John Lato 02 Oct '08

02 Oct '08

Hello, I've recently been looking at Oleg's Iteratee approach to I/O (http://okmij.org/ftp/Haskell/Iteratee/) and I was wondering about something. In general this seems to be a very good approach to handling sequential access, but I don't see a means of applying it where non-sequential (esp. random) access is desired. In fact, the only way I see of doing so is to either hold references to all read data in memory until the file has finished processing, or to iterate over the file multiple times, depending on how the data is to be processed. I can't see how either of these approaches would scale well. Is this an actual problem? Is there already a solution that I'm not aware of? Thanks, John Lato

2 2

One liner?
by Paul Keir 02 Oct '08

02 Oct '08

Hi all, There's a common little situation I keep bumping up against. I don't understand where I'm going wrong, so I've made a little example. It's to do with binding a result to a variable name using "<-". This code works fine: ---------------------------------------------- module Main where import System.Directory (getDirectoryContents) main = do dc <- getDirectoryContents "./foo/" mapM_ putStrLn dc ---------------------------------------------- But if I try to avoid the use of the bind to "dc", I fail: ---------------------------------------------- mapM_ putStrLn (getDirectoryContents "./foo/") ---------------------------------------------- I've tried using map instead of mapM_, and inserted "return"s here and there, but no luck. Can anyone tell me where and why I'm going wrong? The error message is below. Cheers, Paul Couldn't match expected type `[String]' against inferred type `IO [FilePath]' In the second argument of `mapM_', namely `(getDirectoryContents "./foo/")' In the expression: mapM_ putStrLn (getDirectoryContents "./foo/") In the definition of `main': main = mapM_ putStrLn (getDirectoryContents "./foo/")

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csv one-liner
by wman 02 Oct '08

02 Oct '08

I got asked how to do one particular thing in excel, which led to discssion with "our local MSOffice expert". During the discussion I stated that's it too much of a PITA and that I'd rather write a script. Long story short, I promised him a one-liner to "show the power and beauty of Haskell". I got the csv package from hackage, modified the parseCSVFromFile so it's returns IO CSV rather than IO (Either ParseError CSV), and finished with following code (writeFile "output.csv") =<< (liftM printCSV $ liftM (map updateLine) $ parseCSVFromFile "input.csv") Is there room for improvement ? Could it still be made into one-liner without modifying the csv module (and without resorting to case parseCSVFromFile "input.csv" of { Left _ -> []; Right x -> x} kind of tricks) ? Thanks, wman.

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A question about constraints
by jean-christophe mincke 02 Oct '08

02 Oct '08

Hello, Given a type T, this type identifies a set of values and this set can be deduced from the structure of type T. i.e the type String is the set of all possible lists of character whatever their length. This being said, I have the following question: Given a type T, how is it possible to further restrict its set of values? i.e, in the above case, how is it possible to define a type String2 whose elements are any list of characters whose length is <= 5. I believe the best way to deal with that is to make String2 an ADT. This allows the constraint (in this case, the length) to be checked but hides the structure of the type, thus limits the use of pattern matching (in this case I do not want to hide the implementation of the type, so the ADT is not used that way). If one wants to use pattern matching, then the module must provide a way to convert from String2 to a type whose constructors are visible (asString in this exemple) module A ( String2 ,mkString2 ,asString ) where import List data String2 = String2 String mkString2 l = if (length l) <= 5 then String2 l else error "length > 5" asString (String2 l) = l Btw, F# has found a nice solution to this problem, it allows the user to define an "active pattern", that is, a pattern to applies on ADT: http://blogs.msdn.com/dsyme/archive/2007/04/07/draft-paper-on-f-active-patt… Is there another way to address that problem in Haskell? Thank you Regards J-C Mincke

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[Streams] Couldn't match expected type ?`Distribution.Verbosity.Verbosity'
by Stephane Bortzmeyer 02 Oct '08

02 Oct '08

I cannot compile Streams 0.1: % darcs pull Pulling from "http://software.pupeno.com/Streams-0.1"... No remote changes to pull in! % make runhaskell Setup.lhs configure Setup.lhs:11:53: Couldn't match expected type `Distribution.Verbosity.Verbosity' against inferred type `IO FilePath' In the first argument of `readPackageDescription', namely `pkg_descr_file' In a 'do' expression: pkg_descr <- readPackageDescription pkg_descr_file In the expression: do pkg_descr_file <- defaultPackageDesc pkg_descr <- readPackageDescription pkg_descr_file let isWindows = "mingw" `isPrefixOf` System.Info.os config = ... defaultMainNoRead config make: *** [.setup-config] Error 1 % ghc --version The Glorious Glasgow Haskell Compilation System, version 6.8.2

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Restricted file reading monad
by oleg＠okmij.org 02 Oct '08

02 Oct '08

George Pollard wrote: > The structure of an ID3 tag goes something like this: > Header: > - total size of tag > - other header info > A series of frames, each with: > - total size of frame > - other header info > - frame data > > Since the ID3 tag as a whole has size information, I need to pass that > into the frame-reading functions to ensure that I never read past the > end of the total header. This exact same requirement is present within > the frame-reading function itself; it must read the frame data without > reading past the end of the frame. The structure of the chunk-encoded content is similar: first comes the size, then come data of that size. We have to read exactly that amount (and then check for the chunk trailer, CRLF). In a sense, we have a data stream embedded inside another stream. The Iteratee IO framework was specifically designed to process these sorts of arbitrarily nested and encoded data streams. In particular, the file http://okmij.org/ftp/Haskell/Iteratee/IterateeM.hs contains the function -- Read n elements from a stream and apply the given iteratee to the -- stream of the read elements. Unless the stream is terminated early, we -- read exactly n elements (even if the iteratee has accepted fewer). -- This procedure shows a different way of composing two iteratees: -- `vertical' rather than `horizontal' stake :: Monad m => Int -> IterateeG el m a -> IterateeGM el m (IterateeG el m a) The implementation is 11 lines long, counting the `where' line. I believe the code is declarative rather than imperative. The function stake (the analogue of List.take) is then used in enum_chunk_decoded :: Monad m => Iteratee m a -> IterateeM m a The end of the file IterateeM.hs has several complete tests.

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Class Quantification
by oleg＠okmij.org 02 Oct '08

02 Oct '08

Bas van Dijk wrote: > ... it's possible to define 'foo' and 'bar' like so: > > > foo :: (Num c, Num d) => (forall b. Num b => a -> b) -> a -> (c, d) > > foo f x = (f x, f x) > > > bar :: (Read c, Read d) => (forall b. Read b => a -> b) -> a -> (c, d) > > bar f x = (f x, f x) > > Which allows us to write: > > > testFoo = foo fromInteger 1 :: (Int, Float) > > testBar = bar read "1" :: (Int, Float) > > Now I would like to generalise 'foo' and 'bar' to 'bla' so that I can write: > > testBla1 = bla fromInteger 1 :: (Int, Float) > testBla2 = bla read "1" :: (Int, Float) Quantification over classes is *easily* achievable in Haskell. Although functional dependencies are required, overlapping or undecidable instances are not. The technique is also far simpler than that in SYB3 and takes only a few lines to write. The complete code follows. One may note that Rank2 types are *not* needed. Therefore, we do not even have to give signature to the function bla as it can be inferred. That technique suggests that Rank2 types are already present in some form in Haskell (even Haskell98) already. In more detail, the technique is explained in Class-parameterized classes, and the type-level logarithm http://okmij.org/ftp/Haskell/types.html#peano-arithm Type-class overloaded functions: second-order typeclass programming with backtracking http://okmij.org/ftp/Haskell/types.html#poly2 Here is the code {-# LANGUAGE RankNTypes, MultiParamTypeClasses, FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances, TypeSynonymInstances #-} -- the result type determines the argument type class RApply l a b | l b -> a where rapply :: l -> a -> b -- the expected instance instance RApply (a->b) a b where rapply = ($) data LRead = LRead instance Read b => RApply LRead String b where rapply _ = read data LFromInt = LFromInt instance Num b => RApply LFromInt Integer b where rapply _ = fromInteger bla x arg = (rapply x arg, rapply x arg) testBla1 = bla LFromInt 1 :: (Int, Float) testBla2 = bla LRead "1" :: (Int, Float)

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Haskell Weekly News: Issue 87 - October 1, 2008
by Brent Yorgey 02 Oct '08

02 Oct '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20081001 Issue 87 - October 01, 2008 --------------------------------------------------------------------------- Welcome to issue 87 of HWN, a newsletter covering developments in the [1]Haskell community. ICFP was held last week in Victoria, and by all accounts was a great success! This edition of the HWN includes much ICFP and Haskell Symposium-related content, including [2]videos of the Haskell symposium presentations, [3]programming contest results, some [4]notes on the future of Haskell, and slides from [5]a Haskell tutorial and [6]a talk about the Haskell Platform. But ICFP didn't seem to slow down the community all that much: you'll find the usual mix of newly released and updated packages, blog posts, mailing list discussions, and silly quotes as well. Announcements Haskell-Embedded System Design: ForSyDe 3.0 and Tutorial. Alfonso Acosta [7]announced the [8]3.0 release of [9]ForSyDe. The ForSyDe (Formal System Design) methodology has been developed with the objective to move system design (e.g. System on Chip, Hardware and Software systems) to a higher level of abstraction. ForSyDe is implemented as a Haskell-embedded behavioral DSL (Domain Specific Language). The 3.0 release includes a new deep-embedded DSL and embedded compiler, as well as a new user-friendly tutorial. Graphalyze-0.1. Ivan Miljenovic [10]announced the initial release of his graph-theoretic analysis library, [11]Graphalyze. This is a pre-release of the library he is writing for his mathematics honours thesis, "Graph-Theoretic Analysis of the Relationships in Discrete Data". Symposium videos. Malcolm Wallace [12]announced [13]guerrilla videos of the Haskell Symposium 2008 presentations. ICFP programming contest results. Malcolm Wallace [14]sent a link to [15]a video of the ICFP programming contest results presentation. Version 0.4.3 of happs-tutorial is a HAppS job board, done in HAppS.. Thomas Hartman [16]announced version 4 of the [17]self-demoing HAppS tutorial, a HAppS job board. TH code for deriving Binary and NFData instances. Tim Newsham [18]announced some [19]Template Haskell code for automatically deriving Data.Binary and Control.Parallel.Strategies.NFData instances. Notes on the future of Haskell from ICFP. Bryan O'Sullivan [20]posted a [21]writeup from the ICFP conference floor on the future of Haskell and functional programming. datapacker 1.0.1. John Goerzen [22]announced the [23]release of datapacker 1.0.1. A Functional Implementation of the Garsia-Wachs Algorithm. Nicolas Pouillard [24]announced a [25]Haskell implementation of an algorithm that builds a binary tree with minimum weighted path length from weighted leaf nodes given in symmetric order. This can be used to build optimum search tables, to balance a 'ropes' data structure in an optimal way. graphviz-2008.9.20. Ivan Miljenovic [26]announced a new version of [27]Matthew Sackman's Haskell bindings to Graphviz. See Ivan's original announcement for information on what new features are included, and what the difference is among the various graphviz-related packages on Hackage. darcs 2.1.0pre2. Eric Kow [28]announced the release of darcs 2.1.0pre2, formerly known as 2.0.3. See Eric's announcement for a list of new features and bug fixes in this release. protocol-buffers-0.2.9 for Haskell is ready. ChrisK [29]announced the release of the [30]protocol-buffers package, which generates Haskell data types that can be converted back and forth to lazy ByteStrings that interoperate with Google's generated code in C++/Java/python. panda blog engine. Jinjing Wang [31]announced the release of [32]panda, a simple blog engine written in Haskell. OpenSPARC project applicant chosen. Duncan Coutts [33]announced that Ben Lippmeier has been chosen for the [34]OpenSPARC project. Ben will spend three months hacking on GHC to make it perform well on the latest multi-core OpenSPARC chips. Hugs on the iPhone. Alberto Galdo [35]announced that he has gotten Hugs to run on the iPhone, and has made packages available for others who would like to install it as well. Discussion Shooting yourself in the foot in Haskell. John Van Enk [36]asked how to shoot yourself in the foot with Haskell, with humorous results. Total Functional Programming in Haskell. Jason Dagit started a [37]discussion on total functional programming, Haskell, abstraction boundaries and the IO monad, and related topics. Health effects. Andrew Coppin told a [38]story about a chocolate bar and recursion, which led to a discussion of optimization problems, Dedekind cuts, some meta-discussion of the discussion, and entirely too many puns. The container problem. Andrew Coppin [39]asked about the possibility if abstracting over various sorts of containers in Haskell, and why there isn't a widely used library that does this. A discussion of various container libraries and the language issues that arise followed. Red-Blue Stack. Matthew Eastman [40]asked how to implement a certain data structure (red-blue stacks) in Haskell. Several people responded with increasingly clever solutions, and a comparison of mutating vs. non-mutating algorithms. Climbing up the shootout.... Don Stewart began a long and ongoing [41]discussion about improving Haskell's performance on benchmarks in the [42]Shootout, now that there is a quad core machine for running benchmarks! Line noise. Andrew Coppin started an [43]interesting discussion about perceptions of Haskell syntax by programmers who aren't familiar with it. Jobs London FP job in asset management. Michael Bott [44]announced an opportunity for two functional programmers based in London, with a software house specialising in asset management. Blog noise [45]Haskell news from the [46]blogosphere. * Creighton Hogg: [47]Some first steps with Data.Reactive. Creighton gives some simple examples of using Conal Elliott's Reactive library. More to come! * Bryan O'Sullivan: [48]Unix hacking in Haskell: better pseudoterminal support. * Creighton Hogg: [49]One last thought on laziness. In Creighton's opinion, laziness is the single hardest thing to get used to in Haskell. If you're learning Haskell, don't despair, break out the pencil and paper! * Douglas M. Auclair (geophf): [50]Animal as RDR, part III. * Neil Mitchell: [51]General Updates. * Don Stewart (dons): [52]Newest Mersenne Prime. Haskell doesn't even break a sweat computing the largest known prime number. * Douglas M. Auclair (geophf): [53]Animal as RDR, part II. * Bryan O'Sullivan: [54]Using Bloom filters for large scale gene sequence analysis in Haskell. A paper that Bryan and Ketil Malde submitted to PADL 09. "The Cliff's Notes version: Bloom filters are almost unused in bioinformatics; they're tremendously useful; and our Haskell code is really fast. * >>> Zubin Wadia: [55]Simon Peyton Jones & Microsoft Research Cambridge. Zubin thinks quite highly of SPJ and MSR Cambridge. * Bryan O'Sullivan: [56]Slides from my DEFUN 2008 Haskell tutorial. * Mads Lindstroem: [57]Inheritance in Composites and Overlapping Instances. * >>> Micah Cowan: [58]Adventures in Haskell. Micah shares some thoughts on learning Haskell. * Bryan O'Sullivan: [59]Some notes on the future of Haskell and FP. * Well-Typed.Com: [60]Slides from the Haskell Platform talk. * Paul Johnson: [61]Why the banks collapsed, and how a paper on Haskell programming can help stop it happening next time. * >>> Nathan Sanders: [62]Two weeks of Haskell. Nathan shares some thoughts on his first two weeks learning Haskell. * Bryan O'Sullivan: [63]Twittering from ICFP / Haskell symposium / CUFP. * Real-World Haskell: [64]Slides from ACCU talk. * Eric Kow (kowey): [65]darcs weekly news #5. * John Goerzen (CosmicRay): [66]New version of datapacker. * >>> James Cowie: [67]Haskell, the verdict!. James is impressed with Haskell after using it for a few weeks. * >>> Alex Combas: [68]What's all this fuss about Haskell?. Alex is thinking of learning Haskell in his spare time. * Aaron Tomb: [69]Parsing the Linux kernel with Haskell: experience with Language.C. Aaron is impressed by the new Language.C libraries, which parses all 18 million pre-processed lines of Linux kernel source with no problems! Quotes of the Week * Fuse_: Oh, sorry for hijacking mathematical purity with dirty fiscal dynamical systems. :o * mauke: <mauke> data Mushroom badger = Mushroom badger badger badger badger badger badger badger badger badger <leimy> where's the snake <mauke> deriving Snake * ddarius: higher order of lambdabot deployment and management engineers or HOLDME * Botje: #haskell: parallellising your homework answers! * olsner: most everything gives nicer everything than perl * Botje: fuzzy feelings aren't always aerodynamic, unfortunately. * chrisdone: benchmarks only exist to make fun of ruby * Claus Reinke: [on breaking code up into smaller bits] Once your readers understand your code, you can add the one-liner and ask for applause. * Jake Mcarthur: A fold by any other name would smell as sweet. * lispy: Schroedinger's cat is really in a thunk not a box * Bulat: Haskell was developed with goal to hide implementation details from egg-headed scientists and this obviously should have some drawbacks About the Haskell Weekly News New editions are posted to [70]the Haskell mailing list as well as to [71]the Haskell Sequence and [72]Planet Haskell. [73]RSS is also available, and headlines appear on [74]haskell.org. To help create new editions of this newsletter, please see the information on [75]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [76]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://haskell.org/haskellwiki/Video_presentations/Haskell_Symposium_2008 3. http://video.google.com/videoplay?docid=-4697764813432201693 4. http://www.serpentine.com/blog/2008/09/26/some-notes-on-the-future-of-haske… 5. http://www.serpentine.com/blog/2008/09/27/slides-from-my-defun-2008-haskell… 6. http://blog.well-typed.com/2008/09/slides-from-the-haskell-platform-talk/ 7. http://article.gmane.org/gmane.comp.lang.haskell.general/16443 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ForSyDe 9. http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/ 10. http://article.gmane.org/gmane.comp.lang.haskell.general/16442 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16440 13. http://haskell.org/haskellwiki/Video_presentations/Haskell_Symposium_2008 14. http://article.gmane.org/gmane.comp.lang.haskell.general/16438 15. http://video.google.com/videoplay?docid=-4697764813432201693 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45332 17. http://happstutorial.com:5001/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45305 19. http://www.thenewsh.com/~newsham/store/DeriveBinary.hs 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45272 21. http://www.serpentine.com/blog/2008/09/26/some-notes-on-the-future-of-haske… 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45185 23. http://changelog.complete.org/posts/760-New-version-of-datapacker.html 24. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45002 25. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/garsia-wachs 26. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44863 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphviz 28. http://www.haskell.org//pipermail/haskell-cafe/2008-September/048094.html 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44845 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/protocol-buffers 31. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44840 32. http://jinjing.blog.easymic.com/ 33. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44836 34. http://haskell.org/opensparc/ 35. http://www.haskell.org//pipermail/haskell-cafe/2008-September/047838.html 36. http://www.haskell.org//pipermail/haskell-cafe/2008-October/048506.html 37. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45393 38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45370 39. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45242 40. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/45122 41. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/44916 42. http://shootout.alioth.debian.org/u64q/benchmark.php?test=all&lang=all 43. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/44886 44. http://article.gmane.org/gmane.comp.lang.haskell.cafe/45506 45. http://planet.haskell.org/ 46. http://haskell.org/haskellwiki/Blog_articles 47. http://abstractabsurd.blogspot.com/2008/09/some-first-steps-with-datareacti… 48. http://www.serpentine.com/blog/2008/09/30/unix-hacking-in-haskell-better-ps… 49. http://abstractabsurd.blogspot.com/2008/09/one-last-thought-on-laziness.html 50. http://logicaltypes.blogspot.com/2008/09/animal-as-rdr-part-iii.html 51. http://neilmitchell.blogspot.com/2008/09/general-updates.html 52. http://www.cse.unsw.edu.au/~dons/blog/2008/09/30#primes 53. http://logicaltypes.blogspot.com/2008/09/animal-as-rdr-part-ii.html 54. http://www.serpentine.com/blog/2008/09/28/using-bloom-filters-for-large-sca… 55. http://zwadia.com/?p=58 56. http://www.serpentine.com/blog/2008/09/27/slides-from-my-defun-2008-haskell… 57. http://lindstroem.wordpress.com/2008/09/27/inheritance-in-composites-and-ov… 58. http://micah.cowan.name/2008/09/26/computers/software-development/adventure… 59. http://www.serpentine.com/blog/2008/09/26/some-notes-on-the-future-of-haske… 60. http://blog.well-typed.com/2008/09/slides-from-the-haskell-platform-talk/ 61. http://paulspontifications.blogspot.com/2008/09/why-banks-collapsed-and-how… 62. http://sandersn.com/blog/index.php?title=two_weeks_of_haskell 63. http://www.serpentine.com/blog/2008/09/25/twittering-from-icfp-haskell-symp… 64. http://www.realworldhaskell.org/blog/2008/09/25/slides-from-accu-talk/ 65. http://koweycode.blogspot.com/2008/09/darcs-weekly-news-5.html 66. http://changelog.complete.org/posts/760-New-version-of-datapacker.html 67. http://www.jcowie.co.uk/2008/09/haskell-the-verdict/ 68. http://combas3d.com/2008/09/whats-all-this-fuss-about-haskell/ 69. http://www.galois.com/blog/2008/09/17/parsing-the-linux-kernel-with-haskell… 70. http://www.haskell.org/mailman/listinfo/haskell 71. http://sequence.complete.org/ 72. http://planet.haskell.org/ 73. http://sequence.complete.org/node/feed 74. http://haskell.org/ 75. http://haskell.org/haskellwiki/HWN 76. http://code.haskell.org/~byorgey/code/hwn/

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