April 2007 - Haskell-Cafe

Fwd: darcs.haskell.org access for maths hierarchy
by Alexander McPhail 03 Apr '07

03 Apr '07

I have set up a page on the wiki for discussion: http://www.haskell.org/haskellwiki/Haskell_and_mathematics/Hierarchy And about a darcs repo for people to patch against: ---------- Forwarded message ---------- From: Simon Marlow <simonmarhaskell(a)gmail.com> Date: 03-Apr-2007 20:28 Subject: Re: darcs.haskell.org access for maths hierarchy To: Alexander McPhail <haskell.vivian.mcphail(a)gmail.com> Hi there, The plan is to set up a separate server for hosting community projects. Right now we have the server, but we still have to set it up. Hopefully it should be available soon, we'll announce something when it is. Cheers, Simon Alexander McPhail wrote: > Hi, > > There is some movement on the haskell-cafe mailing list to set up a repo > to develop a mathematically sound algebraic class hierarchy. I have > volunteered to coordinate this. > > What is the policy on giving access to darcs.haskell.org > <http://darcs.haskell.org>? > Cheers, > > Vivian > >

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Keeping a symbol table with Parsec
by Joel Reymont 02 Apr '07

02 Apr '07

Folks, Are there any examples of keeping a symbol table with Parsec? I'm translating a parser from OCaml and I do this OUTPUT COLON ID LP NUMERIC_SIMPLE RP { add $3 TypNumOut; SimpleOutputDec ($3, Number) } Meaning that if a keyword Output is followed by ":" and an identifier and then "(NumericSimple)" then add identifier to the symbol table as a Number and box it in a constructor. Then in my lexer I do a lookup to check if I have seen this identifier and if I have seen one of type TypeNumOut I return the token NUM instead of ID. This ensures that I can have rules with the token NUM as opposed to ID everywhere. How would I accomplish the same with Parsec, that is 1) update a symbol table and 2) check identifiers and "return a different token"? Thanks, Joel -- http://wagerlabs.com/

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String to Word64 Conversion
by Dominic Steinitz 02 Apr '07

02 Apr '07

> [Haskell-cafe] String to Word64 Conversion > Ian Sefferman iseff at iseff.com > Sun Apr 1 15:42:07 EDT 2007 > Previous message: [Haskell-cafe] Josephus problem and style > Next message: [Haskell-cafe] Data.ByteStream.Char8.words performance > Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] > I've been spending a lot of time trying to find a clean way to convert > from a String to a Word64 for the Crypto library. > > Specifically, we're trying to encrypt the strings with Blowfish. The > type for the encrypt function is: > > encrypt :: (Integral a) => a -> Word64 -> Word64 > > I assume I would want something like: > toWord64s :: String -> [Word64] > toWord64s = .... > > myEncrypt string = map (Blowfish.encrypt myKey) (toWord64s string) > > I would have to imagine that encrypting strings is a fairly common > thing to do, so a conversion should be trivial, but I can't seem to > find anything on it. I feel like I must be missing something rather > obvious here. Am I? > > Thanks, > Ian Ian, Maybe something like this. I've pretty much taken it from http://darcs.haskell.org/crypto/Data/Digest/SHA1.hs. fromBytes :: (Bits a) => [a] -> a fromBytes input = let dofb accum [] = accum dofb accum (x:xs) = dofb ((shiftL accum 8) .|. x) xs in dofb 0 input blockWord8sIn64 :: [Word8] -> [[Word8]] blockWord8sIn64 = unfoldr g where g [] = Nothing g xs = Just (splitAt 8 xs) getWord64s :: [Word8] -> [Word64] getWord64s = map fromBytes . map (map fromIntegral) . blockWord8sIn64 Don't forget you will need to pad http://www.haskell.org/crypto/doc/html/Codec.Encryption.Padding.html. I don't know what your application is but I suggest NOT using ECB mode which your code suggests you are thinking of doing. The only mode currently supported in the crypto library is CBC but other modes should be trivial to add. Dominic.

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Binary I/O
by Daniel Brownridge 02 Apr '07

02 Apr '07

Hello. I am a Computer Science student attempting to write an emulator using Haskell. One of my main design choices is how to deal with machine code. Clearly it is possible to represent 0's and 1's as ASCII characters, however it strikes me that it would be much nicer to the I/O using raw binary. I don't seem to be able to find much documentation on this. Does anybody know how it's done, or can point me in the direction of some resources. Many thanks Daniel

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Re: [Haskell-cafe] Memory leak in streaming parser
by Oren Ben-Kiki 02 Apr '07

02 Apr '07

On Mon, 2007-04-02 at 13:54 +0100, Malcolm Wallace wrote: > An observation about your state setter functions, ... > You can shorten your code considerably by using the standard named-field > update syntax for exactly this task: > > setDecision :: String -> State -> State > setDecision decision state = state { sDecision = decision } If I do that, the run time insists on the state being "more" evaluated before it changes that specific field. This kills streaming, enforcing each production (including the top one) to be fully parsed before I can access its generated tokens. So the GC won't be hanging on to State objects, but memory still explodes - with unconsumed Token objects. And there's no output from the program until it dies :-( > Not only is it shorter, but it will often be much more efficient, since > the entire structured value is copied once once, then a single field > updated, rather than being re-built piece-by-piece in 15 steps. I know! Is there an efficient way to lazily modify just one field record? > You probably want to be strict in the state component, but not in the > output values of your monad. So as well as replacing > let ... in (finalState, rightResult) > with > let ... in finalState `seq` (finalState, rightResult) > in the (>>=) method in your Monad instance (and in the separate defn of For some strange reason, adding this didn't solve the problem - the GC still refuses to collect the state objects. BTW, forcing the evaluation of the intermediate states (originalState, leftState, rightState etc.) doesn't help either. I have tried to ensure that when '>>=' and '/' will allow the GC to discard old states "as soon as possible", but I'm obviously missing something. Is there a way to get more detailed retainer information than what's available with '-hr'? > you might also need to make all the named fields of your State datatype > strict. If I make any of them strict, streaming goes away :-( Writing a streaming parser in Haskell is turning out to be much harder than I originally expected. Every fix I tried so far either broke streaming (memory blows up due to tokens) or had no effect (memory blows up due to states). I am assuming that there's a magic point in the middle where tokens are consumed and states are GC-ed... but it has eluded me so far. Thanks, Oren Ben-Kiki P.S. I uploaded the package to Hackage. I added a debug-leak production to make it easier to profile this with even less productions involved. ``yes '#' | yaml2yeast -p debug-leak''.

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Memory leak in streaming parser
by Oren Ben-Kiki 02 Apr '07

02 Apr '07

I just created an initial version of a "streaming" parser. This parser is intended to serve as a reference parser for the YAML spec. Efficiency isn't the main concern; the priority was to have it use the BNF productions from the spec without any changes (ok, with tiny, minor, insignificant changes :-) and to allow it to stream large files. I'm happy to say I achieved the first goal, and the parser .hs file simply #includes a file that is, for all intents and purposes, a BNF file. I didn't have as much luck with the second goal. After putting a lot of effort into it, I have got to the point it is "streaming". That is, I can "cat" a large YAML file to the wrapper program and it will "immediately" start spitting out parsed tokens. This took some doing to ensure the resulting token stream is accessible while it is being generated, in the presence of potential parsing failures and, of course, parsing decision points. I must have done "too good a job" converting things to lazy form because, while the parser is streaming, it also hangs on to old state objects for no "obvious" reason. At least it isn't obvious to me after profiling it in any way I could think of and trying to `seq` the "obvious" suspects. Adding a `seq` in the wrong place will of course stop it from being a streaming parser... I'd take it as a kindness if someone who had some deeper knowledge of the Haskell internals would peek at it. It is packaged as Cabal .tar.gz file in http://www.ben-kiki.org/oren/YamlReference - it includes the wrapper program and a regression-test program. To watch it consume all available memory using a very small set of BNF productions, yes '#' | yaml2yeast -p s-l-comments (This basically matches "l-comment*" - each '#\n' is a comment line). You'll get a stream of parsed tokens to stdout and an ever-climbing memory usage in top (or htop). Any advice would be appreciated, Oren Ben-Kiki

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Mutable variables eliminated from .NET | Lambda the Ultimate
by dons＠cse.unsw.edu.au 02 Apr '07

02 Apr '07

As seen on reputable language news site, Lambda the Ultimate. http://lambda-the-ultimate.org/node/2164 Mutable variables eliminated from .NET Redmond, WA: At an unusual press conference held this Sunday morning, Bill Taylor, Microsoft's General Manager of Platform Strategy, announced that after much research into the causes of security holes and instabilities, Microsoft will eliminate mutable variables from the .NET platform and its languages, including C# and VB.NET. "One of our top researchers found that mutable variables were the major root cause preventing us from achieving the great user experience we always strive to deliver," said Taylor. "Once we realized that, eliminating them from .NET was a no-brainer." Given that this announcement was made on a Sunday, reactions have been limited so far, but one prominent VB.NET developer commented that "Compared to the switch from VB6 to VB.NET, this ought to be a breeze." A C# developer was heard to say, "After anonymous delegates, monads shouldn't be a problem." To ensure wide penetration of this significant update, Microsoft will be issuing updated Windows CDs to all licensed customers, free of charge. The new CDs can be identified by the distinctive holographic "Haskell Inside" logo, featuring a holographic version of this[1] portrait of Simon Peyton-Jones, grinning from ear to ear. [1] http://research.microsoft.com/~simonpj/GIFs/spj-snow.jpg

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Re: [Haskell-cafe] ghc-6.7.20070330 on Mac OS X
by Ruben Zilibowitz 01 Apr '07

01 Apr '07

Hi, I managed to build it eventually using the instructions on: http://hackage.haskell.org/trac/ghc/wiki/Building/MacOSX Sorry to Greg - I accidentally sent this to your personal email address first. Ruben On 02/04/2007, at 4:34 AM, Gregory Wright wrote: > > Hi Ruben, > > The GHC wiki also has information on this, and should be your first > stop if you are experiencing build problems: > > http://hackage.haskell.org/trac/ghc/wiki/Building/MacOSX > > At least under MacPorts, I have had no trouble building 6.7-20070330. > I will be releasing a new portfile for ghc-devel in a few days that > will > build the latest from the darcs repository. > > Best Wishes, > Greg > > On Apr 1, 2007, at 11:50 AM, Pepe Iborra wrote: > >> (redirecting to glasgow-haskell-users) >> >> It is well known that the readline lib that comes with OS X is no >> good, and you need to use a replacement. A nice post from the >> blogosphere explaining all this: >> >> http://mult.ifario.us/articles/2006/10/17/ghc-6-6-and-mac-os-x- >> readline-quick-fix >> >> If that doesn't help, please post the errors that you get when >> building the readline package. >> >> Cheers >> pepe >> >

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Re: [Haskell-cafe] Data.ByteStream.Char8.words performance
by Duncan Coutts 01 Apr '07

01 Apr '07

On Sun, 2007-04-01 at 17:25 +0200, Thomas Schilling wrote: > On 31 mar 2007, at 04.09, Duncan Coutts wrote: > > > > The ByteString libs was more-or-less the first high performance thing > > that we wrote and we've learnt plenty more since then. I think > > there's a > > good deal more performance too eek out of it yet, both at the low and > > high level. > > Is there some document available explaining those findings (other > than the ByteString paper)? Not yet. Duncan

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String to Word64 Conversion
by Ian Sefferman 01 Apr '07

01 Apr '07

I've been spending a lot of time trying to find a clean way to convert from a String to a Word64 for the Crypto library. Specifically, we're trying to encrypt the strings with Blowfish. The type for the encrypt function is: encrypt :: (Integral a) => a -> Word64 -> Word64 I assume I would want something like: toWord64s :: String -> [Word64] toWord64s = .... myEncrypt string = map (Blowfish.encrypt myKey) (toWord64s string) I would have to imagine that encrypting strings is a fairly common thing to do, so a conversion should be trivial, but I can't seem to find anything on it. I feel like I must be missing something rather obvious here. Am I? Thanks, Ian

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