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Writing for both State and StateT
by Mark T.B. Carroll 22 Apr '03

22 Apr '03

At the moment I have code like, next_random_probability :: (RandomGen g, Num a, Random a) => State g a next_random_probability = do old_rng <- get let (random_probability, new_rng) = randomR (0, 1) old_rng put new_rng return random_probability next_random_probabilityT :: (RandomGen g, Num a, Random a, Monad m) => StateT g m a next_random_probabilityT = do old_rng <- get let (random_probability, new_rng) = randomR (0, 1) old_rng put new_rng return random_probability Because these just use get and put which are both from MonadState, is it possible to write just one next_random_probability with a more general type signature, maybe mentioning MonadState, or at least two wrappers that call the same worker function, so that the same code is good for both State and StateT? -- Mark

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GHC XmlParse
by Christof Lehmann 22 Apr '03

22 Apr '03

Hello, I have a small program with a 'import XmlParse' - statement. During compiling with ghc --make main.hs I get following error message ghc-5.02.2: chasing modules from: main.hs ghc-5.02.2: can't find module `XmlTypes' Ghc finds modules like IO and System. Which option do I need, that ghc finds the Xml... - modules. thanks -- Christof Lehmann VUB Printmedia GmbH Berlin Bonn Dresden Köln Leipzig Chopinstr. 4 TEL: +49 341 960 50 93 04103 Leipzig FAX: +49 341 960 50 92

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splatterhunks
by William Lee Irwin III 22 Apr '03

22 Apr '03

-- This program takes patch filenames as arguments and splits the patch -- files up on a hunk-by-hunk basis. I have found this useful for Linux -- kernel development, and perhaps others might find it useful in -- similar contexts where patches are the primary method of communication. module Main where import System import List main = getArgs >>= mapM_ splatterHunkFile splatterHunkFile file = mapM_ (\(f,ss) -> writeFile f (unlines ss)) . zip (map (((reverse . takeWhile (/= '/') . reverse $ file)++).("-"++).show) [1..]) . splatterHunks =<< readFile file splatterHunks ss = map (map unlines) $ zipWith (\s -> map (s:)) (map head . (splitList "diff") $ lines ss) (map (splitList "@@") . (splitList "diff") $ lines ss) splitList prefix ss = map ($ss) $ zipWith (\m n -> (if n >= 0 then take (n - m) else id) . drop m) (map fst . filter (\(n,s) -> isPrefixOf prefix s) $ zip [0..] ss) (tail (map fst . filter (\(n,s) -> isPrefixOf prefix s) $ zip [0..] ss) ++ [-1])

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idea: chroot :: FilePath -> IO a -> IO a
by David Roundy 21 Apr '03

21 Apr '03

I have the idea that we ought to be able to implement the equivalent of a unix chroot command, but all within the haskell IO monad. So the idea would be that if I want to do some operation that only requires access to, say /var/cache/test, but involves user-provided input which I don't trust (and if I don't want to trust the security of my parsing of the possibly malicious input), I could run: chroot "/var/cache/test" $ complicated_function "/" scary_user_input which would be the equivalent of complicated_function "/var/cache/test" scary_user_input except that every file and directory access (read or write or stat or whatever) would be forced to be in a subdirectory of /var/cache/test. Moreover, calls such as system would not be allowed (that is, they'd throw an isChrootError exception), since such calls of course could not be verified to touch no file outside of /var/cache/test (at least not using only haskell). Actually, there are two ways this could be done. One is the one mentioned above, which is roughly equivalent to a unix chroot. Another (now that I think about it, probably more elegant) would be to implement a restrict_access type of function, which wouldn't change the meaning of any file paths as a chroot does, but would simply cause any access outside of the specified directory to fail. This would have the advantage of being transparent to the writer of complicated_function--and might be extended to allow access to more than one directory (e.g. for a webserver of only static pages maybe /var/www and /etc/myserver/). As I see it, implementing such a function would require support in the IO monad (some of which may already be there?), since it would need to know for each primitive operation which arguments are file paths, plus whether that operation is even legal in a chroot environment. Or perhaps it's the other way around, and every primitive operation would need to support chroot... I know I would find such a function exceedingly comforting, since I wonder from time to time what would happen if users stick weird filenames in the wrong places, or make symlinks to things they should not have access to. And the cool thing is that with haskell's monadic IO, I think it could be done in a very elegant manner, and in such a way that it is natural (and simple) to wrap a chroot around individual operations, giving finer grained control than I can imagine doing any other way. Any ideas whether such a feat would be possible, and if so how hard it would be? -- David Roundy http://www.abridgegame.org

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Re: HI
by bullins39434＠aol.com 17 Apr '03

17 Apr '03

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Re: Parsec question
by Sarat Chandra 17 Apr '03

17 Apr '03

Thanks, "uust" was the missing link. --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >It is in: > >http://cvs.cs.uu.nl/cgi-bin/cvsweb.cgi/uust/lib/ > >As far as I can see you should be able to check the whole uust tree out, > > Doaitse > > >On donderdag, apr 17, 2003, at 17:06 Europe/Amsterdam, Sarat Chandra >wrote: > >> Doaitse, >> >> I can't find the "Parsing" directory. May be the directory is not >> made visible to public. However, under the "PC" directory, I see >> UU_Parsing.hs and other files (but no examples directory). Can you >> please check it. >> >> Thanks. >> >> --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >>> Parsec cannot do this. If you want this behaviour check out the >>> Parsing >>> library at cvs.cs.uu.nl (directory lib). In the examples directory you >>> find an example parser for Haskell written using these combinators. At >>> the top level there is also a Tiger compiler that is written with >>> these >>> combinators, >>> >>> Doaitse Swierstra >>> >>> >>> On woensdag, apr 16, 2003, at 12:00 Europe/Amsterdam, Sarat Chandra >>> wrote: >>> >>>> I am using Parsec to write a parser. I would like to know >>>> how parse-errors can be accumulated without stopping at the >>>> first error. I would like to skip the input upto some >>>> synchronization point (for e.g a semi-colon) and continue parsing >>>> from there. Thanks. >>>> >>>> _____________________________________________________________ >>>> Get your own FREE e-mail account at http://www.volcanomail.com >>>> >>>> _____________________________________________________________ >>>> Select your own custom email address for FREE! Get you(a)yourchoice.com >>>> w/No Ads, 6MB, POP & more! >>>> http://www.everyone.net/selectmail?campaign=tag >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> _____________________________________________________________ >> Get your own FREE e-mail account at http://www.volcanomail.com >> >> _____________________________________________________________ >> Select your own custom email address for FREE! Get you(a)yourchoice.com >> w/No Ads, 6MB, POP & more! >> http://www.everyone.net/selectmail?campaign=tag >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Re: Parsec question
by Sarat Chandra 17 Apr '03

17 Apr '03

Doaitse, I can't find the "Parsing" directory. May be the directory is not made visible to public. However, under the "PC" directory, I see UU_Parsing.hs and other files (but no examples directory). Can you please check it. Thanks. --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >Parsec cannot do this. If you want this behaviour check out the Parsing >library at cvs.cs.uu.nl (directory lib). In the examples directory you >find an example parser for Haskell written using these combinators. At >the top level there is also a Tiger compiler that is written with these >combinators, > > Doaitse Swierstra > > >On woensdag, apr 16, 2003, at 12:00 Europe/Amsterdam, Sarat Chandra >wrote: > >> I am using Parsec to write a parser. I would like to know >> how parse-errors can be accumulated without stopping at the >> first error. I would like to skip the input upto some >> synchronization point (for e.g a semi-colon) and continue parsing >> from there. Thanks. >> >> _____________________________________________________________ >> Get your own FREE e-mail account at http://www.volcanomail.com >> >> _____________________________________________________________ >> Select your own custom email address for FREE! Get you(a)yourchoice.com >> w/No Ads, 6MB, POP & more! >> http://www.everyone.net/selectmail?campaign=tag >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Parsec question
by Sarat Chandra 16 Apr '03

16 Apr '03

I am using Parsec to write a parser. I would like to know how parse-errors can be accumulated without stopping at the first error. I would like to skip the input upto some synchronization point (for e.g a semi-colon) and continue parsing from there. Thanks. _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Say�n haskell-cafe ,Baskuda.Com`da Bebek / Oyuncak Kategorisi A��ld�!
by Baskuda-4233 16 Apr '03

16 Apr '03

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RE: [OT[ proving programs for novices
by David Bakin 16 Apr '03

16 Apr '03

How would this book relate - in subject, difficulty, audience - to: The Science of Programming by Gries? Algebra of Programming by Bird, De Moor, Moor? Thanks! - Dave -----Original Message----- From: Doaitse Swierstra [mailto:doaitse@cs.uu.nl] Sent: Tuesday, April 15, 2003 12:38 PM To: Bill Wood Cc: Doaitse Swierstra; haskell-cafe(a)haskell.org Subject: Re: [OT[ proving programs for novices One might be interested in the newly published book by Roland Backhouse: "Program Construction : Calculating Implementations from Specifications" http://www.wiley.com/remtitle.cgi?0470848820 I quote from the publishers web site: "The ever-increasing dependence of our lives and livelihoods on the correct functioning of computer software means that logic and program correctness are core elements of all good computer science degrees. This book presents both these topics in one self-contained text. The focus of the book is on "correct-by-construction" program design -- the discipline of calculating programs from their specifications. Modern, calculational logic is introduced in combination with key program construction principles, such as the assignment axiom, loop invariants and bound functions. This material is intertwined with motivational discussion, programming examples and challenging problem-solving exercises, bringing the book alive for its intended audience, undergraduates in computer science and mathematics, as well as professional programmers wishing to further develop their programming skills. The book covers the elements of logic and program correctness that form the foundations of further study --- the logical connectives and their algebraic properties, induction, quantifiers and program construction rules. Substantial examples of program construction are included. Many exercises are provided, all with detailed solutions. " Doaitse Swierstra _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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