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module Crypt_Discordian - code critique requested
by Terrence Brannon 23 Feb '05

23 Feb '05

Hi, I am getting into Haskell so I decided to convert a Perl module of mine: http://cpan.uwinnipeg.ca/htdocs/Crypt-Discordian/Crypt/Discordian.html into Haskell. I was pleased at the cleanliness and conciseness of the Haskell code. However, I am sure that it can be improved on and am soliciting any feedback you may have about this module. Thanks, metaperl on #haskell module Crypt_Discordian where import List vowel_list = "aeiouAEIOU" is_vowel c = c `elem` vowel_list move_vowels lis = move_vowels' lis [] [] move_vowels' [] c v = v ++ c move_vowels' (x:xs) c v | is_vowel x = move_vowels' xs c (x:v) | otherwise = move_vowels' xs (x:c) v remove_spaces str = filter (\x -> x /= ' ') str encrypt str = List.sort $ move_vowels $ remove_spaces str {- The algorithm for Discordian text encryption is given at: http://www.principiadiscordia.com/book/78.php After implementing this, I realized that all the early steps are a farce. But anyway, here is the algorithm in case you don't enjoy tilting your head to read a page: Step 1. Write out message (HAIL ERIS) and put all vowels at the end (HLRSAIEI) Step 2. Reverse order (IEIASRLH) Step 3. Convert to numbers (9-5-9-1-19-18-12-8) Step 4. Put into numerical order (1-5-8-9-9-12-18-19) Step 5. Convert back to letter (AEHIILRS) This cryptographic cypher code is GUARANTEED TO BE 100% UNBREAKABLE .. so says the Principia Discordia. But I think we can generate and test to break it. Many thanks to kosmikus and Pseudonym for their help in developing this module -} -- Carter's Compass: I know I'm on the right track when, by deleting something, I'm adding functionality.

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GUI components for displaying Html pages
by David Owen 23 Feb '05

23 Feb '05

Hi all, I'm looking for a Haskell GUI library which supports the display of rendered Html pages in the same way that web browsers do. I've been getting to grips recently with wxHaskell as it was recommended on haskell-cafe. I was hoping that a special pane component (or something similar) existed in wxHaskell for the purpose. I've looked through the API but can't seem to see anything which looks suitable. Does anybody know if wxHaskell can support this? If not is anybody aware of a Haskell GUI library which caters for this purpose. Also, I am hoping to make use of HaXmL to deal with the Html parsing or failing that attempt a very simple home-made parser. Should anybody out there know of a better way of attacking this aspect then that would be much appreciated too! (Apologies, this email might have been better suited to the libraries mailing list!) Cheers all! David (Swansea, UK)

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WASH defaults in inputFields
by John Goerzen 22 Feb '05

22 Feb '05

Hi, Hope this is not a stupid question, but I RTFM'd and couldn't find the answer. I am designing a form that will be used to edit some data that is in the database. I want users to pull up the form and have all the input fields pre-filled with the current state of the database (so they don't have to re-key all that), then the database gets updated with they hit submit. Simple to do in HTML, but I can't figure out how to do this with Wash. The inputFields don't seem to take a parameter giving a default, nor does there appear to be any way to set it later. Ideas? Thanks, John

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ANN: HAppS -- Haskell Application Server v 0.2
by S. Alexander Jacobson 22 Feb '05

22 Feb '05

HAppS is a Haskell library for building Internet applications, featuring: * HAppS.ACID: Guarantee application integrity in the face of unplanned outages using this module's integrated write-ahead logging and checkpointing framework. * HAppS.DBMS: Do relational operations in Haskell (rather than SQL) on Haskell sets (outside the IO Monad). Define custom indices for your Haskell datatypes (e.g. geographic/geometric types). Use in combination with ACID for a robust relational DBMS customized for your application. * HAppS.Protocols: Expose your application using as an HTTP server and/or by recieving and sending SMTP. - License HAppS is released by HAppS.org under the terms of the GNU General Public License Version 2, a copy of which is enclosed with this package. - How do I get HAppS? More information is available at http://HAppS.org A tarball of HAppS is available at http://HAppS.org/HAppS/happs.tar.gz. HAppS is also available via darcs: darcs get http://happs.org/HAppS ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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RE: [Haskell-cafe] Problems building GreenCard
by Simon Peyton-Jones 22 Feb '05

22 Feb '05

-fno-prune-tydecls is a dead flag. Just remove it. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Dmitri Pissarenko | Sent: 15 February 2005 21:04 | To: haskell-cafe(a)haskell.org | Cc: sof(a)galois.com; alastair(a)reid-consulting-uk.ltd.uk | Subject: Re: [Haskell-cafe] Problems building GreenCard | | Hello! | | I could fix the problem by replacing the line | | GHC_OPTS = -cpp -fglasgow-exts -fno-prune-tydecls | | in file lib/Makefile by this one | | GHC_OPTS = -cpp -fglasgow-exts | | However, I don't know what this -fno-prune-tydecls does and whether it is | important (for using Green Card to access Java). | | Best regards | | Dmitri Pissarenko | -- | Dmitri Pissarenko | Software Engineer | http://dapissarenko.com | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: New to haskell: unresolved overloading question
by Christian Maeder 22 Feb '05

22 Feb '05

Blair Fraser wrote: > I'm new to haskell and I'm working through the class section of the > gentle tutorial. I decided to implement an ApproxEq class (just for > fun), but have run into problems. The code below works fine for units > and bools, but gives an unresolved overloading error for Floats and > Doubles. What's going on here? What does the error message mean and > what did I do wrong? (I'm in Hugs.) > > -- ApproxEq: My first class. > class (Eq a) => ApproxEq a where > (~=) :: a -> a -> Bool > x ~= y = x == y -- By default, check equality > > -- These two override default with same, just checking if it works > instance ApproxEq () where () ~= () = True > instance ApproxEq Bool where x ~= y = x == y > > -- These two override default with different > -- consider floating points equal if they differ by one or less > instance ApproxEq Float where x ~= y = (abs (x-y) <= 1) > instance ApproxEq Double where x ~= y = (abs (x-y) <= 1) More elegant seems to be: instance (Ord a, Num a) => ApproxEq a where x ~= y = (abs (x-y) < 1) However, this requires extensions to "Allow unsafe overlapping instances": hugs -98 +O ghci -fglasgow-exts -fallow-overlapping-instances -fallow-undecidable-instances -fallow-incoherent-instances > -- This one dosn't work either, but it just depends on the other two > instance ApproxEq a => ApproxEq [a] where > [] ~= [] = True > (x:xs) ~= (y:ys) = x ~= y && xs ~= ys > _ ~= _ = False > > Thanks, > Blair

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Re: New to haskell: unresolved overloading question
by Christian Maeder 22 Feb '05

22 Feb '05

Tomasz Zielonka wrote: > Why not forget about ApproxEq for () and Bool and simply define a > function? > > (~=) :: (Ord a, Num a) => a -> a -> Bool > x ~= y = abs (x-y) < 1 Indeed, this works best. The instance for lists is also not too important. Christian

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Literate Haskell
by Dmitri Pissarenko 22 Feb '05

22 Feb '05

Hello! I'm curious what experienced Haskellers think about using literate Haskell in daily work. It seems to me like a good idea, since during coding it often helps to write down one's thoughts (often, I find a solution to a complicated problem in this way). What are your experiences with using literate Haskell? TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Re: [Haskell-cafe] Problems with building GCJNI 1.2
by Antony Courtney 21 Feb '05

21 Feb '05

Hi, Sorry for not jumping in on this discussion sooner. I am the author of GCJNI. GCJNI was developed back when Hugs was the dominant Haskell implementation and GreenCard was the easiest/best way to do foreign language bindings for Haskell because the FFI proposal was still in the formative stages. These days, the Haskell FFI addendum is stable and widely implemented, ghc has become much more widely available and easy to install and use, and (without wishing to sound harsh), GreenCard's FFI code generator was broken and useless the last time I tried to use it (a few years ago). I actually ported GCJNI to the Haskell FFI a few years ago, getting rid of ALL use of GreenCard. I used ghc's 'hsc2hs' tool to help with the marshalling, and made no attempt to port to hugs. I called this newer system 'hsjni'. It worked very well for my needs (using the Java2D rendering engine as the back-end for a prototype Haskell GUI system). I never released hsjni simply due to lack of time while finishing my thesis. I invested a little effort in trying to test hsjni with the latest JDK and get a release together in December, but it got snagged on a silly little bug in hsc2hs's handling of paths which have embedded spaces. A minor bug, to be sure, but since the default installation location for the JDK under Windows is under "C:\Program Files", the bug meant hsjni couldn't work out-of-the-box for the most common installation of the prerequisites. Simon Marlow has since fixed this bug in CVS head; I'm just waiting for the next release of ghc with this fix available before I try again. If you think you'd be interested in having a shot at building 'hsjni' (or you are interested in maintaining it), let me know, and I'll make the sources available for you. Caveat is that I haven't tested it since JDK 1.3, because of this hsc2hs issue. My appologies for not mentioning any of the above on the GCJNI web page. Hopefully the whole GCJNI release and web pages can be deprecated soon, with hsjni offered in its place. Kind Regards, -Antony -- Antony Courtney email: antony(a)aya.yale.edu New York, NY WWW: http://www.apocalypse.org/~antony

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[darcs #222] performance problem with massive changes in a single file
by David Roundy via RT 21 Feb '05

21 Feb '05

I'm cc'ing haskell-cafe on this darcs bug, since I imagine there might be a student (or professor) hanging around there who might be interested in the implementation of an efficient LCS algorithm in haskell. [markjugg - Sun Feb 20 09:15:57 2005]: > Typically in software, 1000's of line aren't changed at the time, which > is why this hasn't been an big issue before. Indeed. The issue here is that darcs uses the exact Hunt-Szymanski LCS algorithm when it computes the diff, while GNU diff uses an approximate --but faster--algorithm, which works "almost" as well. The approximate algorithm is reasonably well-documented, but more complex to implement than the exact one, just because it's harder to understand. This would be a reasonable project for an interested haskell CS student. The LCS is implemented in pure haskell 98, and is of signature lcs :: Ord a => [a] -> [a] -> [a] It's an interesting problem that's easily testable, and has different scaling behavior in different limits (finite alphabet, infinite alphabet, permutations of unique objects). David (ever optimistic for new contributors to darcs!) http://darcs.net

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