March 2003 - Haskell - Haskell.org

source layout
by Per Larsson 06 Mar '03

06 Mar '03

Hi all, I'm looking for some kind of style-guide for layout and indentation of haskell source code, can anyone help me? Thanks, Per

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Re: random permutations
by George Russell 06 Mar '03

06 Mar '03

Andreas wrote > Well, sorting is a special case of permuting, so my idea was to use the library > routine > > List.sortBy :: (a -> a -> Ordering) -> [a] -> [a] > > passing it a comparison function which ignores its arguments and simply returns > a random bit when invoked, e.g. > > permute = sortBy $ \_ _ -> if random() then GT else LT > > Unfortunately, this one-line hack is impossible since random numbers rely on > state and sortBy is not prepared for use with a monad. No this is an extremely bad way of doing it, since some permutations will come up more than others. (Consider what happens with a three-element list.) I think Ralf Hinze's method is the best presented so far. I would write it slightly differently though. In pseudo-code I would proceed as follows: (1) write the values to an array a[1]..a[n] (2) for i from n to 2 do j <- random integer between 1 and i swap a[i] and a[j] At the end the elements of a will be a random permutation. In Haskell you can of course use an STArray for this. Ralf Hinze's method requires you to do n multiplications and n divisions to compute the factorial and then compute a random number. I have to compute n random numbers rather than a single random number, on the other hand I don't have to do the multiplications and divisions. Indeed, since you need more random bits to compute a random big number than a random little number, I don't think in theory my method requires much more work from the random number generator than Ralf Hinze's.

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Random Permutations
by Markus.Schnell＠infineon.com 06 Mar '03

06 Mar '03

Is there a library routine for random permutations? I didn't find any and did a quick hack, which works fine for my application (length of list < 100), but what would be a more elegant way? > permute :: StdGen -> [a] -> [a] > permute gen [] = [] > permute gen xs = (head tl) : permute gen' (hd ++ tail tl) > where (idx, gen') = randomR (0,length xs - 1) gen > (hd, tl) = splitAt idx xs Markus -- Markus Schnell, Infineon Technologies AG

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ANNOUNCE: hmake-3.07
by Malcolm Wallace 06 Mar '03

06 Mar '03

hmake-3.07 ---------- http://www.haskell.org/hmake We announce a new release, 3.07, of hmake, the automatic compilation manager for Haskell programs. This fresh version has the following improved configuration features over previous releases: * Hmake now once again builds cleanly with GHC under Cygwin. * Better handling of config files. Your personal config file is now used as an override for the system-wide config file, rather than being used instead of it. Hence, any global config updates are now automatically propagated to all users. * The new command `hmake-config new' is now needed to begin a fresh personal config file, rather than one being created for you silently against your expectations. * `hmake-config list' can now take a specific compiler argument to show detailed info for that compiler. Regards, Malcolm

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RE: source layout
by Bayley, Alistair 06 Mar '03

06 Mar '03

> There are various pretty-printing libraries for Haskell, for example: Yeah, but that's only half the job. You have to combine these with a Haskell parser in order to get a program with the functionality of (say) 'indent' (or have I misunderstood what the libraries do?) I though this was quite good (but I still use tabs - horrors...) http://www.cs.bris.ac.uk/Teaching/Resources/COMS12100/java/style.html -----Original Message----- From: shae(a)webwitches.com [mailto:shae@webwitches.com] Sent: 06 March 2003 15:08 To: Per Larsson Cc: Haskell Mailing List Subject: Re: source layout Per Larsson <per(a)L4i.se> writes: > I'm looking for some kind of style-guide for layout and indentation of haskell > source code, can anyone help me? There are various pretty-printing libraries for Haskell, for example: http://www.haskell.org/ghc/docs/latest/html/haskell-src/Language.Haskell.Pre tty.html http://www.haskell.org/ghc/docs/latest/html/base/Text.PrettyPrint.html http://www.cs.uu.nl/~daan/pprint.html For editors, there's haskell-mode for emacs which does a good job of indenting intelligently. I've heard the vim mode works well also. A bit of googling turned up these: http://www.haskell.org/~simonmar/libraries/libraries.html http://www.cs.ou.edu/~rlpage/fpclassFall96/handouts/styleGuide.html http://www.cs.bris.ac.uk/Teaching/Resources/COMS12100/java/style.html Hope this helps, -- Shae Matijs Erisson - 2 days older than RFC0226 #haskell on irc.freenode.net - We Put the Funk in Funktion 10 PRINT "HELLO" 20 GOTO 10 ; mapM_ putStrLn $ fix ("hello":) ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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RE: Persistant (as in on disk) data
by Simon Marlow 06 Mar '03

06 Mar '03

> a recent post reminded me of a feature i'd like. > for all i know it is already implemenetd in GHC so pointers > are welcome. > > i'd like to be able to dump data structures to disk, and later load > them. A Binary library was discussed recently on the libraries list. The thread starts here: http://www.haskell.org/pipermail/libraries/2002-November/000691.html It's currently stalled. There are several implementations of Binary: one that comes with NHC and is described in a paper (sorry, don't have a link to hand), a port of this library to GHC by Sven Panne (suffers from bitrot), a derived/simplified version used in GHC which is heavily hacked for speed, and a further derived version of this library by Hal Daume who is adapting it to support bit-by-bit serialisation. I think the outstanding issues are (a) is the API for GHC's Binary library acceptable, or do we need the extra bells and whistles that the NHC version has? (b) can we make a version of Binary that uses a bit-by-bit rather than byte-by-byte serialisation of the data that is as fast (or nearly as fast) as the current byte-by-byte implementation? Perhaps performance isn't that important to the majority of people: please comment if you have an opinion. (c) how do we derive instances of Binary? IMHO: something is better than nothing, so I'd be in favour of just plugging in the Binary library from GHC, and marking it "experimental". Cheers, Simon

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BCTCS 19
by N Ghani 06 Mar '03

06 Mar '03

**** <We apologize for multiple postings.> **** Please can you publicise this amongst your colleagues and particularly PhD students who could take advantage of our grants for accommodation etc +---------------------------------------------------------------------+ CALL FOR PARTICIPATION British Colloquium on Theoretical Computer Science 7th - 9th April 2003 Leicester, United Kingdom http://www.mcs.le.ac.uk/events/bctcs19/ The British Colloquium for Theoretical Computer Science (BCTCS) is an annual conference providing a forum for research in all areas of theoretical computer science. As such, it aims to provide an informal setting within which researchers can meet and discuss recent developments and results in the broad swathe of the subject rather than in just their own area of specialty. The BCTCS is also dedicated to the development and training of postgraduate research students. Indeed, the relaxed nature of the conference provides an excellent environment where postgraduate students may gain the experience of presenting their work to their colleagues and benefit from contact with established researchers in the community. A number of grants are available to fund the accommodation and registration costs of postgraduate students who are willing to give talks. This year, we are pleased to have invited talks in the areas of programming language semantics, category theory, algorithms, formal languages and automata theory given by Prof A. Jung, University of Birmingham, UK Prof F.W. Lawvere, State University of New York, USA Prof K. Mehlhorn, Universitaet des Saarlandes, Germany Dr S. Muthukrishnan, Rutgers University, USA and AT&T Prof. J. Pin, Universite Paris Denis Diderot et CNRS, France Further details of the program etc will be available from the website http://www.mcs.le.ac.uk/events/bctcs19/ and registration, travel, costs etc can be found at http://www.le.ac.uk/conference/bctcs/ For any other issues, please contact bctcs19(a)mcs.le.ac.uk Neil Ghani Dr Conference Organiser +---------------------------------------------------------------------+ | Dr Neil Ghani Email : ng13(a)mcs.le.ac.uk | | Dept of Maths and Computer Science Web : www.mcs.le.ac.uk/~ng13 | | University of Leicester | | University Rd, | | Leicester LE1 7RH Phone : +44 (0)116 252 3807 | | United Kingdom Fax : +44 (0)116 252 3915 | +---------------------------------------------------------------------+

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RE: URI handling code in Haskell available
by Simon Marlow 06 Mar '03

06 Mar '03

> Oops. I didn't find that. Thanks for the pointer. (Thinks: > does it work with HUGS?) It works with the latest hugs, November 2002 (use "hugs +N" to get the hierarchical libraries). > A significant amount of my work went into the test cases and > matching the > parsing code against the (revised work-in-progress) URI spec, > so maybe > there's some residual value there...? When I wrote Network.URI I took the grammar from the RFC, and also a bunch of test cases, which are in GHC's testsuite (fptools/testsuite/tests/ghc-regress/lib/net/uri001.hs). It might not be up to date with the latest rev of the spec, however. Any extra testing you can do and/or comments you have on the API would be appreciated. One thing I know is questionable is that parseURI returns a Maybe URI, when in fact there are no strings for which it can return Nothing (*everything* is a valid URI, it seems!). Cheers, Simon

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www.haskell.org/libraries - a suggestion
by Graham Klyne 06 Mar '03

06 Mar '03

Prompted by my overlooking the GHC library URI code, may I suggest that a reference to the GHC network library be added to the Libraries page at: http://www.haskell.org/libraries/#xml #g ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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Re: Persistant (as in on disk) data
by mike V 06 Mar '03

06 Mar '03

Here is my post from the ffi mail list and some comments. Although not directly related to your question, I believe this whole issue merits further discussion, which unfortunately did not ensue with my post on the ffi mail list. And indeed from time to time it does seem to pop-up. I guess it is like the uncomfortable bed, never uncomfortable enough to be rid of. 1. The answer to your question: look at the Binary package (haskell libs) which implements a class Binary that allows binary IO, whether this package suffers from bit rot I don't know. 2. That haskell does not support a "Binary IO Standard" I believe to be an issue. An issue which with the advent of a "Standard FFI" is ripe to be addressed. 2.1. The binary package mentioned above implements it's own marshalling library which could to some extent(see 2.2.1) be subsumed by the FFI libraries. 2.2. The function of the Binary Class could be replaced by the Class Storable .ie. what is Storable can be written. 2.2.1 Notwithstanding the above, Class Binary may still be required. Haskell may opt for a "Standard Serialised" format across all platforms - this distinction comes into play with Big-endian vs little-endian int representations etc. Which for Storable does not come into play as by default you whish to have the same representation as the standard platform representation. Candidate representations could be ASN, XDR there are plenty of them (I believe that DCE, CORBA, Java etc all define some sort of standard serialisation). 2.2.1.1 There may be a need to define a set of data types similar to the CForeign package eg XDRInt etc, but on first inspection I believe them to be unnecessary. 2.2.2 A standard serialised binary representation would be of some benefit allowing sharing of binary files across platforms. 2.3 Class Storable or Binary could be made derivable, thereby facilitating the easy marshalling of structures to disk, see note below. 2.4 I guess it all comes down to whether the Haskell community feels that no standard binary io is ok. deriving instances of Storable Wed, 05 Feb 2003 20:37:25 +1100 Previous message: haskell finalisers driven underground Next message: deriving instances of Storable Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] -------------------------------------------------------------------------------- Is there any merit in the idea of allowing instances of Storable to be derived in a similar fashion to Show, providing that constituents are of class Storable. for instance (Int, Int) two Ints would be marshalled into consecutive memory locations in their order of declaration. (Int,String) an Int followed by a String dealing with constructors ========================== data X = X1 Int | X2 deriving Storable data Y = Y1 | Y2 deriving Storable three possible alternatives spring to mind A) Indexing Constructors by position X1 -> 0:Int X2 -> 1 where 0, 1 represent the constructor indexes ":" represents that the data items are physically contiguous "->" reads "marshalled as" This has the disadvantage of being sensitive to the constructor order B) using the constructor name as the index X1 -> X1:Int X2 -> X2 has the disadvantage of requiring a variable amount of memory for the tag. C) some other hash on the constructor name ? I would think that implementation would be fairly straight forward? The benefits would be significant - automatic marshalling of structures. uses: storing to disk, passing over network etc etc.. _________________________________________________________________ Hotmail now available on Australian mobile phones. Go to http://ninemsn.com.au/mobilecentral/hotmail_mobile.asp

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