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RE: Hash in Haskell
by Garner, Robin 17 Jun '03

17 Jun '03

Stable names/references may be what you need. http://research.microsoft.com/~simonpj/Papers/weak.htm Cheers -----Original Message----- From: Sergio Sebastián Giro [mailto:sergio@fceia.unr.edu.ar] Sent: Tuesday, 17 June, 2003 12:08 PM To: gilesb(a)cpsc.ucalgary.ca Cc: haskell(a)haskell.org Subject: Re: Hash in Haskell On Mon, 16 Jun 2003 gilesb(a)cpsc.ucalgary.ca wrote: Thanks anyway, but I want to maintain a set of elements of some (fixed) unknown type. In a hash table, I can see in O(1) aprox. if the element belongs or not to set. > Typically, such functions are often used to implement mappings from > something (such as a String) to something else. > > If that is what you want take a look at the type FiniteMap under the > Data area of GHC and HUGS. It implements all the needed functionality > without having to worry about creating a Hash for the keys. > > If you want if for some other reason, you would typically need to define > a class such as: > > Class Hash where > hash::a->Int > > and then implement it on your desired types. Strings are ususally > somewhat easy to create a unique has value, other types will, naturally, > depend on what is in them. > > > > On 16 Jun, Sergio Sebastián Giro wrote: > > Hi, I need some function in Haskell to hash any value from any type to > > Int. I guess that such a function needs to be a primitive, but I don't > > found it in Hugs. Do you know how I can implement it or found it? > > Thanks > > Sergio > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > > -- > Brett G. Giles > Grad Student, University of Calgary > Formal Methods, Category Theory, Semantics of Programming > http://www.cpsc.ucalgary.ca/~gilesb mailto:gilesb@cpsc.ucalgary.ca > > _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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Hash in Haskell
by Sergio Sebastián Giro 17 Jun '03

17 Jun '03

Hi, I need some function in Haskell to hash any value from any type to Int. I guess that such a function needs to be a primitive, but I don't found it in Hugs. Do you know how I can implement it or found it? Thanks Sergio

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FM 2003 Call for Participation
by mailinglist-admin＠fmeurope.org 16 Jun '03

16 Jun '03

Sorry if some of you receive multiple copies of this message. Stefania Gnesi (FM2003 General Chair) ============================================================================== Call for Participation ------------------------------------------------------------------------------ The 12th International FME Symposium Pisa, Italy - September 8-14, 2003 http://fme03.isti.cnr.it - fme03(a)isti.cnr.it ------------------------------------------------------------------------------ FM 2003 is the twelfth in a series of symposia organized by Formal Methods Europe, an independent association whose aim is to stimulate the use of, and research on, formal methods for software development. These symposia have been notably successful in bringing together a community of users, researchers, and developers of precise mathematical methods for software development as well as industrial users. Formal methods have been controversial throughout their history, and the realization of their full potential remains, in the eyes of many practitioners, merely a promise. Have they been successful in industry? If so, under which conditions? Has any progress been made in dispelling the skepticism that surrounds them? Are they worth the effort? Which aspects of formal methods have become so well established in the industrial practices to loose the "formal method" label in the meanwhile? FM 2003 aims to answer these questions, by contributions not only from the Formal Methods community but also from outsiders and even from skeptical people who are most welcome to explain, document, and motivate the source of their reluctance. Satellite Events FM 2003, will host 7 Workshops, 8 Tutorials and 1 Day dedicated to the Industry besides the 3 days of the FME Symposium. Tool demonstrations will also take place during the symposium, with the opportunity of holding presentations for each tool. For full details on the Symposium organization and to register please see the web site http://fme03.isti.cnr.it, or send your query to <mailto:fme03@isti.cnr.it>fme03(a)isti.cnr.it.

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Typesafe MRef's
by George Russell 16 Jun '03

16 Jun '03

Keith wrote (snipped) > But George Russell's implementation relied on looking up something in > one map with a key obtained from another map. I thought type-safe > MRefs should disallow this. However if you disallow lookup up in one map with a key from another, then Ralf Hinze's solution of putting the value inside the key uses no type extentions and works perfectly well (though is probably not quite what was intended).

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hiddencode
by Steffen Mazanek 16 Jun '03

16 Jun '03

Hello, I am using literate programming with \begin{code}...\end{code}. But there is one problem. I want to hide some code of a module in my documentation. Therefore another environment, e.g. called hiddencode, would be very useful. To make things more general: Is there the possiblity to add other code environments? If not I would prefer a command line option. What do you think about this? Ciao, Steffen -- Steffen Mazanek - www.steffen-mazanek.de - GPG: 791F DCB3 Haskell, that's where I just curry until fail, unwords any error, drop all undefined, maybe break, otherwise in sequence span isControl and take max $, id: (d:[])

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RE: Typesafe MRef with a regular monad
by Simon Peyton-Jones 16 Jun '03

16 Jun '03

| If you use Simon PJ's type signatures, you can't really disallow using | a key from one map with another map. Yes, that's a good point. So there are really three issues: a) single-threaded-ness b) making sure you look up in the right map c) making sure the thing you find has the right type Even if you have typed keys, (Key a), then if you look them up in the wrong map, any guarantee that it maps to a value of type 'a' is out of the window. I can think of two solutions i) Guarantee that keys are unique across all maps, so that a key from one map is never in the domain of another. ii) Use the (ST s) and (STRef s) trick, to connect the key with the map. This seems cleaner, but demands more of the programmer. But my main point remains: that some form of typed finite map ought to exist that does no dynamic type checks, because none are necessary. This must be a terribly old problem; and unsafeCoerce seems like a rather brutal "solution". Simon

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problems with working with Handles
by Niels Reyngoud 15 Jun '03

15 Jun '03

Hello, We're two students from the department of computer science at the University of Utrecht (the Netherlands), and we're havind some severe difficulties in working with file handles in Haskell. Consider for example the following program: main = do --let inputfile = "input.txt" let inputtext = "testit" let outputfile = "output.txt" writeFile outputfile "" handle2 <- openFileEx outputfile (BinaryMode WriteMode) hPutStr handle2 (inputtext ++ " extra") handle3 <- openFileEx outputfile (BinaryMode ReadMode) inputtext2 <- hGetContents handle3 handle4 <- openFileEx outputfile (BinaryMode WriteMode) hPutStr handle4 (inputtext ++ " extra2") The text which should be in the outputfile is "testit extra extra2", instead "testit extra2" is written in. Another strange problem is with the following program: ------------- main = do putStr "Give inputfile for use of Super encoding\n" inputfile <- getLine handle <- openFileEx inputfile (BinaryMode ReadMode) text <- hGetContents handle putStr "Give outputfile for use of Super encoding\n" outputfile <- getLine encode text outputfile encode :: String -> String -> IO() encode text outputfile = do outputhandle <- openFileEx outputfile (BinaryMode WriteMode) bwt (runlengthEncode text) outputhandle bwthandle <- openFileEx outputfile (BinaryMode ReadMode) bwttext <- hGetContents bwthandle tracer' bwttext mtfhandle <- openFileEx outputfile (BinaryMode WriteMode) hPutStr mtfhandle (arithmeticEncode (runlengthEncode (movetofront bwttext))) tracer' :: String -> IO() tracer' x = writeFile "temp.txt" x ------------- This only seems to work when we're calling 'tracer' ', so if we're actually doing somewhing with "bwttext" before using it... Also, we're wondering when you can close a handle. Personally we thought you could close it if you are "done" with it, yet if you've captured the contents of a file like this: handle <- openFileEx inputfile (BinaryMode ReadMe) text <- hGetContents handle hClose handle putStr text no text appears on the screen; "text" seems empty. We're testing on a Windows machine by the way. Regards, Niels Reyngoud and Richard Nieuwenhuis

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main modules in GHC, deriving differences between GHC and Hugs
by Graham Klyne 13 Jun '03

13 Jun '03

GHC seems to require a 'main' module in a file in order to generate an exe file. This makes it awkward to create unit test programs, because I generally create one (to run stand-alone) for each major module. Now I want to create a "master test" module that runs all the individual module tests. But if the module tests are all "main" modules it seems I cannot bring them all together into a larger program. Have I overlooked any way to create an executable program from any module containing a main function of the appropriate type? There also seems to be a difference in the way that GHC and Hugs handle deriving clauses. I haven't pinned this down, but I can try to provide more information if this is something the compiler developers not already aware of. #g ------------------- Graham Klyne <GK(a)NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E

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Re: Typesafe MRef with a regular monad
by cwitty＠newtonlabs.com 13 Jun '03

13 Jun '03

Keith Wansbrough <Keith.Wansbrough(a)cl.cam.ac.uk> writes: > > In article <v4j7k7qsp5c.fsf(a)newtonlabs.com>, > > cwitty(a)newtonlabs.com (Carl R. Witty) wrote: > > > > > Here's a hand-waving argument that you need either Typeable (or > > > something else that has a run-time concrete representation of types) > > > or ST/STRef (or something else, probably monadic, that can track > > > unique objects) to do this. > > > > George Russell already showed this, didn't he? You can implement > > Typeable given type-safe MRefs, and you can implement type-safe MRefs > > given Typeable. > > But George Russell's implementation relied on looking up something in > one map with a key obtained from another map. I thought type-safe > MRefs should disallow this. If you use Simon PJ's type signatures, you can't really disallow using a key from one map with another map. Carl Witty

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Re: problems with working with Handles
by Tomasz Zielonka 13 Jun '03

13 Jun '03

On Fri, Jun 13, 2003 at 10:57:21AM -0400, Dean Herington wrote: > Tomasz Zielonka wrote: > > > One can also use Strategies module that comes with GHC (in package > > concurrent), for example: > > Could you tell me more specifically where to find the Strategies module in > GHC? I couldn't find it in the documentation. [tomekz@green load]$ ghci -package concurrent ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.0, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading package concurrent ... linking ... done. Prelude> :m + Strategies Prelude Strategies> :m + IO Prelude Strategies IO> h <- openFile "/etc/termcap" ReadMode Prelude Strategies IO> cs <- hGetContents h Prelude Strategies IO> putStrLn "hmm" `demanding` rnf cs hmm Prelude Strategies IO> hClose h Prelude Strategies IO> length cs 737535 Prelude Strategies IO> Note that you have to use -package Strategies option. I couldn't find this module in the hierarchical libraries. The same works in GHC 5.04.3 To GHC developers: What is the status of this module? Can I assume that future versions of GHC will have it? > Thanks. > Dean Best regards, Tom -- .signature: Too many levels of symbolic links

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