April 2002 - Haskell - Haskell.org

tuple component functions
by trb＠eastpac.com.au 03 Jan '03

03 Jan '03

S.D.Mechveliani writes: > As Haskell has the standard functions fst, snd to decompose (a,b), > maybe, it worths to provide also > tuple31, tuple31, tuple31, > ... > tuple51, tuple52, tuple53, tuple54, tuple55 > > for the tuples of n = 3,4,5 ? I've found some of these useful, except I named them differently: > fst3 :: (a,b,c) -> a > fst3 (x,_,_) = x > snd3 :: (a,b,c) -> b > snd3 (_,x,_) = x > thd3 :: (a,b,c) -> c > thd3 (_,_,x) = x .... never got around to quadruples etc. I also defined (some of these may be untested): > tripl :: a -> (a,a,a) > tripl x = (x,x,x) > curry3 :: ((a, b, c) -> d) -> a -> b -> c -> d > curry3 f x y z = f (x, y, z) > uncurry3 :: (a -> b -> c -> d) -> ((a, b, c) -> d) > uncurry3 f t = f (fst3 t) (snd3 t) (thd3 t) > applyTriple :: (a -> b, a -> c, a -> d) -> a -> (b,c,d) > applyTriple (f,g,h) x = (f x, g x, h x) > cross3 :: (a -> b, c -> d, e -> f) -> (a,c,e) -> (b,d,f) > cross3 (f,g,h) (x,y,z) = (f x, g y, h z) > mapTriple :: (a -> b) -> (a, a, a) -> (b, b, b) > mapTriple = cross3 . tripl > applyFst3 :: (a -> b) -> (a, c, d) -> (b, c, d) > applyFst3 f = applyTriple (f . fst3, snd3, thd3) > applySnd3 :: (a -> b) -> (c, a, d) -> (c, b, d) > applySnd3 f = applyTriple (fst3, f . snd3, thd3) > applyThd3 :: (a -> b) -> (c, d, a) -> (c, d, b) > applyThd3 f = applyTriple (fst3, snd3, f . thd3) > applyArgs3 :: (a -> b) -> (c -> d) -> (e -> f) -> (b -> d -> f -> g) -> (a -> c -> e -> g) > applyArgs3 af1 af2 af3 f = \x y z -> f (af1 x) (af2 y) (af3 z) > rotl :: (a -> b -> c -> d) -> (b -> c -> a -> d) > rotl f y z x = f x y z > rotr :: (a -> b -> c -> d) -> (c -> a -> b -> d) > rotr f z x y = f x y z > rotl4 :: (a -> b -> c -> d -> e) -> (b -> c -> d -> a -> e) > rotl4 f y z t x = f x y z t > rotr4 :: (a -> b -> c -> d -> e) -> (d -> a -> b -> c -> e) > rotr4 f t x y z = f x y z t Some more combinators (only for pairs so far): > twin :: a -> (a,a) > twin x = (x,x) > swap :: (a,b) -> (b,a) > swap (x,y) = (y,x) -- apply a pair of functions to one argument > applyPair :: (a -> b, a -> c) -> a -> (b, c) > applyPair (f, g) x = (f x, g x) -- apply a pair of functions to a pair > cross :: (a -> b, c -> d) -> (a, c) -> (b, d) > cross (f, g) = applyPair (f . fst, g . snd) -- compose a pair of functions onto one function > dotPair :: (a -> b, a -> c) -> (d -> a) -> (d -> b, d -> c) > dotPair (f, g) h = (f . h, g . h) -- compose a pair of functions onto a pair of functions > dotCross :: (a -> b, c -> d) -> (e -> a, f -> c) -> (e -> b, f -> d) > dotCross (f, g) (h, i) = (f . h, g . i) > mapPair :: (a -> b) -> (a, a) -> (b, b) > mapPair = cross . twin > applyFst :: (a -> b) -> (a, c) -> (b, c) > applyFst f = applyPair (f . fst, snd) > applySnd :: (a -> b) -> (c, a) -> (c, b) > applySnd f = applyPair (fst, f . snd) > applyArgs :: (a -> b) -> (c -> d) -> (b -> d -> e) -> (a -> c -> e) > applyArgs af1 af2 f = \x y -> f (af1 x) (af2 y) > betweenFst :: (a -> b -> c) -> (a, d) -> (b, e) -> c > betweenFst = applyArgs fst fst > betweenSnd :: (a -> b -> c) -> (d, a) -> (e, b) -> c > betweenSnd = applyArgs snd snd I find these combinators useful, and probably other people have their own versions - it would be nice to get them standardised, so we all speak the same language. By standardised, I mean a prominent version that will be adopted by users, not necessarily a committee process. Tim

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ICFP programming contest
by trb＠eastpac.com.au 03 Jan '03

03 Jan '03

Michael Hobbs writes: > Just took a look at the results for the ICFP contest. Am I correct in > assuming that "LA" stands for Lennart Augustsson and that "Si^3" stands > for Simon Marlow, Simon Peyton-Jones, Sigbjorn Finne? Is there a URL for the results ? Tim

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Type extensions
by Ronald Legere 04 Jun '02

04 Jun '02

Greetings. I have decided to try and understand the type system of haskell with extensions. As far as I can tell, the following set of extensions has been included, for example in ghc: multiparameter type classes constructor classes existential types explicit universal quantification scoped type signatures funtional dep?? Etc There is probably some overlap, and probably missed a few, as i do not understand what all these things do! ! My question: How do you get started learning all this? which of these is the most important? Is there a paper out there that explains most or all of these extensions and why you would want them and HOW the heck they work together? Ron Legere __________________________________________________ Do You Yahoo!? Yahoo! Greetings - send holiday greetings for Easter, Passover http://greetings.yahoo.com/

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MPC 2002: Deadline extended until 11 February
by mpc02 15 May '02

15 May '02

[Apologies for multiple copies] The deadline for MPC 2002, 6th International Conference on MATHEMATICS OF PROGRAM CONSTRUCTION, 8-10 July, Dagstuhl, Germany (see http://www.cs.ukc.ac.uk/conf/mpc2002/ for a full CFP) has been extended until 11 February 2002. Full papers should be submitted in Postscript or pdf format by e-mail to mpc02(a)ukc.ac.uk. -- Mathematics of Program Construction '02 at Dagstuhl Eerke Boiten, Computing Laboratory, University of Kent at Canterbury, UK +44.1227.827615 (fax 762811)

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Announce+Question: jDrIFT
by John Meacham 08 May '02

08 May '02

I often finding myself going back to good old trusty DrIFT, and have over the past few months made a number of changes to it, many of which i think people would appreciate. I was wondering what i should do to get my changes folded into the main drift, or even if there is a main drift any more? new working features I implemented include: * proper GetOpt command line handling, allows you to specify an output file (-o) as well as list all possible derivations this version can use (-l) and some others. * proper LINE pragmas in generated code * smarter error handling in some cases, parser smarter sometimes. * can deal with/ignore as appropriate some ghc extensions now * new rule to derive Typeable used by the Dynamic library. * new rule to derive Observable from the HOOD object debugger * rules to derive Term, a term representation for generic computation, can be used in a similar fashion to the Strafunski one, but has a number of advantages, fully lazy constant time implode/explode being the main one. (the external library is compatable with their work.) and some other patches that i collected from around the net jDrIFT -l lists the following: Binary, Typeable, Term, OldTerm, Implode, Explode, Observable, test, update, is, has, un, NFData, Eq, Ord, Enum, Show, Read, Bounded, Haskell2Xml features in the works: * smarter rule format, allow descriptions (help info) to be embedded, and options to be passed into the rule generators either from the command line or in the DrIFT pragmas themselves. among other things, the code generation should be able to find out what extensions you wish to let them use and let them fail gracefully if one doesnt exist that is needed. * MultiParameter typeclasses * smarter/rethought import chasing rules. * LibDrIFT, simply write your single rule, import libdrift and it will build to a DrIFT module. these modules can be used standalone executables and behave just like the original drift (with your extension), but if placed in a searchable spot, the main jDrIFT implementation will pick them up and integrate their rules into its capabilities. In Any case i made a prerelease of my modified version available at: http://homer.netmar.com/~john/computer/haskell/jDrIFT/ but would like to somehow merge with the main development tree of this tool, if one exists, if it doesnt look like that will happen then perhaps i will have to branch to a new maintained DrIFT inspired project. -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

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Re: Announce+Question: jDrIFT
by Noel Winstanley 30 Apr '02

30 Apr '02

Hi, I'd be happy to transfer ownership of DrIFT to a good home. I've not had the inclination to maintain DrIFT for ages now, for various reasons: my job takes too much of my coding time; I've lost touch with the latest changes to the haskell report / GHC / MPCs whatever etc; and I became dispirited by the reception that DrIFT initially received (no theoretic foundation -- it munges strings!!). It all seemed less important once I escaped academia... Anyhow, its great to hear of the different plans you have for DrIFT -- I'm glad its of some use to you. Good Luck Noel -- Noel Winstanley Engineer - Esgem Limited www.esgem.com Registered in England at 7 Monarch Court, Emerson's Green, Bristol BS16 7FH. Reg No. 3372135 Tel: 0117 957 2345

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read int lists
by Serge D. Mechveliani 30 Apr '02

30 Apr '02

Dear Haskellers, There is certain site (contact daly(a)idsi.net ) where some computer algebra programs are gathered and compared. I submit here my CA program DoCon written in Haskell. And they require certain large set of tests to fill in. It appears also that many of the tests concern Haskell itself (or its implementation libraries) rather than DoCon library. In particular, they require the code for the task: Import two space separated columns of integers from file. The suggestions are: \Axiom & \\ \Derive & [Transfer Load daTa] (from file.dat) \Macsyma & xy: read_num_data_to_matrix("file", nrows, 2) \Maple & xy:= readdata("file", integer, 2): \Mathematica & xy = ReadList["file", Number, RecordLists -> True] \MuPAD & \\ \Reduce & \\ \DoCon (Haskell) & ?? We need main = readFile "data" >>= (putStr . process) If it was one integer list, then, something like process str = read ("[" ++ (map (\ '\n' -> ',') str) ++ "]") :: [Integer] would do. But the file contains something like ----------- 1 2 3 4 ----------- , and it should convert to ([1,2],[3,4]) :: ([Integer], [Integer]) Although I wonder whether other systems do the needed thing, still, can people suggest any shorter/nicer program than the following one? (use advanced lexical libraries, etc. ...) process :: String -> String process str = shows (firstList [] $ dropWhile (== '\n') $ filter (/= ' ') str ) "\n" firstList :: [Integer] -> String -> ([Integer], [Integer]) firstList ns ('\n':'\n':str) = (reverse ns, secondList str) firstList ns str = case reads str :: [(Integer, String)] of [(n,str')] -> firstList (n:ns) str' _ -> (ns, []) secondList :: String -> [Integer] secondList str = case reads str :: [(Integer, String)] of [(n,str')] -> n:(secondList str') _ -> [] Thank you in advance for the help. ----------------- Serge Mechveliani mechvel(a)botik.ru

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Your message to Hugs-Users awaits moderator approval
by hugs-users-admin＠haskell.org 30 Apr '02

30 Apr '02

Your mail to 'Hugs-Users' with the subject ALL RIGHTS RESERVED Is being held until the list moderator can review it for approval. The reason it is being held: Message body is too big: 133189 bytes but there's a limit of 40 KB Either the message will get posted to the list, or you will receive notification of the moderator's decision.

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(no subject)
by Ricky Kurniawan 30 Apr '02

30 Apr '02

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FME 2002: call for participation
by mailinglist-admin＠fmeurope.org 30 Apr '02

30 Apr '02

Dear collegue, FME 2002 is the eleventh in a series of symposia organised by Formal Methods Europe (www.fmeurope.org) 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. Registration for FME 2002 is now open! Please visit http://floc02.diku.dk/FME/ and http://floc02.diku.dk/floc/register.html for more information and and on-line registration. Don't miss out on this event! _______________________________________________ Mailinglist mailing list Mailinglist(a)fmeurope.org http://www.fmeurope.org/mailman/listinfo/mailinglist

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