July 2001 - 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

3 2

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

2 1

Re: lexical description problem in language report?
by Wolfgang Lux 02 Aug '01

02 Aug '01

Thomas Hallgren wrote > There seems to be a similar problem with qualified identifiers. The > production for lexeme includes varid, conid, etc, rather than qvarid, > qconid, etc. (Perhaps someone forgot to update it when qualified names > were introduced, in Haskell 1.3...) Sorry we must have a different version of the report, but in my copy and also in the version on Simon PJ's web-pages section 2.4 (in the last paragraph) and appendix B include productions for the qualified identifiers. Wolfgang -- Wolfgang Lux Phone: +49-251-83-38263 Institut fuer Wirtschaftinformatik FAX: +49-251-83-38259 Universitaet Muenster Email: wlux(a)uni-muenster.de

4 3

Graphical User Interface Libraries
by Juan Ignacio Garcia Garcia 01 Aug '01

01 Aug '01

Does anybody know a GUI library which goes OK with ghc-5? I have been looking for one, but it seems that they only can be used with old versions of ghc or with hugs. Thanks in advance, J. I. García

2 1

Re: Haskell -- confirmation of subscription -- request 834452
by Gonzalo Cobos Bergillos 31 Jul '01

31 Jul '01

confirm 834452

1 0

Special 1/4 Page printing prices!!!!
by James Horne 31 Jul '01

31 Jul '01

Stellar Concepts and Design Can offer you: 5000 ¼ Page Flyers, full color, Free UV Lamination--$199 5000 Business Cards, Full Color, Free UV Lamination--$199 5000 Business Cards, 5000 Brochures, 5000 Flyers--$999 If you are interested email us @ jhorne(a)stellarconcepts.com Or call 954.489.2250 ext. 14 Fax-954.489.2280

1 0

simple question
by Cagdas Ozgenc 31 Jul '01

31 Jul '01

Hi, I am trying to do some exercies in my Haskell book. I couldn't get my program to work correctly. type Database2 = [ (Person,[ Book ]) ] exampleBase2 :: Database2 exampleBase2 = [ ("Alice", [ "Tintin", "Astrix" ] ), ("Anna", [ "Little Woman" ] ), ("Rory", [ "Tintin" ] ) ] books2 :: Database2 -> Person -> [Book] books2 db person = head [ snd tuple | tuple <- db, fst tuple == person ] borrowers2 :: Database2 -> Book -> [Person] borrowers2 db book = [ person | (person, books) <- db, book <- books ] borrowers2 function should return the names of people that borrowed the "book". However my implementation lists all the people. Book, and Person are of type String. Also could you comment on the quality of the implementation of "books2" function, which is supposed to return the name of the books that a person borrowed (It is working correctly). Thanks

2 1

Re: adventure game
by Ketil Malde 30 Jul '01

30 Jul '01

stanley goof <stanley_goof(a)yahoo.fr> writes: > I am planning to write a text-adventure game in > haskell. Right. > This is the type of game in which you can execute many > commands like 'take'(to take an object), 'goto' to > move from a room to another room, 'look'(to see the > objects in a room), 'open'(to open a drawer), ... I think perhaps Haskell is not ideal for this. Basically, you're describing lots of objects, on each of which you can peform certain actions depending on its type and state. If this doesn't ring a bell with you, I'll spell it out: Object Orientation. :-) You could of course do it in Haskell, and I'm toying with a simulation engine in it which isn't entirely different. I just don't think it's optimal, in particular if you're looking for a problem to hone your Haskell skills on. -kzm -- If I haven't seen further, it is by standing in the footprints of giants

1 0

foldl'
by Jon Fairbairn 28 Jul '01

28 Jul '01

Unless I'm mistaken, foldl' (the strict version of foldl) doesn't appear in (the export list of) the standard prelude or the list library. Is there a good reason for this? New users quite quickly find that they need it. Jón -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk 31 Chalmers Road jf(a)cl.cam.ac.uk Cambridge CB1 3SZ +44 1223 570179 (after 14:00 only, please!)

1 0

RE: computer language shootout
by brk＠jenkon.com 27 Jul '01

27 Jul '01

GHC ranks quite poorly currently. (I think there's an AWK implementation that's ahead of it, nevermind Ruby or Python). There are still a couple of benchmarks that haven't been implemented yet for Haskell, and a couple more that don't make sense for a non-OO language. I spent a little while working over the examples a month or two ago. I was able to shorten a number of them considerably, and even sped up a few. My difficulty was that I was writing for ghc-4.08 on Cygwin (Doug uses 5.02 on linux), so things that improved the speed on my windows box often reduced the speed on Doug's linux box! I'm still pretty new at Haskell, so it's probably worthwhile for some more expert folks to take a look at all the current implementations. I have to say (and this also relates to the newbie question thread) that I don't understand why GHC fares so poorly, and I guess I find it a little frustrating. It seems as though, by programming in Haskell with all its great semantic properties and opportunities for optimization, the compiler should be able to generate code that's enormously faster than the naive implementation, and easily competitive with C (or at least Ocaml!). Does anyone understand why this isn't the case now? Is it just that these things take time and they're being worked on, or do the techniques for this level of optimization not exist yet for lazy functional languages? Bryn > -----Original Message----- > From: Miles Egan [SMTP:miles@caddr.com] > Sent: Friday, July 27, 2001 7:55 AM > To: haskell(a)haskell.org > Subject: computer language shootout > > I apologize if this question has already been asked, but I couldn't find a > searchable version of the mail archive. > > Doug Bagley's computer language shootout, > http://www.bagley.org/~doug/shootout/, > a collection of mini-benchmarks in several languages, doesn't paint a very > flattering picture of GHC's performance. GHC is even ranked below Ruby > and > Python! Has anyone tried to optimize any of the GHC programs? > > Ocaml fares quite well in these tests and a glance at several of the Ocaml > programs suggests that most of them have been fairly aggressively > optimized. > These kinds of benchmarks are kind of silly, but also a good p.r. > opportunity. > > -- > miles > > "We in the past evade X, where X is something which we believe to be a > lion, through the act of running." - swiftrain(a)geocities.com > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

3 3