[Haskell-cafe] Re: What I learned from my first serious attempt low-level Haskell programming
OK, so there are few extra costs for unknown tail calls. First, there might be a pipeline stall if the jump address isn't loaded into a register far enough in advance before the jump. Second, you need to pass information about the number of arguments in the caller. And finally, you need to test the number of arguments in the callee. Under the best of circumstances the argument check costs a load immediate, a compare, and a non-taken branch. But looking at the output from ghc I doubt this is the case. -- Lennart On Apr 10, 2007, at 23:13 , Stefan O'Rear wrote: On Tue, Apr 10, 2007 at 07:59:04PM +0100, Lennart Augustsson wrote: So then tail calls should be very cheap when most of the arguments don't change. On Apr 10, 2007, at 10:17 , Simon Marlow wrote: Lennart Augustsson wrote: It's not that hard to figure out an order to permute the arguments on the stack before a tail call that minimizes that number of moves and temporary locations. Lmlc did this 20 years ago. :) Right, and that's what GHC does too, with a strongly-connected- component analysis of the dependencies between assignments of the args for the tail call. Cheers, Simon The tailcall in question is NOT statically known (it is a variant of CPS), so simpleminded tail recursion optimizations will not help much. Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling GHC
On 30/03/2007, at 4:36 pm, Chris Witte wrote: cp -rp ./../include/* /usr/local/include/mingw cp: cannot stat `./../include/*': No such file or directory The source paths for these copies are derived from the path of the gcc binary ($GccDir). Did you call configure with '--with-gcc=C:/ Mingw/bin/gcc.exe'? I received those errors when I forgot to do that. Loading package base ... linking ... ghc.exe: unable to load package `base' ghc.exe: C:/msys/1.0/local/HSbase.o: unknown symbol `_gettimeofday' I think that 'gettimeofday' is statically linked into the ghc executable, so it's just that GHCi doesn't know about it. Adding a: Sym(gettimeofday) \ line to the RTS_MINGW_ONLY_SYMBOLS #define in rts/Linker.c (from line 265) seemed to fix the problem for me. I'm not sure if this is a GHCi bug or something else being awry. 'gettimeofday' was added to the mingwex library in mingw- runtime-3.10, which was released in July last year, so I would have expected this problem to have come up before now... Regards, Andrew. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: What I learned from my first serious attempt low-level Haskell programming
Lennart Augustsson wrote: So then tail calls should be very cheap when most of the arguments don't change. Yes, but the problem tends to be the arguments that change, and the fact that they are passed on the stack. A C loop would keep the loop-carried variables in registers. On x86_64 you get better code becuase some of the args are passed in registers, but it's not really proper loop optimisation. We know what needs to be done, and we plan to make progress on this soon, hopefully over the summer. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Weaving fun
Thanks for all the wonderful solutions. I put them into one module so other people can try it out: http://hpaste.org/1338 Thanks, Bas van Dijk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: hackage.haskell.org
David Waern wrote: I'd like to set up a Trac for Haddock on hackage.haskell.org. Who should I contact? Let's hold off on this for now. I don't think Haddock warrants a full Trac of its own just yet, the overheads of managing a Trac are pretty high compared to editing the text file called TODO in the root of the Haddock source tree :-) Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Compiling GHC
On 4/11/07, Andrew Appleyard [EMAIL PROTECTED] wrote: The source paths for these copies are derived from the path of the gcc binary ($GccDir). Did you call configure with '--with-gcc=C:/ Mingw/bin/gcc.exe'? I received those errors when I forgot to do that. Yep that fixed that. Thanks. I think that 'gettimeofday' is statically linked into the ghc executable, so it's just that GHCi doesn't know about it. Adding a: Sym(gettimeofday) \ line to the RTS_MINGW_ONLY_SYMBOLS #define in rts/Linker.c (from line 265) seemed to fix the problem for me. I'm not sure if this is a GHCi bug or something else being awry. 'gettimeofday' was added to the mingwex library in mingw- runtime-3.10, which was released in July last year, so I would have expected this problem to have come up before now... I made this change but I still get the error unknown symbol `_gettimeofday' I'm using mingw 5.1.3 which as far as i can tell should use the 3.11 runtime. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weaving fun
I have a simply recursive solution that operates efficiently... Bas van Dijk wrote: Hello, For my own exercise I'm writing a function 'weave' that weaves a list of lists together. For example: weave [[1,1,1], [2,2,2], [3,3]] == [1,2,3,1,2,3,1,2] weave [[1,1,1], [2,2], [3,3,3]] == [1,2,3,1,2,3,1] Note that 'weave' stops when a list is empty. This version of weave works without Data.Sequence or using reverse, (++), or concat: weave :: [[a]] - [a] weave [] = [] weave xss = weave' id xss where weave' _rest ([]:_) = [] -- end when any list is empty weave' rest [] = weave (rest []) -- goto next, check for (weave []) weave' rest ((x:xs):xss) = x : weave' (rest . (xs:)) xss The first parameter of weave' is the usual difference list trick to allow efficient append with simple lists. It works lazily and handles infinite lists. Though if you weave an infinite number of lists together you will get unbounded memory usage. Here it terminates when there is no element after the 15 in the second list: *Main weave [[1..],[11..15],[300..]] [1,11,300,2,12,301,3,13,302,4,14,303,5,15,304,6] -- Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A convenient way to deal with conditional function composition?
Chris Kuklewicz wrote:
Nicolas Frisby wrote:
Not portably.
[EMAIL PROTECTED]:~$ ghc-6.4.2 -e '( (foo++) `Data.Monoid.mappend`
(bar++) ) END'
foobarEND
[EMAIL PROTECTED]:~$ ghc-6.6 -e '( (foo++) `Data.Monoid.mappend`
(bar++) ) END'
fooENDbarEND
-- 6.6 sources
instance Monoid b = Monoid (a - b) where
mempty _ = mempty
mappend f g x = f x `mappend` g x
Stefan
Thanks for the reminder. So the fixed 6.6 code is
import Control.Monad(when)
import Control.Monad.Writer(Writer,tell,execWriter)
import Data.Monoid(Endo(..))
type Writes = Writer (Endo String) ()
data PieceType = Pawn | Other deriving (Eq,Show)
type File = Int
type Square = Int
data Move = Move {
movePiece :: PieceType,
moveFile :: Maybe File,
moveTarget:: Square,
moveIsCapture :: Bool
--movePromotion :: Maybe PieceType
}
deriving (Eq)
instance Show Move where showsPrec = showsPrec_Move
tShow :: Show a = a - Writes
tShow = tell . Endo . shows
tChar :: Char - Writes
tChar = tell . Endo . (:)
tString :: String - Writes
tString = tell . Endo . (++)
showsPrec_Move :: Int - Move - ShowS
showsPrec_Move _ Move { movePiece = p
, moveFile = f
, moveTarget= s
, moveIsCapture = c } = appEndo . execWriter $ do
when (p/=Pawn) (tShow p)
maybe (return ()) tShow f
when c (tChar 'x')
tShow s
testMove = Move Other (Just 6) 10 True
Thanks a lot for all the nice answers, guys.
I have a few remaining questions if you don't mind though. Should
I expect significant performance reduction by using the Writer monad
here, as opposed to the version I wrote? And, most importantly,
I'd like to know how *you* would write this if you had to :-).
Would you juse the Writer monad version?
Thanks,
Maxime
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC 6.6 hangs
Dmitry Antonyuk (lomeo) came up with a piece of code that hung GHC 6.6: newtype Foo a = Foo (Foo a - a) bar x@(Foo f) = f x baz = bar (Foo bar) See the original discussion (in Russian) at: http://lomeo.livejournal.com/35674.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC 6.6 hangs
Hi Dmitry Antonyuk (lomeo) came up with a piece of code that hung GHC 6.6: It's a documented bug in GHC: http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html#bugs-ghc GHC's inliner can be persuaded into non-termination using the standard way to encode recursion via a data type Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: hackage.haskell.org
David Waern wrote: I'd like to set up a Trac for Haddock on hackage.haskell.org. Who should I contact? Let's hold off on this for now. I don't think Haddock warrants a full Trac of its own just yet, the overheads of managing a Trac are pretty high compared to editing the text file called TODO in the root of the Haddock source tree :-) What do you think of the Google bug tracker? Neil and I created a project for Haddock at http://code.google.com/p/haddock/ I'd like to pre-release haddock.ghc and it would be nice to have some place for users to report bugs. /David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: hackage.haskell.org
Let's hold off on this for now. I don't think Haddock warrants a full Trac of its own just yet, the overheads of managing a Trac are pretty high compared to editing the text file called TODO in the root of the Haddock source tree :-) What do you think of the Google bug tracker? Neil and I created a project for Haddock at http://code.google.com/p/haddock/ For reference, it took well under a minute for me to create a new Google Code project, and is unlikely to need maintenance ever. Google rules! Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why Perl is more learnable than Haskell
Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. I've been wanting to learn Haskell for years, literally, but it has been a case of Sisyphus and the Rock. Despite my efforts, I never get to the level of expertise that would make Haskell useful to me. (I don't need elegant factorial or Fibonacci functions in my everyday work.) Sooner or later life intervenes: big project due, long trip abroad, etc., and when I finally return to learning Haskell, I have forgotten almost everything I learned and I have to start all over again. (BTW, I've heard similar stories from many wannabe Haskell programmers.) Arguably, this experience means that I have no business learning Haskell, because it's just not relevant to my work. Maybe so, but I still cling to the fanciful notion that if I knew Haskell well enough, I would find plenty of stuff to do with it in my daily work... Anyway, in contrast to my struggle with Haskell, I learned Perl incrementally over the years, by using it in daily little projects, ranging at first from command-line snippets to 100-line self-contained scripts, and moving on to larger, hairier projects. This daily reinforcement of the little bits of Perl I was picking up was crucial to my being able to retain it and move forward. Perhaps Haskell will never lend itself to something like a Perl one-liner, but still I wish that there were books on Haskell that focused on making Haskell useful to the learner as quickly as possible... If such already exist and I've missed it, please let me know. Or I can always wait until I retire; then I'll probably have a sufficiently long stretch of free time in my hands (barring any operations, strokes, heart attacks, hip fractures, etc.). I bet I could start a Haskell Wannabes Club at the nursing home... kj -- View this message in context: http://www.nabble.com/Why-Perl-is-more-learnable-than-Haskell-tf3559193.html#a9938938 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
kynnjo: Perhaps Haskell will never lend itself to something like a Perl one-liner, but still I wish that there were books on Haskell that focused on making Haskell useful to the learner as quickly as possible... If such already exist and I've missed it, please let me know. There's some things in the works, but for now you can perhaps find something relevant to what you're trying to do here, http://haskell.org/haskellwiki/Blog_articles There's a good breadth of topics covered. Also, I recommend hanging out on #haskell, you'll just see so many interesting haskell snippets, have people to help answer questions, and of course, the lambdabot, that you can't help but learn haskell by osmosis! http://haskell.org/haskellwiki/IRC_channel Good luck. Hope to see you online. -- Don P.S. Have a fix point! Control.Monad.Fix.fix ((1:) . scanl (+) 1) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
My opinion is that learnin haskell is difficult is just for the fact that when you learn programming, you probably begin with C / C++ or some other procedural/OO programming language, so you get used to think in these ways, and when you have to switch to functional paradigm, you find it difficoult. If you first language is LISP probably you find easy Haskell and difficult pearl. 2007/4/11, kynn [EMAIL PROTECTED]: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. I've been wanting to learn Haskell for years, literally, but it has been a case of Sisyphus and the Rock. Despite my efforts, I never get to the level of expertise that would make Haskell useful to me. (I don't need elegant factorial or Fibonacci functions in my everyday work.) Sooner or later life intervenes: big project due, long trip abroad, etc., and when I finally return to learning Haskell, I have forgotten almost everything I learned and I have to start all over again. (BTW, I've heard similar stories from many wannabe Haskell programmers.) Arguably, this experience means that I have no business learning Haskell, because it's just not relevant to my work. Maybe so, but I still cling to the fanciful notion that if I knew Haskell well enough, I would find plenty of stuff to do with it in my daily work... Anyway, in contrast to my struggle with Haskell, I learned Perl incrementally over the years, by using it in daily little projects, ranging at first from command-line snippets to 100-line self-contained scripts, and moving on to larger, hairier projects. This daily reinforcement of the little bits of Perl I was picking up was crucial to my being able to retain it and move forward. Perhaps Haskell will never lend itself to something like a Perl one-liner, but still I wish that there were books on Haskell that focused on making Haskell useful to the learner as quickly as possible... If such already exist and I've missed it, please let me know. Or I can always wait until I retire; then I'll probably have a sufficiently long stretch of free time in my hands (barring any operations, strokes, heart attacks, hip fractures, etc.). I bet I could start a Haskell Wannabes Club at the nursing home... kj -- View this message in context: http://www.nabble.com/Why-Perl-is-more-learnable-than-Haskell-tf3559193.html#a9938938 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- I invented the term Object-Oriented, and I can tell you I did not have C++ in mind. (Alan Kay) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: GHC 6.6 hangs
Neil Mitchell wrote: It's a documented bug in GHC: http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html#bugs-ghc GHC's inliner can be persuaded into non-termination using the standard way to encode recursion via a data type Thanks Neil! Sorry for the noise, I should have checked GHC docs before posting. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
Sorry to hear of your struggles. There has been a lot of work lately on writing Haskell tutorials but there's still a long way to go, unfortunately, as I discovered when I tried recently to find the collection of sample code fragments on the wiki that I'm sure are around somewhere. I had the advantage of coming to Haskell after already having used ML and Common Lisp. But, FWIW, I found it worth persevering: I liked a lot of my legacy Perl scripts more after I ported them to Haskell and now I use Haskell for the sort of thing I might have used bash or perl for previously. (For instance, on the way home last night my GPS' NMEA-0183 data was odd enough that I used Haskell to write a simple daemon that sits between clients and my gpsd and rewrites their conversation; previously, I'd have used Perl for that.) Though, it helps if you get on well with Perl. It didn't suit me very well so I had more motivation to switch than you might. But, now, by choice, I do use Haskell for the kind of thing I'd have previously used a short script for instead, so there might still be light at the end of the tunnel for you. -- Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
I am also coming at haskell from a perl background. While there is some truth to what you say, I do think haskell can be used for keeping simple things simple in a way similar to perl. Though you have to search harder since the documentation / tutorials seem to be more optimized for making hard things possible. (And in fact, much easier than in perl.) But back to the easy, here is a thread concerning one liners in haskell http://groups.google.de/group/fa.haskell/browse_thread/thread/e948ff0ad4d7c0c9/ac0a46d1f841db59?lnk=stq=haskell+one+linersrnum=1hl=en#ac0a46d1f841db59 I think if you really have desire the best route is to complement googling around with asking on #haskell and the newsgroups. It's a *very* friendly community. hope this helps! 2007/4/11, kynn [EMAIL PROTECTED]: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. I've been wanting to learn Haskell for years, literally, but it has been a case of Sisyphus and the Rock. Despite my efforts, I never get to the level of expertise that would make Haskell useful to me. (I don't need elegant factorial or Fibonacci functions in my everyday work.) Sooner or later life intervenes: big project due, long trip abroad, etc., and when I finally return to learning Haskell, I have forgotten almost everything I learned and I have to start all over again. (BTW, I've heard similar stories from many wannabe Haskell programmers.) Arguably, this experience means that I have no business learning Haskell, because it's just not relevant to my work. Maybe so, but I still cling to the fanciful notion that if I knew Haskell well enough, I would find plenty of stuff to do with it in my daily work... Anyway, in contrast to my struggle with Haskell, I learned Perl incrementally over the years, by using it in daily little projects, ranging at first from command-line snippets to 100-line self-contained scripts, and moving on to larger, hairier projects. This daily reinforcement of the little bits of Perl I was picking up was crucial to my being able to retain it and move forward. Perhaps Haskell will never lend itself to something like a Perl one-liner, but still I wish that there were books on Haskell that focused on making Haskell useful to the learner as quickly as possible... If such already exist and I've missed it, please let me know. Or I can always wait until I retire; then I'll probably have a sufficiently long stretch of free time in my hands (barring any operations, strokes, heart attacks, hip fractures, etc.). I bet I could start a Haskell Wannabes Club at the nursing home... kj -- View this message in context: http://www.nabble.com/Why-Perl-is-more-learnable-than-Haskell-tf3559193.html#a9938938 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
-Original Message- From: Mark T.B. Carroll [EMAIL PROTECTED] Sent: Apr 11, 2007 10:18 AM To: kynn [EMAIL PROTECTED] Cc: haskell-cafe@haskell.org Subject: Re: [Haskell-cafe] Why Perl is more learnable than Haskell Sorry to hear of your struggles. There has been a lot of work lately on writing Haskell tutorials but there's still a long way to go, unfortunately, as I discovered when I tried recently to find the collection of sample code fragments on the wiki that I'm sure are around somewhere. A serious omission in Haskell tutorials is a collection of examples of how to write Haskell solutions for problems that would use arrays in any imperative language. I see that arrays can be defined in Haskell, but I don't see their use as computationally efficient in Haskell. http://RepublicBroadcasting.org - Because You CAN Handle The Truth! http://iceagenow.com - Because Global Warming Is A Scam! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On Wed, Apr 11, 2007 at 05:55:08AM -0700, kynn wrote: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) i find that don's haskell hacking blog has been written with the daily hacker in mind: http://cgi.cse.unsw.edu.au/~dons/blog my own experience is that i would gladly replace perl for many tasks if haskell's libraries were *easier to use*. for common and simple tasks like reading data from a network resource (http, ftp), querying a database, accessing xml (dom, etc), its more important to me to have an api that is simple to use than one that takes an interesting approach. perl's apis for these tasks tend to be very simple. hackage seems to be on track to deliver the advantages of the cpan tool and repository, so in that sense i think one of the key advantages of perl has been adopted by the haskell community. both languages have great communities! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
The post on dons' blog about the cpu scaler is a great example on how haskell can easily used in the day-to-day hacking! 2007/4/11, brad clawsie [EMAIL PROTECTED]: i find that don's haskell hacking blog has been written with the daily hacker in mind: http://cgi.cse.unsw.edu.au/~dons/bloghttp://cgi.cse.unsw.edu.au/%7Edons/blog ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- I invented the term Object-Oriented, and I can tell you I did not have C++ in mind. (Alan Kay) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
Hallo, On 4/11/07, riccardo cagnasso [EMAIL PROTECTED] wrote: The post on dons' blog about the cpu scaler is a great example on how haskell can easily used in the day-to-day hacking! Just read it, it's a very nice post. I'm not afraid of math, but it's a relief to see some code I can relate with. :-) -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Left-factoring with Parsec
Suppose I have expr = expr : expr : expr. Can the above be left-factored to fail on empty input so that my parser doesn't go into a loop? Thanks, Joel -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On Wed, Apr 11, 2007 at 05:55:08AM -0700, kynn wrote: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. Haskell useful to the learner as quickly as possible... If such already snip exist and I've missed it, please let me know. Or I can always wait until I retire; then I'll probably have a sufficiently long stretch of free time in my hands (barring any operations, strokes, heart attacks, hip fractures, etc.). I bet I could start a Haskell Wannabes Club at the nursing home... kj My experience is a lot like yours, except I retired 5 years ago, and still haven't learned Haskell. Unfortunately, I've had lots of interruptions that have kept me away from the keyboard. I've got a few unfinished projects, including one I started in Perl years ago, moved to Python, then moved to Haskell. The only useful thing I've programmed since I retired was a program to update my checkbook/bank statement postgresql database using Prolog for parsing entries the way I like to write them in a text file. Someday I'll move this to Haskell :-). I've sworn off other languages since I don't have any deadlines except my own. I never really learned Perl, but I used it a lot for simple one to thirty liners. The thing was, any thing I wanted to do I could find the bits and pieces of in Learning Perl, Programming Perl, or Learning Perl/TK. I have on my shelf Haskell: The craft..., The Haskell school of expression, and The Haskell road to Logic I've read them. I know I should sit down with each one at the computer and work through the exercises. But..,. When my current spate of unavoidable interruptions is over, I'll look into the email on Haskell one-liners, and some of the new tutorials to try to come back up to speed. Not in a nursing home yet! Good luck, John Velman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
If you first language is LISP probably you find easy Haskell and difficult pearl. Hi, my first programming language is lisp (that is, the language I am most fluent in -- recently Common Lisp, earlier Scheme) and I find Haskell a problematic programming language (this is a fresh experience -- I am writing a syndrome-networks based DSS in Haskell now) because it is not a language. Lisp is a language and Haskell is not, in the sense that lisp allows to write programs that can be read aloud and understood from reading the code. Haskell is a notation that is not a literature by itself, and for Haskell, literate programming, that is, writing more comments than code, is a must; while for lisp it is a rather exotic practice. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
kynn wrote: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) [snip] May I ask why you want to learn it so much, if you find it so hard? I'm sure most would disagree with me but maybe you'd be better off with perl for your one liners and scripts if it serves your purpose well. You say that you've heard Haskell is extremely elegant, but is that really the reason you want to start using it as your general purpose and scripting language? I'm also interested in it myself because of it's elegance, and in order to learn different paradigms, to explore the strength of the type system etc etc, but I'm not in a particular rush to be able to use it as the one true language for scripting or web applications, or xyz, as quite a few people lately seem to be asking about. Just curious. -- View this message in context: http://www.nabble.com/Why-Perl-is-more-learnable-than-Haskell-tf3559193.html#a9946886 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Left-factoring with Parsec
I presume your grammar has other clauses for expr, otherwise the loop is inevitable. Assuming you have other clauses you can always left-factor. Here's how those of us with weak memory can remember how to do it: Say that you have expr ::= expr : expr : expr | b Let's call the part from the first : a, since it doesn't matter what it is. So we have expr ::= expr a | b Let's call expr x, and just change notation slightly x = x a + b Now use high school algebra x = x*a + b x - x*a = b x*(1-a) = b x = b / (1-a) x = b * 1/(1-a) Now you have to remember that the Taylor series expansion of 1/(1-a) is 1/(1-a) = 1 + a + a^2 + a^3 + a^4 + ... OK, now put your grammar hat back on. What's 1 | a | aa | aaa | | ... it's just an arbitrary number of a:s, i.e., a* (or 'many a' in parsec). So finally expr = b a* -- Lennart On Apr 11, 2007, at 18:15 , Joel Reymont wrote: Suppose I have expr = expr : expr : expr. Can the above be left-factored to fail on empty input so that my parser doesn't go into a loop? Thanks, Joel -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Skipping keywords with Parsec
Is there a way to have any Parsec combinator skip a certain set of keywords? I tried lexeme = P.lexeme lexer . (skip ) but I don't think lexeme is called for every keyword. Thanks, Joel -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Skipping keywords with Parsec
Just in case I wasn't clear enough, I'm asking about skipping keywords represented by the skip combinator that can be located anywhere within the input. I do know about skipMany and skipMany1, in fact skip is defined in terms of these. On Apr 11, 2007, at 9:04 PM, Joel Reymont wrote: Is there a way to have any Parsec combinator skip a certain set of keywords? I tried lexeme = P.lexeme lexer . (skip ) but I don't think lexeme is called for every keyword. -- http://wagerlabs.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On Wed, Apr 11, 2007 at 02:21:41PM +0100, Will Newton wrote: On 4/11/07, kynn [EMAIL PROTECTED] wrote: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. I've been trying to learn Haskell for some time also, and I've learnt lots of various other languages in the past. I think one of the biggest problems is if there is a considerable learning curve, which Haskell undoubtedly has, there's a nagging question in the back of your head while you try and get a simple task accomplished in an unfamiliar language - why am I bothering with this, I could do it in 5 minutes in Perl/Python/Ruby/...!. And for many simple tasks Perl is a really good fit - it's best to find a task that plays to Haskell's strengths so you get a bit of positive reinforcement while you work. I have been working with Parsec to do some parsing recently and I can definitely recommend it. I don't think I've used such a capable and easy to use parsing framework in any language and it's really kept me going with Haskell where I might have just done it in Python in the past. Writing interpreters is one task where Haskell is really nice. I suggest Unlambda, it makes a nice toy language. The syntax is easy to work with, and continuations make the semantics interesting enough that you can't just rely on the host language acting the same way, like you generally can with mutable state, sequential evaluation and so on (unless you're using something like scheme or ml, but then you probably wouldn't have trouble with Haskell). Brandon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Weaving fun
I've been dying to do this all day but work and then family intervened. Dominic. import Data.List weave = unfoldr f where f ([],_,_) = Nothing f (x:xs,[],zs) = Just (x,([],[],[])) f (x:xs,ys,zs) = Just (x,(ys,zs,xs)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weaving fun
You are correct, my weave did hide the list in the explicit composition of closure(s). I can be even more declarative and let the closure construction be implicit in weave' below... (and this message should be literate Haskell) weave' uses a fixed point and pairs to tie the knot declaratively: import Data.List weave' :: [[a]] - [a] weave' [] = [] weave' xss = let (ans,rest) = helper rest xss in ans where helper :: [[a]] - [[a]] - ([a],[[a]]) helper _rest ([]:_xss) = ([],[]) helper rest [] = (weave' rest,[]) helper rest ((x:xs):xss) = let (ans,rest') = helper rest xss in (x:ans,xs:rest') The next case might be an optimization, since we know that nothing after the [] will be used in the next pass: -- helper rest ((x:[]):xss) = let (ans,_) = helper rest xss -- in (x:ans,[]:[]) My previous weave, uses composition of (xs:) thunks instead of pairs: weave :: [[a]] - [a] weave [] = [] weave xss = helper id xss where helper :: ([[a]] - [[a]]) - [[a]] - [a] helper _rest ([]:_xss) = [] -- done helper rest [] = weave (rest []) helper rest ((x:xs):xss) = x : helper (rest . (xs:)) xss One might imagine an 'optimized' case like in weave': -- helper rest ((x:[]):xss) = let yss = rest ([]:[]) -- in x : helper (const yss) xss Some simple tests such that check should be True check = (ans == test 20 weave) (ans == test 20 weave') test n w = map (take n . w) $ [] : [[]] : [[],[]] : [[1..10]] : [[1,3..10],[2,4..10]] : [[1..],[11..15],[301..],[11..15]] : [[1..],[11..15],[301..]] : [[1..],[11..15],[301..],[]] : [[1..],[11..15],[],[301..]] : [[1..],[],[11..15],[],[301..]] : [[],[1..],[11..15],[],[301..]] : testInf : [] testInf = map enumFrom [1..] ans = [[],[],[],[1,2,3,4,5,6,7,8,9,10],[1,2,3,4,5,6,7,8,9,10] ,[1,11,301,11,2,12,302,12,3,13,303,13,4,14,304,14,5,15,305,15] ,[1,11,301,2,12,302,3,13,303,4,14,304,5,15,305,6] ,[1,11,301],[1,11],[1],[] ,[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
Hi, I'm guessing you're not doing it the right way. cvs -d :pserver:[EMAIL PROTECTED]:/srv/CVSROOT co SYRENE/src By using types, you implementation becomes a lot more readable. Being readable is not enough for being readable aloud. And I think a lot of people here will disagree with you... That's good news. I would not bother to express my option if I thought that there would not be a lot of people who would disagree. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On Wed, Apr 11, 2007 at 05:55:08AM -0700, kynn wrote: Perl is a large, ugly, messy language filled with quirks and eccentricities, while Haskell is an extremely elegant language whose design is guided by a few overriding ideas. (Or so I'm told.) Based on this one would think that it would be much easier to learn Haskell than to learn Perl, but my experience is exactly the opposite. Perhaps it's just that being more elegant doesn't make it easier to learn. There are almost no overriding ideas in SKI combinator calculus, but I wouldn't say it's a nice and easy programming language (Well, OK, I didn't try to master it, so maybe I'm wrong). The biggest problem with Haskell is that not only you can do things differently (than in other languages) - you have to! Also, some tasks are only easy when you know some advanced programming techniques, like parsing with parser combinators. There is also the problem that fundamental concepts are quite entangled, and it's difficult to choose the starting point when learning or teaching. The language also seems a bit schizophrenic. For example, you can say that it has side-effects and that it has no side-effects, and both statements are true in some sense (expression evaluation has no side-effects but there are features like IO, mutable arrays, etc. - it's quite difficult to explain to beginners why there is no contradiction, or where is the trick, in other words). Actually, I don't know which is the biggest problem... and there are more of them. Best regards Tomasz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why Perl is more learnable than Haskell
I thought I could resist this thread but I'll bite =:-() The first language i learned was basic. No real functions, simple step by step instructions. I then learned hypercard, c, c++, python, assembly, vhdl, and too many others! Now i've decided to learn haskell. I view it as a mathematicians language. I do research in the field of medical imaging.. particularly processing large cardiac data sets to figure out characteristics, diseases, etc. Why workflow generally starts out as 1) mathematical idea 2) turn that pure equation into a numerical recipe 3) implement, debug 5) analyze 6) goto step 1. I find doing my thinking in the continous domain makes things a lot easier. But here's where i differ from everyone else. I already have the mathematical relationships all nice and tidy (hopefully!) in my head before i start. I literally just implement it. I don't want to care about threading, IO, message passing, or numerical stability. I have to care about performance but only so far as it hampers my productivity. Preferably the language will do it implicitly. Your average programmer wants a language to do tasks. Having to think about the math and relationships behind it all is rather sickening to them (and me too!). I am a new haskell programmer (basically a week into it!). It is by far the hardest language i've had to pick up. A lot of my code could be structured in a functional way.. but almost all reply on looping techniques (would take a lot of work to rethink my gradient descent method and make it fast!). Regardless of actually using haskell.. i like to transfer these techniques to c++. Before i even knew of haskell i knew some FP methods and i found that using these shrunk my code, shrunk the bugs, and did nice things for performance + concurrency. In fact, I just read a google paper on their batch system. They use to functions: map and reduce. They can easily split it up over their cluster etc... these are the ideas of FP that i like! That and the set-builder notation. I also hate matlab to death. Is there any possibility of using haskell as a replacement using ghci? Mostly i care about linalg when it comes to using matlab. ps: sorry if gmail butchered this reply. I had subscribed to the digest and turns out that was a mistake :D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Google SoC - student allocations
Although there is still about one hour before Google officially publish
the final tally of accepted Summer of Code projects, I think I now can
safely reveal the 9 projects chosen for haskell.org, since we have no
outstanding conflicts with other mentoring orgs.
We received 64 proposals in total. Some students made several
proposals. Of those proposals, we wanted to mentor about 22 individual
students, but Google only gave us funding for 9, so if you weren't
accepted, that doesn't mean your proposal was bad, just that the
competition was stiff. Also, the mentors group tended to place
language- and community-infrastructure projects at a higher priority
than just plain application-oriented libraries.
(By the way, several students who applied to haskell.org also applied to
other organisations, and may well have been accepted by them instead of
us.)
So here they are! The list states
* project title,
* the student who will be funded,
* the primary mentor from haskell.org,
* and a set of backup mentors who have expressed interest in looking
after things too. (These sets may continue to grow.)
---
Darcs Conlict Handling
Jason Dagit,
David Roundy
{ Igloo, Patrik Janssen }
Hackage Web Interface, Doc-Browser
Sascha B?hme,
Ross Paterson
{ Simon Marlow, BryanOS, Bjorn Bringert }
Rewrite the typechecker for YHC and nhc98
Mathieu Boespflug,
Malcolm Wallace
{ Neil Mitchell }
Cabal Configurations
Thomas Schilling,
Michael Isaac Jones
{ Bjorn Bringert, BryanOS, PatrikJ, Simon Marlow, Ross }
Update the Hat tracer
Kenn Knowles,
Malcolm Wallace
{ PatrikJ, BryanOS }
Generalizing Parsec to ParsecT and arbitrary input (ByteStrings)
Paolo Martini,
Philippa Jane Cowderoy
{ Don Stewart, Dmitry Astapov, BryanOS, Bjorn Bringert }
Shared Libraries for GHC
Clemens Fruhwirth,
Simon Marlow
{ BryanOS }
HTTP Library Replacement
Mieczys?aw B?k,
Bryan O'Sullivan
{ Shae Erisson, Dmitry Astapov, Don Stewart, Bulat Ziganshin,
Bjorn Bringert }
Extending GuiHaskell: An IDE for Haskell Hackers
Asumu Takikawa,
Neil David Mitchell
{ Duncan Coutts, Bulat Ziganshin }
---
Congratulations if you got accepted. Commiserations if you didn't. The
official start date of the SoC (when students begin to receive their
initial payments) is 28th May. Until then, the students have courses
and exams (no doubt), but also (we hope) some time to familiarise
themselves with the existing codebase and background of their project.
Regards,
Malcolm
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Matlab in Haskell
Ryan Dickie wrote: I also hate matlab to death. Is there any possibility of using haskell as a replacement using ghci? Yes. The strongly typed linear algebra project (Vectro) does exactly that. With an added guarantee that attempting to add or multiply matrices of inappropriate sizes is a type error. Thus typical errors like forgetting to transpose a matrix/vector are reported before the computation starts. The paper shows a few examples, including a larger example of a learning algorithm. http://ofb.net/~frederik/stla/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why Perl is more learnable than Haskell
Ah... there really needs to be more literature written on switching to the functional paradigm, IMHO. That is really these guys haven't had an easy time with it. On 4/11/07, Ryan Dickie [EMAIL PROTECTED] wrote: I thought I could resist this thread but I'll bite =:-() The first language i learned was basic. No real functions, simple step by step instructions. I then learned hypercard, c, c++, python, assembly, vhdl, and too many others! Now i've decided to learn haskell. I view it as a mathematicians language. I do research in the field of medical imaging.. particularly processing large cardiac data sets to figure out characteristics, diseases, etc. Why workflow generally starts out as 1) mathematical idea 2) turn that pure equation into a numerical recipe 3) implement, debug 5) analyze 6) goto step 1. I find doing my thinking in the continous domain makes things a lot easier. But here's where i differ from everyone else. I already have the mathematical relationships all nice and tidy (hopefully!) in my head before i start. I literally just implement it. I don't want to care about threading, IO, message passing, or numerical stability. I have to care about performance but only so far as it hampers my productivity. Preferably the language will do it implicitly. Your average programmer wants a language to do tasks. Having to think about the math and relationships behind it all is rather sickening to them (and me too!). I am a new haskell programmer (basically a week into it!). It is by far the hardest language i've had to pick up. A lot of my code could be structured in a functional way.. but almost all reply on looping techniques (would take a lot of work to rethink my gradient descent method and make it fast!). Regardless of actually using haskell.. i like to transfer these techniques to c++. Before i even knew of haskell i knew some FP methods and i found that using these shrunk my code, shrunk the bugs, and did nice things for performance + concurrency. In fact, I just read a google paper on their batch system. They use to functions: map and reduce. They can easily split it up over their cluster etc... these are the ideas of FP that i like! That and the set-builder notation. I also hate matlab to death. Is there any possibility of using haskell as a replacement using ghci? Mostly i care about linalg when it comes to using matlab. ps: sorry if gmail butchered this reply. I had subscribed to the digest and turns out that was a mistake :D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On 4/11/07, riccardo cagnasso [EMAIL PROTECTED] wrote: If you first language is LISP probably you find easy Haskell and difficult pearl. I must say I agree here. I spent 10 years programming in prolog before I tried haskell. Most of my problems with haskell are because it has a rather opaque performance model (e.g. when should you use tail recursion, and when should you not). But I happily acknowledge that my experience is probably atypical. ;-) cheers, T. -- Dr Thomas Conway You are beautiful; but learn to work, [EMAIL PROTECTED] for you cannot eat your beauty. -- Congo proverb ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
riccardo cagnasso wrote: My opinion is that learnin haskell is difficult is just for the fact that when you learn programming, you probably begin with C / C++ or some other procedural/OO programming language... Actually, my first language was Scheme; I loved it, and I aced the class, but that was many years ago, and I never had to code real world applications with Scheme. My problems with Haskell are not conceptual, but rather pragmatic. I have not been able to find enough support in Haskell for everyday tasks (e.g. read a stream from a socket; parse it into a simple data structure; process the data in the structure; print out the results to a socket; etc.), and unless I want to code large low-level libraries from scratch just to get conceptually simple tasks done, I can't afford to use Haskell (any more than I could afford to use barebones C, for that matter). And even though my interest in learning Haskell is not a pragmatic one (I'm quite productive with the tools I know; I just want to learn a new way to program, by way of intellectual curiosity), my life is such that, unless I can immediately make use of the language I'm attempting to learn, it just won't stick! The language needs it to be useful not because I need a tool, but because unless it is useful my brain just won't absorb it! kj -- View this message in context: http://www.nabble.com/Why-Perl-is-more-learnable-than-Haskell-tf3559193.html#a9952211 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: April 12, 2007
---
Haskell Weekly News
http://sequence.complete.org/hwn/20070412
Issue 60 - April 12, 2007
---
Welcome to issue 60 of HWN, a weekly newsletter covering developments
in the [1]Haskell community.
With the ICFP deadline passed, your Haskell Weekly News returns to its
regularly scheduled programming. This week: a truckload of new
libraries!
1. http://haskell.org/
Announcements
ndp-0.1: nested data parallelism in Haskell. Roman Leshchinskiy
[2]announced the first release of [3]the NDP package, a library for
writing nested data-parallel programs in Haskell, on shared-memory
multiprocessors. The NDP library is part of the Data Parallel Haskell
project. The paper [4]Data Parallel Haskell: a status report describes
the underlying design and go through an example program.
2. http://article.gmane.org/gmane.comp.lang.haskell.general/15006
3. http://haskell.org/haskellwiki/GHC/Data_Parallel_Haskell
4. http://www.cse.unsw.edu.au/~chak/papers/CLPKM07.html
binary 0.3: bigger, better, faster. Lennart Kolmodin [5]announced
binary 0.3. The 'binary' package provides efficient serialization of
Haskell values to and from lazy ByteStrings. ByteStrings constructed
this way may then be written to disk, written to the network, or
further processed (e.g. stored in memory directly, or compressed in
memory with zlib or bzlib). It's available [6]through Hackage, or via
its [7]homepage.
5. http://article.gmane.org/gmane.comp.lang.haskell.general/15044
6. http://hackage.haskell.org/packages/archive/binary/binary-0.3.tar.gz
7. http://www.cse.unsw.edu.au/~dons/binary.html
Text.HTML.Chunks. Matthew Sackman [8]announced the [9]Text.HTML.Chunks
library, a clone with improvements of the Perl HTML::Chunks module.
The main achievement is the use of template-haskell to combine the
template into the code at compile time. This then allows for static
checking that the variables/fields that the templates are expecting
are indeed being provided and that the templates the code is trying to
use do indeed exist. The template is then incorporated within the
code, removing the dependency on the template.
8. http://article.gmane.org/gmane.comp.lang.haskell.general/15028
9. http://www.wellquite.org/chunks
Phooey 1.0 and GuiTV 0.3. Conal Elliott [10]announced a new version of
Phooey, a library for functional user interfaces. Highlights in this
release: uses new TypeCompose package, which includes a simple
implementation of data-driven computation; new Applicative functor
interface; eliminated the catch-all Phooey.hs module. Now import any
one of Graphics.UI.Phooey.{Monad ,Applicative,Arrow}; Phooey.Monad has
two different styles of output widgets, made by owidget and owidget'
and more. Phooey is also used in GuiTV, a library for composable
interfaces and 'tangible values'.
10. http://article.gmane.org/gmane.comp.lang.haskell.general/15047
The real Monad Transformer. Henning Thielemann [11]announced the real
monad transformer! It has been argued that people avoid Haskell
because of terms from Category theory like 'Monad'. This problem can
now be solved by a wrapper which presents all the internet entirely
without monads! Start [12]the parallel Haskell wiki. Of course the
tool is written in Haskell, that is, Haskell helps solving problems
which only exist because of Haskell. Bug reports and feature requests
can be tracked at [13]here.
11. http://article.gmane.org/gmane.comp.lang.haskell.general/15059
12. http://tinyurl.com/2e32r4
13. https://sourceforge.net/projects/parallelweb
GHC 6.6.1 Release Candidate. Ian Lynagh [14]announced the Release
Candidate phase for GHC 6.6.1. Snapshots beginning with 6.6.20070409
are release candidates for 6.6.1. You can download snapshots from
[15]here.
14. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/11964
15. http://www.haskell.org/ghc/dist/stable/dist/
Haskell Cryptographic Library 4.0.3. Dominic Steinitz [16]announced
the release of a new version of the Haskell Cryptographic Library
based on the [17]crypto proposal. See [18]the crypto home for more
details. There is now no dependency on NewBinary. The downside is the
library contains no support for ASN.1 which will be released in
separate package.
16. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6761
17. http://www.haskell.org/haskellwiki/Crypto_Library_Proposal
18. http://www.haskell.org/crypto/
TagSoup library 0.1. Neil Mitchell [19]announced TagSoup, a library
for extracting information out of unstructured HTML code, sometimes
known as [20]tag-soup. The HTML does not have to be well formed, or
render properly within any particular framework. This library is for
[Haskell-cafe] k-minima in Haskell
What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. R M Send a FREE SMS to your friend's mobile from Yahoo! Messenger. Get it now at http://in.messenger.yahoo.com/___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
mrvr84: What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. R M Is this a homework question? -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Perl is more learnable than Haskell
On Apr 11, 2007, at 23:10 , kynn wrote: rather pragmatic. I have not been able to find enough support in Haskell for everyday tasks (e.g. read a stream from a socket; parse it into a simple The stuff in Network (not Network.Socket) gives you a Handle, which you can treat more or less like any other Haskell Handle (filehandle). Network.Socket should be reserved for when you need to work at a really low level. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon university KF8NH ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
On Thu, Apr 12, 2007 at 08:58:33AM +0530, raghu vardhan wrote: What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. Go read and thoroughly understand Why Functional Programming Matters. Also, your asyptotic complexity bound is just plain wrong. I'd give faster code, but Don is suspicious (and I can never tell these things myself). Stefan ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
On Wed, Apr 11, 2007 at 08:38:48PM -0700, Stefan O'Rear wrote: On Thu, Apr 12, 2007 at 08:58:33AM +0530, raghu vardhan wrote: What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. Go read and thoroughly understand Why Functional Programming Matters. Also, your asyptotic complexity bound is just plain wrong. I'd give faster code, but Don is suspicious (and I can never tell these things myself). Stefan Don tells me (in #haskell) that you are legitimate, so here is the example: kminima k lst = take k $ sort lst If you want to be really explicit about it, here is a sort that will work: sort [] = [] sort l@(x:_) = filter (x) l ++ filter (==x) l ++ filter (x) l (A stable quicksort, btw) Note that this is FASTER than your bound - somewhere between O(n) and O(n*log n). Ain't lazy evaluation great? :) Stefan ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
On Wed, Apr 11, 2007 at 09:20:12PM -0700, Tim Chevalier wrote: On 4/11/07, Stefan O'Rear [EMAIL PROTECTED] wrote: If you want to be really explicit about it, here is a sort that will work: sort [] = [] sort l@(x:_) = filter (x) l ++ filter (==x) l ++ filter (x) l (A stable quicksort, btw) You may be missing a few recursive calls there :-) Indeed. Stefan ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
And just to remind people, the question is to find the indices and not the numbers themselves. For example on input '3, [10,9,8,..., 3,2,1]' the output must be '[9,8,7]'. - Original Message From: Stefan O'Rear [EMAIL PROTECTED] To: raghu vardhan [EMAIL PROTECTED] Sent: Wednesday, 11 April, 2007 11:17:15 PM Subject: Re: [Haskell-cafe] k-minima in Haskell On Thu, Apr 12, 2007 at 09:30:22AM +0530, raghu vardhan wrote: Hmmm. That's not something I was looking for. I'm not sure the running time is good enough (think of k as being 2 - then you should not make more than 2n comparisons) - even with lazy evaluation, quick sort won't have a bound of O(k*n). Muahahahaha! Muahahahahahahahahahaha! Muahaha! Actually it DOES. (this list courtesy of a ghci one-liner) find the 3 minima of [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36] take 3 (sort [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36]) take 3 (sort (filter (71) [71,71,17,14,16,91,18,71,58,75,65,79,76,18,4,45,87,51,93,36]) ++ a bunch of stuff I won't track because it won't be evaluated) (comparisons so far: 20) take 3 (sort [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36]) take 3 (sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) (31) take 3 (sort [14, 16, 18, 4] ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) take 3 (sort (filter (14) [14, 16, 18, 4]) ++ sort (filter (==14) [14, 16, 18, 4]) ++ sort (filter (14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) (39) take 3 (sort [4] ++ sort [14] ++ sort (filter (14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) take 3 (4 : 14 : sort (filter (14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) 4 : 14 : take 1 (sort (filter (14) [14, 16, 18, 4]) ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) (43) 4 : 14 : take 1 (sort [16, 18] ++ filter (==17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36] ++ sort (filter (17) [17, 14, 16, 18, 58, 65, 18, 4, 45, 51, 36])) (47) [4, 14, 16] 47 close enough to O(n*k) for you? (remember this is quicksort we are dealing with, O(n^2) worst case) Stefan Send a FREE SMS to your friend's mobile from Yahoo! Messenger. Get it now at http://in.messenger.yahoo.com/___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] c2hs on mac
Hi, I am having trouble building c2hs on Mac OS X. I noticed that Darwinports has a port for this, but I'd like to install it without using Darwinports because I already have ghc compiled and installed on my system. Does anyone know how to get c2hs to work on the mac (or why it doesn't work in the first place)? Regards, Ruben ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
G'day all. Quoting raghu vardhan [EMAIL PROTECTED]: What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. Pretty much like everyone has says, although it's best to use a real lazy O(n log n) sort, not quicksort-with-dumbest-pivot. To get the indices, use the Schwartzian transform: sortWith :: (Ord b) = (a - b) - [a] - [a] sortWith f = mergeRuns . runs where runs = map (:[]) mergeRuns [] = [] mergeRuns [xs] = xs mergeRuns xss = mergeRuns (mergeRun xss) mergeRun (xs1:xs2:xss) = mergeOne xs1 xs2 : mergeRun xss mergeRun xss = xss mergeOne [] ys = ys mergeOne xs [] = xs mergeOne xs'@(x:xs) ys':(y:ys) = case compare (f x) (f y) of LT - x : mergeOne xs ys' GT - y : mergeOne xs' ys EQ - x : y : mergeOne xs ys getKMinima :: (Ord a) = [a] - [Int] getKMinima k = map fst . take k . sortWith snd . zip [0..] Cheers, Andrew Bromage ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] c2hs on mac
On Thu, 2007-04-12 at 15:20 +1000, Ruben Zilibowitz wrote: Hi, I am having trouble building c2hs on Mac OS X. I noticed that Darwinports has a port for this, but I'd like to install it without using Darwinports because I already have ghc compiled and installed on my system. Does anyone know how to get c2hs to work on the mac (or why it doesn't work in the first place)? What is the problem exactly? Are you using the latest tarball or the darcs version? Duncan ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] k-minima in Haskell
There seems to be some confusion about the question. There are two key things to keep in mind here: 1) You must make at most O(k*n) comparisons (in the worst case) if the list has length n. 2) The output must be the indices and not the numbers themselves. So, any algorithm that sorts is no good (think of n as huge, and k small). Another interesting caveat to this is that if k=2, you can actually solve the problem with just (n+log n) comparisons in worst case(instead of 2*n, that you get by a naive approach), and it's a nice exercise to do this. As a further clarification, this is not a homework question. I genereally do whatever programming I do in Matlab, as I work with matrices (huge ones) and use this function a lot. I just wanted to see how different an implementation you can get in Haskell (I am new to Haskell so I might not be able to come up with the best way to do this). - Original Message From: Stefan O'Rear [EMAIL PROTECTED] To: raghu vardhan [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Sent: Wednesday, 11 April, 2007 10:47:08 PM Subject: Re: [Haskell-cafe] k-minima in Haskell On Wed, Apr 11, 2007 at 08:38:48PM -0700, Stefan O'Rear wrote: On Thu, Apr 12, 2007 at 08:58:33AM +0530, raghu vardhan wrote: What's the best way to implement the following function in haskell: Given a list and an integer k as input return the indices of the least k elements in the list. The code should be elegant and also, more importantly, must not make more than the minimum O(k*length(list)) number of operations. Go read and thoroughly understand Why Functional Programming Matters. Also, your asyptotic complexity bound is just plain wrong. I'd give faster code, but Don is suspicious (and I can never tell these things myself). Stefan Don tells me (in #haskell) that you are legitimate, so here is the example: kminima k lst = take k $ sort lst If you want to be really explicit about it, here is a sort that will work: sort [] = [] sort l@(x:_) = filter (x) l ++ filter (==x) l ++ filter (x) l (A stable quicksort, btw) Note that this is FASTER than your bound - somewhere between O(n) and O(n*log n). Ain't lazy evaluation great? :) Stefan Send a FREE SMS to your friend's mobile from Yahoo! Messenger. Get it now at http://in.messenger.yahoo.com/___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
