Re: functional graph
On Wednesday 16 July 2003 00:02, Hal Daume wrote: But it looks the Graph class works on types a and b where a is the Node type where b is the Edge type, or just the other way around :), I don't have the code right now. Yes, 'Graph n e' is a graph whose nodes are labelled with elements of type n and whose edges are labelled with elements of type e. I posted an imperative graph module on this list. You could try that instead of functional graphs. I'm going to write a functional wrapper for that in the future. Regards, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara KDE Project: http://www.kde.org www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Combining Monads
On Saturday 12 April 2003 23:52, Dominic Steinitz wrote: For the theory, look at Triples, Toposes and Theories by Barr Wells. I think it's chapter 7 but I haven't got it in front of me. This looks like it's quickly getting out of the realm of programming :) Cheers, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara KDE Project: http://www.kde.org www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Sets
I had asked a similar question on haskell lists about how to implement hypergraphs efficiently, which are combinatorics of finite sets (sets of sets). As a matter of fact, I obtained a nice and small finite set implementation that works for me, let me see if it is worth posting. If you are working with larger than trivial hypergraphs and expensive algorithms performance can be a problem, so it would be better to surpass a suboptimal approach. Thanks, On Friday 15 November 2002 10:31 pm, Mark T.B. Carroll wrote: Am I right in thinking that sets of sets don't really work with GHC's Data.Set because Set a things aren't instances of Ord? How should I do sets of sets with it? (e.g. Set.mkSet [Set.unitSet 1] gives No instance for (Ord (Set a))) -- Mark ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eray Ozkural [EMAIL PROTECTED] Software Engineer, BICOM Inc. GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Record of STRefs better than STRef to a Record?
On Thursday 14 November 2002 01:29 am, Jorge Adriano wrote: In some functions I might need only some pure fields, and none of the STRefs, but since I pass something of type 'E s' around, everything ends up beeing monadic. Is using two records (on with STRefs and one with pure fields) the only/best way to avoid this? I would like to use two records, doesn't seem natural, but I also don't like to end up using monadic functions when they are, in fact, pure... Good question. In all Haskell codes I wrote, I ended up writing a lot of monadic functions which seemed to be unavoidable. Then you look at the code as it feels too much like an imperative code and start wondering why you are using a functional language :) Happy new year to all Haskellers by the way. Cheers, -- Eray Ozkural [EMAIL PROTECTED] Software Engineer, BICOM Inc. GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: AW: slide: useful function?
On Monday 02 December 2002 10:50 pm, Christopher Milton wrote: If there are any good ways in which non-mathematicians can get to grips with these terms from category theory, they would be well worth promoting. For example, despite having a good computer science degree (in which I was at least introduced to FP, proof, etc. and even learned to draw the dual graph of hypercubes) I'm really not equipped to understand catamorphisms in terms of algebras and homomorphisms, and don't currently have time to take the math degree I fear I'd need in order to do so. Last time I was looking at category theory books I think I came to the conclusion that Lawvere and Schanuel cover things kindly but Pierce seemed to get the syllabus right, so the right book wasn't quite out there. Check Category Theory for Computing Science by Barr, one of the most coherent textbooks I've ever seen. I think there is almost _nothing_ unnecessary in that book :) Anyway, if you are familiar with graph theory (proving simpler theorems at least, that is) learning category theory is not that hard. The introductory concepts are quite intuitive but it tends to get a little confusing after that (like all grad level math subjects!) My understanding of monads is already a matter of record. Does anyone know of a friendly text that might help new Haskellers to understand functors, etc. and what they mean for program design? I'm not averse to the formal language per se if it can be easily acquired; right now, I worry that I'm using Haskell suboptimally because, not only do I not know the terminology well, but I fear that I'm not even cognisant of the concepts that these terms represent. In that book you will find sections on using category theory for denotational semantics of functional languages which I think is a good thing for those armchair neuroactivity sessions. In a nutshell: if these category theory concepts indeed have an important impact in Haskell land, how to introduce them to working Haskell programmers well enough that they can use them in engineering software that's at least half as good as it could be? (I'm making the assumption here that it would be good for Haskell to be much more widely used - it shouldn't solely be for researchers.) Here's some of what I've come across: Jonathan M. D. Hill, and Keith Clarke An introduction to category theory, category theory monads, and their relationship to functional programming ftp://ftp.dcs.qmw.ac.uk/cpc/jon_hill/qmw681.ps.Z http://www.dcs.qmul.ac.uk/SEL-HPC/Articles/GeneratedHtml/functional.monads. html Monad is one of the simpler category theoretical concepts and I think you don't even need to know too much about category theory to write monadic programs. Going beyond monads is more interesting on the other hand. I haven't been able to catch up with the developments in that area however the Arrow programming discussions in this list seems to be a promising direction for bringing more category theoretical elegance to Haskell programming language. I wonder if there is any available code that makes a good demonstration of such approaches. Regards, -- Eray Ozkural [EMAIL PROTECTED] Software Engineer, BICOM Inc. GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Interpret haskell within haskell.
On Friday 20 December 2002 03:16 pm, David Sankel wrote: I was referring to a haskell interpreter to be used within haskell code. For instance: main = do user_configuration - parseHaskell title - resolveFunction user_configuration title :: String putStr title My next language design will have such an uber-cool standard library that you will be able to evaluate all you want in the world. Now I've got some years of design work to be done if you will excuse me. exa -- who found out that C++ was the worst PL in the world after giving 7 years to it exa -- He also ditched his C++ like imperative OO language design that he wasted valuable time with -- Eray Ozkural [EMAIL PROTECTED] Software Engineer, BICOM Inc. GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: layout rule infelicity
On Thursday 30 May 2002 13:43, Frank Atanassow wrote: Anyway, I have the feeling that, for every person on this list who complains about layout being unintuitive, there are 10 people who would say the opposite. Shall we take a poll? It's not unintuitive, it's counter-intuitive. :) The errors resulting from layout mistakes are hard to spot and are annoying. On the other hand, it has a blend of intuition. If you are writing in a certain, not-so-clear-what style, it makes life easier. :) As you can see I've contradicted myself. ** Type error. -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Space problem: reading a list of records from a binary database
Hi there,
While trying to read a list of records from a binary database I think I've
encountered a space leak but I'm not proficient enough to detect the cause of
the error.
The culprit is the readSessionDB function in SessionDB module which I attach
with other relevant code.
What I do in Session.readSession is using FFI to read a fixed size record from
an input stream. That far, okay. (I have no idea if I'm doing it right,
though)
The problem is, combined with my approach in Session.readSessionDB, it results
in huge amounts of space allocation, about 1MB, whereas the raw data would
consume about 50K. It would be a [Session] with about 3000 elements, each of
which contains 3 Ints and 6 Floats.
I wonder if the following code in SessionDB is the proper way to read a list
of records from a file. I get the feeling that the (s:rest) in the last
return statement causes my problems.
readSessionList :: Handle - IO [Session]
readSessionList h =
do session - readSession h
case session of
Nothing - return []
Just s - do rest - readSessionList h
return (s:rest)
Comments appreciated,
--
Eray Ozkural (exa) [EMAIL PROTECTED]
Comp. Sci. Dept., Bilkent University, Ankara
www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza
GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C
module SessionDB
where
import IO
import System
import IOExts
import Array
import Foreign
import CForeign
import SMA
import Session
readSessionDB :: String - IO [Session]
readSessionDB file =
do loc - locateStock file
case loc of
Nothing - do return []
Just fname - do h - openFileEx fname (BinaryMode ReadMode)
putStrLn (reading ++ (show fname))
list - readSessionList h
return list
readSessionList :: Handle - IO [Session]
readSessionList h =
do session - readSession h
case session of
Nothing - return []
Just s - do rest - readSessionList h
return (s:rest)
module Session
where
import IO
import System
import IOExts
import Array
import Foreign
import CForeign
data Session = Session {stockId, date, sessionId :: Int,
lowestValue, highestValue, lastValue, averageValue,
lot, volume :: Float} deriving (Eq, Show)
emptySession = Session {
stockId = 0,
date = 0,
sessionId = 0,
lowestValue = 0,
highestValue = 0,
lastValue = 0,
averageValue = 0,
lot = 0,
volume = 0
}
readSession :: Handle - IO (Maybe Session)
readSession h =
do eof - hIsEOF h
if eof then return Nothing else
do buf - mallocArray 73:: IO (Ptr CChar)
readChars - hGetBuf h buf 73
-- putStrLn (read ++ (show readChars))
let sidptr = castPtr buf :: Ptr CShort
dateptr = castPtr (plusPtr buf 2) :: Ptr CUInt
sesptr = (plusPtr buf 6) :: Ptr CChar
ptr = castPtr (plusPtr buf 7) :: Ptr CLLong
in do stockid - peek sidptr
date - peek dateptr
sessid - peek sesptr
rec - peekArray 8 ptr
-- destructArray 73 buf
let list = map (\x - (fromIntegral x) / 1) rec
:: [Float]
vals = array (1,8) (zip [1..8] list)
in return (Just Session {stockId = (fromIntegral stockid),
date = (fromIntegral date),
sessionId = (fromIntegral sessid),
lowestValue = vals!1,
highestValue = vals!2,
lastValue = vals!3,
averageValue = vals!4,
lot = vals!5,
volume = vals!6
})
Re: toEnum with international chars
On Tuesday 28 May 2002 13:32, Alastair Reid wrote: Can you explain your problem more clearly? I'm struggling to understand what was wrong given only a fragment of the program, none of the input and only an indication of where the problem lies in the output but not what that problem is. [This probably won't affect the answer though - which will probably be an admission that most Haskell compilers don't support international characters properly.] Oh, my bad, I think I gave a wrong list there. 66 is of course 'B', I was a little sleepless at the time of writing. Now having enjoyed a few hours of sleep I can express more eloquently :) It seems to be the fourth character that is the problem, but then again that's my mistake. Thank you. Still it attracts my attention that I cannot type þ in ghci while I can type it in bash. I think I can't type any of those international chars in ghc. Maybe some bug fix is in order. Regards, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Space problem: reading a list of records from a binary database
On Tuesday 28 May 2002 15:24, Eray Ozkural wrote: Hi there, While trying to read a list of records from a binary database I think I've encountered a space leak but I'm not proficient enough to detect the cause of the error. Thanks to dennisb from #haskell strict flags on Session type solves my problem to a great extent but I still feel a lot of space inefficiency. Somebody care to give some advice on the code? Regards, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
toEnum with international chars
I have a code that reads a string from a list of CChar's shortName = map (toEnum.fromIntegral) shortname When I have a turkish character like Ý the interpreter will: StockList a - readStockInfo h [66,105,108,105,-2,105,109,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32] StockList a *** Exception: Prelude.chr: bad argument The problem is the 66 in the beginning of the list. I'm not giving the entire code, it's not needed... What should I be using to work with such strings? Thanks, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: SUGGESTION: haskell-announce mailing list
On Monday 20 May 2002 23:36, Mark Carroll wrote: cafe has the pleasing connotation that people new to the Haskell fora should feel free to post their questions without fearing that they're bothering the important business of the list of whatever - it makes it very obviously a friendly, open forum. I think the notion of a cyber cafe works well in project oriented mailing lists. It has worked well for KDE folks, too. Thanks, -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo Malfunction: http://mp3.com/ariza GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Hiring Haskell programmers
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Tuesday 12 March 2002 01:17, Mark Carroll wrote: How easy is it to hire reasonable Haskell programmers? Of course, this may mean, hiring people with the aptitude and interest to quickly learn Haskell. Has anyone any experience of this that they can share? I know it's easy. Try me. ;) Sincerely, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8jUqcfAeuFodNU5wRAt1/AKCaN881FMXqzpx+xh1EpnFa/b6k9ACeNuPX aYrkL3CfiF2C6uBzH+3chPs= =U7Xm -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Hiring Haskell programmers
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Tuesday 12 March 2002 03:05, Mark Carroll wrote: Be able to modify or add to the code base within a few weeks, in such a way that somebody doesn't have to come back later and repair your work. (-: So, no, not just the syntax: much harder, in my opinion, is to learn how to phrase even just simple algorithms in an efficient and functional way. When I first learned Standard ML, after years of imperative programming, my brain almost hurt for the first few weeks. I think the practice of software engineering applies here as well as any other language. How hard was it for Cycorp to hire LISP programmers? (Not a good example I know) I would imagine one would have to be a little mathematically oriented for grokking the hack content of course. Any good programmer with a knowledge of declarative programming in the tradition of LISP and Prolog, IMHO, will do the job. Also I'd think that knowledge of the application domain and methods matters more than the programming language. If you require one to write machine learning code, how would you expect him to write a single line without knowing the subject? I'd imagine that persons who are experienced at any programming language which allows a reasonable level of abstraction (say C++), will be quite comfortable with Haskell. The type system of Haskell is a great win, and although the APIs are yet to be standardized (for common programming tasks) it will do a great job in many fields. I wouldn't be particularly enthusiastic about using a language like Haskell to implement a simple thing such as a chatroom but I would imagine it would have great benefits in research where you have to try out a lot of mathematical ideas, in complex symbolic AI tasks, in compiler design/implementation, etc. Therefore, ideally, I would look for somebody who has a) concrete programming experience b) knowledge of symbolic languages c) theoretical knowledge of your domain If I were to find that person who would be really able to program in Haskell, I would look for somebody who has done a variety of things rather than focusing on a single technology/application (just pure mathematics wouldn't do ;). That kind of a person would be able to find his way in any maze. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8jWnvfAeuFodNU5wRAk24AJkBv0bcIdzoBeSWhURsJyYar7GmxgCgor/M k5LFIF6Fa9CWnyujr1de/D4= =9pno -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Conversion/porting to mainstream languages
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Tuesday 12 March 2002 04:36, Ashley Yakeley wrote: How are others dealing with this? How big a project would it be to translate, say, from Haskell to C or Java? Huge. IMO, you'd probably need to rewrite everything. On the plus side, Haskell is typically excellent for exploring any problem domain. So you might end up with better designed and more maintainable Java or C code than you would if you started from scratch. Or not. I would use the right programming language for the tasks at hand. You should not IMO consider porting from one language to another which has radical differences. You will find it almost impossible to make a faithful translation of code that is still comprehensible if you rewrite in C/Java. If there are resource critical tasks, you write them in C/C++. But with Haskell you can pull many tricks which would be otherwise very expensive. Using Haskell at the right level may actually save you a lot of time and money. Especially if you are doing a lot of symbolic processing somewhere. I would almost certainly want to have a high level interpreted environment that runs with a language such as Haskell or ocaml for complex projects ;) It all depends on the application. If you are going to be done with 10.000 lines of C++ code, in a well written and comprehensible way using Haskell might not help you too much. In fact, you will find it quite hard to do some of the everyday tasks in a new language... However, consider a project such as MONO developed by certain famous monkeys. (They like being called like that) How many lines of code? How many would it take if it were written in Haskell? That's exactly the kind of project where Haskell would save you a lot of resources. Look at the applications on your computer. Something a little too complex and it becomes 10's of megabytes in source code That's surely not needed. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8jWyPfAeuFodNU5wRApv9AJwILw5ND1I0pbe5sp59cMh5M0RPDACgjszi aHF6DDW7tCc1csu2Xhyfp7I= =vkgB -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Graphs
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 I used graphs in haskell, but I don't think you'll get anywhere the kind of efficiency of a language like C++ where you have exact control over operations and structures There is the graph code in functional algorithms book Algorithms: a functional programming approach Fethi A. Rabhi, University of Hull, UK Guy Lapalme, Université de Montréal, Canada The code is available online. I recommend you to start with that one. Stay away from finite map stuff in edison if you can. (Although you can get it to implement graphs/hypergraphs after some amount of work) If you're going to prototype an algorithm, you will eventually have to use monads which will be harder to write than the final C++/C implementation. Why is that so? Because if you're writing the graph code in haskell, the really easier/better way is to use things like substitution, infinite graphs, etc. for an elegant and short code, in that it reflects the theoretical construction. But an algorithm designed for a serial machine is so much different. I've written graph algorithms from multilevel graph partitioning to graph clustering, so I think I know what I'm talking about :) If you're using C++, you can prototype an algorithm fairly easily. Here is how you can implement it. use list vectorint to store adjacency lists. use a vector vectorint* to index the adjacency lists. use separate vectors to hold labels. I won't go into the reasons why those are the ones to start with, eventually your super-optimized code will be similar to the above. Don't use a graph library. It will make your job harder! Avoid template libraries if you can (except stdlib...), and resist the temptation to templatize your code. You will find that it's much more easier to write graph algorithms that way. And yes, although it would be in theory be a good idea to be able to prototype your algorithm in an easier-to-use language, such a language does not exist. Unless you can show me graph code side-by-side and prove it to me I will never believe it :) For a start one would have to show me the implementation of non-trivial algorithms such as graph coarsening, all-to-all shortest paths, maximal cliques, etc. in the easier-than-C++ language contrasted with (good) C++ implementation. I'm thinking maybe it would be more-possible in ocaml, but I'm a beginner in ocaml and I don't think I'm enough of a ocaml-hacker to talk about it. Thanks, On Thursday 21 February 2002 18:01, Wojciech Fraczak wrote: Hi everybody, I would like to ask you, if you do not know any graph library for haskell. I would like to use haskell for prototyping some of algorithms on graphs and finite state automata/transducers. In fact what I'm looking for is a good (efficient and easy readable) data type definition for labeled graphs. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8dSjSfAeuFodNU5wRAk8rAJ9CIwZUmEKHpttK2IwTXO0fnk8/egCeOV/A y3yq4cDFx1mZQPC6SbK19JU= =QoPG -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: a universal printer for Haskell?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Wednesday 20 February 2002 08:46, Bernard James POPE wrote: There are numerous ways to provide security for your data types. (In)Visibility isn't security. I have more than often witnessed Java users who thought private keyword was for security. I think it's obvious, with many years of worldwide experience of Internet security, why obscurity is *not* security. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8dCTGfAeuFodNU5wRAjGsAJ4tq8Nqg5Vh4pANHbMZ0JT+u1iVpgCcDY7i PI0TC9Y+DnVAV8AstF2ovmk= =+xqN -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: A View of Monads (Re: performance of monads)
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Hi Richard, On Tuesday 19 February 2002 06:57, Richard Uhtenwoldt wrote: This is a weak argument. First of all it is not the case that imperative coders always specify a total ordering: multitasking, threading and interrupts (and their projections into software as in Unix signals and asynchronous exceptions) are ways of specifying partial ordering when a total ordering would lose. Note that modern cpu designs use out-of-order execution strategies; so on micro-second timescales they ignore the total ordering when doing so suits them and when it preserves semantics. I might add to the above points the obvious. Imperative programming languages in general do _not_ specify a total ordering. Each statement _can_ have a side effect[*] and the compiler is free to rearrange code such that it runs faster and preserves semantics. As written in any compiler textbook from 1970's. Sincerely, [*] The compiler will know when this is possible, and when the statement is free of side effects. You can specify that no side effects occur in C++ for instance. And the compilers also know that certain expressions are always free of side effects, etc. - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8cmZSfAeuFodNU5wRAsG4AJ9ZXV6jVfbIRrRTCzl8YhO/AK1a7QCePCE3 /ST0chxaZYNobn2f32N94sw= =3dOx -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: a universal printer for Haskell?
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Wednesday 20 February 2002 03:35, Ashley Yakeley wrote: At 2002-02-19 09:56, Richard Uhtenwoldt wrote: This is reflection! I'd rather not have Haskell contaminated with such things; Can you say a little more about why you think reflection is bad? Does it make the language implementation run slower? It's ugly, and isn't part of the spirit of the language. The above statement cannot be a basis for any argument against Bernard's proposal. Where Bernard makes a careful analysis of the matter, you introduce your prejudice. Since you are defining the spirit of the language, perhaps you could make a list of the parts of that spirit so that people will not come up with any proposal that violates your understanding of aesthetics. A general concept such as reflection cannot be deemed as worthless in itself. Any system that has a tiny bit of introspective powers can be said to be reflective to some extent, for instance a Haskell interpreter. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8cysgfAeuFodNU5wRAuc2AJ9UW0VRcxSqs0dS/rIN7/YBaXBO2wCfRtbB +5ZG8wk9nZH3Z7WEz7rNvqw= =NevV -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
A View of Monads (Re: performance of monads)
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 Let me offer a differing view of Monads. Monads are a way to write type-safe imperative programs within a functional framework. It's just an advanced version of PROGN kludge in LISP. Since they are based on a linear flow of commands, they seem to necessitate sequential programming. Because of this reason I prefer not to use any monads whenever possible. It seems to eliminate the gist of functional programming. OTOH, the nice thing about Monads is that they, I think, lift the semantics of an imperative language, to the language level. When I look at the analysis of Algol-like languages in Tennent's Semantics of Programming Languages book I see the same thing as Monads: a way to sequence commands, and pipe the effects. Because of these reasons, I think the use of Monads are highly exaggerated. They are sort of like the over-use of template code in C++. In my experience, it doesn't work too well. You will end up writing monadic versions of everything, etc. Of course, they are a nice way to abstact I/O. How else could you do it properly in a functional language? Monads effectively model the operation of a sequential machine (one I/O channel!) in a mathematical way. It's similar to the problem of trying to retrofit a parallel system in a sequential system. Consider a sequential input source, and a parallel algorithm to compute it. You will need an interface between the two. In that respect, whenever I use monads, I feel like going back to an imperative language because it will make my program much less concurrent. Wasn't the most important benefit of using a functional PL architecture independence? I think it has turned to ease of programming now, which isn't any more real. :) Thanks, On Wednesday 16 January 2002 17:05, you wrote: I see a lot of literature that says that monads simulate the effects of imperative programming concepts. I think that's just bad wording. To take a rather trite point of view, in a language such as C /everything/ is done within a monad, and all types, even int, are really IO something (IO Int). In Haskell you may see costs associated with using Monads, but they are mainly to do with dealing with the difficulties that arise from having laziness everywhere. Jón - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8RcrAfAeuFodNU5wRAtSkAJ9dbVF4q33hCcwXedHDYA4MlAYv0wCeNb5p shGjRg01VUmiGYTkW1LlmvM= =mJDL -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
We need Documentation (Was: Re: Integer to String Conversion?)
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Tuesday 04 December 2001 02:51, you wrote: On Tue, 4 Dec 2001, Chris wrote: is there a function that converts Integers to Strings and vice versa? Prelude (reads 123 abc) :: [(Integer, String)] [(123, abc)] Prelude show 123 123 That's the reason why I hadn't been able to join some famous programming contest :) When my brain had already melted I couldn't find how to do this in the documentation for 30 minutes. I had assumed there would have been a specific conversion facility... But I think there are other reasons than my sleepy state at the moment. Why doesn't an author or two who have written Haskell books consider opening their books for public use on the Internet? The Craft Of ... especially seems great. I'm sure many coders would appreciate a non-dead-tree version of that book or a shortened version of the book. The material we have is simply lacking. What we need is a good tutorial and a comprehensive reference book. The current state of documentation is far from that. The tutorial should be a tutorial, it should teach all that is needed for basic programming, and probably go beyond that, with examples explained in detail and such. (The tutorial on the web is not like that). The reference manual again must go ahead with examples, and a logical organization of programming concepts and language features. Otherwise Haskell is never going to find too much appeal in application programming; it will remain in obscurity in research centers and extreme hacker quarters. For coders who have not written papers about Haskell, the documentation is maximally cryptic. I could find only a single decent book in our university's library, it was a functional algorithms book that gave examples in Haskell. Without that book, I could never have written the code I wrote within a small amount of time. There was the Miranda version of The Craft Of.., but I didn't want to do too much guessing. So basically, I was left with that book which had an introductory chapter (I don't remember the exact name of the book) to Haskell and the online docs. The tutorial chapter of the book, which was an algorithms book, turned out to be much better than what the online docs had to offer although its purpose was to teach only a small subset of the language for algorithm design. Thanks, - -- Eray Ozkural (exa) [EMAIL PROTECTED] Comp. Sci. Dept., Bilkent University, Ankara www: http://www.cs.bilkent.edu.tr/~erayo GPG public key fingerprint: 360C 852F 88B0 A745 F31B EA0F 7C07 AE16 874D 539C -BEGIN PGP SIGNATURE- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8DJR0fAeuFodNU5wRAmksAJ4jUaj3zXZxzSFTnd06LTMk+E2TdACfVwBS gwjbfyAbMs/VkSIQEChpw2I= =+YDW -END PGP SIGNATURE- ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
