- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Why is $ right associative instead ofleftassociative?
by John Hughes 08 Feb '06

08 Feb '06

Lennart Augustsson wrote: > I now think :: for type signatures was a bad mistake. > I don't use lists very much. They are not the right data structure > for many things. So : is not as common as :: in my code. > I checked a small sample of code, about 20000 lines of Haskell. > It has about 1000 uses of ':' and 2000 of '::'. Just for interest, I analysed some of my code. Obviously my style is quite different to yours--my type specialiser of 3,500 lines has 240 conses, and only 22 occurrences of '::'. I seem to be using '::' a bit more lately, though, which I suspect is due to using classes much more. I also checked the Agda source code, about 14,000 lines, with about 500 occurrences of cons and 640 of '::'. I think the only conclusion one can draw is that style varies. > In my opinion all the special syntactic sugar for lists should go > away. I don't think lists are special enough to motivate it. What, no list comprehensions?? I'd disagree--sequencing is special, and lists represent it directly. Don't forget, also, that lists are also much more prevalent in beginners' code--and nice notation for beginners helps get people started on Haskell. > But this is not what Haskell' is about. It's supposed to be some > modest extensions to Haskell. Not designing a new perfect language. Right! John

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does haskell have plist's ?
by raptor 08 Feb '06

08 Feb '06

does Haskell have a property lists. Like Lisp ? any pointer to examples ? tia

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haskell reference card ?
by raptor 07 Feb '06

07 Feb '06

is there somewhre Haskell reference card ?

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EclipseFP (Haskell IDE) 0.9.1 released
by Thiago Arrais 07 Feb '06

07 Feb '06

EclipseFP 0.9.1 has been released since last Friday. It is an open-source development environment for Haskell code. EclipseFP integrates GHC with an Haskell-aware code editor and also supports quick file browsing through an outline view, automatic building/compiling and quick one-button code execution. Downloads and more information are available on the project home page http://eclipsefp.sourceforge.net/ We are open for comments and general discussion. Actually we would really appreciate comments from both newbie and veteran Haskell programmers. This is open-source development and everyone on the Haskell community is welcome to participate. Cheers, Thiago Arrais

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Re: [Haskell] Re: Streams: the extensible I/O library
by Bulat Ziganshin 07 Feb '06

07 Feb '06

Hello Peter, Monday, February 06, 2006, 10:24:01 PM, you wrote: moving to nescafe :) PS> > You can find further information about the library at the PS> > page http://haskell.org/haskellwiki/Library/Streams and PS> > download it as http://freearc.narod.ru/Streams.tar.gz PS> Is there any chance of running this code on a non-Windows PS> system? I tried to compile the example programs, but failed PS> for lack of a System.Win32 module. I might be able to port PS> the code, but I figured it would be wise to ask first. of course, it should work under other systems! it's my fault and you can fix this just by adding #ifdef around this import: #if defined(mingw32_HOST_OS) || defined(__MINGW32__) || defined(_MSC_VER) import System.Win32 #endif btw, my "wc" has about the same speed as yours :) thank you for the first bug-report! i re-uploaded the fixed version just now :) -- Best regards, Bulat mailto:bulatz@HotPOP.com

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main features of functional programming paradigm
by Abigail 07 Feb '06

07 Feb '06

Hi, I would like to ask about what are tha main features of functional programming? Additionally, about FAD: A Functional Analysis and Design Methodology What kind of software can i develop with this methodology? thanks for your answers Abigail. __________________________________________________ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! Regístrate ya - http://correo.espanol.yahoo.com/

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Re: [Haskell-cafe] Why is $ right associative instead ofleftassociative?
by John Hughes 06 Feb '06

06 Feb '06

> Quoting Paul Hudak <paul.hudak(a)yale.edu>: > >> Actually, one of the main reasons that we chose (:) is that that's what >> Miranda used. So, at the time at least, it was not entirely clear what >> the "de facto universal inter-language standard" was. > Phil Wadler argued for the ML convention at the time, and wrote a document containing a fair amount of sample code to illustrate what it would look like. We noticed something surprising: instead of (x:xs) and the like, Phil had consistently written (x :: xs) -- note the extra spaces. Somehow, using the longer operator name led him to feel spaces were needed around it. That in turn made his lines longer, encouraged him to split definitions across lines, and so on. When I read the thing, I realised after a while that I was skipping all the code fragments -- because they just looked too big and complicated to take in during a quick reading. It was at least partly that experience that convinced us that using :: for cons would impose a small cost, but a real one, on readability. It may seem trivial, but the sum of many such decisions is significant. The story does illustrate the importance of actually trying out syntactic ideas and seeing how they play--one can be surprised by the result. >> I don't think Haskell Prime should be about changing the look and >> feel of the language. It's about consolidating the most important extensions into the standard, isn't it? Changes that break existing code should be very, very well motivated--if porting code to Haskell Prime is too difficult, people just won't do it. John

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Haskell to call Microsoft COM (Dispatch)
by Gracjan Polak 05 Feb '06

05 Feb '06

Hi all, Is there any library to make Haskell call Microsoft COM functions using Dispatch? E.g I don't need the full COM binary functionality, scripting is enough. Google didn't seem to find anything interesting... beside rolling my own using FFI :) Thanks in advance! -- Gracjan

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Re[2]: [Haskell-cafe] request for help
by Bulat Ziganshin 04 Feb '06

04 Feb '06

Hello Marco, Saturday, February 04, 2006, 4:39:23 PM, you wrote: MAFdA> Hello. MAFdA> English is not my native language (I'm Portuguese). MAFdA> The haskell-cafe mailing list is usually very active and subscribers MAFdA> do help each other, so I believe you will not have any trouble in MAFdA> finding "real" Englishmen who will read and correct the document ;-) thank you. J.P. Bernardy already corrected a part, so i think that Englishmens will help me MAFdA> However, if by any chance you don't, please let me know and I will do it MAFdA> (just tell me how, because the wiki is password-protected). you just need to register itself in this Wiki system. look at the "register" text on the page, i don't remember exact. or may be "login", where you will have chance to register -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Re: Haskell code for this example of flow control
by Dominic Steinitz 04 Feb '06

04 Feb '06

Here are some even older discussions on the subject. I don't know if anyone ever put them into a library or on the wiki. Dominic. http://haskell.org/pipermail/haskell-cafe/2005-May/009784.html http://www.haskell.org//pipermail/libraries/2005-February/003143.html

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request for help
by Bulat Ziganshin 04 Feb '06

04 Feb '06

Hello haskell-cafe, i'm wrote new general i/o library called Streams. it's so great that i hope it will eventually replace using Handles. i plan to present it in Haskell list on Monday. in order to do it i wrote overview of library facilities. the problem is that i'm not native english speaker and i feel that my text is awkward, in best case. when i wrote last time docs about Arrays, Cale Gubbard fixed lots of my misspellings on wiki page :) this time i try to go different way - i published my version of report at the http://haskell.org/haskellwiki/Library/Streams page and ask your help in correcting it. it will allow to include in presentation the proper English text that is much more pleasing for readers than my scribbles :) so, please correct text at this wiki according to English rules. even if you correct paragraph or two, that will forward the work further -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Pythonic monads
by Graham Klyne 03 Feb '06

03 Feb '06

Constructing some code today in Python, using some functional-style coding idioms, I found myself wondering if there would be any real benefit to using a monad-based implementation (i.e. other than to demonstrate that it can be done). The application that sparked this line of thought was a simple filter to trim comments and whitespace out of an XML document. I ended up with a simple state-machine driven filter, thus: [[ # Strip comments from XML strings def stripXmlComments(x): # State table for stripping XML comments stStripXmlComments = \ { 0: match1('<',(1,stateFilterHold),(0,stateFilterPass)) , 1: match1('!',(2,stateFilterHold),(0,stateFilterPass)) , 2: match1('-',(3,stateFilterHold),(0,stateFilterPass)) , 3: match1('-',(4,stateFilterDrop),(0,stateFilterPass)) , 4: match1('-',(5,stateFilterDrop),(4,stateFilterDrop)) , 5: match1('-',(6,stateFilterDrop),(4,stateFilterDrop)) , 6: match1('>',(0,stateFilterDrop),(4,stateFilterDrop)) } return stateFilter(stStripXmlComments,x) # Simple state machine driven filter # # The state table is a dictionary indexed by state values, where the # initial state is 0, and each entry is a function that accepts a next # symbol and returns a pair of (next state, action), where action is # one of 'stateFilterPass', 'stateFilterDrop', 'stateFilterHold'. # stateFilterHold means that the disposition will be determined later. # # The result is an iterator that returns elements from the filtered # subsequence of the supplied sequence. # def stateFilter(stable,seq): queue = [] state = 0 for symbol in seq: (state,action) = stable[state](symbol) (queue,emit) = action(queue,symbol) for e in emit: yield e return def stateFilterPass(q,n): return ([],q+[n]) def stateFilterDrop(q,n): return ([],[]) def stateFilterHold(q,n): return (q+[n],[]) # State transition function to match the specified symbol and return # 'eqval' if matched, otherwise 'neval' def match1(sym,eqval,neval): def m(sym,eqval,neval,next): if next==sym: return eqval return neval return curry(m,sym,eqval,neval) def curry(func, *args): """ Curry multiple arguments: See: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/229472 """ def curried(*args2): args2 = args + args2 return func(*args2) return curried ]] and a test case: [[ def testFilter02(self): fullstr = "<!-abc->  <!- -ghi-->" trimstr = list(stripXmlComments(fullstr)) expstr = list("<!-abc-> <!- -ghi-->") assert trimstr==expstr, \ "stripSpaces, expected:\n"+expstr+"\nFound:\n"+trimstr ]] In thinking about this implementation, it seemed to me that this employed patterns characteristic of a monadic type: each entry in the state table (in this case, an instance of match1, a curried function) is like a step in a monadic computation, updating the monadic value and also returning some value. What I can't quite visualize is if the code in Python would actually look any better if it were implemented with a monadic type, as one might readily choose for a Haskell implementation. Or would there be no real benefit? I have noticed that, while I like to use functional idioms in some of my Python code, and the Python language is easily able to support these (even some lazy evaluation, courtesy of generators), that the code doesn't always look as clean as its Haskell equivalent. In Haskell, composition and currying are fundamental patterns and are directly supported by the syntax. In Python, one has to work harder to achieve these (e.g. the "curry" function above seems rather convoluted to me, for such a fundamental notion). Thoughts? Comments? #g -- Graham Klyne For email: http://www.ninebynine.org/#Contact

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Haskell code for this example of flow control
by Maurício 03 Feb '06

03 Feb '06

Hi, I would like to know what options I have in Haskell to do something similar to this C++ code: double a = 1000; while (a>1) a/=2; I'm able to do that with lists, but I would like to know how to do that with monads and variables with state. Thanks, Maurício

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HUnit
by Matt Roberts 03 Feb '06

03 Feb '06

I am in love with HUnit and QuickCheck. However, I am missing one important functionality I want to call a command line program that will search all the .hs files I have in a particular directory, pull out all HUnit test (based on what they are called, or perhaps their type signature) and run them all. I have done a bit of a search and can't find anything like this, am I going to have to write it myself? Matt

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Known Unknowns
by Chris Kuklewicz 03 Feb '06

03 Feb '06

There is a new combined benchmark, "partial sums" that subsumes several earlier benchmarks and runs 9 different numerical calculations: http://haskell.org/hawiki/PartialSumsEntry I took the Clean entry and, since there were so many recursive computations, I made compute and altCompute higher order functions. No speed optimization work has been done yet, but it seems really fast. A new http://haskell.org/hawiki/KnucleotideEntry has been accepted, replacing the one with the memory leak. The speed is also better, but still poor, due to Data.Hashtable. GHC 6.6.x should eventually help. Also on the topic of poor speed: http://haskell.org/hawiki/NbodyEntry At the bottom of the page is Einar's really cool existing entry (open mutable records). At the top of the page is best effort to replace it, but it runs at almost the same speed. Which is very much slower (10x) than other entries, such as OCaml. It is odd that small scale numerics, such as the partial-sums functions, can be made fast but not medium scale numerics like the n-body integration. There are 5 fixed mass parameters and 30 variables (5*3 positions + 5*3 velocities). Addition, Subtraction, Multiplication, Division. And we can't get it going nearly as fast as it ought to run. Note: The garbage collector is not a factor (%GC time 0.9%). Like the Hashtable glitch, if this were part of real program then a small bit of c-code could be attached via FFI. Are there little known Haskell idioms for doing math? Do we have to write a recursive function with 30 separate parameters? Do we have to peek and poke unboxed doubles? Is there an undocumented -funleash-fortran parameter? Will this be fixable in Haskell' ("Haskell-Prime")?

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Number 1, at least for now
by dons＠cse.unsw.edu.au 02 Feb '06

02 Feb '06

Haskell is now ranked number 1 on the Great Language Shootout! http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=all Hooray :) -- Don

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Re: [Haskell-cafe] EclipseFP (Haskell IDE) 0.9.1 released
by dagit＠eecs.oregonstate.edu 02 Feb '06

02 Feb '06

Quoting Thiago Arrais <thiago.arrais(a)gmail.com>: > 2006/2/1, Graham Klyne <GK(a)ninebynine.org>: > > [I should say that I haven't yet actually tried this software, though I'd > like > > to do so when I get some time.] > > I really hope you find the time to do so. We would be glad to be > hearing from you again. I haven't found time (yet) to look at your new version, but I tried out the stable version from about a week ago and played with it a bit. I might as well tell you what I found then and why I'm unable to use EclipseFP at this time. > At some point of the wave, the integrated environments appear. They > come, as the name says, to integrate the previous tools in an easy to > use and productive environment. Not that the previous tools were hard > to use or counter-productive, it is just that by integrating them much > time is saved from the details and the programmer can spend more time > on the creative and useful things only he can do. I think it's important to keep this aspect, the ramping up and the integration. Particularly, I'm against tools that want to do things their way. I'd much rather have the tool automate the tools I already have instead of creating a new mechanism. For example, I'd rather have the IDE work with my makefiles than ignore them and use some builtin make system. I need to be able to separate from the IDE whenever it becomes cumbersome or when I want to share the code. > > So is there a compelling feature in this Eclipse plugin that isn't easily > > achieved using simpler tools? > > When we write an Eclipse plugin, we get a lot of things for free. Just > to cite one, there is already CVS integration support within every > Eclipse installation, which includes a very neat diff viewer. Adding > support for other version control systems isn't very hard. There are > plugins, for example, for Darcs and Subversion too. I was trying the Darcs plugin in conjunction with EclipseFP as my first attempt at using eclispe. I found that waiting for eclipse to "autobuild" everything in _darcs was a waste of time and just plain silly. Hopefully, there is a way to avoid this excessive building and still use autobuild. I couldn't find it. > Another very nice feature of the Eclipse platform is the refactoring > support. Wouldn't you like to refactor your Haskell code as easily as > selecting some context-menu item? Not to mention code assistance and > 'go to declaration support' (click a module/function/whatever > reference and open its corresponding declaration). This has saved me a > lot of time when browsing code. This is the reason I sought out EclipseFP. I want to automate as much of the refactoring as I can while making it safe. But now let me turn to the reasons I'm not using it anymore. Some of the reasons have to do with eclipse itself (I think), some are related to the very nice plugin you have created, and some are related to the darcs plugin. Some of my problems may even be fixed in the announced version, but I haven't had a chance to check. I wanted to use EclipseFP to help with darcs development. The first problem I encountered was that darcs has a makefile which is growing in complexity. Some files are compiled with this flag, others with that flag. I couldn't figure out how to import the make rules. I did find a way to set the compilation options, but they were per project instead of per file as near as I could tell. I would a makefile import to be automated and to watch the makefile for changes. One direction would be fine for now, but ultimately I would want it to let me change build settings in Eclipse and have it mirrored in the makefile. Does eclipse have a makefile plugin? I also had a problem with autobuild building too much as noted above. I also couldn't figure out a way to ask eclipse to delegate to make for building. The next problem I encountered was the parser was not forgiving enough to parse the darcs source code, as a result everything was colored as a comment. Every file that contained "#include", "#define" or similar threw a lexical error. The code is meant to be run through ghc with the -cpp flag turned on. Is it possible to use ghc-api for parsing the code? I also noticed that when you click on an error so that eclipse will take you to the place of the error, it often took me to lines that were perfectly fine, in fact, I think it was often the wrong file. The first time I created a "Hello, World" project in win32 eclipseFP gave some odd errors that I didn't write down. I haven't seen that error since so I can't make a bug report, but it was certainly confusing. It was to the effect that ghc had crashed while generating the project. After I got that error, I stop using eclipse in windows and switched to OSX. I had some other problems, but don't think they were related enough to list them here. In the end, it was a horrible first experience with eclipse and I'm not looking forward to ever using eclipse again. On the other hand, I want some sort of IDE for Haskell to help automate certain things, like refactoring. I'm a long time fan of emacs, but the more I use emacs the more I see that it may never handle certain things well. For example, using regexp to do syntax highlighting is quick and easy it's also the source of many of the problems with using emacs for coding in Haskell. The indentation is off, block uncomment is not the inverse of block comment, if you use a string like "{-" it throws off the highlighting until a matching -} is found and so on. My advice would be to download the darcs source code and try to use darcs with EclipseFP. You'll see first hand some things that could use some fix'n :) And I think I could stand to use eclipse to test out your changes if you need a tester, but I doubt I'd have much more time to spare than testing. > Of course, you need to write the code to tell the platform about your > language. That's what the EclipseFP team is trying to do. Yes, and I'm very happy to see someone doing this. I wish you the best of luck and when the problems I encountered are fixed I will try eclipse again. Hopefully my rantings will be helpful to you and not make you lose hope :) I really want see you succeed. Thanks, Jason

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RE: [Haskell-cafe] Number 1, at least for now
by Simon Peyton-Jones 02 Feb '06

02 Feb '06

| > though, I think this is a great oprotunity to improve ghc's optimizer. | | Huh, that would be the best thing with the whole shootout endeavour.. Yes indeed. One thing that would be really helpful, as a first step, would be to identify a bunch of concrete examples that GHC "should" have optimised, or perhaps "could" have optimised, and attach them to the GHC wiki somewhere. One place would be here http://haskell.org/haskellwiki/Performance or perhaps somewhere on the developers wiki, or as a task. http://hackage.haskell.org/trac/ghc I'm not promising that anything will happen fast (unless someone else does it!) but it's always much more likely to happen if there's a specific place that advertises low-hanging performance fruit. This is closely related to the "advice to programmers" that Don circulated yesterday, in which he explained how he optimised one particular case. But not quite the same. Simon

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SCC accounting
by Andrew Pimlott 02 Feb '06

02 Feb '06

We've been trying to track down a memory leak, and by adding SCC annotations, pinned it down to a very brief expression. Unfortunately, the expression is just a variable! We even looked at the generated core: (case ([Soutei.Term Logic.BodyVar] -> (...) -> Logic.Frame -> Logic.QState -> FBackTrackT.Stream m_aYsk Logic.QState) lookup_aYPK pred_aXVH ctxIdx_aYpI of wild_B1 { Data.Maybe.Nothing -> GHC.Err.patError ... Data.Maybe.Just x_aXVL -> __scc {pqzifoozq Assertions} x_aXVL }); Note the __scc annotation just before x_aXVL at the end of the expression. Yet in the time and allocation profile, this SCC is charged for a lot of time and allocations in the "individual" column; individual inherited COST CENTRE no. entries %time %alloc %time %alloc pq.foo' 466 50001 8.0 12.1 8.0 13.2 and in the heap profile, it is a major memory leak. The Haskell code looks like predQuery pred = case lookup pred ctxIdx of Just f -> {-# SCC "pq.foo'" #-} f Note that f is a function, which we expect to be expensive when it is called. However, that should be charged to the definition of the function, right? We tried pretty hard to reproduce this in a small test case, but never succeeded. Always, the cost was accounted to the definition of the function in the intuitive way. We're using ghc 6.4.1 and compiling without optimization. Can any ghc hacker suggest how this could happen, or give us any hints on what to try next? Andrew [1] http://haskell.org/ghc/docs/latest/html/users_guide/profiling.html

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unary pattern matching
by John Meacham 01 Feb '06

01 Feb '06

I have often wanted a shorthand syntax for testing if a value matches a given pattern. I want to implement such an extension for jhc but can't decide an appropriate syntax so I thought I'd ask the group. basically I want something like /Left (Just _)/ expands to \x -> case x of Left (Just _) -> True _ -> False so you can do things like when (/Just _/ x) $ putStrLn "x is something" or map /Left (Foo _ 'x')/ xs to get a list of booleans saying whether the xs match or not. however, the '/' syntax clearly doesn't work, nor would anything that conflicts with normal haskell syntax. does anyone have any better ideas? John -- John Meacham - ⑆repetae.net⑆john⑈

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RE: [Haskell-cafe] Known Unknowns
by Simon Peyton-Jones 01 Feb '06

01 Feb '06

| Here's a brief introduction. I intend to write up (on the performance page on | the wiki) a list of things we've done to improve the shootout entries. Yes, do put what you wrote before on the Wiki. (The performance-advice page seems to have vanished but it should be on the user-documentation wiki somewhere. I'm sure we'll find it.) | Multiple calls to sin. Hmm :/ And similar for cos, as well as k*k. Not sure | why GHC isn't removing these (SimonM?), so let's do that by hand GHC doesn't do full CSE. It'd be a relatively easy pass for someone to add, but it can cause space leaks. And it can replace two strictly-evaluated calls with one lazy thunk: let { x = case e of ....; y = case e of .... } in ... ==> let { v = e; x = case v of ...; y = case v of ... } in ... Instead GHC does "opportunistic CSE". If you have let x = e in .... let y = e in .... then it'll discard the duplicate binding. But that's very weak. I've added this to the GHC FAQ Simon

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point-free simplification algoritm.
by Nuno Pinto 31 Jan '06

31 Jan '06

Since it's my first post, hi all! I have been reading this for some days but only now i decided to write something. I am researching a to build a computer assisted simplification algorithm used to simplify pointfree expression.. Example. If i give the program: fst . snd . id . id it will return: fst . snd. it wil also show all steps it made to reach that goal. to do this we must have the laws (such as f. id = f) that help us doing this defined. the program uses a datatype such as: data ExpTree v c = Var v | Term c [ExpTree] exp :: Exp Char PF exp = Term Comp [Term Comp [Term Fst [], Term Comp [Term Snd [], Term Id []]], Term Id []] I have previously defined the catamorphism, hylo and anamorphism for this data type, so recursion is insured. I have also implemented a generic calculador that, given a list of functions will try to aply them and returns the best simplification aswell as the steps made to reach it. I am now trying to implement such functions in a "decent" way, but i am however interested in the theory behind all this. I am looking for algorithms that will help me efficiently simplify the expression to the fullest. I am also interested in knowing what zygomorphisms and paramorphisms are? and how can u build a gcata?? (a cata for all datatypes). I head about "proof-by-exhaustion" and "four color theorem" beeing used to make mathematical proves such as this ones, but i have never seen any example of such and would like to see it, if possible, in haskell.. If anyone can help me find what im looking for, a decent mathematical proofing algoritm.. or just tell me what it is that im looking for :P. or even contribute with any ideas, it would be very much aprecciated. :) TY, and Hi all :D :) and have fun coding haskell :) _________________________________________________________________ Don't just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/

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Correct usage of MonadError, ErrorT?
by Daniel 31 Jan '06

31 Jan '06

Hi, I've got some functions in MonadError with different Error types. I would like to map errors of one Error type onto the other Error type. It seems that the only facility for doing this is mapErrorT, but that seems to force me to work in ErrorT rather than any old instance of MonadError. Am I barking up the wrong tree trying to keep the functions generalised over MonadError? Is there some other paradigm I should use for passing errors across system layers in haskell? I would like to do something like the following, but I don't know how to achieve the 'mapError errMap' part of g. instance Error Int where strMsg s = 0 f :: (MonadError Int m, MonadIO m) => Int -> m String f 0 = do liftIO $ putStrLn "The int is 0, that'll be an error." throwError (-27) f i = do liftIO $ putStrLn ("The int is " ++ show i ++ ", we'll do the division.") return $ show (100 `div` i) g :: (MonadError String m, MonadIO m) => Int -> m String g i = do liftIO $ putStrLn ("Will try to divide by " ++ show i) mapError errMap (f i) h :: (MonadIO m) => Int -> m String h i = (runErrorT (g i)) >>= either (\e -> return ("had an error: " ++ e)) return Thanks Daniel

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RE: [Haskell-cafe] arr f
by Sven Biedermann 30 Jan '06

30 Jan '06

Hello Chris, Many thanks for your input. arr _ = error ... Doesn't work, because it will not be possible to use arrow notation. Today I learned that the function type is abstract and so has no constructor I can pattern match against. I don't know, why. Does something break, if Haskell would offer such a constructor? Since I want to use the arrow notation, I had a close look at the following description, taken from http://www.haskell.org/ghc/docs/latest/html/users_guide/arrow-notation.h tml And revised my problem again (sorry): ------------------------------------------------------------------------ ---- 7.7.1. do-notation for commands Another form of command is a form of do-notation. For example, you can write proc x -> do y <- f -< x+1 g -< 2*y let z = x+y t <- h -< x*z returnA -< t+z You can read this much like ordinary do-notation, but with commands in place of monadic expressions. The first line sends the value of x+1 as an input to the arrow f, and matches its output against y. In the next line, the output is discarded. The arrow returnA is defined in the Control.Arrow module as arr id. The above example is treated as an abbreviation for arr (\ x -> (x, x)) >>> first (arr (\ x -> x+1) >>> f) >>> arr (\ (y, x) -> (y, (x, y))) >>> first (arr (\ y -> 2*y) >>> g) >>> arr snd >>> arr (\ (x, y) -> let z = x+y in ((x, z), z)) >>> first (arr (\ (x, z) -> x*z) >>> h) >>> arr (\ (t, z) -> t+z) >>> returnA Note that variables not used later in the composition are projected out. After simplification using rewrite rules (see Section 7.10, "Rewrite rules ") defined in the Control.Arrow module, this reduces to arr (\ x -> (x+1, x)) >>> first f >>> arr (\ (y, x) -> (2*y, (x, y))) >>> first g >>> arr (\ (_, (x, y)) -> let z = x+y in (x*z, z)) >>> first h >>> arr (\ (t, z) -> t+z) ------------------------------------------------------------------------ --- The arrow I want to create is one to track down dependencies. This doesn't seem to work with arrow notation, because in the example above g -< 2*y isn't used in the following statements but is bound to the next arrow: first g >>> arr (\ (****here==> _ ***, (x, y)) -> let z = x+y in (x*z, z)) >>> So, when tracking down dependencies, the result will depend on g. But it does not! In my eyes, it would be better that the whole proc x delivers an arrow of type a b (c,d) instead of a b c with d being piggy backed from g. So I can see on the wrong type of proc x that I missed out connecting something to some other bits. Another solution would be just to skip g. Can somebody tell me, why the arrow notation is as it is? Greetings Sven -----Original Message----- From: Chris Kuklewicz [mailto:haskell@list.mightyreason.com] Sent: Samstag, 28. Januar 2006 18:01 To: Sven Biedermann Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] arr f Sven Biedermann wrote: > Hello Henrik & Ross, > > Man thanks for your input. I have realised that I should have > explained my problem better. > > So, I try... > > I want to create a datatype like this: > > data D a b = DepVoid (a->b) | -- a = () > DepSingle (a->b) | -- a = a simple ones > DepPair (a->b) | -- a = (c,d) > DepTriple (a->b) | -- a = (c,d,e) > ... > DepFun (a->b) -- a = (c->d) > ... You have a serious typing problem in Haskell with that. Every constructor could be replaced with DepSingle. > Its easy to construct them: > > mkArrVoid :: (() -> c) -> D () c > mkArrVoid f = DepVoid f > > mkArrPair :: ((a,b) -> c) -> D (a,b) c > mkArrPair f = DepPair f > > ... > > Now I want to make D an instance of Arrow: > > instance Arrow (D) where -- my problems stems from > arr f = ??? > > I have no clue to glue the mkArr* functions together to reach what I > want: a different Dep* for different functions f. > What can I pattern match, here? What can I do else? This is not easily fixable, since (arr = DepSingle ) is always a valid choice for the compiler to make. Thus typeclass solutions badly overlap. > > Greetings > > Sven > I can come closer with a GADT. The serious typing problem is still there. So I made arr and pure into error messages. {-# OPTIONS -farrows -fglasgow-exts #-} import Control.Arrow -- GADT style data D x y where DepVoid :: (()->b) -> D () b DepSingle :: (a->b) -> D a b DepPair :: ((a1,a2)->b) -> D (a1,a2) b DepFun :: ( (a1->a2) -> b ) -> D (a1->a2) b -- And these are the constructors, so we could skip them mkArrVoid = DepVoid mkArrSingle = DepSingle mkArrPair = DepPair mkArrFun = DepFun -- The destructor is more annoying (template haskell would help) -- http://haskell.org/hawiki/GADT_20with_20record_20syntax might make this easier getF :: D x y -> (x -> y) getF (DepVoid f) = f getF (DepSingle f) = f getF (DepPair f) = f getF (DepFun f) = f -- This is useful for diagnosing which constructor you have, for testing getF' :: D x y -> Int getF' (DepVoid f) = 1 getF' (DepSingle f) = 2 getF' (DepPair f) = 3 getF' (DepFun f) = 4 instance Arrow D where arr _ = error "Use Dep* instead" -- or arr = DepSingle pure _ = error "Use Dep* instead" -- or pure = DepSingle first arrD = let toPair :: (x->y) -> D (x,d) (y,d) toPair f = DepPair (\(b,d) -> (f b,d) ) in toPair (getF arrD) -- (template haskell would help with defining >>>) (>>>) arr1 arr2 = let comp f = (getF arr2) . f in case arr1 of DepVoid f -> DepVoid (comp f) DepSingle f -> DepSingle (comp f) DepPair f -> DepPair (comp f) DepFun f -> DepFun (comp f) -- This >>> loses the constructor info of arr1 but is simpler (>>>>) arr1 arr2 = DepSingle ( (getF arr2) . (getF arr1) )

2 1

library(s) for numeric constant folding?
by Robert Dockins 29 Jan '06

29 Jan '06

Does anyone know of a good library or libraries which will allow me to perform arithmetic operations on 1) binary integers (signed and unsigned) of various fixed sizes? 2) IEEE 754 floating point numbers (single and double precision). Pure Haskell is preferable, but I'll make do with C bindings. I need to do constant folding for integral and floating point types for a compiler front-end, and I'm hoping that I don't have to write this stuff myself.... Why not just use Float and Double for 2) you ask? Because I need to to EXACTLY IEEE 754 computation, and the Haskell report is pretty dodgy about what implementations are required to provide. Thanks Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG

1 0

Evaluating arithmetic expressions at run time
by Andrew Savige 29 Jan '06

29 Jan '06

Haskell beginner using GHC. I have a function to do some simple arithmetic at run time: myeval :: Int -> Int -> String -> Int myeval x y "+" = (+) x y myeval x y "-" = (-) x y myeval x y "*" = (*) x y -- ... While that works, I'm curious to know if it can be done more elegantly. I'm thinking of something like: myeval :: Int -> Int -> String -> Int myeval x y op = (read op) x y Thanks, /-\ ____________________________________________________ Do you Yahoo!? Listen to over 20 online radio stations and watch the latest music videos on Yahoo! Music. http://au.launch.yahoo.com

7 10

RE: [Haskell-cafe] arr f
by Sven Biedermann 28 Jan '06

28 Jan '06

Hello Henrik & Ross, Man thanks for your input. I have realised that I should have explained my problem better. So, I try... I want to create a datatype like this: data D a b = DepVoid (a->b) | -- a = () DepSingle (a->b) | -- a = a simple ones DepPair (a->b) | -- a = (c,d) DepTriple (a->b) | -- a = (c,d,e) ... DepFun (a->b) -- a = (c->d) ... Its easy to construct them: mkArrVoid :: (() -> c) -> D () c mkArrVoid f = DepVoid f mkArrPair :: ((a,b) -> c) -> D (a,b) c mkArrPair f = DepPair f ... Now I want to make D an instance of Arrow: instance Arrow (D) where -- my problems stems from arr f = ??? I have no clue to glue the mkArr* functions together to reach what I want: a different Dep* for different functions f. What can I pattern match, here? What can I do else? Greetings Sven -----Original Message----- From: Henrik Nilsson [mailto:nhn@Cs.Nott.AC.UK] Sent: Freitag, 27. Januar 2006 21:46 To: Sven Biedermann Cc: haskell-cafe(a)haskell.org Subject: Re: [Haskell-cafe] arr f Hi Sven, > since this is my first post, > > "Hello all" Welcome! > I have a problem with a function taken from class Arrow. > > arr :: (b -> c) -> a b c > > To build my own arrow, i need to distinguish between different kinds > of b or c. For instance, if b has the form (d,e), i want to construct > something different as when having form (d,e,f). I'm not quite sure I understand what you mean. Are you saying that you you want the input to be either a pair or a triple? Then one possibility would be to wrap up the input in the standard Haskell type "Either". For reference, "Either" is defined like this: data Either a b = Left a | Right b Assume g :: T1 -> T2 -> T h :: T1 -> T2 -> T3 -> T for some specific types T1, T2, T3 and T. Now you can define a function "f": f :: Either (T1,t2) (T1,T2,T3) -> T f (Left (x,y)) = g x y f (Right (x,y,z)) = h x y z Thus "f" "distinguish[es] between different kinds" of input. If it is applied to what essentially is a pair, it will compute a result of type "T" using the function "g", whereas if it is applied to what essentially is a triple it will compute a result using the function "h", again of type "T". Lifting "f" into an arrow yields: arr f :: Arrow a => a (Either (T1,T2) (T1,T2,T3)) T I don't know if that was what you really ment by "construct[ing] something different" depending on the input type? Hope that helps, /Henrik -- Henrik Nilsson School of Computer Science and Information Technology The University of Nottingham nhn(a)cs.nott.ac.uk This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

2 1

arr f
by Sven Biedermann 27 Jan '06

27 Jan '06

Dear Haskellers, since this is my first post, "Hello all" I have a problem with a function taken from class Arrow. arr :: (b -> c) -> a b c To build my own arrow, i need to distinguish between different kinds of b or c. For instance, if b has the form (d,e), i want to construct something different as when having form (d,e,f). Could I get a hint how to express my needs, please! Many thanks in advance Sven Biedermann

3 2

Another idea for record field selection and better namespace management
by Brian Hulley 27 Jan '06

27 Jan '06

Hi - To avoid the problems with so many names being put into a module's namespace, data declarations could implicitly define sub-modules and class/instance declarations as follows: module M where data Foo = FooCon {x : Int} would declare (as seen from inside M) Foo, Foo.FooCon, Foo.x and would further declare x and FooCon as instances of a global value type-class and constructor type class as follows (where //varid denotes the global typeclass corresponding to (a record field called) varid, and //conid denotes the global typeclass corresponding to the constructor conid) class //x a b where x : a -> b instance //x Foo Int where x Foo.FooCon{x=p} = p class //FooCon a b where FooCon : a -> b instance //FooCon Int Foo where FooCon = Foo.FooCon The class declarations (generated by the compiler) are global, and there is no danger of conflicts with user class declarations because of the // prefix. The instance declarations (also generated by the compiler) would be inserted into the module itself. This would give at least three advantages: 1) The same names could be used for fields in more than one data declaration and these would be resolved using the well known type class mechanism 2) Some exciting new programming paradigms become instantly available due to the extension of allowing constructor type classes, namely we could then get the effect of extensible data types eg data Col1 a = One a data Col2 a = One a | Two a useOne :: ( //One col a) => col -> a useOne (One x) = x This is a lot more powerful than just OOP, because we could have different views of a data type, selecting out those components which are relevant to particular operations: data Element = TerminalPunct | TerminalValue | NonTerminal | Push | Pop data Action = Push | Pop data Insertion = TerminalValue | NonTerminal | Push without having to artificially construct various injections... 3) If x is a record field, then because a typeclass and instance has been automatically generated, (x p) already uses the type of p to determine which overloaded x to use, so all that remains is to introduce a sugar to get a form of function application syntax that binds stronger than prefix application. I suggest p^x === (x p) It is still possible to be completely explicit, by writing P.x p or p^P.x I think this solves all the problems that I had with the value space idea, and is also a fairly conservative extension to Haskell as it stands at the moment, except I wonder if it is possible to implement type classes for constructors? Regards, Brian.

1 2

graphics Windows Programming
by Andrew U. Frank 26 Jan '06

26 Jan '06

There are several graphics packages to select from... But which one is the easiest to work with for students for a ghci - windows environment. I sense that cairo / gtk2hs does not support ghci. >From the HOpenGL home page I cannot find out what I would need to download for a windows environment (can somebody point me to the right direction?). We have used SOE under hugs but I sense it is not working with ghci? We found it also somewhat deficient for graphics beyond the content of the book - has it been extended and improved? Any advice greatly appreciated! Andrew Frank

2 1

HitchhickersGuideToTheHaskell - Chapter 3 ...
by Dmitry Astapov 25 Jan '06

25 Jan '06

... which deals with QuickCheck and type classes, have been uploaded to http://www.haskell.org/hawiki/HitchhickersGuideToTheHaskell. Any feedback and criticism is gratly appreciated! -- Dmitry Astapov //ADEpt GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D

1 0

Printing functions
by Creighton Hogg 25 Jan '06

25 Jan '06

Hi, I'm working on writing a genetic programming system in Haskell, and I wanted to know what might be a good way to print out the programs that are being generated. There's no instance of Show for functions, but I'd really like to see what's happening so that I know if it's working right. What should I try?

2 1

Hashtable woes
by Chris Kuklewicz 25 Jan '06

25 Jan '06

Hello, This post is a about a tangential issue to the shootout, not the shootout itself. It concerns the lack of a fast mutable hashtable. If you have a good replacement for Data.Hashtable, I would be interested to know about it (and so would the wiki!). The shootout entry "k-nucleotide" is a good test of the hashtable provided by each of the languages: http://shootout.alioth.debian.org/gp4/benchmark.php?test=knucleotide&lang=a… Several of us are building a proposed entry on the wiki at http://haskell.org/hawiki/KnucleotideEntry where I have just posted a plea which I will paste below: On mutable data structures in Haskell This benchmark is completely bottlenecked by Data.Hashtable (in GHC 6.4.1) and this discussion is based on the assumption that I am using Hashtable optimally. I downloaded the GHD 0.17 compiler and the DMD entry to benchmark on my machine. The DMD entry uses the "associative arrays" built into the language: "int[char[]] frequencies" and places [WWW]second (runs in 3.0s). The winning entry is interesting, since the c-code does not have a hash table, and so it uses #include "../../Include/simple_hash.h" which pulls in a dead simple, inline, string to int hashtable and runs in 2s. The entry below runs 16 slower than the DMD entry on my powerbook G4. Profiling shows the bottleneck. I downloaded simple_hash.h and shamelessly optimized it to replace Data.Hashtable for exactly this benchmark code. This sped up the proposed entry by a factor of 4.1 so that it is now about a factor of 4 slower than the DMD entry. This shows that Data.Hashtable is doing *at least* four times more work that is needed for this usage pattern. And even with my over specialized hash table, Haskell is almost 50% slower than OCaml's "module H = Hashtbl.Make(S)" (note that I my code uses the same hash function as OCaml). Unfortunately I cannot submit this optimized hash table entry to the shootout. The only mutable data structure that come with GHC besides arrays is Data.Hashtable, which is not comptetitive with OCaml Hashtbl or DMD's associative arrays (unless there is something great hidden under Data.Graph). Is there any hope for GHC 6.6? Does anyone have pointers to an existing library at all? Perl and Python and Lua also have excellent built in hashtable capabilities. Where is a good library for Haskell? -- Chris Kuklewicz

5 6

compiling lazy functional languages
by Sam Goldman 25 Jan '06

25 Jan '06

Sorry if this is too off-topic for this list. I'm a hobbyist programmer and I've recently become interested in lazy functional languages, particularly the optimization strategies available to them during compilation. I've been playing around with Haskell for about a year and it has been an excellent resource for me. I guess my main question is this: what are the x most compelling directions in optimized compilation for (pure) lazy functional languages in recent research (where x::Nat is an unevaluated thunk in your head) - Sam

4 3

darcs: the first haskell tool more popular than Haskell itself?
by Isaac Jones 25 Jan '06

25 Jan '06

Greetings, Debian has a system called popularity-contest, which is an opt-in survey of package use. I was curious to see the ranking of darcs among Haskell implementations themselves. The results: Darcs ranks higher than ghc and hugs. #<name> is the package name; #<inst> is the number of people who installed this package; #<vote> is the number of people who use this package regularly; #<old> is the number of people who installed, but don't use this package # regularly; #<recent> is the number of people who upgraded this package recently; #<no-files> is the number of people whose entry didn't contain enough # information (atime and ctime were 0). #rank name inst vote old recent no-files (maintainer) 138 darcs 563 159 280 124 0 (Isaac Jones) (51) hugs 304 119 157 28 0 (Isaac Jones) 321 ghc6 194 81 80 33 0 (Ian Lynagh) Hugs is listed in a different category, so the ranking is off. Ian Lynagh pointed me at this nice graph showing the historical installation of the three packages: http://people.debian.org/~igloo/popcon-graphs/index.php?packages=ghc6,darcs… peace, isaac

5 6

Guess what ... Tutorial uploaded! :)
by Dmitry Astapov 24 Jan '06

24 Jan '06

Hi all, Recend thread "Tutorial upload" reminded me of my intentions to write haskell tutorial which I suppresend from the times when Hal Daume began to write YAHT. Unusually low temperature here (-22C) freed me a lot of time this weekend, and the result it here: http://www.haskell.org/hawiki/HitchhickersGuideToTheHaskell This is a work in progress, plus I'm trying it on C++/Java folk around me, so it's bound to be heavily corrected, but main direction could already be seen (I hope). If you want - jump on the wagon, and provide me with (constructive) criticism, edits on hawiki or anything else you see fit. -- Dmitry Astapov //ADEpt GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D

3 4

Performance Tuning & darcs (a real shootout?)
by Jason Dagit 24 Jan '06

24 Jan '06

Hello, This will be a long email so I've tried to give it sections. = Background = I've been using Haskell a while now (close to a year) and I'm still very much a newbie (but I've used other FP langs). I'm also very interested in darcs which, as many of you know, is written in Haskell. I've found a case which darcs does not handle efficiently and I'm trying to get the performance in that case to a satisfactory level. If you create a new repository, create a single large file (say 300mb) and record that file darcs will take a very long time and uses a lot of memory (usually at least 900mb for the 300mb case). Before I begin telling you what I've tried so far, let me give a brief history of previous efforts by others to optimize darcs. As far as I know, the main person to work on optimizing darcs in the past is Ian Lynagh. He was able to convert darcs from stricter algorithms to lazy ones and this made a huge improvement in performance. In theory darcs should be able to lazily read from a file, compute the patch that needs to be written, write that patch and then lazily read the patch while it is applied to the repository. This mostly works as expected, but I've discovered that somewhere near the end of the application the memory needed spikes dramatically. After almost two weeks of poking at darcs doing various benchmarks and profiles I've realized that optimizing Haskell programs is no easy task. I've been following the advice of numerous people from the haskell irc channel and learned a lot about darcs in the process. I've also been using this nifty library that Ian created for this purpose to get a measure for the non-mmap memory usage: http://urchin.earth.li/darcs/ian/memory Potentially useful information about darcs; 1) Uses a slightly modified version of FastPackedStrings. 2) Can use mmap or not to read files (compile time option). =Experiments and Findings= I have a summary of some of my experimentation with darcs here: http://codersbase.com/index.php/Darcs_performance Basically what I have found is that the read of the original file does not cause a spike in memory usage, nor does writing the patch. This would seem to imply that it's during application of the patch that the memory spikes. Modifying darcs to read the patch file and print just the first line of the patch causes some interesting results. The memory usage according to Ian's memory tool stays very low, at about 150kb max, but requesting the first line of the patch appears to make darcs read the entire patch! Darcs will literally grind away for, say, 30 minutes to just print the first line. On a side note, I've tried turing off mmap and running some of the above experiments. Ian's tool reports the same memory usage, and top still reports large amounts of memory used. Does ghc use mmap to allocate memory instead of malloc? Even if it does this shouldn't be a problem for Ian's tool as long as it maps it anonymously. =Questions= So far I've been tracking this performance problem by reading the output of ghc --show-iface and --ddump-simpl for strictness information, using the ghc profiler (although that makes already bad performance much worse), Ian's memory tool, and a lot of experiments and guess work with program modifications. Is there a better way? Are there tools or techniques that can help me understand why the memory consumption peaks when applying a patch? Is it foolish to think that lazy evaluation is the right approach? I've been thinking that perhaps darcs should be modified to use bounded buffers so that we have tight control over the amount of memory consumed during a run. This solution would require a lot of reworking of the existing code, and sounds frightful from a maintenance point of view. I'm also wondering if using mmap is a bad idea. Given the way files are currently mmap'd I think we are limiting darcs to handling files which are small enough to fit in the address space at once (eg., < 4GB on i386). Additionally, it would seem that using mmap does not really reduce memory stress. I'm looking for advice or help in optimizing darcs in this case. I guess this could be viewed as a challenge for people that felt like the micro benchmarks of the shootout were unfair to Haskell. Can we demonstrate that Haskell provides good performance in the real-world when working with large files? Ideally, darcs could easily work with a patch that is 10GB in size using only a few megs of ram if need be and doing so in about the time it takes read the file once or twice and gzip it. If anyone wants to look at the darcs code themselves the unstable version is available via: darcs get --partial http://abridgegame.org/repos/darcs-unstable Just to recap, I'm looking for 1) advice, 2) tips, 3) design ideas, 4) tools, 5) libraries and just about anything else :) Thanks, Jason

4 5

SDL on Mac
by Jake Luck 23 Jan '06

23 Jan '06

Anyone else here using the SDL binding on their Macs? (If memory serves me, at one point, I had gotten libSDL to work with 6.2.2). Now using GHC 6.4.1, while SDLstable-0.2.0 built without any problem for me on Linux, hsc2hs fails on the Mac: % runhaskell Setup.lhs build --verbose Reading parameters from /SDLstable/src/Core/SDL.buildinfo Preprocessing library SDL-0.2.0... /usr/local/bin/hsc2hs -I/fp/include/SDL -D_THREAD_SAFE -oGraphics/UI/SDL/General.hs Graphics/UI/SDL/General.hsc ld: Undefined symbols: _ZCMain_main_closure ___stginit_ZCMain % cat config.mk SDL_CFLAGS=-I/fp/include/SDL -D_THREAD_SAFE SDL_LIBS=-L/fp/lib -lSDLmain -lSDL -framework Cocoa -framework OpenGL PACKAGE=SDL VERSION=0.1.0 MAINTAINER%3Dlemmih(a)gmail.com % cat SDL.buildinfo cc-options: -I/fp/include/SDL -D_THREAD_SAFE ld-options: -L/fp/lib -lSDLmain -lSDL -framework Cocoa -framework OpenGL I am using the Mac OS X binary ghc 6.4.1 from the GHC download page on 10.4.3, linking to the latest libSDL 1.2.9 handbuilt with gcc 3.3. jake

1 0

Can I use Haskell for web programming
by Maurício 23 Jan '06

23 Jan '06

Hi, Can I use Haskell to do what people do with, say, PHP? More and more I have the need for that, and I've been looking into Ruby on Rails. Do you thing Haskell could be a choice? Of course, I don't need something exactly like PHP (for instance, I don't care if I can't insert code in the middle of xhtml pages. If I have to generate everything from Haskell code, I would probably like it. Also, CGI can be a choice). But I need reasonable efficiency and to be able to find someone to host my site. What solutions do you suggest me? Thanks, Maurício

10 14

RE: [Haskell-cafe] Re: Hashtable woes
by Simon Marlow 23 Jan '06

23 Jan '06

On 23 January 2006 15:09, Chris Kuklewicz wrote: > That is good to hear. The benchmark's tests take 1,250,000 > pre-generated > strings as the keys. At the end, the string keys are 18 characters > long, drawn randomly from a set of 4 characters. So the hash > computations are a nontrivial hit. > > Using -A400m I get 39s down from 55s. That is the best > Data.HashTable time I > have seen. (Using -A10m and -A100m were a little slower). > > Using my over optimized c-code hashtable I get 12.3 seconds. The > associative arrays in OCaml and D are still faster. So you see why I > long for GHC 6.6. > > Is Jan-Willem Maessen's Hash available anywhere? I could benchmark > it. Jan-Willem's HashTable attached. It uses unsafeThaw/unsafeFreeze tricks to avoid the GC overheads, for this you need an up to date GHC due to a bug in the garbage collector: grab a STABLE snapshot (6.4.1 won't work). Or remove the unsafeThaw/unsafeFreeze to use it with 6.4.1, and be prepared to bump the heap size. In GHC 6.6 the unsafeThaw/unsafeFreeze tricks aren't required, because the GC is essentially doing it for you - we put a write barrier in the IOArray implementation. Cheers, Simon

1 0

RE: [Haskell-cafe] GHC integers pre-allocation
by Simon Peyton-Jones 23 Jan '06

23 Jan '06

I believe that we statically allocate all ASCII chars, and Ints between -16 and +16. Have a look in ghc/rts/StgMiscClosures.cmm Simon ________________________________ From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Monique Monteiro Sent: 22 January 2006 23:26 To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] GHC integers pre-allocation Hi all, does anyone know if GHC implements any kind of pre-allocation of integers/caracteres ? If yes, which range of values does it use? Thanks in advance, Monique Monteiro

1 0

First steps in Haskell
by Daniel Carrera 23 Jan '06

23 Jan '06

Hello all, I'm trying to write the simplest possible Haskell program, and I'm not getting anywhere. I have installed Hugs, GHC and GHCI. I want to run the following program: fac :: Integer -> Integer fac 0 = 1 fac n | n > 0 = n * fac (n-1) This is what I see: $ hugs Hugs.Base> fac :: Integer -> Integer ERROR - Undefined variable "fac" Hugs.Base> fac 0 = 1 ERROR - Syntax error in input (unexpected `=') $ ghci Prelude> fac :: Integer -> Integer <interactive>:1:0: Not in scope: `fac' Prelude> fac 0 = 1 <interactive>:1:6: parse error on input `=' $ # Write the program to fac.hs $ ghc fac.hs fac.hs:1:0: The main function `main' is not defined in module `Main' When checking the type of the main function `main' This is a real problem for Haskell. I expect that a lot of people try Haskell and give up because they can't even write the simplest function. It's hard not to be put off by this. I love the theory behind Haskell, but the practice of it seems to be a real problem. I hope someone will show me how to make this program work. Even better, I hope someone will fix the compilers and interpreters if they need fixing, or fix the documentation if that's what needs fixing. Best, Daniel. -- /\/`) http://oooauthors.org /\/_/ http://opendocumentfellowship.org /\/_/ \/_/ I am not over-weight, I am under-tall. /

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GHC integers pre-allocation
by Monique Monteiro 22 Jan '06

22 Jan '06

Hi all, does anyone know if GHC implements any kind of pre-allocation of integers/caracteres ? If yes, which range of values does it use? Thanks in advance, Monique Monteiro

1 0

Haskell': Kicking off the process of defining the next Haskell standard.
by Isaac Jones 21 Jan '06

21 Jan '06

let haskell' = succ haskell98 in Announcing the Haskell' ("Haskell-Prime") process. A short time ago, I asked for volunteers to help with the next Haskell standard. A brave group has spoken up, and we've organized ourselves into a committee in order to coordinate the community's work. It will be the committee's task to bring together the very best ideas and work of the broader community in an "open-source" way, and to fill in any gaps in order to make Haskell' as coherent and elegant as Haskell 98. Our task is broadly defined by our mission statement: The Haskell programming language is more-or-less divided into two "branches". The Haskell 98 standard is the "stable" branch of the language, and that has been a big success. A lot of progress has been made over the last few years in the "research" branch of the Haskell language. It is constantly advancing, and we feel that it is time for a new standard which reflects those advancements. Haskell' will be a conservative refinement of Haskell 98. It will be the work of this committee to adopt a set of language extensions and modifications and to standardize a new set of libraries. We will strive to only include tried-and-true language features, and to define them at least as rigorously as Haskell 98 was defined. This standard will reflect the realities of developing practical applications in the Haskell language. We will work closely with the rest of the Haskell community to create this standard. Your Haskell' Committee is as follows (slightly munged email addresses follow): * Manuel M T Chakravarty <chak at cse.unsw.edu.au> * John Goerzen <jgoerzen at complete.org> * Bastiaan Heeren <bastiaan at cs.uu.nl> * Isaac Jones <ijones at galois.com> * John Launchbury <john at galois.com> * Andres Loeh <loeh at iai.uni-bonn.de> * Simon Marlow <simonmar at microsoft.com> * John Meacham <john at repetae.net> * Ravi Nanavati <ravi at bluespec.com> * Henrik Nilsson <nhn at cs.nott.ac.uk> * Ross Paterson <ross at soi.city.ac.uk> * Simon Peyton-Jones <simonpj at microsoft.com> * Don Stewart <dons at cse.unsw.edu.au> * Audrey Tang <autrijus at gmail.com> * Simon J. Thompson <S.J.Thompson at kent.ac.uk> * Malcolm Wallace <Malcolm.Wallace at cs.york.ac.uk> * Stephanie Weirich <sweirich at cis.upenn.edu> The editors are Isaac Jones and John Launchbury. Feel free to contact any of us with any concerns or questions. If you don't know who to direct your questions to, email Isaac Jones ijones(a)syntaxpolice.org. Community involvement is vital to our task, and there will be a way for members of the community to make formal proposals. In the opening phases, please use these more informal resources to help us coordinate Haskell': * The haskell-prime mailing list. All technical discussion will take place here, or (if other meetings take place) be reported here. Anyone can subscribe, and any subscriber can post questions and comments, and participate in discussions. Anyone can read the list archives. http://haskell.org/mailman/listinfo/haskell-prime * A wiki / issue tracking system to document consensus and to track ongoing tasks. This system is publicly readable, but only committee writable so that we may present it as the "official" output of the committee. If you ever feel that the wiki is not accurate as to the consensus, please alert the committee! http://hackage.haskell.org/trac/haskell-prime * A darcs code repository for experiments, proposed libraries,and complex examples. darcs is a decentralized system, so anyone can use it, but patches should be sent to Isaac Jones: http://hackage.haskell.org/trac/haskell-prime/wiki/SourceCode Please join us in making Haskell' a success. your, Haskell' Committee p.s. Please feel free to forward this announcement to appropriate forums.

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Re: Type Eigenvariable
by oleg＠pobox.com 20 Jan '06

20 Jan '06

Bill Wood wrote: > is |nabla x, nabla y. phi(x,y)| logically equivalent to > |forall x, forall y. x <> y only-if phi(x,y)|? I use |P only-if Q| for > |P materially implies Q| First of all, I should remark that Miller and Tiu introduce two calculi (with names that are hardly speakable, even in TeX). One of them is the sequent calculus with globally and locally scoped eigen-variables and the _open_ world of predicates. The other, calculus of definitions, uses the _closed_ world of predicates (the authors neglect to emphasize the closedness, btw). Universal and existentials quantifiers deal with eigenvariables of the global scope; only nabla can affect the locally scoped eigen variables. Also, the only rules that can irrevocable destroy/create locally scoped variables are "False --> X" and "X --> True". Because of these properties, nabla quantification in the open world neither implies nor implied by the universal quantification (ditto for the existential). So, the answer to your question for the open world calculus is no. In the closed world, the matters are muddier and depend on the predicates in the closed world. If we manage to reduce our sequent to the form, "X --> Y" where X has no definition, then, by closed world property, we proved the sequent (regardless of how many locally-scoped variables we have there). So, we can in some cases replace quantifiers. I must acknowledge Chung-chieh Shan for helpful discussions on these matters.

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Type Eigenvariable [was: Simple IO Regions]
by oleg＠pobox.com 20 Jan '06

20 Jan '06

A good explanation is in Section `1. Eigenvariables and generic reasoning' of @inproceedings{MillerTiu, author = {Dale Miller and Alwen Fernanto Tiu}, title = {A Proof Theory for Generic Judgments: An extended abstract}, booktitle = {LICS}, year = {2003}, pages = {118-127}, url = \url{http://users.rsise.anu.edu.au/~tiu/lics03sub.pdf}, crossref = {DBLP:conf/lics/2003}, bibsource = {DBLP, http://dblp.uni-trier.de} } @proceedings{DBLP:conf/lics/2003, title = {18th IEEE Symposium on Logic in Computer Science (LICS 2003), 22-25 June 2003, Ottawa, Canada, Proceedings}, booktitle = {LICS}, publisher = {IEEE Computer Society}, year = {2003}, isbn = {0-7695-1884-2}, key = {LICS}, } The section explains in which sense eigen-variables are _variables_. The paper argues, btw, for the separation of those senses and for a new quantifier to mean uniqueness only. In short, when we write forall x. forall y. body then x may well be equal to y (in body). And so, forall x. forall y. B[x,y] ====> forall z. B[z,z] OTH, when we write |nabla x. nabla y. body| then x and y are guaranteed to be different, and so the implication above no longer holds. Alwen Tiu's web page http://users.rsise.anu.edu.au/~tiu/ lists the journal version of the paper.

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Re: [Haskell-cafe] Packed String parameters
by Scherrer, Chad 19 Jan '06

19 Jan '06

Thanks, Bulat. Taking a look at Hal's FastIO library now... Hal, it looks like your library could be helpful, especially if there is a way to construct a FastIO.Handle from stdin. Can this be done, or do I need to start with an actual file? Thanks, Chad -------------------------------------------------------- Hello Chad, Thursday, January 19, 2006, 1:09:38 AM, you wrote: SC> parameter. The input file is over 1 million lines long. Any ideas? see at the BlockIO and FastIO libraries http://cryp.to/blockio/blockio-2004-10-10.tar.gz http://www.isi.edu/~hdaume/haskell/FastIO.tar.gz -- Best regards, Bulat mailto:bulatz at HotPOP.com

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Re: [Haskell] Simple IO Regions
by mark＠ixod.org 19 Jan '06

19 Jan '06

Brandon Moore <brandonm(a)yahoo-inc.com> writes: (snip) > The term I've heard is "skolem constant", which is a freshly invented > thing distinct from everything else. (snip) There's a nice easy-going example in chapter 8 of http://www.cl.cam.ac.uk/Teaching/2000/LogicProof/notes.pdf where quantifiers are removed from first-order formulae. (this aside moved from haskell to haskell-cafe) -- Mark

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Re: [Haskell] Simple IO Regions
by Keean Schupke 19 Jan '06

19 Jan '06

Hi Oleg, Just made a few modifications and thought it might be useful to people. I have rewritten the functions as "liftR" and "bracketR" over a "MonadIO" monad interface (allowing monad-transformers to be used). This is now usable as Region library, as you can lift any arbitrary IO function into a Region. I don't think I have overlooked anything, and I think it is as safe as the original... but perhaps you would like to check for stupid mistakes... The exported interface is intended to be "liftR", "bracketR" and "runR". See attached "MonadIORegion.hs"... Regards, Keean. oleg(a)pobox.com wrote: >This message shows a very simple implementation of Monadic Regions >(for the particular case of IO and reading the file). The technique >*statically* guarantees that neither a file handle nor any computation >involving the handle can leak outside of the region that created >it. Therefore, the handle can be safely closed (and its resources >disposed of) whenever control leaves the corresponding 'withFile' >block. Many handles can be open simultaneously, the type system >enforces the proper nesting of their regions. The technique has no >run-time overhead and induces no run-time errors. Unlike the previous >implementation of monadic regions, only the basic extensions >(higher-ranked types and one two-parameter type class) are used. No >undecidable instances, no functional dependencies (let alone >overlapping instances) are required. In fact, the implementation uses >only one trivial typeclass and one trivial instance. > >

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(no subject)
by Andreas Bakurov 19 Jan '06

19 Jan '06

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