February 2005 - Haskell-Cafe

ANN: Cabal 0.5 (GHC 6.4 release candidate)
by Isaac Jones 19 Feb '05

19 Feb '05

This is a release-candidate for 0.6, which will be in GHC 6.4. http://www.haskell.org/cabal/download.html The Haskell Cabal The Common Architecture for Building Applications and Libraries. http://www.haskell.org/cabal IMPORTANT INFORMATION: See both the README file and the changelog for important interface changes. DOWNLOAD: The Haskell Cabal has reached pre-release stage. The community should use this release to evaluate the interfaces and explore the concepts of these tools. Download the Cabal here (source and debian versions available): http://www.haskell.org/cabal/download.html BUGS: Please report bugs and wish-list items to libraries(a)haskell.org and Isaac Jones: ijones(a)syntaxpolice.org. ABOUT: The Haskell Cabal is meant to be a part of a larger infrastructure for distributing, organizing, and cataloging Haskell Libraries and Tools. It is an effort to provide a framework for developers to more effectively contribute their software to the Haskell community. Specifically, the Cabal describes what a Haskell package is, how these packages interact with the language, and what Haskell implementations must to do to support packages. The Cabal also specifies some infrastructure (code) that makes it easy for tool authors to build and distribute conforming packages. The Cabal is only one contribution to the larger goal. In particular, the Cabal says nothing about more global issues such as how authors decide where in the module name space their library should live; how users can find a package they want; how orphan packages find new owners; and so on. NOTES: You cannot currently execute the setup scripts with "./Setup.lhs" since Cabal Hugs support isn't ready-for-prime-time. You can compile it with ghc thusly: "ghc -package Cabal Setup.lhs -o setup" and then use the "setup" executable after that. This release is meant to provide the community with concrete information about how the interfaces are shaping up. This release does NOT fix the interfaces, we can't promise not to break anything that relies on these interfaces. We hope that Haskell authors will try to package their software using these tools, and let us know where they fall short. MORE INFORMATION: Please see the web site for the source code, interfaces, and especially the proposal, which will serve as documentation for this release: http://www.haskell.org/cabal/

1 0

Problems with building GCJNI 1.2
by Dmitri Pissarenko 18 Feb '05

18 Feb '05

Hello! I am trying to build GCJNI 1.2 under Windows (cygwin) with GHC 6.2.1 and Green Card 3.01. I am getting following error messages when entering "make". <error-messages> $ make make -C src make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/gcjni/gcjni- 1.2/ src' gcc -MM -I/cygdrive/c/Programme/Java/jdk1.5.0/include -I./win32 > .c_dependences jniInit.c util.c || (rm -f .c_dependences ; exit 1) m4 JNI.m4 > JNI.hs m4 GCJNI.m4 > GCJNI.gc /cygdrive/c/Programme/GreenCard/lib/greencard-3.01/greencard-bin --target ghc - i /cygdrive/c/Programme/GreenCard/lib/greencard-3.01/imports -- libdir=/cygdrive/c/ Programme/GreenCard/lib/greencard-3.01/ GCJNI.gc Warning: unable to find StdDIS along the import path: /cygdrive/c/Programme/Gree nCard/lib/greencard-3.01/, /cygdrive/c/Programme/GreenCard/lib/greencard- 3.01/im ports, user error ("GCJNI.gc", proc. spec "gcJniJObjectToString", line 139: marshall: Don't know how to marshall (declare { jniObjRef_t * } oref in (J Object (foreign oref {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniGetJVMState", line 156: Don't know how to unmarshall ((JVM (addr vmp)),(JEnv (addr envp))) "GCJNI.gc", proc. spec "jniGetEnv", line 160: Don't know how to unmarshall (JEnv (addr envp)) "GCJNI.gc", proc. spec "jniFreeVM", line 167: marshall: Don't know how to marshall (JVM (addr vm)) "GCJNI.gc", proc. spec "jniAddClassPath", line 181: marshall: Don't know how to marshall (string s) "GCJNI.gc", proc. spec "jniAddJVMOpt", line 188: marshall: Don't know how to marshall (string s) "GCJNI.gc", proc. spec "jniFindClass", line 192: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "jniIsInstanceOf", line 200: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniExceptionOccurred", line 206: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "jniExceptionDescribe", line 211: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "jniExceptionClear", line 215: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniDeleteLocalRef", line 224: marshall: Don't know how to marshall (declare { jniObjRef_t * } oref in (J Object (foreign oref {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniNewLocalRef", line 230: marshall: Don't know how to marshall (declare { jniObjRef_t * } lsrc in (J Object (foreign lsrc {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniNewGlobalRef", line 239: marshall: Don't know how to marshall (declare { jniObjRef_t * } loref in ( JObject (foreign loref {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniGetStaticMethodID", line 248: marshall: Don't know how to marshall (declare { jniObjRef_t * } cls in (JO bject (foreign cls {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniGetMethodID", line 255: marshall: Don't know how to marshall (declare { jniObjRef_t * } cls in (JO bject (foreign cls {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniGetStaticFieldID", line 263: marshall: Don't know how to marshall (declare { jniObjRef_t * } cls in (JO bject (foreign cls {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniGetFieldID", line 270: marshall: Don't know how to marshall (declare { jniObjRef_t * } cls in (JO bject (foreign cls {jniFreeObjRef}))) "GCJNI.gc", proc. spec "jniNewStringUTF", line 277: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "jniNewObjectArray", line 285: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniObjToJValue", line 295: marshall: Don't know how to marshall (declare { jniObjRef_t * } oref in (J Object (foreign oref {jniFreeObjRef}))) "GCJNI.gc", proc. spec "gcJniObjFromJValue", line 304: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "jniPushLocalFrame", line 311: marshall: Don't know how to marshall (int count) "GCJNI.gc", proc. spec "gcJniIntToJValue", line 325: marshall: Don't know how to marshall (int val) "GCJNI.gc", proc. spec "gcJniIntFromJValue", line 330: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "gcJniFloatToJValue", line 335: marshall: Don't know how to marshall (float val) "GCJNI.gc", proc. spec "gcJniFloatFromJValue", line 340: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "gcJniDoubleToJValue", line 345: marshall: Don't know how to marshall (double val) "GCJNI.gc", proc. spec "gcJniDoubleFromJValue", line 350: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "gcJniBoolToJValue", line 355: marshall: Don't know how to marshall (bool val) "GCJNI.gc", proc. spec "gcJniBoolFromJValue", line 360: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "gcJniCharToJValue", line 365: marshall: Don't know how to marshall (char val) "GCJNI.gc", proc. spec "gcJniCharFromJValue", line 370: marshall: Don't know how to marshall (addr jvalp) "GCJNI.gc", proc. spec "gcJniAllocJValue", line 377: marshall: Don't know how to marshall (int nv) "GCJNI.gc", proc. spec "gcJniFree", line 386: marshall: Don't know how to marshall (addr a) "GCJNI.gc", proc. spec "gcJniCallStaticVoidMethod", line 391: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallVoidMethod", line 396: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualVoidMethod", line 401: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticObjectField", line 406: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetObjectField", line 414: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticObjectMethod", line 422: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallObjectMethod", line 430: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualObjectMethod", line 439: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticIntField", line 451: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetIntField", line 457: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticIntMethod", line 463: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallIntMethod", line 469: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualIntMethod", line 474: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticCharField", line 481: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetCharField", line 487: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticCharMethod", line 493: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallCharMethod", line 499: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualCharMethod", line 504: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticByteField", line 511: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetByteField", line 517: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticByteMethod", line 523: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallByteMethod", line 529: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualByteMethod", line 534: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticFloatField", line 541: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetFloatField", line 547: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticFloatMethod", line 553: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallFloatMethod", line 559: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualFloatMethod", line 564: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticDoubleField", line 571: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetDoubleField", line 577: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticDoubleMethod", line 583: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallDoubleMethod", line 589: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualDoubleMethod", line 594: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetStaticBooleanField", line 601: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetBooleanField", line 607: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallStaticBooleanMethod", line 613: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallBooleanMethod", line 619: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniCallNonvirtualBooleanMethod", line 624: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniNewObject", line 635: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniIsSameObject", line 649: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniGetObjectClass", line 658: marshall: Don't know how to marshall (JEnv (addr env)) "GCJNI.gc", proc. spec "gcJniAllocArgLocals", line 677: marshall: Don't know how to marshall (int capacity) "GCJNI.gc", proc. spec "gcJniFreeArgLocals", line 682: marshall: Don't know how to marshall (addr als) ) make[1]: *** [GCJNI.hs] Error 1 make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/gcjni/gcjni- 1.2/s rc' make: *** [src] Error 2 </error-messages> I think that the error is caused by missing StdDIS file in the GreenCard directory. The files in this directory are (ls -lAR): <filelist> .: total 0 drwxr-xr-x+ 2 eleonora Kein 0 Feb 15 21:55 bin drwxr-xr-x+ 3 eleonora Kein 0 Feb 15 21:47 lib ./bin: total 1 -rwxr-xr-x 1 eleonora Kein 164 Feb 15 21:55 greencard ./lib: total 0 drwxr-xr-x+ 4 eleonora Kein 0 Feb 15 21:55 greencard-3.01 ./lib/greencard-3.01: total 1867 drwxr-xr-x+ 2 eleonora Kein 0 Feb 15 21:55 Foreign -rwxr-xr-x 1 eleonora Kein 1895082 Feb 15 21:55 greencard-bin.exe drwxr-xr-x+ 3 eleonora Kein 0 Feb 15 21:55 imports -rwxr-xr-x 1 eleonora Kein 6612 Feb 15 21:55 libHSgreencard.a -rwxr-xr-x 1 eleonora Kein 8670 Feb 15 21:55 libHSgreencard.p_a ./lib/greencard-3.01/Foreign: total 4 -rwxr-xr-x 1 eleonora Kein 3309 Feb 15 21:55 GreenCard.gc ./lib/greencard-3.01/imports: total 0 drwxr-xr-x+ 2 eleonora Kein 0 Feb 15 21:55 Foreign ./lib/greencard-3.01/imports/Foreign: total 16 -rwxr-xr-x 1 eleonora Kein 7392 Feb 15 21:55 GreenCard.hi -rwxr-xr-x 1 eleonora Kein 7397 Feb 15 21:55 GreenCard.p_hi </filelist> As you see, there is no StdDIS file among them. AFAIK, the installation of GreenCard 3.01 was successful. I would like to receive a hint about how this problem can be solved. TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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new Haskell hacker seeking peer review
by Sean Perry 18 Feb '05

18 Feb '05

I am learning Haskell, so I decided to implement everyone's favorite, overused Unix command -- cat. Below is my simple implementation, comments about style, implementation, etc. are welcomed. In particular, is my untilEOF idiomatically ok? Is there a better way to accomplish this? Also, while talking about untilEOF, it is slightly annoying that hIsEOF returns IO Bool and that functions like 'not' only want Bool. Sure makes the logic tests feel like more work than they should be. cat.hs: module Main where import IO import System(getArgs) untilEOF :: Handle -> (Handle -> IO ()) -> IO () untilEOF hdl f = do eof <- hIsEOF hdl if eof then return () else do f hdl untilEOF hdl f cat :: Handle -> IO () cat hdl = do line <- hGetLine hdl putStrLn line catFile :: FilePath -> IO () catFile path = do hdl <- openFile path ReadMode untilEOF hdl cat main :: IO () main = do args <- getArgs if (length args) > 0 then mapM_ catFile args else untilEOF stdin cat

3 2

IO and Wash
by John Goerzen 17 Feb '05

17 Feb '05

I'm trying out WASH for a project. It looks nice, but I/O looks tricky. I have a database lookup, and I want to present each row as an option for the user. Page 15 of the Wash user-manual.pdf has an example of using the abstract table to do this. It works fine, but... if a user hits the submit button without selecting anything, they get a JavaScript message saying validation fails. Good, that's what I want to happen. But when Wash tries to re-display the current form, all the data from the database is rendered empty. I am using the example code almost verbatim. Any ideas? Thanks, John

2 11

Haskell-Java co-operation via haskell-jvm-bridge
by Dmitri Pissarenko 17 Feb '05

17 Feb '05

Hello! I have problems with building a simple Haskell program, which uses Java to perform some calculation (via haskell-jvm bridge). A more detailed description of my problem is given here http://dapissarenko.com/resources/2005_02_17_eigenvaluesJava/2005_02_17_eig… All code files related to this problem are available here (approx. 7 MB): http://dapissarenko.com/resources/2005_02_17_eigenvaluesJava/2005_02_17_lik… I appreciate any hint about how to solve the problem. Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

1 0

Showable mutually recursive (fixed-point) datatypes
by Remi Turk 16 Feb '05

16 Feb '05

[WARNING: braindamag(ed|ing) experience following] Hi all, a few days ago I decided I desperately needed a set which could contain (among others) itself. My first idea was > module Main where > import List > import Monad > data Elem s a = V a | R (s (Elem s a)) Now, a self-containing list can be defined as > l :: [Elem [] Integer] > l = [V 42, R [V 6, V 7], R l] As my brain could handle that, and I noticed quite some similiarity between Elem and Either, I decided to try to abstract the thing a little. This is what I ultimately came up with > newtype Comp f g x = Comp (f (g x)) > newtype Rec f = In (f (Rec f)) The idea is that `Elem s a' is basically just `Either a (s SELF)'. Then, instead of defining a special-purpose mutually-recursive "fixed-point type", another type `Comp' is defined to compose two types into one, to enable the standard Fix/Mu/Rec type to be used. > type RecCont s a= s (Either a (RecElem s a)) A recursive container is a container with simple elements (Left a) and recursive container-elements (Right (RecElem s a)) > type RecElem s a= Rec (Comp s (Either a)) And a recursive container-element is, err, a slightly obscured recursive container. (s (Either a SELF)) > el :: a -> Either a (RecElem s a) > el = Left > rec :: RecCont s a -> Either a (RecElem s a) > rec = Right . In . Comp > unRec :: RecElem s a -> RecCont s a > unRec (In (Comp f)) = f And indeed, a list (or set, or whatever) which contains itself is easily defined. > s :: RecCont [] Integer > s = [el 42, rec [el 6, el 7], rec s] The next step was to try to get it an instance of Show. Funny enough, around that time, Shin-Cheng Mu posed the question of how to make Rec an instance of Show[1], the (Haskell98) solution of which I had just found on the HaWiki.[2] > class RecShow f where > recShow :: Show a => f a -> String > instance RecShow f => Show (Rec f) where > show (In f) = "(In (" ++ recShow f ++ "))" > instance Show a => RecShow (Either a) where recShow = show However, I didn't just want some `Rec f' to be an instance of Show, I wanted `Rec (Comp f g)' to be an instance of Show. Which turned out not to be all that easy. My best solution works, but I hope someone has a better idea...? > class CompShow f where > compShow :: (Show a, RecShow g) => f (g a) -> String > instance (CompShow f, RecShow g, Show a) => Show (Comp f g a) where > show (Comp f)= "(Comp (" ++ compShow f ++ "))" > instance CompShow [] where > compShow l = "[" ++ (concat $ intersperse "," $ map recShow l) ++ "]" > instance (CompShow f, RecShow g) > => RecShow (Comp f g) where recShow = show Anyway, once this worked I just had to find some use for it ;) > flatten :: (Monad s, Functor s) => RecCont s a -> s a > flatten = join . fmap (either return (flatten . unRec)) > noI'mNotEvil :: Num a => a -> RecCont IO a > noI'mNotEvil n = do > putStrLn $ showString "Attempt #" $ shows n > $ ": Hi, what's The Answer?" > s <- getLine > return $ if s == "42" > then el n > else rec (noI'mNotEvil (n+1)) > main = do > n <- flatten (noI'mNotEvil 1) > if n > 1 > then putStrLn "Did that really have to take so long?" > else putStrLn "Well done!" [1] http://www.haskell.org//pipermail/haskell/2005-February/015325.html [2] http://www.haskell.org/hawiki/PreludeExts -- Nobody can be exactly like me. Even I have trouble doing it.

1 0

RE: [Haskell-cafe] Point-free style (Was: Things to avoid)
by Simon Marlow 16 Feb '05

16 Feb '05

On 10 February 2005 14:23, Jan-Willem Maessen wrote: > If you're trying to avoid obscurity, why advocate point-free style? > > I ask this question to be deliberately provocative; I'm not trying to > single you out in particular. So, to everybody: What's so great about > point-free style? I completely agree. I find myself tending towards pointfull-style these days, perhaps because I'm getting lazy and find it easier to read code when lots of things have names. I use explicit function definitions and lambda bindings a lot more than I used to - at some point I figured out that the number of characters in my source code isn't the right target for optimisation :-) I don't think a general "things to avoid" section should be advocating not naming things... in fact I would advocate the reverse. Name as many things as possible, at least until you have a good feel for how much point-freeness is going to result in code that you can read again in 6 months time. Cheers, Simon

2 1

RE: [Haskell-cafe] IO and Wash
by Simon Marlow 16 Feb '05

16 Feb '05

On 16 February 2005 14:30, John Goerzen wrote: > On Wed, Feb 16, 2005 at 07:31:07AM +0100, Tomasz Zielonka wrote: >>> verbatim. Any ideas? >> >> I have never used table_io. maybe there's a bug in it. Hmmm, it seems >> to be conceptually wrong. The single purpose of table_io seems to be >> to avoid keeping the result of an IO action in the log. But how is >> WASH going to recreate it when it's needed again as in your example? > > Ahh, I think I understand what you're saying... table_io is not > supposed to be unsafe; that is, it should work without saving data in > the log even if the input would be different on a different session. > But yes, if the validation fails, there would be no way to do that > save re-reading the input. > > It sounds like, in my case, unsafe_io would be better. My input > should never change across a single session. > > The next question is this: the I/O really only needs to be done once. > Once the user has selected an item, that's enough. If my > understanding is correct, on each subsequent screen in my > application, Wash will follow through the entire call history, and > will run the I/O again even if not needed. Is that correct? Or does > the unsafe_io prevent that? You can avoid lots of unnecessary state-saving by judicious use of WASH's 'once' function. eg. ... r <- once ( ... lots of IO ... ) ... will save the value of r in the log, and not repeat the entire inner action each time the script is run. In fact, it might be helpful to note that io = once . unsafe_io Cheers, Simon

2 1

Installation with yum.
by Manoj Kummini 16 Feb '05

16 Feb '05

Hi. I am trying to install haskell on FC3 following the instructions from http://www.haskell.org/fedora/ I copied the lines: root@blandings ~# cat /etc/yum.repos.d/haskell.repo [haskell-stable] name=Haskell Packages (stable) baseurl=http://haskell.org/fedora/haskell/$releasever/$basearch/RPMS.stable gpgcheck=1 installdir=/opt root@blandings ~# When I try to install it, nothing happens, and I get the following message: root@blandings ~# yum install haskell-stable Setting up Install Process Setting up Repo: base repomd.xml 100% |=========================| 1.1 kB 00:00 Setting up Repo: haskell-stable repomd.xml 100% |=========================| 951 B 00:00 Setting up Repo: updates-released repomd.xml 100% |=========================| 951 B 00:00 Reading repository metadata in from local files base : ################################################## 2622/2622 haskell-st: ################################################## 53/53 primary.xml.gz 100% |=========================| 292 kB 03:02 MD Read : ################################################## 684/684 updates-re: ################################################## 684/684 No Match for argument haskell-stable Nothing to do root@blandings ~# I am new to yum, and could not find much help on the web for using this. Could someone tell me what I am missing or point to a URL? Asking the same question in Google Groups fedora got me the answer that I should use # yum -c /etc/yum.repos.d/haskell.repo install haskell-stable but that returned the same message as above. I posted the same question to the haskell list, but I realised that this is probably the correct list to post it to. Thanks Manoj. -- Manoj Kummini Graduate Student, Dept. of Mathematics, The Univ. of Kansas, Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W. http://www.math.ku.edu/~kummini/index.html

1 0

RE: [Haskell-cafe] Unsafe IO and Wash
by Simon Marlow 16 Feb '05

16 Feb '05

On 16 February 2005 14:28, John Goerzen wrote: > On Wed, Feb 16, 2005 at 07:16:50AM +0100, Tomasz Zielonka wrote: >> On Wed, Feb 16, 2005 at 04:33:29AM +0000, John Goerzen wrote: >>> On a related note, Wash seems to be preserving all sorts of >>> unnecessary "state" from previous screens a user visited. >> >> You do know that the current version of WASH rebuilds the >> continuation by repeating all the previous steps, don't you? Until >> WASH can keep the > > Yes. What I don't understand is why. If I have a submit button, and > it is passing one value to the next function, and that value is from > an > entry form on the screen, why would I care about all the previous > state? That's my confusion. It seems unnecessary. WASH would have to store the value of the next function in the log, as a continuation. If that is a top-level function then it's easy, but WASH lets you use an arbitrary expression as the continuation, which might include an arbitrary amount of data captured in the free variables. Storing this continuation directly in the web page would require low-level trawling of the Haskell heap. WASH's Haskell-only solution is so neat because it doesn't need to do this: it just recreates the continuation by recording how it was created. Cheers, Simon

1 0