- Haskell-Cafe - Haskell.org

Strange HTTP module behavior
by John Goerzen 21 Feb '05

21 Feb '05

Hello, I am trying to send a simple SOAP message to an Apache server. I got the HTTP library from the XML-RPC library and thought this would make an easy client. However, I'm having two problems. First, even though I am sending an accurate Content-Length header with my POST message, the server is timing out and returning a 500 Internal Server Error document. Second, after reading that error document, Network.HTTP is generating an error of its own. Here's an strace illustrating it: recvfrom(3, "ssResponse> </soapenv:Body>\n</soapenv:Envelope>", 1000, 0, NULL, N ULL) = 47 recvfrom(3, "", 1000, 0, NULL, NULL) = 0 shutdown(3, 1 /* send */) = 0 shutdown(3, 0 /* receive */) = 0 close(3) = 0 ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0 fcntl(2, F_GETFL) = 0x8002 (flags O_RDWR|O_LARGEFILE|0x800 0) write(2, "\nFail: ", 7) = 7 write(2, "Network.Socket.recv: end of file (end of file)\n", 47) = 47 write(2, "\n", 1) = 1 I *think* that what's happening is that ghc threw an exception for the empty recvfrom response, then the exception handler closed the conection, and then the exception was prnited to stderr. Oh, tcpdump verified that both client and server are sending Connection: close headers. Any ideas? -- John

5 7

Re: Strange HTTP module behavior [PATCH]
by John Goerzen 21 Feb '05

21 Feb '05

On Fri, Feb 18, 2005 at 11:36:57PM +0100, Bjorn Bringert wrote: > John Goerzen wrote: > >It turns out that Network.Socket.recv raises an EOF error when it gets > >back 0 bytes of data. HTTP is expecting it to return an empty list for > >some reason. > > > >The below patch fixed it for me. > > [...] > > Hmm, strange. Is that recv behavior a bug or a feature? I don't know, but it's explicitly there whatever it is. From ghc 6.2.2: let len' = fromIntegral len if len' == 0 then ioError (mkEOFError "Network.Socket.recv") else peekCStringLen (ptr,len') It appears this change was committed to fptools in version 1.26 of Socket.hsc on July 15, 2002. http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/libraries/network/Network… Which arguably is not what one would expect recv to do, and in any case is undocumented at http://www.haskell.org/ghc/docs/latest/html/libraries/network/Network.Socke… Still, 2002 was awhile back, so I'm still surprised nobody else noticed. -- John

3 2

Re: [Haskell-cafe] Literate Haskell
by yeoh＠cs.wisc.edu 20 Feb '05

20 Feb '05

> Date: Fri, 18 Feb 2005 21:21:00 +0100 > From: Dmitri Pissarenko <mailing-lists(a)dapissarenko.com> > > Hello! > > I'm curious what experienced Haskellers think about using literate > Haskell in daily work. > > It seems to me like a good idea, since during coding it often helps to > write down one's thoughts (often, I find a solution to a complicated > problem in this way). I use LHS by default. Here's some stats on the single LHS file I've been hacking away at: Lines of comments over code: 53% Char count of comments/code: 49% This is for a 754-line file. I'm real big on notes/comments, since I have often stared in bewilderment at my own code years later wondering what the heck I was doing. The puzzlement is unusual; normally, it's a good laugh. I use TextPad, and some of the comments are sidelined Haskell snippets, like on a pasteboard. Syntax coloring is active throughout the file, except in comments enclosed by "--/", which is my little kludge on TextPad to get it to work out right. Works nicely so far.

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ANN: Cabal 0.5 (GHC 6.4 release candidate)
by Isaac Jones 20 Feb '05

20 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 19 Feb '05

19 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

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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

transformation of point-free expressions
by Daniel Fischer 16 Feb '05

16 Feb '05

G'day ye all, is there an *elegant* way to transform ( (.) (flip (.) (flip ($)))) . flip (.) . flip (.) to the more compact form flip (.) . flip ? And more general, is there an algorithm to simplify such expressions (other than take a piece of paper, apply it to the appropriate number of arguments and see what you get)? Thanks in advance, Daniel

1 0

Problems building GreenCard
by Dmitri Pissarenko 15 Feb '05

15 Feb '05

Hello! I'm trying to build GreenCard 3.01 (latest release according to http://www.haskell.org/greencard/) under Windows with cygwin and GHC 6.2.1. I'm getting these errors: <errors> $ make prefix=/cygdrive/c/Programme/GreenCard/ install install-pkg make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/g reencard-3.01/src' rm -f .depend touch .depend ghc -M -optdep-f -optdep.depend -optdep-xFiniteMap -optdep-xPretty -recomp -O - f glasgow-exts Casm.lhs DIS.lhs Decl.lhs ErrMonad.lhs FillIn.lhs FillInMonad.l hs GCToken.lhs GreenCard.lhs Lex.lhs LexM.lhs ListUtils.lhs MarshallMonad.lhs Na me.lhs NameSupply.lhs Package.lhs PrettyUtils.lhs Proc.lhs Process.lhs Target.lh s Type.lhs Parse.hs make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/gr eencard-3.01/src' make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/g reencard-3.01/src' ghc -recomp -O -fglasgow-exts -c Target.lhs -o Target.o ghc -recomp -O -fglasgow-exts -c PrettyUtils.lhs -o PrettyUtils.o ghc -recomp -O -fglasgow-exts -c Casm.lhs -o Casm.o Casm.lhs:544: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:577: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:616: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... Casm.lhs:631: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... ghc -recomp -O -fglasgow-exts -c ListUtils.lhs -o ListUtils.o ghc -recomp -O -fglasgow-exts -c ErrMonad.lhs -o ErrMonad.o ghc -recomp -O -fglasgow-exts -c Name.lhs -o Name.o ghc -recomp -O -fglasgow-exts -c DIS.lhs -o DIS.o ghc -recomp -O -fglasgow-exts -c Type.lhs -o Type.o ghc -recomp -O -fglasgow-exts -c Decl.lhs -o Decl.o ghc -recomp -O -fglasgow-exts -c FillInMonad.lhs -o FillInMonad.o ghc -recomp -O -fglasgow-exts -c NameSupply.lhs -o NameSupply.o ghc -recomp -O -fglasgow-exts -c FillIn.lhs -o FillIn.o ghc -recomp -O -fglasgow-exts -c GCToken.lhs -o GCToken.o ghc -recomp -O -fglasgow-exts -c MarshallMonad.lhs -o MarshallMonad.o ghc -recomp -O -fglasgow-exts -c Proc.lhs -o Proc.o ghc -recomp -O -fglasgow-exts -c LexM.lhs -o LexM.o ghc -recomp -O -fglasgow-exts -c Lex.lhs -o Lex.o ghc -recomp -O -fglasgow-exts -Onot -c Parse.hs -o Parse.o Parse.hs:1733: Warning: Pattern match(es) are overlapped In a case alternative: _ -> ... ghc -recomp -O -fglasgow-exts -c Process.lhs -o Process.o ghc -recomp -O -fglasgow-exts -c Package.lhs -o Package.o ghc -recomp -O -fglasgow-exts -cpp -DBEGIN_GHC_ONLY='-}' -DEND_GHC_ONLY='{- ' - DBEGIN_NOT_FOR_GHC='{-' -DEND_NOT_FOR_GHC='-}' -DPURE_WIN32=0 -c GreenCard.lhs -o GreenCard.o ghc -c ErrorHook.c -o ErrorHook.o ghc -recomp -O -fglasgow-exts -o greencard-bin Casm.o DIS.o Decl.o ErrMonad. o FillIn.o FillInMonad.o GCToken.o GreenCard.o Lex.o LexM.o ListUtils.o Marshall Monad.o Name.o NameSupply.o Package.o PrettyUtils.o Proc.o Process.o Target.o Ty pe.o Parse.o ErrorHook.o sed < greencard.ghc.in > greencard "s|@libdir@|/cygdrive/c/Programme/GreenCard// lib/greencard-3.01|g" chmod a+x greencard install -D greencard-bin /cygdrive/c/Programme/GreenCard//lib/greencard- 3.01/gre encard-bin install -D greencard /cygdrive/c/Programme/GreenCard//bin/greencard make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/gr eencard-3.01/src' make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/g reencard-3.01/lib' ../src/greencard-bin --libdir=. Foreign/GreenCard.gc ghc -package-name greencard -cpp -fglasgow-exts -fno-prune-tydecls -c Foreign/ GreenCard.hs -o Foreign/GreenCard.o -hisuf hi ghc.exe: unrecognised flags: -fno-prune-tydecls Usage: For basic information, try the `--help' option. make[1]: *** [Foreign/GreenCard.o] Error 1 rm Foreign/GreenCard.hs make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/gr eencard-3.01/lib' make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/g reencard-3.01/src' make[1]: Nothing to be done for `install'. make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/gr eencard-3.01/src' make[1]: Entering directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/g reencard-3.01/lib' ../src/greencard-bin --libdir=. Foreign/GreenCard.gc ghc -package-name greencard -cpp -fglasgow-exts -fno-prune-tydecls -prof -c For eign/GreenCard.hs -o Foreign/GreenCard.p_o -hisuf p_hi ghc.exe: unrecognised flags: -fno-prune-tydecls Usage: For basic information, try the `--help' option. make[1]: *** [Foreign/GreenCard.p_o] Error 1 rm Foreign/GreenCard.hs make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/greencard- 3.01/gr eencard-3.01/lib' make: *** [install] Error 2 </errors> How can I fix them? TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

1 1

RE: [Haskell-cafe] Point-free style
by Tim Docker 15 Feb '05

15 Feb '05

Ketil Malde wrote: > (.) . (.) .(.) > > I entered it into GHCi, and got > > :: forall a a b c a. > (b -> c) -> (a -> a -> a -> b) -> a -> a -> a -> c I spent a minute or so attempting to intuit the type signature of this, before cheating and entering it into ghci also. Is there a straightforward technique by which type signatures can be "hand calculated", or does one end up needing to run the whole inference algorithm in one's head? Tim

12 17

RE: [Haskell-cafe] Parsing in Haskell
by Simon Marlow 15 Feb '05

15 Feb '05

On 15 February 2005 10:36, Johan Glimming wrote: > I want to implement a little algebraic specification language in > Haskell, and I have a working C implementation available which uses > yacc/flex. > > What is the best way of replacing yacc/bison and (f)lex when migrating > the project into Haskell? There are yacc & lex equivalents for Haskell, in the form of Happy (http://www.haskell.org/happy) and Alex (http://www.haskell.org/alex) respectively. Cheers, Simon

1 0

Parsing in Haskell
by Johan Glimming 15 Feb '05

15 Feb '05

Hi I want to implement a little algebraic specification language in Haskell, and I have a working C implementation available which uses yacc/flex. What is the best way of replacing yacc/bison and (f)lex when migrating the project into Haskell? Best Wishes, Johan

4 3

RE: [Haskell-cafe] Top 20 ``things'' to know in Haskell
by Bayley, Alistair 15 Feb '05

15 Feb '05

Were you thinking of something like "[n] Things a Java Programmer Should Know About Ruby" ? http://jimweirich.tadalist.com/lists/public/14055 Perhaps you'd like to start a page on the wiki. A link from here, maybe? http://haskell.org/hawiki/FrequentlyAskedQuestions The libraries I think I used the most when starting were: Data.List Data.Char Data.Maybe Data.Either System.IO (reading and writing files) System.Environment (for getArgs) Data.Set Data.FiniteMap (soon to be replaced) Of course, a lot of this is already in the Prelude, so you'll be using it indirectly. > -----Original Message----- > From: Jacques Carette [mailto:carette@mcmaster.ca] > Sent: 07 February 2005 15:31 > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Top 20 ``things'' to know in Haskell > > The recent post of Graham Klyne (below) reminds me that I > have meant to ask: > is there a ``top 20'' things a serious programmer should know > when writing > code in Haskell? Of course there is a lot of programming > language theory > that would be great to know, but I mean really down-to-earth > things like the > 2 items below (module Maybe, the 'maybe' function). > > The Haskell libraries are quite large, and it is unrealistic > to try to get > familiar with all of them right away. But getting a > ``small'' list would be > very useful - I think of this as step 2 after one learns to > get comfortable > with a language. I had done this (for Maple) for training > new hires at > Maplesoft, and I definitely noticed that they became more idiomatic > programmers faster this way. > > Jacques > > PS: of course, this could already exist on haskell.org and/or > the Wiki, but > not in an 'obvious' enough place as I missed it... > > -----Original Message----- > From: haskell-cafe-bounces(a)haskell.org > [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Graham Klyne > Sent: February 7, 2005 10:09 AM > To: Yuri D'Elia; haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Re: [Haskell] [newbye] 'Just a' > > You might also be interested in the library function 'maybe': > http://www.haskell.org/onlinereport/standard-prelude.html#$vmaybe > > or maybe (sic) Maybe.fromMaybe in: > http://www.haskell.org/onlinereport/maybe.html > > #g ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

15 27

RDF and stuff (was: Point-free style ...)
by Graham Klyne 15 Feb '05

15 Feb '05

At 23:00 10/02/05 -0500, David Menendez wrote: >Here's another one: > > addTriple (s,p,o) = addArc s p o . addNode s . addNode p . addNode o It looks like you're playing around with RDF here. A quick check of your web site shows a Semantic Web angle to some of your workings. I also see you show up in some of the ESW work. You may be interested that I have a full RDF/XML parser in Haskell (based on a modified version of HaXML) (and also a reasonably competent Notation3 parser). It passes all of Dave Beckett's RDF parser test cases, which include all the W3C RDF core WG test cases, (except one to do with I18N handling). I haven't yet found time to wrap it all up neatly, but the code is available here: RDF/XML parser and test code: http://www.ninebynine.org/Software/HaskellRDF/RDF/Harp/ Supporting code for RDF node handling: http://www.ninebynine.org/Software/HaskellRDF/RDF/Label/ Modified HaXML parser: http://www.ninebynine.org/Software/HaskellUtils/HaXml-1.12/ URI parser (above should also work with library version in next GHC): http://www.ninebynine.org/Software/HaskellUtils/Network/ Possibly uses some other support modules from: http://www.ninebynine.org/Software/HaskellUtils/ I had been meaning to wrap all this into my Swish package (http://www.ninebynine.org/RDFNotes/Swish/Intro.html) but real work intervened. I do intend to return to this when I can find an excuse to make it part of the new day job. #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

1 0

Automatic pointless translation
by oleg＠pobox.com 15 Feb '05

15 Feb '05

This message is a literate Haskell98 code for translating proper linear combinators into a point-free style. That is, we will be converting (closed, albeit that is not strictly a requirement) terms of the form ``\x1 ... xn -> term'' where each variable xi has at most one occurrence in term. The technique can be easily generalized to non-linear terms. Other possible generalizations is automatical derivation of the point-less code from the _signature_ of a function. The body of the function isn't actually needed, for applicative and tuple fully-polymorphic functions. > module PF where Our terms have the following simple structure > data Term = Var String > | CId -- identity > | CC -- composition > | CK -- const > | CF -- flip > | A Term Term > deriving (Eq, Show) and a bit of standard term-rewriting grind > occurs v v' | v == v' = True > occurs v (A t1 t2) = occurs v t1 || occurs v t2 > occurs _ _ = False > > ground (Var _) = False > ground (A t1 t2) = ground t1 && ground t2 > ground _ = True We introduce term normalization. A normalized term has the following structure data NT = Ground | A NT Var | A NT Ground that is, the term tree is linear with respect to variables. After normalization, our (closed) source term \x1 ... xn -> term becomes \x1 ... xn -> term' y1 ... ym where each y1 is either a variable or a ground term, and term' is ground. Furthermore, if we drop ground terms from the list y1 ... ym, it becomes a permutation of a subset of x1 ... xn. The normalization is easily performed by tree rotations > norm t | ground t = t > norm (A t1 v@(Var _)) = A (norm t1) v > norm (A t1 t2) | ground t2 = A (norm t1) t2 > norm (A t1 (A t2 t3)) = norm (A (A (A CC t1) t2) t3) > norm v@(Var _) = A CId v > norm c = c As you can see, guards are prominent. A few tests > test1 = norm (A (Var "f") (A (A (Var "g") (Var "a")) (Var "b"))) > -- \f g h x y -> f (g x) (h y) > test2 = norm (A (A (Var "f") (A (Var "g") (Var "x"))) > (A (Var "h") (Var "y"))) > > test32 = norm (A CF (A (A (A (A CId CC) CC) (Var "f")) (Var "g"))) > test34 = norm (A (A CC (A CC CF)) (A (A CId CC) CC)) > test35 = norm (A (A CC (A (Var "g") CF)) (A (A CId CC) CC)) The next step is elimination of variables using eta-reductions, const introductions, and flips to bring the variables into the right position. The function `elim' takes a list of free variables to eliminate, in reverse order, and the term. The function returns the point-free term. > elim [] t = t > -- eta reduction, linearity assumption > elim (h:r) (A t v) | h == v = elim r t > -- if \a b -> t a b then > -- \a b x -> const (t a b) x > elim (h:r) t | not (occurs h t) = elim r (norm (A CK t)) > elim v@(h:r) t = elim v (norm (doflip h t)) > where > doflip v (A (A t v1) v2) | v == v1 = (A (A (A CF t) v2) v1) > doflip v (A t v2) = A (doflip v t) v2 > doflip v t = error $ (show v) ++ "\n" ++ (show t) And that is it. We just need to print the terms nicely: > print_nice (Var v) = show v > print_nice (A (A CC x) y) = "(" ++ (print_nice x) ++ " . " > ++ (print_nice y) ++ ")" > print_nice (A CC x) = "(" ++ (print_nice x) ++ " .)" > print_nice (A x y) = "(" ++ print_nice x ++ ") (" ++ > print_nice y ++ ")" > print_nice CC = "(.)" > print_nice CK = "const" > print_nice CId = "id" > print_nice CF = "flip" > > report' vars term = elim (reverse $ (map Var) vars) (norm term) > report vars = print_nice . report' vars We are ready for some tests: The first two tests are trivial: \f x y -> f x y > test11 = report ["f","x","y"] (A (A (Var "f") (Var "x")) (Var "y")) *PF> test11 "id" And \f x y -> f y x > test12 = report ["f","x","y"] (A (A (Var "f") (Var "y")) (Var "x")) *PF> test12 "(flip . id)" the next one is simple too: \f x y -> f x > test13 = report ["f","x","y"] (A (Var "f") (Var "x")) *PF> test13 "((const .) . id)" Now we can try \f g a b -> f (g a b) > test14 = report ["f","g","a","b"] > (A (Var "f") (A (A (Var "g") (Var "a")) (Var "b"))) *PF> test14 "((.) . (.))" and \f g h x y -> f (g x) (h y) > test15 = report ["f","g","h","x","y"] > (A (A (Var "f") (A (Var "g") (Var "x"))) (A (Var "h") (Var "y"))) *PF> test15 "((flip .) . ((.) . ((.) .)))" The reported derivation was ((flip . ((.) .)) .) . (.) These terms are equivalent. One may look at their types, which are identical. One may also apply these terms to suitable arguments, e.g., ((flip .) . ((.) . ((.) .))) (,) ((,) 1) ((,) 2) 3 4 This sub-thread started from \f g a b -> f (g a b): two-to-one composition, aka triple-(.). Can we generalize? Certainly: \f g a b c -> f (g a b c) > test16 = report ["f","g","a","b","c"] > (A (Var "f") > (A (A (A (Var "g") (Var "a")) (Var "b")) (Var "c"))) *PF> test16 "(((.) . (.)) . (.))" \f g a b c d -> f (g a b c d) > test17 = report ["f","g","a","b","c","d"] > (A (Var "f") > (A (A (A (A (Var "g") (Var "a")) (Var "b")) (Var "c")) > (Var "d"))) *PF> test17 "((((.) . (.)) . (.)) . (.))" *PF> ((((.) . (.)) . (.)) . (.)) ((,) 1) (,,,) 10 11 12 13 (1,(10,11,12,13)) \f g h a b c d -> f (g a b) (h c d) > test18 = report ["f","g","h","a","b","c","d"] > (A (A (Var "f") > (A (A (Var "g") (Var "a")) (Var "b"))) > (A (A (Var "h") (Var "c")) (Var "d"))) *PF> test18 "((flip .) . (((flip .) .) . (((.) . (.)) . (((.) . (.)) .))))" It really begins to look like Unlambda...

1 0

Parse error in a package file
by Dmitri Pissarenko 14 Feb '05

14 Feb '05

Hello! I'm building the haskell-jvm-bridge (http://sourceforge.net/projects/jvm- bridge/). The final step of the building procedure is to install the package of haskell- jvm-bridge. When I enter ghc-pkg -a -f javavm.ghc-pkg I'm getting the error javavm.ghc-pkg: parse error in package config file The original file looks as shown below. <original-file> Package { name = "javavm", import_dirs = ["c:/Programme/haskell-jvm-bridge-0.3- RC1/imports/"], source_dirs = [], library_dirs = [ "c:/Programme/haskell-jvm-bridge-0.3-RC1/lib/"-L ], hs_libraries = [], extra_libraries = ["stdc++","JVMBridge","JVMInvocation","HaskellJVMBridge"-L,"jvm_imp"], include_dirs = [], c_includes = [], package_deps = ["lang","concurrent","haskell98"], extra_ghc_opts = ["-fglasgow-exts","-fallow-undecidable-instances"], extra_cc_opts = [], extra_frameworks = [-L ], extra_ld_opts = [ "-Wl,-rpath,c:/Programme/haskell-jvm-bridge-0.3-RC1/lib/"-L ] } </original-file> I noted that some package files have the form [ Package, Package, ... ], and changed the original file: <original-file> [Package { name = "javavm", import_dirs = ["c:/Programme/haskell-jvm-bridge-0.3- RC1/imports/"], source_dirs = [], library_dirs = [ "c:/Programme/haskell-jvm-bridge-0.3-RC1/lib/"-L ], hs_libraries = [], extra_libraries = ["stdc++","JVMBridge","JVMInvocation","HaskellJVMBridge"-L,"jvm_imp"], include_dirs = [], c_includes = [], package_deps = ["lang","concurrent","haskell98"], extra_ghc_opts = ["-fglasgow-exts","-fallow-undecidable-instances"], extra_cc_opts = [], extra_frameworks = [-L ], extra_ld_opts = [ "-Wl,-rpath,c:/Programme/haskell-jvm-bridge-0.3-RC1/lib/"-L ] }] </original-file> This didn't help me, I got the same error message. Please tell me what's wrong with this package file. Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

2 2

Fwd: [Haskell-cafe] Point-free style
by shiqi cao 14 Feb '05

14 Feb '05

---------- Forwarded message ---------- From: shiqi cao <shiqicaoml(a)gmail.com> Date: Sun, 13 Feb 2005 21:25:56 -0500 Subject: Re: [Haskell-cafe] Point-free style To: Tim Docker <timd(a)macquarie.com.au> On Mon, 14 Feb 2005 11:24:12 +1100, Tim Docker <timd(a)macquarie.com.au> wrote: > Ketil Malde wrote: > > > (.) . (.) .(.) > > > > I entered it into GHCi, and got > > > > :: forall a a b c a. > > (b -> c) -> (a -> a -> a -> b) -> a -> a -> a -> c > > I spent a minute or so attempting to intuit the type signature of this, > before cheating and entering it into ghci also. > > Is there a straightforward technique by which type signatures can be > "hand calculated", or does one end up needing to run the whole inference > algorithm in one's head? Hi Ketil, I think the type signatures can be derived by hand. First let us take a look the type of (.) (.) :: forall c a b. (b -> c) -> (a -> b) -> a -> c one thing need to be taken into account is (.) is left associative, but composition of two functions , like f(g(x)), brings the inner function into our mind first intuitively. Since we know the type of (.) calculating the (.).(.) is algebra manipulation, but be careful. The left hand (.) and right hand (.) are not identical in terms of type. Let us call the left one (.)_1, right one (.)_2 and the middle one (.)_3. Let us type (.)_2 first since the type of (.)_1 is based on (.)_2 (.)_2 :: (b -> c) -> (a->b) -> (a -> c) ----X---- ---------Y---------- Let X = (b -> c) and Y = (a->b) -> (a -> c) (.)_2 :: X -> Y Then (.)_3 must be (Y -> Z) -> (X -> Y) -> (X -> Z) Then (.)_2 must be (Y -> Z) Since (.)_3 is derived (.).(.) has type (X->Z), we need to find out what Z is. (.)_2 :: (Y -> Z) => (.)_2 :: ((a->b) -> (a -> c)) -> Z [1] (.) :: forall C A B. (B -> C) -> (A -> B) -> (A -> C) => (.)_2 :: ((a->b) -> (a -> c)) -> (d -> (a -> b)) -> (d -> (a -> c)) [2] There d is an arbitrary type. [1] and [2] => Z = (d -> (a -> b)) -> (d -> (a -> c)) => (.).(.) :: (X -> Z) = (b -> c) -> (d -> (a -> b)) -> (d -> (a -> c)) GHCi result is (.).(.) :: forall a b c a1. (b -> c) -> (a -> a1 -> b) -> a -> a1 -> c Shiqi Cao

1 0

Getting an attribute of an object
by Dmitri Pissarenko 13 Feb '05

13 Feb '05

Hello! I have a list of instances of the ClassifiedImage class, which is defined as follows. data ClassifiedImage = ClassifiedImage {imageFileName :: String, subjectID :: String} deriving Show Attribute imageFileName contains a file name of a certain image. I want to "transform" the list [ClassifiedImage] into a list [(ClassifiedImage, Image)], where Image is content of the file with name imageFileName. That is, I want to have a routine, which iterates through the list of ClassifiedImages, reads each file (with filename contained in the attribute ClassifiedImage.imageFileName) and stores its content in a variable. I have already a function, which reads the content of a file. My idea is to use map for this task: readClassifiedImages :: [ClassifiedImage] -> [(ClassifiedImage, Image)] readClassifiedImages classifiedImages = do return map readerFunc classifiedImages readerFunc denotes some function, which takes the attribute imageFileName of a ClassifiedImage instance. I suppose that this readerFunc looks like shown below. readerFunc :: ClassifiedImage -> (ClassifiedImage, Image) readerFunc classifiedImage = (classifiedImage, fileContent) where fileName = classifiedImageFileName classifiedImage fileContent = readImage fileName classifiedImageFileName :: ClassifiedImage -> String In order for this function to work, I need to define classifiedImageFileName, which "returns" the imageFileName attribute of an instance of ClassifiedImage class. How can I define this function? Can I use map for readImage function, which is in the IO domain? If not, what tutorial can help me? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Re: Point-free style (Was: Things to avoid)
by oleg＠pobox.com 11 Feb '05

11 Feb '05

Jan-Willem Maessen wrote: ] Is it really clear or obvious what ] ] > map . (+) ] ] means? Perhaps the following two examples might be more convincing: > u=uncurry > e=((partition $ u(==)).) . zip > f x=(x\\).(x\\) It is obviously clear what 'e' and 'f x' do. The second example, which even contains the type signature to increase comprehension: > prod:: (MCompose a b (c -> d) e, MCompose f g (b,g) d) => > (h -> a) -> (c -> f) -> h -> e > > prod = (. ((. (,)) . mcomp)) . mcomp Here `prod' is indeed the categorical product. The second example is taken from http://pobox.com/~oleg/ftp/Haskell/categorical-maxn.lhs which has the following comment about that code fragment: The constraints in the prod's type are intricately related. The final expression for prod bears some similarity with Unlambda code. Perhaps because both Unlambda and the category theory eschew "elements" in favor of combinations of arrows. Probably there are other similarities.

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Re: [Haskell-cafe] Re: Point-free style
by Matthew Roberts 11 Feb '05

11 Feb '05

just a few quick observations comming from an imperative background, I found point free code very difficult to understand when learning Haskell. It is not that it is hard to understand the concepts of point-free style, it is that it is hard to know when something is point-free. It is "another option" and I think the best way to make a language "readable" is to stick to a few simple rules and clean semantics. Since, you can't write all your code point-free, I say write it all pointed - consistency is the thing! also, the term "point free" confused me for quite a while. Point-free code has lots of points (periods) and so I kept thinking it was the other way around. matt On 11/02/2005, at 7:19 AM, Henning Thielemann wrote: > > On 10 Feb 2005, Peter Simons wrote: > >> Now compare that to the following function, which does the >> some thing but without point-free notation: >> >> incrEach' :: Integer -> [Integer] -> [Integer] >> incrEach' i is = is >>= \i' -> return (i'+i) > > point-free again > > is >>= return . (i+) > > :-] > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell] [newbye] 'Just a'
by Graham Klyne 10 Feb '05

10 Feb '05

[I've switched my response to the Haskell-cafe list] What do you intend if both (get a) and (get b) return Nothing? You might also be interested in the library function 'maybe': http://www.haskell.org/onlinereport/standard-prelude.html#$vmaybe or maybe (sic) Maybe.fromMaybe in: http://www.haskell.org/onlinereport/maybe.html Using one of these, I think your function could reasonably be expressed as a simple one-liner. #g -- At 19:33 04/02/05 +0100, Yuri D'Elia wrote: >Hi all. I'm experimenting with haskell and its type system. >I've done a function which scans a list, and returns "Just a" >value if the element is found, or Nothing. > >get :: a -> Maybe a > >and implemented > >getAorB :: Maybe a -> Maybe a -> a >getAorB a b = ... > >a function which returns "Just (get a)" or "Just (get b)" if (get a) is >Nothing (excluding failures in both). By now, I've implemented it in >terms of pattern matching: > >getAorB a b = f (get a) (get b) > where f (Just a) Nothing = a > f Nothing (Just a) = a > >but I'd like to know if there are other possible ways to do it, possibly >without enforcing an evaluation order like pattern matching does. > >_______________________________________________ >Haskell mailing list >Haskell(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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Contravariance
by Johan Glimming 09 Feb '05

09 Feb '05

Hi I have a problem with contravariance in the bananas in space setting. If you take catamorphism from a function space such as A=A->A to a type such as BxC, then the negative occurrence of X in the functor GXY=X->Y swaps around BxC into B+C. This means that maybe in this particular case Meijer-Hutton's original Haskell code for cata/ana does not work, since the type for cata would force BxC and B+C to be the same type. I might be wrong about this, and I wonder anybody can comment on this. Med vänliga hälsningar / Yours Sincerely, Johan Glimming

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Name My Functor Classes
by Ashley Yakeley 09 Feb '05

09 Feb '05

These classes seem like they might correspond to concepts in category theory: class Functor f where fmap :: (a -> b) -> f a -> f b -- must satisfy: -- fmap id = id -- fmap (p . q) = (fmap p) . (fmap q) class (Functor f) => C1 f where f1 :: f (a -> b) -> f a -> f b class (C1 f) => C2 f where return :: a -> f a -- must satisfy: -- fmap = f1 . return class (C2 f) => Monad f where (>>=) :: f a -> (a -> f b) -> f b -- must satisfy: -- fmap ab fa = fa >>= (return . ab) -- f1 fab fa = fab >>= (\ab -> fmap ab fa) -- (return a) >>= p = p a -- (fa >>= p) >>= q = fa >>= (\a -> p a >>= q) What are good names for C1, C2 and f1? -- Ashley Yakeley, Seattle WA

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Re: Top 20 ``things'' to know in Haskell
by John Hughes 09 Feb '05

09 Feb '05

> >Message: 9 >Date: Mon, 7 Feb 2005 10:31:30 -0500 >From: "Jacques Carette" <carette(a)mcmaster.ca> >Subject: [Haskell-cafe] Top 20 ``things'' to know in Haskell >To: <haskell-cafe(a)haskell.org> >Message-ID: <000701c50d2a$189f5590$1b447182(a)cas.mcmaster.ca> >Content-Type: text/plain; charset="us-ascii" > >The recent post of Graham Klyne (below) reminds me that I have meant to ask: >is there a ``top 20'' things a serious programmer should know when writing >code in Haskell? Of course there is a lot of programming language theory >that would be great to know, but I mean really down-to-earth things like the >2 items below (module Maybe, the 'maybe' function). > >The Haskell libraries are quite large, and it is unrealistic to try to get >familiar with all of them right away. But getting a ``small'' list would be >very useful - I think of this as step 2 after one learns to get comfortable >with a language. I had done this (for Maple) for training new hires at >Maplesoft, and I definitely noticed that they became more idiomatic >programmers faster this way. > >Jacques > >PS: of course, this could already exist on haskell.org and/or the Wiki, but >not in an 'obvious' enough place as I missed it... > > Beginners might find this useful: http://www.cs.chalmers.se/Cs/Grundutb/Kurser/d1pt/d1pta/ListDoc/ It's guide to finding the right list function which leads you to it by asking you what you are trying to achieve. john >-----Original Message----- >From: haskell-cafe-bounces(a)haskell.org >[mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Graham Klyne >Sent: February 7, 2005 10:09 AM >To: Yuri D'Elia; haskell-cafe(a)haskell.org >Subject: [Haskell-cafe] Re: [Haskell] [newbye] 'Just a' > >You might also be interested in the library function 'maybe': > http://www.haskell.org/onlinereport/standard-prelude.html#$vmaybe > >or maybe (sic) Maybe.fromMaybe in: > http://www.haskell.org/onlinereport/maybe.html > >#g >-- > > > > > > >

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Re: [Haskell-cafe] How to write (FxF' . delta) AxB --> F A
by Johan Glimming 08 Feb '05

08 Feb '05

> proj :: (Functor f) => (f:*:f') (a,b) -> f a > proj (Pair x _) = fmap fst x Yes I think that was what I needed. ;-) It seems I also need fsplit :: (Functor f, Functor f') => (f a, f' b) -> (f :*: f') (a,b) for same data (f:*:f') o = Pair (f o) (f' o) Which takes (FA, F'B) into FxF' (A,B). I am confused by the fact of having two instances of F and somehow I need to map on both of them simultaneously. Med vänliga hälsningar / Yours Sincerely, Johan Glimming

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RE: [Haskell-cafe] how to name third party libraries?
by Simon Peyton-Jones 08 Feb '05

08 Feb '05

Send mail to libraries(a)haskell.org, saying what's in your libraries, and suggesting names. The process usually converges pretty rapidly. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of S. | Alexander Jacobson | Sent: 07 February 2005 22:55 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] how to name third party libraries? | | Is there documentation somewhere about how to name | third party libraries? | | For example, if I have HTTP and SMTP libraries, | what should I call them? | | -alex- | | | | ______________________________________________________________ | S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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help with some code. it doesn't whant to compile.
by pablo daniel rey 08 Feb '05

08 Feb '05

hello i'm new to haskell so i'm sorry if this is a stupid question, but i'm having problems with some basic code. the code : data Maybe Dir = Just Dir | Nothing data Dir = Left | Right | Up | Down data Piece = Vertical | Horizontal | CodeA | CodeB flow = [(Horizontal, Left, Left), (Horizontal, Right, Right), (Vertical, Down, Down), (Vertical, Up, Up), ................ etc ] fst :: (a,b,c) -> a fst (x,y,z) = x scnd :: (a,b,c) -> b scnd (x,y,z) = y third :: (a,b,c) -> c third (x,y,z) = z element :: [(Piece, Dir, Dir)] -> Maybe Dir element [] = Nothing element xs = Just (third (head xs)) chgDir :: Piece -> Dir -> Maybe Dir chgDir p d = element (filter (\x -> p == (fst x)) (filter (\x -> d == (scnd x)) flow)) the error i get : Instances of (Eq Dir, Eq Piece) required for definition of chgDir i don't know what's happening. help!!! thanks in advance

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how to name third party libraries?
by S. Alexander Jacobson 08 Feb '05

08 Feb '05

Is there documentation somewhere about how to name third party libraries? For example, if I have HTTP and SMTP libraries, what should I call them? -alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Re: [Haskell] help with some basic code that doesn't work
by Cale Gibbard 07 Feb '05

07 Feb '05

Delete data Maybe Dir = Just Dir | Nothing as it is unnecessary "Maybe a" is defined already for any type "a" (and doesn't make sense, Dir occuring before the = sign would indicate that it is a type variable, but it is uppercase), and also change data Dir = Left | Right | Up | Down data Piece = Vertical | Horizontal | CodeA | CodeB to data Dir = Left | Right | Up | Down deriving Eq data Piece = Vertical | Horizontal | CodeA | CodeB deriving Eq Equality isn't defined by default on user-defined datatypes, so that you can add your own definition. In this case your type is pretty simple, so you can use the derived instance of Eq, so that (==) and (/=) get defined for Dir and Piece. You should also add the line import Prelude hiding (Left, Right) as these are the names of the data constructors for the Either type, and you will get ambiguity errors if you don't rename them or hide the ones in the Prelude. Lastly, you should probably rename your 'fst' to 'frst' or some such, so that it doesn't overlap with the Prelude function of the same name. hope this helps, - Cale On Mon, 7 Feb 2005 20:36:55 +0000, pablo daniel rey <listas(a)pablodanielrey.com.ar> wrote: > hello > i'm new to haskell so i'm sorry if this is a stupid question, but i'm having problems with some basic code. > the code : > > data Maybe Dir = Just Dir | Nothing > data Dir = Left | Right | Up | Down > data Piece = Vertical | Horizontal | CodeA | CodeB > > flow = [(Horizontal, Left, Left), > (Horizontal, Right, Right), > (Vertical, Down, Down), > (Vertical, Up, Up), ................ etc ] > > fst :: (a,b,c) -> a > fst (x,y,z) = x > > scnd :: (a,b,c) -> b > scnd (x,y,z) = y > > third :: (a,b,c) -> c > third (x,y,z) = z > > element :: [(Piece, Dir, Dir)] -> Maybe Dir > element [] = Nothing > element xs = Just (third (head xs)) > > chgDir :: Piece -> Dir -> Maybe Dir > chgDir p d = element (filter (\x -> p == (fst x)) (filter (\x -> d == (scnd x)) flow)) > > the error i get : > > Instances of (Eq Dir, Eq Piece) required for definition of chgDir > > i don't know what's happening. > help!!! > thanks in advance > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

1 0

"Parsing" a string
by Dmitri Pissarenko 07 Feb '05

07 Feb '05

Hello! I have to read a PGM image and transform it into a list of Int values. I read the image (this is an ASCII PGM format) using the readFile function and get a string with the contents of the file. This string contains height and widht of the image at the beginning, and then the pixel values follow. I need to read the height and width, then "cut" them from the string, create an array (or finite map) of Int's (for this I need to know the height and width), and then recursively process the pixel values (i. e. put them into the array). The string is structured as follows: <string> P2 # comment # comment 320<WHITESPACE>243<WHITESPACE>255 130 130 130 130 130 130 130 130 130 130 </string> P2 is the magic number. All lines starting with # are comments and must be ignored. 320 and 243 are width and height. <WHITESPACE> is either a space, or tab, or newline. At the moment, I don't have an idea about how to read width and height. One possible approach would be to convert the string into a list of strings A, using newline as separator. Then, I could create list A' with comments removed. Then, A' can be transformed into a string A'' again. From A'' I know that width is contained between the end of P2 and the first occurrence of whitespace (Char.isSpace). I also know that height is contained between first and second occurrence of white space. I could use some sort of regular expression analogons to access width and height. I have several questions concerning this approach: 1) How can I transform a string into a list of strings, separated by some character (in Java one uses StringTokenizer for this) ? 2) How do the aforementioned "regular expressions' analogons" work in Haskell? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Haskell binding to Berkeley DB?
by Dimitry Golubovsky 06 Feb '05

06 Feb '05

Hi, Has anyone tried/been successful on developing such a binding? Google returns reference to a message written 2 years ago (on the gtkhs mailing list) that someone developed it partially: http://www.haskell.org/pipermail/gtkhs/2003-January/000317.html and a description of a student's assignment: http://www.cse.unsw.edu.au/db/thesis/topicinfo/MMTC13.html The rest of links that Google returns are of little relevance. Any ideas? Dimitry Golubovsky Middletown, CT

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Haskell binding to Berkeley DB?
by Alain Cremieux 04 Feb '05

04 Feb '05

> > >Hi, > >Has anyone tried/been successful on developing such a binding? > >Google returns reference to a message written 2 years ago (on the gtkhs >mailing list) that someone developed it partially: > >http://www.haskell.org/pipermail/gtkhs/2003-January/000317.html > > > Hi Dimitry, I have made some progress since this posting, but it is not finished. My binding is written using the c-code from the lisp binding available here : http://users.actrix.gen.nz/mycroft/cl.html I have a low-level binding, and a medium-level binding, and both work. But I'd like to make a high-level binding, maybe based on the ideas from Oleg described here : From enumerators to cursors: turning the left fold inside out <http://okmij.org/ftp/Haskell/index.html#fold-stream> and here : Takusen: a DBMS access library built around a left-fold enumerator <http://okmij.org/ftp/Haskell/index.html#takusen> Anyhow, I can send you my code, no documentation available but with some examples, Alain

1 0

create a type for selecting functions already in the module
by Oterman-Fernandez, Ana-Maria 04 Feb '05

04 Feb '05

Hi! I have implemented a module with some functions and now I would like to create a type for selecting between this functions: For example: if f1, f2,...fn are the names of the functions in the module, I need to do something like this: data Consult = f1 | f2 |....| fn for applying them whenever the user wants. but by this way is not possible. Do you know how can I do this? Thank you! Ana Maria The data contained in, or attached to, this e-mail, may contain confidential information. If you have received it in error you should notify the sender immediately by reply e-mail, delete the message from your system and contact +44 (0) 1332 242424 (the Rolls-Royce IT Security Director) if you need assistance. Please do not copy it for any purpose, or disclose its contents to any other person. An e-mail response to this address may be subject to interception or monitoring for operational reasons or for lawful business practices. (c) 2005 Rolls-Royce plc Registered office: 65 Buckingham Gate, London SW1E 6AT Company number: 1003142. Registered in England.

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MonadPlus instance for IO
by David Roundy 02 Feb '05

02 Feb '05

I'm sure I'm doing something stupid, but somehow ghc isn't recognizing the existance of a MonadPlus instance for IO: DarcsIO.lhs:48: No instance for (MonadPlus IO) arising from use of `mplus' at DarcsIO.lhs:48 In the definition of `foo': foo = (fail "aaack") `mplus` (fail "foobar") Any idea what I'm doing wrong? I'm using $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.2.2 packaged for debian. -- David Roundy http://www.darcs.net

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RE: [Haskell-cafe] File path programme
by Simon Marlow 02 Feb '05

02 Feb '05

[ moving to libraries(a)haskell.org ] On 26 January 2005 12:22, Malcolm Wallace wrote: >> Could we just punt this library for this release. After all we can >> add libraries in a later point release (eg 6.4.1) you just can't >> change existing APIs. > > FWIW, I agree with Duncan, Ben, and Peter, that the new > System.FilePath interface is broken, and the implementation more so. > It would be better to redesign FilePaths as an algebraic datatype. Ok, I'll go with the concensus. System.FilePath in its current state will be removed from the base package. Isaac or Krasimir: can you make the required changes to Cabal? (the code is already duplicated in Distribution.Compat.FilePath, just remove the import for GHC). So let's aim for 6.6 to do it right, and design an abstract type for path names. We have to think about the migration path: Haskell 98 programs must continue to work, so at least IO.FilePath must still be a String, and IO.openFile must still take a String. We can therefore: (a) make System.IO.FilePath be the new type, which is different from, and incompatible with, IO.FilePath. Similarly for System.IO.openFile, System.Directory.removeFile, and so on. (b) or just define a new type, and force you to insert read/show to convert where necessary, eg. before calling openFile. (a) is kind of the right thing, but (b) is a lot less painful in the short term. Since we'll be migrating to a new IO library at some point, (b) is probably fine (the new IO library can use the new FilePaths exclusively), but we'll need to migrate System.Directory too. Would someone like to take up the reigns on the design for the new library? Cheers, Simon

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RE: [Haskell-cafe] MonadPlus instance for IO
by Simon Peyton-Jones 02 Feb '05

02 Feb '05

that instance seems to be only in Control.Monad.Error in the 'mtl' package. It's not in the standard base package. You may need to import an mtl module to tell GHC to look there. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | David Roundy | Sent: 02 February 2005 13:18 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] MonadPlus instance for IO | | I'm sure I'm doing something stupid, but somehow ghc isn't recognizing the | existance of a MonadPlus instance for IO: | | DarcsIO.lhs:48: | No instance for (MonadPlus IO) | arising from use of `mplus' at DarcsIO.lhs:48 | In the definition of `foo': | foo = (fail "aaack") `mplus` (fail "foobar") | | Any idea what I'm doing wrong? I'm using | | $ ghc --version | The Glorious Glasgow Haskell Compilation System, version 6.2.2 | | packaged for debian. | -- | David Roundy | http://www.darcs.net | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

1 0

The Nature of Char and String
by John Goerzen 02 Feb '05

02 Feb '05

Char in Haskell represents a Unicode character. I don't know exactly what its size is, but it must be at least 16 bits and maybe more. String would then share those properties. However, usually I'm accustomed to dealing with data in 8-bit words. So I have some questions: * If I use hPutStr on a string, is it guaranteed that the number of 8-bit bytes written equals (length stringWritten)? + If no, what is the representation written? I'm assuming UTF-8. How could I find out how many bytes were actually written? + If yes, what happens to the upper 8 bits? Are they simply stripped off? * If I run hGetChar, is it possible that it would consume more than one byte of input? How can I determine whether or not this has happend? * Does Haskell treat the "this is a Unicode file" marker special in any way? * Same questions on withCString and related String<->CString conversions. -- John

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RE: [Haskell-cafe] Re: ocr'ed version of "The implementation offunctional languages"
by Simon Peyton-Jones 02 Feb '05

02 Feb '05

Matthew Yes, I'm happy for you to OCR the book, but can I ask that whatever you get be made accessible from my web site, so there's one place people can go to find everything that's available? What would OCR buy us? Searching, I guess, which is a fantastic plus. Anything else? Thanks very much for offering to help. I've replied to haskell-café, so everyone knows what's up, but we can now save everyone's bandwidth by narrowing the thread to Ivan, Marnie (who did the original work), you, and me. If anyone else wants to join in, do yell. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Ivan | Boldyrev | Sent: 31 January 2005 06:48 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] Re: ocr'ed version of "The implementation offunctional languages" | | On 9005 day of my life Matthew Roberts wrote: | > I have just embarked on creating a ocr'ed version of the jpeg images | > that have been made available for "The implementation of functional | > languages". | | I have high-resolution scans of this books. If Simon permits, I will | create OCR from these scans. But I think, we must obtain author's | permission before OCR'ing. | | PNG version of scans will be released soon. While size of page is | same, quality is much better, probably it will improve speed of | scanning. | | And compact DjVu version will be released too. Perhaps I could use | OCR'ed text for creating searchable version of DjVu? | | > However, my ocr software is clunky at best and (not surprisingly) it is | > slow going. | | What kind of software do you use? | | -- | Ivan Boldyrev | | Assembly of a Japanese bicycle requires greatest peace of spirit. | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell] Typing in haskell and mathematics
by Iavor Diatchki 01 Feb '05

01 Feb '05

Hello, On Fri, 28 Jan 2005 10:01:33 -0500, Jacques Carette <carette(a)mcmaster.ca> wrote: > The previous post on record syntax reminded me of some 'problems' I had noticed where Haskell and mathematics have a > (deep) usage mismatch. It is interesting that my sentiment is exactly the opposite. Mathematicians (the applied kind, not the pure) tend to be quite sloppy about their notation relaying _a lot_ on the context and the fact that people know what they are talking about. I find that this makes their explanations harder to understand rather than easier. > First, consider a syntax for other component-wise function application? For example, it would be convenient to have > (f,g) @ (x,y) > be (f x, g y). In some languages [with dynamic typing], one can even do (f,g) (x,y) :-) I am not sure what you mean, but you can define exactly that (except for the @ sign which is special syntax already): (f,g) `ap2` (x,y) = (f x, g y) > Yes, I am aware that this untypeable in Haskell, because polymorphism is straight-jacketed by structural rules. What do you mean by this: ap2 :: (a -> b, c - d) -> (a,c) -> (b,d) But > in mathematics, it is convenient and extremely common to: > 1) look at the type a -> b as being a *subtype* of b (though I have never seen it phrased that way in print) I don't think subtyping is what you are thinking of. Perhaps you are referring to the correspondance between b-expressions with a free a-variable, and functions a->b. In Haskell we don't have expressions with free variables as first class values. There might be some interesting things to work out for such beasts. > 2) to consider every 'natural transformation' available and use it (tuples of functions <-> obvious function on > tuples) Are you suggesting that natural transformations should be applied automatically? There are many problems with this: which operations should happen automatically? Type inference (if it works at all) will be hard to do, but perhaps these are technical details. Fundamentally the "sloppy" math notation assumes that what the author wrote is correct and should simply be given "the obvious" meaning. This is pretty much the idea with dynamic typing. I find the restrictions of static typing very convenient (well most of the time :-) as they capture "stupid' errors. > > Seeing a -> b as a subtype of b allows one to take any function f : b -> b -> c (like + ) and 'lift' it to > ff : (a -> b) -> (a -> b) -> (a -> c) > via the obvious definition > ff g h = \x -> f (g x) (h x) > This is done routinely in mathematics. The meaning of the expression (sin + cos) should be immediately obvious. Such > 'lifting' is used even in first-year calculus courses, but not in Haskell. Apart from the fact that this does not seem like a good idea, you can already do things like this in Haskell: liftOp op f g x = f x `op` f x This is all you need, especially if you are prepared to stick to the "usual" mathematical convention of not using curried functions, but instead using tuples to pass multiple arguments. > > The "same" phenomenon is what allows one to 'see' that there is an obvious function > apply_tuple:: (a->b,c->d) -> (a,c) -> (b,d) > so that > (f,g) (a,b) > only has one possible meaning, if the built-in apply function were to be overloaded. There are many interesting things one could do if application was to be overloaded but this hardly seems like a motivating example. You can already use the 'ap2' combinator from above. I can see that it is annoying to have ap2, ap3, etc. You can define a generic "ap_n" using dependent types, or using the encoding tomasz posted, but that hardly seems to be a "deep" problem. > > Similarly, there are "obvious" maps > apply_T :: T (a->b) -> a -> T b > for any datatype constructor T (as has been noticed by all who do 'generic' programming). Is this really true? Consider: data T a = T (a -> Int) What shoud apply_T do? applyT :: (essentially) ((a -> b) -> Int) -> a -> (b -> Int) perhaps: applyT (T f) a = T (\b -> f (const b)) but that probably does not behave as you would like it. Of course you could restrict the datatypes for which apply_T can be derived. This means that > [f, g, h] x == [f x, g x, h x] > but also (in mathematics at least) > {f, g, h} x == {f x, g x, h x} > where {} denotes a set, and the equality above is extensional equality, and so on. I agree that it would be nice to automatically derive functions such as apply_T, etc. This (as you point out) is the idea of generic programming. This however does not suggest that we should replace application... > Note that some computer algebra systems use #1 and #2 above all the time to define the operational meaning of a lot of > syntactic constructs [where I personally extended the use of such rules in the implementation & operational semantics > of Maple]. What hope is there to be able to do something 'similar' in a Haskell-like language? I think it is already possible to do simillar things. I am sure there is room for improvement, but it is important that the consequences of changing a language are worked out in details. It is time for me to go to school :-) bye Iavor

4 8

Problems with building haskell-jvm-bridge-0.3.RC1
by Dmitri Pissarenko 01 Feb '05

01 Feb '05

Hello! I'm trying to build Haskell-JVM bridge (http://sourceforge.net/projects/jvm- bridge/) under Windows (cygwin) and with Java 1.5. I can execute "configure" without errors. When I execute make, I get a lot of errors. Due to a limited size of my buffer, I can show you only the last lines of make's output: JVMBridge.cpp: In function `jboolean JVMBridge_CallNonvirtualBooleanMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:778: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:779: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:780: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:781: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:783: error: `CallNonvirtualBooleanMethodA' undeclared (first use this function) JVMBridge.cpp:785: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jbyte JVMBridge_CallNonvirtualByteMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:793: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:794: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:795: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:796: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:798: error: `CallNonvirtualByteMethodA' undeclared (first use this function) JVMBridge.cpp:800: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jchar JVMBridge_CallNonvirtualCharMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:808: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:809: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:810: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:811: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:813: error: `CallNonvirtualCharMethodA' undeclared (first use this function) JVMBridge.cpp:815: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jshort JVMBridge_CallNonvirtualShortMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:823: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:824: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:825: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:826: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:828: error: `CallNonvirtualShortMethodA' undeclared (first use this function) JVMBridge.cpp:830: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_CallNonvirtualIntMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:838: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:839: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:840: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:841: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:843: error: `CallNonvirtualIntMethodA' undeclared (first use this function) JVMBridge.cpp:845: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: At global scope: JVMBridge.cpp:850: error: parse error before `*' token JVMBridge.cpp:853: error: `object' was not declared in this scope JVMBridge.cpp:853: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:853: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:711: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:853: error: initializer list being treated as compound expression JVMBridge.cpp:854: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:854: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:853: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:854: error: initializer list being treated as compound expression JVMBridge.cpp:855: error: `methodID' was not declared in this scope JVMBridge.cpp:855: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:855: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:854: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:855: error: initializer list being treated as compound expression JVMBridge.cpp:856: error: `vl' was not declared in this scope JVMBridge.cpp:856: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:856: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:855: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:856: error: initializer list being treated as compound expression JVMBridge.cpp:857: error: redefinition of `jvalue*valueArray' JVMBridge.cpp:712: error: `jvalue*valueArray' previously defined here JVMBridge.cpp:857: error: `vl' was not declared in this scope JVMBridge.cpp:858: error: parse error before `=' token JVMBridge.cpp:860: error: `vl' was not declared in this scope JVMBridge.cpp:860: error: ISO C++ forbids declaration of ` JVMBridge_DestroyValueList' with no type JVMBridge.cpp:860: error: redefinition of `int JVMBridge_DestroyValueList' JVMBridge.cpp:715: error: `int JVMBridge_DestroyValueList' previously defined here JVMBridge.cpp:861: error: ISO C++ forbids declaration of `DebugShowLong' with no type JVMBridge.cpp:861: error: redefinition of `int DebugShowLong' JVMBridge.cpp:716: error: `int DebugShowLong' previously defined here JVMBridge.cpp:861: error: initializer list being treated as compound expression JVMBridge.cpp:861: error: invalid conversion from `const char*' to `int' JVMBridge.cpp:862: error: parse error before `return' JVMBridge.cpp: In function `jfloat JVMBridge_CallNonvirtualFloatMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:868: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:869: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:870: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:871: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:873: error: `CallNonvirtualFloatMethodA' undeclared (first use this function) JVMBridge.cpp:875: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jdouble JVMBridge_CallNonvirtualDoubleMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:883: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:884: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:885: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:886: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:888: error: `CallNonvirtualDoubleMethodA' undeclared (first use this function) JVMBridge.cpp:890: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `_jobject* JVMBridge_CallNonvirtualObjectMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:898: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:899: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:900: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:901: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:903: error: `CallNonvirtualObjectMethodA' undeclared (first use this function) JVMBridge.cpp:905: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `void JVMBridge_CallStaticVoidMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:913: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:914: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:915: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:917: error: `CallStaticVoidMethodA' undeclared (first use this function) JVMBridge.cpp:919: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_CallStaticBooleanMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*) ': JVMBridge.cpp:925: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:926: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:927: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:929: error: `CallStaticBooleanMethodA' undeclared (first use this function) JVMBridge.cpp:931: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jbyte JVMBridge_CallStaticByteMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:939: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:940: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:941: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:943: error: `CallStaticByteMethodA' undeclared (first use this function) JVMBridge.cpp:945: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jchar JVMBridge_CallStaticCharMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:953: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:954: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:955: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:957: error: `CallStaticCharMethodA' undeclared (first use this function) JVMBridge.cpp:959: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jshort JVMBridge_CallStaticShortMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:967: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:968: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:969: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:971: error: `CallStaticShortMethodA' undeclared (first use this function) JVMBridge.cpp:973: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_CallStaticIntMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:981: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:982: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:983: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:985: error: `CallStaticIntMethodA' undeclared (first use this function) JVMBridge.cpp:987: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: At global scope: JVMBridge.cpp:992: error: parse error before `*' token JVMBridge.cpp:995: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:995: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:856: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:995: error: initializer list being treated as compound expression JVMBridge.cpp:996: error: `methodID' was not declared in this scope JVMBridge.cpp:996: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:996: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:995: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:996: error: initializer list being treated as compound expression JVMBridge.cpp:997: error: `vl' was not declared in this scope JVMBridge.cpp:997: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:997: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:996: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:997: error: initializer list being treated as compound expression JVMBridge.cpp:998: error: redefinition of `jvalue*valueArray' JVMBridge.cpp:857: error: `jvalue*valueArray' previously defined here JVMBridge.cpp:998: error: `vl' was not declared in this scope JVMBridge.cpp:999: error: parse error before `=' token JVMBridge.cpp:1001: error: `vl' was not declared in this scope JVMBridge.cpp:1001: error: ISO C++ forbids declaration of ` JVMBridge_DestroyValueList' with no type JVMBridge.cpp:1001: error: redefinition of `int JVMBridge_DestroyValueList' JVMBridge.cpp:860: error: `int JVMBridge_DestroyValueList' previously defined here JVMBridge.cpp:1002: error: ISO C++ forbids declaration of `DebugShowLong' with no type JVMBridge.cpp:1002: error: redefinition of `int DebugShowLong' JVMBridge.cpp:861: error: `int DebugShowLong' previously defined here JVMBridge.cpp:1002: error: initializer list being treated as compound expression JVMBridge.cpp:1002: error: invalid conversion from `const char*' to `int' JVMBridge.cpp:1003: error: parse error before `return' JVMBridge.cpp: In function `jfloat JVMBridge_CallStaticFloatMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1009: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1010: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1011: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1013: error: `CallStaticFloatMethodA' undeclared (first use this function) JVMBridge.cpp:1015: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jdouble JVMBridge_CallStaticDoubleMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1023: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1024: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1025: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1027: error: `CallStaticDoubleMethodA' undeclared (first use this function) JVMBridge.cpp:1029: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `_jobject* JVMBridge_CallStaticObjectMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1037: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1038: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1039: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1041: error: `CallStaticObjectMethodA' undeclared (first use this function) JVMBridge.cpp:1043: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_IsSameObject(JNIEnv*, _jobject*, _jobject*)': JVMBridge.cpp:1051: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1052: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_IsInstanceOf(JNIEnv*, _jobject*, _jobject*)': JVMBridge.cpp:1059: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1060: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_ThrowException(JNIEnv*, _jobject*)': JVMBridge.cpp:1067: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_ExceptionPending(JNIEnv*)': JVMBridge.cpp:1092: error: `ExceptionCheck' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_MonitorEnter(JNIEnv*, _jobject*)': JVMBridge.cpp:1105: error: `MonitorEnter' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_MonitorExit(JNIEnv*, _jobject*)': JVMBridge.cpp:1111: error: `MonitorEnter' undeclared (first use this function) JVMBridge.cpp: In function `char* JVMBridge_GetStringUTFChars(JNIEnv*, _jobject*)': JVMBridge.cpp:1158: error: `GetStringUTFLength' undeclared (first use this function) JVMBridge.cpp:1162: error: `GetStringUTFRegion' undeclared (first use this function) JVMBridge.cpp:1167: error: `GetStringUTFChars' undeclared (first use this function) JVMBridge.cpp:1170: error: `ReleaseStringUTFChars' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_GetStringUTFLength(JNIEnv*, _jobject*)': JVMBridge.cpp:1178: error: `GetStringUTFLength' undeclared (first use this function) JVMBridge.cpp: In function `_jobject* JVMBridge_DefineClass(JNIEnv*, const char*, _jobject*, const jbyte*, long int)': JVMBridge.cpp:1192: error: `DebugShowPointer' cannot be used as a function make[2]: *** [JVMBridge.lo] Error 1 make[2]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/haskell-jvm- bridg e-0.3.RC1/Native' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/haskell-jvm- bridg e-0.3.RC1/Native' make: *** [all] Error 2 Have you an idea what I can do to fix these errors? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

2 1

Re: mathematical notation and functional programming
by Henning Thielemann 31 Jan '05

31 Jan '05

On Mon, 31 Jan 2005, Chung-chieh Shan wrote: > (Is Lemming the same person as Henning Thielemann?) Yes. :-) > > For the expression '1+x' I > > conclude by type inference that 'x' must be a variable for a scalar > > value, since '1' is, too. But the expression '1/O(n^2)' has the scalar > > value '1' on the left of '/' and a set of functions at the right side. > > Type inference fails, so my next try is to make the operands compatible > > in a somehow natural way. > > It seems to me that your classification of certain notations as "wrong" > and others as "right" assumes a certain type inference system that > allows adding a number to a placeholder but disallows dividing a > function by a set of functions. Let's see if we share a common interpretation of notation before discussing who uses it consistently and who does not. :-) For me 1, x and + are identifiers. The strings "1", "x" and "+" are not mathematical objects. But '1' denotes a unique mathematical object. Only almost, because depending on the underlying explanation it may be identified with the natural number 1, with the rational number 1, with the real 1, with the complex 1, you will probably need a different representation. Further this representation depends on how you represent natural numbers, reals and so on, e.g. by sets. '+' also denotes a mathematical object, more precisely a function, and again we have ambiguities like that for '1', since '+' might be the natural addition, the rational one or even a mixed one. 'x' denotes no special mathematical object but it may be replaced by one, and the special thing is, that within a certain scope all occurences of 'x' must be replaced with the same mathematical object. Functions are special, in the sense that if I write "1+2" I don't want to consider this as the sequence of three objects denoted by "1", "+", "2" but I want that the function denoted by "+" is applied on the values denoted by "1" and "2". So I imagine a layer of notation and a layer of mathematical objects. Do you share this interpretation? What are consequences of this interpretation? "2+2" and "4" denote the same object. A function has only access to the value (the mathematical object) but not to the generating expression. So how can I define e.g. differentation with respect to a variable? I can't, but I don't miss it because I can define it for functions, and yes Jerzy :-), also for other objects. For me differentiation was introduced by limits. The definition of limits don't need expressions as mathematical objects, the differentation of functions don't need them, too. But later we got used to differentiate expression (e.g. x^2 + y^2 is turned into 2*x * dx + 2*y * dy), but no-one defined what that is. What are the consequences of treating expressions as mathematical objects, too? "2+2" and "4" are different expressions. I guess we would still ask for a value, thus we need a mathematical function which maps expressions to values. I think Mathematicas Evaluate is made for this purpose. If mathematical functions can transform expressions - is it possible that they change my writing? ;-) Indeed, I really like this separation: On the one side expression, on the other side mathematical objects. Simplifications of expressions are nothing I allow a mathematical function. But if I simplify an expression I must assert that the denoted mathematical object remains the same. Differentation of a function is possible if you only know its graph, but a computer algebra system can find an expression for the derivation if you have an expression for the function. There are many functions that can be integrated, but a computer algebra system cannot find an expression without the Integrate function for it. When a pupil says "the function can not be integrated" he means that he couldn't find an expression for the integrated function without the integral sign. When a professor teaching calculus says "the function can not be integrated" he means that there is some divergence. It seems to me that in this case the pupil considers expressions as mathematical objects and the professor does not. > Lambda notation also involves much ambiguity and many implicit > conversions. Following the interpretation above I like to see lambda as a notation instead of an mathematical operator. lambda expressions denote functions. I can replace every occurence of lambda expressions textually. If "\A -> B" occurs I can also write "f" and "where holds \forall A f(A)=B". So lambda notation involves no more ambiguities than the rest of the notation. > > You use 'ask' twice in the second expression. Does this mean that there > > may be two different values for 'ask'? If this is the case your second > > interpretation differs from my second interpretation. > > No -- when I use "ask" I mean the one defined in Control.Monad.Reader. Sorry for my imprecise question :-) What I meant was that 'ask' somehow injects a value into the mathematical operation, I wondered if the values it introduces are equal or not.

1 0

Re: mathematical notation and functional programming
by Chung-chieh Shan 31 Jan '05

31 Jan '05

(Is Lemming the same person as Henning Thielemann?) On 2005-01-30T21:24:24+0100, Lemming wrote: > Chung-chieh Shan wrote: > > Wait a minute -- would you also say that "1+x" has no meaning at the > > first glance, because "x" is a variable whereas "1" is an integer, so > > some lifting is called for? > For me 'x' is a place holder for a value. But you can only adds two *numbers* to get a number. It makes no sense to add a number to a placeholder. So it makes no sense to write "1+x", no? > For the expression '1+x' I > conclude by type inference that 'x' must be a variable for a scalar > value, since '1' is, too. But the expression '1/O(n^2)' has the scalar > value '1' on the left of '/' and a set of functions at the right side. > Type inference fails, so my next try is to make the operands compatible > in a somehow natural way. It seems to me that your classification of certain notations as "wrong" and others as "right" assumes a certain type inference system that allows adding a number to a placeholder but disallows dividing a function by a set of functions. > Since mathematical notation invokes many > implicit conversions, it's sometimes no longer unique or obvious what > implicit conversion to use. Many users of O(n^2) seem to consider it as > a placeholder for some expression, where the value of the expression is > bounded by n^2. Lambda notation also involves much ambiguity and many implicit conversions. In particular, "x" can mean the identity function from integers to integers as well as the identity function from booleans to booleans, as well as a function that maps an integer-boolean pair to the integer of the pair, as well as a function that maps an integer-boolean pair to the boolean of the pair, and so on. > > Right; they are control operators in the sense that call/cc is a control > > operator. > So they seem to be operators that work on expressions rather than > values. In this respect they are similar to the lambda operator, aren't > they? Yes. > You use 'ask' twice in the second expression. Does this mean that there > may be two different values for 'ask'? If this is the case your second > interpretation differs from my second interpretation. No -- when I use "ask" I mean the one defined in Control.Monad.Reader. > Church style, System F(-omega), alpha-conversion, lambda calculus, eta > reduction, currying - Where can I find some introduction to them? What > about Haskell Curry? What about Bourbaki? - I have heard they worked > hard to find a unified notation. (I'm sure that other people would have better suggestions, but I rather like Benjamin Pierce's book "Types and programming languages".) Ken -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig War crimes will be prosecuted. War criminals will be punished. And it will be no defense to say, "I was just following orders."' George W. Bush, address to the nation, 2003-03-17 http://www.whitehouse.gov/news/releases/2003/03/20030317-7.html

1 0

RE: UTF-8 BOM, really!? (was: [Haskell-cafe] Re: File path progr amme)
by Bayley, Alistair 31 Jan '05

31 Jan '05

> From: Aaron Denney [mailto:wnoise@ofb.net] > > Better yet would be to have the standard never allow the BOM. > > Since some things can't handle it, on output we should never emit it, > but still must handle it on input. Bah. I don't see how banning it from input would help; as I understand it, it's meant to be ignored anyway, so there's no loss or gain there. Whether or not to emit the BOM on output should be a user choice, surely? > From: Graham Klyne [mailto:GK@ninebynine.org] > > How can it make sense to have a BOM in UTF-8? UTF-8 is a sequence of > octets (bytes); what ordering is there here that can > sensibly be varied? >From http://www.unicode.org/faq/utf_bom.html#BOM : "Q: Where is a BOM useful? A: A BOM is useful at the beginning of files that are typed as text, but for which it is not known whether they are in big or little endian format..." i.e. it helps when you need to guess what the encoding of a given file might be. Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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File paths and internationalization/localization
by Graham Klyne 31 Jan '05

31 Jan '05

I don't offer any answers, but the problems raised on this list concerning file paths using local language characters would appear to have some parallels in the world of URIs. Martin Duerst and others at W3C have been working on the problem of internationalization (I18N) of URIs, and their proposals were recently published as a Proposed Standard RFC [1]. If this area is being considered in the design of Haskell libraries, there may be some lessons there to be copied. #g -- [1] ftp://ftp.rfc-editor.org/in-notes/rfc3987.txt ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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