May 2007 - Libraries - Haskell.org

Ord instance for Data.Map?
by Henning Thielemann 21 May '07

21 May '07

I wonder whether the Ord instance is a good choice as constraint for Data.Map, Data.Set and so on. I want to manage complex numbers and residue classes in a set, or polynomials as keys of maps, but I hesitate to make them instances of Ord, because "a<b" shall remain a type error for complex numbers, residue classes and polynomials. Also in Haskore we abuse Ord instance to get canonical form of arranged notes. However there is no notion of magnitude for notes, so the Ord instance is rather artificial. I have a work-around in mind: I could introduce class Eq a => Indexable a where compareIndex :: a -> a -> Ordering then make several mathematical object types instances of this class. Then make a wrapper type newtype IndexableToOrd a = Cons a which maps the Indexable instance to an Ord instance: instance Indexable a => Ord (IndexableToOrd a) where compareIndex (Cons x) (Cons y) = compare x y Then I do not insert complex numbers immediately in a set, but wrap them in IndexableToOrd and insert the wrapped values in a set. Cumbersome, isn't it? So my question is: Was the Ord constraint for Data.Map a good idea? If yes, are there simpler work-arounds than mine? I think, that '<' and '>' imply something like comparisons of magnitudes and the Data.Map doesn't require that notion and it is happy with any total ordering. Btw. is there a Data.Map.unzip?

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darcs patch: fix failure to compile with cabal included with ghc 6.6
by David Roundy 21 May '07

21 May '07

I'm not sure if this is sufficient, or even a good idea, but removing this type signature makes Setup.hs able to run on my system with an older cabal. David Wed May 16 09:18:47 PDT 2007 David Roundy <droundy(a)darcs.net> * fix failure to compile with cabal included with ghc 6.6

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darcs patch: add test that X11 will actually build.
by David Roundy 21 May '07

21 May '07

Just for future benefits, it seems a good idea to occasionally check that the X11 library actually can be built. This patch is untested, since the X11 library won't build for me. David Wed May 16 09:26:26 PDT 2007 David Roundy <droundy(a)darcs.net> * add test that X11 will actually build.

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terminateProcess
by Johannes Waldmann 18 May '07

18 May '07

according to documentation of System.Process.terminateProcess, "This function should not be used under normal circumstances." Well, then what function then *should* be used normally? I have the following code in a multithreaded Haskell program, which does not work (if this thread is killed, the external process keeps running after the Haskell program exits) bracket ( System.Process.runCommand cmd ) ( terminateProcess p ) ( polling_waitForProcess ) It took me a while to figure out why "waitForProcess" here does not work: Control.Concurrent.throwTo says "If the target thread is currently making a foreign call, then the exception will not be raised (and hence throwTo will not return until the call has completed.") That's why I defined let polling_waitForProcess p = do me <- getProcessExitCode p case me of Just e -> return () Nothing -> do threadDelay ( 10^5 ) polling_waitForProcess p any hints appreciated, J.W.

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Proposal: ByteString based datagram communication (Ticket #1238 )
by Robert Marlow 18 May '07

18 May '07

I've made a proposal to add ByteString based datagram communication to Network.Socket and Network. Details are at: http://hackage.haskell.org/trac/ghc/ticket/1238#preview I rushed to get this done before I go on a trip tomorrow so I haven't completed testing and won't be available to discuss it for the next 9 days. As such, if discussion is needed, an extended deadline would be appreciated. Testing windows is a bit awkward for me since I don't have a windows machine, so if anyone can test that platform I'd be very appreciative. I'll try to work through the problems I was having with hugs and test when I get back unless someone else wants to test it first. Thanks. -- Robert Marlow MITS Co-operative Limited http://www.mits.coop/

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darcs patch: fix failure to compile with cabal includ... (and 1 more)
by David Roundy 17 May '07

17 May '07

Here's a fixed patch for testing that X11 actually builds. This time it calls autoreconf as the README instructs. David Wed May 16 09:18:47 PDT 2007 David Roundy <droundy(a)darcs.net> * fix failure to compile with cabal included with ghc 6.6 Wed May 16 09:55:02 PDT 2007 David Roundy <droundy(a)darcs.net> * add fixed test that X11 builds

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cgi-compat and ghc-6.6.1
by Johannes Waldmann 15 May '07

15 May '07

What is the status of cgi-compat with ghc-6.6.1? I have some older code that wants Network.CGI.Compat, which seems not available in ghc-6.6.1 standard installation. When I build cgi-compat from source cgi-compat-2006.9.6.tar.gz it will complain about missing "fps". I delete this requirement from cgi.cabal and then can build and install. But now when I compile my program, the message is Could not find module `Network.CGI.Compat': it was found in multiple packages: cgi-compat-2006.9.6 cgi-3001.1.1 I can ghc-pkg hide cgi-3001.1.1 and that seems to solve it for the moment. If I find the time, I probably should change my sources to use the newer API - is there a "migration guide" somewhere? Best regards, Johannes Waldmann.

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Is there already a list class?
by Marc Weber 13 May '07

13 May '07

Hello. Is here the right place to request a list class? eg class List l e where (:) :: e -> l e -> l e head :: .. This might be used in Data.Set, Data.Map class StorableAsList l e t where fromList :: l e -> t toList :: t -> l e I'd like to help implementing/ writing it. Do you consider this beeing a useful enhancement? Cheers Marc Weber

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The Proper Definition of (evaluate :: a -> IO a)
by Isaac Dupree 11 May '07

11 May '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The obvious "evaluate x = x `seq` return x" fails one of the following laws for evaluate: " evaluate x `seq` y ==> y evaluate x `catch` f ==> (return $! x) `catch` f evaluate x >>= f ==> (return $! x) >>= f Note: the first equation implies that (evaluate x) is not the same as (return $! x). " However, strictness does not obey the monad laws. A correct definition for IO would be "evaluate x = (x `seq` return x) >>= return", or equally, "(return $! x) >>= return", or even more horrible-looking, "fmap id (return $! x)"! This works because (at least in present Haskell implementations) IO's (>>=) is not strict in its first argument. Noticing that this function has been implemented (slightly wrongly) for NHC in base, so I mention this odd suggestion. Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGPHKtHgcxvIWYTTURAmT2AKC+pipeHff1jVOCqxjOOz2p+6/JqQCeNqAN bjkaLwbn+BRVCya2e49diF4= =J9iV -----END PGP SIGNATURE-----

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Re: Fwd: Report this to bug-autoconf@gnu.org
by Simon Marlow 10 May '07

10 May '07

Forwarding to list on behalf of "Marek Burza" <mkburza(a)gmail.com>. > ---------- Forwarded message ---------- > From: "Marek Burza" <mkburza(a)gmail.com <mailto:mkburza@gmail.com>> > To: libraries(a)haskell.org <mailto:libraries@haskell.org> > Date: Thu, 10 May 2007 09:50:23 +0200 > Subject: Fwd: Report this to bug-autoconf(a)gnu.org > <mailto:bug-autoconf@gnu.org> > Hi, > > When I tried to install network package an error ocurred to me > below you can find a more detailed description on what it is and how it > can be fixed > - I figured you might be interested > > Best regards, > Mark > > ---------- Forwarded message ---------- > From: *Ralf Wildenhues* < Ralf.Wildenhues(a)gmx.de > <mailto:Ralf.Wildenhues@gmx.de>> > Date: 10-May-2007 08:59 > Subject: Re: Report this to bug-autoconf(a)gnu.org > <mailto:bug-autoconf@gnu.org> > To: Marek Burza < mkburza(a)gmail.com <mailto:mkburza@gmail.com>> > Cc: bug-autoconf(a)gnu.org <mailto:bug-autoconf@gnu.org> > > Hello Marek, > > Thanks for the report. > > * Marek Burza wrote on Wed, May 09, 2007 at 05:57:45PM CEST: > > > > I was trying to install an extension (network-2.0) to Haskell on cygwin > > and I got an error or warning which requested to be reported to you :) > > You can see the output below and if you need more info I'll be glad to > > provide it to you. > [...] > > > checking winsock.h usability... no > > checking winsock.h presence... yes > > configure: WARNING: winsock.h: present but cannot be compiled > > configure: WARNING: winsock.h: check for missing prerequisite headers? > > configure: WARNING: winsock.h: proceeding with the preprocessor's result > > configure: WARNING: ## ------------------------------------ ## > > configure: WARNING: ## Report this to bug-autoconf(a)gnu.org > <mailto:bug-autoconf@gnu.org>. ## > > configure: WARNING: ## ------------------------------------ ## > > checking for winsock.h... yes > [...] > > Please read > > http://www.gnu.org/software/autoconf/manual/html_node/Present-But-Cannot-Be… > > and then show that to the maintainer of the Haskell package, who can > fix this in his package. The error becomes clearer if you look at the > part of the config.log file that deals with this compile failure (and > maybe also some Cygwin documentation). > > > nlv13536@NLVEHVRES2DT1C9 $ runghc Setup.hs build > > Preprocessing library network-2.0.. . > > Building network-2.0... > > cbits\ancilData.c: In function `sendFd': > > > > cbits\ancilData.c:47:0: > > error: variable `msg' has initializer but incomplete type > [...] > > FWIW, these may or may not be followup errors; I don't know. > > Cheers, > Ralf >

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