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Is www.haskell.org down?
by DekuDekuplex＠Yahoo.com 06 Jun '10

06 Jun '10

Since yesterday, I have been unable to connect to www.haskell.org. Is the site down? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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Reporting a problem with binary-0.5
by Pete Chown 05 Jun '10

05 Jun '10

I've been trying to get in touch with the maintainers of the Binary package, to report an issue. When I emailed the addresses given on Hackage, I got an automated response saying I had used an address that was no longer current. I don't want to put pressure on anyone to fix my bug -- I didn't pay anything for Binary, so it wouldn't be fair for me to have that kind of expectation. At the same time, I don't really want my bug report to go missing just because someone's email address has changed. Does anyone know who I should be talking to? Or is there a bug tracker for the Hackage packages somewhere? I noticed this problem when I ran into some trouble with the network-dns package. It would hang up as soon as I tried to send a query. Eventually I traced the problem to the binary module, and reduced it to this short test case: module Main where import qualified Data.Binary.Get as G import qualified Data.ByteString.Lazy as B main = do urandom <- B.readFile "/dev/urandom" let urandomParser :: G.Get [Int] urandomParser = do v <- G.getWord32be rest <- urandomParser return $ fromIntegral v : rest seeds = G.runGet urandomParser urandom print $ take 4 seeds This code attempts to create an infinite list of random numbers -- a technique also used by network-dns. It turns out that this code works with binary-0.4.4 but not with binary-0.5.0.2. Both were built with ghc-6.12.1 on Ubuntu. (I haven't tested with the intermediate versions of the binary module.) It seems that with binary-0.5.0.2 there is some unwanted strictness; something is evaluated for the whole list, even though it is only the first few elements that are required. Incidentally, if the test case is changed like this: --- get_monad.hs 2010-05-28 11:31:02.399202535 +0100 +++ get_monad2.hs 2010-05-28 13:44:25.515486013 +0100 @@ -1,10 +1,12 @@ module Main where +import Control.Monad + import qualified Data.Binary.Get as G import qualified Data.ByteString.Lazy as B main = do - urandom <- B.readFile "/dev/urandom" + urandom <- liftM (B.take 64) $ B.readFile "/dev/urandom" let urandomParser :: G.Get [Int] urandomParser = do v <- G.getWord32be the program exits with an error: get_monad2.hs: too few bytes. Failed reading at byte position 68 This seems to demonstrate that the program is reading more data than it needs to. Thanks, Pete

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Difference between div and /
by Maciej Piechotka 05 Jun '10

05 Jun '10

I started to wonder what is the difference between div and / so they are 2 separate symbols. div: Take a Integral divide and round (down) (/): Take a Fractional divide and usually round In some applications I would like to use any of those but it is not possible. Is this unification taken into account while reworking numeric classes? I.e. why not: class Num a => Divisable a where (/) :: a -> a -> a class (Real a, Enum a, Divisable a) => Integral a where quot :: a -> a -> a rem :: a -> a -> a div = (/) mod :: a -> a -> a x `quotRem` y = (x `quot` y, x `rem y) x `divMod` y = (x `div` y, x `mod` y) toInteger :: a -> Integer class Divisable a => Fractional a where recip = (1/) :: a -> a fromRational :: Rational -> a (Example does not take into account other refactoring) Regards PS. Why is Fd/cPid etc. Integral or even Num? What does (stdin + stderr) `mod` stdout mean (result will be stdin).

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Proposal filed to GHC, expecting supporters vote: Type supplement for constructor specific uses of sum types
by Gabriel Riba 05 Jun '10

05 Jun '10

Hi! I have filed a new proposal to GHC bugs/whishes process based on the previous discussion here. The proposal address is http://hackage.haskell.org/trac/ghc/ticket/4116#comment:2 ( I had some formatting problems with the first posting, so it is better read at comment:2) Voters admitted: GHC prioritizes bugs/features based on the length of supporters email list at the CC field of the ticket as explained here: http://hackage.haskell.org/trac/ghc/wiki/ReportABug#Ifalreadyreportedvotefo… You may add also any change proposal. Cheers. Gabriel

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Problems with Haskell Platform
by Dominic Steintiz 05 Jun '10

05 Jun '10

I seem to be in some sort package dependency hell (which I thought the Haskell Platform did away with). I install ghc using my package manager (I'm on opensuse). > dom1@fourier:~> ghc --version > The Glorious Glasgow Haskell Compilation System, version 6.12.1 > dom1@fourier:~> cabal --version > cabal-install version 0.8.2 > using version 1.8.0.4 of the Cabal library > dom1@fourier:~> cabal update > Downloading the latest package list from hackage.haskell.org But > dom1@fourier:~> cabal upgrade cabal-install > Resolving dependencies... > Downloading HTTP-4000.0.9... > Configuring HTTP-4000.0.9... > Preprocessing library HTTP-4000.0.9... > Building HTTP-4000.0.9... > > Network/StreamSocket.hs:30:7: > Could not find module `Network.Socket': > There are files missing in the `network-2.2.1.7' package, > try running 'ghc-pkg check'. > Use -v to see a list of the files searched for. > cabal: Error: some packages failed to install: > HTTP-4000.0.9 failed during the building phase. The exception was: > ExitFailure 1 > cabal-install-0.8.2 depends on HTTP-4000.0.9 which failed to install. And trying to install the Haskell Platform via http://hackage.haskell.org/platform/2010.1.0.0/cabal/haskell-platform-2010.… > dom1@fourier:~> cabal install > Resolving dependencies... > cabal: dependencies conflict: ghc-6.12.1 requires directory ==1.0.1.1 > however > directory-1.0.1.1 was excluded because ghc-6.12.1 requires directory > ==1.0.1.0 Which is somewhat baffling. So I uninstalled ghc via the package manager and downloaded the linux binaries at http://haskell.org/ghc/dist/6.12.1/ghc-6.12.1-i386-unknown-linux-n.tar.bz2 But sadly > dom1@fourier:~/Downloads/ghc-6.12.1> ./configure > checking for path to top of build tree... ./configure: line 1687: > utils/ghc-pwd/ghc-pwd: cannot execute binary file > configure: error: cannot determine current directory And indeed it is true > dom1@fourier:~/Downloads/ghc-6.12.1> utils/ghc-pwd/ghc-pwd > bash: utils/ghc-pwd/ghc-pwd: cannot execute binary file I'm not sure where to go from here. I think my options are a) build ghc from source or b) find the source for ghc-pwd and compile it and then try configure again. Any help would be appreciated. Dominic.

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Proposal: Sum type branches as extended types (as Type!Constructor)
by Gabriel Riba 05 Jun '10

05 Jun '10

Extending sum types with data constructors would spare runtime errors or exception control, when applying functions to inappropriate branches, as in the example ... data List a = Nil | Cons a (List a) -- List!Nil and List!Cons -- as extended types * Actual system, with runtime errors (as in GHC Data.List head) or exception throwing hd :: List a -> a hd (Cons x _) -> x hd Nil -> error "error: hd: empty list" -- error or exception throwing * Proposed system extending types with constructors as Type!Constructor: User must do pattern matching before applying the constructor-specific type function. In ''var @ (Constructor _ _)'' the compiler should append the constructor to the type as a pair (Type, Constructor) as an extended type for ''var'' No need for runtime errors or exception control hd :: List!Cons a -> a hd (Cons x _) = x using it: headOf :: List a -> Maybe a headOf list = case list of li @ (Cons _ _) -> Just hd li -- extTypeOf li == ( 'List', 'Cons') -- should pass typechecker for List!Cons li @ Nil -> Just hd li -- compiler error !! -- extTypeOf ('List','Nil') don't match _ -> Just hd list -- compiler error !! -- extTypeOf ('List',Nothing) don't match Maybe we could take out importance on the number of _ wildcards (constructor arity) with a syntax like. li @ (Cons ...) li @ (Nil ...) Cheers! Gabriel Riba Faura.

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Cabal -j
by Louis Wasserman 04 Jun '10

04 Jun '10

What, if anything, stands in the way of parallelizing Cabal installs, make -j style? Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

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Re: [Haskell-cafe] Issue with "connectTo" function in "network" package
by aditya siram 04 Jun '10

04 Jun '10

Great! If there is a wiki or FAQ page for networking with Haskell it might be worth updating. -deech On 6/4/10, Roman Cheplyaka <roma(a)ro-che.info> wrote: > /etc/hosts is the file responsible for resolving 'localhost' hostname. > As you can see from it, there are two entries for localhost: one > contains IPv4 address (127.0.0.1) and another contains IPv6 address > (::1). > > The behaviour you observe is kinda bug in connectTo function. Instead of > trying all of the addresses, this function just tries the first one. > Until it is fixed (I'm gonna write and send a patch soon), can you live > with this temporary hack? If for some reason the answer is "no", you > have to use low-level functions from Network.Socket module for now. > > > * aditya siram <aditya.siram(a)gmail.com> [2010-06-04 14:15:47-0500] >> Doing (1) solves my problem. What did I do and why did it work? Thanks >> a lot for your help! >> -deech >> >> On 6/4/10, Roman Cheplyaka <roma(a)ro-che.info> wrote: >> > Confirm if any of the following solves the problem: >> > >> > 1. commenting out (by prepending putting hash sign '#' in the beginning >> > of the line) the following line in /etc/hosts: >> > >> > ::1 localhost ip6-localhost ip6-loopback >> > >> > 2. executing as root the following command: >> > >> > rmmod ipv6 >> > >> > * aditya siram <aditya.siram(a)gmail.com> [2010-06-04 13:51:29-0500] >> >> Here's my GHCI session (with my network card off): >> >> Prelude Network Network.Socket> connectTo "localhost" (PortNumber 3000) >> >> *** Exception: connect: does not exist (Connection refused) >> >> Prelude Network Network.Socket> connectTo "127.0.0.1" (PortNumber 3000) >> >> {handle: <socket: 7>} >> >> >> >> The OS is Ubuntu (Lucid) Linux. The contents of "/etc/hosts" and >> >> "/etc/nsswitch.conf" are: >> >> >> >> > cat /etc/nsswitch.conf >> >> # /etc/nsswitch.conf >> >> # >> >> # Example configuration of GNU Name Service Switch functionality. >> >> # If you have the `glibc-doc-reference' and `info' packages installed, >> >> try: >> >> # `info libc "Name Service Switch"' for information about this file. >> >> >> >> passwd: compat >> >> group: compat >> >> shadow: compat >> >> >> >> hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4 >> >> networks: files >> >> >> >> protocols: db files >> >> services: db files >> >> ethers: db files >> >> rpc: db files >> >> >> >> netgroup: nis >> >> >> >> > cat /etc/hosts >> >> 127.0.0.1 localhost >> >> 127.0.1.1 deech-mac-ubuntu >> >> >> >> # The following lines are desirable for IPv6 capable hosts >> >> ::1 localhost ip6-localhost ip6-loopback >> >> fe00::0 ip6-localnet >> >> ff00::0 ip6-mcastprefix >> >> ff02::1 ip6-allnodes >> >> ff02::2 ip6-allrouters >> >> ff02::3 ip6-allhosts >> >> >> >> >> >> -deech >> >> >> >> On 6/4/10, Roman Cheplyaka <roma(a)ro-che.info> wrote: >> >> > * aditya siram <aditya.siram(a)gmail.com> [2010-06-03 22:30:33-0500] >> >> >> Hi all, >> >> >> I had an issue where using the connectTo [1] function would fail to >> >> >> connect to "localhost" if my wireless card was turned off. The >> >> >> moment >> >> >> I turned on my wireless connection it worked. But if I use connectTo >> >> >> with "127.0.0.1" [2] with my network off it works. >> >> >> >> >> >> I confirmed that "localhost' resolves to "127.0.0.1" by pinging >> >> >> "localhost" from command line with the Internet off. >> >> >> >> >> >> Is this a bug in "connectTo"? >> >> >> >> >> >> -deech >> >> >> >> >> >> [1] connectTo "localhost" (PortNumber some_number) >> >> >> [2] connectTo "127.0.0.1" (PortNumber some_number) >> >> > >> >> > How exactly did it fail? Did it throw an exception? If so, what was >> >> > the >> >> > exception? >> >> > >> >> > Which operating system did you observe that under? >> >> > >> >> > If that was Linux, can you show the contents of the following files >> >> > on >> >> > that system: >> >> > >> >> > /etc/nsswitch.conf >> >> > /etc/hosts >> >> > >> >> > -- >> >> > Roman I. Cheplyaka :: http://ro-che.info/ >> >> > "Don't let school get in the way of your education." - Mark Twain >> >> > _______________________________________________ >> >> > Haskell-Cafe mailing list >> >> > Haskell-Cafe(a)haskell.org >> >> > http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > >> > >> > -- >> > Roman I. Cheplyaka :: http://ro-che.info/ >> > "Don't let school get in the way of your education." - Mark Twain >> > > > -- > Roman I. Cheplyaka :: http://ro-che.info/ > "Don't let school get in the way of your education." - Mark Twain >

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Issue with "connectTo" function in "network" package
by aditya siram 04 Jun '10

04 Jun '10

Here's my GHCI session (with my network card off): Prelude Network Network.Socket> connectTo "localhost" (PortNumber 3000) *** Exception: connect: does not exist (Connection refused) Prelude Network Network.Socket> connectTo "127.0.0.1" (PortNumber 3000) {handle: <socket: 7>} The OS is Ubuntu (Lucid) Linux. The contents of "/etc/hosts" and "/etc/nsswitch.conf" are: > cat /etc/nsswitch.conf # /etc/nsswitch.conf # # Example configuration of GNU Name Service Switch functionality. # If you have the `glibc-doc-reference' and `info' packages installed, try: # `info libc "Name Service Switch"' for information about this file. passwd: compat group: compat shadow: compat hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4 networks: files protocols: db files services: db files ethers: db files rpc: db files netgroup: nis > cat /etc/hosts 127.0.0.1 localhost 127.0.1.1 deech-mac-ubuntu # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters ff02::3 ip6-allhosts -deech On 6/4/10, Roman Cheplyaka <roma(a)ro-che.info> wrote: > * aditya siram <aditya.siram(a)gmail.com> [2010-06-03 22:30:33-0500] >> Hi all, >> I had an issue where using the connectTo [1] function would fail to >> connect to "localhost" if my wireless card was turned off. The moment >> I turned on my wireless connection it worked. But if I use connectTo >> with "127.0.0.1" [2] with my network off it works. >> >> I confirmed that "localhost' resolves to "127.0.0.1" by pinging >> "localhost" from command line with the Internet off. >> >> Is this a bug in "connectTo"? >> >> -deech >> >> [1] connectTo "localhost" (PortNumber some_number) >> [2] connectTo "127.0.0.1" (PortNumber some_number) > > How exactly did it fail? Did it throw an exception? If so, what was the > exception? > > Which operating system did you observe that under? > > If that was Linux, can you show the contents of the following files on > that system: > > /etc/nsswitch.conf > /etc/hosts > > -- > Roman I. Cheplyaka :: http://ro-che.info/ > "Don't let school get in the way of your education." - Mark Twain > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Tricks with GMap -- question about conflicts w/ indexed type families
by Ryan Newton 04 Jun '10

04 Jun '10

GMaps -- families of map implementations indexed by the key type -- are an example on the wiki: http://www.haskell.org/haskellwiki/GHC/Type_families I've been using something like this myself. It sure would be nice to have a fully developed version on Hackage, and I may try to submit this myself if no one else has already done it. But I'm running into a problem in achieving a particular optimization that I want -- namely, small tuple keys packed into Ints. For example, with a key type (Int16,Int16) it's possible to pack the key into a plain Int and use Data.IntMap. In fact, in the rough/partial implementation here (http://people.csail.mit.edu/newton/gmap/GMap.hs) I have a class for things that fit in a word: class FitInWord v where toWord :: v -> Word fromWord :: Word -> v (Or fitInInt for that matter.) Which includes things like small tuples: instance FitInWord (Int16,Int16) where toWord (a,b) = shiftL (fromIntegral a) 16 + (fromIntegral b) fromWord n = (fromIntegral$ shiftR n 16, fromIntegral$ n .&. 0xFFFF) (If you know a better idea than using templates/program generation to generate every combination of small scalar tuples that fit in a word.... let me know.) What I would next *like* to do is something like the following: import qualified Data.IntMap as DI instance FitInWord t => GMapKey t where data GMap t v = GMapInt (DI.IntMap v) deriving Show empty = GMapInt DI.empty lookup k (GMapInt m) = DI.lookup (wordToInt$ toWord k) m insert k v (GMapInt m) = GMapInt (DI.insert (wordToInt$ toWord k) v m) alter fn k (GMapInt m) = GMapInt (DI.alter fn (wordToInt$ toWord k) m) toList (GMapInt m) = map (\ (i,v) -> (fromWord$ intToWord i, v)) $ DI.toList m The problem is that there's already a more general instance of GMapKey that handles pairs by representing them as nested GMaps: instance (GMapKey a, GMapKey b) => GMapKey (a, b) where data GMap (a, b) v = GMapPair (GMap a (GMap b v)) .... Ideally, I want both of these to coexist (and to prioritize the more specific one). With normal type classes, OverlappingInstances can handle this, but with type families I get an error like the following: Conflicting family instance declarations: data instance GMap t v -- Defined at Intel/GMap.hs:108:7-10 data instance GMap (a, b) v -- Defined at Intel/GMap.hs:225:7-10 Any fixes? Thanks, -Ryan

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