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Re: [Haskell-cafe] The state of Hackage: what are we doing about it?
by Bas van Dijk 02 Jun '10

02 Jun '10

On Wed, Jun 2, 2010 at 2:20 PM, Uwe Schmidt <si(a)fh-wedel.de> wrote: > For ranking the results for a package search, a download statistic could be > very useful and could easily be integrated. If such a statistic would be > available in machine readable format (csv, xml, plain text, ...), we could > integrate that. Ordering by nr of direct/indirect reverse dependencies might also be useful. We could add a .csv file version of the main reverse dependency page which you can index easily: http://bifunctor.homelinux.net/~roel/hackage/packages/archive/revdeps-list.… We should probably compress the .csv file to reduce some network bandwidth. Although that's not really a problem for us because we're on a high bandwidth link. Note that .csv files are already provided for individual packages. Here's the one for the latest network for example: http://bifunctor.homelinux.net/~roel/hackage/packages/archive/network/2.2.1… Format: package name-version, nr of direct rev. deps., nr of indirect rev. deps., 'D' for Direct rev. dep. and 'I' for Indirect rev. dep.. Regards, Bas

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Re: Remaining problems with the Batteries Included page
by Yitzchak Gale 02 Jun '10

02 Jun '10

On http://hackage.haskell.org/platform/contents.html, only one click away from "Get the Haskell Platform". - "optimzing" ? - no link for deepseq Thanks, Yitz

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Re: proposal #4095: add Applicative instance for Either
by Ross Paterson 01 Jun '10

01 Jun '10

Ashley Yakeley <ashley(a)semantic.org> writes: > I currently have my own implementations for these: > instance Foldable Identity > instance Traversable Identity > instance Applicative Identity The transformers package has such instances (but currently for a different Identity type). > instance Foldable (Either p) > instance Traversable (Either p) > instance Applicative (Either p) > instance Foldable ((,) p) > instance Traversable ((,) p) The Applicative one is proposed here. The others should also be added.

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The state of Hackage: what are we doing about it?
by Don Stewart 01 Jun '10

01 Jun '10

I see fairly regular complaints about too many Haskell libraries, bewildering choice of difficult-to-determine quality. I've tried to summarize the state of Hackage, and what projects are active to make it easier to find high quality libraries: http://tinyurl.com/2cqw9sb Thoughts? -- Don

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Add Applicative instance for STM
by Bas van Dijk 31 May '10

31 May '10

Hi, I was rewriting my threads package to use TVars instead of MVars when I noticed that the following gave a type error: new ∷ IO ThreadGroup new = atomically $ ThreadGroup <$> newTVar 0 <*> newTMVar () because of a missing Applicative instance for STM. So I propose adding one: http://hackage.haskell.org/trac/ghc/ticket/4076 Discussion period: a few days, since I think this is hardly controversial. Regards, Bas

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Proposal: Make Data.Map.insertWith' and friends consistently force the value inserted
by Ian Lynagh 31 May '10

31 May '10

Hi all, Currently, Data.Map.insertWith' (and friends) only force the value inserted when the combining function creates it: Prelude Data.Map> insertWith' (+) "foo" undefined empty `seq` () () Prelude Data.Map> insertWith' (+) "foo" undefined (singleton "foo" 1) `seq` () *** Exception: Prelude.undefined I think it would be more consistent for it to always force it: Prelude Data.Map> insertWith' (+) "foo" undefined empty `seq` () *** Exception: Prelude.undefined Prelude Data.Map> insertWith' (+) "foo" undefined (singleton "foo" 1) `seq` () *** Exception: Prelude.undefined Patch: hunk ./Data/Map.hs 460 insertWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a insertWithKey' f kx x t = case t of - Tip -> singleton kx x + Tip -> singleton kx $! x Bin sy ky y l r -> case compare kx ky of LT -> balance ky y (insertWithKey' f kx x l) r Ticket: http://hackage.haskell.org/trac/ghc/ticket/4109 Suggested discussion deadline: 14 June 2010. Thanks Ian

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proposal #4095: add Applicative instance for Either
by Ross Paterson 26 May '10

26 May '10

The proposal is to add this instance to Control.Applicative: instance Applicative (Either e) where pure = Right Left e <*> _ = Left e Right f <*> r = fmap f r This is not the only possible instance for Either, but this one is compatible with the usual Monad instance. Deadline: 15th June 2010

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Text.Regex library with bytestrings?
by Kathleen Fisher 24 May '10

24 May '10

Is it possible to use the Text.Regex API with ByteStrings instead of Strings? It looks like there is support for using PCREs with either Strings and ByteStrings, but if you want to use the high-level API in Text.Regex (ie, mkRegex, matchRegexAll, etc), you have to use Strings. For Bytestrings, you can use the lower level API in Text.Regex.Posix.ByteString, but then you are in the IO monad, which I'd rather avoid. Am I missing something? Thanks for any pointers! Kathleen

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ANN: Enhancements to timezone processing in Data.Time
by Yitzchak Gale 24 May '10

24 May '10

The new timezone-series and timezone-olson packages provide enhancements to timezone processing in Haskell's time package, Data.Time. http://hackage.haskell.org/package/timezone-series http://hackage.haskell.org/package/timezone-olson These enhancements are related to the fact that the Data.Time.TimeZone data type does not fully represent a timezone - it only represents a specific clock setting for a timezone, as is traditional for time APIs. But that leads to a number of limitations, such as: o For utcToLocalTime and localTimeToUTC, it is up to the user to ensure that the TimeZone and time specified are consistent with each other. These functions can give wrong results if the specified clock setting was not actually in effect at the specified moment in the given timezone. o It is difficult to compute the amount of time between two moments expessed in terms of the local clock, because you need to know the history of clock changes that happened in between. o When a ZonedTime is constructed, it is up to the user to ensure that its components are consistent with each other and make sense. o Given a ZonedTime, there is no way to construct another ZonedTime for a different moment in the same timezone, unless you know that the same clock setting is in effect at the new moment. Besides those issues - it's just nice to have a type that truly models a timezone. The timezone-series package introduces two new datatypes: TimeZoneSeries, which represents a timezone with all of its clock settings and when each is in effect, and ZoneSeriesTime, which represents a moment within a specific timezone. This package also includes variants of utcToLocalTime and localTimeToUTC which take a TimeZoneSeries instead of a TimeZone as parameter and always give the correct result. The timezone-olson package provides a pure Haskell parser and renderer for binary Olson timezone files. That provides an easy way to create rich TimeZoneSeries objects for most of the timezones of the world on many platforms. I have tried to write these packages in a way that is consistent as much as possible with Data.Time - naming conventions, providing expected services such as ParseTime and FormatTime instances, etc. These packages are distributed on Hackage under a BSD3 license. Caveats: o These packages contain preliminary versions of the software and should be considered highly experimental. Expect there to be bugs, and do not rely on any stability of the exposed interfaces at the moment. o So far, there is no easy solution for Windows users to create a TimeZoneSeries. On Windows, timezone series information is in the registry in a propreitary format, and I don't have a parser for that at the moment. In the meantime, Windows users can copy the Olson files from a Unix system, or compile the Olson files themselves from the zoneinfo sources. I hope to have a much better solution in the near future, and, of course, contributions are welcome. o There is not yet a truly platform-independent way of finding the Olson files for Unix-like platforms. Nowadays /usr/share/zoneinfo is a very popular location for them, but some platforms have them elsewhere. o getCurrentTimeZone is still the best way to get the "official" clock setting for the current moment on the local computer for the local time zone, or for whatever time zone you fool the OS into thinking that you are in. There is also Mark Aylett's zoneinfo package. Those bindings to the C API give you clock settings that are most likely to be consistent with what is used by other apps on the same local computer. But the C API gives you a clock setting, not a timezone. And the system timezone database on the local computer could be out of date. And the interface, which involves setting global process state and then calling effectful procedures, is awkward to say the least and prone to cause trouble. So I think it's nice to have a pure Haskell Olson parser. I would like to take this opportunity to thank once again Ashley Yakely for his fantastic work in creating Haskell's advanced time API in Data.Time. Enjoy, Yitz

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Cabal sqlite3 installation problems
by Hok Shun Poon 23 May '10

23 May '10

Hello, This is a question about how cabal-install finds 'installed foreign libraries' when trying to satisfy dependencies for packages like hdbc-sqlite3 on Windows. Sadly, the current setup means that I must use Windows 7 to develop code. I've already followed steps on http://wiki.github.com/jgoerzen/hdbc/frequentlyaskedquestions to place the .dll and the .h files in the correct places; it's just that cabal never seems to find it, despite being given --extra-lib-dirs= and --extra-include-dirs= directives. The message is as follows: > cabal install hdbc-sqlite3 --extra-lib-dirs=D:\dev\libs\database\sqlite Resolving dependencies... Configuring HDBC-sqlite3-2.3.0.0... cabal: Missing dependency on a foreign library: * Missing C library: sqlite3 This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. cabal: Error: some packages failed to install: HDBC-sqlite3-2.3.0.0 failed during the configure step. The exception was: ExitFailure 1 The strangest thing is, I've successfully made cabal build this package before (with a different version of Haskell Platform)... what's going on? I'm using cabal-install version 0.8.2 and Cabal library version 1.8.0.2. Hok

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