January 2015 - Libraries

removing constraints
by Ross Paterson 22 Jan '15

22 Jan '15

Recent changes to avoid warnings have removed some constraints from module interfaces: * in Data.Array, Ix i was removed from: instance Ix i => Functor (Array i) instance Ix i => Foldable (Array i) bounds :: Ix i => Array i e -> (i,i) elems :: Ix i => Array i e -> [e] * in Data.Ratio, Integral a was removed from: instance (Integral a, Show a) => Show (Ratio a) numerator :: (Integral a) => Ratio a -> a denominator :: (Integral a) => Ratio a -> a These constraints are not needed by the GHC implementations, but might be needed for other possible implementations, so in a sense the changes are leaking the GHC implementations. This seems most clear in the Functor and Foldable instances for Array, and elems. Portable implementations of these will require the Ix constraint -- I think it should be restored. The other cases are more arguable. For example the change to Data.Ratio declares that the pair is kept in reduced form, but one could argue that requiring that is no bad thing.

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locale: decimal comma vs. point
by Henning Thielemann 21 Jan '15

21 Jan '15

If I export a label track from Audacity the time stamps are formatted with decimal commas instead of decimal points. E.g. 1.5s is formatted as "1,5" not "1.5". I guess this is because I have German locale as default. I want to write numbers from Haskell compatible to this format and thus I want to know whether I have to format numbers with decimal commas or decimal points. However an according information or even better, a locale-aware printf seems to be missing in old-locale. :-(

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Hackage is flooded with old package versions reuploads
by kyra 21 Jan '15

21 Jan '15

Hi, guys, It looks old (and even ancient) versions of many packages gets uploaded to hackage over and over again in ever increasing amounts. The username of uploader for vast majority of these uploads is HerbertValerioRiedel. While this is harmless I wonder what idea stands behind this? Cheers, Kyra

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Announcing a solution to the records problem
by Nikita Volkov 19 Jan '15

19 Jan '15

This thing seems to be going viral on social networks already, nonetheless here's a link for those of you, who aren't yet informed: http://nikita-volkov.github.io/record/

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New maintainer for the boxes library
by Andrés Sicard-Ramírez 14 Jan '15

14 Jan '15

Hi, The current maintainers (Eelis van der Weegen and Benno Fünfstück) of the boxes library (http://hackage.haskell.org/package/boxes) don't want to be maintainers any more. Does someone want to become the new maintainer of this library? Best, -- Andrés

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System.Posix.IO.ByteString
by Erik de Castro Lopo 12 Jan '15

12 Jan '15

Hi All, I'm playing around with some low level IO and found the following function: System.Posix.IO.fdRead :: Fd -> ByteCount -> IO (String, ByteCount) Ok, close, but what if I need a ByteString instead. I then found this: System.Posix.IO.ByteString.fdRead :: Fd -> ByteCount -> IO (String, ByteCount) which is identical to the one above. The ByteString in the module name suggests it would be using ByteString instead of String? Can anyone explain this for me? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Data.ByteString.Unsafe.unsafeWipe
by Erik de Castro Lopo 12 Jan '15

12 Jan '15

Discussion period: one month When handling sensitive information (like a user's password) it is desirable to only keep the data around for as short a time as possible. Specifically, relying on the garbage collector to clean it up is simply not good enough. I therefore propose that the following function to be added to the Data.ByteString.Unsafe module: -- | Overwrites the contents of a ByteString with \0 bytes. unsafeWipe :: ByteString -> IO () unsafeWipe bs = BS.unsafeUseAsCStringLen bs $ \(ptr, len) -> let go i | i < 0 = return () | otherwise = pokeElemOff ptr i 0 >> go (i - 1) in go (len - 1) It is added to the Unsafe module because it break referential transparency but since ByteStrings are always kept in pinned memory, it should not otherwise be considered unsafe. It could be used as follows: main = do passwd <- getPassword doSomethingWith passwd unsafeWipe passwd restOfProgram Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Cabal: Specify multiple package databases in config file
by Jessica Hamilton 11 Jan '15

11 Jan '15

Hi All, Is it possible to specify multiple package databases in Cabal's config file? Currently, I have two installed package databases. One is the system readonly package database, and the other is the system writable package database. This structure is due to how packaging works on Haiku, so can't be changed. A similar structure would also exist for user package databases. My Cabal config file currently looks like: package-db: /packages/ghc/.self/lib/package.conf.d I need this to be something like: package-db: /packages/ghc/.self/lib/package.conf.d; /system/non-packaged/lib/ghc/package.conf.d Is this possible with the Cabal config file? If so, what is the correct syntax to use? Many Thanks, Jessica

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Stream type
by Christopher Done 10 Jan '15

10 Jan '15

Is this type defined anywhere in base or elsewhere standardish? https://gist.github.com/chrisdone/516489f4f27846712225#file-type-hs-L52 data Stream a = Stream a (Stream a) Ciao

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Re: Version of the pretty-printing library in GHC 7.10.1
by Andrés Sicard-Ramírez 09 Jan '15

09 Jan '15

On 9 January 2015 at 13:33, David Terei <d(a)davidterei.com> wrote: > I'd suggest GHC move to pretty 1.1.2.0. I'll shoot an email about that > to see if we can get it changed. > Thanks! -- Andrés

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