- Haskell-Cafe - Haskell.org

Data.Foldable UArray
by Marcus D. Gabriel 23 Feb '14

23 Feb '14

Hello, I wanted to make a simple Data.Foldable UArray, and I naively modelled it on > instance Ix i => Foldable (Array i) where > foldr f z = Prelude.foldr f z . elems with, of course, > instance Ix i => Foldable (UArray i) where > foldr f z = Prelude.foldr f z . elems which did not work yielding the following type message Could not deduce (IArray UArray a) arising from a use of `elems' from the context (Ix i) bound by the instance declaration at ... Possible fix: add an instance declaration for (IArray UArray a) In the second argument of `(.)', namely `elems' In the expression: Data.List.foldr f z . elems In an equation for `foldr': foldr f z = Data.List.foldr f z . elems I clearly do not understand something because I cannot make this work, and I am not sure why. With the Haskell type system or even with ghc extensions, can one even make a Data.Foldable UArray? If so, how? Thanks in advance, - Marcus

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[ANN] cabal-bounds: A command line program for managing the bounds/versions of the dependencies in a cabal file.
by Daniel Trstenjak 23 Feb '14

23 Feb '14

Hi all, If you have several cabalized projects, then it can be quite time consuming to keep the bounds of your dependencies up to date. Especially if you're following the package versioning policy, then you want to raise your upper bounds from time to time, to allow the building with newer versions of the dependencies. `cabal-bounds` tries to automate this update process to some degree. So a typical update process might look like: $> # update the version infos of all libraries $> cabal update $> # drops the upper bound of all dependencies in 'myproject.cabal', most likely you want to ignore 'base' $> cabal-bounds drop --upper --ignore=base myproject.cabal $> # create a cabal sandbox for building of 'myproject' $> cabal sandbox init $> # build 'myproject' $> cabal install $> # update the upper bound of all dependencies in 'myproject.cabal' by the cabal build information $> cabal-bounds update --upper --ignore=base myproject.cabal dist/dist-sandbox-*/setup-config Perhaps the currently most annoying thing is, that you have to live with the reformating of your `cabal` file done by the pretty printer of the `Cabal` library. https://github.com/dan-t/cabal-bounds Greetings, Daniel

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Is the wiki really this out of date?
by Dominic Steinitz 23 Feb '14

23 Feb '14

I just looked at the wiki page for the IRC channel: http://www.haskell.org/haskellwiki/IRC_channel. It’s got some great charts but they last seem to have been updated in 2009. Is that really the case? And does anyone know how to get them up to date. I can see this: http://tunes.org/~nef/logs/haskell/ so I think the chart showing kb of text per day should be easy enough. Not sure about the social graph or the noun chart though. I know I can get number of people on the channel by /names but that only gives a snapshot. Has anyone any idea on how to get historical data on number of names? Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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ANNOUNCE: Win32-dhcp-server
by Michael Steele 22 Feb '14

22 Feb '14

I'm pleased to announce the first version of Win32-dhcp-server [1]. The purpose of this library is to query and control a Microsoft DHCP server. Enough functionality is defined so so that Ipv4 client lease and reservation records can be manipulated from software. I started this at the 2011 Portland hackathon (HacPDX-II), and have been working on it off and on since then. After adding support for a few more commands last month I realized it was probably ready to publish. Please report any bugs, comments, or feature requests to the github [2] repository. [1]: http://hackage.haskell.org/package/Win32-dhcp-server [2]: https://github.com/mikesteele81/Win32-dhcp-server -- -- Michael Steele

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Hdevtools cabal support
by Maxim Kulkin 22 Feb '14

22 Feb '14

Hi, I'm pretty new to Haskell, but was doing Haskell development for several month. I'm fan of Vim editor and was happy to find out that there are good tools to support Haskell development with Vim, e.g. vim-hdevtools. But it turned out that it not of much use in my project where we rely on Cabal packages and sandboxes. As part of scratching own itch I have implemented support for Cabal packages for Hdevtools. I invite everyone interested to try, review and provide feedback on this. The patch is not yet merged into master branch, so to install it you need to check it out from my repository: git clone https://github.com/maximkulkin/hdevtools.git cd hdevtools git checkout cabal-support cabal install So, to be able to use hdevtools with Cabal, you just need to run hdevtools from inside your Cabal project, e.g. hdevtools check src/MyFile.hs hdevtools info src/MyOtherFile.hs DoThat Hope this will save someone's day. Max

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Problems on installing sizes-types package
by Rodrigo Ribeiro 21 Feb '14

21 Feb '14

Hello to all! I'm trying to install the sized-types package, a dependency for kansas lava: http://hackage.haskell.org/package/sized-types using cabal, and the following error message is returned: Data/Sized/Sparse/Matrix.hs:61:26: Could not deduce (Eq a) arising from a use of `prune' from the context (Size m, Size n, Size m', Size n', n ~ m', Num a) bound by the type signature for mm :: (Size m, Size n, Size m', Size n', n ~ m', Num a) => Matrix (m, n) a -> Matrix (m', n') a -> Matrix (m, n') a at Data/Sized/Sparse/Matrix.hs:50:7-112 Is it a known issue? Is there some way to solve it? I'm using GHC 7.6.3 and plataform 2013.2.0.0. Best, Rodrigo

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Haskell Platform website error
by Omari Norman 21 Feb '14

21 Feb '14

Inaccuracy in Haskell Platform website: it says version 2013.2.0.0 includes containers-0.4.2.1: http://www.haskell.org/platform/changelog.html However the containers included in GHC 7.6.3 and, therefore, with this version of Haskell Platform is in fact version 0.5.0.0. There's no apparent contact link on the website; who should I report this to? Thanks. --Omari

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Haskell Statistics
by Dominic Steinitz 21 Feb '14

21 Feb '14

Hi I am looking for statistics on usage of Haskell, ghc and the Haskell Platform and their growth. Current usage would be great but I’d also like usage by year or month. Useful proxies might be number of people signed up to haskell-cafe and #haskell (also by year or month). The impression I have from the number of jobs posted recently is that Haskell is experiencing some growth. I have the redmonk stats: http://redmonk.com/sogrady/category/programming-languages/ and http://sogrady-media.redmonk.com/sogrady/files/2014/01/lang-rank-114-wm.png which shows that Haskell is maintaining its position. My google trend analysis shows Haskell roughly matching Scala and both of them somewhat higher than F#. I admit to being a google trend novice so caveat lector! I have this using google trends: http://www.google.com/trends/explore#q=haskell%20programming%2C%20scala%20p… Thanks in advance for any help in this. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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hmatrix-labeled: request for comments
by Nikita Karetnikov 21 Feb '14

21 Feb '14

I like how easy it is to import data in R and Octave. (See [1] for a typical workflow.) Since I couldn’t find any matching library on Hackage, I cooked up my own [2] in a couple of days. Here’s an example. Let’s start by creating a poorly formatted dataset: $ cat > test.txt One Two Longish Four Foo 1 -2 3.0 4.0 Looooooong 5.0 6.0 -72.0 8.0 Baz 41.0 4.2324234e7 43.0 1.111111144E-12 Then we parse it with ‘readFile’, mangle the data a bit, and display in GHCi: λ> import qualified Data.Packed.LMatrix.IO as L λ> import qualified Data.Packed.LMatrix as L λ> do m <- L.readFile "test.txt"; return . L.trans . L.reverseRows $ L.map (+1) m (4><3) Baz Looooooong Foo One 42.0 6.0 2.0 Two 4.2324235e7 7.0 -1.0 Longish 44.0 -71.0 4.0 Four 1.0000000000011111 9.0 5.0 Now I’m wondering how to make it better. I’m planning to add the documentation, augment the parser to accept CSV, and maybe support other matrix libraries. What’s missing? Would you like to see it on Hackage? And if not, why? [1] http://astrostatistics.psu.edu/su09/lecturenotes/pca.html [2] https://gitorious.org/hmatrix-labeled

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fromString and toString
by Ben Foppa 20 Feb '14

20 Feb '14

I know we have class IsString a where fromString :: String -> a But do we have an inverse generic function toString defined anywhere? IsString implies that the type `a` is a subset of String; if all we have is fromString, then IsString defines *supersets* of String. To me, the most logical thing would be that IsString defines bijections to String (i.e. things that are subsets *and* supersets). The reason this came up is that I'm getting pretty sick of type-juggling different string types from different libraries (String, Text, various ByteStrings), especially since I have to tweak all the functions I use if a type changes; discovering fromString was fantastic, but without toString, I can't define something like reString :: (IsString a, IsString b) => a -> b which is great to have if your putStrLn only accepts one kind of string, and you have several distinct ones floating around. Thanks, Ben

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