February 2014 - Haskell-Cafe

Is the wiki really this out of date?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 20 Feb '14

20 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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Re: [Haskell-cafe] Rewrite NetBSD kernel driver using Ajhc Haskell compiler
by Kiwamu Okabe 20 Feb '14

20 Feb '14

Hi Johnny, On Thu, Feb 20, 2014 at 5:37 PM, Johnny Billquist <bqt(a)update.uu.se> wrote: > Are you saying that you essentially avoid GC by creating a large fresh heap > every time you call something written in Haskell, and then delete the heap > when the Haskell function returns? And that the current piece of code > running in Haskell is short enough that GC never is done? No, does not delete. Pool it. See following code compiled by Ajhc. Ajhc compile Haskell code into C code. https://gist.github.com/master-q/9109334 Please note auichIntr() function that is entry point C => Haskell. https://gist.github.com/master-q/9109334#file-hsmain-c-L2051 int auichIntr(HsPtr x272) { arena_t arena; gc_t gc; gc = NULL; arena = NULL; jhc_alloc_init(&gc,&arena); jhc_hs_init(gc,arena); int x273 = ((int)fFE$__CCall_auichIntr(gc,arena,(uintptr_t)x272)); jhc_alloc_fini(gc,arena); return x273; } The code post-calls jhc_alloc_fini() that pool Haskell heap (named megablock) into free_megablocks. https://github.com/ajhc/ajhc/blob/d93468e34f4514209048d4a92b1549e079ccd3fb/… void jhc_alloc_fini(gc_t gc,arena_t arena) { -- snip -- SLIST_FOREACH(pg, &arena->monolithic_blocks, link) { SLIST_INSERT_HEAD(&free_monolithic_blocks, pg, link); } SLIST_FOREACH(mb, &arena->megablocks, next) { SLIST_INSERT_HEAD(&free_megablocks, mb, next); } if(arena->current_megablock) { SLIST_INSERT_HEAD(&free_megablocks, arena->current_megablock, next); } Also s_alloc(), Haskell heap allocator, try to get Haskell heap from the pool. If not found, it posix_memalign new megablock. https://github.com/ajhc/ajhc/blob/d93468e34f4514209048d4a92b1549e079ccd3fb/… struct s_megablock * s_new_megablock(arena_t arena) { jhc_rts_lock(); struct s_megablock *mb = SLIST_FIRST(&free_megablocks); if (mb) { SLIST_REMOVE(&free_megablocks, mb, s_megablock, next); } else { mb = malloc(sizeof(*mb)); #ifdef _JHC_JGC_LIMITED_NUM_MEGABLOCK static int count = 0; if (count >= _JHC_JGC_LIMITED_NUM_MEGABLOCK) { abort(); } mb->base = aligned_megablock + (MEGABLOCK_SIZE) * count; count++; #else mb->base = jhc_aligned_alloc(MEGABLOCK_SIZE); #endif Regards, -- Kiwamu Okabe

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Text and ByteString safety (was Naming scheme for partial functions)
by Lucas Paul 19 Feb '14

19 Feb '14

I'm still a little new to Haskell. Could someone explain how Text and ByteString "push the boundaries of 'unsafe'"? On Sat, Feb 15, 2014 at 8:40 AM, Antoine Latter <aslatter(a)gmail.com> wrote: > Yeah, that's a good point.Text and Bytestring (and other similar packages) > have been pushing the boundaries of 'unsafe' and are in wide use.

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