March 2010 - Haskell-Cafe

cabal through PHPProxy
by Dupont Corentin 31 Mar '10

31 Mar '10

Hello, i'm using PHPProxy to go on the internet (www.phpproxy.fr) How can i tell cabal to use this? Cheers, Corentin

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Shootout update
by Isaac Gouy 31 Mar '10

31 Mar '10

On Mar 30, 1:26 am, Simon Marlow <marlo...(a)gmail.com> wrote: > The shootout (sorry, Computer Language Benchmarks Game) ... In a different time, in a different place, "the shootout" meant a football once again flying over the cross bar or harmlessly into the arms of the keeper and England once more exiting an international competition. Here in "the west" it has meant slaughter - back in 2004 crossed-pistols were suggested as the website image. Wading through Google search results comprised of porn sites and college mass murder just wasn't a bright happy start to the day for me - so after Virginia Tech I changed the name. I should probably have moved everything to a new project (a new URL).

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Do I need to roll my own?
by David Leimbach 31 Mar '10

31 Mar '10

I'm looking at iteratee as a way to replace my erroneous and really inefficient lazy-IO-based backend for an expect like Monad DSL I've been working for about 6 months or so now on and off. The problem is I want something like: expect "some String" send "some response" to block or perhaps timeout, depending on the environment, looking for "some String" on an input Handle, and it appears that iteratee works in a very fixed block size. While a fixed block size is ok, if I can put back unused bytes into the enumerator somehow (I may need to put a LOT back in some cases, but in the common case I will not need to put any back as most expect-like scripts typically catch the last few bytes of data sent before the peer is blocked waiting for a response...) Otherwise, I'm going to want to roll my own iteratee style library where I have to say "NotDone howMuchMoreIThinkINeed" so I don't over consume the input stream. Does that even make any sense? I'm kind of brainstorming in this email unfortunately :-) Dave

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building "encoding" on Windows?
by wagnerdm＠seas.upenn.edu 31 Mar '10

31 Mar '10

I'm trying to help a non-Haskell person build wyvern (shameless plug in case you like go: http://dmwit.com/wyvern) but (s)he's having trouble building the "encoding" library. Has any Windows person done it successfully or is willing to try it? I tried contacting the "encoding" maintainer a few days ago, but haven't heard back. Thanks! ~d P.S. I thought it might just be a missing library, but the encoding library itself comes with "system_encoding.h". ----- Forwarded message from wilemien(a)googlemail.com ----- Date: Thu, 25 Mar 2010 09:36:43 +0000 From: Willemien <wilemien(a)googlemail.com> Subject: Re: hi from willemien To: wagnerdm(a)seas.upenn.edu On Thu, Mar 25, 2010 at 2:52 AM, <wagnerdm(a)seas.upenn.edu> wrote: > Quoting Willemien <wilemien(a)googlemail.com>: > >> Tried >> cabal install sgf >> error some packages failed to install >> encoding-0.6.3 failed during the configure step > > Ah, yes! I knew about this problem, and totally forgot. The "encoding" > package uses some tools, but can't depend on them properly (bad!). Try > this (capitalization matters): > > cabal install HaXml > cabal install sgf > > Does that work? I'll update the website shortly. > ~d > Sorry no cabal install HaXml goes well (but takes longer than 2 minutes) Cabal install sgf not more specific: last lines are Configuring encoding-0.6.3... Setup.exe Missing dependency on foreign library: * Missing Header file: System_encoding.h 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 Allready 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: encoding-0.6.3 failed during the configure step. The exception was: exit: ExitFailure 1 sgf-0.1.1 depends on encoding 0.6.3 which faild to install. Hope you can solve it Willemien ----- End forwarded message -----

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Data.Graph?
by Lee Pike 31 Mar '10

31 Mar '10

Apologies if this request isn't 'appropriate' for this venue (perhaps it's a Haskell' request and/or has been discussed before)... I'd like it if there were a "Data.Graph" in the base libraries with basic graph-theoretic operations. Is this something that's been discussed? For now, it appears that Graphalyze on Hackage is the most complete library for graph analysis; is that right? (I actually usually just want a pretty small subset of its functionality.) Thanks, Lee

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Announce: Haskell Platform 2010.1.0.0 (beta) release
by Don Stewart 31 Mar '10

31 Mar '10

Live from (post-) Zurihac, I'm pleased to announce the 2010.1.0.0 (beta branch) release of the Haskell Platform, supporting GHC 6.12. http://hackage.haskell.org/platform/ The Haskell Platform is a comprehensive, robust development environment for programming in Haskell. For new users the platform makes it trivial to get up and running with a full Haskell development environment. For experienced developers, the platform provides a comprehensive, standard base for commercial and open source Haskell development that maximises interoperability and stability of your code. The 2010.1.0.0 release is a beta release for the GHC 6.12 series of compilers. It currently doesn't provide a Windows installer (which defaults to GHC 6.10.4 for now). We expect to make the stable branch with GHC 6.12.2 in soon. This release includes a binary installer for Mac OS X Snow Leopard, as well as source bundles for an Unix system, and a new design. The Haskell Platform would not have been possible without the hard work of the Cabal development team, the Hackage developers and maintainers, the individual compiler, tool and library authors who contributed to the suite, and the distro maintainers who build and distribute the Haskell Platform. Thanks! -- Don (for The Platform Infrastructure Team)

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Implementation of Functional Languages - a tutorial
by C K Kashyap 31 Mar '10

31 Mar '10

Hi Everybody, I've started reading SPJ's book - When I tried to execute some sample code in miranda, I found that Miranda does not seem to recognize things like import Utils or module Langauge where ... Has someone created a clean compilable miranda source out of this book? -- Regards, Kashyap

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Shootout update
by Simon Marlow 31 Mar '10

31 Mar '10

The shootout (sorry, Computer Language Benchmarks Game) recently updated to GHC 6.12.1, and many of the results got worse. Isaac Gouy has added the +RTS -qg flag to partially fix it, but that turns off the parallel GC completely and we know that in most cases better results can be had by leaving it on. We really need to tune the flags for these benchmarks properly. http://shootout.alioth.debian.org/u64q/haskell.php It may be that we have to back off to +RTS -N3 in some cases to avoid the last-core problem (http://hackage.haskell.org/trac/ghc/ticket/3553) at least until 6.12.2. Any volunteers with a quad-core to take a look at these programs and optimise them for 6.12.1? Cheers, Simon

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Benchmarking and Garbage Collection
by Neil Brown 31 Mar '10

31 Mar '10

Hi, I'm looking at benchmarking several different concurrency libraries against each other. The benchmarks involve things like repeatedly sending values between two threads. I'm likely to use Criterion for the task. However, one thing I've found is that the libraries have noticeably different behaviour in terms of the amount of garbage created. Criterion has an option to perform GC between each benchmark, but I think that the benchmark is only fair if it takes into account the GC time for each system; it doesn't seem right for two systems to be counted as equal if the times to get the results are the same, but then one has to spend twice as long as the other in GC afterwards. Here's some options I've considered: * I could make a small change to Criterion to include the time for performing GC in each benchmark run, but I worry that running the GC so often is also misrepresentative (might 100 small GCs take a lot longer than one large GC of the same data?) -- it may also add a lot of overhead to quick benchmarks, but I can avoid that problem. * Alternatively, I could run the GC once at the end of all the runs, then apportion the cost equally to each of the benchmark times (so if 100 benchmarks require 0.7s of GC, add 0.007s to each time) -- but if GC is triggered somewhere in the middle of the runs, that upsets the strategy a little. * I guess a further alternative is to make each benchmark a whole program (and decently long), then just time the whole thing, rather than using Criterion. Has anyone run into these issues before, and can anyone offer an opinion on what the best option is? Thanks, Neil.

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Numeric.LinearProgramming - confusion in constructors for bounds
by Ozgur Akgun 31 Mar '10

31 Mar '10

Hi everyone and Alberto, Numeric.LinearProgramming[1] provides a very nice interface for solving LP optimisation problems, and the well-known simplex algorithm itself. I must say I quite liked the interface it provides, simple yet sufficient. But, to my understanding, there is a confusion in the constructor name (symbols actually) for constraints. In LP, one needs to write constraints in the form of ==, <=, or >= only. You *cannot *write a constraint using strict inequalities. The algorithm has nothing wrong, but I guess it would be better to have constructor symbols right. See [2] If this is a design choice, I think it should explicitly be stated. Regards, [1] http://hackage.haskell.org/package/hmatrix-glpk [2] http://hackage.haskell.org/packages/archive/hmatrix-glpk/0.1.0/doc/html/Num… -- Ozgur Akgun

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