July 2009 - Haskell-Cafe

Re: [Haskell-cafe] Where can I get GHC for Solaris?
by John Ky 09 Jul '09

09 Jul '09

Hi Aycan, This is the version of make I am using: joky@sun05:~ $ make -v GNU Make 3.81 Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. This program built for sparc-sun-solaris2.9 joky@sun05:~ $ uname -a SunOS sun05 5.9 Generic_118558-30 sun4u sparc SUNW,Sun-Fire-280R Thanks, -John On Wed, Jul 8, 2009 at 4:48 PM, Aycan iRiCAN <aycan.irican(a)core.gen.tr>wrote: > Çar, 2009-07-08 tarihinde 09:55 +1000 saatinde, John Ky yazdı: > > Hi, > > > > I had a go with the binary dist, and got this error message on the > > make install: > > > > /home/a-m/joky/.tools/ghc-6.8.2/lib/ghc-6.8.2"' > > -DPKG_DATADIR='"/export/home/a-m/joky/.tools/ghc-6.8.2/share/ghc-6.8.2"' > package.conf.in \ > > | grep -v '^#pragma GCC' \ > > | sed -e 's/""//g' -e 's/:[ ]*,/: /g' \ > > > > | /export/home/a-m/joky/ghc-6.8.2/utils/ghc-pkg/ghc-pkg.bin > > --global-conf > /export/home/a-m/joky/.tools/ghc-6.8.2/lib/ghc-6.8.2/package.conf update - > --force > > ld.so.1: ghc-pkg.bin: fatal: libm.so.2: version `SUNW_1.2' not found > > (required by > > file /export/home/a-m/joky/ghc-6.8.2/utils/ghc-pkg/ghc-pkg.bin) > > ld.so.1: ghc-pkg.bin: fatal: libm.so.2: open failed: No such file or > > directory > > Killed > > make[1]: *** [install] Error 137 > > make[1]: Leaving directory `/export/home/a-m/joky/ghc-6.8.2/rts' > > make: *** [install] Error 2 > > Are you using gmake? > > -- > aycan > >

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Haskell Platform on Ubuntu
by Rafael Gustavo da Cunha Pereira Pinto 08 Jul '09

08 Jul '09

Is there anyone working on a Haskell Platform package for Ubuntu? GHC in Ubuntu is a pain! Regards Rafael Gustavo da Cunha Pereira Pinto

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Re: [Haskell] Haskell Hack Day, Edinburgh, 30 August 2009
by Johan Tibell 08 Jul '09

08 Jul '09

On Wed, Jul 8, 2009 at 12:12 PM, Eric Kow <kowey(a)darcs.net> wrote: > Dear Haskellers, > > I am pleased to report that we will be having a Haskell Hack Day in > Edinburgh, on Sunday 30 August (before the ICFP begins). The day will > be held at the ICFP conference venue, the Royal College of Physicians. > > The Hack Day will be free and open to all. > Come join us; it'll be a lot of fun! My flight arrives too late for actually taking part in the hackathon but I would be up for some beers after if anyone is interested. -- Johan

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ANN: texmath 0.1.0.1 - conversion of LaTeX math to MathML
by John MacFarlane 08 Jul '09

08 Jul '09

I'm pleased to announce an early release of texmath, a Haskell library for converting LaTeX math formulas to MathML. Hackage: http://hackage.haskell.org/package/texmath-0.1.0.1 Github: http://github.com/jgm/texmath/tree/master The package includes a standalone test program, testTeXMathML, and a CGI script, texmath-cgi, that can be used in web apps. This script is used in the demos at http://johnmacfarlane.net/texmath.xhtml http://johnmacfarlane.net/texmath.html texmath supports most of basic LaTeX and AMS extensions, but I'm sure some things have been left out, so let me know if you try a formula that should work but doesn't. John

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simple state monad exercises? (besides labeling trees)
by Thomas Hartman 07 Jul '09

07 Jul '09

Can someone give some simple common scenarios where the state monad is useful, besides labeling trees? References to puzzles like those in project Euler or similar would be nice. Thanks!

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lazy data structure for best-first search
by Martin Hofmann 07 Jul '09

07 Jul '09

I am looking for a good (preferably lazy) way to implement some kind of best-first search. The problem is, the expansion of the 'best' node in the search space forces other 'inferior' nodes to expand too. So my function expand :: Node -> ([Node],(Node -> [Node])) does not only return some successor nodes, but also a function to expand other Nodes with certain characteristics. So in fact, after one expansion, I need to fold over my complete search space, maybe updating other nodes and recompute the value of the cost function for the affected nodes. At the moment I am using StateT monad transformers, and retrieving the affected Nodes from a map (to avoid going through whole space), but this is not very elegant and I doubt whether it is efficient, too. I have already read through Spivey's paper "Algebras for combinatorial search". Unfortunately, he only proposes the use of heuristics and best-first search in combination with his framework for future work. Does anybody now some further papers on this topic? Thanks a lot in advance, Martin

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Adaptive transactions
by Ryan Ingram 07 Jul '09

07 Jul '09

It seems to me that the Adaptive framework[1][2] is well-suited to STM transactions. Consider this snippet: > expensive_transaction :: STM Int -- does a bunch of work > > example :: TVar Int -> STM Int > example t = (+) <$> readTVar t <*> expensive_transaction If the TVar passed to example is rapidly changing (perhaps it represents the current time), then this transaction will starve; it never gets a chance to complete, even if the values used by expensive_transaction aren't changing at all, we still re-evaluate the entire action each time we "retry" this transaction. But STM has a wonderful property: what we need to commit a transaction is just the result value and a transaction log; both of these depend only on the values of TVars read by that transaction. So, if "expensive_transaction" doesn't refer to the TVar "t", then even if "t" is rapidly changing, the transaction log generated by "expensive_transaction" must not change, and we can just re-generate the part of the transaction log for "readTVar t" and recompute the (+). This gets even better when considering big processes that are blocked by an explicit "retry"; if some change in input is just going to cause the transaction to retry again (and go back to sleep), we'd like that to happen as quickly as possible. Has anyone looked down this path? It seems quite promising to me. -- ryan [1] http://hackage.haskell.org/package/Adaptive [2] Acar et al, Adaptive Functional Programming, POPL 2002 http://citeseer.ist.psu.edu/old/752721.html

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Re: what about moving the record system to an addendum?
by John Meacham 07 Jul '09

07 Jul '09

Well, without a replacement, it seems odd to remove it. Also, Haskell currently doesn't _have_ a record syntax (I think it was always a misnomer to call it that) it has 'labeled fields'. None of the proposed record syntaxes fit the same niche as labeled fields so I don't see them going away even if a record syntax is added to haskell in the future. I would like to see the simple modifications to the record syntax listed on this page though http://hackage.haskell.org/trac/haskell-prime/wiki/ExistingRecords and a reworking of the standard to not refer to the current system as a 'record syntax' but rather a 'labeled fields' syntax. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/

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[Haskell] ANNOUNCE: ChristmasTree 0.1 (excuses for second attempt)
by S.Doaitse Swierstra 07 Jul '09

07 Jul '09

We are pleased to announce the availability of the package "ChristmasTree", which contains the code associated with our paper at the last Haskell symposium: @inproceedings{1411296, author = {Marcos Viera and S. Doaitse Swierstra and Eelco Lempsink}, title = {Haskell, do you read me?: constructing and composing efficient top-down parsers at runtime}, booktitle = {Haskell '08: Proceedings of the first ACM SIGPLAN symposium on Haskell}, year = {2008}, isbn = {978-1-60558-064-7}, pages = {63--74}, location = {Victoria, BC, Canada}, doi = {http://doi.acm.org/10.1145/1411286.1411296}, publisher = {ACM}, address = {New York, NY, USA}, } The name of the package stands for: "Changing Haskell's Read Implementation Such That by Manipulating Abstract Syntax Trees it Reads Expressions Efficiently" which, given the time of year, seems appropriate. Feel free to download and unpack this "present" at what for the Dutch is called "Sinterklaasavond" (http://en.wikipedia.org/wiki/Sinterklaas) Arthur Baars Marcos Viera Eelco Lempsink Doaitse Swierstra PS: the package uses our library supporting transformation of typed abstract syntax, which we placed in a separate package TTTAS

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Implementing Las Vegas algorithms in Haskell
by Matthias Görgens 07 Jul '09

07 Jul '09

A Las Vegas algorithm, like randomized quicksort, uses a source of randomness to make certain decisions. However its output is unaffected by the randomness. So a function > f :: RandomGen g => g -> a -> b implementing a Las-Vegas-Algorithm 'looks' like a pure function, ignoring its first argument and depending solely on its second argument. What is an idiomatic way to implement such a function? I believe, Monads are too linear and strict.

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