July 2009 - Haskell-Cafe

Optimizing Compiler for the ICFP 09 contest's VM
by Matthias Görgens 07 Jul '09

07 Jul '09

The byte code for the virtual machine of this years ICFP specified a language with single assignment per simulation step. Interestingly most memory locations get overwritten each simulation step before they are read. That means, those locations don't have to be remember between steps. Also locations that never get overwritten (e.g. location associated with Noops), are constant. Thus the variables state of the simulation is orders of magnitude smaller than the naive 2^16 * 32 bit + 1 bit. I wrote a small program that analyses the dataflow of a byte code program (and initial memory setup) for the VM. After analyzing my program emits Haskell code to run the given byte code. If anyboby is interested, I can document my program and put it online somewhere. I also made pretty graphs of the dataflow with graphviz.

3 3

ANN: bloxorz clone
by Patai Gergely 07 Jul '09

07 Jul '09

Hello all, This post is not about my own creation, it's just a little fun program written by a student of mine. You can install the bloxorz package to try it out, and read more about its background on my blog: http://just-bottom.blogspot.com/2009/07/playing-and-learning.html Gergely -- http://www.fastmail.fm - Access all of your messages and folders wherever you are

3 6

DHUG: meeting tomorrow (July 7th) in Utrecht
by Chris Eidhof 07 Jul '09

07 Jul '09

Hi everyone, The Dutch HUG [1] will meet again tomorrow. This time we'll meet in Utrecht again, at the Stairway To Heaven. The meeting will start at 19h. The venue is a sometimes a bit noisy, but there's beer and nice big tables. If you want to hear everything about the Dutch HUG straight from the horse's mouth: make sure you're at the meetings and subscribed to the mailing list [2]. We already have more than 40 members after two meetings! See you tomorrow! -chris [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug

1 0

How to read safely?
by Magicloud Magiclouds 07 Jul '09

07 Jul '09

Hi, Read often throws runtime errors, which breaks the robust of the problem. How to deal with it? Without lost too much proformance (so reads is a no). At least, if its error could be catched, that'd be better. -- 竹密岂妨流水过山高哪阻野云飞

8 9

Could FFI support pass-by-value of structs?
by Maurício 07 Jul '09

07 Jul '09

It's not usual, but it is allowed to have values of structs passed between functions directly instead of using pointers: /*****/ struct ex { int x; int y; int z; }; ex example_functions (ex p) { (...) } /*****/ Would it be possible to allow that in Haskell FFI by, say, allowing any instance of Storable to be used in a 'foreign' declaration? Like: -- data Ex = (...) instance Storable Ex where sizeOf _ = ... alignment = sizeOf (...) foreign import ccall "example_functions" exampleFunction :: Ex -> IO Ex -- Thanks, Maurício

6 21

Where can I get GHC for Solaris?
by John Ky 07 Jul '09

07 Jul '09

Hi, Anyone know where I can get the GHC compiler and libraries for Solaris?: SunOS sun05 5.9 Generic_118558-30 sun4u sparc SUNW,Sun-Fire-280R I tried to compile GHC myself and got the following error: $ ./configure --enable-hc-boot checking build system type... sparc-sun-solaris2.9 checking host system type... sparc-sun-solaris2.9 checking target system type... sparc-sun-solaris2.9 Canonicalised to: sparc-sun-solaris2 checking for ghc... no checking for nhc... no checking for nhc98... no checking for hbc... no checking for ld... /usr/ccs/bin/ld checking for path to top of build tree... ./configure: -v0: command not found ./configure: utils/pwd/pwd: No such file or directory configure: error: cannot determine current directory Thanks -John

2 1

BostonHaskell: Next meeting - July 16th at MIT CSAIL Reading Room (32-G882)
by Ravi Nanavati 06 Jul '09

06 Jul '09

I'm pleased to announce the July meeting of the Boston Area Haskell Users' Group. Based on the feedback from the June meeting and the constraints of our speakers, the July meeting has been scheduled for Thursday, July 16th from 6:30pm - 8:30pm. Like the June meeting, it will be held in the MIT CSAIL Reading Room (32-G882, i.e. a room on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). We have the following two talks scheduled: "An Introduction to GHC Hacking" by Alec Heller "Haskell on the iPhone" by Ryan Trinkle (a more in-depth discussion than his on-the-spot Lightning Talk last month). As always, there will be a break between the talks for discussion and mingling. We have openings for Lightning Talks (5-minute talk, 2-minute Q&A) during that period. We are also open to short, relevant advertisements (like my Hac Phi plug last month). If you're interested in giving a Lightning Talk, have an advertisement you'd like to share or are interested in speaking at a future meeting, please contact me at ravi_n(a)alum.mit.edu. I'd also appreciate it if people who can (and can't) attend this meeting fill out the attendance poll here: http://www.learnmyself.com/poll10828x74C54f13 I apologize for the URL, but Google Groups seems to ban JavaScript and I didn't want to delay this announcement while I tried to come up with something more convenient. Responding to this poll will help with two things: 1. Getting an idea of what fraction of the Boston-area Haskell community can and can't attend this meeting (to help with future scheduling). 2. Giving me an estimated count of attendees, should I manage to secure a sponsor for refreshments. Sponsorship of or other assistance with refreshments is still being eagerly solicited. If you have any questions about the meeting please send them to the BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the July meeting! Thank you, - Ravi Nanavati

1 0

Catering for similar operations with and without state
by Phil 06 Jul '09

06 Jul '09

Hi, I'm trying to think around a problem which is causing me some difficulty in Haskell. I'm representing a stateful computation using a State Transform - which works fine. Problem is in order to add flexibility to my program I want to performs the same operation using different techniques - most of which require no state. My program at the moment is a stack of state monads/transforms. I have a random number generator as a state monad (seed=state), feeding a Box Muller (normal) generator implemented as a state transform (state is 'maybe' normal, so it only spits out 1 normal at a time), which in turn feeds another state machine. This all works fine, but I want to add flexibility so that I can chop and change the Box Muller algorithm with any number of other normal generators. Problem is most of them do not need to carry around state at all. This leaves me with a messy solution of implementing lots of state monads that don't actually have a state, if I want to maintain the current paradigm. This strikes me as really messy - so I'm hoping someone can point me in the direction of a more sensible approach? Currently I have my Box Muller implemented as below - this works: class NormalClass myType where generateNormal :: myType Double type BoxMullerStateT = StateT (Maybe Double) type BoxMullerRandomStateStack = BoxMullerStateT MyRngState instance NormalClass BoxMullerRandomStateStack where generateNormal = StateT $ \s -> case s of Just d -> return (d,Nothing) Nothing -> do qrnBaseList <- nextRand let (norm1,norm2) = boxMuller (head qrnBaseList) (head $ tail qrnBaseList) return (norm1,Just norm2) But say I have another instance of my NormalClass that doesn't need to be stateful, that is generateNormal() is a pure function. How can I represent this without breaking my whole stack? I've pretty much backed myself into a corner here as my main() code expects to evalStateT on my NormalClass: main = do let sumOfPayOffs = evalState normalState (1,[3,5]) -- (ranq1Init 981110) where mcState = execStateT (do replicateM_ iterations mc) 0 normalState = evalStateT mcState Nothing If it wasn't for this I was thinking about implementing the IdentityT transformer to provide a more elegant pass-through. I've never tried designing my own Monad from scratch but this crossed my mind as another possibillity - i.e. a Monad that either has a state of maybe double, or has no state at all? I may be talking rubbish here of course :-) I'm pretty daunted by where to even start - but I want to improve this as the quick and dirty solution of implementing a load of state monads with no state just to cater for the above method strikes me as very ugly, and as I can easily see ways of doing this in C or C++, I figure there must be a better approach in Haskell - I'm just thinking in the right way! Any advice or hints would be great, Cheers, Phil.

3 2

LINQ, SQL and hs-dotnet
by Günther Schmidt 06 Jul '09

06 Jul '09

Hi all, is there anyone who has already tried using LINQ2SQL with hs-dotnet and would care to share the experience? I'm trying to figure out what exactly it would take to access an SQL database via LINQ / hs-dotnet. Ie. whether or not it's necessary to create Entity classes, or if one can just use LINQ to generate SQL. Günther

1 0

Haskell Platform 2009.2.0.1 and GLUT32.DLL on Windows: which version?
by Peter Verswyvelen 06 Jul '09

06 Jul '09

I know GLUT32.DLL is not bundled with the Haskell Platform installer, but which GLUT32.DLL should I use? Every DLL I tried (even building FreeGLUT myself<http://netsuperbrain.com/blog/posts/freeglut-windows-hopengl-hglut/#more-136>) gives the error: *"The procedure entry point glutAddMenuEntry could not be located in the dynamic library glut32.dll"* Any hints as to which glut32 version to use would be highly appreciated. Thanks, Peter

2 2