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Kind polymorphism
by Martijn van Steenbergen 23 Nov '09

23 Nov '09

Hello, Are there currently any known problems that would hinder the implementation of kind polymorphism [1], e.g. unresolved inelegancies or technical limitations, or is it only a matter of finding the time to implement it? Thanks, Martijn. [1] http://hackage.haskell.org/trac/haskell-prime/wiki/KindInference

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Graph drawing library for Haskell
by Victor Mateus Oliveira 22 Nov '09

22 Nov '09

Hi, Anyone knows a good library for graph diagram drawing? Or a haskell binding for one? Something like jgraph. http://www.jgraph.com/jgraph.html []s' Victor -- GNU/Linux user #446397 - http://counter.li.org

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Existential type question
by Michael Snoyman 22 Nov '09

22 Nov '09

Hi all, I've come across some code I just can't figure out how to write appropriately. Below is a silly example that demonstrates what I'm trying to do. I don't really have the appropriate vocabulary to describe the issue, so I'll let the code speak for itself. In particular, I'm trying to understand what the correct type signatures for unwrapMyData and bin should be. Thanks, Michael --- {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} class Monad m => MonadFoo x m where foo :: x -> m a data MyData a = forall i. Integral i => MyLeft i | MyRight a instance Monad MyData where return = MyRight (MyLeft i) >>= _ = MyLeft i (MyRight x) >>= f = f x instance Integral i => MonadFoo i MyData where foo = MyLeft bar :: MonadFoo Int m => Int -> m String bar 0 = return "zero" bar i = foo i baz :: String -> MyData String baz "zero" = MyRight "Zero" baz _ = MyLeft (-1 :: Integer) --This works: unwrapMyData (MyLeft i) = foo (fromIntegral i :: Integer) unwrapMyData (MyLeft i) = foo i -- This is what I'd like to work unwrapMyData (MyRight a) = return a bin i = do a <- bar i b <- unwrapMyData $ baz a return $ b ++ "!!!" instance Show a => MonadFoo a IO where foo = fail . show -- I know, it's horrible... main = do res <- bin 0 putStrLn res

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What's wrong with code.haskell.org ?
by Andy Stewart 22 Nov '09

22 Nov '09

Hi all, I can't use `darcs get --partial http://code.haskell.org/gtk2hs/` to get source code, and can't push patch. What's wrong with code.haskell.org? Rest for weekend? :) -- Andy

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haskell code from hi
by Ozgur Akgun 22 Nov '09

22 Nov '09

Is there possibly a way of getting source code, given a *.hi file? Yes you're right I deleted all my *.hs files, while trying to remove *.hi ones!! Desperately, -- Ozgur Akgun

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ANN: GPipe-1.1.0 with greatly improved performance
by Tobias Bexelius 22 Nov '09

22 Nov '09

Hi, GPipe 1.1.0 is now available on Hackage. This update includes the following: * BIG performance increase: The previous shader cache keys grew exponential in size in relation to the GPipe program. This is now fixed with a completely new shader generator so the cache key sizes are linear relative to the program. In addition, the cache now uses patricia trees instead of an ordinary map, which will be a big performance win in programs with many shaders. In the simple example on http://www.haskell.org/haskellwiki/GPipe I got an performance increase of factor 2.7(!), and expect it to be even larger for more complex programs. * Other minor fixes: Fixed so min, max, abs and sign no longer works on Vertex Int and Fragment Int types, since its not supported in GLSL 1.20. Reexport of Vec-Boolean instances so you dont need to import that package on its own any more. Added IfB instances for the associated type Color. Cheers Tobias _________________________________________________________________ Nya Windows 7 gör allt lite enklare. Hitta en dator som passar dig! http://windows.microsoft.com/shop

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How to understand such a newtype ?
by zaxis 22 Nov '09

22 Nov '09

newtype X a = X (ReaderT XConf (StateT XState IO) a) #ifndef __HADDOCK__ deriving (Functor, Monad, MonadIO, MonadState XState, MonadReader XConf, Typeable) #endif In `X (ReaderT XConf (StateT XState IO) a)`, X is a type constructor, how to understand `(ReaderT XConf (StateT XState IO) a)` ? And why use `#ifndef __HADDOCK__` ? Sincerely! ----- fac n = foldr (*) 1 [1..n] -- View this message in context: http://old.nabble.com/How-to-understand-such-a-newtype---tp26462332p2646233… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell as an alternative to Java
by Philippos Apolinarius 21 Nov '09

21 Nov '09

I wonder whether the Haskell community tryed to reproduce the study Lisp as an alternative to Java, by Ron Garret / Erann Gat. However, since that study was reproduced in almost every other language (with a fair amount of cheating going on, I believe :-), I am sure that there is a Haskell version (without cheating, I am sure :-). Here is a paper about the original study: http://www.flownet.com/gat/papers/lisp-java.pdf Here is Norvig's solution to the original problem: http://www.norvig.com/java-lisp.html Could someone send me a link to a Haskell solution, with comments? I have seen a solution in Clean, but since it was a homework in the college where I study, I am quite sure that my fellow students have just translated Norvig's solution to Clean. Therefore, it would be great if one could send me a link to a Clean solution too. __________________________________________________________________ Be smarter than spam. See how smart SpamGuard is at giving junk email the boot with the All-new Yahoo! Mail. Click on Options in Mail and switch to New Mail today or register for free at http://mail.yahoo.ca

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Fwd: Error in building buster 1.51
by Лев Никитин 21 Nov '09

21 Nov '09

Hello. I try to install buster 1.51. It has been uploaded on hackage. During building there is an error. Same error can been seen on hackage (look at build failre: http://hackage.haskell.org/packages/archive/buster/2.51/logs/failure/ghc-6.… ). How to fix it? Thanks

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Fwd: [BostonHaskell] Next meeting: November 24th at MIT (32-G882)
by Ravi Nanavati 20 Nov '09

20 Nov '09

---------- Forwarded message ---------- From: Ravi Nanavati <ravi_n(a)alum.mit.edu> Date: Fri, Nov 20, 2009 at 4:00 PM Subject: Next meeting: November 24th at MIT (32-G882) To: bostonhaskell(a)googlegroups.com I'm pleased to announce the November meeting of the Boston Area Haskell Users' Group. Based on the available days remaining in November, the meeting has been scheduled for Tuesday, November 24th from 6:30pm to 8:30pm. Like recent meetings, 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). Based on the response to my previous message, I'm developing a QuickCheck-focused joint programming exercise. If anyone wants to help with that, I'd appreciate it (since I'm trying to pull this together at the last minute). My plan is to introduce QuickCheck and start with a couple of warm-up exercises before our traditional break. After the break I'd like to use QuickCheck to find a subtle bug or two in some interesting, nontrivial (but not too large or complicated) Haskell program. I've found some introductory material to use as a starting point, but I don't have the right sort of Haskell program handy. If anyone has an interesting Haskell program they can share that is a good fit for this exercise, please let me know (the sooner the better). Since the meeting is going to be focused on a programming exercise, I don't think we'll have room for any larger presentations (at least based on our experience at the September meeting), but I'm there will be room for lightning talks or other advertisements if anyone has an interest in doing that. The November attendance poll is at: http://doodle.com/hyv5a76ib6untwtp As always, 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, since I have talked my wife into baking some more goodies and bringing drinks again. Helping with BostonHaskell (besides volunteering to speak at future meetings): 1. Sponsorship of refreshments is still being eagerly solicited (especially as, for personal reasons, the Cupcake Fund is running low). 2. Please let me know if you're willing to arrive early (6pm) to stand by the door and let people into the 8th floor. I'm guessing 1 or 2 volunteers is enough here. 3. If someone is willing to edit the HaskellWiki page, post to reddit or otherwise publicize the meeting please just go ahead and do that (especially as I'm sending this out a bit later than intended). If you have any questions about the meeting please send them to them BostonHaskell mailing list: bostonhaskell(a)googlegroups.com or contact me directly. I look forward to seeing many Boston-area Haskellers at the November meeting! Thank you, - Ravi Nanavati

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