November 2009 - Haskell-Cafe

Re: ANNOUNCE: deepseq-1.0.0.0
by Simon Marlow 23 Nov '09

23 Nov '09

On 19/11/2009 11:52, Sittampalam, Ganesh wrote: > Yitzchak Gale wrote: >> Simon Marlow wrote: >>> So then what shall we call the a -> () version? >>> One possibility is to go back to calling it rnf. >> >> In light of apfelmus' comment, I vote for rnf. >> >> And in that case, how about the analogous alternative for seq itself: >> >> hnf :: a -> () > > I think it would be whnf since it doesn't evaluate under lambdas. > > I also vote for rnf, because we should have a good reason for changing > names of things. Various people would prefer rnf. Ok, unless there are any further objections, I'll change the names back to class NFData a where rnf :: a -> () and also add deepseq :: a -> b -> b but I'll leave the module name as Control.DeepSeq. Cheers, Simon

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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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