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Fwd: job position
by Mario Blažević 02 Sep '11

02 Sep '11

For anybody interested in programming languages or markup languages, there is an open job position for a junior developer at Stilo (http://www.stilo.com/) Haskell is currently used only for prototyping, but there are plans to begin some major development in Haskell within a year. The job ad is attached.

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Regular Expression Parsing via derivatives
by Alex Clemmer 02 Sep '11

02 Sep '11

Hi Haskell people, I've been snooping through various mailing lists and the current Haskell implementation of regular expressions and I was wondering if there has been a discussion about implementing regex parsing with derivatives. If so, I haven't seen it. If not, I'd like to have a discussion about it -- if for no other reason than to decide whether I should implement it as a library, or (to attempt to implement it) as a core feature. For those of you who don't know, recent work by Might and Darais<http://arxiv.org/abs/1010.5023>indicates that parsing CFGs can be done better ( *i.e.*, significantly faster) than more "traditional" approaches<http://swtch.com/%7Ersc/regexp/regexp1.html>. Might's presenting at ICFP later in September about it. I guess the first thing I should ask is, which mailing list is actually the right place to field this inquiry. I considered dropping it in the main haskell list, but wasn't sure how people would respond. -- Alex

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Finger Tree without using Monoid
by Xinyu LIU 02 Sep '11

02 Sep '11

Hi, I was trying to implement MTF (move-to-front) algorithm, However, neither Array nor List satisfied all aspects. Array: Although the random access is O(1), However, move an element to front takes O(N) in average; List: Although move to front is O(1), However, random access takes O(N) in average; I dig out the paper [1] and find the Finger Tree solution. There is already good Finger Tree implementation in Haskell as Data.Sequence [2] based on [3]. I wrote a simple version based on the original paper, but avoid using Monoid when augment (or cache) the size of the tree. The idea is to wrap every element as a leaf of node. This idea is similar to the Chris Okasaki's binary random access list [4]. As one test case, I tested move to front with Finger Tree. Here is the code (sorry for a bit long): >>> module FingerTree where import Test.QuickCheck data Node a = Br Int [a] deriving (Show) -- size, branches data Tree a = Empty | Lf a | Tr Int [a] (Tree (Node a)) [a] -- size, front, middle, rear deriving (Show) type FList a = Tree (Node a) -- Auxiliary functions for calculate size of node and tree size :: Node a -> Int size (Br s _) = s sizeL :: [Node a] -> Int sizeL = sum .(map size) sizeT :: FList a -> Int sizeT Empty = 0 sizeT (Lf a) = size a sizeT (Tr s _ _ _) = s -- Auxiliary functions for building and unboxing node(s) wrap :: a -> Node a wrap x = Br 1 [x] unwrap :: Node a -> a unwrap (Br 1 [x]) = x wraps :: [Node a] -> Node (Node a) wraps xs = Br (sizeL xs) xs unwraps :: Node a -> [a] unwraps (Br _ xs) = xs -- Helper function for building tree tree :: [Node a] -> FList (Node a) -> [Node a] -> FList a tree f Empty [] = foldr cons' Empty f tree [] Empty r = foldr cons' Empty r tree [] m r = let (f, m') = uncons' m in tree (unwraps f) m' r tree f m [] = let (m', r) = unsnoc' m in tree f m' (unwraps r) tree f m r = Tr (sizeL f + sizeT m + sizeL r) f m r -- Operations at the front of the sequence cons :: a -> FList a -> FList a cons a t = cons' (wrap a) t cons' :: (Node a) -> FList a -> FList a cons' a Empty = Lf a cons' a (Lf b) = tree [a] Empty [b] cons' a (Tr _ [b, c, d, e] m r) = tree [a, b] (cons' (wraps [c, d, e]) m) r cons' a (Tr _ f m r) = tree (a:f) m r uncons :: FList a -> (a, FList a) uncons ts = let (t, ts') = uncons' ts in (unwrap t, ts') uncons' :: FList a -> ((Node a), FList a) uncons' (Lf a) = (a, Empty) uncons' (Tr _ [a] Empty [b]) = (a, Lf b) uncons' (Tr _ [a] Empty (r:rs)) = (a, tree [r] Empty rs) uncons' (Tr _ [a] m r) = (a, tree (unwraps f) m' r) where (f, m') = uncons' m uncons' (Tr _ (a:f) m r) = (a, tree f m r) head' :: FList a -> a head' = fst . uncons tail' :: FList a -> FList a tail' = snd . uncons -- Operations at the rear of the sequence snoc :: FList a -> a -> FList a snoc t a = snoc' t (wrap a) snoc' :: FList a -> Node a -> FList a snoc' Empty a = Lf a snoc' (Lf a) b = tree [a] Empty [b] snoc' (Tr _ f m [a, b, c, d]) e = tree f (snoc' m (wraps [a, b, c])) [d, e] snoc' (Tr _ f m r) a = tree f m (r++[a]) unsnoc :: FList a -> (FList a, a) unsnoc ts = let (ts', t) = unsnoc' ts in (ts', unwrap t) unsnoc' :: FList a -> (FList a, (Node a)) unsnoc' (Lf a) = (Empty, a) unsnoc' (Tr _ [a] Empty [b]) = (Lf a, b) unsnoc' (Tr _ f@(_:_) Empty [a]) = (tree (init f) Empty [last f], a) unsnoc' (Tr _ f m [a]) = (tree f m' (unwraps r), a) where (m', r) = unsnoc' m unsnoc' (Tr _ f m r) = (tree f m (init r), (last r)) last' :: FList a -> a last' = snd . unsnoc init' :: FList a -> FList a init' = fst . unsnoc -- Concatenation concat' :: FList a -> FList a -> FList a concat' t1 t2 = merge t1 [] t2 merge :: FList a -> [Node a] -> FList a -> FList a merge Empty ts t2 = foldr cons' t2 ts merge t1 ts Empty = foldl snoc' t1 ts merge (Lf a) ts t2 = merge Empty (a:ts) t2 merge t1 ts (Lf a) = merge t1 (ts++[a]) Empty merge (Tr s1 f1 m1 r1) ts (Tr s2 f2 m2 r2) = Tr (s1 + s2 + (sizeL ts)) f1 (merge m1 (nodes (r1 ++ ts ++ f2)) m2) r2 nodes :: [Node a] -> [Node (Node a)] nodes [a, b] = [wraps [a, b]] nodes [a, b, c] = [wraps [a, b, c]] nodes [a, b, c, d] = [wraps [a, b], wraps [c, d]] nodes (a:b:c:xs) = (wraps [a, b, c]):nodes xs -- Splitting splitAt' :: Int -> FList a -> (FList a, Node a, FList a) splitAt' _ (Lf x) = (Empty, x, Empty) splitAt' i (Tr _ f m r) | i < szf = let (xs, y, ys) = splitNodesAt i f in ((foldr cons' Empty xs), y, tree ys m r) | i < szf + szm = let (m1, t, m2) = splitAt' (i-szf) m (xs, y, ys) = splitNodesAt (i-szf - sizeT m1) (unwraps t) in (tree f m1 xs, y, tree ys m2 r) | otherwise = let (xs, y, ys) = splitNodesAt (i-szf -szm) r in (tree f m xs, y, foldr cons' Empty ys) where szf = sizeL f szm = sizeT m splitNodesAt :: Int -> [Node a] -> ([Node a], Node a, [Node a]) splitNodesAt 0 [x] = ([], x, []) splitNodesAt i (x:xs) | i < size x = ([], x, xs) | otherwise = let (xs', y, ys) = splitNodesAt (i-size x) xs in (x:xs', y, ys) -- Random access operations getAt :: FList a -> Int -> a getAt t i = unwrap x where (_, x, _) = splitAt' i t extractAt :: FList a -> Int -> (a, FList a) extractAt t i = let (l, x, r) = splitAt' i t in (unwrap x, concat' l r) setAt :: FList a -> Int -> a -> FList a setAt t i x = let (l, _, r) = splitAt' i t in concat' l (cons x r) -- move the i-th element to front moveToFront :: FList a -> Int -> FList a moveToFront t i = let (a, t') = extractAt t i in cons a t' -- auxiliary functions fromList :: [a] -> FList a fromList = foldr cons Empty toList :: FList a -> [a] toList Empty = [] toList t = (head' t):(toList $ tail' t) -- testing prop_cons :: [Int] -> Bool prop_cons xs = xs == (toList $ fromList xs) prop_snoc :: [Int] -> Bool prop_snoc xs = xs == (toList' $ foldl snoc Empty xs) where toList' Empty = [] toList' t = (toList' $ init' t)++[last' t] prop_concat :: [Int]->[Int]->Bool prop_concat xs ys = (xs ++ ys) == (toList $ concat' (fromList xs) (fromList ys)) prop_lookup :: [Int] -> Int -> Property prop_lookup xs i = (0 <=i && i < length xs) ==> (getAt (fromList xs) i) == (xs !! i) prop_update :: [Int] -> Int -> Int -> Property prop_update xs i y = (0 <=i && i < length xs) ==> toList (setAt (fromList xs) i y) == xs' where xs' = as ++ [y] ++ bs (as, (_:bs)) = splitAt i xs prop_mtf :: [Int] -> Int -> Property prop_mtf xs i = (0 <=i && i < length xs) ==> (toList $ moveToFront (fromList xs) i) == mtf where mtf = b : as ++ bs (as, (b:bs)) = splitAt i xs <<< It can be found at: https://github.com/liuxinyu95/AlgoXY/blob/algoxy/datastruct/elementary/arra… [Reference] [1]. Jon Bentley, Daniel Sleator, Robert Tarjan, Victor Wei. "A locally adaptive data compression scheme." Communication of the ACM.1986. [2]. http://hackage.haskell.org/packages/archive/fingertree/0.0/doc/html/Data-Fi… [3]. Ralf Hinze and Ross Paterson, "Finger trees: a simple general-purpose data structure", *Journal of Functional Programming* 16:2 (2006) pp 197-217. http://www.soi.city.ac.uk/~ross/papers/FingerTree.html [4]. Purely Functional Random-Access Lists by Chris Okasaki. Functional Programming Languages and Computer Architecutre, June 1995, pages 86-95. -- Larry, LIU Xinyu https://sites.google.com/site/algoxy/ https://github.com/liuxinyu95/AlgoXY

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Is it a bug in haskell-src-meta package?
by bob zhang 01 Sep '11

01 Sep '11

Hi, all parseExp "(,) 3 4 " => Right (AppE (AppE (ConE GHC.Unit.(,)) (LitE (IntegerL 3))) (LitE (IntegerL 4))) where's GHC.Unit.(,) ? Many thanks best, bob

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Pointed, but not Applicative
by Sönke Hahn 01 Sep '11

01 Sep '11

Hi! I was reading through the Typeclassopedia ([1]) and I was wondering which type could be an instance of Pointed, but not of Applicative. But I can't think of one. Any ideas? Sönke [1] http://www.haskell.org/haskellwiki/Typeclassopedia

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Data structure
by yrazes 01 Sep '11

01 Sep '11

Hi guys, I want to compare data structure between Haskell, Java, Lisp and C. I am wondering if I could compare list comprehention in haskell with the vector class in Java, macros in common lisp and dynamic arrays in C. Thanks, Julita

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Haskell Weekly News: Issue 197
by Daniel Santa Cruz 01 Sep '11

01 Sep '11

Welcome to issue 197 the HWN, a newsletter covering developments in the Haskell community. This release covers the week of August 21 to 27, 2011. [1] http://goo.gl/8hDku Announcements Liyang HU announced HakkaTaikai, a Haskell hackathon in Tokyo, on Sunday September 25th, 2011. [2] http://goo.gl/tJ4F4 Qiuchi Jian wondered if anyone would be interested in joining him in translating the 2010 Haskell Report into Chinese. [3] http://goo.gl/QDdeF Johan Tibell announced the results of this year's "State of Haskell" survey. [4] http://goo.gl/26Evg New and Updated Projects * network-address (New - Sebastian Nowicki) Provides data structures for IP addresses as well as subnetworks. [5] http://goo.gl/LTuUK * shelltestrunner (Update - Simon Michael) Tests command-line programs or arbitrary shell commands. [6] http://goo.gl/uKHMo * netwire (Update - Ertugrul Soeylemez) An arrowized functional reactive programming library written with networking applications in mind. [7] http://goo.gl/yM0hy * instinct (New - Ertugrul Soeylemez) Library for neural networks. [8] http://goo.gl/yM0hy Quotes of the Week * elliott: i'm here to prove theorems and compile code and I'm all out of code * shachaf: To deepSeq is a fundamental right * djahandarie: I wonder if De Bruijn was any good at remembering names. * JaffaCake: In the beginning there were 8 registers, and That Was Enough For Everyone. * frezik: "The compiler accepted it, why can't you?" * Cale: the units of the monoids in the algebras for the monoid monad * _Ray_: fucking hell, math and cs need to stop having awesome interesting things. it's ruining my life. * accel: next time I'll read a few research papers before I start trolling hakell * ddarius: isJust :: Maybe a -> Bool; isJust = unsafeCoerce Top Reddit Stories * Interested in a 2nd edition of "Real World Haskell"? Domain: self.haskell, Score: 130, Comments: 33 On Reddit: [9] http://goo.gl/fNS6P Original: [10] http://goo.gl/fNS6P * GHC on ARM: Merged into GHC HEAD Domain: ghcarm.wordpress.com, Score: 78, Comments: 7 On Reddit: [11] http://goo.gl/BvFvX Original: [12] http://goo.gl/ZKDYx * Why Haskell is Kinda Cool Domain: amtal.github.com, Score: 56, Comments: 27 On Reddit: [13] http://goo.gl/9ealD Original: [14] http://goo.gl/0AJIn * Haskell for Kids: Week 2! Domain: cdsmith.wordpress.com, Score: 55, Comments: 20 On Reddit: [15] http://goo.gl/0Qm5z Original: [16] http://goo.gl/DzdUy * Results from the State of Haskell, 2011 Survey Domain: blog.johantibell.com, Score: 54, Comments: 18 On Reddit: [17] http://goo.gl/BAQye Original: [18] http://goo.gl/l6sc1 * PyPy: We need Software Transactional Memory Domain: morepypy.blogspot.com, Score: 49, Comments: 2 On Reddit: [19] http://goo.gl/6dPjT Original: [20] http://goo.gl/kNCma * mmmodularity! - A modular package language for Haskell Domain: skilpat.tumblr.com, Score: 48, Comments: 8 On Reddit: [21] http://goo.gl/6dfSf Original: [22] http://goo.gl/os9IJ * A Tutorial Introduction to the Lambda Calculus Domain: utdallas.edu, Score: 34, Comments: 9 On Reddit: [23] http://goo.gl/OtPrs Original: [24] http://goo.gl/zTIx4 * Functional representation of Rubik's cube Domain: pnyf.inf.elte.hu, Score: 30, Comments: 3 On Reddit: [25] http://goo.gl/TMOnc Original: [26] http://goo.gl/EoYbu * monad-control, for more flexible transformers Domain: yesodweb.com, Score: 27, Comments: 14 On Reddit: [27] http://goo.gl/XF6GZ Original: [28] http://goo.gl/ijd6V * A different haskell emacs mode (work in progress) Domain: chrisdone.com, Score: 26, Comments: 5 On Reddit: [29] http://goo.gl/lfmxF Original: [30] http://goo.gl/7qvho Top StackOverflow Questions * Haskell: How does non-strict and lazy differ? votes: 25, answers: 5 Read on SO: [31] http://goo.gl/2KJVY * forall in Scala votes: 18, answers: 5 Read on SO: [32] http://goo.gl/ejOwF * What is the name of this monad-like functional programming pattern? votes: 16, answers: 1 Read on SO: [33] http://goo.gl/Rv1BC * Is (reverse . f . reverse) efficient? votes: 11, answers: 4 Read on SO: [34] http://goo.gl/U7qLu * Haskell Space Overflow votes: 8, answers: 4 Read on SO: [35] http://goo.gl/5uBY2 * How to write recursive lambda expression in Haskell? votes: 8, answers: 2 Read on SO: [36] http://goo.gl/TokK2 * Is the random number generator in Haskell thread-safe? votes: 8, answers: 4 Read on SO: [37] http://goo.gl/ERVpl * How can I create a tuple where each of the members are compared by an expression? votes: 7, answers: 5 Read on SO: [38] http://goo.gl/BiUpC * Haskell cartesian product of infinite lists votes: 7, answers: 4 Read on SO: [39] http://goo.gl/DC9M5 * How to implement a generic hierarchy of structures with injected functionality votes: 7, answers: 6 Read on SO: [40] http://goo.gl/IoMT6 About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18899 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91853 4. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18894 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18893 6. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18900 7. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91845 8. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/91845 9. http://www.reddit.com/r/haskell/comments/jtdrz/interested_in_a_2nd_edition_… 10. http://www.reddit.com/r/haskell/comments/jtdrz/interested_in_a_2nd_edition_… 11. http://ghcarm.wordpress.com/2011/08/27/current-status-merged-into-ghc-head/ 12. http://www.reddit.com/r/haskell/comments/jwgxj/ghc_on_arm_merged_into_ghc_h… 13. http://amtal.github.com/2011/08/25/why-haskell-is-kinda-cool.html 14. http://www.reddit.com/r/haskell/comments/juemg/why_haskell_is_kinda_cool/ 15. http://cdsmith.wordpress.com/2011/08/23/haskell-for-kids-week-2/ 16. http://www.reddit.com/r/haskell/comments/js4kd/haskell_for_kids_week_2/ 17. http://blog.johantibell.com/2011/08/results-from-state-of-haskell-2011.html 18. http://www.reddit.com/r/haskell/comments/jqfey/results_from_the_state_of_ha… 19. http://morepypy.blogspot.com/2011/08/we-need-software-transactional-memory.… 20. http://www.reddit.com/r/haskell/comments/jrprb/pypy_we_need_software_transa… 21. http://skilpat.tumblr.com/post/9411500320/a-modular-package-language-for-ha… 22. http://www.reddit.com/r/haskell/comments/jvlrw/mmmodularity_a_modular_packa… 23. http://www.utdallas.edu/~gupta/courses/apl/lambda.pdf 24. http://www.reddit.com/r/haskell/comments/jt0m1/a_tutorial_introduction_to_t… 25. http://pnyf.inf.elte.hu:8000/Rubik_en.xml 26. http://www.reddit.com/r/haskell/comments/jwfz2/functional_representation_of… 27. http://www.yesodweb.com/blog/2011/08/monad-control 28. http://www.reddit.com/r/haskell/comments/jtuk9/monadcontrol_for_more_flexib… 29. http://chrisdone.com/posts/2011-08-21-haskell-emacs.html 30. http://www.reddit.com/r/haskell/comments/js3sm/a_different_haskell_emacs_mo… 31. http://stackoverflow.com/questions/7140978/haskell-how-does-non-strict-and-… 32. http://stackoverflow.com/questions/7213676/forall-in-scala 33. http://stackoverflow.com/questions/7135540/what-is-the-name-of-this-monad-l… 34. http://stackoverflow.com/questions/7152183/is-reverse-f-reverse-efficient 35. http://stackoverflow.com/questions/7140732/haskell-space-overflow 36. http://stackoverflow.com/questions/7141229/how-to-write-recursive-lambda-ex… 37. http://stackoverflow.com/questions/7153255/is-the-random-number-generator-i… 38. http://stackoverflow.com/questions/7136921/how-can-i-create-a-tuple-where-e… 39. http://stackoverflow.com/questions/7141287/haskell-cartesian-product-of-inf… 40. http://stackoverflow.com/questions/7157841/how-to-implement-a-generic-hiera…

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 31 Aug '11

31 Aug '11

You also don't need mutual recursion for this explicit recursion since I imagine it would use up more stack space. -- Doing the one dimensional case. f011 :: [Int] -> Int f011 (t:u:v:xs) = f011helper t u v xs f011helper :: Int -> Int -> Int -> [Int] -> Int f011helper t u v (w:ws) | ws == [] = t*u*v*w | otherwise = max (t*u*v*w) (f011helper u v w ws) -- Note: f011helper does not call f011. On Mon, Aug 29, 2011 at 9:40 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > Got it. > > f :: [Int] -> Int > f (t:u:v:xs) = helper t u v xs > > helper :: Int -> Int -> Int -> [Int] -> Int > helper t u v (w:ws) > | ws == [] = t*u*v*w > | otherwise = max (t*u*v*w) (f (u:v:w:ws)) > > I tend to overlook mutual recursion in my toolbox. Good going! :) > > Thanks for the enlightenment. > > On Sun, Aug 28, 2011 at 4:54 PM, KC <kc1956(a)gmail.com> wrote: >> Try something like the following: >> >> -- Project Euler 11 >> >> -- In the 20×20 grid below, four numbers along a diagonal line have >> been marked in red. >> >> -- <snip> >> >> -- The product of these numbers is 26 × 63 × 78 × 14 = 1788696. >> >> -- What is the greatest product of four adjacent numbers in any >> direction (up, down, left, right, or diagonally) in the 20×20 grid? >> >> >> import Data.List >> >> -- Doing the one dimensional case. >> f011 :: [Int] -> Int >> f011 (t:u:v:xs) = f011helper t u v xs >> >> f011helper :: Int -> Int -> Int -> [Int] -> Int >> f011helper t u v (w:ws) >> | ws == [] = t*u*v*w >> | otherwise = yada nada mada >> >> -- What are yada nada mada? >> >> -- The 20x20 grid case will become: >> f0112D :: [[Int]] -> Int >> -- where [[Int]] is a list of lists of rows, columns, major diagonals, >> & minor diagonals. >> -- -- Regards, KC

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Re: [Haskell-cafe] Project Euler: request for comments
by KC 31 Aug '11

31 Aug '11

You might like this zipping & folding version. Explicit recursion has the disadvantage that one has to read the entire function in order to figure out what's going on; whereas using the higher order functions makes things much easier to grasp. listof4tuples xs = (zip4 xs (tail xs) (tail (tail xs)) (tail (tail (tail xs)))) prods xs = map prods4 (listof4tuples xs) prods4 (t,u,v,w) = t*u*v*w maxprods4 xs = maximum $ prods xs On Mon, Aug 29, 2011 at 9:40 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > Got it. > > f :: [Int] -> Int > f (t:u:v:xs) = helper t u v xs > > helper :: Int -> Int -> Int -> [Int] -> Int > helper t u v (w:ws) > | ws == [] = t*u*v*w > | otherwise = max (t*u*v*w) (f (u:v:w:ws)) > > I tend to overlook mutual recursion in my toolbox. > > Thanks for the nnlightenment. > > On Sun, Aug 28, 2011 at 4:54 PM, KC <kc1956(a)gmail.com> wrote: >> Try something like the following: >> >> -- Project Euler 11 >> >> -- In the 20×20 grid below, four numbers along a diagonal line have >> been marked in red. >> >> -- <snip> >> >> -- The product of these numbers is 26 × 63 × 78 × 14 = 1788696. >> >> -- What is the greatest product of four adjacent numbers in any >> direction (up, down, left, right, or diagonally) in the 20×20 grid? >> >> >> import Data.List >> >> -- Doing the one dimensional case. >> f011 :: [Int] -> Int >> f011 (t:u:v:xs) = f011helper t u v xs >> >> f011helper :: Int -> Int -> Int -> [Int] -> Int >> f011helper t u v (w:ws) >> | ws == [] = t*u*v*w >> | otherwise = yada nada mada >> >> -- What are yada nada mada? >> >> -- The 20x20 grid case will become: >> f0112D :: [[Int]] -> Int >> -- where [[Int]] is a list of lists of rows, columns, major diagonals, >> & minor diagonals. >> >> >> >> >> On Sun, Aug 28, 2011 at 5:10 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: >>> No. The answer I posted is not good. >>> It worked, by chance, on a couple of small examples I tried but it >>> could end up comparing sequence of 4 numbers that where not initially >>> adjacent. >>> >>> On Sun, Aug 28, 2011 at 12:32 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: >>>> Maybe this? >>>> >>>> f x@(a:b:c:d:[]) = x >>>> f (a:b:c:d:e:ys) = if e >= a >>>> then f (b:c:d:e:ys) >>>> else f (a:b:c:d:ys) >>>> >>>> On Sat, Aug 27, 2011 at 8:26 PM, KC <kc1956(a)gmail.com> wrote: >>>>> Think of the simplest version of the problem that isn't totally trivial. >>>>> >>>>> e.g. A one dimensional list of numbers. >>>>> >>>>> What would you do? >>>>> >>>>> Note: you only want to touch each element once. >>>>> >>>>> The 2 dimensional case could be handled by putting into lists: rows, >>>>> columns, major diagonals, and minor diagonals. >>>>> >>>>> This isn't the fastest way of doing the problem but it has the >>>>> advantage of avoiding "indexitis". >>>>> >>>>> >>>>> On Fri, Aug 26, 2011 at 6:15 PM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: >>>>>> Like: >>>>>> 20*19*21*18 >>>>>> is bigger than >>>>>> 100*100*3*2 >>>>>> ? >>>>>> >>>>>> If so I need to think about how to formalize it. >>>>>> >>>>>> Thanks for the hint. >>>>>> >>>>>> On Fri, Aug 26, 2011 at 8:55 PM, KC <kc1956(a)gmail.com> wrote: >>>>>>> Is Problem 11 the 4 consecutive #'s problem? >>>>>>> >>>>>>> If so what must be true for 4 #'s to have a large product? >>>>>>> >>>>>>> Hint: x * y * z * 2 is that going to be larger? >>>>>>> >>>>>>> -- >>>>>>> -- >>>>>>> Regards, >>>>>>> KC >>>>>>> >>>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> -- >>>>> Regards, >>>>> KC >>>>> >>>> >>> >> >> >> >> -- >> -- >> Regards, >> KC >> > -- -- Regards, KC

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Deriving laws by systematic transformations
by Armando Blancas 31 Aug '11

31 Aug '11

Studying Wadler's "Comprehending Monads" and "Theorems for free!", I've been unable to derive law (iv) and I'm not sure about (iii). Will appreciate a pointer to similar examples or a massive hint. Here's my attempt at (iii): map f . unit x = map f [x] = [f x] = unit (f x) = (unit . f) x map f . unit = unit .f >From the Monads article: unit :: x -> M x join :: M (M x) -> M x For example, unit 3 = [3] and join [[1,2], [3]] = [1,2,3] (iii) map f . unit = unit . f (iv) map f . join = join . map (map f) Laws (iii) and (iv) may be derived by systematic transformations of the polymorphic types of unit and join.

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Off-topic: Mathematics
by Andrew Coppin 31 Aug '11

31 Aug '11

This is fairly wildly off-topic but... does anybody know of a good forum where I can ask questions about mathematics and get authoritative answers? (Apart from "go visit the nearest university", that is.)

11 22

iOS and Haskell
by Vasili I. Galchin 31 Aug '11

31 Aug '11

Hello, I know nothing about the architecture of iOS running on an iPad. However, I have a friend who just bought the newer iPad. It seems that either C++ or Objective C is available on iPad for development(actually the icon says C++). What are the prospects of getting Haskell ported to iOS? Vasili

3 2

Parallel Haskell Digest 5
by Eric Y. Kow 31 Aug '11

31 Aug '11

Parallel Haskell Digest ======================= Edition 5 2011-08-31 Hello Haskellers! Eric here, reprising my role as Parallel Haskell Digester. Many thanks to Nick for good stewardship of the digest and nice new directions for the future. This month we have Erlang PhDs (and a postdoc), new partners, two Monad Reader articles in progress and some strategies. As usual, this digest is made possible by the [Parallel GHC Project][n0]. News ---------------------------------------------------------------------- [Scalable Erlang PostDoc and 2 PhD Studentships][n1] (8 Aug) What, Erlang?! Yes, you are reading the right digest. If you're generally into parallelism and concurrency in functional programming languages, you may be especially interested to know about this announcement from Phil Trinder. > RELEASE project - A High-level Paradigm for Reliable Large-scale > Server Software - is funded by the EU Framework 7 programme for 36 > months from October 2011. Its aim is to scale the radical > concurrency-oriented programming paradigm to build reliable > general-purpose software, such as server-based systems, on massively > parallel machines (100 000 cores). Word of the Month ---------------------------------------------------------------------- Last month, we had `par` and `pseq` as our twin words of the month. Let's pursue this little train of parallel thought; our next word the month is *strategy*. Strategies have been around since the 1993 paper [Algorithm + Strategy = Parallelism][asp]; that's before even we started using monads in Haskell! They've recently been revamped in Simon Marlow's [Seq no More][seq-nm] paper, and it's this version of strategies that we'll be exploring here. Strategies are built on top of the `par` and `pseq` primitives we saw in the [last digest][phd4]. They provide a nice way to express the often complicated logic we need to make the best use of parallelism in our code. Use of strategies can also help to make parallel code easier to read and maintain because they allow us to more cleanly separate the core logic from our code that which pertains to our use of parallelism. Before delving into strategies, let's take a small notational detour by introducing the `Eval` monad. Suppose we wanted a parallel version of the `map` function, something that would apply a function to each item of a list. Using the `par` and `pseq` from the last digest, we might express this function parMap :: (a -> b) -> [a] -> [b] parMap f [] = [] parMap f (a:as) = b `par` bs `pseq` (b:bs) where b = f a bs = parMap f as If we look carefully at the code we can observe that there is something inherently sequential in the way we have expressed this parallel computation: first spark off `f a` then recurse to the tail of the list, and finally cons. The `Eval` monad builds off the insight that expressing parallelism is fundamentally (perhaps counterintuitively) about ordering things. Monads are well-suited for expressing ordering relationships, and so they have been been pressed to work for expressing parallel computation as well. data Eval a instance Monad Eval runEval :: Eval a -> a rpar :: a -> Eval a rseq :: a -> Eval a `Eval` is just a strict identity monad, with `rpar` and `rseq` as counterparts to `par` and `pseq`. We use `Eval` to compose sequences of parallel computation, which we extract the results of by using the `runEval` function. If you're not familiar with monads, you can get away with just treating `Eval` as new notation, or rather, borrowed notation, the same that we use IO, parser combinator libraries, QuickCheck and a plethora of other useful monads. It's worth noting also that despite appearances, we are still in purely functional territory -- no IO here! -- with the notion of sequencing being limited to controlling parallelism and evaluation depth. To make use of `Eval` for our `parMap` function, we could write a version like the below. It introduces a change of type, from returning `[b]` to `Eval [b]`. In the general case, we could just use the `runEval` function to get our result back, but we are not baking it into `parMap` because we would typically want to use then function within a greater `Eval` context anyway. parMap :: (a -> b) -> [a] -> Eval [b] parMap f [] = return [] parMap f (a:as) = do b <- rpar (f a) bs <- parMap f as return (b:bs) As before, this function captures the basic idea of its sequential counterpart `map`: apply function, recurse to tail, cons new head to new tail. This is a passable parallel map, but there are still two things which are unfortunate about it. First, we have repeated the implementation of map, not a big deal for such a small function but a potential maintenance problem for more complex code. Second, we have only captured one sort of parallel evaluation firing off sparks for all the cons cells, but in practice getting parallelism right requires some often careful tuning to get the right level of granularity and account for dependencies. For instance, what if instead of doing each cell in parallel, we wanted to bunch them up into chunks so as to minimise the coordination overhead? What we need is a way to express ideas about running code in parallel (such as “break into chunks and run each chunk simultaneously"), preferably avoid duplicating existing code or otherwise making it more complicated than it needs to be. This is where strategies come in. A strategy is just a function that turns some data into an `Eval` sequence. We've already encountered two strategies above, `rpar` which sparks off a parallel evaluation, and `rseq` which evaluates its argument to weak head normal form. Many more strategies possible particularly when they are custom designed for specific data types. Also, if we have a strategy, we can imagine wanting to use it. This we capture with `using`, which applies the strategy function and runs the resulting sequence. Parallel evaluation aside, you can almost pretty much think of <code>x `using` s</code> as being semequivalent to as `id x` but you'll want to watch out for a couple of caveats described the tutorial [Parallel and Concurrent Programming in Haskell][smtutorial]. Strategy a = a -> Eval a using :: a -> Strategy a -> a x `using` s = runEval (s x) Now that we've put a name to the idea of building `Eval` sequences, we can think about trying to generalise our `parMap`. One way would be to write a higher-order strategy. This `parList` function is almost identical to `parMap`, except that instead of applying any function to a list we limit ourselves to just applying some strategy on it. parList :: Strategy a -> Strategy [a] parList strat [] = return [] parList strat (x:xs) = do x' <- rpar (x `using` strat) xs' <- parList xs strat return (x':xs') We can then define `parMap` by parameterising `parList` with `rseq` to get a parallel list strategy which we then apply to `map f xs`. (Food for thought: why `parList rseq` instead of `parList r0`? Reply to the Haskell-Cafe posting if you think you know why!) parMap :: (a -> b) -> [a] -> Eval [b] parMap f xs = map f xs `using` parList rseq We have now achieved two things. First we've improve the modularity of our code by separating algorithm (`map f xs`) from coordination (`parList rseq`). Notice how we are now reusing map instead of reimplementing it, and notice as well how we now have a reusable `parList` that we can use apply to any situation that involves a list. Second, by isolating the algorithm from the coordination code we have given ourselves a lot more flexibility to switch strategies. To bunch our list up into coarser-grained chunks, for example, we could just swap out `parList` with `parListChunk` parMap :: (a -> b) -> [a] -> Eval [b] parMap f xs = map f xs `using` parListChunk 100 rseq In this word of the month, we have very lightly touched on the idea of strategies as a compositional way of expressing parallel coordination and improving the modularity of our code. To make use of strategies, we basically need to be aware of two or three things: 1. How to apply a strategy: <code>foo `using` s</code> evaluates the value `foo` with strategy `s` 2. Useful strategies from the library: the basics are `r0` which does nothing, `rseq` which evaluates its argument to weak head normal form, `rdeepseq` which evaluates it all the way down to normal form, and `rpar` which sparks the value for parallel evaluation. Be sure to check out [Control.Parallel.Strategies][straddock] for more sophisticated strategies such as `parListChunk`, which divides the list into chunks and applies a strategy to each one of the chunks in parallel. 3. (Optionally) How to build strategies, the simplest way being to use the `dot` function to compose two strategies sequentially. If you implement your own strategies instead of combining those from the library, you may want to have a look at the [Seq no More][seq-nm] for a little safety note. If you want to know more about strategies, the first place to look is probably the tutorial [Parallel and Concurrent Programming in Haskell][smtutorial] (there is a nice example in there, implementing a parallel K-means algorithm) and followed by the Control.Parallel.Strategies API. You could also just dive in and give it a try on some of your own code. It's sometimes just a matter of grabbing a strategy and `using` it. Parallel GHC Project Update ---------------------------------------------------------------------- The Parallel GHC Project is an MSR-funded project to push forward the use of parallel Haskell in the real world. The aim is to demonstrate that parallel Haskell can be employed successfully in industrial projects. Speaking of industrial projects, our recent search for a new project partner has been successful! In fact, we will be welcoming two new partners to the project, the research and development group of Spanish telecoms company Telefónica, and VETT a UK-based payment processing company. We are excited to be working with the teams at Telefónica I+D and VETT. There may be some Cloud Haskell in our future; stay tuned for more details about the respective partner projects. Also coming up are a couple of Monad Reader articles featuring work from the Parallel GHC project. Kazu Yamamoto has been writing an article for the upcoming Monad Reader special edition on parallelism and concurrency. He'll be revisiting Mighttpd (pronounced "Mighty"), a high-performance web server written in Haskell in late 2009. Since Mighttpd came out the Haskell web programming landscape has evolved considerably, with the release of GHC 7 and development of several web application frameworks. The new mighttpd takes advantage of GHC 7's new IO manager as well as the Yesod Web Application Interface (WAI) and the HTTP engine Warp. Do check out his article when it comes out for proof that "we can implement a high performance web server in Haskell, which is comparable to highly tuned web servers written in C", or if you can't wait, try his [most recent slides][mighttpd] on the topic. Bernie Pope and Dmitry Astapov have been working on an article about the Haskell MPI binding developed in the context of this project. You can find out more about the binding on its [Hackage][hackage-mpi] and [GitHub][github-mpi] pages. Blogs, Papers, and Packages ---------------------------------------------------------------------- * [Data Parallel Haskell and Repa for GHC 7.2.1][b1] (11 Aug) Ben Lippmeier has updated the Data Parallel Haskell libraries on Hackage to go with the newly released GHC 7.2.1. While DPH is still a technology preview, this new version is significantly more robust than previous ones. If nested data parallelism isn't what you're after, Ben has also updated the Repa library for parallel arrays. See [PH Digest 3][phd3] for more details. * [thespian: Lightweight Erlang-style Actors for Haskell][b2] (18 Aug) Alex Constandache update Hackage with this intriguing library. I wrote to Alex asking about about the relationship with Cloud Haskell. It turns out Alex had somewhat similar goals in mind and may be focusing on Cloud Haskell instead. * [dbus-core 0.9][b3] (23 Jul) John Millikin announced "the first significant release to dbus-core in a while" with significant improvements to both the API and implementation. In particular, dbus-client has been merged into dbus-core. See the announcement for more details then a quick code sample showing the new simple API in action. For the curious, D-Bus is an inter-process communication mechanism used in desktop environments like Gnome. Mailing list discussions --------------------------------------------------------------------- * [How to ensure code executes in the context of a specific OS thread?][m1] (4 Jul) Jason Dagit has found the correct handling of GUI events on OS X requires checking for events and responding to them from the main thread. He wanted to know if such thing was even possible on the threaded RTS, particularly so that he could use the library from GHCi. David Pollak has a [bit of code][hs-ipad] that provides a runOnMain function using an FFI call to a bit objective C code. Simon Marlow pointed out that for compiled code, the main thread is a bound thread, bound to the main thread of the process. Simon is specifically talking about the threaded RTS here as this is already trivially true of the non-thread one. The question still remains open for GHCi. * [Cloud Haskell][m2] (22 Jul) Tom Murphy was curious to see anybody was using [Cloud Haskell][cloud-hs] yet. It looks like we have a couple people who are *thinking* of using it: Tim Cowlishaw might be using it for his masters thesis project (A Haskell EDSL for agent-based simulation). Julian Porter, who we mentioned in the last digest for his Monad Reader article, is planning to make his MapReduce monad framework work on the distribute cluster. Now how about those of us who have actually given it try? As for the Parallel GHC project, it's worth mentioning that our new partners are planning to use Cloud Haskell in their projects. We'll be sure to report back to the community about the results. * [A language that runs on the JVM or .NET...][m4] (31 Jul) KC was hoping for a version of Haskell "that runs on the JVM or .NET has the advantage of Oracle & Microsoft making those layers more parallelizable". Austin Seipp replied that it basically boils down to it being [a lot of work][why-no-jvm]. Chris Smith also cautions that while there may be many good reasons to easy to want a Haskell.Net or a Jaskell, Haskell parallelism and concurrency may not be one of them. Parallel and concurrent Haskell code relies generates a large volume of lightweight threads. Simply using their JVM or CLR counterparts as they are would not do. Are you interested in seeing a serious and long-term effort towards Haskell on the JVM? See the [FAQ][why-no-jvm] and get in touch! * [Error in the asynchronous exception operational semantics][m6] (9 Aug) Edward Z. Yang noticed at the end of [Asynchronous Exceptions as an Effect][async1] (Harrison et. al) that the authors have found an error in the operational semantics described in [Asynchronous Exceptions in Haskell][async2]. Anybody know what it is? Meanwhile, David Barbour took the opportunity to say > All you need to know about asynchronous exceptions is: *don't use them!* > They're too difficult to reason about, in terms of failure modes and such. > Use TVars or MVars instead. * [Haskell Actors, Linda, publish / subscribe models?][m7] (13 Aug) Dmitri O. Kondratiev needs to "build a framework to coordinate task producers / consumers distributed in the same and different address spaces. He needs to scale a data processing application somewhat Hadoop-like way yet in more flexible manner, without Hadoop-specific distributed FS constraints." At this point, Ryan Newton suggested "Cloud Haskell", which was greeted by with joy and great enthusiasm. "Finally Erlang actor model of communication comes to Haskell!" Keep us posted, Dmitri. * [More generic parfoldr than this... ][m8](23 Jul) Prabhat Totoo tried to implement a parallel foldr function by breaking the input listed chunks, mapping foldr over each chunk, and running foldr over the list of results. This solution only works if the input and output of the folded function have the same type. Prabhat wanted to know how he could go about generalising his parallel fold. Also while doing some timings, he noticed that the regular presumably sequential fold improved with multiple cores. What's up with that? Conal Elliott make the point that Prabhat's current parallelise-by-reassociating solution is only correct for an associative operation, which is forcibly of type (a -> a -> a). Have a look at the the rest of the thread for an exploration of parallel fold by Kevin Hammond, Conal Elliot and Sebastien Fischer. Stack Overflow and Reddit ---------------------------------------------------------------------- * [Are 'par' and 'pseq' good for data parallelism?][s1] * [Difference between MVar and a TVar?][s2] * [How to sort a list [MVar a] using a values?][s3] * [Understanding BlockedIndefinitelyOnMVar in Concurrent code][s4] * [Poor performance / lockup with STM][s5] * [If one of Haskell's goals is concurrency, then why is it based on the λ-calculus and not on a process calculus?][s6] Help and Feedback ---------------------------------------------------------------------- If you'd like to make an announcement in the next Haskell Parallel Digest, then get in touch with me, Eric Kow, at <parallel(a)well-typed.com>. Please feel free to leave any comments and feedback! [phd3]: http://www.well-typed.com/blog/55 [phd4]: http://www.well-typed.com/blog/56 [smtutorial]: http://community.haskell.org/~simonmar/par-tutorial.pdf [asp]: http://www.macs.hw.ac.uk/~dsg/gph/papers/abstracts/strategies.html [seq-nm]: http://research.microsoft.com/apps/pubs/default.aspx?id=138042 [mighttpd]: http://www.mew.org/~kazu/material/2011-mighttpd.pdf [hackage-mpi]: http://hackage.haskell.org/package/haskell-mpi [github-mpi]: https://github.com/bjpop/haskell-mpi [straddock]: http://hackage.haskell.org/packages/archive/parallel/3.1.0.1/doc/html/Contr… [hs-ipad]: https://github.com/dpp/LispHaskellIPad [cloud-hs]: http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/ [why-no-jvm]: http://www.haskell.org/haskellwiki/GHC:FAQ#Why_isn.27t_GHC_available_for_.N… [async1]: http://www.cs.missouri.edu/~harrison/papers/mpc08.pdf [async2]: http://community.haskell.org/~simonmar/papers/async.pdf [actors]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/actor [ph-libs]: http://www.haskell.org/haskellwiki/Applications_and_libraries/Concurrency_a… [n0]: http://www.haskell.org/haskellwiki/Parallel_GHC_Project [n1]: http://www.haskell.org/pipermail/haskell-cafe/2011-August/094484.html [b1]: http://tumblr.justtesting.org/post/8778213236 [b2]: http://hackage.haskell.org/package/thespian-0.999 [b3]: http://www.haskell.org/pipermail/haskell-cafe/2011-July/094203.html [m1]: http://www.haskell.org/pipermail/haskell-cafe/2011-July/093722.html [m2]: http://www.haskell.org/pipermail/haskell-cafe/2011-July/094176.html [m4]: http://www.haskell.org/pipermail/haskell-cafe/2011-July/094398.html [m6]: http://www.haskell.org/pipermail/haskell-cafe/2011-August/094521.html [m7]: http://www.haskell.org/pipermail/haskell-cafe/2011-August/094614.html [m8]: https://groups.google.com/d/topic/parallel-haskell/97dmSXickYM/discussion [s1]: http://stackoverflow.com/questions/6844378/are-par-and-pseq-good-for-data-p… [s2]: http://stackoverflow.com/questions/6915079/difference-between-tvar-and-tmvar [s3]: http://stackoverflow.com/questions/6955651/how-to-sort-a-list-mvar-a-using-… [s4]: http://stackoverflow.com/questions/6847307/understanding-blockedindefinitel… [s5]: http://stackoverflow.com/questions/6439925/poor-performance-lockup-with-stm [s6]: http://www.reddit.com/r/haskell/comments/jlipx/if_one_of_haskells_goals_is_… -- Eric Kow <http://erickow.com>

2 1

bitSize
by Andrew Coppin 31 Aug '11

31 Aug '11

Quoting the Haddock documentation for Data.Bits.bitSize: "Return the number of bits in the type of the argument. The actual value of the argument is ignored. The function bitSize is undefined for types that do not have a fixed bitsize, like Integer." Does anybody else think it would be *far* more useful if bitSize applied to an Integer would tell you how many bits that particular Integer is using? Especially given that it can vary? Is there a way to actually determine how many bits are in an Integer?

11 25

GHCI Feature Request: Last Successful Compilation State Saved
by aditya siram 31 Aug '11

31 Aug '11

Hi all, I would like for the GHCI interpreter to save its environment before reloading a file and allowed the user to revert back to that state if the compilation was unsuccessful. Many times I've changed files, loaded them, hit a compilation error and needed, for example, the inferred type signature of some function. Even though that function hasn't been changed I have to either fix my code, undo a bunch of changes or comment out the last change I made and reload in order to do a ":type" on the function. This really breaks the flow of development. Thanks for considering. -deech

7 12

installing/reinstalling haskell platform with profiling enabled on windows
by MH 30 Aug '11

30 Aug '11

How can I install/reinstall haskell platform with profiling enabled on windows? Or the other way to put it, how can I install/reinstall haskell platform on windows with my own cabal options? I googled on it and didn't find any solutions for windows OS. Thanks, Malik

2 1

Text.Parsec.Prim
by Roly Perera 30 Aug '11

30 Aug '11

Hi, I seem to have some trouble accessing this module. I would like to use the type synonym ParsecT directly. I'm running GHC 6.12.1. According to Hoogle, the type I want is part of parsec-3.1.1, in module Text.Parsec.Prim. But if try to import Text.Parsec.Prim, GHC complains Could not find module `Text.Parsec.Prim': Can anyone help me with this? In the 2+ years I've been using parsec I've never managed to use ParsecT directly, but now it would be very useful. thanks, Roly In verbose mode, GHC reports: Glasgow Haskell Compiler, Version 6.12.1, for Haskell 98, stage 2 booted by GHC version 6.12.1 Using binary package database: /usr/lib/ghc-6.12.1/package.conf.d/package.cache Using binary package database: /home/rolyp/.ghc/x86_64-linux-6.12.1/package.conf.d/package.cache hiding package Cabal-1.8.0.2 to avoid conflict with later version Cabal-1.10.2.0 hiding package QuickCheck-1.2.0.0 to avoid conflict with later version QuickCheck-2.1.0.2 hiding package base-3.0.3.2 to avoid conflict with later version base-4.2.0.0 wired-in package ghc-prim mapped to ghc-prim-0.2.0.0-9d35c97e886f807a1e6d024aaa91dcec wired-in package integer-gmp mapped to integer-gmp-0.2.0.0-9a51ffb34a83618a1a3d4e472b9977a0 wired-in package base mapped to base-4.2.0.0-2cc27b7e43511c4ca001642a7f77a8f6 wired-in package rts mapped to builtin_rts wired-in package haskell98 mapped to haskell98-1.0.1.1-0fdaf3b26bc38c43ce8371edf538dbf6 wired-in package template-haskell mapped to template-haskell-2.4.0.0-bbc7c61990d2fe9d20be2deb924f833c wired-in package dph-seq mapped to dph-seq-0.4.0-52cfd6db5fc09a2abf793cd6a856a392 wired-in package dph-par mapped to dph-par-0.4.0-b4f339fed900d7bc4b3db61526caf863 Hsc static flags: -static

3 3

Ambiguous module name `System.Directory'
by informationen 30 Aug '11

30 Aug '11

Hi, i am using ghc version 7.0.3 and a pretty recent version of the haskell-platform. Whenever i use the System.Directory module, i run into this conflict: Ambiguous module name `System.Directory': it was found in multiple packages: system-fileio-0.2.1 directory-1.1.0.0 How can i resolve this conflict permamently (i know about :set -hide-package ... )? And shouldn't there be a rule in the haskell platform which forbids modules of the same name? Greetings Chris

5 5

[CUFP 2011] Birds of a Feather sessions
by Ashish Agarwal 30 Aug '11

30 Aug '11

========================================================= Birds of a Feather sessions (BOFs) Commercial Users of Functional Programming Workshop (CUFP 2011) http://cufp.org/bofs-2011 Tokyo, Japan, September 22 - 23 ========================================================= Following last year's success, CUFP 2011 will again include Birds of a Feather sessions. BoFs provide a place for our community to gather informally at CUFP and reach consensus on matters of importance. Any CUFP attendee can propose a BoF session, and grab one of the spare rooms to hold a discussion. Attendance in the evening is open to all. BoF sessions facilitate ad-hoc discussions and provide a place to gather and start off the chat, before moving on during the evening to a local restaurant or pub. There is no deadline for proposing a session, but we encourage you to do so at the earliest possible time to help us with planning and to publicize your proposed discussion. Attendees are also free to show up even if you have not confirmed, but again earlier confirmation will help us with planning. Please see http://cufp.org/bofs-2011 for details on how to propose a BoF session or confirm attendance at one of them. Scheduled BoFs will be listed here as they are confirmed. General information on CUFP 2011 can be found at http://cufp.org/conference/2011. The conference is co-located with ICFP. You can register for CUFP at the main ICFP website http://www.icfpconference.org/icfp2011.

1 0

Re: [Haskell-cafe] Decompressing and http-enumerator
by Herbert Valerio Riedel 30 Aug '11

30 Aug '11

On Mon, 2011-08-29 at 16:50 +0100, Colin Adams wrote: > On 29 August 2011 16:45, Michael Snoyman <michael(a)snoyman.com> wrote: > "chunked" is the only valid transfer-encoding[1], while gzip > must be > specified on the content-encoding header[2]. For a simple > example of > these two, look at the response headers from Haskellers[3] in > something like Chrome developer tools. > > [1] > http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.6 > [2] > http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.5 > [3] http://www.haskellers.com/ > > Well [1] contradicts your claim: > > "The Internet Assigned Numbers Authority (IANA) acts as a registry for > transfer-coding value tokens. Initially, the registry contains the > following tokens: "chunked" (section 3.6.1), "identity" (section > 3.6.2), "gzip" (section 3.5), "compress" (section 3.5), and > "deflate" (section 3.5). " This added paragraph was actually one of the major changes between RFC2068 and RFC2616, in order to enhance the "Transfer-Encoding" field to become "full-fledged" as the "Content-Encoding" field was, as the previous definitions were deemed to have "significant problems".[1] So, using 'Content-Encoding: gzip' was required before RFC2616... but w/ RFC2616 'Transfer-Encoding: gzip, chunked' becomes possible too... It's also been a long standing bug/deficiency in Firefox[2]. So, RFC2616 differentiates between the 'entity' (= the actual information content, mostly end-to-end) and the 'message' (= transfer "wire format", mostly hop-by-hop). The content-* headers pertain to the 'entity', whereas the transfer-* headers describe the 'message' format. But I have to admit, that we have an unfortunate situation here, where the real-world implementations of RFC2616 don't follow the intent of the RFC (or alternatively: they implement the obsolete RFC2068). And I'm well aware that a 100% compliant RFC2616 implementation most likely will cause a lot of trouble in terms of interoperability... maybe the HTTPbis[3] effort will improve on the situation... Long story short: HTTP client libraries should be flexible enough to let the client-code decide whether transparent decoding of the specified Content-Encoding is desired or not. [1]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html#sec19.6.3 [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=68517 [3]: http://tools.ietf.org/wg/httpbis/

1 0

GHC API question
by Chris Smith 30 Aug '11

30 Aug '11

I'm using the GHC API in GHC 7.2, and running into some problems. For background, I have working code that uses compileExpr to get a value from a dynamically loaded module. However, I'd like to do some profiling, and it appears that compileExpr doesn't work from executables that are built with profiling. So instead, I tried to take a more circuitous route... I'm using getModuleInfo and modInfoTyThings to get a list of all the declarations in the module, and finding the one I want, which I call var. This all works fine, and I can print the type and the name, and I know I have the right thing and it's got the correct type. But then I do: session <- getSession v <- liftIO $ getHValue session var return (unsafeCoerce# v) and I get a segfault when I try to access the resulting value. Keep in mind that this is the same value that works fine when I access it with compileExpr on an expression I've constructed to retrieve it. Any ideas what's going on? Am I missing a step? -- Chris Smith

4 6

Unexpected Typeable behaviour; Prelude.undefined
by Philip Holzenspies 30 Aug '11

30 Aug '11

L.S., I'm currently writing code where I want some ADTs to be parametric with a monad. There are some extra conditions that I place on my parameter, but I've boiled things down to minimal reproducibility. When I define MyADT as follows: import Data.Typeable data MyADT m = MyADT (m ()) instance (Typeable1 m, Monad m) => Typeable (MyADT m) where typeOf t@(MyADT _) = mkTyCon "MyADT" `mkTyConApp` [typeOf1 ((return :: Monad m => MyADT m -> m (MyADT m)) t)] it compiles fine and GHCi works as expected on a single instance of MyADT: *Main> typeOf (MyADT (return () :: IO ())) MyADT IO However, as soon as I place my data type in a structure of sorts, things break down: *Main> typeOf [(MyADT (return () :: IO ()))] *** Exception: Prelude.undefined *Main> typeOf (Just (MyADT (return () :: IO ()))) *** Exception: Prelude.undefined *Main> typeOf ((return :: a -> IO a) (MyADT (return () :: IO ()))) *** Exception: Prelude.undefined But if I stick a number in a similar structure, typeOf works just fine: *Main> typeOf ((return :: a -> IO a) 5) IO Integer I don't quite understand where the undefined comes from. I'm certainly not using it anywhere (as shown by the minimal reproduction above). Weirder still, when I *do* introduce a nice error, that too does not come up, viz. import Data.Typeable data MyADT m = MyADT (m ()) instance (Typeable1 m, Monad m) => Typeable (MyADT m) where typeOf t@(MyADT _) = error "foobar" with GHCi-session: *Main> typeOf (MyADT (return () :: IO ())) *** Exception: foobar *Main> typeOf ((return :: a -> IO a) (MyADT (return () :: IO ()))) *** Exception: Prelude.undefined *Main> typeOf $ Just (MyADT (return () :: IO ())) *** Exception: Prelude.undefined *Main> typeOf $ Just 42 Maybe Integer FYI, I'm using GHC 7.0.3, as installed with the Haskell Platform 2011.2.0.1. Am I overlooking something? Any help would be appreciated. Regards, Philip

4 4

Decompressing and http-enumerator
by Michael Snoyman 30 Aug '11

30 Aug '11

Hi all, Erik just opened an issue on Github[1] that affected me very recently as well when writing some automated Hackage checking code[2]. The issue is that http-enumerator sees the content-encoding header and decompresses the tarball, returning an uncompressed tarfile. I can avoid this with rawBody = False, but that's not a real solution, since that also disables chunked response handling. So one possible solution is to just add an option to never decompress response bodies, but that's a bit of a hack. The real question is: what's the correct way to handle these tarballs? Web browsers seem to know not to decompress them, but AFAICT http-enumerator is correctly following the spec by decompressing. Another possibility is to determine whether or not to decompress based on the content type, using either a white or black list (e.g., never compress TAR files, always decompress HTML files, etc). I'm open to suggestions here. Michael [1] https://github.com/snoyberg/http-enumerator/issues/30 [2] https://github.com/yesodweb/maintenance/blob/master/release/sdist-check.hs

6 11

Re: [Haskell-cafe] [xmonad] Cabal install problem
by Brent Yorgey 30 Aug '11

30 Aug '11

On Tue, Aug 30, 2011 at 12:30:08AM +0300, Tayfur Yilmaz wrote: > > > > > > Quoting Tayfur Yilmaz <yilmaz.tayfur(a)gmail.com>: > > > > > > >Hi everyone > > > >I have some problem for install 'cabal-install package' I downloaded > > and > > > >succesfully build a binary source ghc-7.0.2. Then I want to install > > > >cabal-0.10.2 and ? see some warning and last output like this > > > >Linking Setup ... > > > >Configuring Cabal-1.10.1.0... > > > >Setup: At least the following dependencies are missing: > > > >base >=4 && <3 && >=2 && <5, unix >=2.0 && <2.5 > > > > > > > >Error during cabal-install bootstrap: > > > >Configuring the Cabal package failed > > > > > > > >Then ? want to use cabal-0.8 and output like this > > > >Linking Setup ... > > > >Configuring Cabal-1.8.0.2... > > > >Setup: At least the following dependencies are missing: > > > >base >=4 && <3 && >=1 && <5, > > > >filepath >=1 && <1.2, > > > >unix >=2.1 && <2.5 > > > > > > > >Error during cabal-install bootstrap: > > > >Configuring the Cabal package failed > > > > > > > >So Which compatible versiyon for cabal-install version I use Kde4 on > > > >Pardus<http://www.pardus.org.tr/> > > > > > > > >Best Regards > > Can someone describe install packages sort list.. > I read some document and > 1.Firstly ı download a binary version of Ghc (version 7.0.2) > (bootstrap.py) bootstrap.py? There should not be any python scripts involved in installing a binary version of GHC. Where did you download it from? After installing it, does it work? If you type ghci at a command prompt, what happens? -Brent > 2. cabal-install package download and install bu I send this bug > > And now I want to build hackage platform > > Command > $ sudo ./configure > Output > ************************************************** > * > * Haskell Platform Source Installer > * > * For the Haskell Platform 2011.2.0.1 and GHC 7.0.3 > * > ************************************************** > checking build system type... i686-pc-linux-gnu > checking host system type... i686-pc-linux-gnu > checking target system type... i686-pc-linux-gnu > *checking for ghc... notfound* > configure: error: > This installer for the Haskell Platform requires ghc to be installed first > * If ghc is installed not on the PATH then use --with-ghc= and > --with-ghc-pkg=* > Command > $ sudo ./configure --with-ghc= --with-ghc-pkg= > Output > ************************************************** > * > * Haskell Platform Source Installer > * > * For the Haskell Platform 2011.2.0.1 and GHC 7.0.3 > * > ************************************************** > checking build system type... i686-pc-linux-gnu > checking host system type... i686-pc-linux-gnu > checking target system type... i686-pc-linux-gnu > *checking for hsc2hs... notfound* > configure: error: The hsc2hs program could not be found. > It is usually installed along with ghc. You may need to specify > --with-hsc2hs= > > Command > sudo ./configure --with-ghc= --with-ghc-pkg= --with-hsc2hs= > Output > ************************************************** > * > * Haskell Platform Source Installer > * > * For the Haskell Platform 2011.2.0.1 and GHC 7.0.3 > * > ************************************************** > checking build system type... i686-pc-linux-gnu > checking host system type... i686-pc-linux-gnu > checking target system type... i686-pc-linux-gnu > checking version of ghc... > *configure: error: does not seem to work (or maybe it is not actually ghc). > * > > > I build ghc binary and why I can't solve this problems.

2 1

Trouble with Haddock
by anonymous 29 Aug '11

29 Aug '11

First time using haddock. I'm unable to include code examples in the module header. Haddock fails with this error: haddock module header parse failed: Cannot parse header documentation paragraphs It's about 12 lines of code, which doesn't seem like much compared to other packages. e.g. -- | describing module -- -- > code -- > ... -- > code module Foo ( .... I tried @...@ code blocks, but that didn't work either. If I shorten the code to 3 lines or so, it will work.

2 1

Re: [Haskell-cafe] Dynamic loading of module
by Arnaud Bailly 29 Aug '11

29 Aug '11

Hello Albert, Thanks for taking the time to help me fix this package stuff. So I wiped out my package.conf.d/ and tried to reinstall my stuff. Installing template-haskell 2.5.0.0 is ok (2.6 is not, fails to compile on ghc 7.0.3) but then: D:\projets\>ghc --make -package ghc main <command line>: cannot satisfy -package ghc (use -v for more information) I suspect I really *do* have to reinstall haskell-platform. Here is the output of ghc-pkg list -v: using cache: C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d\package.cache using cache: D:/Program Files/Haskell Platform/2011.2.0.1\lib\package.conf.d\package.cache D:/Program Files/Haskell Platform/2011.2.0.1\lib\package.conf.d: Cabal-1.10.1.0 (Cabal-1.10.1.0-55f781465ee9f32289755ad706c71f0f) GLUT-2.1.2.1 (GLUT-2.1.2.1-2d30997b9a19d27be388572e75af52bf) HTTP-4000.1.1 (HTTP-4000.1.1-267a332938fa742ba5a5d59de0b46d60) HUnit-1.2.2.3 (HUnit-1.2.2.3-102fbfbd594cd6d38461f5c68d880996) OpenGL-2.2.3.0 (OpenGL-2.2.3.0-a58ce3ad6070e6b7932a3e779be57f75) Win32-2.2.0.1 (Win32-2.2.0.1-26cf39fdf591bdac61b11d5a443c62ab) array-0.3.0.2 (array-0.3.0.2-8e9cd0144e87fa9cc86cc9031631c4f3) base-4.3.1.0 (base-4.3.1.0-f520cd232cc386346843c4a12b63f44b) bin-package-db-0.0.0.0 (bin-package-db-0.0.0.0-97d865e5935b41538bcb29fc1040ae7d) bytestring-0.9.1.10 (bytestring-0.9.1.10-cd85f14e02463c02ba4c77d7adcdb54f) cgi-3001.1.7.4 (cgi-3001.1.7.4-659440ce11c2975fd9c9c471a1e8ff3b) containers-0.4.0.0 (containers-0.4.0.0-18deac99a132f04751d862b77aab136e) deepseq-1.1.0.2 (deepseq-1.1.0.2-09b3aed0c4982bbc6569c668100876fa) directory-1.1.0.0 (directory-1.1.0.0-3a2367d72569467a8af8a231656ff1b8) extensible-exceptions-0.1.1.2 (extensible-exceptions-0.1.1.2-d8c5b906654260efd7249f497d17a831) ffi-1.0 (builtin_ffi) fgl-5.4.2.3 (fgl-5.4.2.3-595811d6eabb1e1768685703ea66e982) filepath-1.2.0.0 (filepath-1.2.0.0-f132e9f7703da4e20a47ff2b9acf1ea1) (ghc-binary-0.5.0.2 (ghc-binary-0.5.0.2-aba2b5dca5546ea1a972188de48f87b5)) ghc-prim-0.2.0.0 (ghc-prim-0.2.0.0-e1f7c380581d61d42b0360d440cc35ed) haskell-src-1.0.1.4 (haskell-src-1.0.1.4-7428a8c9049cd6bf5abdc0bbd2d417c5) (haskell2010-1.0.0.0 (haskell2010-1.0.0.0-53d9cd65595c551eea0c0269f534b5e0)) haskell98-1.1.0.1 (haskell98-1.1.0.1-35ec26bae828637c1638c8be441b3d68) hpc-0.5.0.6 (hpc-0.5.0.6-481dbb43fb624c21ad3bb9434675e3ac) html-1.0.1.2 (html-1.0.1.2-a494249f98a0f38b1a8db28bc70f8b0b) integer-gmp-0.2.0.3 (integer-gmp-0.2.0.3-91607778cf3ae8f3948a50062b4f8479) mtl-2.0.1.0 (mtl-2.0.1.0-fb4d1695269b74308c1517c06b76e6e8) network-2.3.0.2 (network-2.3.0.2-47657e39a6118a978d9f443d72e85d4a) old-locale-1.0.0.2 (old-locale-1.0.0.2-6e2a3c0744e8cf4e0ac2d4e58659f7b5) old-time-1.0.0.6 (old-time-1.0.0.6-445ce39cbcebd38069c25c0f383b728d) parallel-3.1.0.1 (parallel-3.1.0.1-6eaa564e1ef1537bc88ad1fea6c90fe2) parsec-3.1.1 (parsec-3.1.1-9da59b00c02e52f9f62f3c87c7e0e2ec) pretty-1.0.1.2 (pretty-1.0.1.2-abc7c632374e50e1c1927987c2651f0f) process-1.0.1.5 (process-1.0.1.5-b3dded8e54a2e13d22af410bdcfafff4) random-1.0.0.3 (random-1.0.0.3-1abde37180be5476311abeefe300abc2) regex-base-0.93.2 (regex-base-0.93.2-9e1b027c41dbec856469a30982495bb9) regex-compat-0.93.1 (regex-compat-0.93.1-31c61fe0aee45e8a9853edf7a844f74e) regex-posix-0.94.4 (regex-posix-0.94.4-f5eb628ea5dae5f91552d5ea0e26359d) rts-1.0 (builtin_rts) stm-2.2.0.1 (stm-2.2.0.1-57e291244ee02349552a4f79caeb4ffe) syb-0.3 (syb-0.3-8db7bc4339a1cb8a6f2a46c40447ef0b) text-0.11.0.6 (text-0.11.0.6-398a3f02891247aea46662fc7379c4a5) time-1.2.0.3 (time-1.2.0.3-74ef6ac31cee9aec02b036978af002d2) transformers-0.2.2.0 (transformers-0.2.2.0-2fe7b735c63a6cbe8724038d8e4d812a) xhtml-3000.2.0.1 (xhtml-3000.2.0.1-ace31b2e48c396e565655b0f34f5d2b7) zlib-0.5.3.1 (zlib-0.5.3.1-5fbdf714525b76e0e601c2ffb25f2044) C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\package.conf.d: QuickCheck-2.4.1.1 (QuickCheck-2.4.1.1-04d68679694a517ba23022a4c6bc1cde) ghc-paths-0.1.0.8 (ghc-paths-0.1.0.8-be391faf057d651dbb92b73671fe9eee) template-haskell-2.5.0.0 (template-haskell-2.5.0.0-87f4f416a22a910e480ac9f269479a5f) utf8-string-0.3.7 (utf8-string-0.3.7-dcbcb8de655cdfe1c4c28c094f8c6799) Thanks again, Arnaud On Sat, Aug 27, 2011 at 8:59 PM, Albert Y. C. Lai <trebla(a)vex.net> wrote: > You have too many instances of template-haskell. The important parts are: > > > package ghc-7.0.3-**fc75cf67c86ba2c0d64b07024a18d3**b4 is unusable due to > missing or recursive dependencies: > template-haskell-2.5.0.0-**7d9b1443ac5ab69e5ed705a487990d**eb > > package template-haskell-2.5.0.0-**7d9b1443ac5ab69e5ed705a487990d**eb is > shadowed by package template-haskell-2.5.0.0-** > 87f4f416a22a910e480ac9f269479a**5f > > and in "ghc-pkg list -v": > > D:/Program Files/Haskell Platform/2011.2.0.1\lib\**package.conf.d: > > > template-haskell-2.5.0.0 (template-haskell-2.5.0.0-** > 7d9b1443ac5ab69e5ed705a487990d**eb) > > C:\Documents and Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\ > **package.conf.d: > > > template-haskell-2.5.0.0 (template-haskell-2.5.0.0-** > 87f4f416a22a910e480ac9f269479a**5f) > > I don't know how you got to this unsafe state. But my article explains > what's wrong with it. (Though my example has different version numbers on > top of different ABI hashes). > > The user instance of template-haskell (**87f4f416a22a910e480ac9f269479a**5f) > is getting into the way. Lose it by doing "ghc-pkg unregister --user > template-haskell" on it. Oh, it will complain about breaking other packages; > well, lose them too. > > (Or go one step further and lose all of C:\Documents and > Settings\abailly\Application Data\ghc\i386-mingw32-7.0.3\**package.conf.d > which means losing all user packages.) > > (Reinstalling haskell platform changes nothing, as long as some user > package gets into the way.) >

3 10

Problems creating Haskell-dll without -fvia-C
by KlasI 29 Aug '11

29 Aug '11

Hi! I recently read a haskell-cafe-thread telling me that the compiler option -fvia-C will be removed. This gets me a bit worried... I use -fvia-C when I build my haskell dll, and it works just fine (Haskell 2010.2.0.0): ghc -c Adder.hs -O2 -fvia-C ghc -c StartEnd.c ghc -shared -o Adder.dll Adder.o Adder_stub.o StartEnd.o Adder.def Next I create a lib which can be imported in Visual C++: lib /machine:i386 /def:SingThing.def BUT...if I remove the flag -fvia-C, the program crashes when I run it:( I've tried experimenting with a few things: * Haskell FFI's calling conventions ccall/stdcall * Skipping the .def file * Skipping "lib /machine:i386 /def:SingThing.def", instead trying the approach descibed in: http://blogs.msdn.com/b/satnam_singh/archive/2011/04/19/creating-a-windows-… Can anyone please give me a hint of whats going on? I guess it must be somthing with pointers and calling conventions, but I'm banging my head against the wall now:( Cheers Klas (Btw... I should mention that the simple Adder.hs example actually works without -fvia-C, my dll is more advanced, but I'm following the same compiling procedure) -- View this message in context: http://haskell.1045720.n5.nabble.com/Problems-creating-Haskell-dll-without-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

1 0

Memory management issue in notmuch-haskell bindings
by Ben Gamari 29 Aug '11

29 Aug '11

It seems that the notmuch-haskell bindings (version 0.2.2 built against notmuch from git master; passes notmuch-test) aren't dealing with memory management properly. In particular, the attached test code[1] causes talloc to abort. Unfortunately, while the issue is consistently reproducible, it only occurs with some queries (see source[1]). I have been unable to establish the exact criterion for failure. It seems that the crash is caused by an invalid access to a freed Query object while freeing a Messages object (see Valgrind trace[3]). I've taken a brief look at the bindings themselves but, being only minimally familiar with the FFI, there's nothing obviously wrong (the finalizers passed to newForeignPtr look sane). I was under the impression that talloc was reference counted, so the Query object shouldn't have been freed unless if there was still a Messages object holding a reference. Any idea what might have gone wrong here? Thanks! Cheers, - Ben [1] Test case, import Data.List import Control.Monad import System.Environment import Foreign.Notmuch dbpath = "/home/ben/.mail" getAddresses :: Database -> String -> IO [String] getAddresses db q = do query <- queryCreate db q msgs <- queryMessages query addrs <- mapM (flip messageGetHeader $ "From") msgs return addrs main = do db <- databaseOpen dbpath DatabaseModeReadOnly --addrs2 <- getAddresses db "tag:haskell" -- This succeeds addrs3 <- getAddresses db "to:dietz" -- This fails --print addrs2 --print addrs3 databaseClose db [2] Crashed session and backtrace, [1217 ben@ben-laptop ~] $ ghc test.hs -auto-all -rtsopts -prof && gdb ./test GNU gdb (Ubuntu/Linaro 7.2-1ubuntu11) 7.2 Copyright (C) 2010 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>... Reading symbols from /home/ben/test...(no debugging symbols found)...done. (gdb) run Starting program: /home/ben/test [Thread debugging using libthread_db enabled] Program received signal SIGABRT, Aborted. 0x00007ffff5979d05 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64 64 ../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory. in ../nptl/sysdeps/unix/sysv/linux/raise.c (gdb) bt #0 0x00007ffff5979d05 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64 #1 0x00007ffff597dab6 in abort () at abort.c:92 #2 0x00007ffff6de038c in talloc_abort (reason=0x7ffff6de56e8 "Bad talloc magic value - access after free") at ../talloc.c:210 #3 0x00007ffff6de0271 in talloc_abort_access_after_free (ptr=0x769190, location=0x7ffff7bd4e04 "lib/messages.c:142") at ../talloc.c:229 #4 talloc_chunk_from_ptr (ptr=0x769190, location=0x7ffff7bd4e04 "lib/messages.c:142") at ../talloc.c:250 #5 _talloc_free (ptr=0x769190, location=0x7ffff7bd4e04 "lib/messages.c:142") at ../talloc.c:1164 #6 0x00007ffff7bc7e65 in notmuch_messages_destroy (messages=0x769190) at lib/messages.c:142 #7 0x00000000004de1c9 in scheduleFinalizers () #8 0x00000000004e013d in GarbageCollect () #9 0x00000000004d9e40 in scheduleDoGC.clone.18 () #10 0x00000000004db0e0 in exitScheduler () #11 0x00000000004d9066 in hs_exit_ () #12 0x00000000004d940a in shutdownHaskellAndExit () #13 0x00000000004d8a91 in real_main () #14 0x00000000004d8ade in hs_main () #15 0x00007ffff5964eff in __libc_start_main (main=0x408ed0 <main>, argc=1, ubp_av=0x7fffffffe4f8, init=<value optimized out>, fini=<value optimized out>, rtld_fini=<value optimized out>, stack_end=0x7fffffffe4e8) at libc-start.c:226 #16 0x0000000000407791 in _start () (gdb) [3] Valgrind output, ==25241== Memcheck, a memory error detector ==25241== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al. ==25241== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info ==25241== Command: ./test ==25241== ==25241== Conditional jump or move depends on uninitialised value(s) ==25241== at 0x52BB510: inflateReset2 (in /lib/x86_64-linux-gnu/libz.so.1.2.3.4) ==25241== by 0x52BB605: inflateInit2_ (in /lib/x86_64-linux-gnu/libz.so.1.2.3.4) ==25241== by 0x5F211BE: ChertTable::lazy_alloc_inflate_zstream() const (chert_table.cc:1672) ==25241== by 0x5F23B06: ChertTable::read_tag(Cursor*, std::string*, bool) const (chert_table.cc:1264) ==25241== by 0x5F260F9: ChertTable::get_exact_entry(std::string const&, std::string&) const (chert_table.cc:1210) ==25241== by 0x5F26DE2: ChertTermList::ChertTermList(Xapian::Internal::RefCntPtr<ChertDatabase const>, unsigned int) (chert_termlist.cc:44) ==25241== by 0x5EFF2E5: ChertDatabase::open_term_list(unsigned int) const (chert_database.cc:891) ==25241== by 0x5E7E7FB: Xapian::Document::termlist_begin() const (omdocument.cc:176) ==25241== by 0x4E41822: _notmuch_message_ensure_metadata(_notmuch_message*) (message.cc:309) ==25241== by 0x4E429DC: _notmuch_message_ensure_filename_list(_notmuch_message*) (message.cc:632) ==25241== by 0x4E42C37: notmuch_message_get_filename (message.cc:698) ==25241== by 0x4E41CA7: _notmuch_message_ensure_message_file(_notmuch_message*) (message.cc:403) ==25241== ==25241== Invalid read of size 4 ==25241== at 0x5C25DED: _talloc_free (talloc.c:242) ==25241== by 0x4E39E64: notmuch_messages_destroy (messages.c:142) ==25241== by 0x4DE1C8: scheduleFinalizers (in /home/ben/test) ==25241== by 0x4E013C: GarbageCollect (in /home/ben/test) ==25241== by 0x4D9E3F: scheduleDoGC.clone.18 (in /home/ben/test) ==25241== by 0x4DB0DF: exitScheduler (in /home/ben/test) ==25241== by 0x4D9065: hs_exit_ (in /home/ben/test) ==25241== by 0x4D9409: shutdownHaskellAndExit (in /home/ben/test) ==25241== by 0x4D8A90: real_main (in /home/ben/test) ==25241== by 0x4D8ADD: hs_main (in /home/ben/test) ==25241== by 0x6F4FEFE: (below main) (libc-start.c:226) ==25241== Address 0x8324e90 is 64 bytes inside a block of size 136 free'd ==25241== at 0x4C282ED: free (vg_replace_malloc.c:366) ==25241== by 0x5C29884: _talloc_free_internal (talloc.c:714) ==25241== by 0x5C25F22: _talloc_free (talloc.c:667) ==25241== by 0x4E452BF: notmuch_query_destroy (query.cc:358) ==25241== by 0x4DE1C8: scheduleFinalizers (in /home/ben/test) ==25241== by 0x4E013C: GarbageCollect (in /home/ben/test) ==25241== by 0x4D9E3F: scheduleDoGC.clone.18 (in /home/ben/test) ==25241== by 0x4DB0DF: exitScheduler (in /home/ben/test) ==25241== by 0x4D9065: hs_exit_ (in /home/ben/test) ==25241== by 0x4D9409: shutdownHaskellAndExit (in /home/ben/test) ==25241== by 0x4D8A90: real_main (in /home/ben/test) ==25241== by 0x4D8ADD: hs_main (in /home/ben/test) ==25241== ==25241== Invalid read of size 8 ==25241== at 0x5C26251: _talloc_free (talloc.c:249) ==25241== by 0x4E39E64: notmuch_messages_destroy (messages.c:142) ==25241== by 0x4DE1C8: scheduleFinalizers (in /home/ben/test) ==25241== by 0x4E013C: GarbageCollect (in /home/ben/test) ==25241== by 0x4D9E3F: scheduleDoGC.clone.18 (in /home/ben/test) ==25241== by 0x4DB0DF: exitScheduler (in /home/ben/test) ==25241== by 0x4D9065: hs_exit_ (in /home/ben/test) ==25241== by 0x4D9409: shutdownHaskellAndExit (in /home/ben/test) ==25241== by 0x4D8A90: real_main (in /home/ben/test) ==25241== by 0x4D8ADD: hs_main (in /home/ben/test) ==25241== by 0x6F4FEFE: (below main) (libc-start.c:226) ==25241== Address 0x8324e80 is 48 bytes inside a block of size 136 free'd ==25241== at 0x4C282ED: free (vg_replace_malloc.c:366) ==25241== by 0x5C29884: _talloc_free_internal (talloc.c:714) ==25241== by 0x5C25F22: _talloc_free (talloc.c:667) ==25241== by 0x4E452BF: notmuch_query_destroy (query.cc:358) ==25241== by 0x4DE1C8: scheduleFinalizers (in /home/ben/test) ==25241== by 0x4E013C: GarbageCollect (in /home/ben/test) ==25241== by 0x4D9E3F: scheduleDoGC.clone.18 (in /home/ben/test) ==25241== by 0x4DB0DF: exitScheduler (in /home/ben/test) ==25241== by 0x4D9065: hs_exit_ (in /home/ben/test) ==25241== by 0x4D9409: shutdownHaskellAndExit (in /home/ben/test) ==25241== by 0x4D8A90: real_main (in /home/ben/test) ==25241== by 0x4D8ADD: hs_main (in /home/ben/test) ==25241== ==25241== ==25241== HEAP SUMMARY: ==25241== in use at exit: 192,328 bytes in 555 blocks ==25241== total heap usage: 19,852 allocs, 19,297 frees, 35,375,726 bytes allocated ==25241== ==25241== LEAK SUMMARY: ==25241== definitely lost: 0 bytes in 0 blocks ==25241== indirectly lost: 0 bytes in 0 blocks ==25241== possibly lost: 27,799 bytes in 292 blocks ==25241== still reachable: 164,529 bytes in 263 blocks ==25241== suppressed: 0 bytes in 0 blocks ==25241== Rerun with --leak-check=full to see details of leaked memory ==25241== ==25241== For counts of detected and suppressed errors, rerun with: -v ==25241== Use --track-origins=yes to see where uninitialised values come from ==25241== ERROR SUMMARY: 4 errors from 3 contexts (suppressed: 4 from 4)

2 4

only anecdotal .... not a proof of a trend ...
by Vasili I. Galchin 29 Aug '11

29 Aug '11

Hello, I received two job postings ... my comments follows the postings: ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- *#1 Software Developer* * * Location: Austin, TX Duration: 6 months Rate : $60/hr -$70/hr on w2 *Required:* *- Straight C experience - Generally need a pure C programmer to ideally create 1 C file that can be compiled in Win32/Win64/Dos/Shell/Linux* a. Prefer C, not C++, but if only C++ still consider it. b. Past contractors tried to do too large of things like templates, huge class structures, etc. so we prefer C over C++ c. Upper level Windows programming such as .NET detracts because client wants them to think about all targets, not just Windows *- Linux experience – Generally need to get a Windows GUI application to be re-compiled and run in Linux* a. Hard to find, so first do a key word search of Linux b. Programming applications background is a big plus c. Looking for GUI experience so they can scope how the Win32 app looks then implement the same experience in Linux d. Client is lacking in Linux background, so need someone that needs minimal help with Linux. *Desired:* - Application development – Have several Win32 applications that need to be compiled as Win64 then tested a. Experience in testing and familiar with looking for corner case scenarios - Low level hardware/software interaction knowledge a. Apps require running a SMI to initiate contact, need candidate to understand difference between virtual and flat addressing ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- *#2 SMTP EMAIL SERVER - C* Elance - United States See original job posting at Elance »<http://www.indeed.com/rc/clk?jk=6f0fdd27079eb247&from=vj&grandfrom=ja&tk=16…> Developer to provide ANSI C software to send (receive not required) email using an SMTP Server. This software must support: ? AUTH_LOGIN (base 64 encoding) ? NTLM ? NTLM2 ? CRAM MD5 This software is targeted to run on an embedded microcontroller but can be developed in Linux or Windows. The following requirements MUST be met: ? No C++, No C++ Classes...etc ? No .NET ? No DLLs ? No Libraries ? No OS dependencies (Windows/QNX/MQX or any other OS) ? No OS Function Calls ? 100% ANSI C Source is required. Desired Skills: C ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Both seem to want to have nothing with C++ (dare I say OOPS?). I work in mainstream industry. Have others on the mail list seen such job postings recently? Is there now a trend against C++ due to somewhat loose type checking and very statefullness? (Unlike Haskell which splits pure and monads very clearly vis strong types). #1 To C++ templates are much more bulky(and ugly) compared Haskell's polymorphic types. However, it caused me to think where we Haskell programmers can do "too large of things". ??? Perhaps an unfair question given that I have no access to the current C++ code. #2 >From the context of #2, I can tell the author didn't mean all of the "?"'s but instead maybe "!". The OS QNX is a hard real-time OS that uses a message passing IPC. I have worked QNX and have written a device driver for QNX. This job posting maybe very unfair argument against C++/OOPs as maybe the thought is that C++ adds to much "non-determinism" to a hard real-time problem. In the real-time extension to the POSIX API is a function "mlock" which locks a process into memory(no swapping) which seriously helps to cut down on non-determinism. Here Haskell would be worse with its garbage collector with its attending non-determinism. No "OS function calls" seems way over the top. Sorry for my meandering thinking .... Regards, Vasili

2 4

Re: [Haskell-cafe] Project Euler: request for comments
by KC 29 Aug '11

29 Aug '11

Try something like the following: -- Project Euler 11 -- In the 20×20 grid below, four numbers along a diagonal line have been marked in red. -- <snip> -- The product of these numbers is 26 × 63 × 78 × 14 = 1788696. -- What is the greatest product of four adjacent numbers in any direction (up, down, left, right, or diagonally) in the 20×20 grid? import Data.List -- Doing the one dimensional case. f011 :: [Int] -> Int f011 (t:u:v:xs) = f011helper t u v xs f011helper :: Int -> Int -> Int -> [Int] -> Int f011helper t u v (w:ws) | ws == [] = t*u*v*w | otherwise = yada nada mada -- What are yada nada mada? -- The 20x20 grid case will become: f0112D :: [[Int]] -> Int -- where [[Int]] is a list of lists of rows, columns, major diagonals, & minor diagonals. On Sun, Aug 28, 2011 at 5:10 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > No. The answer I posted is not good. > It worked, by chance, on a couple of small examples I tried but it > could end up comparing sequence of 4 numbers that where not initially > adjacent. > > On Sun, Aug 28, 2011 at 12:32 AM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: >> Maybe this? >> >> f x@(a:b:c:d:[]) = x >> f (a:b:c:d:e:ys) = if e >= a >> then f (b:c:d:e:ys) >> else f (a:b:c:d:ys) >> >> On Sat, Aug 27, 2011 at 8:26 PM, KC <kc1956(a)gmail.com> wrote: >>> Think of the simplest version of the problem that isn't totally trivial. >>> >>> e.g. A one dimensional list of numbers. >>> >>> What would you do? >>> >>> Note: you only want to touch each element once. >>> >>> The 2 dimensional case could be handled by putting into lists: rows, >>> columns, major diagonals, and minor diagonals. >>> >>> This isn't the fastest way of doing the problem but it has the >>> advantage of avoiding "indexitis". >>> >>> -- -- Regards, KC

2 2

Re: [Haskell-cafe] Make shared library - questions
by David Banas 28 Aug '11

28 Aug '11

> I'm trying to compile shared library. This library will use as part of > plugin for some program. > If I compile library with option -dynamic my library has links for HS > libraries like libHSbase-4.2.0.2-ghc6.12.3.so and so on. > But program has crashed constantly. > > Is it possible to make shared library without -dynamic flag? I want to > try > to make library without dependencies. I struggled with this, too. Here's my makefile, which is now working: 1 GCC = gcc 2 CFLAGS += -I/usr/lib/ghc-6.12.3/include/ -g -fPIC 3 4 HC = ghc 5 HC_OPTS = -cpp $(EXTRA_HC_OPTS) 6 EXTRA_HC_OPTS = -package parsec 7 HC_LOPTS = -no-hs-main -shared -package parsec 8 #GHCOPTS := -prof -auto-all -caf-all 9 10 HSRCS = AMIParse.hs AMIModel.hs ApplicativeParsec.hs 11 CSRCS = ami_model.c ami_test.c 12 SRCS = $(HSRCS) $(CSRCS) 13 OBJS = AMIParse.o AMIModel.o ami_model.o AMIModel_stub.o ApplicativeParsec.o 14 15 .SUFFIXES : .o .hs .hi .lhs .hc .s .c 16 .PHONY : all depend rebuild clean 17 18 all: ami_test 19 20 ami_test: ami_test.o libami.so 21 $(HC) -dynamic -o $@ -L. -lami ami_test.o 22 23 libami.so : $(OBJS) 24 rm -f $@ 25 $(HC) -o $@ $(HC_LOPTS) $^ 26 27 depend: 28 $(HC) -M $(HC_OPTS) $(HSRCS) 29 30 rebuild: 31 $(MAKE) clean 32 $(MAKE) all 33 34 clean: 35 rm -f *.hi *.o *.out ami_test *.so 36 37 # Standard suffix rules 38 .o.hi: 39 @: 40 41 .lhs.o: 42 $(HC) -c $< $(HC_OPTS) 43 44 .hs.o: 45 $(HC) -c $< $(HC_OPTS) 46 47 .o-boot.hi-boot: 48 @: 49 50 .lhs-boot.o-boot: 51 $(HC) -c $< $(HC_OPTS) 52 53 .hs-boot.o-boot: 54 $(HC) -c $< $(HC_OPTS) 55 56 # Individual cases 57 AMIModel_stub.o: AMIModel.hs 58 $(HC) -c $< $(HC_OPTS) 59 60 # DO NOT DELETE: Beginning of Haskell dependencies 61 ApplicativeParsec.o : ApplicativeParsec.hs 62 AMIParse.o : AMIParse.hs 63 AMIParse.o : ApplicativeParsec.hi 64 AMIModel.o : AMIModel.hs 65 AMIModel.o : AMIParse.hi 66 # DO NOT DELETE: End of Haskell dependencies Good luck! -db

1 0

haskell-src-exts should depend on happy
by Ozgur Akgun 28 Aug '11

28 Aug '11

Hi, cabal installing haskell-src-exts fails, because of an unlisted dependency to the happy executable. The following succeeds: cabal install happy; cabal install haskell-src-exts Thanks, Ozgur

3 2

Class instances in haddock documentation missing
by Joachim Breitner 28 Aug '11

28 Aug '11

Hi, the haddock information generated on hackage lists class instances per class and per data type e.g. on http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/Data-Eq.h… or http://hackage.haskell.org/packages/archive/xhtml/3000.2.0.1/doc/html/Text-… For some reason, the documentation generated on Debian does not. Does anybody have an idea why that could be? We use ./Setup haddock --hyperlink-source to build the documentation, using the haddock that is shipped with ghc (2.9.2 at the moment). Greetings, Joachim -- Joachim "nomeata" Breitner Debian Developer nomeata(a)debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C JID: nomeata(a)joachim-breitner.de | http://people.debian.org/~nomeata

1 1

Re: [Haskell-cafe] Project Euler: request for comments
by KC 28 Aug '11

28 Aug '11

Think of the simplest version of the problem that isn't totally trivial. e.g. A one dimensional list of numbers. What would you do? Note: you only want to touch each element once. The 2 dimensional case could be handled by putting into lists: rows, columns, major diagonals, and minor diagonals. This isn't the fastest way of doing the problem but it has the advantage of avoiding "indexitis". On Fri, Aug 26, 2011 at 6:15 PM, Oscar Picasso <oscarpicasso(a)gmail.com> wrote: > Like: > 20*19*21*18 > is bigger than > 100*100*3*2 > ? > > If so I need to think about how to formalize it. > > Thanks for the hint. > > On Fri, Aug 26, 2011 at 8:55 PM, KC <kc1956(a)gmail.com> wrote: >> Is Problem 11 the 4 consecutive #'s problem? >> >> If so what must be true for 4 #'s to have a large product? >> >> Hint: x * y * z * 2 is that going to be larger? >> >> -- >> -- >> Regards, >> KC >> > -- -- Regards, KC

1 0

Modules and a main function
by michael rice 27 Aug '11

27 Aug '11

W/r/t the code below, would somebody please explain the sense of having a main function in a module that is not named Main.hs? Michael From: http://www.haskell.org/haskellwiki/State_Monad ============ module StateGame where import Control.Monad.State -- Example use of State monad -- Passes a string of dictionary {a,b,c} -- Game is to produce a number from the string. -- By default the game is off, a C toggles the -- game on and off. A 'a' gives +1 and a b gives -1. -- E.g -- 'ab' = 0 -- 'ca' = 1 -- 'cabca' = 0 -- State = game is on or off & current score -- = (Bool, Int) type GameValue = Int type GameState = (Bool, Int) playGame :: String -> State GameState GameValue playGame [] = do (_, score) <- get return score playGame (x:xs) = do (on, score) <- get case x of 'a' | on -> put (on, score + 1) 'b' | on -> put (on, score - 1) 'c' -> put (not on, score) _ -> put (on, score) playGame xs startState = (False, 0) main = print $ evalState (playGame "abcaaacbbcabbab") startState

3 5

HJavaScript: representing build-in global function.
by Станислав Черничкин 27 Aug '11

27 Aug '11

Hi Cafe! Does someone know how to represent js build-in global function (such as parseInt(), parseFloat(), eval()) with HJavaScript? Perhaps JConst: JCall (JConst "parseInt") (JString "123")? -- Sincerely, Stanislav Chernichkin.

1 0

Project Euler: request for comments
by Oscar Picasso 27 Aug '11

27 Aug '11

Hi, I order to improve my Haskell skills I started (again) to solve the project euler problems with this language. I am now at problem 11 and would really appreciate any comment about my code in order to make it more elegant or efficient. My solutions can be found here: http://fp.opicasso.com/tag/projecteuler Oscar Picasso

2 5

Re: [Haskell-cafe] How to make callCC more dynamic
by oleg＠okmij.org 27 Aug '11

27 Aug '11

bob zhang wrote: > I thought the right type for ContT should be > newtype ContT m a = ContT {runContT :: forall r. (a-> m r) -> m r} > and > other control operators > shift :: Monad m => (forall r . (a-> ContT m r) -> ContT m r) -> ContT m a > reset :: Monad m => ContT m a -> ContT m a > callCC :: ((a-> (forall r . ContT m r)) -> ContT m a) -> ContT m a > unfortunately, I can not make callCC type check, and don't know how to > do it. Precisely that problem was discussed in http://okmij.org/ftp/continuations/undelimited.html#proper-contM Your ContT is CPS1 in the above article. The article shows why you cannot write callCC with the above type of ContT. The article talks about other types. BTW, if you faithfully defined the monad for undelimited control than shift/reset cannot be expressed. Undelimited continuations are strictly less expressible than delimited ones. The above page gives the pointers to the papers with the proof.

2 2

Re: [Haskell-cafe] Project Euler: request for comments
by KC 27 Aug '11

27 Aug '11

Is Problem 11 the 4 consecutive #'s problem? If so what must be true for 4 #'s to have a large product? Hint: x * y * z * 2 is that going to be larger? -- -- Regards, KC

1 0

Dynamic loading of module
by Arnaud Bailly 26 Aug '11

26 Aug '11

Hello, I stumbled upon this blog post describing a method from dynamically loading modules using GHC api. While trying to test the given method, I got the following error which obviously tells me my packages are not correctly installed but I have no idea how to fix this. D:\projets\>ghc -package ghc main.hs --make <command line>: cannot satisfy -package ghc: ghc-7.0.3-fc75cf67c86ba2c0d64b07024a18d3b4 is unusable due to missing or recursive dependencies: template-haskell-2.5.0.0-7d9b1443ac5ab69e5ed705a487990deb (use -v for more information) When I run ghc-pkg check, I got which obviously is bad. There are problems in package test-framework-0.3.3: dependency "regex-posix-0.94.4-7963833a181f95ba404a78e3e76d835a" doesn't exist There are problems in package QuickCheck-2.4.0.1: dependency "template-haskell-2.5.0.0-e5fd973432385747440288b48f6a6a5a" doesn't exist There are problems in package snap-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package snap-server-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package snap-core-0.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package heist-0.5.2: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package xmlhtml-0.1.5: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package authenticate-0.9.0.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package http-enumerator-0.6.5.1: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package zlib-enum-0.2.1: dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package yesod-static-0.1.0: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "pureMD5-2.1.0.3-cb7a7a936930b56c62f9207838b99efb" doesn't exist There are problems in package yesod-form-0.1.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "data-default-0.2.0.1-14197e607852c0357951d749c098bd34" doesn't exist There are problems in package yesod-core-0.8.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package warp-0.4.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package wai-extra-0.4.0.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package wai-app-static-0.1.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package wai-0.4.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package hjsmin-0.0.14: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package aeson-0.3.2.6: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package tls-extra-0.2.3: dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package tls-0.6.4: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package cprng-aes-0.2.1: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist There are problems in package cryptocipher-0.2.12: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist dependency "tagged-0.2.2-74797b2dae44925f852c0beab1f9f3e6" doesn't exist There are problems in package blaze-textual-0.1.0.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package SHA-1.4.1.3: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist There are problems in package RSA-1.0.6.1: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist dependency "pureMD5-2.1.0.3-cb7a7a936930b56c62f9207838b99efb" doesn't exist There are problems in package persistent-0.5.0: dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package mime-mail-0.3.0: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package hxt-9.1.1: dependency "binary-0.5.0.2-72c84eaab351d41e936261d8d5d416f5" doesn't exist There are problems in package http-types-0.6.4: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "case-insensitive-0.2.0.1-6cb260512f91ae60284372c0208aa00e" doesn't exist There are problems in package hamlet-0.8.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package cryptohash-0.7.0: dependency "cereal-0.3.3.0-81dac2655ecff64c5fc69671490df093" doesn't exist dependency "crypto-api-0.6.1-6854b68ffc32d8880becebcf8b612932" doesn't exist dependency "tagged-0.2.2-74797b2dae44925f852c0beab1f9f3e6" doesn't exist There are problems in package cookie-0.2.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package blaze-html-0.4.1.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package blaze-builder-enumerator-0.2.0.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist There are problems in package attoparsec-text-0.8.5.0: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist There are problems in package asn1-data-0.5.0: dependency "attoparsec-0.8.6.1-3d4c24cfa94f97cbeb7d6cf43ef70284" doesn't exist dependency "attoparsec-enumerator-0.2.0.3-d5a7e5b640b4b27be4c6d0c9a314dd0a" doesn't exist dependency "enumerator-0.4.10-d65a90206db2a5203c1c906e6f58a6c9" doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. test-framework-0.3.3 QuickCheck-2.4.0.1 snap-0.5.1 snap-server-0.5.1 snap-core-0.5.1 heist-0.5.2 xmlhtml-0.1.5 authenticate-0.9.0.1 http-enumerator-0.6.5.1 zlib-enum-0.2.1 yesod-static-0.1.0 yesod-form-0.1.0.1 yesod-core-0.8.2 warp-0.4.0.1 wai-extra-0.4.0.1 wai-app-static-0.1.0 wai-0.4.0 hjsmin-0.0.14 aeson-0.3.2.6 tls-extra-0.2.3 tls-0.6.4 cprng-aes-0.2.1 cryptocipher-0.2.12 blaze-textual-0.1.0.0 SHA-1.4.1.3 RSA-1.0.6.1 persistent-0.5.0 mime-mail-0.3.0 hxt-9.1.1 http-types-0.6.4 hamlet-0.8.2 cryptohash-0.7.0 cookie-0.2.1 blaze-html-0.4.1.1 blaze-builder-enumerator-0.2.0.2 attoparsec-text-0.8.5.0 asn1-data-0.5.0 test-framework-quickcheck2-0.2.10 test-framework-hunit-0.2.6 yesod-persistent-0.1.0 yesod-json-0.1.1 persistent-template-0.5.0.1 certificate-0.9.0.1 haskell-platform-2011.2.0.1 Is there anything I can do to fix this without wiping out and reinstalling haskell platform ? THanks in advance Arnaud

2 1

RFC: decodeFloat
by Daniel Fischer 26 Aug '11

26 Aug '11

Occasionally, the behaviour of decodeFloat and its consequences causes concern and/or bug reports (e.g. http://hackage.haskell.org/trac/ghc/ticket/3898) The main problem is the treatment of NaNs and infinities (that it doesn't distinguish between 0.0 and -0.0 is a minor thing), which are converted as if they were ordinary finite values. Thus, for example, decodeFloat (1/0 :: Double) = (2^52,972) and consequently floor (1/0 :: Double) = 2^1024 (corresponding for round, truncate, ceiling, properFraction), significand (1/0 :: Double) = 0.5, Prelude> uncurry encodeFloat (decodeFloat (1/0 :: Float)) :: Double 3.402823669209385e38 and similar meaningless/nonsensical results for NaNs. At its type, decodeFloat :: RealFloat a => a -> (Integer, Int), I see only two reasonable options, 1. leave the behaviour as it is, just warn about the exceptional cases in the documentation, 2. let decodeFloat raise an error when its argument is a NaN or infinite. Both options have disadvantages, 1. makes it easy to get meaningless results when there's a non-finite value around, 2. incurs a nontrivial performance penalty. Paying that performance penalty when dealing only with known-to-be-good values is undesirable, but so are meaningless results. A third option would be providing both behaviours by adding a function. That could take several forms, a) leave decodeFloat as is and add safeDecodeFloat outside the RealFloat class, that would check the value first and then either raise an error on NaN/Infinity or return a Maybe (Integer, Int), b) add a function to the RealFloat class, either leave decodeFloat as is and add safeDecodeFloat with the behaviour as in a) or change decodeFloat according to 2. and add unsafeDecodeFloat with the current behaviour. The drawback of a) is that safeDecodeFloat would have to perform two checks, while with IEEE Doubles/Floats, the result could be determined by one check (which would also be simpler than each of isNaN and isInfinite). Also, which module should export it? The drawback of b) is adding a function to RealFloat, as if that wasn't big enough already. Since both behaviours allow a default definition in terms of the other, only code that by chance uses the new name would break. What would be the community's preferred way to handle this issue? Cheers, Daniel

1 0

Make shared library - questions
by Sergiy Nazarenko 26 Aug '11

26 Aug '11

Hi ! I'm trying to compile shared library. This library will use as part of plugin for some program. If I compile library with option -dynamic my library has links for HS libraries like libHSbase-4.2.0.2-ghc6.12.3.so and so on. But program has crashed constantly. Is it possible to make shared library without -dynamic flag? I want to try to make library without dependencies. According to http://www.well-typed.com/blog/30 theoretically I can do this but I found this impossible - http://hackage.haskell.org/trac/ghc/ticket/3704 My options to compile: ghc -O2 --make -no-hs-main -dynamic -shared -fPIC -optl '-shared' -optc '-DMODULE=MyLib' -o MyLib.so MyLib.hs module_init.c -optl-Wl -lHSrts-ghc6.12.3 If I try compile without -dynamic I get error: /usr/bin/ld: /usr/local/lib/ghc-6.12.3/base-4.2.0.2/libHSbase-4.2.0.2.a(Conc__270.o): relocation R_X86_64_32 against `base_GHCziConc_ensureIOManagerIsRunning1_closure' can not be used when making a shared object; recompile with -fPIC /usr/local/lib/ghc-6.12.3/base-4.2.0.2/libHSbase-4.2.0.2.a: could not read symbols: Bad value collect2: ld returned 1 exit status My system is: Cenos 5.6 ghc6.12.3 gcc-4.2.1 Cheers, Sergiy

2 1

a minor bug (memory leak) in ListLike package
by bob zhang 26 Aug '11

26 Aug '11

Hi, John, there is a space leak problem in ListLike typeclass, in the method genericLength calclen !accum cl = calclen accum cl = --- thank you for your nice library btw, is there any way to derive ListLike interface automatically? for such type : newtype List a = List {[a]} Best,bob

5 10

hoogle data no connection to host http://code.galois.com/darcs/haskell-platform ...
by informationen 26 Aug '11

26 Aug '11

Hi, i installed Hoogle succesfullly with cabal install hoogle then i try to run hoogle data but the connection to http://code.galois.com/darcs/haskell-platform/haskell-platform.cabal times out. How can i download the data needed for the hoogle command line tool? Greetings Chris

2 1

ANN: shelltestrunner 1.1
by Simon Michael 26 Aug '11

26 Aug '11

I'm pleased to announce shelltestrunner 1.1. shelltestrunner tests command-line programs or arbitrary shell commands. It reads simple declarative tests specifying a command, some input, and the expected output, error output and exit status. Tests can be run selectively, in parallel, with a timeout, in color, and/or with differences highlighted. Projects using it include hledger, yesod, and berp. shelltestrunner is free software released under GPLv3+. New in 1.1: * bump process dependency to allow building with GHC 7.2.1 * new `-a/--all` flag shows all failure output without truncating Home page: http://joyful.com/shelltestrunner Install: $ cabal install shelltestrunner

2 1

ping haskell.org timeout
by Greg Fitzgerald 26 Aug '11

26 Aug '11

"cabal update" hangs. "ping haskell.org" times out. But haskell.org and hackage webpages are loading just fine. What's going on? Thanks, Greg

3 4

Cabal-1.10.1.0 and bytestring-0.9.2.0 hackage problem.
by Bertram Felgenhauer 26 Aug '11

26 Aug '11

Dear list, Cabal-1.10.1.0 contains a bug that causes it to fail to parse the test-suite target of bytestring-0.9.2.0. Since cabal-install parses all package descriptions to before resolving dependencies, users with that version of Cabal are stuck. Now it seems somebody realised this problem and removed bytestring-0.9.2.0 from hackage. However, 1. http://hackage.haskell.org/package/bytestring is now broken. 2. The downloadeble package index (00-index.tar) still contains the bytestring-0.9.2.0 cabal file, so the problem persists. As a workaround, one can remove the cabal file from the downloaded index manually, tar -f ~/.cabal/packages/hackage.haskell.org/00-index.tar --delete bytestring/0.9.2.0 (or rebuild Cabal / cabal-install starting with 'cabal unpack Cabal; cabal unpack cabal-install') But it really needs to be fixed on the hackage server. Best regards, Bertram

3 2

do-re-mi
by Albert Y. C. Lai 25 Aug '11

25 Aug '11

do, a block, a monad block rec, a knot tied in the block mu, a name that calls itself (mu is pronounced as me in modern Greek) forM_, a long long list to run SO, a state aborting threads (SO is stack overflow) la, a state to follow SO T's, tranformers of monads that will bring us back to do

3 2

Haddock chokes on function arguments
by Arnaud Bailly 25 Aug '11

25 Aug '11

Hello, while trying to generate Haddock documentation (Haddock version 2.9.2, (c) Simon Marlow 2006), it chokes on the following fragment -- |Apply a given function over all elements of a list and select one of the -- results. selector :: (Arbitrary b) => [a] -> -- ^ Elements to select from (a -> b) -> -- ^ Constructor to apply to selected element Gen b selector list ctor = oneof (map (return . ctor) list) with the following error message: ' parse error on input `-- ^ Elements to select from I am puzzled as this is exactly how arguments are supposed to be documented, according to http://www.haskell.org/haddock/doc/html/ch03s02.html#id565220 Any clues ? Arnaud

3 4

PhD/PostDoc opening in programming techniques and technologies
by Ralf Laemmel 25 Aug '11

25 Aug '11

PhD/PostDoc opening in programming techniques and technologies in the Software Languages Team [1] in Koblenz. Applicants can safely assume that functional programming plays a huge role in this. The application deadline is 31 Aug. A German description of formalities is available [2]. One essential component of the position is research, teaching as well as development efforts on 101companies [3]. Regards, Ralf [4] [1] http://softlang.wikidot.com/ [2] http://softlang.uni-koblenz.de/docs/Ausschreibungstext_WiMi_HPII-Laemmel.pdf [3] http://101companies.org/ [4] http://softlang.wikidot.com/rlaemmel:home

1 0