- Haskell-Cafe - Haskell.org

Parallel Strategy
by mukesh tiwari 19 Apr '12

19 Apr '12

Hello All I am trying to understand the Strategies ( http://hackage.haskell.org/packages/archive/parallel/3.2.0.2/doc/html/Contr…) and wrote this quick code. import Data.Listimport Control.Parallel.Strategies fun :: [ Int ] -> [ Int ]fun [] = []fun ( x : xs ) = ( x + 1 ) : fun xs main = do let xs = ( fun [ 1..1000000 ] ) `using` parListChunk 500000 rdeepseq return () When I am running this code due to laziness , the xs is not evaluating. [mukesh.tiwari@user ParallelStrat]$ time ./Main +RTS -N1 -s 48,320 bytes allocated in the heap 5,928 bytes copied during GC 38,592 bytes maximum residency (1 sample(s)) 14,656 bytes maximum slop 1 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 0 colls, 0 par 0.00s 0.00s 0.0000s 0.0000s Gen 1 1 colls, 0 par 0.00s 0.00s 0.0002s 0.0002s Parallel GC work balance: -nan (0 / 0, ideal 1) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 1 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 2 (bound) : 0.00s ( 0.00s) 0.00s ( 0.00s) SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled) INIT time 0.00s ( 0.00s elapsed) MUT time 0.00s ( 0.00s elapsed) GC time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 0.00s ( 0.00s elapsed) Alloc rate 48,368,368 bytes per MUT second Productivity 0.0% of total user, 0.0% of total elapsed gc_alloc_block_sync: 0whitehole_spin: 0gen[0].sync: 0gen[1].sync: 0 real 0m0.003suser 0m0.002ssys 0m0.001s [mukesh.tiwari@user ParallelStrat]$ time ./Main +RTS -N2 -s 48,248 bytes allocated in the heap 40 bytes copied during GC 38,440 bytes maximum residency (1 sample(s)) 18,904 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 0 colls, 0 par 0.00s 0.00s 0.0000s 0.0000s Gen 1 1 colls, 0 par 0.00s 0.00s 0.0001s 0.0001s Parallel GC work balance: -nan (0 / 0, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 1 (bound) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 2 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled) INIT time 0.00s ( 0.00s elapsed) MUT time 0.00s ( 0.00s elapsed) GC time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 0.00s ( 0.00s elapsed) Alloc rate 48,248,000,000,000 bytes per MUT second Productivity 100.0% of total user, 0.0% of total elapsed gc_alloc_block_sync: 0whitehole_spin: 0gen[0].sync: 0gen[1].sync: 0 real 0m0.004suser 0m0.000ssys 0m0.004s The library doc suggest that parListChunk divides a list into chunks, and applies the strategy evalList strat to each chunk in parallel. Looking at the source code ( http://hackage.haskell.org/packages/archive/parallel/3.2.0.2/doc/html/src/C…) , list is split into chunks and then strategy is applied parallel to every chunk. Could some one please tell me what is wrong with this concept and why the code above is showing laziness. Regards Mukesh Tiwari

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Template Haskell vs Rewrite Rules?
by Ismael Figueroa Palet 19 Apr '12

19 Apr '12

I'm working on getting annotated versions of all instances of a function of a typeclass, and was wondering what are the relation/differences between Template Haskell and the Rewrite Rules section. Of course this is specific to GHC. Another question, in Racket, primitive function application is denoted #%app. And using macros I can re-export #%app to be a different function f, so a program: (g a) is rewritten into (f g a) is there a way to do the same thing using TH or Rewrite Rules? Thanks -- Ismael

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Administrative questions about Haskell GSOC (Google Summer of Code)
by Ryan Newton 19 Apr '12

19 Apr '12

Hello, As someone new to the GSOC system there are some things I'm confused about. There's a bunch of info out there, and I certainly haven't read all of it. Who are the "program administrator" and "organization administrator" for the Haskell organization? Those roles are mentioned in the manual here: http://en.flossmanuals.net/GSoCMentoring/what-is-gsoc/ Presumably those are the people that actually click "accept" on the melange site: https://google-melange.appspot.com/gsoc/homepage/google/gsoc2012 How many slots did we get? Is the system just to accept the top rated student proposals? If I can find the answers to these questions maybe I can update the Wiki for next year so it has a bit more info for mentors and about the process as well as students: http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2012 Thank you, -Ryan

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Rewrite rules for enumFromTo
by Michael Snoyman 19 Apr '12

19 Apr '12

Hi all, Following a little thread on Reddit[1], I'm trying to add rewrite rules to conduit to make some simple usages of `yield` more efficient. I've pushed these changes to a branch on Github[2]. However, I'm not able to fully optimize the following program: import Data.Conduit import qualified Data.Conduit.List as CL main :: IO () main = do x <- mapM_ yield [1..1000] $$ CL.fold (+) 0 print (x :: Int) Ideally, I would like to rewrite the entirety of `mapM_ yield [1..1000]` to `Data.Conduit.List.enumFromTo 1 1000` and thereby avoid the intermediate list. However, whenever I add such a rule, it doesn't fire. Instead, -ddump-rule-firings tells me: Rule fired: Class op enumFromTo Rule fired: mapM_ yield Rule fired: Class op + Rule fired: Class op >>= Rule fired: Class op show Rule fired: eftIntList I'm quite a novice at rewrite rules; can anyone recommend an approach to get my rule to fire first? Thanks, Michael PS: In case you're wondering, the `mapM_ yield` rule turns `mapM_ yield` into `yieldMany`. So ideally, I'd like to have another rule that turns `yieldMany [x..y]` into `Data.Conduit.List.enumFromTo x y`. [1] http://www.reddit.com/r/haskell/comments/sdzmx/many_ways_to_skin_a_conduit/… [2] https://github.com/snoyberg/conduit/tree/rewrite

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Haskell Weekly News: Issue 223
by Daniel Santa Cruz 19 Apr '12

19 Apr '12

Welcome to issue 223 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 8 to 14, 2012. Quotes of the Week * merijn: I'm tempted to just do unsafePerformIO newEmptyMVar at the top level quicksilver: I can't really be expected to deal with your sinfulness. That's between you and your god. * acowley: Good haskell code is 20 LANGUAGE pragmas, 40 imports, then one line of perl. * deggis: oh. running GHC HEAD. must try that next week if coffee just someday isn't enough * dmwit: hGetContents does not close its handle. dmwit: hGetContents semicloses its handle. * monochrom: isTrue = (unsafeCoerce :: Either a b -> Bool) . (unsafeCoerce :: Maybe c -> Either a b) . (unsafeCoerce :: Bool -> Maybe c) * dmwit: For basically all good properties P, IEEE 754 is not P. * Cale: Little known fact: For any positive integer n, the infinite sequence of Project Euler problems has only finitely many elements whose solution is not divisible by n. Top Reddit Stories * Announcing Yesod 1.0 Domain: yesodweb.com, Score: 101, Comments: 42 On Reddit: [1] http://goo.gl/izD19 Original: [2] http://goo.gl/oTSto * Why reasoning about space usage in Haskell is hard Domain: ro-che.info, Score: 63, Comments: 14 On Reddit: [3] http://goo.gl/yIkI4 Original: [4] http://goo.gl/IAQtu * GHC HEAD now has type level natural number/ literals Domain: github.com, Score: 63, Comments: 18 On Reddit: [5] http://goo.gl/GfGbB Original: [6] http://goo.gl/Lkp6v * Working Together Domain: yesodweb.com, Score: 62, Comments: 31 On Reddit: [7] http://goo.gl/o3G85 Original: [8] http://goo.gl/jBdJA * How less is more : polymorphic types can improve safety even in monomorphic functions Domain: blog.malde.org, Score: 61, Comments: 13 On Reddit: [9] http://goo.gl/fzUlO Original: [10] http://goo.gl/WHE3A * A Hopefully Fair and Useful Comparison of Haskell Web Frameworks Domain: softwaresimply.blogspot.com, Score: 60, Comments: 30 On Reddit: [11] http://goo.gl/WuDuL Original: [12] http://goo.gl/DXBA8 * First impressions of Haskell: A review of my Haskell adventure Domain: binarysculpting.com, Score: 46, Comments: 36 On Reddit: [13] http://goo.gl/gG0fl Original: [14] http://goo.gl/ZqUT3 * A "radix tree" import syntax? Domain: self.haskell, Score: 41, Comments: 26 On Reddit: [15] http://goo.gl/kBOLZ Original: [16] http://goo.gl/kBOLZ * Using ContT to please the eye Domain: self.haskell, Score: 28, Comments: 15 On Reddit: [17] http://goo.gl/hbFrs Original: [18] http://goo.gl/hbFrs * Designing a DCPU-16 emulator in Haskell: on determinism and I/O Domain: jaspervdj.be, Score: 28, Comments: 6 On Reddit: [19] http://goo.gl/KHIgP Original: [20] http://goo.gl/NT89i Top StackOverflow Questions * What are type quantifiers? votes: 15, answers: 3 Read on SO: [21] http://goo.gl/d3hnH * Haskell: How does 'atomicModifyIORef' work? votes: 12, answers: 2 Read on SO: [22] http://goo.gl/3b5dK * Is there a runtime penalty associated with typeclasses? votes: 12, answers: 1 Read on SO: [23] http://goo.gl/Isw7k * Timing out pure functions votes: 11, answers: 1 Read on SO: [24] http://goo.gl/aTzVG * Haskell - simple constructor comparison (?) function votes: 11, answers: 3 Read on SO: [25] http://goo.gl/ZC6CC * Partial Application with Infix Functions votes: 10, answers: 3 Read on SO: [26] http://goo.gl/QvabF * Haskell: Why is there no type mismatch (and why does this compile)? votes: 9, answers: 2 Read on SO: [27] http://goo.gl/1gxFE * “Dependent optional” data in Haskell votes: 9, answers: 4 Read on SO: [28] http://goo.gl/9K5Wx * How can I help SpecConstr in GHC? votes: 8, answers: 2 Read on SO: [29] http://goo.gl/PGa4C * How to get good performance when writing a list of integers from 1 to 10 million to a file? votes: 7, answers: 2 Read on SO: [30] http://goo.gl/Kym6r * Efficiently turn a ByteString into a hex representation votes: 7, answers: 1 Read on SO: [31] http://goo.gl/aq2ct Until next time, Daniel Santa Cruz References 1. http://www.yesodweb.com/blog/2012/04/announcing-yesod-1-0 2. http://www.reddit.com/r/haskell/comments/s0tr2/announcing_yesod_10/ 3. http://ro-che.info/articles/2012-04-08-space-usage-reasoning.html 4. http://www.reddit.com/r/haskell/comments/rzu8a/why_reasoning_about_space_us… 5. https://github.com/ghc/packages-base/blob/b5b5ec18819fb85ebf1bdb6345ac03178… 6. http://www.reddit.com/r/haskell/comments/s0vln/ghc_head_now_has_type_level_… 7. http://www.yesodweb.com/blog/2012/04/working-together 8. http://www.reddit.com/r/haskell/comments/s2ei5/working_together/ 9. http://blog.malde.org/posts/polymorphic-types-are-safer.html 10. http://www.reddit.com/r/haskell/comments/s7q3b/how_less_is_more_polymorphic… 11. http://softwaresimply.blogspot.com/2012/04/hopefully-fair-and-useful-compar… 12. http://www.reddit.com/r/haskell/comments/s3pbm/a_hopefully_fair_and_useful_… 13. http://binarysculpting.com/2012/04/12/a-review-of-my-haskell-adventure/ 14. http://www.reddit.com/r/haskell/comments/s6okb/first_impressions_of_haskell… 15. http://www.reddit.com/r/haskell/comments/s2o8p/a_radix_tree_import_syntax/ 16. http://www.reddit.com/r/haskell/comments/s2o8p/a_radix_tree_import_syntax/ 17. http://www.reddit.com/r/haskell/comments/s49kk/using_contt_to_please_the_ey… 18. http://www.reddit.com/r/haskell/comments/s49kk/using_contt_to_please_the_ey… 19. http://jaspervdj.be/posts/2012-04-12-st-io-dcpu-16.html 20. http://www.reddit.com/r/haskell/comments/s5xqb/designing_a_dcpu16_emulator_… 21. http://stackoverflow.com/questions/10062253/what-are-type-quantifiers 22. http://stackoverflow.com/questions/10102881/haskell-how-does-atomicmodifyio… 23. http://stackoverflow.com/questions/10148897/is-there-a-runtime-penalty-asso… 24. http://stackoverflow.com/questions/10071560/timing-out-pure-functions 25. http://stackoverflow.com/questions/10112733/haskell-simple-constructor-comp… 26. http://stackoverflow.com/questions/10131300/partial-application-with-infix-… 27. http://stackoverflow.com/questions/10091874/haskell-why-is-there-no-type-mi… 28. http://stackoverflow.com/questions/10136222/dependent-optional-data-in-hask… 29. http://stackoverflow.com/questions/10145954/how-can-i-help-specconstr-in-ghc 30. http://stackoverflow.com/questions/10080273/how-to-get-good-performance-whe… 31. http://stackoverflow.com/questions/10099921/efficiently-turn-a-bytestring-i…

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Visi 0.1 is available for OS X
by David Pollak 18 Apr '12

18 Apr '12

Folks, Visi 0.1 is available as an executable for OS X 10.7 ( http://tunaforcats.com/visi_0_1.tar.bz ) The blog post announcement is available at http://blog.goodstuff.im/visi-01-for-os-x/ Visi is written mostly in Haskell (which is totally awesome, btw). I'll be hacking on Visi this weekend at BayHac '12 ( http://www.haskell.org/haskellwiki/BayHac2012) Thanks, David -- Visi.Pro, Cloud Computing for the Rest of Us http://visi.pro Lift, the simply functional web framework http://liftweb.net Follow me: http://twitter.com/dpp Blog: http://goodstuff.im

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Re: [Haskell-cafe] [Haskell] ANN: cabal-install-0.14.0
by Felipe Almeida Lessa 18 Apr '12

18 Apr '12

On Tue, Apr 17, 2012 at 1:59 PM, Andres Löh <andres.loeh(a)googlemail.com> wrote: > * Completely new modular dependency solver (default in most cases) Great! =D -- Felipe.

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ghc/profiling and very big "entries"
by Emmanuel CHANTREAU 18 Apr '12

18 Apr '12

Hello I got this line in the profile output: COST CENTRE MODULE no. entries %time %alloc %time %alloc ticks bytes addDeduction L42s.Maths.Prover.Base 22730 2362045 1.1 4.6 52.3 52.6 81 614808848 And it seems that "addDeduction" has been called 2 362 045 times ? But from other (personal) log files this function should be called less than 10 000 times. I wonder if the laziness of haskell can grow the "entries" field which is defined by: "The number of times this particular point in the call tree was entered.", but what "enter" means for ghc is a question for me. Thank you for answering -- Emmanuel Chantréau http://www.maretmanu.org/emmanuel/

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ANNOUNCE: haskell-src-exts-1.13.2
by Niklas Broberg 18 Apr '12

18 Apr '12

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.13.2! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Darcs repo: http://code.haskell.org/haskell-src-exts This release contains only a few small tweaks and bug-fixes. Changelog: 1.13.1 --> 1.13.2 =============== * Fix the bug with the precedence of unary prefix minus. Previously it was resolved as binding more tightly than any infix operator, now it is correctly treated as having the same fixity as binary infix minus. 1.13.0 --> 1.13.1 =============== * Allow an optional semi before the closing tag of an element. This achieves a similar effect for XmlSyntax in do blocks as DoAndIfThenElse does for the if construct. No more need to indent the closing tag one step further than the opening tag. * Add a dummy 'noLoc :: SrcLoc' to L.H.E.SrcLoc, to use when generating code. It could definitely be done more elegantly, but not without inducing another major version bump, so later. * Fix a regression from 1.11.x where the parser would crash upon encountering non-simple class/data declaration heads, e.g. 'data A [a]'. Now fails with a parse error as intended. Cheers, /Niklas

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ANNOUNCE: pipes-core 0.1.0
by Paolo Capriotti 17 Apr '12

17 Apr '12

I'm pleased to announce the release of version 0.1.0 of pipes-core, a library for efficient, safe and compositional IO, similar in scope to iteratee and conduits. http://hackage.haskell.org/package/pipes-core This release fixes a mistake in the previous version which violated the category laws in certain cases. I have now written a fairly explicit proof of the category laws for the current implementation, which I'll try to keep updated as the library evolves: https://github.com/pcapriotti/pipes-core/wiki/Category-laws-for-pipes --- # CHANGELOG for pipes-core: ## Version 0.1.0 - Significant simplification of the internals. - Removed `ensure` primitive. # CHANGELOG for pipes-extra: ## Version 0.1.0 - Improved naming in Control.Pipe.Coroutine. - Replaced ChunkPipe with PutbackPipe. --- BR, Paolo Capriotti

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