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ghci Vim completion within Vim - need some advice
by Marc Weber 18 Mar '11

18 Mar '11

Hi, https://github.com/MarcWeber/vim-addon-async implements a hacky way to run external processes asynchronously. An external helper application send stdout of the process to Vim which adds the bytes to the buffer. Its not perfect but quite usable. Now I'd like to show the completion of \t sent to ghci to the user. I've done so for Ruby, Python and Scala: Vim sends input to ghci, and the reply is catched and put into Vim's completion list. issue 1): ghci's tab only works if its connected to a "terminal". This can be fixed easily by using a pseudo terminal issue 2): ghci's prompt sends data to /dev/tty (the controlling terminal) rather than to stdout/err. I don't know how to fix issue 2). Any ideas? The result could look like this python REPL screenshot: http://mawercer.de/~marc/vim-addon-async-python-repl.jpg Marc Weber

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Re: [Haskell-cafe] [Agda] Defining subtraction for naturals
by wren ng thornton 18 Mar '11

18 Mar '11

On 3/17/11 4:22 PM, Martin Escardo wrote: > On 17/03/11 18:35, wren ng thornton wrote: >> (2) Use saturating subtraction, i.e. if the result would drop below zero >> then return zero; > > This is what people working with quantales do. > > Subtraction y-z, when it exists, is the solution in s to the equation > s+z =y. > > Truncated subtraction y - z is the supremum of the set of solutions s to > the inequality s+z <= y, when this supremum exists. (In your example, > when z>y, the set of solutions is empty, and the empty set has supremum > zero.) > > This amounts to saying that the truncated subtraction function (-) - z > is the right adjoint to the addition function (-) + z. > > So (2) is very natural. Thanks! That's exactly the kind of thing I was looking for. I'd been needlessly thinking of it as a hack :) -- Live well, ~wren

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X11 package bug: XClientMessageEvent long data
by Dylan Alex Simon 18 Mar '11

18 Mar '11

Does anyone know the current maintenance status of the X11 package? I emailed Spencer Janssen a number of months ago and never heard back. So, I'll put this here in case any one else runs into it or can get it to the right place. This is a proposed bug fix for a problem I ran into using xmonad client messages to send remote commands on 64LP architectures (i.e., amd64), wherein the C X11 library and Haskell's disagree about the size of client message arguments. Tue Nov 16 23:41:49 EST 2010 Dylan Simon <dylan(a)dylex.net> * change XClientMessageEvent long data The XClientMessageEvent.data.l field is actually a long, not an int, so it must be interpreted as such, even though format is set to 32 in this case. Ostensibly this is an Xlib bug, but it is unlikely to be fixed there. diff -rN -u old-src/Graphics/X11/Xlib/Extras.hsc new-src/Graphics/X11/Xlib/Extras.hsc --- old-src/Graphics/X11/Xlib/Extras.hsc 2011-03-15 22:40:39.687844812 -0400 +++ new-src/Graphics/X11/Xlib/Extras.hsc 2011-03-15 22:40:39.724522814 -0400 @@ -601,7 +601,7 @@ 16 -> do a <- peekArray 10 datPtr return $ map fromIntegral (a::[Word16]) 32 -> do a <- peekArray 5 datPtr - return $ map fromIntegral (a::[Word32]) + return $ map fromIntegral (a::[CLong]) _ -> error "X11.Extras.clientMessage: illegal value" return $ ClientMessageEvent { ev_event_type = type_

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How large is the Haskell community ?
by Aaron Gray 17 Mar '11

17 Mar '11

I was wondering if anyone had an idea or estimate as to how large the Haskell community is ? Aaron

18 22

Haskell report minutiae
by wren ng thornton 17 Mar '11

17 Mar '11

So I have a rules-lawyering question about how specified the overflow behavior is for the types Int and Word. * In the Haskell 2010 report it seems to be specified that (sections 18.1, 23.1): "All arithmetic is performed modulo 2^n, where n is the number of bits in the type." And this seems to apply to Int and Word as well as Int8, Word8, Int16, Word16, Int32, Word32, Int64, Word64. * However, in the Haskell 98 report ---and this verbiage is retained in the same section of H2010--- there is no such guarantee (section 6.4): "The results of exceptional conditions (such as overflow or underflow) on the fixed-precision numeric types are undefined; an implementation may choose error (_|_, semantically), a truncated value, or a special value such as infinity, indefinite, etc." * However, the FFI addendum to H98 does specify modulo behavior for the Int8, Word8, Int16, Word16, Int32, Word32, Int64, Word64 types (section 5.3): "There is, however, the additional constraint that all arithmetic on the fixed-sized types is performed modulo 2^n." But it is unclear whether this also applies to Int and Word. So when it comes to interpreting the report(s) and ensuring proper implementation, which is it? Are Int and Word arithmetic modular, or not? Did the specification change between H98 and H98+FFI or between H98+FFI and H2010? -- Live well, ~wren

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Weird warnings from recent GHC snapshot
by Michael Vanier 17 Mar '11

17 Mar '11

I run haskell on Mac OS X (Snow Leopard). After upgrading my Xcode installation to 4.0 I had a tricky time getting ghc working again; the version bundled with the Haskell Platform no longer works and I had to compile a recent snapshot (ghc-7.1.20110315) from source. This worked fine, but now when I compile my code I keep getting really weird warnings. For instance: ld: warning: could not create compact unwind for .LFB3: non-standard register 5 being saved in prolog and SpecConstr Function `$w$j{v s3hL} [lid]' has one call pattern, but the limit is 0 Use -fspec-constr-count=n to set the bound Use -dppr-debug to see specialisations SpecConstr Function `$w$j{v s3ic} [lid]' has two call patterns, but the limit is 1 Use -fspec-constr-count=n to set the bound Use -dppr-debug to see specialisations The code seems to work, but this is quite irritating. Is there anything that can be done about these warnings? Thanks, Mike

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Lazy evaluation and tail-recursion
by Yves Parès 17 Mar '11

17 Mar '11

Hello, A question recently popped into my mind: does lazy evaluation reduce the need to "proper" tail-recursion? I mean, for instance : fmap f [] = [] fmap f (x:xs) = f x : fmap f xs Here fmap is not tail-recursive, but thanks to the fact that operator (:) is lazy, I think that it may still run in constant space/time, am I right?

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Data.Time.Calendar.Day does not seem to have an instance for Read
by C K Kashyap 17 Mar '11

17 Mar '11

Hi, I was wondering if this is a defect - Prelude> import Data.Time.Calendar Prelude Data.Time.Calendar> read "2011-10-10" :: Day <interactive>:1:1: No instance for (Read Day) arising from a use of `read' Possible fix: add an instance declaration for (Read Day) In the expression: read "2011-10-10" :: Day In an equation for `it': it = read "2011-10-10" :: Day Prelude Data.Time.Calendar> The documentation says that Day has an instance for Read. Regards, Kashyap

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Data.ByteString.Lazy.ByteString vs Data.ByteString.Lazy.Internal.ByteString
by C K Kashyap 17 Mar '11

17 Mar '11

Hi, I noticed that even though I declare the type of a function in my code as Data.ByteString.Lazy.ByteString ... when I check it out in ghci using :t, it shows this - Data.ByteString.Lazy.Internal.ByteString Is this expected? Regards, Kashyap

7 11

Type trickery
by Andrew Coppin 17 Mar '11

17 Mar '11

The well-known ST monad uses an ingenious hack to make it impossible for distinct ST computations to interact with each other. Is there a way to do something similar so that I can create "cursors" that reference a (mutable) container, and then write a function that takes two cursor arguments which are statically guaranteed to refer to the same container?

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Haskell Weekly News: Issue 173
by Daniel Santa Cruz 17 Mar '11

17 Mar '11

Welcome to issue 173 of the HWN, a newsletter covering developments in the [1]Haskell community. This release covers the week of March 06-12, 2011. For a (easier to read) HTML version goto: http://bit.ly/gQCQHf Announcements Bas van Dijk [2]annouced updates to regions (0.9), regions-mtl (0.3.1.5), and regions-monadstf (0.3.1.5) Don Stewart [3]gave us reason to celebrate with the announcement of the new Haskell Platform 2011.2, the "single, standard Haskell distribution for everyone." Most of you have probably already heard/gotten this new release, but in case you haven't... Remi Turk [4]annouced the first release of cinvoke, "a binding to the C library cinvoke, allowing functions to be loaded and called whose names and types are not known before run-time." Quotes of the Week * kmc: [After discussing monads, containers, and tortillas] therefore the key difference between a container and a monad is delicious carne asada * edwardk: [you mean #haskell has a 2 phD/nick average ?] clearly this is why SPJ stays away, he doesn't want to dilute that metric. * byorgey: The magic of printf is that it is well-typed but you need not actually know what the types are. * monochrom: How do I extract the IO out of IO String? * kmc: ghc -XTwitter -ddump-tweets * xplat: because, you know, you have to write a quicksort so differently in java than any other language. first you create an AbstractSequenceSubrangeFactory interface, and then you create the implementation for ArrayList ... Top Reddit Stories * The Haskell Platform 2011.2 is out!: From (hackage.haskell.org.nyud.net) scored 80 with 34 comments. Read on [5]reddit or the [6]original post. * Umm... yes... you can now write new GHC compiler passes in Coq (!!?): From (cs.berkeley.edu) scored 55 with 16 comments. Read on [7]reddit or the [8]original post. * The Type Technology Tree (mapping Type Extensions in GHC): From (blog.ezyang.com) scored 53 with 5 comments. Read on [9]reddit or the [10]original post. * a message from Tokyo: From (haskell.org) scored 47 with 9 comments. Read on [11]reddit or the [12]original post. * Haskellâs Niche: Hard Problems: From (cdsmith.wordpress.com) scored 43 with 16 comments. Read on [13]reddit or the [14]original post. * Functional flocks : modelling and visualizing flocking behavior in Haskell: From (syntacticsalt.com) scored 21 with 0 comments. Read on [15]reddit or the [16]original post. * Tech Talk Video: Faster Persistent Data Structures Through Hashing: From (corp.galois.com) scored 20 with 5 comments. Read on [17]reddit or the [18]original post. * Recursion is a low-level operation: From (blog.fogus.me), scored 18 with 25 comments. Read on [19]reddit or the [20]original post. * Yesod 1.0 Roadmap: From (docs.yesodweb.com) scored 17 with 9 comments. Read on [21]reddit or the [22]original post. * Type inference weirdness: From (self.haskell), scored 13 with 26 comments. Read on [23]reddit. Top StackOverflow Answers * [25]haskell beginner - recursive recursion votes: 10 This can be improved substantially by using a different algorithm: The smallest number which can be divided by a set of numbers (in this case, the set is [1..10]) is the least common multiple of those numbers. Haskell even has a least common multiple function (lcm) built-in which you can use: Prelude> foldl lcm 1 [1..10] 2520 If you prefer not to use ... * [26]Reasoning laziness votes: 10 I believe the problem is that Data.Vector is not strict in its elements. So although your reasoning is right, when accumulating the histogram your thunks looks like: <1+(1+(1+0)) (1+(1+0)) 0 0 (1+(1+(1+(1+0)))) ... > Rather than <3 2 0 0 4 ...> And only when you print are those sums computed. I don't see a strict accum function in the ... * [27]What are some compelling use cases of infinite data structures? votes: 13 Here are two examples, one big and one small: Why Functional Programming Matters by John Hughes has a good example, of a chess game. The move tree for a chess game is not actually infinite, but its big enough that it might as well be infinite (call it "near-infinite"). In a strict language you can't actually treat it as a tree, because there isn't enough ... * [28]Computational cost of applicative style votes: 14 I really suspect they'll be compiled down to the same thing in most cases. I did a tiny test, import Control.Applicative test1 :: (b -> b -> c) -> (a -> b) -> (a -> b) -> a -> c test1 bracket takeConn putConn pool = bracket (takeConn pool) (putConn pool) test2 :: (b -> b -> c) -> (a -> b) -> (a -> b) -> a -> ... Top StackOverflow Questions * what does "exists" mean in Haskell type system? (votes: 20, answers: 4) [29]read * Is there a book which teaches about compilers using Haskell? (votes: 12, answers: 3) [30]read * Reasoning laziness (votes: 10, answers: 1) [31]read * What are some compelling use cases of infinite data structures? (votes: 10, answers: 5) [32]read * The difference between +1 and -1 (votes: 9, answers: 3) [33]read About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. I'm in dire need of finding good "quotes of the week". If you happen to come across any, please don't hesitate to send it along. Until next time, Daniel Santa Cruz References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/18554 3. http://article.gmane.org/gmane.comp.lang.haskell.platform/1519 4. http://article.gmane.org/gmane.comp.lang.haskell.general/18543 5. http://www.reddit.com/r/haskell/comments/g1g0a/the_haskell_platform_20112_i… 6. http://hackage.haskell.org.nyud.net/platform/?2011-2 7. http://www.reddit.com/r/haskell/comments/fze1q/umm_yes_you_can_now_write_ne… 8. http://www.cs.berkeley.edu/~megacz/coq-in-ghc/ 9. http://www.reddit.com/r/haskell/comments/fz0ve/the_type_technology_tree_map… 10. http://blog.ezyang.com/2011/03/type-tech-tree/ 11. http://www.reddit.com/r/haskell/comments/g2m0t/a_message_from_tokyo/ 12. http://www.haskell.org/pipermail/glasgow-haskell-users/2011-March/020166.ht… 13. http://www.reddit.com/r/haskell/comments/g382d/haskells_niche_hard_problems/ 14. http://cdsmith.wordpress.com/2011/03/13/haskells-niche-hard-problems/ 15. http://www.reddit.com/r/haskell/comments/g2v75/functional_flocks_modelling_… 16. http://syntacticsalt.com/2011/03/10/functional-flocks/ 17. http://www.reddit.com/r/haskell/comments/g030j/tech_talk_video_faster_persi… 18. http://corp.galois.com/blog/2011/3/8/tech-talk-video-faster-persistent-data… 19. http://www.reddit.com/r/haskell/comments/g1ajf/recursion_is_a_lowlevel_oper… 20. http://blog.fogus.me/2011/03/09/recursion-is-a-low-level-operation/ 21. http://www.reddit.com/r/haskell/comments/fywf1/yesod_10_roadmap/ 22. http://docs.yesodweb.com/blog/road-to-yesod-1-0 23. http://www.reddit.com/r/haskell/comments/g2aiv/type_inference_weirdness/ 25. http://stackoverflow.com/questions/5250012/haskell-beginner-recursive-recur… 26. http://stackoverflow.com/questions/5274700/reasoning-laziness/5275489#52754… 27. http://stackoverflow.com/questions/5284458/what-are-some-compelling-use-cas… 28. http://stackoverflow.com/questions/5230043/computational-cost-of-applicativ… 29. http://stackoverflow.com/questions/5235116/what-does-exists-mean-in-haskell… 30. http://stackoverflow.com/questions/5234398/is-there-a-book-which-teaches-ab… 31. http://stackoverflow.com/questions/5274700/reasoning-laziness 32. http://stackoverflow.com/questions/5284458/what-are-some-compelling-use-cas… 33. http://stackoverflow.com/questions/5210182/the-difference-between-1-and-1

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Re: [Haskell-cafe] haskell mailing lists followup?
by wren ng thornton 16 Mar '11

16 Mar '11

On 3/14/11 2:01 AM, pteer(a)acanac.net wrote: > Hi Wren; > > I CC'ed you on email I sent Thu, 10 Mar after seeing your post on > haskell-cafe Thu Mar 10 07:24:45 CET "Haskell mail server fail?". Did > you see that email? I didn't see it; though it looks like it just showed up in my inbox. The only other replies I've seen are from: [cc: haskell-cafe] On 3/10/11 2:18 AM, David Virebayre [cc: haskell-cafe] On 3/10/11 7:44 AM, Daniel Fischer Earlier today I got messages from the three lists I'm on (libraries@, haskell-cafe@, glasgow-haskell-users@) about delivery being disabled due to excessive bounces. The re-enabling codes in those emails were expired ---which is supposed to take a few days--- despite only getting them at 4:00am today. I've since logged in to re-enable delivery, though it'll only be a matter of time until it happens again. > Have you tried to reply to pteer(a)acanac.net? Have > you started seeing Haskell mailing list traffic again? Nope (well now I have), and nope. Actually, while writing this, I did just see: [Haskell-cafe] ANN: Monad.Reader special Poetry and Fiction Edition On 3/15/11 7:35 PM, Brent Yorgey come through. So maybe re-enabling delivery fixed it this time? > [...] I've seen web pages > reporting problems with google-based lists tripping over SPF when > misconfigured for forwarding, and so forth. It would be helpful to > see the error messages. Yeah, I've run into problems with SPF before. But since it's not just me I don't think it's an @freegeek.org problem. > I've successfully transferred messages to myself dummied up using smtp > connecting directly to my haskell-cafe list address. I haven't > received any approval messages from recent attempts to set up new > target addresses on the same receiving email host. Non-Haskell > mailing lists have continued uninterrupted, but haskell lists to > teerlist(a)acanac.net last received on 04 Mar. Ditto. My other mailing lists are coming through fine (e.g., agda(a)lists.chalmers.se) which also indicates the issue is on the @haskell.org side. -- Live well, ~wren

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Writing functions over GADTs
by Dominic Mulligan 16 Mar '11

16 Mar '11

Dear all, I'm working on a small proof assistant in Haskell. In the logic that I'm implementing it's very important that I distinguish between `large' and `small' types for consistency reasons. I have worked to get this distinction reflected in my types with the use of GADTs, like so: data Type :: * -> * where SVariable :: Decoration -> Type Small LVariable :: Decoration -> Type Large Bound :: Index -> Type Small Universal :: Decoration -> Type a -> Type Large LFormer :: Decoration -> ArgList Large -> Variety -> Type Large SFormer :: Decoration -> ArgList Small -> Variety -> Type Small where: data ArgList :: * -> * where Empty :: ArgList a SmallCons :: Type Small -> ArgList a -> ArgList a LargeCons :: Type Large -> ArgList a -> ArgList Large Great, but one problem. How do you write functions over these data types? Consider as an example the function `toList', which drops an `ArgList a' down into a vanilla Haskell list `[a]'. Attempting a straightforward implementation like so: toList :: ArgList a -> [Type a] toList Empty = [] toList (SmallCons h t) = h : toList t toList (LargeCons h t) = h : toList t Gives a type error, as the type variable `a' gets instantiated to Small when typechecking the second clause of the function definition, and Large when type checking the third clause. Perversely, it's much easier to write a more complex function: forget :: (forall a. Type a -> b) -> ArgList a -> [b] forget f Empty = [] forget f (SmallCons h t) = f h : forget f t forget f (LargeCons h t) = f h : forget f t As we can use RankNTypes to make things `more polymorphic', and prevent type variables being instantiated too soon. It seems plausible that `toList' could be defined in terms of `forget', taking `f' to be the identity function, but this does not work either as we then get type errors about inferred types being less polymorphic than expected. So, is there a standard way writing function like `toList' in Haskell? Am I going about thinking of using GADTs in the wrong way? I've searched everywhere and cannot seem to find the correct solution (and I'm now at the very border of my Haskell knowledge). My coworker showed me a way of doing this in O'Caml using polymorphic variants. This allows us to form a subtype of both `Small' and `Large'. I'm taken to believe that HList can simulate many of the properties that polymorphic variants enjoy, so perhaps the answer lies there? Any help gratefully received. Regards, Dominic Mulligan

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Static linking problem // CentOS 5.5 - GHC 6.12.3
by frode k 16 Mar '11

16 Mar '11

I've installed GHC version 6.12.3 on CentOS 5.5 x86_64. I'm trying to run a very simple Haskell program as CGI following the guide at: http://www.haskell.org/haskellwiki/Practical_web_programming_in_Haskell My .hs file I'm trying to use looks like this: -------------------------------------------------------------- import Network.CGI import Text.XHtml page :: Html page = body << h1 << "Hello World!" cgiMain :: CGI CGIResult cgiMain = output $ renderHtml page main :: IO () main = runCGI $ handleErrors cgiMain -------------------------------------------------------------- If I compile it using dynamic linking I can run it from the command line, since the environment is correct: # ghc haskell_v2.hs --make -o haskell_v2.cgi Linking haskell_v2.cgi ... # ./haskell_v2.cgi Content-type: text/html; charset=ISO-8859-1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" " http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" ><body ><h1 >Hello World!</h1 ></body ></html > [root@vps-1040050-2953 haskellTest]# However I do of course want to run it through CGI on a webserver. I'm running lighttpd. If I try to run the file compiled above I get "500 - Internal Server Error", most likely since the enviroment is not correct for dynamic linked files: # ldd haskell_v2.cgi librt.so.1 => /lib64/librt.so.1 (0x00002aff22c25000) libutil.so.1 => /lib64/libutil.so.1 (0x00002aff22e2e000) libdl.so.2 => /lib64/libdl.so.2 (0x00002aff23031000) libgmp.so.3 => /usr/lib64/libgmp.so.3 (0x00002aff23236000) libm.so.6 => /lib64/libm.so.6 (0x00002aff2346f000) libc.so.6 => /lib64/libc.so.6 (0x00002aff236f2000) libpthread.so.0 => /lib64/libpthread.so.0 (0x00002aff23a4a000) /lib64/ld-linux-x86-64.so.2 (0x00002aff22a08000) # file haskell_v2.cgi haskell_v2.cgi: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped Hence I wanted to use static linking ( http://www.haskell.org/haskellwiki/Web/Literature/Static_linking ). However trying to compile using the "-optl-static" option fails: # ghc haskell_v2.hs --make -optl-static -fforce-recomp -o haskell_v2.cgi [1 of 1] Compiling Main ( haskell_v2.hs, haskell_v2.o ) Linking haskell_v2.cgi ... /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(HsNet.o): In function `hsnet_getaddrinfo': HsNet.c:(.text+0x11): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sAwu_info': (.text+0xd45d): warning: Using 'gethostbyaddr' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syh4_info': (.text+0x4364): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sygm_info': (.text+0x424f): warning: Using 'gethostent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syx3_info': (.text+0x5318): warning: Using 'sethostent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sxz5_info': (.text+0x12c6): warning: Using 'endhostent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syJY_info': (.text+0x605d): warning: Using 'getnetbyaddr' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sycm_info': (.text+0x3e75): warning: Using 'getnetbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sybC_info': (.text+0x3de7): warning: Using 'getnetent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syyg_info': (.text+0x5458): warning: Using 'setnetent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sxz5_info': (.text+0x1296): warning: Using 'endnetent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syGE_info': (.text+0x5d42): warning: Using 'getprotobynumber' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sylC_info': (.text+0x474f): warning: Using 'getprotoent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syvQ_info': (.text+0x51d8): warning: Using 'setprotoent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sxz5_info': (.text+0x12f6): warning: Using 'endprotoent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syEu_info': (.text+0x5a25): warning: Using 'getprotobyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syAp_info': (.text+0x55c4): warning: Using 'getservbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syCX_info': (.text+0x584c): warning: Using 'getservbyport' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `syoz_info': (.text+0x49ef): warning: Using 'getservent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sytu_info': (.text+0x5098): warning: Using 'setservent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/network-2.3/ghc-6.12.3/libHSnetwork-2.3.a(BSD.o): In function `sxz5_info': (.text+0x1326): warning: Using 'endservent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_create.o): In function `timer_create': (.text+0x124): undefined reference to `pthread_once' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_create.o): In function `timer_create': (.text+0x171): undefined reference to `pthread_attr_init' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_create.o): In function `timer_create': (.text+0x1b8): undefined reference to `pthread_attr_setdetachstate' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `__start_helper_thread': (.text+0x3f): undefined reference to `pthread_attr_init' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `__start_helper_thread': (.text+0x4c): undefined reference to `pthread_attr_setstacksize' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `__start_helper_thread': (.text+0x92): undefined reference to `pthread_create' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `__start_helper_thread': (.text+0xc6): undefined reference to `pthread_attr_destroy' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `__start_helper_thread': (.text+0xd4): undefined reference to `pthread_atfork' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `timer_helper_thread': (.text+0x1e1): undefined reference to `pthread_exit' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/librt.a(timer_routines.o): In function `timer_helper_thread': (.text+0x21b): undefined reference to `pthread_create' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `init_mparams': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:2486:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:2490:0: undefined reference to `pthread_mutex_init' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:2493:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `internal_malloc_stats': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:2861:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:2888:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `internal_realloc': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:3777:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:3819:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `internal_memalign': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:3868:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:3915:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `ialloc': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:3998:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4052:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `dlmalloc': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4085:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4186:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `dlfree': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4211:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4285:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `dlmalloc_trim': /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4362:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/dlmalloc.c:4364:0: undefined reference to `pthread_mutex_unlock' /usr/haskell//lib/ghc-6.12.3/libHSffi.a(closures.o): In function `dlmmap': /home/ian/zz/ghc-6.12.3/libffi/build/src/closures.c:438:0: undefined reference to `pthread_mutex_lock' /home/ian/zz/ghc-6.12.3/libffi/build/src/closures.c:440:0: undefined reference to `pthread_mutex_unlock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2.o): In function `uw_init_context_1': (.text+0x1be5): undefined reference to `pthread_once' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__deregister_frame_info_bases': (.text+0x10bc): undefined reference to `pthread_mutex_lock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__deregister_frame_info_bases': (.text+0x10cd): undefined reference to `pthread_mutex_unlock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__register_frame_info_table_bases': (.text+0x117f): undefined reference to `pthread_mutex_lock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__register_frame_info_bases': (.text+0x1238): undefined reference to `pthread_mutex_lock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `_Unwind_Find_FDE': (.text+0x14b6): undefined reference to `pthread_mutex_unlock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `_Unwind_Find_FDE': (.text+0x14c7): undefined reference to `pthread_mutex_lock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__register_frame_info_table_bases': (.text+0x119e): undefined reference to `pthread_mutex_unlock' /usr/lib/gcc/x86_64-redhat-linux/4.1.2/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function `__register_frame_info_bases': (.text+0x1257): undefined reference to `pthread_mutex_unlock' collect2: ld returned 1 exit status There are two main categories of error messages above: 1 : ...requires at runtime the shared libraries from the glibc version used for linking 2a : undefined reference to `pthread_....' 2b : undefined reference to `pthread_mutex_lock' I've had no luck in sorting out how to solve this and an quite new to both Linux and Haskell. I never managed to install (build from source failed) the entire Haskell Platform on CentOS 5.5, is that needed? Anyone has got any idea what might causing these errors? Regards, Frode

3 4

unix-compat and GHC 7.0.2
by Michael Snoyman 15 Mar '11

15 Mar '11

Hi all, I'm having trouble compiling unix-compat with GHC 7.0.2. I'm fairly certain that other users are not running into this, but I'm not sure what would be wrong on my system. Here's the error I'm getting: Resolving dependencies... Configuring unix-compat-0.2.1.1... cabal: Missing dependency on a foreign library: * Missing header file: HsUnixCompat.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. cabal: Error: some packages failed to install: unix-compat-0.2.1.1 failed during the configure step. The exception was: ExitFailure 1 Any ideas? Thanks, Michael

3 3

Question on a common pattern
by tsuraan 15 Mar '11

15 Mar '11

In my code, I'm doing this quite a lot: x <- someIO case x of Opt1 -> ... Having a line for extracting the value from the IO (or STM) and then acting on the value seems unnatural. Is there a more concise way to do this? This code: case someIO of Opt1 -> ... Doesn't work, but is there something like that, that is valid?

9 11

simple stm question
by qld3303 15 Mar '11

15 Mar '11

I recently upgraded to ghc 7.0.2 from 6.12.3, along with the Haskell platform, and noticed that the following code no longer works as expected: waitFor tvar = atomically $ do count <- readTVar tvar check (count == 0) worker tchan tvar = loop where loop = do putStrLn "checking" finished <- atomically $ isEmptyTChan tchan threadDelay 50000 if finished then atomically $ do val <- readTVar tvar writeTVar tvar $ (subtract 1) val else (atomically $ readTChan tchan) >> loop test = do tchan <- newTChanIO pure $ forM_ [1..5] $ writeTChan tchan -- THIS LINE tvar <- newTVarIO 1 forkIO $ worker tchan tvar waitFor tvar putStrLn "DONE" This will work if I use atomically, but otherwise it does nothing, tchan remains empty afterwards. I'm not clear how this should behave.

3 3

ANN: craftwerk-0.1, craftwerk-cairo-0.1, craftwerk-gtk-0.1
by Malte Harder 15 Mar '11

15 Mar '11

Dear all, I just released the first version of the Craftwerk graphics library for 2d vector graphics. Craftwerk is intended to act as an abstract interface to different backend drivers. The library itself has a TikZ (http://sourceforge.net/projects/pgf) driver builtin to output vector graphics for use in LaTeX documents. The craftwerk-cairo library supplies a Cairo output function to the library. The aim is to support these two backends in a seamless manner such that graphics created with either backend are not or nearly not distinguishable. The third package (craftwerk-gtk) contains convenience functions to display graphics created with craftwerk directly in a Gtk window, including the basic zooming, PDF & TikZ export via a file chooser dialog. It also allows to create a simple user interface that passes options to the rendering function. The feature support is rather rudimentary at the moment, but for current Cairo users most features should be already available from within the craftwerk API. The aim is to support more high level functions like TikZ offers. The project started when I realized that I need to prepare a lot of visualizations at university twice, once for display and once for print. I hope that this library proves to be useful for people with similar tasks. A great thing would be if the Chart library allows to plug another backend in. I haven't really looked into that, but this would allow me to leave Gnuplot and R behind for most purposes and at the same time get higher quality output that is better integrable. I started learning Haskell only half a year ago and this is my first real project. So far I have to say that I enjoy it very much. Therefore, if you find some weird constructions or have any comments about the design of the library, I'm looking forward for any feedback! The source repository can be found under: https://github.com/mahrz/Craftwerk and packages here: http://hackage.haskell.org/package/craftwerk-0.1 http://hackage.haskell.org/package/craftwerk-cairo-0.1 http://hackage.haskell.org/package/craftwerk-gtk-0.1 Best, Malte -- Malte Harder malte.harder(a)gmail.com

2 2

Re: [Haskell-cafe] Uninstall Haskell Platform on Mac OS X
by Jesse Schalken 14 Mar '11

14 Mar '11

This leaves the symlinks "alex", "cabal", "cabal.real", "cabal.wrap" and "happy" in "/usr/bin", and also leaves "/Library/Frameworks/HaskellPlatform.framework", and while I can remove those myself how can I be certain there isn't something else left behind? On Tue, Mar 15, 2011 at 1:31 AM, Anders Persson <anders.cj.persson(a)gmail.com > wrote: > This is what I do. > > At a terminal prompt: > > sudo /Library/Frameworks/GHC.framework/Versions/Current/Tools/Uninstaller > > sudo rm -r /Library/Haskell > > Cheers, > Anders > > On Mar 14, 2011, at 3:22 PM, Jesse Schalken wrote: > > Simple question which an hour of googling and a question on #haskell > couldn't satisfy. :( > > I have installed the Haskell Platform 2011.2.0.0 on Mac OS X 10.6.6. > > Now how do I *uninstall* it? > > Thanks, > Jesse > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

2 1

writing to a fifo when the reader stops reading
by briand＠aracnet.com 14 Mar '11

14 Mar '11

Hi all, here's the code: writer = do threadDelay 100000 threadWaitWrite fd fdWrite fd ((show x) ++ "\n") writer fd (x+1) pretty simple, it just keeps writing. What happens though is that, eventually, the reader goes away, i.e. "closes" the fifo. When that happens I get: ghc: fdWriteBuf: resource vanished (Broken pipe) which make sense, sort of. I write a value, let's say 10, and the reader reads it. It's the last value so it "closes" the fifo. Now there's nothing reading, so when I get to threadWaitWrite, I would expect the program to wait, just as it does when it starts up and there is no reader. looking for some guidance. Thank you, Brian

3 3

Uninstall Haskell Platform on Mac OS X
by Jesse Schalken 14 Mar '11

14 Mar '11

Simple question which an hour of googling and a question on #haskell couldn't satisfy. :( I have installed the Haskell Platform 2011.2.0.0 on Mac OS X 10.6.6. Now how do I *uninstall* it? Thanks, Jesse

3 3

Re: [Haskell-cafe] ANN: unordered-containers - a new, faster hashing-based containers library
by Louis Wasserman 14 Mar '11

14 Mar '11

A couple thoughts: size takes O(n). That's just depressing. Really. Do you think union, intersection, etc. could be supported? Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

21 48

Some quick experiments with GHC 7.0.2 in Intel's Manycore Testing Lab (32 cores)
by José Pedro Magalhães 14 Mar '11

14 Mar '11

Hi all, I've played a bit with Intel's Manycore Testing Lab ( http://software.intel.com/en-us/articles/intel-many-core-testing-lab/) Part of the agreement to use it requires that you report back your experiences, which I did in an Intel forum post ( http://software.intel.com/en-us/forums/showthread.php?t=81396) I thought this could be interesting to the Haskell community in general as well, so I'm reposting here, and pasting the text below for convenience. I've replaced the images with links. Cheers, Pedro As per the agreement with Intel, I am reporting my experiences with the > Intel Manycore Testing Lab (Linux). This was my first time in the lab, and I > wanted to test GHC's [1] SMP parallelism [2] features. > > The first challenge was to actually get GHC to work on the lab. There was a > working version of ghc under /opt/ghc6.13/bin/ghc, but I really needed GHC > 7. So first I built GHC 7.0.2-rc2, which worked without much trouble. > > Next step was to get all the necessary libraries in place. Since the lab > has no direct internet access, cabal-install [3] wouldn't be of much use. > Instead, I downloaded a snapshot of hackage [4] with the latest version of > every package and manually installed the packages I needed. A bit boring, > but doable. > > Finally I was ready to compile my programs and test. First thing I tried > was an existing algorithm I had which, at some point, takes a list of about > 500 trees and, for each tree, computes a measure which is expressed as a > floating point number. This is basically a map over a list transforming each > tree into a float. Each operation is independent of the others, and all > require the same input, so it seems ideal for parallelisation. A quick > benchmark revealed the following running times: > > http://dreixel.net/images/perm/ParList.png > > (Note the non-linear number of cores at the end of the x-axis.) Apparently > there are performance gains with up to 6 cores; adding more cores after this > makes the total running time worse. > > While this might sound bad, do note that all that was necessary to > parallelise this algorithm was a one line change: basically, at the point > where the list of floats @l@ is generated, it is replaced with @l `using` > parList rdeepseq@. This change, together with recompilation using > -threaded, is all that is necessary to parallelise this program. > > Later I performed a more accurate benchmark, this time using the equality > function (take two elements and compare them for equality). The first step > was to parallelise the equality function, which, again, is a very simple > task: > > -- Tree datatype > data Tree a = Leaf | Bin a (Tree a) (Tree a) > > -- Parallel equality > eqTreePar :: Tree Int -> Tree Int -> Bool > eqTreePar Leaf Leaf = True > eqTreePar (Bin x1 l1 r1) (Bin x2 l2 r2) = x1 == x2 && par l (pseq r (l && > r)) > where l = eqTreePar l1 l2 > r = eqTreePar r1 r2 > eqTreePar _ _ = False > > `par` and `pseq` are the two primitives for parallelisation in GHC [5]. The > performance graph follows: > > http://dreixel.net/images/perm/ParEq.png > > (This time I ran the benchmark several times; the error bars on the graph > are the standard deviations.) Again we get performance improvements with up > to 6 cores, and after that performance decreases. What I find really nice is > the improvement with two cores, which is almost a 50% decrease in running > time. The ratios for 2 to 4 cores wrt. the running time with 1 core are > 0.52, 0.39, and 0.35, respectively. This is really good for such a simple > change in the source code, and most people only have up to 4 cores anyway. > In any case, the results of this (very preliminary) experiment seem to > indicate that GHC's SMP parallelism is not particularly optimized for a high > number of cores (yet). > > I'm planning to explore this line of research further, and I'm hoping to be > able to conduct more experiments in the near future. Feel free to contact me > if you want more information on what I've done. > > > Cheers, > Pedro > > [1] http://www.haskell.org/ghc/ > [2] http://www.haskell.org/ghc/docs/latest/html/users_guide/using-smp.html > [3] http://hackage.haskell.org/package/cabal-install > [4] http://hackage.haskell.org > [5] > http://hackage.haskell.org/packages/archive/parallel/latest/doc/html/Contro… >

2 1

Re: [Haskell-cafe] Data.ByteString.Lazy.ByteString vs Data.ByteString.Lazy.Internal.ByteString
by Antoine Latter 14 Mar '11

14 Mar '11

The ghc-binary package is used internal to GHC, and isn't gauranteed to be present from one version to the next, nor do I expect the GHC team to promise it will have a stable interface. You'd really be better of instaling the package "binary", or something similar. On Mar 14, 2011 5:34 AM, "Christian Maeder" <Christian.Maeder(a)dfki.de> wrote:

1 0

ICFP 2011 Deadline Extension
by Wouter Swierstra 14 Mar '11

14 Mar '11

===================================================================== ICFP 2011: International Conference on Functional Programming http://www.icfpconference.org/icfp2011 ===================================================================== On behalf of the Program Committee of ICFP 2011, I would like to announce a deadline extension for authors affected by the recent earthquake in Japan. The Program Committee will accept titles and abstracts until Monday 4 April at 23:59, and full submissions until Thursday 7 April at 23:59 from those authors affected by the earthquake. Our thoughts go out to the victims of this tragedy. Wouter Swierstra ICFP Publicity Chair

1 0

Re: [Haskell-cafe] [Haskell] Linker flags for foreign export.
by Max Bolingbroke 14 Mar '11

14 Mar '11

Hi Jason, On 8 March 2011 05:28, Jason Dusek <jason.dusek(a)gmail.com> wrote: > gcc -g -Wall -O2 -fPIC -Wall -o import \ > -I/usr/lib/ghc-6.12.1/include/ \ > import.c exports.so In my experience, the easiest way to do this is to use gcc to build object files from C source files, and then specify those object files on the ghc command line in order to get GHC to do the linking step. This will deal with linking in the correct RTS and, if you specify appropriate -package flags, dependent packages as well. If you want a C main function then see user guide section 8.2.1.1 at http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html. Cheers, Max

2 7

Yesod 0.7.1 using GHC 7.0.2 on Arch Linux
by Ertugrul Soeylemez 14 Mar '11

14 Mar '11

Hello there, today I have upgraded to GHC 7.0.2 by doing a system update on my Arch Linux box (x86, 32 bits), and I'm having difficulties to install Yesod. Its dependencies seem to have been installed without problems, but the Yesod package itself fails. The complete build log follows: % cabal install yesod Resolving dependencies... Configuring yesod-0.7.1... Preprocessing library yesod-0.7.1... Preprocessing executables for yesod-0.7.1... Building yesod-0.7.1... [1 of 1] Compiling Yesod ( Yesod.hs, dist/build/Yesod.o ) Registering yesod-0.7.1... [1 of 2] Compiling CodeGen ( CodeGen.hs, dist/build/yesod/yesod-tmp/CodeGen.o ) [2 of 2] Compiling Main ( scaffold.hs, dist/build/yesod/yesod-tmp/Main.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package bytestring-0.9.1.10 ... linking ... done. Loading package base64-bytestring-0.1.0.2 ... linking ... done. Loading package array-0.3.0.2 ... linking ... done. Loading package containers-0.4.0.0 ... linking ... done. Loading package cereal-0.3.0.0 ... linking ... done. Loading package filepath-1.2.0.0 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package old-time-1.0.0.6 ... linking ... done. Loading package unix-2.4.2.0 ... linking ... done. Loading package directory-1.1.0.0 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package data-default-0.2.0.1 ... linking ... done. Loading package tagged-0.2 ... linking ... done. Loading package crypto-api-0.5.2 ... linking ... done. Loading package pureMD5-2.1.0.3 ... linking ... done. Loading package pretty-1.0.1.2 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package transformers-0.2.2.0 ... linking ... done. Loading package deepseq-1.1.0.2 ... linking ... done. Loading package text-0.11.0.5 ... linking ... done. Loading package blaze-builder-0.2.1.4 ... linking ... done. Loading package blaze-html-0.4.1.0 ... linking ... done. Loading package file-embed-0.0.3.1 ... linking ... done. Loading package time-1.2.0.3 ... linking ... done. Loading package unix-compat-0.2.1.1 ... linking ... done. Loading package enumerator-0.4.7 ... linking ... done. Loading package mtl-2.0.1.0 ... linking ... done. Loading package parsec-3.1.1 ... linking ... done. Loading package network-2.2.1.10 ... linking ... done. Loading package wai-0.3.2 ... linking ... done. Loading package utf8-string-0.3.6 ... linking ... done. Loading package web-routes-0.23.4 ... linking ... done. Loading package wai-app-static-0.0.1.1 ... linking ... done. Loading package random-1.0.0.3 ... linking ... done. Loading package clientsession-0.4.1 ... linking ... done. Loading package cookie-0.0.0 ... linking ... done. Loading package failure-0.1.0.1 ... linking ... done. Loading package extensible-exceptions-0.1.1.2 ... linking ... done. Loading package QuickCheck-2.4.0.1 ... linking ... done. Loading package blaze-builder-enumerator-0.2.0.1 ... linking ... done. Loading package json-types-0.1 ... linking ... done. Loading package json-enumerator-0.0.1 ... linking ... done. Loading package hamlet-0.7.2 ... linking ... done. Loading package monad-peel-0.1 ... linking ... done. Loading package zlib-0.5.3.1 ... linking ... done. Loading package zlib-bindings-0.0.0 ... linking ... done. Loading package wai-extra-0.3.3 ... linking ... done. Loading package web-routes-quasi-0.6.3.1 ... linking ... done. Loading package yesod-core-0.7.0.1 ... linking ... done. Loading package yesod-static-0.0.0.1 ... linking ... done. Loading package SHA-1.4.1.3 ... linking ... done. Loading package RSA-1.0.6.1 ... linking ... done. Loading package data-object-0.3.1.6 ... linking ... done. Loading package attoparsec-0.8.5.0 ... linking ... done. Loading package bytestring-nums-0.3.2 ... linking ... done. Loading package bytestring-trie-0.2.3 ... linking ... done. Loading package JSONb-1.0.3 ... linking ... done. Loading package attempt-0.3.0 ... linking ... done. Loading package convertible-text-0.3.0.9 ... linking ... done. Loading package data-object-json-0.3.1.5 ... linking ... done. Loading package attoparsec-enumerator-0.2.0.3 ... linking ... done. Loading package network-bytestring-0.1.3.4 ... linking ... done. Loading package asn1-data-0.4.6 ... linking ... done. Loading package certificate-0.7.0 ... linking ... done. Loading package primitive-0.3.1 ... linking ... done. Loading package vector-0.7.0.1 ... linking ... done. Loading package cryptocipher-0.2.6 ... linking ... done. Loading package cryptohash-0.6.3 ... linking ... done. Loading package tls-0.3.3 ... linking ... done. Loading package http-enumerator-0.3.1 ... linking ... done. Loading package tagsoup-0.12 ... linking ... done. Loading package xml-1.3.7 ... linking ... done. Loading package authenticate-0.8.2.2 ... linking ... done. Loading package control-monad-attempt-0.3.0 ... linking ... done. Loading package dataenc-0.13.0.5 ... linking ... done. Loading package process-1.0.1.5 ... linking ... done. Loading package mime-mail-0.1.0.1 ... linking ... done. Loading package stm-2.2.0.1 ... linking ... done. Loading package pool-0.0.1 ... linking ... done. Loading package persistent-0.4.1 ... linking ... done. Loading package ranges-0.2.3 ... linking ... done. Loading package email-validate-0.2.6 ... linking ... done. Loading package xss-sanitize-0.2.6 ... linking ... done. Loading package yesod-persistent-0.0.0.1 ... linking ... done. Loading package yesod-form-0.0.0.2 ... linking ... done. Loading package yesod-json-0.0.0.1 ... linking ... done. Loading package yesod-auth-0.3.1 ... linking ... done. Loading package cmdargs-0.6.8 ... linking ... done. Loading package MonadCatchIO-mtl-0.3.0.2 ... linking ... done. Loading package Cabal-1.10.1.0 ... linking ... done. Loading package ghc-binary-0.5.0.2 ... linking ... done. Loading package bin-package-db-0.0.0.0 ... linking ... done. Loading package hpc-0.5.0.6 ... linking ... done. Loading package ghc-7.0.2 ... ghc: /usr/lib/ghc-7.0.2/ghc-7.0.2/libHSghc-7.0.2.a: no string tables, or too many ghc: panic! (the 'impossible' happened) (GHC version 7.0.2 for i386-unknown-linux): loadArchive "/usr/lib/ghc-7.0.2/ghc-7.0.2/libHSghc-7.0.2.a": failed Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug cabal: Error: some packages failed to install: yesod-0.7.1 failed during the building phase. The exception was: ExitFailure 1 Is this really a bug? If yes, is it a known one? I couldn't find anything on the internet so far. Many thanks in advance. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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ANN: hsmagick 0.5
by Vincent Gerard 14 Mar '11

14 Mar '11

Hello Haskellers, I am currently taking over the maintainership of hsmagick, a FFI bindings library to ImageMagick. Therefore, I am pleased to announce the 0.5 release of hsmagick. http://hackage.haskell.org/package/hsmagick Major changes: ------ * imageToBlob and blobToImage functions using ByteStrings * Use of ForeignPtr instead of Ptr as memory references representation. Thanks to Steffen Siering patches, the internal representation has been changed from Ptr to ForeignPtr. The finalization of ForeignPtr should resolve space leaks issues. * destroyImage function is exposed, to release the memory immediately. * hsmagick builds with GHC 7 The source repository is now hosted on github https://github.com/vincentg/hsmagick Please, do not hesitate to contact me by email or with github for any questions, requests, bugs, patches, anything about hsmagick. Cheers, Vincent Gerard (Please make sure not to reply to haskell(a)haskell.org.)

1 0

binary twidling modules
by rusi 13 Mar '11

13 Mar '11

I am not sure what would be the generic names I am asking for... examples are the nearest I can get. In perl there is pack/unpack http://perldoc.perl.org/perlpacktut.html Likewise in python there is struct module http://docs.python.org/library/struct.html What is/are the Haskell equivalents?

2 1

Haddock fails on parsing Hamlet
by Mathew de Detrich 13 Mar '11

13 Mar '11

Since the site for signing up to haddock mailing list seems to be down ( http://projects.haskell.org/cgi-bin/mailman/listinfo/haddock) I thought I would post this here Haddock fails to parse (and therefore closes prematurely) when generating documentation for the Hamlet package found here ( http://hackage.haskell.org/package/hamlet) This furthermore prevents the hamlet from being built on archlinux using cabal2arch/AUR/bauerbill The error when creating the documentation is Warning: Text.Hamlet.Quasi: We do not support associated types in instances yet. These instances are affected: Text.Hamlet.Quasi.HamletValue (Text.Hamlet.Quasi.Hamlet url), Text.Hamlet.Quasi.HamletValue Text.Blaze.Internal.Html haddock coverage for dist/build/tmp17309/Text/Hamlet/Quasi.hs: 9/14 64% dist/build/tmp17309/Text/Cassius.hs:340:23: parse error on input `AbsoluteUnit' Aborting... On the previous haskell-platform this did not happen Thanks

3 3

ANN: bash-0.0.0
by Jason Dusek 13 Mar '11

13 Mar '11

Many-a-time, have I used higher level languages to generate Bash scripts. Here, for the first time, I have taken the time to write a structured and safe Bash pretty printer, leveraging some work on shell escaping I did some months ago. http://hackage.haskell.org/packages/archive/bash/0.0.0/doc/html/Language-Ba… A wide range of Bash constructs are supported. It's easiest to point out what's not supported at present: . Arithmetic substitutions (those within "$(( ))"). . Bash's test special form (using "[[ ]]"). Ordinary uses of the test command are of course fully supported. . Specialized expression de-referencing forms that allow substitution and substring selection; the only thing supported in this domain is defaulting and length: ${#var} # Length of var in bytes. ${var:-} # If var is not set, yield the empty string. Many other forms that are tedious to get right -- special variable names, array expansions, even eval -- are fully supported. I'll be using this tool to support a config generation system. Another interesting application is generating Bash completion scripts. If you decide to use it and have trouble please let me know; this is the first Language.Something that I have written and it may not present the friendliest interface. Do let me know, also, if the omitted syntactic structures would be helpful to you and I will see what I can do to include them. -- Jason Dusek Linux User #510144 | http://counter.li.org/

4 4

Cmdargs and common flags
by Magnus Therning 13 Mar '11

13 Mar '11

I'm looking for a good way of dealing with common flags in cmdargs. Currently what I do requires a bit of repetition that I'd really like to get rid of: 1. Data types data Modes = Cmd1 { foo :: String, ... } | Cmd2 { foo :: String, ... } 2. Mode specifications cmd1 = Cmd1 { foo = def &= help "..", ...} cmd2 = Cmd2 { foo = def &= help "..", ...} I have no idea how to deal with the repetition in the data types, so all suggestions are welcome. For the repetition in the mode specifications I attempted to factor the common bits into a "variable": flagFoo = "" &= help ".." but that resulted in only the first command getting the proper specification. I suppose this comes down to the impurity, but how do I work around that? (Especially, are there any good examples of using the pure part of the API?) /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus

3 5

Light and fast http server
by Victor Oliveira 12 Mar '11

12 Mar '11

Hi cafe, There are a lot of http servers in hackage. I didn't have used none. I would like to know if one of them is something closer of the nginx. I need some light and fast. It don't need support all http, just the basics is fine. Suggestions? []s Victor

5 4

Light and fast http server
by Greg Weber 12 Mar '11

12 Mar '11

> > snap or warp/yesod. maybe in a few years we will have a winner for the platform... > --dons > On Friday, March 11, 2011, Vo Minh Thu <noteed(a)gmail.com> wrote: > 2011/3/11 Victor Oliveira <rhapsodyv(a)gmail.com>: >> Hi cafe, >> >> There are a lot of http servers in hackage. I didn't have used none. >> I would like to know if one of them is something closer of the nginx. >> I need some light and fast. It don't need support all http, just the > basics is fine. >> Suggestions? > > Snap and Warp come to mind. Have a look at this reddit thread: > > http://www.reddit.com/r/programming/comments/flpao/the_haskell_high_perform… > > Cheers, > Thu To be clear, Yesod and Snap are web frameworks. If you want just a web server, then your main options are snap-server or Warp as has been pointed out. The happstack framework also has a server, but they are planning on switching it out in the future. As for speed, warp is at least twice as fast as snap-server. As for lightness- * snap-server and Warp support a similar feature set, with some differences that might be important, depending on your needs. * Warp has a much smaller code base * lightness may be a perception of how you interface with the server. I don't know how you would interface with snap-server except through the Snap framework. Warp can be used with Yesod, but runs on the WAI interface. The WAI inteface allows you to change your mind and deploy to a different server in the future. Hopefully it will also allow you to use different frameworks in the future, although this is not the case yet. But just as important, it is also designed to support easy and re-usable low-level web programming.

1 0

cabal install yesod gives an error on ghc 7.02
by Vagif Hagverdiyev 12 Mar '11

12 Mar '11

cabal install yesod gives an error on ghc 7.02: http://hackage.haskell.org/trac/ghc/ticket/5004 One of the commenters on that ticcket says: "found that providing an unstripped version of libHsghc-7.0.2.a allows for successful linking. " Where can i get that unstripped version of libHsghc-7.0.2.a ?

2 2

possible bug for ghc 7 + xcode 4 on snow leopard?
by Carter Schonwald 12 Mar '11

12 Mar '11

Hey All, As of installing xcode 4 earlier today, i'm getting errors of the form ld: library not found for -lcrt1.10.5.o collect2: ld returned 1 exit status for any haskell code that invokes ld in its cabal install process. 1) is this related to some problem in xcode / what the haskell code defaults to linking to? 2) is this something completely unrelated? thanks! -Carter

3 8

Error while registering packages: cairo & glib
by Daniel Díaz 12 Mar '11

12 Mar '11

Hi, cafe, When I have updated my Haskell Platform version to 2011.2.0.0, and I try to install cairo or glib, during the registering I read the following: Registering glib-0.12.0... Installing library in C:\Documents and Settings\User\Datos de programa\cabal\glib-0.12.0\ghc-7.0.2 Registering glib-0.12.0... setup.exe: internal error: unexpected package db stack: [UserPackageDB] And then, the instalation fails. Searching in Google, I have found some links related: * http://www.mail-archive.com/haskell-cafe@haskell.org/msg81071.html * http://hackage.haskell.org/trac/hackage/ticket/731 But I never had this problem before. Thanks for any help, Daniel Díaz

2 1

Reference monad
by Joshua Ball 12 Mar '11

12 Mar '11

Hi, Suppose I want the following functions: newRef :: a -> RefMonad (Ref a) readRef :: Ref a -> RefMonad a writeRef :: Ref a -> a -> RefMonad () for some appropriate data Ref = ... Obviously these functions are already satisfied by IORefs and STM. But if I wanted to implement my own (for fun)... would it be possible? Particularly, in a pure way, without unsafePerformIO? runRefMonad :: RefMonad a -> a I could try to do it with a state monad, and keep all of the refs in a Data.Map, but then I would have to solve the garbage collection problem, so that doesn't really work. Josh "Ua" Ball

3 2

Flexible Wrappers - an Introduction
by Iain Alexander 12 Mar '11

12 Mar '11

There are three flexible wrappers provided in the initial flexiwrap package [1]. (More may be required in the future.) short long wraps FW FlexiWrap values FWT FlexiWrapT unary type constructors FWCTC FlexiWrapCTC binary operators which combine two unary type constructors The short names are frequently convenient since type signatures can get quite long. The suffixes are a simple encoding of the kind of the wrapped quantity, description of which I defer to a later post. The first parameter to each of these is a phantom - it plays no part in the implementation type, but serves as an index to generate multiple distinct types from each wrapper. In addition, by using a type-level list here, we can use it to specify any number of instance implementations. By way of a rather contrived but simple example, the module Data.Flex.SmallCheck.Wrap implements and uses an instance selector called FWEqFirst to implement an Eq instance which compares pairs by their first element. It is used there by defining a type FW (FWEqFirst :*: TNil) (Bool, Bool) which has the requisite properties. The initial proof-of-concept version of the package provides only a limited number of instance selectors (with the associated machinery) for each wrapper. FW (in Data.Flex.Wrap) has only an implementation for Eq instances, with FWDefaultEq to explicitly specify the default implementation which simply delegates to the underlying wrapped type. FWT (Data.Flex.WrapT) has FWTDefaultFunctor (Functor) FWTDefaultApplicative (Applicative) FWTDefaultMonadAll (the combination of FWTDefaultMonad and FWTDefaultMonadState) FWTDefaultMonad (Monad) FWTDefaultMonadState (MonadState) which all again delegate to the underlying type. There is also a separate module Data.Flex.WrappedMonad which provides selectors to implement Functor and Applicative instances for a Monad which lacks them. FWWrapMonad (the combination of FWMonadFunctor and FWMonadApplicative) FWMonadFunctor (Monad => Functor) FWMonadApplicative (Monad => Applicative) FWCTC (Data.Flex.WrapCTC) has FWCTCDefaultFunctor (Functor) FWCTCDefaultMonad (Monad) which simply delegate to the application of the wrapped binary operator to two constructor arguments, but provides underlying machinery for these together with MonadPlus and MonadTrans. Data.Flex.Compose contains the (:.) (alias O) type composition operator as found in e.g. the TypeCompose package [2]. It contains a fairly literal translation of Mark Jones and Luc Duponcheel's scheme for monad composition [3], FWCompP - use the "prod" construction FWCompD - use the "dorp" construction FWCompS - use the "swap" construction and selectors for MonadTrans and MonadPlus FWCompDefaults (the combination of FWCompTrans and FWCompMonadPlus) FWCompTrans (MonadTrans) FWCompMonadPlus (a synonym for FWCompMonadPlusR) FWCompMonadPlusR (using the MonadPlus instance of the right-hand argument of the composition) FWCompMonadPlusL (using the MonadPlus instance of the left-hand argument of the composition) Data.Flex.FlipT contains the operator FlipT which flips the arguments of an operator such as (:.). FWFlipDefaults (the combination of FWFlipMonad and FWFlipMonadPlus) FWFlipMonad (Monad) FWFlipMonadPlus (MonadPlus) These delegate the implementation to the underlying binary operator, which it wraps with FWCTC, passing the phantom selector list along. So, to recap the example given in the package release announcement: data FWStrict = FWStrict type Strict = FW (FWStrict :*: TNil) type StrictT = FWCTC (FWFlipDefaults :*: FWCompMonadPlusL :*: FWCompDefaults :*: FWCompS :*: TNil ) (FlipT O) Strict defines a (e.g. monad, but in general constructor) transformer StrictT. FWCTC is a flexible wrapper. Its first parameter is an HList-like type-level list of instance specifications. O is the type composition operator, and FlipT flips its arguments. Strict is a user-defined wrapper type. (This is strict vs. loose, not strict vs. lazy. It is intended to be used to wrap values of a data structure which satisfy certain criteria.) FWCompMonadPlusL specifies a particular MonadPlus instance (which delegates to the left operand of the composition, which is the right operand of the flipped composition, i.e. whatever argument you pass to StrictT), and FWCompS specifies the Jones/Duponcheel SComp construction [3]. The other two items in the list (apart from the TNil terminator) specify default implementations of other instances. [1] http://hackage.haskell.org/package/flexiwrap-0.0.1 [2] http://hackage.haskell.org/package/TypeCompose [3] http://web.cecs.pdx.edu/~mpj/pubs/RR-1004.pdf

1 0

Need help to solve this question
by Chatura Roche 12 Mar '11

12 Mar '11

Both sections relate to the case study: Index for a document of text. SECTION A: Given the attached Haskell code which produces an index of words, make the following alterations by modifying existing functions and including new functions where necessary : 3) Treat a capitalised word (one or more capitals) as being different from the word in all lower case (but they should still be sorted alphabetically) – unless it is at the start of a sentence with only the initial letter capitalised. A sentence is terminated by a ‘.’, ‘?’ or ‘!’. import Prelude type Doc = String type Line = String type Word = String makeIndex :: Doc -> [ ([Int], Word) ] makeIndex = shorten . -- [([Int], Word)] -> [([Int], Word)] amalgamate .-- [([Int], Word)] -> [([Int], Word)] makeLists . -- [(Int, Word)] -> [([Int], Word)] sortLs . -- [(Int, Word)] -> [(Int, Word)] allNumWords .-- [(Int, Line)] -> [(Int, Word)] numLines . -- [Line] -> [(Int, Line)] splitUp -- Doc -> [Line] splitUp :: Doc -> [Line] splitUp [] = [] splitUp text = takeWhile (/='\n') text : -- first line (splitUp . -- splitup other lines dropWhile (==’\n’) . -- delete 1st newline(s) dropWhile (/='\n')) text -- other lines numLines :: [Line] -> [(Int, Line)] numLines lines -- list of pairs of = zip [1 .. length lines] lines -- line no. & line -- for each line -- a) split into words -- b) attach line no. to each word splitWords :: Line -> [Word] -- a) splitWords [] = [] splitWords line = takeWhile isLetter line : -- first word in line (splitWords . -- split other words dropWhile (not.isLetter) . -- delete separators dropWhile isLetter) line -- other words where isLetter ch = (‘a’<=ch) && (ch<=’z’) (‘A’<=ch) && (ch<=’Z’) numWords :: (Int, Line) -> [(Int, Word)] -- b) numWords (number, line) = map addLineNum ( splitWords line) -- all line pairs where addLineNum word = (number, word) -- a pair allNumWords :: [(Int, Line)] -> [(Int, Word)] allNumWords = concat . map numWords -- doc pairs sortLs :: [(Int, Word)] -> [(Int, Word)] sortLs [ ] = [ ] sortLs (a:x) = sortLs [b | b <- x, compare b a] -- sort 1st half ++ [a] ++ -- 1st in middle sortLs [b | b <- x, compare a b] -- sort 2nd half where compare (n1, w1) (n2, w2) = (w1 < w2) -- 1st word less (w1 == w2 && n1 < n2) -- check no. makeLists :: [(Int, Word)] -> [([Int], Word)] makeLists = map mk -- all pairs where mk (num, word) = ([num], word) -- list of single no. amalgamate :: [([Int], Word)] -> [([Int], Word)] amalgamate [ ] = [ ] amalgamate [a] = [a] amalgamate ((n1, w1) : (n2, w2) : rest)-- pairs of pairs | w1 /= w2 = (n1, w1) : amalgamate ((n2, w2) : rest) | otherwise = amalgamate ((n1 ++ n2, w1) : rest) -- if words are same grow list of numbers shorten :: [([Int], Word)] -> [([Int], Word)] shorten = filter long -- keep pairs >4 where long (num, word) = length word > 4 -- check word >4

2 1

Uncatchable error
by Daniel Díaz 12 Mar '11

12 Mar '11

Hi, cafe, I'm working in a program where I use many connections with Network.HTTP. Sometimes, connections are closed while my program is reading them, and an error appears: <socket: XXX>: Data.ByteString.hGetLine: invalid argument (Bad file descriptor) All I need is to handle this error. The function 'catch' doesn't work. I guess this error comes from a call to 'error' function, or something similar. What I can do? Thanks in advance, Daniel Díaz

4 5

Help with how to concatenate with own datatypes
by eldavido 11 Mar '11

11 Mar '11

Hi, I´m doing a project in haskell and I need to define an operator that concatenate some own defined data types, just like the operator ++ does for lists. I don´t see how to define the operator recursively since this adding function (:) doesn´t work on my own data types. This is my code: data Allele = Aone | Atwo deriving Show type Lifespan = Int data Population = Pop [(Allele,Allele,Lifespan)] deriving Show genepool :: Population genepool = Pop [] --can only concatenate 2 elements (+-) :: Population -> Population -> Population Pop [(a,b,c)] +- Pop [] = Pop [(a,b,c)] Pop [(a,b,c)] +- Pop [(d,e,f)] = Pop [(a,b,c),(d,e,f)] --and thats why this function goes non-exhaustive. gpinsertaoneaone :: Int -> Int -> Population gpinsertaoneaone 0 age = genepool gpinsertaoneaone n age = Pop [(Aone,Aone,70-age)] +- gpinsertaoneaone (n-1) age Thx for help and advice! -- View this message in context: http://haskell.1045720.n5.nabble.com/Help-with-how-to-concatenate-with-own-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

2 2

ContT and ST stack
by Anakim Border 11 Mar '11

11 Mar '11

Dear list, I have the following (simplified) piece of code: find :: Int -> [Int] find i = runST . (`runContT` return) $ callCC $ \escape -> do return [] which used to compile correctly under GHC 6.12.3. Now that I've switched to 7.0.2 it gets rejected with the following error: Couldn't match expected type `forall s. ST s c0' with actual type `m0 r0' Expected type: ContT r0 m0 a0 -> forall s. ST s c0 Actual type: ContT r0 m0 a0 -> m0 r0 In the second argument of `(.)', namely `(`runContT` return)' In the expression: runST . (`runContT` return) I'm a little bit lost at what exactly is the problem. Anyone can suggest a solution? Thanks! AB

6 9

Convert a function to a string of operators?
by Evgeny Grablyk 11 Mar '11

11 Mar '11

Hello! I was wondering if it was possible to "convert" a function (which may also call functions) to a plain list of operators on parameters. Example: foo a b = a + b bar a b = a * b baw a b c = bar (foo a b) c baw' a b c = (a + b) * c Any way to get `baw'' from `baw'? Preferrably as a String. -- Evgeny

6 6

Re: [Haskell-cafe] possible bug for ghc 7 + xcode 4 on snow leopard?
by Carter Schonwald 11 Mar '11

11 Mar '11

to answer the question of the other poster, ghc 7.0.2 packaged installer, 64 bit build Jurrien, I wound up doing something similar, namely just wholesale copying the 10.5 sdk into the sdks folder. i'm still curious why this problem even exists! 2011/3/10 Jurriën Stutterheim <j.stutterheim(a)students.uu.nl> > I solved it by making a symlink from /Developer/SDKs/MacOSX10.6.sdk to > /Developer/SDKs/MacOSX10.5.sdk (which is missing with XCode 4). So far it > seems to work :) > > > Jurriën > > > On 10 Mar, 2011, at 06:53 , Carter Schonwald wrote: > > > after experimenting by just naively moving the old Developer directory > back to its original location preceding the installation of xcode 4, > everything builds properly now. > > > > still, this is not a reasonable long term solution. Any ideas about how > this might be fixed? > > > > On Thu, Mar 10, 2011 at 12:33 AM, Carter Schonwald < > carter.schonwald(a)gmail.com> wrote: > > Hey All, > > As of installing xcode 4 earlier today, > > > > i'm getting errors of the form > > ld: library not found for -lcrt1.10.5.o > > collect2: ld returned 1 exit status > > > > for any haskell code that invokes ld in its cabal install process. > > 1) is this related to some problem in xcode / what the haskell code > defaults to linking to? > > 2) is this something completely unrelated? > > > > thanks! > > -Carter > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

3 2

hsc2hs not figuring out #include paths?
by Edward Amsden 11 Mar '11

11 Mar '11

I'm trying to write some bindings using hsc2hs. At the top of my .hsc file, I have #include <jack/types.h> #include <jack/jack.h> When I compile a .c file with just these two lines in gcc, it works fine (the jack directory is in /usr/local/include). When I try to run hsc2hs, it complains that it cannot find the header files. Any ideas? How do I set the include path (via cabal or just in hsc2hs) for hsc2hs? -- Edward Amsden Student Computer Science Rochester Institute of Technology www.edwardamsden.com

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Parallel Haskell stories
by Simon Peyton-Jones 11 Mar '11

11 Mar '11

Friends I'm giving a talk at a developer conference in London on Friday 18th, about parallel programming in Haskell. http://skillsmatter.com/event/scala/functionalpx-2011/ad-1382 I know that some of you have been using Haskell for parallel or concurrent programming quite a bit, so this email is just to ask could you contribute a little vignette or story about using Haskell in a *parallel/concurrent* application that I could use to illustrate my talk? I can rant all I like about the glories of Haskell, but I'm a biased witness. It's much more convincing if I can illustrate with true tales from the trenches. I'm interested in both parallelism and concurrency, so for example the success of Warp in using Concurrent Haskell is in scope. I can't say a lot about any one example, obviously, but what would be great would be - an idea of how Haskell helped (esp if you have a head to head comparison) - code snippets that illustrate how lovely it all is - brief performance indicators *Insight* is the key word. I don't just want to say "Company X used Haskell to do Y" because that doesn't convey any re-usable insights or ideas. What is the essence? I'll start writing in earnest on Monday 14th; the talk is on Friday. I have plenty to say already, so treat this as an opportunity not an obligation. But still, examples would be good! Do let me know if you have one. Simon

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Why don't my OS threads terminate?
by Bas van Dijk 11 Mar '11

11 Mar '11

Dear all, At work, I'm developing a webapplication with happstack. When I let it run for some time (< 5min.) it crashes with the following message: "failed to create OS thread: Resource temporarily unavailable" This happens because the server continuously creates OS threads but never terminates them. This keeps going on until I hit the OS thread limit. I would like to know why the OS threads are created and more importantly why they aren't terminated. Unfortunately I can't publish the source code because it's proprietary software. Hopefully the following description may give an idea what's going on: The webapplication is basically a simple measurement application: The client side (HTML, Javascript, JQuery) contains a plot which shows the measurements that the server generates. The client contains a loop which first longpolls[2] the server to wait for a new measurement, the server will then block (using takeMVar) until (using putMVar) a measurement is available. The client then retrieves the measurement from the server including all other relevant data. These requests all happen asynchronously using ajax calls[1]. The server starts by forking a thread which runs the measure loop. At each iteration the measure loop reads data from a file then fits that data to a model. For fitting I use my levmar fitting library[3]. The coefficients of the fitted model are then used to calculate a measurement. I believe the OS threads are created by my levmar library. This library uses bindings-levmar[4] which is a binding to a C library. bindings-levmar uses safe FFI calls because the levmar C procedures are reentrant (they need to call back into Haskell to execute the model function). I believe the RTS creates an OS thread for each safe FFI call. When I replace my levmar fit function with a function which just returns a random number the problem disappears. The problem also doesn't appear in a standalone application I have which just uses my levmar fit function to fit all the datafiles, without the webserver. It seems that the combination of happstack and levmar causes the OS threads to not terminate. I tried space profiling the application but that did not reveal anything interesting. I even used threadscope to look at the application eventlog (see: [5]) but that also looked normal. Hopefully someone can point me where to look next. Thanks, Bas [1] http://api.jquery.com/jQuery.ajax/ [2] http://en.wikipedia.org/wiki/Push_technology#Long_polling [3] http://hackage.haskell.org/package/levmar [4] http://hackage.haskell.org/package/bindings-levmar [5] http://bifunctor.homelinux.net/~bas/crash.eventlog

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ANNOUNCE: cinvoke 0.1 released
by Remi Turk 11 Mar '11

11 Mar '11

I am happy to finally announce cinvoke 0.1, a binding to the C library cinvoke[1], allowing functions to be loaded and called whose names and types are not known before run-time. Why? Sometimes you can't use the Haskell foreign function interface because you parse the type of the function from somewhere else, i.e. you're writing an interpreter for a language that has an FFI itself. What? The main function it exports is: cinvoke :: Symbol -> RetType b -> [Arg] -> IO b And because code is worth a thousand words, here's a small program that uses libc to write a 1Gb buffer of random garbage to a file: > module Main where > > import Foreign.CInvoke > > main = do > cxt <- newContext > libc <- loadLibrary cxt "libc.so.6" > malloc <- loadSymbol libc "malloc" > creat <- loadSymbol libc "creat" > write <- loadSymbol libc "write" > free <- loadSymbol libc "free" > let sz = 2^30 > buf <- cinvoke malloc (retPtr retVoid) > [argCSize sz] > fd <- cinvoke creat retCInt [argString "/tmp/test", argCUInt 0o644] > n <- cinvoke write retCSize [argCInt fd, argPtr buf, argCSize sz] > cinvoke free (retPtr retVoid) [argPtr buf] It hopefully works on any machine on which cinvoke works, but has only been tested on linux x86_64. As the current version of cinvoke only installs a static library, it does not work from GHCi at the moment (without hacking cinvoke to build a shared library). More interesting examples are included in examples/ in the package. Where? Hackage: http://hackage.haskell.org/package/cinvoke Cheers, Remi [1] http://www.nongnu.org/cinvoke/

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ANNOUNCE: Haskell Platform 2011.2 released!
by Don Stewart 11 Mar '11

11 Mar '11

We're pleased to announce the 2011.2 release of the Haskell Platform: a single, standard Haskell distribution for everyone. Download the Haskell Platform 2011.2.0.0: http://haskell.org/platform/ The specification, along with installers (including Windows, Apple and Unix installers for a full Haskell environment) are available. The Haskell Platform is a single, standard Haskell distribution for every system, in the form of a blessed library and tool suite for Haskell distilled from the thousands of libraries on Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. When you install the Haskell Platform, you get the latest stable compiler, an expanded set of core libraries, additional development tools, and cabal-install – so you can download anything else you need from Hackage. This release ships with GHC 7. What you get is specified here: http://hackage.haskell.org/platform/contents.html Thanks! -- The Platform Infrastructure Team P.S. a big thanks to Mark Lentczner and Mikhail Glushenkov who built the Mac and Windows installers!

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