March 2011 - Haskell-Cafe

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 16 Mar '11

16 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

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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

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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 14 Mar '11

14 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.

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ANN: craftwerk-0.1, craftwerk-cairo-0.1, craftwerk-gtk-0.1
by Malte Harder 14 Mar '11

14 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

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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 > > >

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