August 2011 - Haskell-Cafe

Re: [Haskell-cafe] Failed link to mixed-language shared object
by David Banas 21 Aug '11

21 Aug '11

> ghc -dynamic -o ami_test -L. -lami ami_test.o > ./libami.so: undefined reference to `__stginit_haskell98_MarshalArray_' > ./libami.so: undefined reference to `__stginit_haskell98_MarshalError_' > collect2: ld returned 1 exit status I was able to solve this by changing these lines: import MarshalArray import MarshalError to read: import Foreign.Marshal.Array import Foreign.Marshal.Error I don't understand why this worked, since the available symbols in the 2 respective libraries appear totally similar: dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g haskell98-1.0.1.1/libHShaskell98-1.0.1.1.a | grep 'MarshalArray' MarshalArray__1.o: 00000030 T __stginit_haskell98_MarshalArray 00000000 T __stginit_haskell98_MarshalArray_ dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g -D haskell98-1.0.1.1/libHShaskell98-1.0.1.1-ghc6.12.3.so | grep 'MarshalArray' 00002b68 T __stginit_haskell98_MarshalArray 00002b24 T __stginit_haskell98_MarshalArray_dyn dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g base-4.2.0.2/libHSbase-4.2.0.2.a | grep '__stginit_.*Foreign.*Marshal.*Array' 0000006c T __stginit_base_ForeignziMarshalziArray 00000000 T __stginit_base_ForeignziMarshalziArray_ {Some output omitted.} dbanas@dbanas-eeepc:/usr/lib/ghc-6.12.3$ nm -g -D base-4.2.0.2/libHSbase-4.2.0.2-ghc6.12.3.so | grep '__stginit_.*Foreign.*Marshal.*Array' 003dc8cc T __stginit_base_ForeignziMarshalziArray 003dc834 T __stginit_base_ForeignziMarshalziArray_dyn Can anyone shed some light on this? Thanks!

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Embedding Perl RegEx in Haskell
by C K Kashyap 21 Aug '11

21 Aug '11

Dear Haskell folks, I was attempting to do an EDSL that would allow me to describe regular expressions in Hakell and generate Perl as target - https://github.com/ckkashyap/LearningPrograms/blob/master/Haskell/edsl/rege… $ ghci regex.hs GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. [1 of 1] Compiling Main ( regex.hs, interpreted ) Ok, modules loaded: Main. *Main> let hello = stringToRegularExpression "hello" *Main> let world = stringToRegularExpression "world" *Main> :t hello hello :: RegularExpression *Main> :t world world :: RegularExpression *Main> let re = listToSequence [ hello, oneOrMore world, hello ] *Main> re hello(world)+hello *Main> :t re re :: RegularExpression I am looking for suggestions on how I could encode the anchors - ^ and $ and also how I could refer to captures. My goal is to be able to extend the idea to create an EDSL that could be used to build Perl tasks - such as filters, report generators etc Arguably this could be seen as a pointless exercise because I could chose to do the scripting in Haskell itself but I have a practical problem that I have to deal with clusters that have a little dated version of Linux where I could not really build the Haskell and where Haskell generated executables don't seem to run. When I started out with this idea, I was thinking of embedding Perl in Haskell but later I thought that perhaps that will sort of beat the point of "DS" bit in EDSL. So, I have started on this idea of trying to encode very precise "tasks". Regards, Kashyap

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Existential question
by Tom Schouten 20 Aug '11

20 Aug '11

{-# LANGUAGE ExistentialQuantification #-} -- Dear Cafe, this one works. data Kl' s i o = Kl' (i -> s -> (s, o)) iso' :: (i -> Kl' s () o) -> Kl' s i o iso' f = Kl' $ \i s -> (\(Kl' kl') -> kl' () s) (f i) -- Is there a way to make this one work also? data Kl i o = forall s. Kl (i -> s -> (s, o)) iso :: (i -> Kl () o) -> Kl i o iso f = Kl $ \i s -> (\(Kl kl) -> kl () s) (f i) {- Couldn't match type `s0' with `s' because type variable `s' would escape its scope This (rigid, skolem) type variable is bound by a pattern with constructor Kl :: forall i o s. (i -> s -> (s, o)) -> Kl i o, in a lambda abstraction The following variables have types that mention s0 s :: s0 (bound at /home/tom/meta/haskell/iso.hs:11:17) In the pattern: Kl kl In the expression: \ (Kl kl) -> kl () s In the expression: (\ (Kl kl) -> kl () s) (f i) -}

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Segfault in the libc malloc using FFI (occurs only in x86_64)
by Vincent Gerard 20 Aug '11

20 Aug '11

Hi cafe, I have been struggling with this issue for the past days. I have investigated at the Haskell, C and even at assembly level... Perhaps I'm missing something big ?? I hope someone familiar with FFI could help me on this Segfault. My env is: Linux Debian 3.0.0-1, SMP, GHC 7.0.4, x86_64, eglibc 2.13-10 (This issues occurs as well on others people with /= env, but only with x86_64 arch) The bug is in the hsmagick library (FFI bindings to GraphicsMagick), for which I am the maintainer. -- So here is a reproducer (Works fine in 32 bit, segfault in 64). You should have hsmagick + GraphicsMagick dev libs installed. import Graphics.Transform.Magick.Images main = do initializeMagick c <- readImage "image.jpg" putStrLn "End" -- Executing this program, compiled with standard options, a Segfault occurs at runtime. If I compile this small program with -threaded option an assertion error is thrown at runtime: main: malloc.c:3096: sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, >fd_nextsize))+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) >- 1))) && ((old_top)->size & 0x1) && ((unsigned long)old_end & >pagemask) == 0)' failed. This assertion error is cryptic for me... but it maybe could help someone here. However, having a C experience, investigating a Segfault is in my habits, so let's install debugs symbols on everything and dig with gdb. Here is the backtrace: Program received signal SIGSEGV, Segmentation fault. 0x00007ffff510292c in malloc_consolidate (av=0x7ffff540fe60) at malloc.c:5161 (this is inside the eglibc source) 5161 unlink(p, bck, fwd); (gdb) bt #0 0x00007ffff510292c in malloc_consolidate (av=0x7ffff540fe60) at malloc.c:5161 #1 0x00007ffff5104d64 in _int_malloc (av=0x7ffff540fe60,bytes=8520) at malloc.c:4373 #2 0x00007ffff5107420 in __libc_malloc (bytes=8520) at malloc.c:3660 #3 0x00007ffff67bf311 in CloneImageInfo (image_info=0x0) at magick/image.c:1012 #4 0x0000000000439dfa in hsmagickzm0zi5_GraphicsziTransformziMagickziFFIHelpers_mkNewImageInfo1_info () Yay, the Segfault is deep in the libc after a regular malloc (8520bytes) (I dug into the GraphicsMagick source starting from magick/image.c:1012) And this libc call is called by a call to CloneImageInfo(NULL) from Haskell, which is correct as it is graphicsMagick way to allocate an empty ImageInfo data structure. (http://www.graphicsmagick.org/api/image.html#cloneimageinfo) I tried in a C program to execute (after initializing ImageMagick) image_info=CloneImageInfo((ImageInfo *) NULL); And of course .... no Segfault... Let's look at the FFI call... This FFI call is the done by the mkNewImageInfo as shown in the trace. The Haskell FFI layer here has done the right job, calling the C function with the right args (NULL) Here is all the code related to mkNewImageInfo (the last Haskell part we see in the backtrace) --- mkNewImageInfo :: IO (ForeignPtr HImageInfo) mkNewImageInfo = mkFinalizedImageInfo =<< mkNewImageInfo_ mkFinalizedImageInfo :: Ptr HImageInfo -> IO (ForeignPtr HImageInfo) mkFinalizedImageInfo = newForeignPtr imageInfoFinalizer mkNewImageInfo_ :: IO (Ptr HImageInfo) mkNewImageInfo_ = clone_image_info nullPtr -- CALL before the Segfault destroyImageInfo :: Ptr HImageInfo -> IO () destroyImageInfo = destroy_image_info foreign import ccall "static magick/api.h &DestroyImageInfo" imageInfoFinalizer :: FunPtr (Ptr HImageInfo -> IO ()) foreign import ccall "static magick/api.h CloneImageInfo" clone_image_info :: Ptr HImageInfo -> IO (Ptr HImageInfo) -- To me, this code is right (and works perfectly in 32 bit). Furthermore, as the call is made with a nullPtr arg, no data structure is used ... I tried this code without using ForeignPtr Finalizers (hsmagick <= 0.4) and the Segfault occurs as well ... I even had a look at the generated assembly, which also looks right... It seems there is a real segmentation error, or an illegal access to a memory page... But I could not find the root cause of this error. And an additionnal piece to the puzzle, when running the program inside valgrind, there is no Segfault and the program works as expected. So if anyone have an idea on how only on 64bits arch an Haskell FFI call could led to a Segfault in the libc malloc, it would make my day, perhaps my week :) Thanks ! Vincent Gerard

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Simon PJ in Australia
by Simon Peyton-Jones 19 Aug '11

19 Aug '11

This is a message for Australian FPers -- sorry to spam the rest of you. I'm crossing the planet to Australia for YOW (Melbourne Dec 1-2, Brisbane Dec 5-6). http://www.yowconference.com.au/YOW2011/ I'm committed for the conference dates of course, but I could spend a few days before or afterwards, hanging out with some of you guys. Hack on GHC, give a talk, eat pizza, university departments, Haskell users groups, surfing (on water, that is).... Do drop me (not the list) a line if any of that sounds fun. Simon PS: John Hughes is coming to Yow too, so you could try luring him into your lair too.

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Question about data
by Paul Reiners 19 Aug '11

19 Aug '11

I've created a simple type declaration: data MathExpression = Float | Add MathExpression MathExpression | Subtract MathExpression MathExpression | Multiply MathExpression MathExpression | Divide MathExpression MathExpression deriving (Show) Now how do I create an instance of MathExpression which is just a Float? This doesn't work: *Main> let pi = 3.14 :: MathExpression <interactive>:1:10: No instance for (Fractional MathExpression) arising from the literal `3.14' Possible fix: add an instance declaration for (Fractional MathExpression) In the expression: 3.14 :: MathExpression In an equation for `pi': pi = 3.14 :: MathExpression

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why is Random in System?
by Evan Laforge 19 Aug '11

19 Aug '11

I've noticed there's a convention to put modules having to deal with randomness into System.Random. I thought System was for OS interaction? Granted getting a random seed usually means going to the OS, but isn't the rest of it, like generating random sequences, distributions, selecting based on probability, shuffling, etc. all non-OS related algorithms? I'm not sure where I would expect Random to go, perhaps Math or maybe the toplevel, but under System seems, well, random... I notice random-fu puts it under Data, which is also not where I'd look, except that you always look in Data because everything goes into Data... but algorithms dealing with random numbers aren't really data structures either, are they?

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Can I have a typeclass for topological spaces?
by Grigory Sarnitskiy 19 Aug '11

19 Aug '11

Hello! I just wonder whether it is possible to have a typeclass for topological spaces?

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Failed link to mixed-language shared object.
by David Banas 19 Aug '11

19 Aug '11

Hi all, Does this trigger recollection in anyone: dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ make ghc -dynamic -o ami_test -L. -lami ami_test.o ./libami.so: undefined reference to `__stginit_haskell98_MarshalArray_' ./libami.so: undefined reference to `__stginit_haskell98_MarshalError_' collect2: ld returned 1 exit status make: *** [ami_test] Error 1 dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ ? Know what I need to do? Thanks, -db

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Problem with types
by Anupam Jain 19 Aug '11

19 Aug '11

Hi all, Suppose I have a compound data type - data M o = M (String,o) Now, I can define a function that works for ALL M irrespective of o. For example - f :: M o -> M o f (M (s,o)) = M (s++"!", o) I can also use this function in an expression, applying it to different types without problem - p = (m1',m2') where m1 = M ("1", ()) m2 = M ("2", True) m1' = f m1 m2' = f m2 Main*> p (M ("1!",()),M ("2!",True)) However, if I try to parameterise over the function 'f' it does not work! - p f = (m1',m2') where m1 = M ("1", ()) m2 = M ("2", True) m1' = f m1 m2' = f m2 It doesn't even typecheck, producing the error - "Couldn't match expected type 'Bool' with actual type '()'" Is there a particular reason for this? How can I define a function like 'p' within Haskell? Thanks, Anupam Jain

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