- Glasgow-haskell-users

Tuning -funfolding-use-threshhold
by dons＠cse.unsw.edu.au 27 Nov '06

27 Nov '06

Does this thread on haskell-cafe, about getting better bit shifting results, indicate we should be tweaking the default unfolding-use threshold? Do the recent bit shifting/inlining patches improve things? http://thread.gmane.org/gmane.comp.lang.haskell.cafe/16849/focus=16849 I'm thinking that users shouldn't need to resort to manual -funfolding-use-threshhold settings? -- Don

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Passing arrays between Haskell and C without overhead
by Brian Hulley 26 Nov '06

26 Nov '06

Hi, For a 3d graphics library, I'd like to have a 4x4 matrix of floats which I can pass from Haskell to C without having to copy all 16 floats each time, something like: data Mat44f = Mat44f Float# Float# ... Float# foreign import ccall c_setWorldTransform :: Ptr Mat44f -> IO () setWorldTransform :: Mat44f -> IO () setWorldTransform mat = withSafePtr mat c_setWorldTransform where withSafePtr :: a -> (Ptr a -> IO b) -> IO b would supply a pointer directly to the Haskell heap representation of (a) and would ensure that (a) doesn't get garbage collected until the IO action is completed. (Note that this is not the same as Foreign.Marshal.Utils.with, which uses alloca and poke to copy the matrix - I'm trying to avoid this overhead of copying.) However there is no such function afaics so the only solutions at present seem to be to either make Mat44f an instance of Storable and use alloca (which involves copying all 16 floats just so that C can read it even though I'd expect the heap representation to already be identical since there is only one constructor and all fields are unboxed) or else pass the 16 floats individually by: foreign import ccall c_SetWorldTransform' :: Float# -> Float# -> ... -> Float# -> IO () setWorldTransform (Mat44f m11 m12 m13 m14 ... m44) = c_SetWorldTransform' m11 m12 m13 ... m44 In this second case the C function will have to manually put these 16 floats back into an array so that it will have a pointer to a temporary array of 16 floats to use internally (eg to pass to the DirectX api which will then make its own copy of it), so in both cases there is a wasteful deconstruction then reconstruction of the original array of 16 floats stored on the Haskell heap. Similar problems arise when trying to pass an array from C back to Haskell, but in this case it's clear some copying will be needed so that one ends up with a value stored on the Haskell heap - the "double copy" problem only arises in the direction from Haskell to C. I've also thought about just implementing all the math functions in C and using mallocForeignPtrArray so that the data type would be: newtype Mat44f = Mat44f (ForeignPtr CFloat) While this would make passing between C and Haskell very fast, it seems a pity to have to sacrifice the ability to code the math ops directly in Haskell in a functional style with all the attendant optimizations one could expect from GHC (using ForeignPtr requires unsafePerformIO, withForeignPtr, and lots and lots of peek/pokeElemOff's in a monadic style - rather gross compared to pattern matching etc) So my questions are: 1) Is there any reason why there can't be a function (withSafePtr) to avoid all this marshalling overhead when we know (or specify via a pragma) that Haskell stores the data already in a form compatible with C, or is there some other way to represent a 4x4 matrix such that it can be manipulated in Haskell and passed without overhead to C? 2) Does withSafePtr already exist somewhere? 3) Would it be a good idea to make Storable one of the classes which can be automatically derived? Thanks, Brian. -- http://www.metamilk.com

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Hacking on GHC interactively with GHCi
by Clemens Fruhwirth 25 Nov '06

25 Nov '06

Hello everyone, I would like to hack on GHC interactively. My aim is to load ghc into ghci and start hacking a source file in one emacs buffer, while the other hosts an inferior-haskell session connected to GHCi. I really like this kind of development style and found it to be way more productive than "edit/compile/test/restart from edit". To context of the following is the compiler/ subtree, as I'm primarily interested in that. I tried to: * load all GHC compiler source files into ghci, fails because of occassional unboxed types (bytecode generated can't deal with them) * load all .o files (with unboxed types) and load a modified source in interpreted mode. This doesn't work well because for that approach you need to mix the source with the object in the same directory (copy compiler/**/*.[l]hs to stage1 or stage2). This, fails because there seem to be some sources missing, I have not investiged where the .o-boot files come from like compiler/stage2/basicTypes/OccName.o-boot. With source files, GHCi just ignores the existing .o file (resumable because it can't check whether the .o file is more recent than the source file) * load "ghci -package ghc" and load main/Main.hs. This work pretty well, but only in comparsion to the other approaches -- that means loading does not fail. Invoking ":main -c foobar.hs" freezes the ghci session. With this approach I can not change any module withing the packaged ghc. Is that true? But that's what I want to do (in particular to the parser part). So, before I start to work towards a particular end of these 3 approaches, is there anyone how develops ghc in an interactive way using ghci with partial :reload-ing of modules? The GHC user guide has a good illustration of what I'm looking for http://www.haskell.org/ghc/docs/latest/html/users_guide/ghci-compiled.html Any hint is appreciated. -- Fruhwirth Clemens - http://clemens.endorphin.org for robots: sp4mtrap(a)endorphin.org

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Gtk2Hs and GHC 6.6
by Michael T. Richter 24 Nov '06

24 Nov '06

OK, my last post on this was put into moderator limbo for being too large and then never released nor rejected. Here's try number two. I won't attach the full build output because that's apparently what put it into moderator limbo in the first place. I'm trying to build Gtk2Hs under GHC 6.6. I've built it successfully under 6.4.1 and 6.4.2 -- no muss, no fuss, no bother. Something big seems to have changed in 6.6, however, that breaks the Gtk2Hs build in a bad way. Here are some representative errors: First, we see that it did find the right GHC version: checking for ghc... /usr/local/bin/ghc checking version of GHC... 6.6 checking for ghc-pkg... /usr/local/bin/ghc-pkg But now we get some strange package problems. Each of these is a representative. The full build has dozens of these -- I think I've got each flavour though: tools/c2hs/base/general/Binary.hs:59:7: Could not find module `Data.FiniteMap': Use -v to see a list of the files searched for. make[1]: *** Deleting file `tools/c2hs/c2hsLocal.deps' tools/c2hs/base/admin/Common.hs:54:0: Failed to load interface for `Config': it is a member of package ghc-6.6, which is hidden make[2]: *** [tools/c2hs/base/admin/Common.o] Error 1 make[2]: Leaving directory `/home/michael/Development/Gtk2Hs/gtk2hs-0.9.10' make[1]: *** [glib/System/Glib/Types.hs] Error 2 make[1]: Leaving directory `/home/michael/Development/Gtk2Hs/gtk2hs-0.9.10' <no location info>: can't find file: glib/System/Glib/Types.hs make: *** Deleting file `glib/libHSglib_a.deps' glib/System/Glib.hs:12:0: Failed to load interface for `System.Glib.UTFString': Use -v to see a list of the files searched for. make[1]: *** [glib/System/Glib.o] Error 1 make[1]: Leaving directory `/home/michael/Development/Gtk2Hs/gtk2hs-0.9.10' make: *** [all] Error 2 So I'm left with the question: what am I doing wrong (if anything)? Or what do I need to do to get Gtk2Hs to compile under 6.6? -- Michael T. Richter Email: ttmrichter(a)gmail.com, mtr1966(a)hotpop.com MSN: ttmrichter(a)hotmail.com, mtr1966(a)hotmail.com; YIM: michael_richter_1966; AIM: YanJiahua1966; ICQ: 241960658; Jabber: mtr1966(a)jabber.cn "I would not flinch from sacrificing a million lives for India's liberty!" --Mahatma Gandhi

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evaluate to lazy?
by Andreas Marth 22 Nov '06

22 Nov '06

Hi! With the following code: module Guess where import Prelude hiding (catch) import Control.Exception (evaluate, catch) guess :: [String] -> IO String guess sl = do res <- catch (evaluate (concat $ sl ++ [error "some error message", "blah blah blah"])) (\e -> return ("error#"++show e)) return res -- only for demonstration coded like this normally a call to sysalloc comes here what will a) guess [] b) guess [""] c) guess [" "] return? The idea was to return the string, catch every error if any occour, convert it into a string and prefix it with "error#" and return this string then. The reason to do this is to create a stable DLL with the error handling in non haskell land. At the moment every exception raised crashes the whole system, which is unacceptable. Unfortunately the c) case still raises an exception. I think at least the library description needs a hint that 'evaluate (" "++error "some error message")' does not raise the error (which I find strange!) and hence catch won't catch it. Is this behaivior really desired or should we consider it a bug? Thanks, Andreas PS: I circumvent this issue by using 'rnf' and 'using' from Control.Parallel.Strategies

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Creating Loadable Dynamic Libraries in OSX
by Alfonso Acosta 22 Nov '06

22 Nov '06

Hi, I succesfully created dynamic loadable libraries (.so) with GHC6.6 under LinuxX86 using some C glue code and linking with -optl -shared. Now I would like to port my code to OSX but linking with "-optl -bunde" fails giving a "local relocation entries in non-writable section" error. I think that is becase under OSX, GHC calls gcc with -mdynamic-no-pic preventing my FFI stub object files to be linked. Does anyone know why is -mdynamic-no-pic used or a workaround? Thanks in advance, Alfonso Acosta

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Re: Bad control characters in GHCi 6.6 (Mac OS X PPC)
by Björn Buckwalter 21 Nov '06

21 Nov '06

On 10/19/06, Simon Marlow <simonmar(a)microsoft.com> wrote: > See this page that I just created: > > http://hackage.haskell.org/trac/ghc/wiki/Building/MacOSX I tried these instructions, first by using my existing (darwinports) readline in /opt/local, and when that failed by first installing readline in /usr/local per the instructions. Neither fixed the problem. I don't know why but perhaps I failed to remove the traces of my initial install completely. In the end I gave up and installed Greg Heartsfield's binary package which remedied my problems (thanks Greg!). Thanks anyway Simon, -Bjorn Buckwalter

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Request for testing help from ghc-6.6 users on Win9x
by Sigbjorn Finne 21 Nov '06

21 Nov '06

Hi, a couple of users have been reporting problems with ghc-6.6 on the line of OS editions that reached its pinnacle as Windows ME, in particular when invoking GHCi. An alleged fix is available, but we'd really appreciate if it could be tested more widely before declaring victory (and push the changes into the next GHC release). To try it out, download http://galois.com/~sof/ghc9x.zip and unpack its contents on top of the bin/ directory of your ghc-6.6 install. [To avoid any irreversible damage, you may very well want to move the original bin/ghc.exe out of the way first. ] If you could ping me with a yay/nay on whether that GHCi usage, that'd be very helpful. thx --sigbjorn

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runtime fusion for Data.ByteString.cons ?
by Claus Reinke 21 Nov '06

21 Nov '06

I noticed that ByteString is drastically slower than String if I use cons a lot. according to the source, that is expected because of the memcpy for the second parameter. but it seems to me that construction should be able to play the dual trick to deconstruction (which does not copy the tail, but returns an indirection into the original list). roughly speaking: when constructing a ByteString via cons h t, we know the length of the result (1+length t), and instead of creating t in a separate storage location then copying it over to the result, we could try to create it inplace. or rather, we could delay construction of ByteStrings until we know whether we need to allocate fresh memory for them or whether they can be created by filling some context. this rough idea runs into a couple of issues in practice: - first of all, it seems to be a runtime fusion (unless we do whole program optimization, simplifier rewrites won't do, although unfolding recursions might still expose some opportunities for a static variant of this fusion) - if t is shared, we'd like to redirect these shared references to an indirection into the tail of cons h t ignoring the second point for now, if we look into the source for cons, we find something like: cons :: Word8 -> ByteString -> ByteString cons c (PS x s l) = unsafeCreate (l+1) $ \p-> ... poke p c; memcpy (p+1).. now, let's imagine a pre-ByteString as a not-yet allocated ByteString: data PreBS = PrePS l f so that createBS :: PreBS -> ByteString createBS (PrePS l f) = unsafeCreate l f consPre :: Word8 -> ByteString -> PrePS consPre c (PS x s l) = PrePS (l+1) $ \p-> ... poke p c; memcpy (p+1).. cons :: Word8 -> ByteString -> ByteString cons c bs = createBS (consPre c bs) then we could express our fusion as consPre c (create (PrePS l f)) = PrePS (l+1) $ \p-> ... poke p c; f (p+1).. in other words, in a typical map-like recursion scheme, we do not create, copy & release the tails recursively, but delay creation until we know where to embed our ByteString, at which point we do a sequence of pokes, no memcpy. but note that we are matching on a function application here, even though we are not in a simplifier rule, so this doesn't work as it stands.. this is as far as I got so far.. (see attached example for a manual use of pre-ByteStrings to speed up a map). now my questions for you:-) - does this make sense? - can it be made to work? as we probably cannot redirect shared references to t in (cons h t), can we identify the situations where t is not shared, as in a map, or can we just ignore any shared references (they will point to a "create (PrePS ..)" combination, and should just keep working, since we bypass those combinations instead of rewriting them)? a tentative idea would be to overload create so that it produces a proper, allocated ByteString where such is expected, but can also just pass through the PreBS where the context can handle it? class Create r where create :: PreBS -> r instance Create ByteString where create (PrePS l f) = unsafeCreate l f instance Create PreBS where create = id consPre :: Word8 -> ByteString -> PrePS consPre c (PS x s l) = PrePS (l+1) $ \p-> ... poke p c; memcpy (p+1).. cons :: Word8 -> ByteString -> ByteString cons c bs = create (consPre c bs) consPre' :: Word8 -> PrePS -> PrePS consPre' c (PrePS l f) = PrePS (l+1) $ \p-> ... poke p c; f (p+1).. so that "consPre c (create (PrePS ..))" works as normal, while "consPre' c (create (PrePS ..))" uses the fusion path. or something like that;-) Claus

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First Call for Papers: TFP 2007, New York, USA
by TFP 2007 21 Nov '06

21 Nov '06

CALL FOR PAPERS Trends in Functional Programming 2007 New York, USA April 2-4, 2007 http://tltc.shu.edu/tfp2007/ OR http://cs.shu.edu/tfp2007/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming languages, focusing on providing a broad view of current and future trends in Functional Programming. It aspires to be a lively environment for presenting the latest research results through acceptance by extended abstracts. A formal post-symposium refereeing process then selects the best articles presented at the symposium for publication in a high-profile volume. TFP 2007 is co-hosted by Seton Hall University and The City College of New York (CCNY) and will be held in New York, USA, April 2-4, 2007 at the CCNY campus. The TFP symposium is the successor to the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh, Scotland in 2003 (co-located with IFL), in Munich, Germany in 2004, in Tallinn, Estonia in 2005 (co-located with ICFP and GPCE), and in Nottingham, UK in 2006 (co-located with Types). For further general information about TFP please see the TFP homepage at http://cs.shu.edu/tfp2007/ . SCOPE OF THE SYMPOSIUM The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles leading-edge, previously unpublished research work Position Articles on what new trends should or should not be Project Articles descriptions of recently started new projects Evaluation Articles what lessons can be drawn from a finished project Overview Articles summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Articles on the following subject areas are particularly welcomed: o Dependently Typed Functional Programming o Validation and Verification of Functional Programs o Debugging for Functional Languages o Functional Programming and Security o Functional Programming and Mobility o Functional Programming to Animate/Prototype/Implement Systems from Formal or Semi-Formal Specifications o Functional Languages for Telecommunications Applications o Functional Languages for Embedded Systems o Functional Programming Applied to Global Computing o Functional GRIDs o Functional Programming Ideas in Imperative or Object-Oriented Settings (and the converse) o Interoperability with Imperative Programming Languages o Novel Memory Management Techniques o Parallel/Concurrent Functional Languages o Program Transformation Techniques o Empirical Performance Studies o Abstract/Virtual Machines and Compilers for Functional Languages o New Implementation Strategies o any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2007 program chair, Marco T. Morazan, at tfp2007(a)shu.edu. BEST STUDENT PAPER AWARD TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A prize for the best student paper is awarded each year. SUBMISSION AND DRAFT PROCEEDINGS Acceptance of articles for presentation at the symposium is based on the review of extended abstracts (6 to 10 pages in length) by the program committee. Accepted abstracts are to be completed to full papers before the symposium for publication in the draft proceedings and on-line. The submission must clearly indicate to which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate whether the main author or authors are research students. Formatting details can be found at the TFP 2007 website. Submission procedures will be posted on the TFP 2007 website as the submission deadline is reached. The papers in the draft proceedings will also be made available on-line under the following conditions, with which all authors are asked to agree: The documents distributed by this server have been provided by the contributing authors as a means to ensure timely dissemination of scholarly and technical work on a noncommercial basis. Copyright and all rights therein are maintained by the authors or by other copyright holders, notwithstanding that they have offered their works here electronically. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each author's copyright. These works may not be reposted without the explicit permission of the copyright holder. POST-SYMPOSIUM REFEREEING AND PUBLICATION In addition to the draft symposium proceedings, we intend to continue the TFP tradition of publishing a high-quality subset of contributions in the Intellect series on Trends in Functional Programming. All TFP authors will be invited to submit revised papers after the symposium. These will be refereed using normal conference standards and a subset of the best papers, over all categories, will be selected for publication. Papers will be judged on their contribution to the research area with appropriate criteria applied to each category of paper. Student papers will be given extra feedback by the Program Committee in order to assist those unfamiliar with the publication process. Important DATES Abstract Submission: February 1, 2007 Notification of Acceptance: February 20, 2007 Registration Deadline: March 2, 2007 Camera Ready Full Paper Due: March 9, 2007 TFP Symposium: April 2-4, 2007 PROGRAMME COMMITTEE John Clements California Polytechnic State University, USA Marko van Eekelen Radboud Universiteit Nijmegen, The Netherlands Benjamin Goldberg New York University, USA Kevin Hammond University of St. Andrews, UK Patricia Johann Rutgers University, USA Hans-Wolfgang Loidl Ludwig-Maximilians Universität München, Germany Rita Loogen Philipps-Universität Marburg, Germany Greg Michaelson Heriot-Watt University, UK Marco T. Morazán (Chair) Seton Hall University, USA Henrik Nilsson University of Nottingham, UK Chris Okasaki United States Military Academy at West Point, USA Rex Page University of Oklahoma, USA Ricardo Pena Universidad Complutense de Madrid, Spain Benjamin C. Pierce University of Pennsylvania, USA John Reppy University of Chicago, USA Ulrik P. Schultz University of Southern Denmark, Denmark Clara Segura Universidad Complutense de Madrid, Spain Jocelyn Sérot Université Blaise Pascal, France Zhong Shao Yale University, USA Olin Shivers Georgia Institute of Technology, USA Phil Trinder Heriot-Watt University, UK David Walker Princeton University, USA ORGANIZATION Symposium Chair: Henrik Nilsson, University of Nottingham, UK Programme Chair: Marco T. Morazan, Seton Hall University, USA Treasurer: Greg Michaelson, Heriot-Watt University, UK Local Arrangements: Marco T. Morazan, Seton Hall University, USA SPONSORS The Department of Mathematics and Computer Science, Seton Hall University The Department of Computer Science, The City College of New York The Center for Algorithms and Interactive Scientific Software of The City College of New York The Grove School of Engineering of The City College of New York We are actively looking for additional TFP sponsors, who may, for example, help to subsidise attendance by research students. If you or your organisation might be willing to sponsor TFP, or if you know someone who might be willing to do so, please do not hesitate to contact the Program Chair, Marco T. Morazan, or the Symposium Chair, Henrik Nilsson. Your students will be grateful! ************************************************************************************ Dr. Marco T. Morazan TFP 2007 Program Committee Chair http://cs.shu.edu/tfp2007/

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