August 2007 - Haskell

Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 07 Apr '11

07 Apr '11

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

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Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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The real Monad Transformer
by Henning Thielemann 13 Nov '08

13 Nov '08

It was argued that people avoid Haskell because of terms from Category theory like 'Monad'. This problem can now be solved by a wrapper which presents all the WWW without monads! Start e.g. at http://saxophone.jpberlin.de/MonadTransformer?source=http%3A%2F%2Fwww%2Ehas… Of course the tool is written in Haskell, that is, Haskell helps solving problems which only exist because of Haskell. Bug reports and feature requests can be tracked at https://sourceforge.net/projects/parallelweb

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APLAS07 - Call for Participation
by Corneliu Popeea 31 Aug '07

31 Aug '07

Call for Participation The Fifth Asian Symposium on Programming Languages and Systems November 29 - December 1, 2007 Singapore http://www.comp.nus.edu.sg/~aplas07/ http://flint.cs.yale.edu/aplas2007/ Scope of the Conference ----------------------- APLAS aims at stimulating programming language research by providing a forum for the presentation of recent results and the exchange of ideas and experience in topics concerned with programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming languages community. The APLAS series is sponsored by the Asian Association for Foundation of Software (AAFS), which has recently been founded by Asian researchers in cooperation with many researchers from Europe and the USA. The past formal APLAS symposiums were successfully held in Sydney (2006, Australia), Tsukuba (2005, Japan), Taipei (2004, Taiwan) and Beijing (2003, China) after three informal workshops held in Shanghai (2002, China), Daejeon (2001, Korea) and Singapore (2000). Proceedings of the past symposiums were published in Springer-Verlag's LNCS 2895, 3302, 3780, and 4279. Conference Location ------------------- APLAS'07 will be held at Kent Ridge Guild House, National University of Singapore. Singapore is a dynamic city rich in contrast and color where you'll find a harmonious blend of culture, cuisine, arts and architecture. A bridge between the East and the West for centuries, Singapore, located in the heart of fascinating Southeast Asia, continues to embrace tradition and modernity today. Brimming with unbridled energy and bursting with exciting events, the city offers countless unique, memorable experiences waiting to be discovered. Registration ------------ The early registration deadline is set on 28Sept07. The registration fees will cover conference proceeding, banquet dinner, and lunches/teas. Deadline Full Fees Student Fees early 28Sep07 S$600 S$400 online 23Nov07 S$650 S$425 on-site 29Nov07 S$700 S$450 Payment can be made with credit cards. Exchange rate (subject to fluctuation) is approx. US$1 = S$1.53 Online registration can be made at: http://www.comp.nus.edu.sg/~aplas07/local.html#registration Accommodation ------------- A special rate S$155 per nite (excluding taxes but inclusive of daily breakfast) is applicable to attendees of APLAS 2007 at Rendezvous Hotel Singapore: http://www.rendezvoushotels.com/singapore/ The hotel is located in city center. A free daily shuttle bus will be provided between this hotel and the conference site (at NUS) during the conference period. Our block of rooms is guaranteed till 28Sept07, so advanced booking is encouraged as some rooms may be released after this date. For reservation, please use a special form that can be found at: http://www.comp.nus.edu.sg/~aplas07/Hotel.APLAS07.pdf Poster Session -------------- APLAS07 will include a poster session. Submission deadline is 14 Sept 2007. For details, please see: http://www.comp.nus.edu.sg/~aplas07/posters.html Conference Program ------------------ 29 Nov (Thu) ------------ 915- 930 Opening note 930-1030 Invited Talk X10: Programming Parallel Machines, Productively Vijay Saraswat (IBM TJ Watson Research Lab) 1100-1230 Session 1 The Nuggetizer: Abstracting Away Higher-Orderness for Program Verification Paritosh Shroff (Johns Hopkins University), Christian Skalka (University of Vermont) and Scott F. Smith (Johns Hopkins University) Local Reasoning for Storable Locks and Threads Alexey Gotsman (University of Cambridge), Josh Berdine (Microsoft Research), Byron Cook (Microsoft Research), Noam Rinetzky (Tel Aviv University) and Mooly Sagiv (Tel Aviv University) Monadic, Prompt Lazy Assertions in Haskell Frank Huch (CAU Kiel) and Olaf Chitil (University of Kent) 1345-1515 Session 2 Translation Correctness for First-Order Object-Oriented Pattern Matching Burak Emir (EPFL Lausanne), Qin Ma (OFFIS) and Martin Odersky (EPFL Lausanne) Persistent Oberon: A Programming Language with Integrated Persistence Luc Blaser (ETH Zurich) More Typed Assembly Languages for Confidentiality Dachuan Yu (DoCoMo Communication Laboratories USA) 1515-1630 Poster Session 1630-1730 Session 3 A Novel Test Case Generation Method for Prolog Programs Based on Call Patterns Semantics Lingzhong Zhao (Guilin University of Electronic Technology), Tianlong Gu (Guilin University of Electronic Technology), Junyan Qian (Guilin University of Electronic Technology) and Guoyong Cai (Guilin University of Electronic Technology) On a Tighter Integration of Functional and Logic Programming Frank Huch (CAU Kiel) and Bernd Brassel (CAU Kiel) 1800-2000 Reception 30 Nov (Fri) ------------ 930-1030 Invited Talk Scalable Simulation of Biological Signaling Networks Vincent Danos (University of Paris VII & CNRS) 1100-1230 Session 4 Timed, Distributed, Probabilistic, Typed Processes Martin Berger (Imperial College London) and Nobuko Yoshida (Imperial College London) A Probabilistic Applied Pi-Calculus Jean Goubault-Larrecq (ENS Cachan), Catuscia Palamidessi (Ecole Polytechnique) and Angelo Troina (ENS Cachan & Ecole Polytechnique) Type-Based Verification of Correspondence Assertions for Communication Protocols Daisuke Kikuchi (Tohoku University) and Naoki Kobayashi (Tohoku University) 1400-1530 Session 5 Deriving Compilers and Virtual Machines for a Multi-Level Language Atsushi Igarashi (Kyoto University) and Masashi Iwaki (Kyoto University) Finally Tagless, Partially Evaluated (Tagless Staged Interpreters for Simpler Typed Languages) Jacques Carette (McMaster University), Oleg Kiselyov (FNMOC) and Chung-chieh Shan (Rutgers University) Polymorphic Delimited Continuations Kenichi Asai (Ochanomizu University) and Yukiyoshi Kameyama (University of Tsukuba) 1600-1730 Session 6 Adjunct Elimination in Context Logic for Trees Cristiano Calcagno (Imperial College London), Thomas Dinsdale-Young (Imperial College London) and Philippa Gardner (Imperial College London) Positive Arithmetic without Exchange is a Subclassical Logic Stefano Berardi (University of Torino) and Makoto Tatsuta (National Institute of Informatics, Japan) Mixed Inductive/Coinductive Types and Strong Normalization Andreas Abel (University of Munich) 1900-2100 Banquet 1 Dec (Sat) ------------ 930-1030 Invited Talk Static and Dynamic Analysis : Better Together Sriram Rajamani (Microsoft Research India) 1100-1230 Session 7 The Semantics of "Semantic Patches" in Coccinelle: Program Transformation for the Working Programmer Neil Jones (University of Copenhagen) and Rene Rydhof Hansen (University of Copenhagen) An Efficient SSA-based Algorithm for Complete Global Value Numbering Jiu-Tao Nie (Peking University) and Xu Cheng (Peking University) A Systematic Approach to Probabilistic Pointer Analysis Alessandra Di Pierro (University of Verona), Chris Hankin (Imperial College London) and Herbert Wiklicky (Imperial College London) 1400-1530 Session 8 Complete Lattices and Up-to Techniques Damien Pous (ENS Lyon) A Trace Based Bisimulation for the Spi Calculus: An Extended Abstract Alwen Tiu (Australian National University) CCS with Replication in the Chomsky Hierarchy: The Expressive Power of Divergence Frank Valencia (Ecole Polytechnique), Cinzia Di Giusto (University of Bologna), Jesus Aranda (Ecole Polytechnique) and Mogens Nielsen (University of Aarhus) 1600-1700 Session 9 Call-by-Name and Call-by-Value in Normal Modal Logic Yoshihiko Kakutani (University of Tokyo) Call-by-Value is Dual to Call-by-Name, Extended Daisuke Kimura (National Institute of Informatics, Japan) 1700-1715 Closing note Organization ------------- GENERAL CHAIR Joxan Jaffar (National University of Singapore, Singapore) PROGRAM CHAIR Zhong Shao (Yale University, USA) PROGRAM COMMITTEE Lars Birkedal (IT University of Copenhagen, Denmark) Martin Hofmann (Univ of Munich, Germany) Kohei Honda (Queen Mary, University of London, UK) Atsushi Igarashi (Kyoto University, Japan) Suresh Jagannathan (Purdue University, USA) Annie Liu (State University of New York at Stony Brook, USA) Shin-Cheng Mu (Academia Sinica, Taiwan) Henrik Nilsson (University of Nottingham, UK) Michael Norrish (NICTA, Australia) Jens Palsberg (University of California, Los Angeles, USA) G. Ramalingam (Microsoft Research, India) Zhendong Su (University of California, Davis, USA) Martin Sulzmann (National University of Singapore, Singapore) Eijiro Sumii (Tohoku University, Japan) Jerome Vouillon (CNRS, France) Kwangkeun Yi (Seoul National University, Korea) Jian Zhang (Chinese Academy of Sciences, China) POSTER SESSION CHAIR Eijiro Sumii (Tohoku University, Japan) LOCAL ARRANGEMENT CHAIR Wei-Ngan Chin (National University of Singapore, Singapore)

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new SOE package and the annoucement of GLFW
by Paul L 30 Aug '07

30 Aug '07

Hi all, After much struggle to bring the SOE source to be compatible with the latest GHC, I'm pleased to announce that it's available at http://www.haskell.org/soe It's has been tested on Windows (both XP and Vista), Linux and Mac OS X under GHC 6.6.1. The code now requires a Haskell package GLFW, an interface to the GLFW OpenGL Framework (http://glfw.sourceforge.net) which is an alternative to GLUT for OpenGL based programs. Most SOE code examples are not affected by this change except that they now make use of the included SOE.hs instead of the previous SOEGraphics module. The SOE.hs now handles all window and drawing activities through GLFW and OpenGL. The music part of SOE code has also been brought up to date. Please help to report bugs or suggestions if you have any. Help is also needed to make the GLFW Haskell package fully compatible with cross-platform Cabal installation steps. Regards, Paul Liu

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ghc as a library and profiling
by Sönke Hahn 29 Aug '07

29 Aug '07

Hi! I am working on a program that uses ghc as a library to typecheck code. I want to profile the program (compiling with '-prof -auto-all' and running with '+RTS -p'). Trying to compile, results in the following message: Could not find module `GHC': Perhaps you haven't installed the profiling libraries for package ghc-6.6.1? I built ghc-6.6.1 from source without changing any configuration files. The building guide (http://hackage.haskell.org/trac/ghc/wiki/Building/QuickStart) says, this would install the compiler WITH profiling libraries. As i understand it, this somehow excludes the ghc package. (Maybe because it is not widely used?) Is this understanding right? Is it possible (and if, how) to compile ghc with a profiling version of the ghc package? I tried to add GhcStage2HcOpts = -Rghc-timing -prof -auto-all GhcStage2LibHcOpts = -prof -auto-all to mk/build.mk, but i am getting the following build error in stage 2: ghc-6.6.1: combination not supported: Threaded/Profiling Do i need to disable thread support? How would i do that? A second idea that comes to my mind is this: The ghc package is hidden in the standard installation, so i unhided (unhid?) it via 'ghc-pkg expose ghc'. Maybe it just exposed the non-profiling version and kept the profiling version hidden? How would i expose both? Any help appreciated... Sönke

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TryTypeCast hackery possible?
by Andreas Schropp 28 Aug '07

28 Aug '07

While reading on Oleg's typeclass-overloaded functions via "local" (*) backtracking (http://okmij.org/ftp/Haskell/poly2.txt) it occured to me that in order to support true Prolog-style instance/clause selection (Oleg seems to only use guards not based on unification-success), one would need TryTypeCast (mixture of TypeCast and TypeEq from HList paper: unify if possible and return HTrue, otherwise return HFalse). After a bit of experimentation my best try is this: -- should i somehow express the "local" functional dependencies -- res=HTrue a -> b and res=HTrue b -> a? class TryTypeCast a b res | a b -> res -- pretending polymorphism in t to prevent early unification of a and b, -- as seen in HLIST paper class TryTypeCast' t a b res | t a b -> res class TryTypeCast'' t a b res | t a b -> res instance TryTypeCast' () a b res => TryTypeCast a b res instance TryTypeCast'' t a b res => TryTypeCast' t a b res instance TryTypeCast'' () a a HTrue instance TypeCast HFalse res => TryTypeCast'' () a b res But it doesnt work (of course? is there even a workaround?) in the interesting cases, as unresolved overlapping gets into my way. (*) it seems that in the current model only "tail-recursive", in the search path sense, only needing local choice between success or search-deepening (the traditional append/3 would be tail-recursive in this way; not sure if this is standard terminology), predicates are possible. How to extend on that? I thought about a history of clause/instance selections per "predicate", hacking up Oleg's GFN-Interpreter in that regard, or even employing type-level CPS, based on the notion of closures in Oleg's Computable Types I (http://www.haskell.org/pipermail/haskell/2006-September/018486.html)

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Sun slots transactional memory into Rock
by Bulat Ziganshin 28 Aug '07

28 Aug '07

Hello haskell, "Hoping to improve the state of server software, Sun Microsystems has confirmed that it will include support for transactional memory with the first generation of its Rock processors due out in the second half of next year." http://www.theregister.com/2007/08/21/sun_transactional_memory_rock/ -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Issue about use of WinHugs
by Zhao, Bingfeng 25 Aug '07

25 Aug '07

Hi, list I'm new to WinHugs, what's wrong with isUpper of my WinHugs? Hugs> filter isUpper "ABCDEfgh" ERROR - Undefined variable "isUpper" Hugs> filter Char.isUpper "ABCDEfgh" ERROR - Undefined qualified variable "Char.isUpper" Hugs> :version -- Hugs Version Sep 2006 Best Regards, bingfeng

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Generic combination of generic types
by Rob Myers 24 Aug '07

24 Aug '07

Hi there, This is a question about combining data types in a generic way. I am using Haskell to write a first implementation of a new generic algorithm to decide a fairly large class of modal logics. Type classes provide an excellent way to generically define a modal language. In particular you only need to define the data type of the modal operator (e.g. it could be indexed by rationals) and also a special matching rule, which is used in the proof checker. However I also want to combine different modal languages to create new ones *in a generic fashion*. The "modal language" I'm talking about is just a data-type with a single type variable: data L a = F | T | Atom Int | Neg (L a) | And (L a) (L a) | Or (L a) (L a) | M a (L a) deriving (Eq,Show) // convention: clause([positive literals,negative literals]) newtype Clause a = Clause ([L a],[L a]) deriving (Eq,Show) with a type class like this: class (Eq a) => Logic a where match :: Clause a -> [[L a]] and instances like: data K = K deriving (Eq,Show) instance Logic K where match (Clause (pls,nls)) = ... data G = G Int deriving (Eq,Show) instance Logic G where match (Clause(pls,nls)) = ... data KD = KD deriving (Eq,Show) instance Logic KD where match (Clause (pl,nl)) = ... I have various such instances of logics and I want to combine them in particular ways. For example I might want to interlace three instances in a new language such as: data L1 = F1 | T1 | Atom1 Int | Neg1 L1 | And1 L1 L1 | Or1 L1 L1 | MCP L2 L3 deriving (Eq,Show) data L2 = F2 | T2 | Atom2 Int | Neg2 L2 | And2 L2 L2 | Or2 L2 L2 | MK L1 deriving (Eq,Show) data L3 = F3 | T3 | Atom3 Int | Neg3 L3 | And3 L3 L3 | Or3 L3 L3 | MKD L1 deriving (Eq,Show) or data L1 = F1 | T1 | Atom1 Int | Neg1 L1 | And1 L1 L1 | Or1 L1 L1 | MK L2 deriving (Eq,Show) data L2 = F2 | T2 | Atom2 Int | Neg2 L2 | And2 L2 L2 | Or2 L2 L2 | MKD L1 deriving (Eq,Show) ... the idea being that a different language(s) appear after the modalities (MCP, MK, MKD above). Put simply I want to take some data types and construct a new (specifically ordered) data type(s) defined in terms of these. I also want to be able to define recursive functions over this language, with which I'm having a problem (see below). I originally tried this by defining a language: data L a = F | T | Atom Int | Neg (L a) | And (L a) (L a) | Or (L a) (L a) | M a deriving (Eq,Show) Note the last term is "M a" not "M a (L a)" as in the first type. Using this 'a' I could write terms like: M (K,And F (M (KD,F))), i.e. use tupling to define in the first component the data type of the modality and in the second component (and third if considering binary modal operators) defining what comes after the modality. I found with this approach I was able to match these types e.g. note the "(K,a)" data K = K deriving (Eq,Show) instance Logic (K,a) where match (Clause (pl,nl)) = However, crucially, I cannot seem to define recursive functions because on each recursive step I am changing the type of terms considered. The underlying algorithm requires me to strip off a layer of modalities (e.g. M (K,F) goes to F) at each step. For example if I have M (K,M (KD,F)) this has type: L (K,L (KD,L a)), if I pass to the subterm M (KD,F), then this has type: L (KD,L a). Thus Haskell could not resolve this type ('unification would produce infinite data type'). However this method seems very attractive because it only needs one data type to define many different languages. I've tried alternate approaches, for example explicitly defining the interlaced language, such as: data L1 = F1 | T1 | Atom1 Int | Neg1 L1 | And1 L1 L1 | Or1 L1 L1 | MCP L2 L3 deriving (Eq,Show) data L2 = F2 | T2 | Atom2 Int | Neg2 L2 | And2 L2 L2 | Or2 L2 L2 | MK L1 deriving (Eq,Show) data L3 = F3 | T3 | Atom3 Int | Neg3 L3 | And3 L3 L3 | Or3 L3 L3 | MKD L1 deriving (Eq,Show) However this becomes messy because I then need to define all of my operations (e.g. find conjunctive normal form) on these new constructors. It seems that I need to use the actual constructor to pattern match... I can't use some ADT functions. I've also tried the first method above with 2 type variables, with the same problems (unification of infinite data type). Does anyone have any ideas? Frankly I'd be impressed if someone even takes the time to read though this. Thanks, Rob

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