January 2006 - 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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Visual Haskell: Could not find module `Control.Monad.Writer'
by Bernd Holzmüller 02 Mar '06

02 Mar '06

Hi all, I am playing around with Visual Haskell, V0.1 (which really is great stuff!). In the main module I wrote the following import: import Control.Monad.Writer for which I get the error message: Could not find module `Control.Monad.Writer': use -v to see a list of the files searched for I use the GHCOptions: -fglasgow-exts -fallow-overlapping-instances. Is this a bug in Visual Haskell or what's wrong here? Thanks, Bernd

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IO == ST RealWorld
by Twan van Laarhoven 22 Feb '06

22 Feb '06

Is there any reason why IO should not be defined as: > type IO a = ST RealWorld a in implementations that support ST? This way IORef/STRef and IOArray/STArray can be merged. I know under the hood they already share code, but this way they can also share an interface. Twan

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GLUT gears speed
by Wolfgang Jeltsch 18 Feb '06

18 Feb '06

Hello, what's the reason behind the HOpenGL gears only being about 2/3 as fast as glxgears on my computer? Since I don't use any 3D acceleration, I thought that most of the CPU's time is spend for rendering and displaying so that speed differences between Haskell and C shouldn't matter that much. Best wishes, Wolfgang

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Everything Your Professor Failed to Tell You About Functional Programming
by Shannon -jj Behrens 01 Feb '06

01 Feb '06

Shameless plug: I wrote an article for "Linux Journal" called "Everything Your Professor Failed to Tell You About Functional Programming". Hopefully you will enjoy the article. http://www.linuxjournal.com/article/8850 (By the way, I'm not on the cafe mailing list, so please cc me on any replies.)

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Re: [Haskell] page names on the new Haskell wiki
by Wolfgang Jeltsch 31 Jan '06

31 Jan '06

Am Freitag, 27. Januar 2006 19:54 schrieb John Peterson: > You're absolutely right! Please move pages as needed. Old habits die > hard! > > John Hello, I just started moving pages. But know I wonder which case I should use for inner-title words. Should the page title be "Books and tutorials" or "Books and Tutorials", for example? Since pages are only small documents, I chose the lower-case alternative but currently the Haskell website uses upper-case. Best wishes, Wolfgang

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Type-Level arithmetic library
by Robert Dockins 31 Jan '06

31 Jan '06

While cleaning up my home directory, I discovered some code I worked on a while ago which implements type level arithmetic. I have cleaned it up and decided to release. This library includes the following operations on type level naturals: addition subtraction multiplication division remainder GCD and also contains the following predicates test for zero test for equality < > <= >= This library uses a binary representation and can handle numbers at the order of 10^15 (at least). It also contains a test suite to help validate the somewhat unintuitive algorithms. You can retrieve this library with the following command darcs get --partial --tag '0.1' http://www.eecs.tufts.edu/~rdocki01/ typenats/ Enjoy, Rob Dockins PS Please let me know if you come up with useful ways to use this library! (I'm mostly just curious) Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG

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Haskell Weekly News: January 30, 2006
by dons＠cse.unsw.edu.au 31 Jan '06

31 Jan '06

Haskell Weekly News: January 30, 2006 Greetings, and thanks for reading the 22nd issue of HWN, a weekly newsletter for the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list and to [2]The Haskell Sequence. [3]RSS is also available. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://sequence.complete.org/node/feed New Releases * C-- Frontend. Robert Dockins [4]announced the initial alpha release of a [5]C-- frontend (parser, pretty printer, and semantic checker) written in Haskell. The goal when beginning this project was to create a modular frontend that could be used both by people writing and by those targeting C-- compilers. This implementation attempts to follow the C-- spec as exactly as possible. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/13174 5. http://www.cminusminus.org/ * Type level arithmetic. Robert Dockins [6]also released a library for arithmetic on the type level. This library uses a binary representation and can handle numbers at the order of 10^15 (at least). It also contains a test suite to help validate the somewhat unintuitive algorithms. 6. http://article.gmane.org/gmane.comp.lang.haskell.general/13206 Haskell' This section covers activity on [7]Haskell' this week. The topics this week have been diverse. Next week we'll try to cover activity on the wiki as well. From the mailing list: * [8]Wildcard type annotations * [9]Reworking the Numeric class * [10]Partial application ideas * [11]A more flexible hierarchical module namespace * [12]Record updates * [13]On the importance of libraries * [14]Syntactic support for existentials * [15]Module system/namespace management * [16]Fixing the monomorphism restriction * [17]k patterns * [18]~ patterns * [19]Kind annotations * [20]Class method types * [21]A Match class * [22]Scoped type variables in class instances * [23]Inline comment syntax 7. http://hackage.haskell.org/trac/haskell-prime 8. http://www.haskell.org/pipermail/haskell-prime/2006-January/000001.html 9. http://www.haskell.org/pipermail/haskell-prime/2006-January/000002.html 10. http://www.haskell.org/pipermail/haskell-prime/2006-January/000004.html 11. http://www.haskell.org/pipermail/haskell-prime/2006-January/000009.html 12. http://www.haskell.org/pipermail/haskell-prime/2006-January/000014.html 13. http://www.haskell.org/pipermail/haskell-prime/2006-January/000023.html 14. http://www.haskell.org/pipermail/haskell-prime/2006-January/000031.html 15. http://www.haskell.org/pipermail/haskell-prime/2006-January/000032.html 16. http://thread.gmane.org/gmane.comp.lang.haskell.prime/15 17. http://thread.gmane.org/gmane.comp.lang.haskell.prime/31 18. http://thread.gmane.org/gmane.comp.lang.haskell.prime/54 19. http://thread.gmane.org/gmane.comp.lang.haskell.prime/65 20. http://article.gmane.org/gmane.comp.lang.haskell.prime/102 21. http://article.gmane.org/gmane.comp.lang.haskell.prime/123 22. http://article.gmane.org/gmane.comp.lang.haskell.prime/28 23. http://thread.gmane.org/gmane.comp.lang.haskell.prime/104 Discussion * Adding Impredicative Types to GHC. Simon Peyton-Jones [24]pushed a patch into GHC to handle impredicative polymorphism (see [25]Boxy types: type inference for higher-rank types and impredicativity). Secondly, GHC now supports GADTs in the more simplified way described in [26]Simple unification-based type inference for GADTs 24. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13254 25. http://research.microsoft.com/~simonpj/papers/boxy/ 26. http://research.microsoft.com/~simonpj/papers/gadt/ * New IO library. Bulat Ziganshin [27]sought information on the low-level IO mechanisms used in GHC's IO libraries, in the context of his work on a high-performance IO lib. Some interesting points relating to IO primitives were raised. 27. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/9261 Darcs Corner Darcs is popular. Isaac Jones [28]brought to our attention the results of the Debian package popularity contest. For the first time a program written in Haskell is more popular than the Haskell toolchain itself. Congratulations to the darcs developers! 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/11089 Quote of the Week <araujo> Haskell is bad, it makes you hate other programming languages. Contributing to HWN You can help us create new editions of this newsletter. Please see the [29]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 29. http://sequence.complete.org/hwn-contrib

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Re: Contents of Haskell Digest, Vol 29, Issue 33
by 조희연 31 Jan '06

31 Jan '06

-----Original Message----- From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of haskell-request(a)haskell.org Sent: Tuesday, January 31, 2006 1:41 AM To: haskell(a)haskell.org Subject: Haskell Digest, Vol 29, Issue 33 Send Haskell mailing list submissions to haskell(a)haskell.org To subscribe or unsubscribe via the World Wide Web, visit http://www.haskell.org/mailman/listinfo/haskell or, via email, send a message with subject or body 'help' to haskell-request(a)haskell.org You can reach the person managing the list at haskell-owner(a)haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Haskell digest..." Today's Topics: 1. Re: IO == ST RealWorld (John Meacham) 2. ACM PPDP'06 call for papers (Simon Marlow) 3. Visual Haskell: Could not find module `Control.Monad.Writer' (Bernd Holzm?ller) 4. TFP2006: Third Call for Papers (Henrik Nilsson) 5. Re: page names on the new Haskell wiki (Wolfgang Jeltsch) 6. Re: page names on the new Haskell wiki (Sam Goldman) 7. Re: IO == ST RealWorld (Marcin 'Qrczak' Kowalczyk) ---------------------------------------------------------------------- Message: 1 Date: Sun, 29 Jan 2006 04:32:05 -0800 From: John Meacham <john(a)repetae.net> Subject: Re: [Haskell] IO == ST RealWorld To: haskell <haskell(a)haskell.org> Message-ID: <20060129123205.GE10970(a)momenergy.repetae.net> Content-Type: text/plain; charset=utf-8 On Mon, Jan 23, 2006 at 09:55:39PM +0100, Twan van Laarhoven wrote: > Is there any reason why IO should not be defined as: > > type IO a = ST RealWorld a > in implementations that support ST? > > This way IORef/STRef and IOArray/STArray can be merged. I know under the > hood they already share code, but this way they can also share an interface. ST doesn't have exceptions which IO does. It would be no good to make ST pay for the cost of exception handling. GHC handles them behind the scenes (I think?) but in jhc they are explicit and IO is defined as follows: > data World__ > > data IOResult a = FailIO World__ IOError | JustIO World__ a > newtype IO a = IO (World__ -> IOResult a) I belive other implementations have used continuations for IO as well. John -- John Meacham - brepetae.netbjohnb ------------------------------ Message: 2 Date: Mon, 30 Jan 2006 09:30:40 -0000 From: "Simon Marlow" <simonmar(a)microsoft.com> Subject: [Haskell] ACM PPDP'06 call for papers To: <haskell(a)haskell.org> Message-ID: <2E9B33CE230409489A7ED37E5E34090F03515208@EUR-MSG- 20.europe.corp.microsoft.com> Content-Type: text/plain; charset="us-ascii" [ posting on behalf of Agostino Cortesi <cortesi(a)unive.it> ] ................................................................ PPDP 2006 Preliminary Call For Papers 8th ACM-SIGPLAN International Symposium on Principles and Practice of Declarative Programming Venice, Italy, July 10-12, 2006 http://www.dsi.unive.it/ppdp2006/ ................................................................ IMPORTANT DATES Submission 15 March 2006 Notification 22 April 2006 SCOPE: PPDP 2006 is a forum for the declarative programming communities, gathering researchers working on logic, constraint and functional programming, but also on other programming language paradigms like visual programming, executable specification languages, database languages, AI and knowledge representation languages for the "semantic web". MAIN TOPICS: Logic, Constraint, and Functional Programming; Database, AI and Knowledge Representation Languages; Visual Programming; Executable Specification for Languages; Applications of Declarative Programming; Methodologies Program Design and Development; Declarative Aspects of Object-Oriented Programming; Concurrent Extensions to Declarative Languages; Declarative Mobile Computing; Paradigm Integration; Proof Theoretic and Semantic Foundations; Type and Module Systems; Program Analysis and Verification; Program Transformation; Abstract Machines and Compilation; Programming Environments. PROCEEDINGS: Proceedings will be published by ACM Press. RELATED EVENTS: PPDP 2006 will be co-located with the 33rd International Colloquium on Automata, Languages and Programming (ICALP 2006), which will take place on July 9-16, 2006 (http://icalp06.dsi.unive.it) CONFERENCE CHAIR: Annalisa Bossi, U. Ca' Foscari di Venezia PROGRAM CHAIR: Michael Maher, National ICT Australia PROGRAM COMMITTEE: Nick Benton (Microsoft Research, UK) Annalisa Bossi (U. Ca' Foscari di Venezia, Italy) Manuel Chakravarty (U. NSW, Australia) Bart Demoen (K. U. Leuven, Belgium) Moreno Falaschi (U. Udine, Italy) Radha Jagadeesan (DePaul U., USA) Bharat Jayaraman (SUNY Buffalo, USA) Yukiyoshi Kameyama (U. Tsukuba, Japan) Andy King (U. Kent, UK) Francois Laburthe (Bouyges, France) David Sands (Chalmers U., Sweden) Christian Schulte (KTH, Sweden) Pascal Van Hentenryck (Brown U., USA) Roland Yap (NUS, Singapore) =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- prof. agostino cortesi tel. 0039 041 234.8450 dipartimento di informatica fax 0039 041 234.8419 universita' ca' foscari mail cortesi(a)dsi.unive.it via torino 155 url www.dsi.unive.it/~cortesi 30170 Venezia location: studio n.1

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