February 2002 - Haskell

Verba Volant
by request＠logos.net 21 Feb '02

21 Feb '02

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declaring a generic type in type synonyms
by Andre W B Furtado 21 Feb '02

21 Feb '02

Is is possible to declare a generic type without using "data" or "newtype"? For example, I woud like that "pair" is a type synonym for "(t,t)" where t is a generic type, but just saying: > type pair = (t,t) won't work: i get a parse error. Thanks, -- Andre

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Graphs
by Wojciech Fraczak 21 Feb '02

21 Feb '02

Hi everybody, I would like to ask you, if you do not know any graph library for haskell. I would like to use haskell for prototyping some of algorithms on graphs and finite state automata/transducers. In fact what I'm looking for is a good (efficient and easy readable) data type definition for labeled graphs. Thanks, Wojtek

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Monadic Call/CC?
by Ashley Yakeley 21 Feb '02

21 Feb '02

Has anyone investigated monadic call-with-current-continuation in Haskell? Given this: class (Monad m) => PeirceMonad m where { peirceM :: ((a -> m b) -> m a) -> m a; }; ...which Monads can be made PeirceMonads? The corresponding non-monadic function: peirce :: ((a -> b) -> a) -> a; probably can't be defined. -- Ashley Yakeley, Seattle WA

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Re: forcing IO operations
by Jay Cox 21 Feb '02

21 Feb '02

On Wed, 20 Feb 2002, Andre W B Furtado wrote: > hi, you sent me "blank" email (nothing besides my own message). Were you > trying to tell something? :) > > -- Andre Heh, actually I was. I curse the day that the designers of pine put (control-X) for sending a letter next to (control-C) for killing it :) Please don't take offense to this, but do you feel unsafePerformIO is really necessary for your application? There's got to be another way... In Systematic Design of Monads [1] there is given a systematic method to wrap monads around other monads. I was going to email you an example monad which wraps around the IO monad. Granted, its a state monad wrapped around the IO monad, which may not be of much use except for organizational purposes. I've essentially stolen the design from the aforementioned paper, but since the paper appears to be for Gofer, the Haskell precursor, I decided to modernize it a bit. By the way, seems like there might be something along the lines of this in the hugs library. (If not, I'm sure I remember something about reader and writer monad wrappers) Jay Cox [1]written by John Hughes & Magnus Carlson (1996) Appologies to both since I cant give a more specific reference to the paper. John (or Magnus), you wouldn't have happened to taken the time to have updated the code from that paper, have you? If you already have, I appologize for not refering to it and using it as well :) ---- If you cut and paste the following lines I think they ought to be able to run as in a haskell.lhs source file. You proposed using some runMyMonad function. in order to combine IO actions with your code the runction returns and IO (blah). see, the IO is hidden within the new monad but IO actions are still being threaded through MyMonad. >newtype MyNewStateMonad m s a = StateMonad (s -> m (a,s)) > > >bindST (StateMonad x) f = > StateMonad (\s -> ( x s >>= \(v,s') -> let StateMonad g = f v in g s')) > >unitST v = StateMonad (\s -> return (v,s)) > > >instance Monad m => Monad( MyNewStateMonad m s) where > (>>=) = bindST > return = unitST > > >type MyMonad a = MyNewStateMonad IO Int a > >runMyMonad :: MyMonad a -> Int ->IO (a,Int) -- (a,Int) the state tuple >runMyMonad (StateMonad f) = f that's it! the remainder is mostly example code it: 1. lifts print and getLine to monadic actions under MyMonad (aka MyNewStateMonad IO Int) 2. has an example monadic action (add50toMyMonadState) which has absoultely nothing to do with the underlying IO monad. 3. lifted a sequence of IO actions to be executed under MyMonad via arbitrarysequence 4. combines all the actions under MyMonad into monad_actions so that they may be run with runMyMonad. note the line: y<- runMyMonad monad_actions 0 the 0 initializes the state of the MyMonad, (hence this is why runMyMonad is typed MyMonad a -> Int ->IO (a,Int) ) >liftIOtoMyMonad' :: (a -> IO ()) -> a -> MyMonad () >liftIOtoMyMonad' p q = > StateMonad $ \s -> do p q > return ((),s) > >liftIOtoMyMonad :: IO a -> MyMonad a >liftIOtoMyMonad p = > StateMonad $ \s -> do y <- p > return (y,s) > >liftIOtoMyMonad_ :: IO () -> MyMonad () >liftIOtoMyMonad_ m = liftIOtoMyMonad' (const m) () > > >getLineMM = liftIOtoMyMonad getLine >printMM = liftIOtoMyMonad' print >arbitrarysequence = > liftIOtoMyMonad $ > do print "What's your name?" > name <-getLine > print $ "Your name is " ++ name > > >add50toMyMonadState :: MyMonad () >add50toMyMonadState = StateMonad(\s -> return ((),50+s)) > > >monad_actions= do arbitrarysequence > printMM "What's your password" > pass <- getLineMM > printMM ("Your password is: " ++ pass) > add50toMyMonadState > return 3 > > >main = do y<- runMyMonad monad_actions 0 > print $ "State:" ++ show (snd y) ++ " Value:" ++ show (fst y) If you are reading this you should be instead copying it to some file and playing with it instead!

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ICFP 2002: write now!
by Simon Peyton-Jones 20 Feb '02

20 Feb '02

Don't miss your chance to submit a paper to ICFP02. It'll be fun! Simon PJ ICFP 2002 International Conference on Functional Programming October 4-6, 2002, Pittsburgh, USA Final call for papers -------------------------------------------- Submission deadline: 21 March 2002 18:00 UTC -------------------------------------------- Program Chair: Simon Peyton Jones (Microsoft Research) Full call for papers including submission details: http://icfp2002.cs.brown.edu/CfP/ ICFP 2002 seeks original papers on the full spectrum of the art, science, and practice of functional programming. The conference invites submissions on all topics ranging from principles to practice, from foundations to features, and from abstraction to application. The scope covers all languages that encourage programming with functions, including both purely applicative and imperative languages, as well as languages that support objects and concurrency. Topics of interest include, but are not limited to, the following: Foundations: formal semantics, lambda calculus, type theory, monads, continuations, control, state, effects. Design: modules and type systems, concurrency and distribution, components and composition, relations to object-oriented and logic programming, multiparadigm programming. Implementation: abstract machines, compile-time and run-time optimization, just-in-time compilers, memory management, foreign-function and component interfaces. Transformation and analysis: abstract interpretation, partial evaluation, program transformation, theorem proving, specification and verification. Software development techniques for functional programming: design patterns, specification, verification and validation, debugging, test generation, etc. Human productivity of functional programming: visual, graphical (etc) approaches, evaluating language usability, empirical studies of human effectiveness, etc. Applications and domain-specific languages: scientific and numerical computing, symbolic computing and artificial intelligence, systems programming, databases, graphic user interfaces, multimedia programming, Web programming. Practice and experience: functional programming in education and industry, ramifications on other paradigms and computing disciplines. Functional pearls elegant, instructive examples of functional programming. General Chair: Mitchell Wand (Northeastern University) Program Committee Matthias Blume (Lucent) Margaret Burnett (Oregon State University) Manuel Chakravarty (University of New South Wales) Matthew Flatt (University of Utah) Haruo Hosoya (Kyoto University) Uwe Nestmann (EPFL, Lausanne) Chris Okasaki (United States Military Academy) Norman Ramsey (Harvard University) David Sands (Chalmers University) Olin Shivers (Georgia Tech) Stephanie Weirich (Cornell) Joe Wells (Heriot Watt University)

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RE: foralls in class assertions
by Simon Peyton-Jones 20 Feb '02

20 Feb '02

OK, so it does look as though it's the same idea as that described in our paper. Good. I have not implemented, yet. As always my implementation priorities are strongly influenced by my perception of whether some enhancement would be used. Maybe you can outline why such a change would be useful to you? I only have the example in our paper as motivation so far. Simon | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 20 February 2002 01:08 | To: Simon Peyton-Jones; Haskell List | Subject: RE: foralls in class assertions | | | At 2002-02-19 09:21, Simon Peyton-Jones wrote: | | >I don't know if it makes sense. You've written down some syntax, | >but it's not clear to me what you intend by it. | | Hmm... it should be straightforward... | | > instance (forall a. Eq a => Eq (f a)) => Eq (Rose f a) where.. | | I assume that the 'a' quantified in (forall a. ...) is not | the same as | the 'a' in 'Rose f a'? | | >| instance | >| ( | >| forall a. HasIdentity (m a a), | >| forall a b c. Composable (m b c) (m a b) (m a c) | >| ) => | >| Category m; | | This means 'if for all a, "HasIdentity (m a a)", and also for | all a b c, | "Composable (m b c) (m a b) (m a c)", then "Category m"'. | | "(forall a. HasIdentity (m a a))" as a class assertion declares a | property of m. It says that for all types a, there's an instance | "HasIdentity (m a a)". | | >| Or even allow the foralls their own context: | >| | >| foo :: (forall a. (C a b) => D a c) => T b c; | | This means foo has type (T b c), where for every type a for | which there's | an instance "C a b", there's an instance "D a c". | | >| class | >| ( | >| forall a. HasIdentity (m a a), | >| forall a b c. Composable (m b c) (m a b) (m a c) | >| ) => | >| Category m; | | Personally I think the 'superclass' arrow in class | declarations should | point the other way, as in '<='. After all, instances of the | class imply | instances of the superclasses, not the other way around. | | But that aside, this means '"Category" is a class on m, | provided that for | all types a, there's an instance "HasIdentity (m a a)", and | also for all | types a b c, there's an instance "Composable (m b c) (m a b) | (m a c)"'. | | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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RE: Haskell 98 Report
by Simon Peyton-Jones 20 Feb '02

20 Feb '02

I don't want to do that until its finished! Which I earnestly hope will be soon. Simon | -----Original Message----- | From: David Feuer [mailto:dfeuer@cs.brown.edu] | Sent: 20 February 2002 08:43 | To: haskell(a)haskell.org | Subject: Haskell 98 Report | | | Is the revised Haskell98 report going to be put in its proper | place on the web site any time soon? As it is, it is sitting | off to the side while the old Report sits in the seat of honor. | | David Feuer | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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CFP : ASIA-PEPM 2002
by Chin Wei Ngan 20 Feb '02

20 Feb '02

CALL FOR PAPERS ACM SIGPLAN ASIAN Symposium on Partial Evaluation and Semantics-Based Program Manipulation (ASIA-PEPM'02) Aizu, JAPAN, September 12-14 2002 (co-located with FLOPS2002) http://www.comp.nus.edu.sg/asia-pepm02 Submission deadline: 1st March 2002 The ASIA-PEPM'02 symposium will bring together researchers working in the areas of semantics-based program manipulation, partial evaluation, and program analysis. The symposium focuses on techniques, supporting theory, and applications for the analysis and manipulation of programs. Technical topics include, but are not limited to: * Program manipulation techniques: transformation, specialization, normalization, reflection, rewriting, run-time code generation, multi-level programming. * Program analysis techniques: abstract interpretation, static analysis, binding-time analysis, type-based analysis. * Related issues in language design and models of computation: imperative, functional, logical, constraint-based, object-oriented, parallel, concurrent, secure, domain-specific. * Programs as data objects: staging, meta-programming, incremental computation, mobility, tools and techniques, prototyping and debugging. * Applications: systems programming, scientific computing, embedded systems, graphics, security, model checking, compiler generation, compiler optimization, decompilation. Original results that bear on these and related topics are solicited. Papers investigating novel uses and applications of program manipulation are especially encouraged. Authors concerned about the appropriateness of a topic are welcome to consult with the program chair prior to submission. SUBMISSION INFORMATION Papers should be submitted electronically via the workshop's Web page. Exceptionally, submissions may be emailed to the program chair: asiapepm(a)comp.nus.edu.sg. Acceptable formats are PostScript or PDF, viewable by gv. Submissions should not exceed 5000 words, excluding bibliography and figures. Submitted papers will be judged on the basis of significance, relevance, correctness, originality, and clarity. They should clearly identify what has been accomplished and why it is significant. The work described should not have been previously published in a major forum. Authors must indicate if a closely related paper is also being considered for another conference or journal. The proceeding of the symposium will be published by ACM Press. A special issue of Higher-Order Symbolic Computation is also planned. LOCAL ARRANGEMENT Mizuhito Ogawa (NTT, Japan) GENERAL CHAIR Kenichi Asai (Ochanomizu University, Japan) PROGRAM CHAIR Wei-Ngan Chin (National University of Singapore, Singapore) PROGRAM COMMITTEE Manuel Chakravarty (University of New South Wales, Australia) Tyng-Ruey Chuang (Academia Sinica, Taiwan) Charles Consel (ENSEIRB, France) Oege de Moor (University of Oxford, UK) Masami Hagiya (University of Tokyo, Japan) Nevin Heintze (Agere Systems, USA) Neil Jones (Univ of Copenhagen, Denmark) Yanhong Annie Liu (SUNY at Stony Brook, USA) Atsushi Ohori (JAIST, Japan) Alberto Pettorossi (University of Roma, Italy) Simon Peyton Jones (Microsoft, UK) Carolyn Talcott (Stanford University, USA) Zhe Yang (University of Pennsylvania, USA)

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Haskell 98 Report
by David Feuer 20 Feb '02

20 Feb '02

Is the revised Haskell98 report going to be put in its proper place on the web site any time soon? As it is, it is sitting off to the side while the old Report sits in the seat of honor. David Feuer

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