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RE: overlapping instances and functional dependencies
by Hal Daume 19 Aug '03

19 Aug '03

Suppose somewhere we have an instance: instance C Int Bool Int when the first instance decl you have says we also have instance C Int (x,y,Bool) Int in this case, Int + (x,y,Bool) should uniq. specify Int. however, we also have: instance C a (a,c,b) c where, if we let a=Int, b=Bool, c=Char, then we get that Int + (Int,Char,Bool) should uniq. specify Char. these two confict because if, in the first case, we instantiate x to Int and y to Char, then one says that the third param should be a Bool and the other says the third param should be a Char. (or at least this is my understanding -- someone might correct me) - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-admin(a)haskell.org > [mailto:haskell-admin@haskell.org] On Behalf Of Wolfgang Jeltsch > Sent: Friday, August 08, 2003 4:33 PM > To: The Haskell Mailing List > Subject: overlapping instances and functional dependencies > > > Hello, > > I have this code: > class C a b c | a b -> c where > f :: a -> b -> c > > instance C a b c => C a (x,y,b) c where > f a (_,_,b) = f a b > > instance C a (a,c,b) c where > f _ (_,c,_) = c > ghci -fglasgow-exts -fallow-overlapping-instances compiles it without > complaint but hugs -98 +o says: > ERROR "ClassProblem.hs":7 - Instances are not consistent > with dependencies > *** This instance : C a (a,b,c) b > *** Conflicts with : C a (b,c,d) e > *** For class : C a b c > *** Under dependency : a b -> c > Can anyone tell me what the reason for this is and, maybe, > how to avoid these > problems with Hugs? > > Wolfgang > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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Re: Haddock Problems
by Dominic Steinitz 19 Aug '03

19 Aug '03

I realise I have to give an explicit type for the functions but this still doesn't get rid of the warnings. Dominic. ----- Original Message ----- From: "Dominic Steinitz" <dominic.steinitz(a)blueyonder.co.uk> To: <haskell(a)haskell.org> Sent: Monday, August 18, 2003 6:06 PM Subject: Haddock Problems > Can someone tell me why I get the following warnings and also why the > generated documentation is blank? > > Many thanks, Dominic. > > [dom@redearth crypto]$ haddock Codec/Encryption/DES.hs > Warning: module not found: Word > Warning: module not found: Codec.Encryption.DESAux > Warning: module not found: Prelude > Warning: Codec.Encryption.DES: the following names could not be resolved: > encrypt decrypt > > Here's the offending module. > > -------------------------------------------------------------------------- -- > - > -- | > -- Module : Codec.Encryption.DES > -- Copyright : (c) Dominic Steinitz 2003 > -- License : BSD-style (see the file libraries/base/LICENSE) > -- > -- Maintainer : dominic.steinitz(a)blueyonder.co.uk > -- Stability : experimental > -- Portability : portable > -- > -- Takes the DES module supplied by Ian Lynagh and wraps it so it can > -- used with the standard modes. > -- <http://web.comlab.ox.ac.uk/oucl/work/ian.lynagh/>. > -- > -------------------------------------------------------------------------- -- > - > > module Codec.Encryption.DES ( > -- * Function types > encrypt, decrypt > ) where > > import Codec.Encryption.DESAux > import Word > > -- | Basic DES encryption which takes a key and a block of plaintext > -- and returns the encrypted block of ciphertext according to the standard. > > encrypt = flip des_enc > > -- | Basic DES decryption which takes a key and a block of ciphertext and > -- returns the decrypted block of plaintext according to the standard. > > decrypt = flip des_dec > >

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Haddock Problems
by Dominic Steinitz 19 Aug '03

19 Aug '03

Can someone tell me why I get the following warnings and also why the generated documentation is blank? Many thanks, Dominic. [dom@redearth crypto]$ haddock Codec/Encryption/DES.hs Warning: module not found: Word Warning: module not found: Codec.Encryption.DESAux Warning: module not found: Prelude Warning: Codec.Encryption.DES: the following names could not be resolved: encrypt decrypt Here's the offending module. ---------------------------------------------------------------------------- - -- | -- Module : Codec.Encryption.DES -- Copyright : (c) Dominic Steinitz 2003 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : dominic.steinitz(a)blueyonder.co.uk -- Stability : experimental -- Portability : portable -- -- Takes the DES module supplied by Ian Lynagh and wraps it so it can -- used with the standard modes. -- <http://web.comlab.ox.ac.uk/oucl/work/ian.lynagh/>. -- ---------------------------------------------------------------------------- - module Codec.Encryption.DES ( -- * Function types encrypt, decrypt ) where import Codec.Encryption.DESAux import Word -- | Basic DES encryption which takes a key and a block of plaintext -- and returns the encrypted block of ciphertext according to the standard. encrypt = flip des_enc -- | Basic DES decryption which takes a key and a block of ciphertext and -- returns the decrypted block of plaintext according to the standard. decrypt = flip des_dec

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more unsafePerformIO questions (is it safe to use with ReadMode Handles)?
by Hal Daume 18 Aug '03

18 Aug '03

Hi folks, I'm finishing up my Haskell interface to WordNet (http://www.cogsci.princeton.edu/~wn/) and have a standard unsafePerformIO question :). Basically, the interface functions by first calling an initialization function, 'initializeWordNet :: IO WordNetEnv'. WordNetEnv is essentially just a record of a lot of Handles which we will be reading from and doing binary search in. All the functions which use the WordNetEnv (i.e., every other function in the interface) basically do the following: - take one handle from the WordNetEnv and do binary search in it, read a line. - use that line to read another line from another of the handles - parse that last one of course, therefore, all of these functions have type '... -> IO something'. However, one of the "rules of thumb" for using unsafePerformIO is when you can imagine a functional interface doing the same thing. I can: simply read in all the databases in initializeWordNet and then do Data.List.lookup on the results. Does this mean it's safe to wrap all these functions in unsafePerformIO? If not, I'll probably just create a WordNet Reader monad and wrap things up like that -- if you have to be in a monad anyway, there's no reason to pass the WordNetEnv around everywhere. But still, if possible, it would be nice for these to be pure. - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume

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Re: Type class problem
by oleg＠pobox.com 18 Aug '03

18 Aug '03

> I defined type recursion and naturals as > >newtype Mu f = In {unIn :: f (Mu f)} > >data N f = S f | Z > >type Nat = Mu N > An application of Mu should be showable if the functor maps showable types > to showable types, so the most natural way to define the instance seemed > to be > instance (Show a => Show (f a)) => Show (Mu f) where > show (In x) = show x > Of course that constraint didn't work. Well, it can if we write it in a bit different way: instance (Show (f (Mu f))) => Show (Mu f) where show (In x) = show x instance Show (N (Mu N)) where show Z = "Z" show (S k) = "S "++show k *Main> show (In (S (In (S (In Z))))) "S S Z" This solution is akin to that of breaking the type recursion when defining the fixpoint combinator fix. Only here we face the recursion on constraints. I believe the same solution should work for the Observable class. You didn't post the definition of the Observable class, so I couldn't test my claim. Flags used: ghci -fglasgow-exts -fallow-undecidable-instances /tmp/a.hs

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help!
by Trouble ... 18 Aug '03

18 Aug '03

Hi! I'm new to this whole programming thing, and I was wondering if someone can help me out with the following question: How do I translate a string into an integer. For example, I need to know how to translate "one hundred" into 100, or "fifty thousand ten " into 50 010 etc etc .. I need to know how to do this for single numbers, hundreds, thousands and millions using Haskell. Thanx for your time and help. _________________________________________________________________ Hot chart ringtones and polyphonics. Go to http://ninemsn.com.au/mobilemania/default.asp

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Compositional Verification of UML Models
by M.M. Bonsangue 15 Aug '03

15 Aug '03

(We apologize for the reception of multiple copies) ************** DEADLINE IS APPROACHING: CALL FOR PAPER *************** Call for Papers Compositional Verification of UML Models Workshop of the UML 2003 Conference The definition of UML has been motivated by the need for a standard notation for modelling system architectures and behaviours at functional and implementation level. The main fqocus has been essentially on terminology, notation and syntax without addressing semantic, validation and methodology issues which are important for formal design and verification techniques. This workshop addresses the application of formal methods and techniques that exploit the architectural structure of UML models in a compositional manner. TOPICS The workshop topics include (but are not limited to): * semantic foundations of architectural and component-based design within UML * compositional techniques for the analysis embedded and real-time systems in UML * compositional model checking of UML behavioural models * compositional deductive methods based on OCL * methodologies based on compositional formal techniques FORMAT OF THE WORKSHOP The workshop will consist of presentations of the accepted papers, which will be the basis for an intensive discussion on the workshop topics. Extended abstracts of the presentations will be published after the workshop by Elsevier Science as a volume of the Electronic Notes in Theoretical Computer Science. For an up-to-date program and invited talks see the workshop web-site http://fmco.liacs.nl/compuml.html SUBMISSIONS Authors are invited to submit by August 25th an extended abstract not exceeding 20 pages electronically to F.S.de.Boer(a)cwi.nl. Submissions must be either in Postscript or PDF format and prepared for USLetter or A4 page sizes. Submissions will be evaluated by the program committee for inclusion in the proceedings, which will be published by Electronic Notes in Theoretical Computer Science series. Papers must contain original contributions, be clearly written, and include appropriate reference to and comparison with related work. Simultaneous submissions to other conferences are not allowed. IMPORTANT DATES 25 August Submission deadline 10 September Notification to authors 1 October Deadline for preliminary version 21 October Workshop date 21 November Deadline for final version PROGRAM COMMITTEE Frank de Boer (CWI, NL) Marcello Bonsangue (LIACS, NL) Werner Damm (OFFIS, DE) Susanne Graf (Verimag, France) David Harel (Weizmann Institute, Israel) Jozef Hooman (University of Nijmegen, NL) Bernhard Josko (OFFIS, DE) Amir Pnueli (Weizmann Institute, ISR) Willem-Paul de Roever (Kiel University, DE) Joseph Sifakis (Verimag, FR) ORGANIZERS Frank de Boer (CWI, NL) Marcello Bonsangue (LIACS, NL) Bernhard Josko (OFFIS, DE) SPONSORS This workshop is sponsored by the European R&D project OMEGA - Correct Development of Real-time Embedded Systems (http://www-omega.imag.fr) and the German-Dutch project Mobi-J (main sponsor of FMCO, http://fmco.liacs.nl)

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Type class problem
by Brandon Michael Moore 14 Aug '03

14 Aug '03

To try some of the examples from paper "Recursion Schemes from Comonads", I wanted to define instances of Show and Observable for types defined as the fixed point of a functor. I defined type recursion and naturals as >newtype Mu f = In {unIn :: f (Mu f)} >data N f = S f | Z >type Nat = Mu N An application of Mu should be showable if the functor maps showable types to showable types, so the most natural way to define the instance seemed to be instance (Show a => Show (f a)) => Show (Mu f) where show (In x) = show x Of course that constraint didn't work, so I made a class PShow with a method that witnessed the constraint >class PShow f where > pshow :: (Show a) => f a -> String Now I could define a generic show instance for Mu, and got a Show instance for Nat by defing a PShow instance for N >instance (PShow f) => Show (Mu f) where > show (In x) = pshow x >instance PShow N where > pshow Z = "Z" > pshow (S k) = "S "+show K show (In (S (In (S (In Z))))) -> "S S Z" This works fine, but you need to be able to use the method of P<Class> in the definition of <Class> (Mu f). I couldn't figure out how to do the same thing with Observable (the use of the class methods is a few layers away from the public interface). I tried to define a set of mutaully recursive definitions instance (Observable (f (Mu f))) => Observable (Mu f) where observer (In x) = send "In" (return In << x) instance (Observable a) => Observable (N a) where observer Z = send "Z" (return Z) observer (S x) = send "S" (return S << x) unfortunately, the class constraint solver doesn't doesn't like this. I get an error message like Constraint Stack Overflow: Observable (N (Mu N)) Observable (Mu N) Observable (N (Mu N)) Observable (Mu N) ... I expected that that constraint solver would realize it could construct a dictionary transformer with a type like Observer Nat -> Observer Nat and take the fixed point to get an instance for Nat. I haven't looked at the implementation, but it seems like it would be easy to add the constraint we are trying to derive to the list of assumptions when trying to construct all the anteceedents of an instance declaration. Can anyone tell me how to 1) get around this 2) modify GHC to handle this :) Brandon

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ICFP 2003 / PLI 2003 -- final call for participation
by Olin Shivers 14 Aug '03

14 Aug '03

The following message is a courtesy copy of an article that has been posted to comp.lang.scheme,comp.lang.scheme.scsh,comp.lang.dylan,comp.lang.functional,comp.lang.lisp,comp.lang.lisp.franz,comp.lang.lisp.mcl,comp.lang.lisp.x,comp.lang.apl,comp.lang.clos as well. ICFP 2003, the International Conference on Functional Programming, will be happening two weeks from now, 8/25-27. If you are contemplating registering for the conference, note that on-line/remote registration closes on Friday (8/15) -- although walk-in/on-site registration will be available up to and through the conference. I append the programme of talks to this message. For more information, see the conference web page http://www.cc.gatech.edu/~shivers/icfp03/schedule.html -Olin Shivers ------------------------------------------------------------------------------- ICFP 2003 program ----------------- http://www.cc.gatech.edu/icfp03/schedule.html http://www.cc.gatech.edu/icfp03/schedule.txt Affiliated with PLI 2003 August 25-29, 2003 Uppsala, Sweden =============================================================================== Monday 25 August 2003 Invited talk: 9:00-10:00 ------------------------ Conservation of information: Applications in functional, reversible, and quantum computing Thomas Knight, Jr. (MIT Artificial Intelligence Laboratory) Session I: 10:30-12:30 ---------------------- Scripting the type-inference process Bastiaan Heeren, Jurriaan Hage, Doaitse Swierstra (Universiteit Utrecht) Discriminative sum types locate the source of type errors Matthias Neubauer, Peter Thiemann (Universität Freiburg) MLF: Raising ML to the power of System F Didier Le Botlan, Didier Rémy (INRIA Rocquencourt) An extension of HM(X) with bounded existential and universal data-types Vincent Simonet (INRIA Rocquencourt) Session II: 2:15-3:45 --------------------- CDuce: an XML-centric general-purpose language Véronique Benzaken (LRI, Université Paris Sud, Orsay), Giuseppe Castagna (CNRS, LIENS, École Normale Supérieure), Alain Frisch (LIENS, École Normale Supérieure, Paris) Compiling regular patterns Michael Levin (University of Pennsylvania) Software is discrete mathematics Rex Page (University of Oklahoma) Session III: 4:15-6:00 ---------------------- Global abstraction-safe marshalling with hash types James Leifer (INRIA Rocquencourt), Gilles Peskine(INRIA Rocquencourt), Peter Sewell (University of Cambridge), Keith Wansbrough (University of Cambridge) Dynamic rebinding for marshalling and update, with destruct-time lambda Gavin Bierman (University of Cambridge), Michael Hicks (University of Maryland, College Park), Peter Sewell (University of Cambridge), Gareth Stoyle (University of Cambridge), Keith Wansbrough (University of Cambridge) Iterative-free program analysis Mizuhito Ogawa (Japan Advanced Institute of Science and Technology), Zhenjiang Hu (University of Tokyo), Isao Sasano (Japan Advanced Institute of Technology and Science) Report on ICFP 2003 & 2004 Olin Shivers & Kathleen Fisher =============================================================================== Tuesday 26 August 2003 Invited talk: 9:00-10:00 ------------------------ From Hilbert space to Dilbert space: Context semantics as a language for games and flow analysis Harry Mairson (Brandeis University) Session IV: 10:30-12:30 ----------------------- A theory of aspects David Walker (Princeton University), Steve Zdancewic (University of Pennsylvania), Jay Ligatti (Princeton University) Dependency-style Generic Haskell Andres Löh, Dave Clarke, Johan Jeuring (Universiteit Utrecht) Functional automatic differentiation with Dirac impulses Henrik Nilsson (Yale University) A user-centred approach to functions in Excel Simon Peyton Jones (Microsoft Research), Alan Blackwell (University of Cambridge), Margaret Burnett (Oregon State University) Session V: 2:15-3:45 -------------------- A sound and complete axiomatization of delimited continuations Yukiyoshi Kameyama (University of Tsukuba), Masahito Hasegawa (Kyoto University) Call-by-value is dual to call-by-name Philip Wadler (Avaya Labs) Disjunctive normal forms and local exceptions Emmanuel Beffara (CRNS, Université Paris 7), Vincent Danos (CRNS, Université Paris 7) Session VI: 4:15-6:00 --------------------- An effective theory of type refinements Yitzhak Mandelbaum (Princeton University), David Walker (Princeton University), Robert Harper (Carnegie Mellon University) A static type system for JVM access control Tomoyuki Higuchi, Atsushi Ohori (Japan Advanced Institute of Science and Technology) Parsing polish, step by step (functional pearl) John Hughes (Chalmers University), Doaitse Swierstra (Universiteit Utrecht) Programming contest awards presentation John Hughes et al. (Chalmers University of Technology) =============================================================================== Wednesday 27 August 2003 Session VII: 9:00-10:30 ----------------------- Boxes go bananas: Encoding higher-order abstract syntax with parametric polymorphism Geoffrey Washburn, Stephanie Weirich (University of Pennsylvania) FreshML: Programming with binders made simple Mark Shinwell, Andrew Pitts, Murdoch Gabbay (University of Cambridge) Meta-programming through typeful code representation Chiyan Chen, Hongwei Xi (Boston University) Session VIII: 11:00-11:30 ------------------------- Optimistic evaluation: An adaptive evaluation strategy for non-strict programs Robert Ennals (University of Cambridge), Simon Peyton Jones (Microsoft Research) Invited talk (joint with PPDP'03): 11:30-12:30 ---------------------------------------------- Understanding aspects Mitchell Wand (Northeastern University)

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Announce: release candidate 1 of buddha version 1.0
by Bernard James POPE 14 Aug '03

14 Aug '03

Announcing buddha version 1.0 release candidate 1 ------------------------------------------------- www.cs.mu.oz.au/~bjpop/buddha Buddha is a declarative debugger for Haskell 98. It is based on program transformation and relies on GHC version 5.04 or greater (but not version 6 yet). It also needs GHC's libraries compiled for profiling. This is the first candidate release of buddha version 1.0 New features include: - a more user friendly interface than previous versions, - the ability to show higher-order arguments by name or by value (similar to Hood), - deriving Ix is now supported (all standard deriving statements should work now). This is a release candidate. There will probably be a number of candidates before the final version 1.0 is done. Other candidates will not be announced to this list. This candidate has been tested only on Linux (Debian and Mandrake). Previous versions have worked on OS X and Solaris x86, but I don't have access to those machines at the moment. GHC version 6.0 is still not supported by buddha. If there is a great demand for this then I will sort it out faster. Cheers, Bernie.

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