- Haskell - Haskell.org

Re: Functional dependencies and type inference (2)
by oleg＠pobox.com 06 Dec '05

06 Dec '05

Louis-Julien Guillemette wrote: > Say we are using a GADT to represent a simple language of boolean > constants and conditionals, > > data Term a where > B :: Bool -> Term Bool > Cnd :: Term Bool -> Term t -> Term t -> Term t > > and we would like to perform a type-safe CPS conversion over this > language. We encode the relationship between the types in the source > language and those in the CPS-converted language using a class and a > fundep: Here's the code that seems to do what you wished. Liberty is taken to extend the language so we can CPS convert more interesting terms. Here are the tests > term1 = Cnd (Cnd (B True) (B False) (B False)) (B True) (B False) > test1 = shw (cps term1 id) "" *CPS> test1 "Cnd (B True)(Cnd (B False)(B True)(B False))(Cnd (B False)(B True)(B False))" > term2 = Cnd (Cmp (Cnd (B True) (I 1) (I 2)) (I 3)) > (B True) (Cmp (B True) (B False)) > test2 = shw (cps term2 id) "" *CPS> test2 "Cnd (B True)(Cnd (Cmp (I 1)(I 3))(B True)(Cmp (B True)(B False))) (Cnd (Cmp (I 2)(I 3))(B True)(Cmp (B True)(B False)))" The code: {-# OPTIONS -fglasgow-exts #-} {-# OPTIONS -fallow-undecidable-instances #-} module CPS where data Term a where B :: Bool -> Term Bool Cnd :: Term Bool -> Term t -> Term t -> Term t I :: Int -> Term Int Cmp :: Term t -> Term t -> Term Bool -- Note the polymorphic answertype class CpsForm t cps_t | t -> cps_t where cps :: Term t -> (Term cps_t -> Term w) -> Term w instance CpsForm t t where cps (B b) c = c (B b) cps (I b) c = c (I b) cps (Cnd p q r) c = cps p (\p' -> Cnd p' (cps q c) (cps r c)) cps (Cmp p q) c = cps p (\p' -> cps q (\q' -> c (Cmp p' q'))) shw:: Term t -> String -> String shw (B t) = ("B "++) . shows t shw (I t) = ("I "++) . shows t shw (Cnd p q r) = ("Cnd "++) . (showParen True (shw p)) . (showParen True (shw q)) . (showParen True (shw r)) shw (Cmp p q) = ("Cmp "++) . (showParen True (shw p)) . (showParen True (shw q)) term1 = Cnd (Cnd (B True) (B False) (B False)) (B True) (B False) test1 = shw (cps term1 id) "" term2 = Cnd (Cmp (Cnd (B True) (I 1) (I 2)) (I 3)) (B True) (Cmp (B True) (B False)) test2 = shw (cps term2 id) ""

2 3

TPLP special issue call for papers
by Maria Garcia de la Banda 05 Dec '05

05 Dec '05

------- Blind-Carbon-Copy X-Mailer: exmh version 2.0.2 2/24/98 To: mbanda Subject: TPLP special issue call for papers Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Mon, 05 Dec 2005 21:09:40 +1100 From: Maria Garcia de la Banda <mbanda(a)mosca.csse.monash.edu.au> [Apologies for multiple copies] - --------------------------------------------------------------------------- CALL FOR PAPERS Special Issue of Theory and Practice of Logic Programming on Implementation of Logic Programming Systems. Guest Editors: Bart Demoen and Maria Garcia de la Banda Logic programming saw the light more than 30 years ago, with the first implementation of Prolog appearing in 1972 by Philippe Roussel and Alain Colmerauer. Since then, implementation has been one of the driving forces of the field and has generated a significant amount of both theoretical research and running systems. While a certain maturity has been reached for some of the more traditional aspects of Logic Programming, new areas have also emerged and are currently being explored. Work in these new areas has resulted in many different languages and systems such as OZ, Mercury, CIAO, Erlang, XSB, SModels, DLV, ECLiPSe, B-Prolog, HAL, SICStus, etc. Therefore, the journal on Theory and Practice of Logic Programming (TPLP) is planning a special issue on the implementation of logic programming systems to appear in 2007. The aim of this special issue of Theory and Practice of Logic Programming is to attract high-quality research papers on the implementation of logic programming systems. The focus of this issue is on implementation itself, therefore we expect papers whose main contribution resides in presenting implementation issues per se. The emphasis is on system design, implementation techniques, and integration, rather than on topics such as performance, new paradigms, analysis domains or applications. In-depth surveys introducing newcomers into the field and comparisons of different implementation techniques are also solicited. TOPICS Topics of interest include but are not limited to: * Answer set programming * Compilation * Concurrency * Constraint Support * Databases * Debugging * Distributed Programming * Memoization * Memory management * Model generation * Parallelism * Programming environments * System integration Submissions Revised and enhanced versions of papers published at conferences that have not appeared in archival journals are eligible for submission. Papers describing important past research in this area which have not been published in archival journal papers are also solicited. Surveys and comparison of state of the art techniques are also solicited. For any doubt regarding the appropriateness of the topic of a paper for this special issue please email either to Bart Demoen (Bart.Demoen(a)cs.kuleuven.be) or to Maria Garcia de la Banda (mbanda(a)csse.monash.edu.au) Papers should be written in English, and formatted using the LaTeX style files developed by Cambridge University Press for TPLP and which can be downloaded from ftp://ftp.cup.cam.ac.uk/pub/texarchive/journals/latex/tlp-cls/ To submit please send an e-mail version to both Bart Demoen (Bart.Demoen(a)cs.kuleuven.be) and Maria Garcia de la Banda (mbanda(a)csse.monash.edu.au) For further information, please look at: http://www.csse.monash.edu.au/~mbanda/tplp_special_implementation Important Dates - --------------- First call for papers December 2005 Submission June 15, 2006 Notification February 15, 2006 Final version due: May 1, 2007 Publication 2007/2008 ------- End of Blind-Carbon-Copy

1 0

ANNOUNCE: hmp3, an ncurses mp3 player
by dons＠cse.unsw.edu.au 03 Dec '05

03 Dec '05

hmp3 0.1 : an ncurses mp3 player hmp3 is a lightweight ncurses-based mp3 player written in Haskell. It uses mpg321 or mpg123 as its decoding backend. It is designed to be simple, fast and robust. A screenshot can be found at: http://www.cse.unsw.edu.au/~dons/hmp3.html The source: darcs get http://www.cse.unsw.edu.au/~dons/code/hmp3 Thanks go to Stefan Wehr and Sam Bronson, who helped a lot with beta testing. In particular Sam, who burnt many cpu cycles. Thanks! Cheers, Don

3 5

Call for Participation: FOOL/WOOD 2006
by Kathleen Fisher 02 Dec '05

02 Dec '05

CALL FOR PARTICIPATION 2006 International Workshop on Foundations and Developments of Object-Oriented Languages FOOL/WOOD '06 http://www.research.att.com/~kfisher/FOOL/FOOLWOOD.html Sponsored by ACM SIGPLAN January 14, 2000 Charleston, South Carlolina, USA Following POPL '06 The search for sound principles for object-oriented languages has given rise to much work on the theory of programming languages during the past 20 years, leading to a better understanding of the key concepts of object-oriented languages and to important developments in type theory, semantics, and program verification. The FOOL/WOOD workshops bring together researchers to share new ideas and results in these areas. The next workshop, FOOL/WOOD '06, will be held in Charleston, South Carolina, on Saturday January 14, 2006, the day after POPL'06. Six contributed papers will be presented; in addition, there will be invited talks by Gilad Bracha, Dave Clarke, and perhaps one other person. To register for the workshop, use the standard POPL registration form, available through: http://www.cs.princeton.edu/~dpw/popl/06/ The early registration deadline ends ****December 10th****. Please make your hotel arrangments as soon as possible. To keep down the cost of registration, we will not be providing printed proceedings. All papers will be available online before the workshop, so you may print the papers you wish to have on hand before the meeting. ------------------------------------------------------------------------ -- Accepted papers: Parameterized Modules for Classes and Extensible Functions. Keunwoo Lee and Craig Chambers. Ego: Controlling the Power of Simplicity. Andi Bejleri, Jonathan Aldrich, and Kevin Bierhoff. A Foundation for Trait-Based Metaprogramming. John Reppy and Aaron Turon. Modularly Typesafe Interface Dispatch in JPred. Christopher Frost and Todd Millstein. Hybrid Object Types, Invariants, and Refinements. Cormac Flanagan and Stephen N. Freund. Property Types: Semantic Programming for Java Aaron Stump and Ian Wehrman. Invited talks: Gilad Bracha Dave Clarke The full program will be available shortly from www.research.att.com/~kfisher/FOOL/FOOLWOOD.html ------------------------------------------------------------------------ -- Program committee: Eric Allen (Sun Microsystems Laboratories) Gavin Bierman (Microsoft Research) Stephen Freund (Williams College) Paola Giannini (Universita del Piemonte Orientale) Gary T. Leavens (Iowa State University) James Noble (Victoria University of Wellington) Didier Remy (INRIA Rocquencourt) Christopher Stone (Harvey Mudd College) [Chair] Mads Torgersen (University of Aarhus) ------------------------------------------------------------------------ ---

1 0

RE: [Haskell] fptools mirror in darcs ready for testing
by Simon Marlow 02 Dec '05

02 Dec '05

Seconded - many thanks to John for the hard work he's put into this. Cheers, Simon On 01 December 2005 00:24, Donald Bruce Stewart wrote: > Hooray!! Thanks John > > jgoerzen: >> Hello everyone, >> >> Finally! Simon Marlow's plan[1] for moving from CVS to darcs for >> fptools, GHC, etc. is happening. Thanks to some feedback from him >> and the author of Tailor, as well as some free time finally, I've >> been able to convert things from CVS to darcs according to the plan. >> >> So, the first phase is to have live, updated darcs mirrors of CVS >> repos as appropriate. We now have that. >> >> Please feel free to darcs get --partial any of these. (Trust me, you >> *REALLY* want to use --partial. You'd be downloading over 13,000 >> patches otherwise on some of these.) >> >> http://cvs.haskell.org/darcs/ghc >> GHC HEAD >> http://cvs.haskell.org/darcs/ghc.ghc-6.4 >> GHC ghc-6-4-branch >> http://cvs.haskell.org/darcs/libraries >> libraries dir from fptools, HEAD >> http://cvs.haskell.org/darcs/libraries.ghc-6.4 >> libraries dir from fptools, ghc-6-4-branch >> http://cvs.haskell.org/darcs/nofib >> nofib dir from fptools, HEAD (there were no commits on >> ghc-6-4-branch for nofib) http://cvs.haskell.org/darcs/testsuite >> testsuite dir from fptools, HEAD >> http://cvs.haskell.org/darcs/testsuite.ghc-6.4 >> testsuite dir from fptools, ghc-6-4-branch >> >> Please note that you cannot pull patches between branches. This is >> because it is not really possible to have an automated CVS to darcs >> conversion that preserves enough information to do so. However, once >> the 6.4 branches go away, this will become nicely possible with >> future branches. >> >> Also please note that these repos are READ ONLY for now. Nobody will >> be accepting darcs patches until Simon (or someone) gives the word. >> >> These will all be updating daily as soon as I get around to writing >> a cron job. >> >> [1] >> http://www.haskell.org//pipermail/cvs-ghc/2005-November/027174.html >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell

1 0

cabal and ghcconfigure.h
by Robert Dockins 01 Dec '05

01 Dec '05

I've just run across a problem with my cabal build system -- I'm not yet sure if this is a cabal problem or a system configuration problem. I've been developing a package on OSX using the ghc 6.4.1 and cabal from darwinports. All is fine and dandy. However, today I've sucked my darcs repo down to my machine at home (running Gentoo linux) and now my package won't build. (this time with GHC 6.4.1 from portage and cabal 1.1.3) It halts while apparently running an Alex generated lexer through CPP, with the error: ghcconfig.h: No such file or directory My GHC install has this file at /usr/lib/ghc-6.4.1/include, but it clearly isn't in the include path that cabal is using. So the question is -- is this a cabal bug of some kind, or is the gentoo setup messed up some how? How should I proceed? Thanks Rob Dockins

2 1

RE: [Haskell] GADT type inference problem
by Simon Peyton-Jones 01 Dec '05

01 Dec '05

This is a bug, thank you. I've added it to the test suite, but I'm in the middle of revising the GADT impl so I won't fix it right off. Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of | oleg(a)pobox.com | Sent: 01 December 2005 05:57 | To: haskell(a)haskell.org | Subject: [Haskell] GADT type inference problem | | | Let us consider the following simple code | | > {-# OPTIONS -fglasgow-exts #-} | > | > module Foo where | > | > data Term a where | > B :: Bool -> Term Bool | > C :: Term Bool -> Term t -> Term t | > I :: Int -> Term Int | > | > shw (I t) = ("I "++) . shows t | > shw (B t) = ("B "++) . shows t | > shw (C p q) = ("Cnd "++) . (shw p) . (shw q) | | It loads in GHCi 6.4 and 6.4.1: | | Prelude> :l /tmp/g.hs | Compiling Foo ( /tmp/g.hs, interpreted ) | Ok, modules loaded: Foo. | *Foo> :t I 1 | I 1 :: Term Int | *Foo> :t B True | B True :: Term Bool | | However, when we do | | *Foo> :t shw | shw :: Term Bool -> String -> [Char] | | The inferred type of shw shows that it takes the values of | Term *Bool*. And yet the very first clause of shw mentions (I t), which | GHCi correctly reports to be of the type Term Int... | | It seems the last clause of shw confuses GHCi: if we remove it, the | inferred type of shw is "Term a -> String -> [Char]", as one would expect. | | That is not a type expression printing problem: | | *Foo> shw (I 1) | | <interactive>:1:5: | Couldn't match `Bool' against `Int' | Expected type: Term Bool | Inferred type: Term Int | In the application `I 1' | | the first clause of shw notwithstanding... | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

1 0

GADT type inference problem
by oleg＠pobox.com 30 Nov '05

30 Nov '05

Let us consider the following simple code > {-# OPTIONS -fglasgow-exts #-} > > module Foo where > > data Term a where > B :: Bool -> Term Bool > C :: Term Bool -> Term t -> Term t > I :: Int -> Term Int > > shw (I t) = ("I "++) . shows t > shw (B t) = ("B "++) . shows t > shw (C p q) = ("Cnd "++) . (shw p) . (shw q) It loads in GHCi 6.4 and 6.4.1: Prelude> :l /tmp/g.hs Compiling Foo ( /tmp/g.hs, interpreted ) Ok, modules loaded: Foo. *Foo> :t I 1 I 1 :: Term Int *Foo> :t B True B True :: Term Bool However, when we do *Foo> :t shw shw :: Term Bool -> String -> [Char] The inferred type of shw shows that it takes the values of Term *Bool*. And yet the very first clause of shw mentions (I t), which GHCi correctly reports to be of the type Term Int... It seems the last clause of shw confuses GHCi: if we remove it, the inferred type of shw is "Term a -> String -> [Char]", as one would expect. That is not a type expression printing problem: *Foo> shw (I 1) <interactive>:1:5: Couldn't match `Bool' against `Int' Expected type: Term Bool Inferred type: Term Int In the application `I 1' the first clause of shw notwithstanding...

2 1

Functional dependencies and type inference (2)
by Louis-Julien Guillemette 30 Nov '05

30 Nov '05

Say we are using a GADT to represent a simple language of boolean constants and conditionals, data Term a where B :: Bool -> Term Bool Cnd :: Term Bool -> Term t -> Term t -> Term t and we would like to perform a type-safe CPS conversion over this language. We encode the relationship between the types in the source language and those in the CPS-converted language using a class and a fundep: class CpsForm a b | a -> b instance CpsForm Bool Bool A natural formulation of the type of the CPS transformation would be cps :: CpsForm t cps_t => Term t -> (Term cps_t -> Term ()) -> Term () cps (B b) c = c (B b) -- doesn't type-check! cps (Cnd p q r) c = cps p (\p' -> Cnd p' (cps q c) (cps r c)) -- type-checks OK but the first clause of the function doesn't type-check: Couldn't match the rigid variable `cps_t' against `Bool' `cps_t' is bound by the type signature for `cps' Expected type: Term cps_t Inferred type: Term Bool In the application `B b' In the first argument of `c', namely `(B b)' On the contrary, if we push the (otherwise implicit) quantifier inside the parentheses: cps' :: Term t -> (forall cps_t . CpsForm t cps_t => Term cps_t -> Term ()) -> Term () cps' (B b) c = c (B b) -- type-checks OK cps' (Cnd p q r) c = cps' p (\p' -> Cnd p' (cps' q c) (cps' r c)) -- doesn't type-check! then the second clause fails to type-check: Couldn't match the rigid variable `cps_t' against `Bool' `cps_t' is bound by the polymorphic type `forall cps_t. (CpsForm t cps_t) => Term cps_t -> Term ()' Expected type: Term Bool Inferred type: Term cps_t In the first argument of `Cnd', namely `p'' In a lambda abstraction: \ p' -> Cnd p' (cps' q c) (cps' r c) This case seems to be an instance of a problem discussed earlier. (http://www.haskell.org/pipermail/haskell-cafe/2005-August/011053.html) Any suggestion on a way to get around this problem in current Haskell? And, any hope to get this fixed in a future release of GHC? Thanks Louis-Julien

2 1

Haskell Weekly News: November 29, 2005
by John Goerzen 29 Nov '05

29 Nov '05

Haskell Weekly News: November 29, 2005 Greetings, and thanks for reading the 17th issue of HWN, a weekly newsletter for the Haskell community. Each Tuesday, new editions will be posted (as text) to [1]the Haskell mailing list and (as HTML) to [2]The Haskell Sequence. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ Discussion Monads in other languages. A very interesting [3]thread covering availability of monads for other programming languages. 3. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/9430 Haskell in higher education. John Hughes posted a [4]survey aimed at those teaching Haskell in higher education. 4. http://thread.gmane.org/gmane.comp.lang.haskell.general/12680 GHC 6.6 progress. Jim Apple mentioned the [5]wiki page on GHC 6.6. 5. http://haskell.org/hawiki/GHC_206_2e6 GHC targetting Java. John Goerzen [6]asked about the apparent support for a Java target in the GHC source tree. Simon Peyton-Jones noted that it is no longer supported. 6. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/8970 Darcs Corner P2P repositories. There was a lot of [7]discussion on the Darcs lists about using a P2P network for storing Darcs information. 7. http://thread.gmane.org/gmane.comp.version-control.darcs.user/8883 About Haskell Weekly News Want to continue reading HWN? Please help us create new editions of this newsletter. Please see the [8]contributing information, or send stories to hwn -at- complete -dot- org. There is also a Darcs repository available. 8. http://sequence.complete.org/hwn-contrib

1 0