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Functional and Declarative Programming (REVISED PUBLICATION DATES)
by S.J.Thompson 11 May '05

11 May '05

Functional and Declarative Programming in Education (FDPE05) A one day workshop at ICFP05 Sunday, 25 September 2005, Tallin, Estonia http://www.cs.kent.ac.uk/~sjt/fdpe05/ SECOND CALL FOR SUBMISSIONS Overview Functional and declarative programming plays an important role in computing education at all levels. The aim of this workshop is to bring together educators and others who are interested in exchanging ideas on how to use a functional or declarative programming style in the classroom. Scope The workshop will cover a wide spectrum of functional and declarative programming techniques: - programming courses using traditional functional and declarative programming languages (Haskell, Mathematica, ML, Prolog, Scheme, ...); - programming courses teaching functional programming in commercial languages (e.g. C, C++, or Common LISP); - programming courses teaching functional program design in modern OO languages like Java, C#, or Eiffel; - pedagogic programming environments to support functional and declarative programming; - teaching tools implemented with functional and declarative languages; - declarative programming language extensions and implementations with pedagogical relevance; - application courses that benefit heavily from functional and declarative programming (e.g. theorem proving or hardware design). Furthermore, the workshop will also cover all levels of education: secondary school; college and university; post-college and continuing professional education. Submissions Submissions are sought in two forms: - 30 minute papers, to be reviewed by the workshop organisers and to be published in the proceedings. - 10 minute slots for `tips and tricks': these will be made available through the workshop web site. Submissions will be refereed by the workshop organisers who will call upon other members of the functional/declarative programming community for expert advice. Participants who choose to deliver a standard presentation are asked to submit a draft PDF paper of five pages; presenters of short talks are asked to submit an abstract of 250 words. Important dates: Submission deadline: June 5 Review deadline: June 15 Final decision: June 20 Final submission: July 12 Proceedings will be published by SIGPLAN through ACM's publishers. Organisers Robby Findler, University of Chicago, USA Michael Hanus, University of Kiel, Germany Simon Thompson, University of Kent, UK FDPE05: http://www.cs.kent.ac.uk/~sjt/fdpe05/ ICFP05: http://www.brics.dk/~danvy/icfp05/

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ANNOUNCE: pesco-cmdline-2.0
by Sven Moritz Hallberg 11 May '05

11 May '05

Dear Haskell users, I'm happy to announce the release of version 2 of my command line parsing module. This is mainly a restructuring release adding only a minor (but convenient) feature. Thus the news: * Adds a short-cut function 'stdargs' for standardized handling of --help etc. * Module renamed to System.Console.Cmdline.Pesco * Comes as a Cabal package. * Follows the ECT versioning scheme. Cabal package: http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-2.0.tgz API Reference: http://scannedinavian.org/~pesco/man/html3/ System.Console.Cmdline.Pesco.3hs.html http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-man-2.0.pdf Design & Implementation: http://scannedinavian.org/~pesco/distfiles/pesco-cmdline-2.0.pdf Feedback is obviously appreciated. Regards, Sven Moritz

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Haskell-Server hGetChar
by Tobe 11 May '05

11 May '05

Hi peeps ! I got a serious problem here :-) .......................................................... main = withSocketsDo ( do socket <- listenOn (PortNumber 9900) print "Server online" loop socket) loop socket = do (handling, host, port) <- accept socket forkIO (client handling) loop socket client handling = do anfrage <- hGetLine handling -- HERE ! let anfrage2 = umwandlungder anfrage ergebnis <- resultOrError (proofEngine anfrage2) let endergebnis = teste ergebnis hPutStr handling endergebnis hClose handling ............................................................................ IŽm using hGetLine at the mom, but I need to use hGetChar for further editing in this prog. Since I ainŽt really into haskell, I mailed you. This Prog is supposed to get a String of following form: "STRING 3 a&b" or "STRING 5 a & b" So, I suggest when reading the chars in loop, I need a Escape Character...How would you solve this ? Thx, Tobe -- Best regards, Tobe mailto:tobe@playahs.de

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Token Definition in Haskell
by Peter Theissen 10 May '05

10 May '05

Hello, i´m extending a functional language for some features. (-> www.VeriFun.de) Now i want to compare our lexing mechanism with the Haskell lexer. Therefore i need a description of the token definition regarding Haskell 98. I already searched a lot but didnt find a short and useful description of the grammar which is used to parse Haskell expressions. Although a description of the Parser would be nice. I would be very glad if somebody could give me further information and some references so that i can mention them in my paper. Cheers, Peter

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Functional and Declarative Programming in Education 2005 (2nd call)
by S.J.Thompson 10 May '05

10 May '05

Functional and Declarative Programming in Education (FDPE05) A one day workshop at ICFP05 Sunday, 25 September 2005, Tallin, Estonia http://www.cs.kent.ac.uk/~sjt/fdpe05/ SECOND CALL FOR SUBMISSIONS Overview Functional and declarative programming plays an important role in computing education at all levels. The aim of this workshop is to bring together educators and others who are interested in exchanging ideas on how to use a functional or declarative programming style in the classroom. Scope The workshop will cover a wide spectrum of functional and declarative programming techniques: - programming courses using traditional functional and declarative programming languages (Haskell, Mathematica, ML, Prolog, Scheme, ...); - programming courses teaching functional programming in commercial languages (e.g. C, C++, or Common LISP); - programming courses teaching functional program design in modern OO languages like Java, C#, or Eiffel; - pedagogic programming environments to support functional and declarative programming; - teaching tools implemented with functional and declarative languages; - declarative programming language extensions and implementations with pedagogical relevance; - application courses that benefit heavily from functional and declarative programming (e.g. theorem proving or hardware design). Furthermore, the workshop will also cover all levels of education: secondary school; college and university; post-college and continuing professional education. Submissions Submissions are sought in two forms: - 30 minute papers, to be reviewed by the workshop organisers and to be published in the proceedings. - 10 minute slots for `tips and tricks': these will be made available through the workshop web site. Submissions will be refereed by the workshop organisers who will call upon other members of the functional/declarative programming community for expert advice. Participants who choose to deliver a standard presentation are asked to submit a draft PDF paper of five pages; presenters of short talks are asked to submit an abstract of 250 words. These should be submitted by June 4, 2005. Comments from the organizers and notice of acceptance will be sent to authors by July 15, 2005. Proceedings will be published by SIGPLAN. Details of the publication procedure will be given on the workshop web site in due course. Organisers Robby Findler, University of Chicago, USA Michael Hanus, University of Kiel, Germany Simon Thompson, University of Kent, UK FDPE05: http://www.cs.kent.ac.uk/~sjt/fdpe05/ ICFP05: http://www.brics.dk/~danvy/icfp05/

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Fixed-length vectors in Haskell, Part 2: Using no extensions
by David Menendez 10 May '05

10 May '05

This is the second of two modules implementing fixed-length vectors in Haskell. The first used GADTs, a recent extension which currently requires GHC 6.4. This module uses no extensions to Haskell 98. This message is literate Haskell. To use, save it as "Vector_H98.lhs". > module Vector_H98 where In Vector_GADT, we used a single type constructor, Vec, which was parameterized by a type representing its length. When the data constructor was Nil, the length was Zero, when the constructor was Cons, the length was Succ n, where n was the length of vector passed to Cons. Without GADTs, we can't tie the type parameter to the data constructors. Instead, we split Nil and Cons into separate types corresponding to Vec Zero and Vec (Succ n): > data Vec_0 a = Nil > data Vec_s v a = Cons a (v a) Some aliases for convenience: > type Vec_1 = Vec_s Vec_0 > type Vec_2 = Vec_s Vec_1 > type Vec_3 = Vec_s Vec_2 > type Vec_4 = Vec_s Vec_3 Once again, it's possible to declare head and tail as total functions: > vhead :: Vec_s v a -> a > vhead (Cons x xs) = x > > vtail :: Vec_s v a -> v a > vtail (Cons x xs) = xs Unfortunately, every other useful function requires us to distinguish between Nil and Cons values. Since those now belong to different types, we have to use a type-class. Using Ralf Hinze's technique again, we create a class for vector types and a class for vector functions: > class Functor v => Vec v where vecCase :: VecCase g => g v > > instance Vec Vec_0 where vecCase = caseNil > instance Vec v => Vec (Vec_s v) where vecCase = caseCons > > class VecCase g where > caseNil :: g Vec_0 > caseCons :: Vec v => g (Vec_s v) (More on that Functor superclass later.) Our example functions from before are less convenient to write. > newtype ZipWith a b c v = ZipWith > { runZipWith :: (a -> b -> c) -> v a -> v b -> v c } > > vzipWith :: Vec v => (a -> b -> c) -> v a -> v b -> v c > vzipWith = runZipWith vecCase > > instance VecCase (ZipWith a b c) where > caseNil = ZipWith (\f Nil Nil -> Nil) > caseCons = ZipWith (\f (Cons x xs) (Cons y ys) -> > Cons (f x y) (vzipWith f xs ys)) > -- > newtype Foldr a b v = Foldr > { runFoldr :: (a -> b -> b) -> b -> v a -> b } > > vfoldr :: Vec v => (a -> b -> b) -> b -> v a -> b > vfoldr = runFoldr vecCase > > instance VecCase (Foldr a b) where > caseNil = Foldr (\f z Nil -> z) > caseCons = Foldr (\f z (Cons x xs) -> f x (vfoldr f z xs)) > -- > > toList :: Vec v => v a -> [a] > toList = vfoldr (:) [] > > inner :: (Vec v, Num a) => v a -> v a -> a > inner x y = vfoldr (+) 0 (vzipWith (*) x y) > > -- > newtype MkVec a v = MkVec { runVec :: a -> v a } > > vec :: Vec v => a -> v a > vec = runVec vecCase > > instance VecCase (MkVec a) where > caseNil = MkVec (\_ -> Nil) > caseCons = MkVec (\x -> Cons x (vec x)) > -- > newtype FromList a v = FromList { runFromList :: [a] -> Maybe (v a) } > > fromList :: Vec v => [a] -> Maybe (v a) > fromList = runFromList vecCase > > instance VecCase (FromList a) where > caseNil = FromList (\_ -> Just Nil) > caseCons = FromList (\l -> case l of > x:xs -> fmap (Cons x) (fromList xs) > [] -> Nothing > ) Declaring class instances for vectors is also less convenient; we have to declare separate instances for Vec_0 and Vec_s: > instance Functor Vec_0 where > fmap f Nil = Nil > > instance Functor v => Functor (Vec_s v) where > fmap f (Cons x xs) = Cons (f x) (fmap f xs) This means that a function which uses, say, vec and fmap together would need to have (Vec v, Functor v) in its context. We can avoid this by explicitly making Functor a superclass of Vec, but this obviously isn't practical for every class. Here are the instances for Show, Eq, and Num. Note that the instances for Vec_s don't depend on those for Vec_0. (In fact, the instances for Vec_0 are somewhat pointless, as it only has one value: Nil. They're included for completeness.) > instance Show (Vec_0 a) where show _ = "[]" > instance (Vec v, Show a) => Show (Vec_s v a) where > show = show . toList > > instance Eq (Vec_0 a) where Nil == Nil = True > instance (Vec v, Eq a) => Eq (Vec_s v a) where > x == y = vfoldr (&&) True (vzipWith (==) x y) > > instance (Num a) => Num (Vec_0 a) where > (+) = const > (*) = const > (-) = const > negate = id > abs = id > signum = id > fromInteger = const Nil > > instance (Num a, Vec v) => Num (Vec_s v a) where > (+) = vzipWith (+) > (*) = vzipWith (*) > (-) = vzipWith (-) > negate = fmap negate > abs = fmap abs > signum = fmap signum > fromInteger = vec . fromInteger > > -- > newtype Diag a v = Diag { runDiag :: v (v a) -> v a } > > diag :: Vec v => v (v a) -> v a > diag = runDiag vecCase > > instance VecCase (Diag a) where > caseNil = Diag (\_ -> Nil) > caseCons = Diag (\(Cons x xs) -> > Cons (vhead x) (diag (fmap vtail xs))) > -- > > instance Monad Vec_0 where > return _ = Nil > m >>= k = Nil > > instance Vec v => Monad (Vec_s v) where > return = vec > m >>= k = diag (fmap k m) We can't declare a type synonym for matrices, because vector lengths are no longer a separate part of the type signature, but we can still define matrix functions. > mat :: (Vec v, Vec w) => a -> v (w a) > mat x = vec (vec x) > > fromLists :: (Vec v, Vec w) => [[a]] -> Maybe (v (w a)) > fromLists xs = mapM fromList xs >>= fromList > > row :: v a -> Vec_1 (v a) > row v = Cons v Nil > > col :: Vec v => v a -> v (Vec_1 a) > col = fmap (\v -> Cons v Nil) > > -- > newtype Transpose a w v = Transpose > { runTranspose :: v (w a) -> w (v a) } > > transpose :: (Vec v, Vec w) => v (w a) -> w (v a) > transpose = runTranspose vecCase > > instance Vec w => VecCase (Transpose a w) where > caseNil = Transpose (\Nil -> vec Nil) > caseCons = Transpose (\(Cons x xs) -> > vzipWith Cons x (transpose xs)) > -- > > mult :: (Vec v, Vec t, Vec w, Num a) => v (t a) -> t (w a) -> v (w a) > mult x y = fmap (\r -> fmap (inner r) y') x > where y' = transpose y > > -- > newtype IdMat a v = IdMat { runIdMat :: v (v a) } > > idMat :: (Vec v, Num a) => v (v a) > idMat = runIdMat vecCase > > instance Num a => VecCase (IdMat a) where > caseNil = IdMat Nil > caseCons = IdMat (Cons (Cons 1 (vec 0)) (fmap (Cons 0) idMat)) > -- -- David Menendez <zednenem(a)psualum.com> <http://www.eyrie.org/~zednenem/>

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Cabal problems
by Peter Simons 10 May '05

10 May '05

Hi, I've run into a problem when trying to build a package with Cabal using a different GHC version than the one found in the $PATH. It looks like this: $ runghc Setup.lhs configure --with-compiler=/opt/ghc/bin/ghc-6.2.2 Warning: No license-file field. Configuring hsemail-0.0-2005-02-14... configure: looking for package tool: ghc-pkg near compiler in /opt/ghc/bin/ghc-6.2.2 Cannot find package tool: /opt/ghc/bin/ghc-pkg.2 Apparently there's some problem in the path manipulation code. I also wonder why Cabal complains about a missing License field, because the file contains: License: GPL Last but not least, Cabal fails when the package description file contains comments after the value. The entry Extensions: CPP -- some comment for example, will cause this error: *** Exception: Line 13: Parse of field 'extensions' failed I am using the Cabal version that's shipped with GHC's CVS-HEAD. Peter

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RE: Should inet_ntoa Be Pure?
by Simon Marlow 10 May '05

10 May '05

On 07 May 2005 11:59, Dominic Steinitz wrote: > Does anyone know why these are in the IO monad? Aren't they pure > functions converting between dotted-decimal strings and a 32-bit > network byte ordered binary value? > > Dominic. > > http://www.haskell.org/ghc/docs/latest/html/libraries/network/Network.So cket.html#v%3Ainet_addr > http://www.haskell.org/ghc/docs/latest/html/libraries/network/Network.So cket.html#v%3Ainet_ntoa Clearly it should be pure. To avoid breaking the interface, we could add: showHostAddress :: HostAddress -> String and deprecate inet_ntoa? Cheers, Simon

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RE: [Haskell] Proposal: Relative Module Imports
by Simon Marlow 10 May '05

10 May '05

On 06 May 2005 18:33, Samuel Bronson wrote: > On 5/6/05, Simon Marlow <simonmar(a)microsoft.com> wrote: >> (d) I hoped that something like grafting would provide a more >> general solution. > > Grafting sounds like a very nice solution just from the name, but I > don't recall hearing of it before. Where can I read about it? The thread started here: http://www.haskell.org/pipermail/libraries/2003-August/001310.html Cheers, Simon

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announce: wxHaskell 0.9.4, windows bug fix release
by Daan Leijen 08 May '05

08 May '05

Announcement: wxHaskell version 0.9.4, update 1 ---------------------------------------------------------------------- <http://wxhaskell.sourceforge.net> This is a bugfix release of wxHaskell version 0.9.4 for Windows platforms with GHC 6.4. The interpreter GHCi 6.4 now works with wxHaskell without problems. Thanks to Sigbjorn Finne for fixing this bug. As always, first uninstall before re-installing: - click on "wxhaskell-0.9.4\bin\wxhaskell-unregister.bat" - remove the "wxhaskell-0.9.4" directory - unzip the new release - click on "wxhaskell-0.9.4\bin\wxhaskell-register.bat" Have fun, Daan Leijen. ---------------------------------------------------------------------- wxHaskell is a portable GUI library for Haskell. The goal of the project is to provide an industrial strength portable GUI library, but without the burden of developing (and maintaining) one ourselves. wxHaskell is therefore build on top of wxWidgets -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. Furthermore, it is a mature library (in development since 1992) that supports a wide range of widgets with native look-and-feel, and it has a very active community (ranked among the top 25 most active projects on sourceforge). Since most of the interface is automatically generated from the wxEiffel binding, the current release of wxHaskell already supports about 75% of the wxWindows functionality -- about 2900 methods in 500 classes with 1400 constant definitions. wxHaskell has been build with GHC 6.x on Windows, MacOS X and Unix systems with GTK. A binary distribution is available for Windows, Linux (RPM) and MacOS X. And even if you don't intend to write GUI's yourself, it will be fun to check out the screenshots at <http://wxhaskell.sourceforge.net>. ---------------------------------------------------------------------- Version 0.9.4-1 ------------- Bugfixes: - Compile the wx library with -fvia-C. This prevents crashes in GHCi-6.4.(Fix is found by Sigbjorn Finne) Version 0.9.4 ------------- Backward compatible additions: - Adapted the configuration, make files, and install scripts to work with GHC 6.4. - Adapted the wxHaskell C-layer to work with wxWidgets 2.6.0 - Made "Object" an instance of Ord Version 0.9 ------------- Non backward compatible changes: - Changed "image" attribute to "picture" Backward compatible additions: - Added Multiple OpenGL Canvas example and fixed old example. - Much improved process support in WXCore.Process. Use "processExecAsyncTimed" instead of "processExecASync". - Full printing support in WXCore.Print - Added SpintControl events. - Fixed bug in MultiListBoxes where selections would only be added. - Added "pixelBufferGetPixels" and "pixelBufferSetPixels" and according functions for images. - Added "image" and made it an instance of the "Sized" class exported "imageCreateFromPixels" and "imageCreateFromPixelArray" - Added "drawImage" - Removed dependency on "readline" package in ghc 6.2.2 - Added "--cache" argument to configure script Bug fixes: - fixed "on command" event handlers in submenus.

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