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ANN: New release of ZeroTH
by Robin Green 24 Jun '09

24 Jun '09

This announcement will only be of interest to Haskell programmers using, or thinking of using, Template Haskell. I am very pleased to announce a new release (2009.6.23.3) of ZeroTH (also known as zeroth), a tool for preprocessing Haskell code to run splices and remove Template Haskell dependencies: http://hackage.haskell.org/package/zeroth For example, you could use it to reduce the size of your Haskell program binaries, if you use Template Haskell. (zeroth now actually uses itself on itself, for this very purpose, and you can use the Distribution.ZeroTH module for that in your own cabal projects.) It's still very much a hack - in that it would probably be more efficient and clean to implement it as an option to GHC - but hopefully now at least it's a slightly *better* hack. Lemmih has kindly agreed to hand over the job of being maintainer of ZeroTH to me. So please send any patches or complaints my way. The new darcs repository for the project, which is a darcs 2 repository, is at: http://patch-tag.com/publicrepos/zerothDarcs2 For this release, the "cabal" command-line tool is the only officially supported means of installation. So you should do something like: cabal update cabal install zeroth to install it. To get a summary of command-line options, type: zeroth --help Major changes from previous releases: * Much more Haskell code is now supported. This is partly because the code has been updated to work with the just-released haskell-src-exts 1.0.0; and partly because it supports a wider variety of Template Haskell code, including code which refers to definitions declared in the same source file. * It is now compulsory to specify any Haskell language extensions you are using in the input file, with a LANGUAGE pragma. (For debugging purposes, zeroth prints to stderr the result of parsing the LANGUAGE pragma, if any. If haskell-src-exts doesn't understand the LANGUAGE pragma, this will be Nothing. But that shouldn't happen.) * Template Haskell imports are now *automatically* stripped by default by zeroth, and so cpphs doesn't need to be run if you aren't otherwise using CPP. * New command-line options have been added (see zeroth --help). * Error messages are now more informative. * Librification! Almost anything can benefit from being made into a library, and zeroth is no exception. Of course, the executable is still there. * You can still use it on certain code which doesn't compile in GHC (yes, really, I've tested this!) but you now have to use the --only-splices option if you want to do this. Obviously, the splices themselves have to compile. --only-splices also makes zeroth faster. It is very lightly tested, so it might not work for your code out of the box. Please let me know if you have any problems with it, no matter how small. Happy hacking, -- Robin

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Re: [Haskell] ANN: Reusable Corecursive Queues via Continuations
by Felipe Lessa 24 Jun '09

24 Jun '09

On Mon, Jun 22, 2009 at 10:31:34PM -0400, Leon Smith wrote: > Also, a substantially revised draft of the associated paper, "Lloyd > Allison's Corecursive Queues: Why Continuations Matter" is now available. > [3] This paper will appear in the upcoming Monad Reader issue 14, and > comments would be most appreciated. As per [1], it seems n+k patterns will be removed from Haskell', so you may want to remove them from the paper as well. [1] http://hackage.haskell.org/trac/haskell-prime/wiki/Status -- Felipe.

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memoization using unsafePerformIO
by Jan Christiansen 23 Jun '09

23 Jun '09

Hi, I have tried to implement a memo function using stable names and weak pointers like it is presented in the paper "stretching the storage manager". There is an abstract datatype SNMap a b which implements a map that maps values of type StableName a to values of type b. The map is located in an IORef. {-# NOINLINE memo #-} memo :: (a -> b) -> a -> b memo f = unsafePerformIO (do tref <- newSNMap return (applyWeak f tref)) {-# NOINLINE applyWeak #-} applyWeak :: (a -> b) -> SNMap a (Weak b) -> a -> b applyWeak f tbl arg = unsafePerformIO (do sn <- makeStableName arg lkp <- lookupSNMap tbl sn case lkp of Nothing -> not_found sn Just weak -> do val <- deRefWeak weak case val of Just result -> return result Nothing -> not_found sn) where not_found sn = do let res = f arg weak <- mkWeak arg res Nothing insertSNMap tbl sn weak return res Using this memo function I have implemented a fibonacci function like it is defined in the paper. fib :: Int -> Int fib = memo ufib ufib :: Int -> Int ufib 0 = 1 ufib 1 = 1 ufib n = fib (n-1) + fib (n-2) When I compile this program with 6.10.3 fib yields the correct results up to 18 but for 19 it detects a loop. Can anybody give me a hint how I can avoid this behaviour (and still use unsafePerformIO ; ) )? Cheers, Jan

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ANN: haskell-src-exts-1.0.0
by Niklas Broberg 23 Jun '09

23 Jun '09

Fellow Haskelleers, It is with great pleasure I hereby announce the first stable release of the haskell-src-exts package, version 1.0.0! haskell-src-exts is a package for Haskell source code manipulation. In particular it defines an abstract syntax tree representation, and a parser and pretty-printer to convert between this representation and String. It handles (almost(*)) all syntactic extensions to the Haskell 98 standard implemented by GHC, and the parsing can be parametrised on what extensions to recognise. I wish to thank the glorious Haskell community, for giving me the chance to work on this project as part of Haskell.org's GSoC programme, but also for simply being such a nice place to be! Special thanks to everyone who helped me with testing and bug reports during the final stretch of release candidates, in particular the many excellent reports from Ganesh Sittampalam, Sebastian Fischer, and Neil Mitchell who is also mentoring the project. You're all awesome! haskell-src-exts-1.0.0: ================= Via cabal: cabal install haskell-src-exts-1.0.0 Via darcs: darcs get http://code.haskell.org/haskell-src-exts On hackage: http://hackage.haskell.org/package/haskell-src-exts-1.0.0 Changes from 0.5.7, the last release candidate: ====================================== * CPP lines are no longer ignored, which means haskell-src-exts will now invariably give a parse error on files with CPP pragmas in them. CPP is not supported by haskell-src-exts, and this is more intuitive than parsing e.g. all branches of an #if pragma, which is invariably give unintended results. * Fixed a stupid introduced bug where extensions passed int he parse mode were ignored. * fromParseOk is now exported, not just defined (doh). * ScopedTypeVariables now implies TypeOperators, as per GHC. I'm sure there are more implications that are missing from haskell-src-exts, I will add them as I find out about them. Thanks once again, and Happy Haskell Hacking to all! Cheers, /Niklas (*) The only two exceptions are NewQualifiedOperators and UnicodeSyntax.

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Ann: Emping-0.6 and Tests/Examples
by Hans van Thiel 23 Jun '09

23 Jun '09

Hello All, Version 0.6 of Emping is now, imo, at the level of a working prototype. It is available on Hackage (but won't build there because it uses Gtk2Hs. It did build with Cabal on FC8 with GhC 6.8 and Gtk2Hs 0.9.13). The package includes a user guide, but see the update on my web site about two UI corner case bugs (program hangs). My site http://www.muitovar.com discusses three examples of possible use, with tests using SQLite, OO Calc and dotty. There's also a .zip archive of all sources (two data sets from the UCI machine learning repository) and .csv and .dot files with the results. All comments most welcome... Emping is a (prototype) interactive tool for the discovery and analysis of (universal, not statistical) predictive rules in tables of nominal data. Best Regards, Hans van Thiel

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INAP 2009: 2nd Call for Papers
by Pedro Salgueiro 23 Jun '09

23 Jun '09

[apologies for cross-posting; please distribute] --- (PLEASE DISTRIBUTE) ------------------------------------------------------------ Second Call for Papers INAP 2009 18th International Conference on Applications of Declarative Programming and Knowledge Management November 5-7, 2009 Evora, Portugal http://www.di.uevora.pt/inap2009/ http://inap.dialogengines.com/ ------------------------------------------------------------ Organized by the Portuguese AI Society (APPIA), the INAP Committee and the Society of Logic Programming (GLP e.V.) == Overview == Declarative Programming is a family of advanced paradigms for the modeling and solving of complex problems. These specification and implementation methods have attracted more and more attention over the past years, e.g. in the domains of databases and natural language processing, for modeling and the processing of combinatorial problems, and for establishing systems for the web. == INAP 2009 == INAP is a communicative and dense forum for intensive discussion of applications of important technologies related to Prolog, Logic and Constraint Programming as well as closely related advanced software. It comprehensively covers the impact of programmable logic solvers in the Internet Society, its underlying technologies, and leading edge applications in industry, commerce, government, and societal services. INAP 2009 continues a tradition of successful workshops cast around the applications of declarative programming, which were held in Kobe (1997), Tokyo (1995, 1996, 1998 - 2001), Potsdam (2004), Fukuoka (2005) and Wuerzburg (2007). We invite the submission of high quality papers on the described topics, especially, but not exclusively, on different aspects of Declarative Programming, Constraint Processing and Knowledge Management as well as their use for Distributed Systems and the Web: - Knowledge Management, e.g. Data Mining, Decision Support, Deductive Databases - Distributed Systems and the Web, e.g. Agents and Concurrent Engineering, Semantic Web - Constraints, e.g. Constraint Systems, Extensions of Constraint (Logic) Programming - Theoretical Foundations, e.g. Deductive Databases, Nonmonotonic Reasoning - Systems and Tools for Academic and Industrial Use - Knowledge-based Web Services - Logic Solvers and Applications == Workshop Format == The technical program of the workshop will include invited presentations (to be announced), regular technical sessions with presentations of the accepted papers, system demonstrations and a panel discussion. == Conference Venue == The conference will be held at the University of Evora, Portugal in November 5-7, 2009. Evora is a nice and quiet historical city located in the south of Portugal that can be reached from Lisbon by train or coach in under 2 hours. It is a small city of 60.000 inhabitants, 120 km inland from Lisbon and classified by Unesco as World Heritage. The University of Evora was established in the 16th Century and is the 2nd oldest Portuguese University. The social program is promising since the region is very rich in historical sites (Stone Age, Roman, Medieval and Renaissance remains) and also offers a very special gastronomy. See http://en.wikipedia.org/wiki/%C3%89vora for more information. == Important Dates == Paper Submission Deadline: June 29, 2009 Notifications to Authors: August 17, 2009 Camera-ready Version Deadline: September 14, 2009 INAP 2009 Workshop: November 5-7, 2009 == Submission Guidelines == Participants should submit a paper (maximum 15 pages, PDF format), describing their work in topics relevant to the workshop. Accepted papers will be presented during the workshop. At least one author of an accepted contribution is expected to register for the workshop, and present the paper. All submissions should include the author's name(s), affiliation, complete mailing address, and email address. Authors are requested to prepare their submissions, following the LNCS/LNAI Springer format. Please see: http://www.springer.de/comp/lncs/authors.html for further details. The submission should be submitted through the electronic submission site: http://www.easychair.org/conferences/?conf=inap2009 The deadline for receipt of submissions is June 29, 2009. Papers received after this date will not be reviewed. Eligible papers will be peer-reviewed by at least three members of the Program Committee. Authors will be notified via email of the results by August 17, 2009. Authors of accepted papers are expected to improve their paper based on reviewers' comments and to send a camera ready version of their manuscripts by September 14, 2009. Accepted papers will be included in the workshop proceedings, which will be distributed to the participants. As in previous editions, we plan to publish selected papers in a proceedings volume in the Springer Lecture Notes in Artificial Intelligence (LNAI) series. == Organizing Committee == Vitor Nogueira vbn AT di.uevora.pt Salvador Abreu spa AT di.uevora.pt Pedro Salgueiro pds AT di.uevora.pt Universidade de Evora Portugal == Program Committee == Salvador Abreu, University of Evora, Portugal (co-chair) Sergio Alvarez, Boston College, USA Philippe Codognet, CNRS/JFLI, Tokyo, Japan Vitor Santos Costa, University of Porto, Portugal Daniel Diaz, University of Paris I, France Ulrich Geske, University of Potsdam, Germany Gopal Gupta, UT Dallas, USA Petra Hofstedt, Technical University of Berlin, Germany Ulrich Neumerkel, Technical University of Vienna, Austria Vitor Nogueira, University of Evora, Portugal Enrico Pontelli, New Mexico State University, USA Irene Rodrigues, University of Evora, Portugal Carolina Ruiz, Worcester Polytechnic Institute, USA Dietmar Seipel, University of Wuerzburg, Germany (co-chair) Terrance Swift, CENTRIA, Portugal Hans Tompits, Technical University of Vienna, Austria Masanobu Umeda, Kyushu Institute of Technology, Japan Armin Wolf, Fraunhofer FIRST, Berlin, Germany Osamu Yoshie, Waseda University, Japan == Contact Information == inap2009(a)di.uevora.pt Universidade de Evora Departamento de Informatica Largo dos Colegiais, 2 7004-516 Evora - PORTUGAL

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IMO ghc 6.8.2 misleading warning messages
by Vasili I. Galchin 23 Jun '09

23 Jun '09

Hello, For: parseOptional = Parse.parseOptional I got warning messages: Swish/HaskellUtils/ParseURI.hs:77:4: Warning: Defined but not used: `parseOptional' Swish/HaskellUtils/ParseURI.hs:77:4: Warning: Definition but no type signature for `parseOptional' Inferred type: parseOptional :: forall a b. Parse.Parser a [b] -> [a] -> [([b], [a])] IMO the warning messages should be reversed! (parseOptional was never "used" .. called ... but I would strongly prefer the type signature warning first. Kind regards, Vasili

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Getting my mind around UArray -> STUArray conversion
by Scott Michel 23 Jun '09

23 Jun '09

I'm trying to get my mind around how to thaw and then freeze a UArray. Theoretically, what I've written below should be a no-op, but I keep getting typing errors that I can't figure out. GHCI 6.10.3 says: Couldn't match expected type `UArray ix a' against inferred type `ST s (STUArray s ix1 e)' In the first argument of `(>>=)', namely `(unsafeThaw mem :: ST s (STUArray s ix e))' In the expression: (unsafeThaw mem :: ST s (STUArray s ix e)) >>= (\ mmem -> unsafeFreeze mmem) In the definition of `wombat': wombat val idx mem = (unsafeThaw mem :: ST s (STUArray s ix e)) >>= (\ mmem -> unsafeFreeze mmem) I'm figuring that usafeThaw with the type annotation should have given GHIC enough clue. Any suggestions? -scooter (WOMBAT = Waste Of Money Brains And Time) import Control.Monad; import Control.Monad.ST; import Data.Array.ST; import Data.Array.Unboxed; import Data.Array.MArray; import Data.Word; wombat :: (IArray UArray e, Ix ix, MArray (STUArray s) e (ST s)) => e -> ix -> UArray ix e -> UArray ix e wombat val idx mem = (unsafeThaw mem :: ST s (STUArray s ix e)) >>= (\mmem -> unsafeFreeze mmem)

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STM/Data Invariant related Segfault with GHC 6.10.3
by Jan Schaumlöffel 23 Jun '09

23 Jun '09

Hello, I just discovered that programs compiled with GHC 6.10.3 segfault when accessing a TVar created under certain conditions. This happens when the TVar is created and a data invariant is added (using alwaysSucceeds) in the same atomic block. The invariant does not necessarily have to read the TVar in question, a mere "alwaysSucceeds (return ())" is enough. It looks like by adding the invariant the TVar allocation is not kept after the block. The appended code snippets show how to reproduce this behaviour. IMHO the first version should work, too. Is there anything one can do to (reliably) work around this problem? Is there maybe an underlying problem that causes this? Regards, Jan module Main where import GHC.Conc -- this segfaults: main = do { t <- atomically (do { t1 <- newTVar 0 ; alwaysSucceeds (readTVar t1) ; return t1 }) ; atomically $ readTVar t } -- it works if written like this: main2 = do { t <- newTVarIO 0 ; atomically $ alwaysSucceeds (readTVar t) ; atomically $ readTVar t } -- works also if no invariant is added: main3 = do { t <- atomically (do { t1 <- newTVar 0 ; return t1 }) ; atomically $ readTVar t } -- works also if invariant is added later: main4 = do { t <- atomically (do { t1 <- newTVar 0 ; return t1 }) ; atomically $ alwaysSucceeds (readTVar t) ; atomically $ readTVar t } -- If you're happy and you know it, syntax error!

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haskelldb + sqlite problem.
by Magicloud Magiclouds 23 Jun '09

23 Jun '09

Hi, I am using haskelldb and haskelldb-hdbc-sqlite3. Well, I finally got the source compiled and ran, I got this error: App: user error (SQL error: SqlError {seState = "", seNativeError = 21, seErrorMsg = "prepare 74: SELECT subject,\n timestamp\nFROM notes as T1\nORDER BY timestamp DESC: library routine called out of sequence"}) Any clue what I should check? Thanks. -- 竹密岂妨流水过山高哪阻野云飞

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ANN: hledger 0.6.1 released
by Simon Michael 23 Jun '09

23 Jun '09

I have released hledger 0.6.1 which fixes a build problem with ghc 6.8. You can ignore this release if you use a newer ghc or if one of the http://hledger.org/binaries works for you. Thanks to Andreas Reuleaux for the report. More reports welcome on irc, list or http://code.google.com/p/hledger/issues . Best, -Simon (sm)

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Re: [Haskell-cafe] rewrite rules
by Daniel Schüssler 23 Jun '09

23 Jun '09

Hi Sjoerd, I don't know the cause of the problem, but if I add this rule, it works: {-# RULES "inline_map" forall g x. map g x = transform (. g) x -#} maybe, for whatever reason, the 'map' is inlined "too late" for the transform/transform rule to see it? Greetings, Daniel On Monday 22 June 2009 11:41:33 Sjoerd Visscher wrote: > Hi all, > > I have a rewrite rule as follows: > > {-# RULES > "transform/transform" forall (f::forall m. Monoid m => (a -> m) -> (b - > > > m)) > > (g::forall m. Monoid m => (b -> m) -> (c > -> m)) > (l::FMList c). transform f (transform g > l) = transform (g.f) l > #-} > > It fires on this code: > > print $ transform (. (*2)) (transform (. (+1)) (upto 10)) > > But it doesn't fire on this code: > > print $ map (*2) (map (+1) (upto 10))) > > with > > map g x = transform (. g) x > > and with or without {-# INLINE map #-}. > > What am I doing wrong? > > -- > Sjoerd Visscher > sjoerd(a)w3future.com > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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ICFP09 Call for Participation
by Matthew Fluet (ICFP Publicity Chair) 22 Jun '09

22 Jun '09

===================================================================== Call for Participation The 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) http://www.cs.nott.ac.uk/~gmh/icfp09.html Edinburgh, Scotland, 31 August - 2 September 2009 ===================================================================== ICFP 2009 provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. Preliminary program: * Accepted papers: + http://web.cecs.pdx.edu/~apt/icfp09_accepted_papers/accepted.html * Invited speakers: + Guy Steele -- Organizing Functional Code for Parallel Execution: or, foldl and foldr Considered Slightly Harmful + Benjamin Pierce -- Lambda, the Ultimate TA: Using a Proof Assistant to Teach Programming Language Foundations +Dan Piponi -- Commutative Monads, Diagrams and Knots Schedule including related workshops: * Aug 30: ACM SIGPLAN Workshop on ML * Aug 30: ACM SIGPLAN Workshop on Generic Programming * Aug 31-Sep 2: ICFP09 * Sep 3: ACM SIGPLAN Haskell Symposium * Sep 3: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 4: Commercial Users of Functional Programming * Sep 4: ACM SIGPLAN Workshop on Mechanizing Metatheory * Sep 4: ACM SIGPLAN Workshop on Approaches and Applications of Inductive Programming * Sep 5: ACM SIGPLAN Erlang Workshop * Sep 5: ACM SIGPLAN Developer Tracks on Functional Programming * Sep 5: ACM SIGPLAN Haskell Implementors Workshop Registration information: * http://www.regmaster.com/conf/icfp2009.html * Early registration deadline: July 30, 2009 Local arrangements (including travel and accommodation): * http://www.haskell.org/haskellwiki/ICFP_2009_Local_Arrangements * Conference reservation/rate deadline: July 20, 2009 * ICFP09 coincides with the final week of the Edinburgh International Festival, one of the premier arts and cultural festivals in the world. The opportunity to attend the Festival is a plus! Due to the popularity of Edinburgh during the festival period, we strongly recommend booking accommodation early. Conference organizers: * General Chair: Graham Hutton (University of Nottingham) * Program Chair: Andrew Tolmach (Portland State University) * Local Arrangements Chairs: Philip Wadler (University of Edinburgh), Kevin Hammond (University of St Andrews), and Gregory Michaelson (Heriot-Watt University) * Workshop Co-Chairs: Christopher Stone (Harvey Mudd College), and Michael Sperber (DeinProgramm) * Programming Contest Chair: Andrew Gill (University of Kansas) * Publicity Chair: Matthew Fluet (Toyota Technological Institute at Chicago) ===================================================================== ===================================================================== And, don't forget about the ICFP Programming Contest this weekend!! * http://www.icfpcontest.org * Friday, June 26 to Monday, June 29 * Organizers: Computer Systems Design Laboratory (University of Kansas)

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Documentation on hackage
by Uwe Schmidt 22 Jun '09

22 Jun '09

Dear Haskellers, who needs this kind of documentation? http://hackage.haskell.org/packages/archive/tfp/0.2/doc/html/Types-Data-Num… isn't this a kind of spam? Cheers, Uwe

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Cross platform getProcessID
by John Van Enk 22 Jun '09

22 Jun '09

In the unix package, we have getProcessID. Is there a corresponding method for finding the process ID in Windows? /jve

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Creating a new Haskell mailing list
by Ryan Trinkle 22 Jun '09

22 Jun '09

Hi all, I'm interested in starting a mailing list on haskell.org. Who should I talk to about such things? Thanks, Ryan

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traversal transformations
by Sjoerd Visscher 22 Jun '09

22 Jun '09

Hi, While playing with Church Encodings of data structures, I realized there are generalisations in the same way Data.Foldable and Data.Traversable are generalisations of lists. The normal Church Encoding of lists is like this: > newtype List a = L { unL :: forall b. (a -> b -> b) -> b -> b } It represents a list by a right fold: > foldr f z l = unL l f z List can be constructed with cons and nil: > nil = L $ \f -> id > cons a l = L $ \f -> f a . unL l f Oleg has written about this: http://okmij.org/ftp/Haskell/zip-folds.lhs Now function of type (b -> b) are endomorphisms which have a Data.Monoid instance, so the type can be generalized: > newtype FM a = FM { unFM :: forall b. Monoid b => (a -> b) -> b } > fmnil = FM $ \f -> mempty > fmcons a l = FM $ \f -> f a `mappend` unFM l f Now lists are represented by (almost) their foldMap function: > instance Foldable FM where > foldMap = flip unFM But notice that there is now nothing list specific in the FM type, nothing prevents us to add other constructor functions. > fmsnoc l a = FM $ \f -> unFM l f `mappend` f a > fmlist = fmcons 2 $ fmcons 3 $ fmnil `fmsnoc` 4 `fmsnoc` 5 *Main> getProduct $ foldMap Product fmlist 120 Now that we have a container type represented by foldMap, there's nothing stopping us to do a container type represented by traverse from Data.Traversable: {-# LANGUAGE RankNTypes #-} import Data.Monoid import Data.Foldable import Data.Traversable import Control.Monad import Control.Applicative newtype Container a = C { travC :: forall f b . Applicative f => (a -> f b) -> f (Container b) } czero :: Container a cpure :: a -> Container a ccons :: a -> Container a -> Container a csnoc :: Container a -> a -> Container a cpair :: Container a -> Container a -> Container a cnode :: Container a -> a -> Container a -> Container a ctree :: a -> Container (Container a) -> Container a cflat :: Container (Container a) -> Container a czero = C $ \f -> pure czero cpure x = C $ \f -> cpure <$> f x ccons x l = C $ \f -> ccons <$> f x <*> travC l f csnoc l x = C $ \f -> csnoc <$> travC l f <*> f x cpair l r = C $ \f -> cpair <$> travC l f <*> travC r f cnode l x r = C $ \f -> cnode <$> travC l f <*> f x <*> travC r f ctree x l = C $ \f -> ctree <$> f x <*> travC l (traverse f) cflat l = C $ \f -> cflat <$> travC l (traverse f) instance Functor Container where fmap g c = C $ \f -> travC c (f . g) instance Foldable Container where foldMap = foldMapDefault instance Traversable Container where traverse = flip travC instance Monad Container where return = cpure m >>= f = cflat $ fmap f m instance Monoid (Container a) where mempty = czero mappend = cpair Note that there are all kinds of "constructors", and they can all be combined. Writing their definitions is similar to how you would write Traversable instances. So I'm not sure what we have here, as I just ran into it, I wasn't looking for a solution to a problem. It is also all quite abstract, and I'm not sure I understand what is going on everywhere. Is this useful? Has this been done before? Are there better implementations of foldMap and (>>=) for Container? Finally, a little example. A Show instance (for debugging purposes) which shows the nesting structure. newtype ShowContainer a = ShowContainer { doShowContainer :: String } instance Functor ShowContainer where fmap _ (ShowContainer x) = ShowContainer $ "(" ++ x ++ ")" instance Applicative ShowContainer where pure _ = ShowContainer "()" ShowContainer l <*> ShowContainer r = ShowContainer $ init l ++ "," ++ r ++ ")" instance Show a => Show (Container a) where show = doShowContainer . traverse (ShowContainer . show) greetings, -- Sjoerd Visscher sjoerd(a)w3future.com

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packages on Hackage?
by Vasili I. Galchin 22 Jun '09

22 Jun '09

Hello, Haskell packages on Hackage can be hosted anywhere, yes? If a Haskell package is hosted on Hackage, how often is it backed up? Vasili

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Slightly off-topic: Lambda calculus
by Andrew Coppin 22 Jun '09

22 Jun '09

OK, so I'm guessing there might be one or two (!) people around here who know something about the Lambda calculus. I've written a simple interpretter that takes any valid Lambda expression and performs as many beta reductions as possible. When the input is first received, all the variables are renamed to be unique. Question: Does this guarantee that the reduction sequence will never contain name collisions? I have a sinking feeling that it does not. However, I can find no counter-example as yet. If somebody here can provide either a proof or a counter-example, that would be helpful.

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ANN: haskell-src-exts 1.0.0 rc1 (aka 0.5.2)
by Niklas Broberg 22 Jun '09

22 Jun '09

Fellow Haskelleers, I'm pleased to report that I feel I have now completed the first milestone in my GSoC project for haskell-src-exts: Full Code Support. This means I feel ready to take that scary leap that means to drop the safe 0.x version numbering (experimental) and finally make the first stable release, version 1.0.0. But before I take that leap I want the library to be thoroughly tested, so I can with confidence say that it truly *is* stable. Therefore, I hereby announce the release on hackage of haskell-src-exts-0.5.2, which I consider (almost) a release candidate for 1.0.0. * Via cabal: cabal install haskell-src-exts * On Hackage: http://hackage.haskell.org/package/haskell-src-exts-0.5.2 * Via darcs: darcs get http://code.haskell.org/haskell-src-exts I would be delighted if as many as possible would consider testing it on their code, even those of you who feel that you may not have any immediate use of the library, just to cover as much code base as possible in the hunt for potential bugs and misfeatures. Testing it is really easy, four simple steps: > cabal install haskell-src-exts [...] > ghci [...] Prelude> :m Language.Haskell.Exts Prelude Language.Haskell.Exts> parseFile "YourFileHere.(l)hs" If you get a parse error on a file that you feel should have been accepted, let me know! If the parser gives you an AST result for a file that you feel it shouldn't have accepted, let me know! Here's the bug tracker: http://trac.haskell.org/haskell-src-exts/report/1 The reason I say it is "almost" a release candidate is that while I consider the functionality to be in place, I will tidy up the exports, add a few more convenient functions to export, and add a lot of documentation, before I make the actual release. If you have a request for a particularly conventient function to add to the list of exports from the package, it's thus not too late to get it into 1.0.0. :-) What's cool in haskell-src-exts-0.5.2: ============================ * Support for all syntactic extensions supported by GHC, with two exceptions: UnicodeSyntax and NewQualifiedOperators. These will likely be added in the next feature release. Exclusive support for the newly registered XmlSyntax and RegularPatterns extensions. No support (yet) for Hugs-specific extensions (RestrictedTypeSynonyms, ExtensibleRecords, HereDocuments). No support for CPP. Also does not support the GHC-specific relaxation of layout in do-blocks, which is an unregistered extension (that should be registered!). * Support for parametrising the parsing on what extensions it should recognise. With no extensions given, it assumes Haskell98. Note that 'parseFile' will look for language pragmas in your source file to decide what extensions to use when parsing. If you want to be explicit, you can use 'parseFileWithExts', or 'parseFileWithMode' that lets you set a few other things as well. I intend to add some convenient names of extension groups, such as 'ghcExtensions' and 'glasgowExts', this is one area where I would particularly welcome suggestions. * Support for correct fixities of infix operators. By default it uses the fixities defined in the Prelude, as well as in the current document (including local let-bound fixities). Use 'parseFileWithMode' to set a different set of fixities. Language.Haskell.Exts.Fixity defines preludeFixities and baseFixities (all fixities defined in the base package), as well as combinators for defining your own sets. Much thanks to Neil Mitchell for the meat of this code. * No (known) bugs! :-) Special note for users of HaRP/HSP: I've uploaded a new version of hsx, hsx-0.5.0, that works with haskell-src-exts-0.5.2. There is one known bug in this version though, it cannot handle 'proc' entities from the Arrows extensions, I'm still considering how to fix that. In the mean time you can use it just fine, as long as your files don't contain any 'proc' blocks (which the old version couldn't handle anyway). Cheers and happy Haskelling, /Niklas

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secure store for passwords on CLIENT side
by Iliya Kuznetsov 22 Jun '09

22 Jun '09

Hello, haskellers, I've faced with some issue: how to store passwords securely on client's side? Of course there are many technics how to hash them on server side but sure all of them can't be used in my case (because of nature of hash). There is some platform-independent application written on Haskell and it requires login name/password for asking some web services through SOAP. I can ask it every time when it's called, but probably I should prepare some way to store this secure info on somewhere. The other side (in most cases!) can use only plain authorization method. For me the best way for this task -- storing the puzzled password somewhere in user's home directory ($HOME or %APPDATA% or in Mac's place for that), but I don't know how to puzzle it securely. One idea is to use GPG-alike approach: make secret key automatically and store it in user's home and just encrypt the given passphrase with that secret key after logging on and decrypt with public key when needed. But this probably is overmuch for that task. -- Iliya Kuznetsov

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Haskell Weekly News: Issue 122 - June 21, 2009
by Brent Yorgey 22 Jun '09

22 Jun '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090621 Issue 122 - June 21, 2009 --------------------------------------------------------------------------- Welcome to issue 122 of HWN, a newsletter covering developments in the [1]Haskell community. Are you ready for the [2]12th Annual ICFP programming contest? It begins this Friday, don't miss it! Let's reclaim Haskell's rightful place as the programming language of choice for discriminating hackers. Announcements Haskell protocol-buffers version 1.5.0. Chris Kuklewicz [3]announced version 1.5.0 of the [4]protocol-buffers, [5]protocol-buffers-descriptor, and [6]hprotoc packages to Hackage. This catches up to Google's version 2.1.0: support for "repeated" fields for primitive types; fields can now be marked deprecated; the type name resolver will no longer resolve type names to fields; and more. 12th Annual ICFP Contest. Mark Huntington Snyder [7]announced the 12th Annual [8]ICFP Programming Contest, hosted by the University of Kansas Computer Systems Design Laboratory at the Information and Telecommunication Technology Center. The contest will be held on the weekend of June 26-29. The contest task will be released sixteen seconds after 13:00 Central Daylight Time (US) on Friday, and entries will be accepted until 13:00:16 CDT on Monday. There is no preregistration required, and participation is free and open to all. Teams may participate from any location, and may use any programming language(s). Read the [9]contest blog or subscribe to the [10]RSS feed to receive timely updates before and during the contest. clock 0.1 released. Cetin Sert [11]announced the release of [12]clock, a package for convenient access to high-resolution clock and timer functions of different operating systems. It is planned to consist of two layers; the lower layer will provide direct access to OS-specific clock and timer functions like clock_gettime of Posix or GetTickCount of Windows, and its upper layer shall then provide a common API for all supported systems. Currently only the lower level is being developed. Turbinado V0.7. Alson Kemp [13]announced version 0.7 of [14]Turbinado, a Ruby-On-Rails-like web server and web framework for Haskell. It is designed to make creating web application using Haskell both easy and joyful. The primary additions in version 0.7 are FastCGI support and a new templating system (which includes HAML and HTML support). Additional details can be found [15]here. haskeline-class. Antoine Latter [16]announced [17]haskeline-class, a small library providing a newtyped MonadState instance for haskeline which lifts the class operations to an inner monad (as opposed to its existing instance). hyena. Johan Tibell [18]announced the first release of [19]hyena, a library for building web servers, based on the work on [20]iteratee style I/O by Oleg Kiselyov. The library allows you to create web servers that consume their input incrementally, without resorting to lazy I/O. This should lead to more predictable resource usage. Haskell-based iPhone development. Conal Elliott [21]announced a [22]collaboration wiki page for anyone working with Haskell to make iPhone apps. Fwd: Boston Haskell June 23rd meeting: openings for Lightning Talks. Ravi Nanavati [23]announced that there are several available slots for "lightning" (5 minute) talks at the June 23 meeting of the [24]Boston Area Haskell Users' Group. haskell-src-exts 1.0.0 rc1. Niklas Broberg [25]announced a series of release candidates for haskell-src-exts-1.0.0 (as of this writing, the most recent release candidate is version 0.5.6). This version is intended to fully support parsing of almost all Haskell extensions. Please help with testing! BostonHaskell: Next meeting - June 23rd at MIT CSAIL Reading Room (32-G882). Ravi Nanavati [26]announced the second meeting of the [27]Boston Area Haskell Users' Group, scheduled for Tuesday, June 23rd from 6:30pm - 8:30pm. It will be held in the MIT CSAIL Reading Room (32-G882, i.e. a room on the 8th floor of the Gates Tower of the MIT's Stata Center at 32 Vassar St in Cambridge, MA). Talks include "Automagic Font Conversion with Haskell Typeclasses" by Frank Berthold, and "Intermediate Language Representations via GADTs" by Nirav Dave. traversal transformations. Sjoerd Visscher [28]exhibited some code for Church-encoded container structures using their Foldable instance, and later [29]announced the [30]fmlist package based on the same code, along with a surprising example of a lazy 'middle-infinite' list (where elements can be taken from the beginning or the end!). hledger 0.6 released. Simon Michael [31]announced the release of [32]hledger 0.6. See the announcement for a list of the new features and other information. Discussion Adding swap to Data.Tuple. roconnor [33]proposed adding swap and swap' functions to Data.Tuple. Revamping the module hierarchy. Johan Tibell began an interesting [34]discussion about package names, module names, and the module hierarchy. Confusion on the third monad law when using lambda abstractions. Jon Strait [35]asked about the third monad law, leading to some clarification on what precisely the law says, and some interesting discussion on idiomatic use of the (<=<) (Kleisli composition) operator. Need some help with an infinite list. Gunther Schmidt [36]asked for some help generating a particular infinite list, and got a number of interesting suggestions. Blog noise [37]Haskell news from the [38]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Thomas ten Cate: [39]Cosmetics. Nice-looking icons for EclipseFP! * Niklas Broberg: [40]GSoC status report, week 4. More release candidates for haskell-src-exts 1.0.0. * >>> Uwe Hoffmann: [41]publishing nike runs, part 4: string templates. Real-world example of using HStringTemplate. * Andy Gill: [42]Call for Participation in the 12th Annual ICFP Programming Contest!. June 26-29! * Sebastian Fischer: [43]Reinventing Haskell Backtracking. * Remco Niemeijer: [44]Programming Praxis - Monte Carlo factorization. Remco implements Pollard's factorization algorithm in 9 lines of Haskell. * >>> Lee Duhem: [45]Understanding Functions Which Use 'instance Monad []' by Equational Reasoning. * Alex McLean: [46]Patterns in Haskell. A Haskell music generation EDSL. * David Amos: [47]Group generators for graph symmetries. * >>> adam: [48]Experience writing a ray tracer in Haskell. Adam's final project in a Haskell class taught by Mark Jones and Tim Sheard. * Petr Rockai: [49]soc progress 4. * Yaakov Nemoy: [50]Haskell Bindings to C from Start to Finish. Yaakov outlines his experience getting c2hs and the FFI to work. * Alex McLean: [51]Patterns in Haskell. Representing rhythmic patterns in Haskell. * >>> Abhishek Tiwari: [52]Haskell for Bioinformatics. * Roman Cheplyaka: [53]Shootout. A hilarious comic featuring sound advice on Haskell optimization. * Ketil Malde: [54]Dephd updates. * Neil Mitchell: [55]Draft paper on Derive, comments wanted. * Remco Niemeijer: [56]Programming Praxis - Who Owns The Zebra?. * Erik de Castro Lopo: [57]Two More for the Debian New Queue.. * David Amos: [58]Graph symmetries. * Alson Kemp: [59]Announce: Turbinado V0.7. * Gergely Patai: [60]You can draw your own graphs now!. * >>> Jens Petersen: [61]Haskell cabal-install rocks . Quotes of the Week * Botje: <Cheery> oh man. de bruijn again kicked me to groin <Botje> the easy fix is to label your groin as (-1) :) * Pseudonym: Telling dons that something has been added to the shootout is the new telling Oleg that it can't be done in the type system. About the Haskell Weekly News New editions are posted to [62]the Haskell mailing list as well as to [63]the Haskell Sequence and [64]Planet Haskell. [65]RSS is also available, and headlines appear on [66]haskell.org. To help create new editions of this newsletter, please see the information on [67]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [68]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://icfpcontest.org/ 3. http://article.gmane.org/gmane.comp.lang.haskell.libraries/11331 4. http://hackage.haskell.org/package/protocol-buffers 5. http://hackage.haskell.org/package/protocol-buffers-descriptor 6. http://hackage.haskell.org/package/hprotoc 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17298 8. http://icfpcontest.org/ 9. http://www.icfpcontest.org/wordpress 10. http://www.icfpcontest.org/wordpress/?feed=rss2 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17279 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/clock 13. http://article.gmane.org/gmane.comp.lang.haskell.general/17277 14. http://wiki.github.com/turbinado/turbinado 15. http://www.alsonkemp.com/turbinado/announce-turbinado-v07/ 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60246 17. http://hackage.haskell.org/package/haskeline-class 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60117 19. http://hackage.haskell.org/package/hyena 20. http://hackage.haskell.org/package/iteratee 21. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60104 22. http://haskell.org/haskellwiki/IPhone 23. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60091 24. http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group 25. http://article.gmane.org/gmane.comp.lang.haskell.cafe/59993 26. http://article.gmane.org/gmane.comp.lang.haskell.cafe/59991 27. http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group 28. http://article.gmane.org/gmane.comp.lang.haskell.cafe/59894 29. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60120 30. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fmlist 31. http://www.haskell.org/pipermail/haskell-cafe/2009-June/062787.html 32. http://hledger.org/ 33. http://article.gmane.org/gmane.comp.lang.haskell.libraries/11326 34. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11325 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60105 36. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/59999 37. http://planet.haskell.org/ 38. http://haskell.org/haskellwiki/Blog_articles 39. http://eclipsefp.wordpress.com/2009/06/20/cosmetics/ 40. http://nibrofun.blogspot.com/2009/06/gsoc-status-report-week-4.html 41. http://www.codemanic.com/uwe/2009/06/publishing-nike-runs-part-4-string-tem… 42. http://blog.unsafeperformio.com/?p=53 43. http://www-ps.informatik.uni-kiel.de/~sebf/pub/atps09.html 44. http://bonsaicode.wordpress.com/2009/06/19/programming-praxis-monte-carlo-f… 45. http://leeduhem.wordpress.com/2009/06/19/understanding-functions-which-use-… 46. http://yaxu.org/patterns-in-haskell/ 47. http://haskellformaths.blogspot.com/2009/06/group-generators-for-graph-symm… 48. http://blog.finiteimprobability.com/2009/06/18/experience-writing-a-ray-tra… 49. http://web.mornfall.net/blog/soc_progress_4.html 50. http://loupgaroublond.blogspot.com/2009/06/haskell-bindings-to-c-from-start… 51. http://yaxu.org/patterns-in-haskell/ 52. http://www.abhishek-tiwari.com/2009/06/haskell-for-bioinformatics.html 53. http://ro-che.blogspot.com/2009/06/shootout.html 54. http://blog.malde.org/index.php/2009/06/16/dephd-updates/ 55. http://neilmitchell.blogspot.com/2009/06/draft-paper-on-derive-comments-wan… 56. http://bonsaicode.wordpress.com/2009/06/16/programming-praxis-who-owns-the-… 57. http://www.mega-nerd.com/erikd/Blog/CodeHacking/Debian/safe_uniplate.html 58. http://haskellformaths.blogspot.com/2009/06/graph-symmetries.html 59. http://www.alsonkemp.com/turbinado/announce-turbinado-v07/ 60. http://just-bottom.blogspot.com/2009/06/you-can-draw-your-own-graphs-now.ht… 61. http://juhp.blogspot.com/2009/06/haskell-cabal-install-rocks.html 62. http://www.haskell.org/mailman/listinfo/haskell 63. http://sequence.complete.org/ 64. http://planet.haskell.org/ 65. http://sequence.complete.org/node/feed 66. http://haskell.org/ 67. http://haskell.org/haskellwiki/HWN 68. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] Slightly off-topic: Lambda calculus
by Keith Sheppard 22 Jun '09

22 Jun '09

forgot to cc the cafe :-) On Sun, Jun 21, 2009 at 1:08 PM, Keith Sheppard<keithshep(a)gmail.com> wrote: > hmm, it's been a while but... > > i think this "infinite loop" with a free variable would cause collision > > (\a . a a) (\b . b b d) > > On Sun, Jun 21, 2009 at 12:53 PM, Andrew > Coppin<andrewcoppin(a)btinternet.com> wrote: >> OK, so I'm guessing there might be one or two (!) people around here who >> know something about the Lambda calculus. >> >> I've written a simple interpretter that takes any valid Lambda expression >> and performs as many beta reductions as possible. When the input is first >> received, all the variables are renamed to be unique. >> >> Question: Does this guarantee that the reduction sequence will never contain >> name collisions? >> >> I have a sinking feeling that it does not. However, I can find no >> counter-example as yet. If somebody here can provide either a proof or a >> counter-example, that would be helpful. >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > > -- > keithsheppard.name > -- keithsheppard.name

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Re: [Haskell-cafe] Obscure weirdness
by Raynor Vliegendhart 21 Jun '09

21 Jun '09

On 6/20/09, Andrew Coppin <andrewcoppin(a)btinternet.com> wrote: > > Is this a known bug in GHC 6.10.1? Will upgrading fix it? (Obviously, it's > quite a lot of work to change GHC.) Suffice it to say that my program is > quite big and complicated; it worked fine when it was still small and > simple. ;-) There is a bug in ghci 6.10.1 that seems to be fixed in 6.10.3 (not sure whether it's fixed in 6.10.3). Certain non-terminating expressions causes ghci to crash immediately and go back to the prompt: ---------------------------------------- C:\>ghci GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> let loop = loop in loop C:\> ---------------------------------------- Compiling a module with a non-terminating expression first with ghc and then loading it in ghci does not seem to result in a crash.

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Edinburgh Haskell users meeting this afternoon
by Dougal Stanton 21 Jun '09

21 Jun '09

Hello Haskell users If you're in the Edinburgh (Scotland!) area and interested in Haskell we may have just the thing for you. I will be meeting one other Haskell Cafe list member at Doctor's pub at 4pm this afternoon (Sunday 21 June). This could be the start of something bigger, so if you're interested in Haskell please drop in and swell the numbers. The conversation will probably be about some of the basics - what is currying? what are typeclasses? what does the "deriving" keyword do? - so don't feel nervous about being out of your depth! If I can get a table, I will try to display a copy of Hudak's _Haskell School of Expression_ prominently. Please come up and say hello, or fire me back a note if you can't make it but are still interested in making this a regular meeting. Don't be shy about joining us if you're available though! Thanks everyone! Dougal -- Dougal Stanton dougal(a)dougalstanton.net // http://www.dougalstanton.net

1 0

Need some help with an infinite list
by Günther Schmidt 21 Jun '09

21 Jun '09

Hi guys, I'd like to generate an infinite list, like ["a", "b", "c" .. "z", "aa", "ab", "ac" .. "az", "ba", "bb", "bc" .. "bz", "ca" ...] When I had set out to do this I thought, oh yeah no prob, in a heartbeat. Uhm. Help, pls! Günther PS: I know this should be a no-brainer, sry

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ANN: haskeline-class
by Antoine Latter 21 Jun '09

21 Jun '09

I'd like to announce a small library newly on hackage: haskeline-class http://hackage.haskell.org/package/haskeline-class Haskeline is an easy to use library, with a reasonable interface. The one quirk that got in my way was that its 'InputT' monad transformer defined its own instance of MonadState which allowed the user of the library to peer into the guts of Haskeline. What I really wanted at the time was an instance of MonadState which lifted the class operations to an inner monad. So I wrote a small newtype wrapper and a support class to work around this. If anyone else has the same issue, the code is now on Hackage. I've heard that this won't even be needed in the next major release of Haskeline, but I'll likely keep this package up-to-date if anyone finds the MonadHaskeline class useful. Antoine

1 0

Obscure weirdness
by Andrew Coppin 21 Jun '09

21 Jun '09

OK, so here's an interesting problem... I've been coding away all day, but now my program is doing something slightly weird. For a specific input, it summarily terminates. The registered exception handler does not fire. There is no output to stdout or stderr indicating what the problem is. It just *stops* half way through the printout. Weirder: If I run it in GHCi, then GHCi itself terminates. (I didn't think you could *do* that!) It's not as if my program is anything unusual. There are no unsafe functions. No FFI. Nothing. Just regular high-level Haskell. Is this a known bug in GHC 6.10.1? Will upgrading fix it? (Obviously, it's quite a lot of work to change GHC.) Suffice it to say that my program is quite big and complicated; it worked fine when it was still small and simple. ;-)

5 6

unique identity and name shadowing during type inference
by Geoffrey Irving 21 Jun '09

21 Jun '09

Hello, I am designing a type inference algorithm for a language with arbitrary function overloading. For various reasons (beyond the scope of this email), it's impossible to know the full type of an overloaded function, so each function is assigned a unique primitive type and the inference algorithm gradually learns more information about the primitive. For example, if we declare an identity function f x = x the algorithm will create a primitive type F, and record f :: F. If we use the function a few times, f 1 f "blah" the algorithm will infer F Int = Int F String = String My question is: what's the best way to represent these unique primitive types in Haskell? A new type primitive needs to be created whenever we process a function declaration. Nested function declarations produce a different primitive each time the parent is invoked with different argument types. These separate primitives can escape if local functions are returned, so the inference algorithm must be able to keep them separate and learn more about them after their parent function is forgotten. Here are a few ways I know of: 1. Thread a uniqueness generator monad through the whole algorithm. I'd prefer to avoid this extra plumbing if possible. 2. Label primitives with the full context of how they were created. If function f declares a nested function g, and f is called with Int and Char, the primitives for g would be labeled with "f Int" and "f Char" to keep them separate. This is similar to lambda lifting. 3. Scary hacks involving makeStableName and unsafePerformIO. Some sort of context would have to be thrown around here to make sure GHC doesn't merge the different makeStableName calls. Unfortunately, method (2) is complicated by the fact that variable names are not unique even in the internal representation (I'm using the trick from [1]), so I'm not sure what the minimal unique "context" would be. Does anyone know other methods outside of (1), (2), or (3), or clean ways of structuring (2) or (3)? Thanks! Geoffrey [1]: http://www.haskell.org/~simonmar/bib/ghcinliner02_abstract.html

2 1

Re: Wiki user accounts
by Gwern Branwen 21 Jun '09

21 Jun '09

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On Mon, Jun 15, 2009 at 1:18 PM, Ashley Yakeley wrote: > For requesting accounts: who would receive the email, and which person > would create the account? > Why not just list everyone's email and let the requester pick who to send the request to? - -- gwern -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEAREKAAYFAko2ik8ACgkQvpDo5Pfl1oK4fwCeJvNQpc0ubJl0AmfDebmudxUq UrEAn3rwVLmLRl1RIcJLpZET6SjrssYD =Mhng -----END PGP SIGNATURE-----

5 12

Tree Semantics and efficiency
by Rouan van Dalen 21 Jun '09

21 Jun '09

Hi everyone. I would like to confirm the following semantics. I want a tree which can be traversed both downwards and upwards. To do this i need to store the following for each node: o) a reference to the parent node (so we can traverse up the tree). This must be a reference as i dont want to copy the parent node each time) o) a list of child nodes that belong to this node. It is important to store only a reference to the parent and not a copy of the entire parent for efficiency. How would one write this in Haskell so that it has the above mentioned semantics. Or does GHC do that automatically for me so I don't need to do it explicitly? I am thinking of writing something like this (naive implementation) : Tree = TreeNode String Tree [Tree] -- TreeNode <data> <ParentReference> <ChildNodes> OR (implementation using IORef for parentNode reference) Tree = TreeNode String (IORef Tree) [Tree] -- TreeNode <data> <ParentReference> <ChildNodes> Thanks in advance Rouan.

5 4

Confusion on the third monad law when using lambda abstractions
by Jon Strait 20 Jun '09

20 Jun '09

Hi everyone, I use and love Haskell, but I just have this nagging concern, that maybe someone can help me reason about. If I'm missing something completely obvious here and making the wrong assumptions, please be gentle. :) I'm reading the third (bind associativity) law for monads in this form: m >>= (\x -> k x >>= h) = (m >>= k) >>= h Now considering the definition of liftM2: liftM2 f m1 m2 = m1 >>= (\x1 -> m2 >>= (\x2 -> return (f x1 x2))) Isn't this liftM2 definition in the same form as the LHS of the third law equation, with (\x2 -> return (f x1 x2)) being the h function? Comparing this definition with the third law equation, the equation doesn't work because on the RHS equivalent; the x1 argument would be lost. So, why wasn't I finding a mention of a qualification that states that the third law only applies as long as the function in the h position doesn't reference arguments bound from previous 'binds'? It took going all the way back to Philip Wadler's 1992 paper, 'Monads for functional programming' to find reassurance: "The scope of variable x includes h on the left but excludes h on the right, so this law is valid only when x does not appear free in h." I'm also thinking of the Maybe monad, where Nothing >>= \x -> Just (x + 1) >>= \y -> return (y + 2) evaluates to Nothing after the first monadic bind and doesn't evaluate the rest of the expression. However, Nothing >>= Just . (+ 1) >>= return . (+ 2) should evaluate through the first and second monadic bind, evaluating to Nothing each time, of course. For the Maybe monad, both expressions give the same result, but if there were another monad defined like, data MadMaybe a = Nothing | Perhaps | Just a instance Monad MadMaybe where (Just x) >>= k = k x Nothing >>= _ = Perhaps Perhaps >>= _ = Nothing - then the two previous expressions run in the MadMaybe monad would evaluate to different values. Since the first of the previous expressions evaluates like the LHS of the third law equation above and the second expression evaluates like the RHS, the expressions should be equivalent, but they are not. Does this put into question the third monad law's relevance to Haskell monads, or is it that MadMaybe shouldn't be made a monad because it violates the third law? Thanks for any insight. Jon

9 12

hs-dotnet users?
by Günther Schmidt 20 Jun '09

20 Jun '09

Hi all, I'm just touching base with Sigbjorns hs-dotnet package. Are there other users of this package out there who would like to share their experience? Günther

1 0

Use MySQL from Haskell
by Maciej Podgurski 20 Jun '09

20 Jun '09

Hello, I'm trying to use MySQL from Haskell but it seems impossible for me to install one of the MySQL packages on my Windows XP machine. First I tired to install hsql-mysql-1.7.1 on GHC 6.10.3 but installing haskelldb-hsql failed with a hidden package error. So I added the old-time package to the cabal file but there still was a compile error (something due to the change from Exception to Exception e => e). So I switched to GHC 6.8.3 and tried it again. Now it says: Configuring hsql-mysql-1.7.1... Warning: 'extra-lib-dirs: /usr/lib/mysql' directory does not exist. Warning: 'include-dirs: /usr/include/mysql' directory does not exist. Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package process-1.0.0.1 requires filepath-1.1.0.0 package directory-1.0.0.1 requires filepath-1.1.0.0 package Cabal-1.6.0.3 requires filepath-1.1.0.2 Setup: Missing dependency on a foreign library: * Missing C library: mysqlclient This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. There's no Haskell package mysqlclient and I don't know how to install a C library in Haskell. So I switched to HDBC-2.1.1 and got the next compile error: Building convertible-1.0.5... Data/Convertible/Instances/Num.hs:671:0: warning: no newline at end of file [...] [5 of 8] Compiling Data.Convertible.Instances.C ( Data/Convertible/Instances/C.hs, dist\build/Data/C onvertible/Instances/C.o ) [6 of 8] Compiling Data.Convertible.Instances.Time ( Data/Convertible/Instances/Time.hs, dist\build/ Data/Convertible/Instances/Time.o ) Data/Convertible/Instances/Time.hs:64:0: Duplicate instance declarations: instance Typeable NominalDiffTime -- Defined at Data/Convertible/Instances/Time.hs:(64,0)-(65,42) instance Typeable NominalDiffTime -- Defined in time-1.1.3:Data.Time.Clock.UTC Data/Convertible/Instances/Time.hs:67:0: Duplicate instance declarations: instance Typeable UTCTime -- Defined at Data/Convertible/Instances/Time.hs:(67,0)-(68,34) instance Typeable UTCTime -- Defined in time-1.1.3:Data.Time.Clock.UTC So please help me, what GHC/package configuration will I need to use MySQL from my Haskell programs on Windows? I really like Haskell but all those "broken" packages are really discouraging. :( Best wishes, Maciej

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Installing agda through cabal
by Paulo J. Matos 20 Jun '09

20 Jun '09

Hi all, I am trying to install agda through cabal but I get this: $ cabal install alex Resolving dependencies... [1 of 1] Compiling Main ( /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs, /tmp/alex-2.3.116333/alex-2.3.1/dist/setup/Main.o ) /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs:6:51: Warning: In the use of `buildVerbose' (imported from Distribution.Simple.Setup): Deprecated: "Use buildVerbosity instead" /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs:7:51: Warning: In the use of `defaultUserHooks' (imported from Distribution.Simple): Deprecated: "Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2 compatibility in which case you must stick with defaultUserHooks" Linking /tmp/alex-2.3.116333/alex-2.3.1/dist/setup/setup ... Warning: defaultUserHooks in Setup script is deprecated. Configuring alex-2.3.1... Preprocessing executables for alex-2.3.1... Building alex-2.3.1... [ 1 of 16] Compiling Set ( src/Set.hs, dist/build/alex/alex-tmp/Set.o ) [ 2 of 16] Compiling DFS ( src/DFS.hs, dist/build/alex/alex-tmp/DFS.o ) [ 3 of 16] Compiling Sort ( src/Sort.hs, dist/build/alex/alex-tmp/Sort.o ) [ 4 of 16] Compiling CharSet ( src/CharSet.hs, dist/build/alex/alex-tmp/CharSet.o ) [ 5 of 16] Compiling Map ( src/Map.hs, dist/build/alex/alex-tmp/Map.o ) [ 6 of 16] Compiling Paths_alex ( dist/build/autogen/Paths_alex.hs, dist/build/alex/alex-tmp/Paths_alex.o ) [ 7 of 16] Compiling Util ( src/Util.hs, dist/build/alex/alex-tmp/Util.o ) [ 8 of 16] Compiling AbsSyn ( src/AbsSyn.hs, dist/build/alex/alex-tmp/AbsSyn.o ) [ 9 of 16] Compiling ParseMonad ( src/ParseMonad.hs, dist/build/alex/alex-tmp/ParseMonad.o ) [10 of 16] Compiling Scan ( dist/build/alex/alex-tmp/Scan.hs, dist/build/alex/alex-tmp/Scan.o ) [11 of 16] Compiling Output ( src/Output.hs, dist/build/alex/alex-tmp/Output.o ) [12 of 16] Compiling Info ( src/Info.hs, dist/build/alex/alex-tmp/Info.o ) [13 of 16] Compiling NFA ( src/NFA.hs, dist/build/alex/alex-tmp/NFA.o ) [14 of 16] Compiling DFA ( src/DFA.hs, dist/build/alex/alex-tmp/DFA.o ) [15 of 16] Compiling Parser ( dist/build/alex/alex-tmp/Parser.hs, dist/build/alex/alex-tmp/Parser.o ) [16 of 16] Compiling Main ( src/Main.hs, dist/build/alex/alex-tmp/Main.o ) Linking dist/build/alex/alex ... Installing executable(s) in /home/pmatos/.cabal/bin pmatos@drserver ~ $ cabal install agda Resolving dependencies... Configuring Agda-2.2.2... cabal: alex version >=2.0.1 && <3 is required but it could not be found. cabal: Error: some packages failed to install: Agda-2.2.2 failed during the configure step. The exception was: exit: ExitFailure 1 As you can see, I had just finished installing alex 2.3.1, so why does cabal still request alex >=2.0.1 && <3? Cheers, Paulo Matos

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duplicate definition for symbol
by Henk-Jan van Tuyl 20 Jun '09

20 Jun '09

L.S., I am trying to run a program in GHCi, but I get a meesage that an object file is loaded twice; it appears that two different versions of package "process" are loaded, see the session text below. How can I solve this? GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> :load "Main.lhs" [1 of 1] Compiling Main ( Main.lhs, interpreted ) Ok, modules loaded: Main. *Main> :main Loading package syb ... linking ... done. Loading package base-3.0.3.0 ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.0 ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.1 ... linking ... done. Loading package filepath-1.1.0.1 ... linking ... done. Loading package Win32-2.2.0.0 ... linking ... done. Loading package directory-1.0.0.2 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. Loading package time-1.1.2.2 ... linking ... done. Loading package stm-2.1.1.2 ... linking ... done. Loading package split-0.1.1 ... linking ... done. Loading package HUnit-1.2.0.3 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package process-1.0.1.1 ... linking ... done. Loading package haskell98 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.0.1 ... linking ... done. Loading package hslogger-1.0.7 ... linking ... done. Loading package process-1.0.1.0 ... GHCi runtime linker: fatal error: I found a duplicate definition for symbol _runInteractiveProcess whilst processing object file C:\Programs\ghc\ghc-6.10.1\process-1.0.1.0\HSprocess-1.0.1.0.o This could be caused by: * Loading two different object files which export the same symbol * Specifying the same object file twice on the GHCi command line * An incorrect `package.conf' entry, causing some object to be loaded twice. GHCi cannot safely continue in this situation. Exiting now. Sorry. -- Met vriendelijke groet, Henk-Jan van Tuyl -- http://functor.bamikanarie.com http://Van.Tuyl.eu/ --

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Running a "sub-process" which dies with the main program
by Deniz Dogan 19 Jun '09

19 Jun '09

Hi I couldn't come up with a better subject than this one, so anyways... I have a small program which spawns a subprocess. However, when I hit C-c, the subprocess won't die, instead it will just keep running until it's done or until I kill it. I've looked around in System.Process for something suitable for my needs, but I can't seem to find it. Any ideas? -- Deniz Dogan

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Could someone give me a sample about haskelldb?
by Magicloud Magiclouds 19 Jun '09

19 Jun '09

Hi, I am learning it following the very few documents on its site. Well, I failed, with the import modules, I still cannot compile it. The error is on "T.*". 6 import Database.HaskellDB.HDBC.SQLite3 7 import Database.HaskellDB 8 import Database.HaskellDB.DBSpec 9 import Database.HaskellDB.DBSpec.PPHelpers 10 import Database.HaskellDB.Query 48 q = do 49 t <- table $ Table "notes" [] 50 restrict ( t!T.done .<>. False ) 51 r <- project ( T.subject << t!T.subject ) 52 order [ desc r T.priority 53 , desc r T.dt ] 54 return r -- 竹密岂妨流水过山高哪阻野云飞

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FFI question
by Vasili I. Galchin 19 Jun '09

19 Jun '09

Hello, I would like to write bindings from Haskell to Java. Is this possible? If so, where are examples? Vasili

1 0

Runtime strictness analysis for polymorphic HOFs?
by Paul Chiusano 19 Jun '09

19 Jun '09

Hello, I was recently trying to figure out if there was a way, at runtime, to do better strictness analysis for polymorphic HOFs, for which the strictness of some arguments might depend on the strictness of the strictness of function types that are passed as arguments [1]. As an example, consider foldl. The 'seed' parameter of foldl can be made strict as long as the binary function used for the fold is strict in its arguments. Unfortunately, because strictness analysis is done statically, Haskell can't assume anything about the strictness of the binary function - assuming we only compile one instance of foldl, it must be the most conservative version possible, and that means making the seed parameter lazy. :-( I started thinking about ways you could to a check at runtime for this sort of thing, something to the effect of asking foldl, before heap-allocating a thunk for the seed parameter, whether that parameter could be made strict. foldl could then inspect other arguments that have been supplied, and based on these arguments, evaluate or go ahead with creating a thunk the seed parameter. It's a runtime cost, sure, but would it be more than the cost of having to do an additional heap allocation? In any case a small runtime cost might be worth it if the analysis becomes more uniform. So, my question is: does doing this sort of runtime analysis seem like a horrible idea? Is it even possible? Has anyone tried this in the past? (So far I haven't found anything, but would love references if people have them.) Note that I'm not suggesting Haskell should do anything like this. I'm playing around with the ideas because I'm interesting in creating a lazy language and I was hoping to have strictness analysis be very predictable and uniform, something the programmer can count on and use to simply reason about space usage ... which might be hopelessly unrealistic goal! I guess the more general question is - is "perfect" strictness analysis (however that is defined) possible, if we're willing to incur some runtime cost? What would that look like? Best, Paul [1]: More background on my thinking here - a bit half-baked, so bear with me! http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-1.ht… http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-2.ht…

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how to #include files within parsec ... without unsafePerformIO?
by Leonard Siebeneicher 19 Jun '09

19 Jun '09

Hi Neil, Hi Daniel. Thank you for your help, using parsec 3.0.0 and liftIO was the solution. After installing new parsec I have had to use import Text.Parsec ... instead of ... import Text.ParserCombinators.Parsec ... to get it work. It seems Text.ParserCombinators.Parsec refers to old Parsec 2 Have a nice week--end, Leonard

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Compiling to C
by Greg Santucci 19 Jun '09

19 Jun '09

Hi all, I'd like to call Haskell functions from C and receive its output as a string. Is compiling a Haskell program to C using ghc -C HaskellSource.hs the preferred method of doing this? Regards, Greg

1 1

About the Monad Transformers
by .shawn 19 Jun '09

19 Jun '09

On page 141 of "Yet another Haskell Tutorial" (9.7 Monad Transformers) mapTreeM action (Leaf a) = do lift (putStrLn ("Leaf" ++ show a)) b <- action a return (Leaf b) mapTreeM :: (MonadTrans t, Monad (t IO), Show a) => (a -> t IO a1) -> Tree a -> t IO (Tree a1) Why does the type signature of mapTreeM look like this? And what does it mean by "The lift tell us that we're going to be executing a command in an enclosed monad. In this case the enclosed monad is IO"? Why does the author put lift here? How does the lift work? I have no idea about the explanation in the book...is there anyone can give me some hints about this? Thank you in advance! _________________________________________________________________ Messenger10年嘉年华，礼品大奖等你拿！ http://10.msn.com.cn

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Fwd: [Haskell-cafe] Re: curious about sum
by Alberto G. Corona 19 Jun '09

19 Jun '09

However it does not work as I expected. I ´m interested in memory management. I though that ghci> let l= [1..1000000] ghci> foldl' (+) 0 l would produce a stack overflow, since the list can not be freed, because l points to the beginning of the list however it succeed My conclussion is that, in the case of sum, with the lazy evaluation, isn´t the list what is the cause of the stack overflow, but the lazy structure 0 + 1 +2 + 3 +4.... created by foldl before the final evaluation I tried to test how I can force a stack overflow, in the strict case. Since foldl' is strict, the only way is to create a long long initial list. ghci> let l= [1..100000000] -- 100 times larger, two 0's added ghci> foldl' (+) 0 l as in the previous case, l will not garbage collect, and foldl' must build the real list [1,2,3,4..] . at the end perhaps a stack overflow willl be produced This is not the case in my windows system.ghc 6.10.1. instead of that, ghci grow to gigabyte size and more. I stopped the process or my machine would be irresponsive. My question is: Why the process does not grow also in the lazy case and instead produces a stack overflow inmediately? Yes I know that all of this is bizantine since strictness analysis would solve this when compiled, but I think that there are somethig that i don´t understand. It´s a bug perhaps??? 2009/6/18 Edward Kmett <ekmett(a)gmail.com> > On Thu, Jun 18, 2009 at 9:14 AM, Gleb Alexeyev <gleb.alexeev(a)gmail.com>wrote: > >> Thomas Davie wrote: >> >>> No, I think it's extremely useful. It highlights that numbers can both >>> be lazy and strict, and that the so called "useless" lazy sum, is in fact, >>> useful. >>> >>> But lazy sum should have beed defined in terms of foldr, not foldl. And >> foldl is not strict enough for strict sum. Therefore the current choice in >> the worst of both worlds. >> > > > I definitely agree with that sentiment. > > -Edward Kmett > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

2 2

how to #include files within parsec ... without unsafePerformIO?
by Leonard Siebeneicher 18 Jun '09

18 Jun '09

Dear reader, I wonder whether there is a 'general' working solution to include files within a parsec parser. Without the need of unsafePerformIO. Appending an example program, using unsafePerformIO. Thanx for reading. Greetings, Leonard Siebeneicher --- Begin: experiment.hs --- import Text.ParserCombinators.Parsec import System.IO.Unsafe my_str :: Parser String my_str = many1 anyToken wrap_input :: Parser String -> Parser String wrap_input p = do i <- getInput setInput readI a <- my_str setInput i b <- my_str return $ a ++ " //\n\n " ++ b where {- Aaaah ... any solution without unsafePerformIO? -} readI = unsafePerformIO (readFile "experiment.hs") main = case parse (wrap_input my_str) "" "eintest" of Left err -> putStrLn "Error raised" Right ostr -> putStrLn ostr --- End: experiment.hs --- ___ Thinking about a special type like data MyInclude = PlainText String | IncludeFile String the parser could generate [MyInclude] data, but it does not work generally.

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curious about sum
by Keith Sheppard 18 Jun '09

18 Jun '09

Is there any reason that sum isn't strict? I can't think of any case where that is a good thing. Prelude> sum [0 .. 1000000] *** Exception: stack overflow -Keith -- keithsheppard.name

19 37

Unicode workaround for getDirectoryContents under Windows?
by Shu-yu Guo 18 Jun '09

18 Jun '09

Hello all, It seems like getDirectoryContents applies codepage conversion based on the default program locale under Windows. What this means is that if my default codepage is some kind of Latin, Asian glyphs get returned as '?' in the filename. By '?' I don't mean that the font is lacking the glyph and rendering it as '?', but I mean 'show (head (getDirectoryContents "C:\\Music"))' returns something that looks like like "?? ????". This is a problem as I can't get the filenames of my music directory, some of which are in Japanese and Chinese, some of which have accents. If I change the default codepage to Japanese, say, then I get the Japanese filenames in Shift-JIS and I lose all the accented letters. I have filed this as a bug already, but is there a workaround in the meantime (I don't know the Win32 API, but didn't see anything that looked like it would help under System.Win32 anyways) that lets me gets the list of files in a directory that's encoded in some kind of Unicode? Cheers, -- shu

7 30

Profiling/cost centre question
by Sebastian Reese 18 Jun '09

18 Jun '09

Hi there, I mailed to this list in May (http://www.haskell.org/pipermail/haskell-cafe/2009-May/062126.html) with no answer at all. So I wrote a smaller program to demonstrate my problem/question. Maybe now someone can help me now. I wrote a small program that does nothing but listening on a TCP port. After connection is done it simply terminates. #> cat Test.hs module Main where import Network main :: IO () main = (do servSock <- {-# SCC "cc1" #-}listenOn . PortNumber $ 10000 (handle, host, port) <- {-# SCC "cc2" #-}accept servSock return () )`catch` (putStrLn . show) #> I compile, run (connection from elsewhere, so program terminates) and watch the .prof output #> ghc --make -threaded -O2 -prof -caf-all -auto-all Test.hs Linking Test ... #> ./Test +RTS -p #> cat Test.prof Thu Jun 18 12:24 2009 Time and Allocation Profiling Report (Final) Test +RTS -p -RTS total time = 0.32 secs (16 ticks @ 20 ms) total alloc = 32,384 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc MAIN MAIN 100.0 7.8 CAF GHC.Conc 0.0 4.0 CAF GHC.Handle 0.0 26.8 cc1 Main 0.0 3.8 cc2 Main 0.0 55.8 ... snip ... #> My actual question is, where does the 100% individual time from MAIN come from, how can I debug that in other programs and where does this MAIN cost centre come from? thanks for your help Sebastian ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

1 0

ANNOUNCE: hyena
by Johan Tibell 18 Jun '09

18 Jun '09

I am pleased to announce the first release of hyena, a library for building web servers, based on the work on iteratee style I/O by Oleg Kiselyov. The library allows you to create web servers that consume their input incrementally, without resorting to lazy I/O. This should lead to more predictable resource usage. This is an early alpha release so expect the API to change in the future. In particular, I'm working on converting the current definition of iteratees/enumerators used to the one in the iteratee package [1]. I decided to release this version, based on a simple left fold, due to requests by several people who already started using hyena. Get it: cabal install hyena And on Hackage: http://hackage.haskell.org//package/hyena 1. http://hackage.haskell.org/package/iteratee -- Johan

2 1

Haskell on Android
by Vasili I. Galchin 18 Jun '09

18 Jun '09

Hello, Let me change the subject ... I think everybody understood my "thrust" but let me make more provocative. Don, please let me expose my ignorance for the greater good and time my personal scorn ;^) ... "EDSL" time => Embedded Domain-Specific Language?? If so, can you please be more specific! I don't mind to be a grunt for Haskell. Kind regards, Vasili

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