September 2008 - Haskell

Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 07 Apr '11

07 Apr '11

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

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Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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ANNOUNCE: cabal-install 0.5
by Duncan Coutts 05 Dec '08

05 Dec '08

cabal-install 0.5 ================= cabal-install version 0.5 is out: http://haskell.org/cabal/download.html or get it from hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install If you are already using a cabal-install pre-release then you can just: $ cabal update $ cabal install cabal-install New features in cabal-install ============================= Command line improvements ------------------------- The most immediately noticeable thing is that the command line interface now has all the commands that runhaskell Setup.hs has. Of course it still has the features to download and install packages from hackage. It also gained an upload command. So it now provides a command line interface to the whole Cabal/Hackage system. There’s no need to use runhaskell Setup.hs ever again. There is also bash command line completion support included which I find is a great time saver. Installing and upgrading ------------------------ The next big thing is that it includes a new package dependency resolution system that finds correct and sensible solutions more of the time and has better default behaviour. The new behaviour should be similar to other package managers that people are used to. For example, suppose you’ve got xmonad-0.5 installed and version 0.7 is the latest on hackage, then $ cabal install xmonad will install xmonad-0.7. The older version, xmonad-0.5, will remain installed. The behaviour of install is to upgrade as little as possible to satisfy your request, but sometimes you want to upgrade all the dependencies too. Supposing now that we have xmonad-0.7 installed, but we’re still using X11-1.4.1 and the latest version on hackage is X11-1.4.2, then $ cabal upgrade xmonad will install X11-1.4.2 and *re-install* xmonad-0.7, this time built against the newer X11-1.4.2. So in general, the install command will install the latest version of things but will try and use any existing installed versions of dependencies while the upgrade command will also try to use the latest versions of all dependencies. As a special case, cabal upgrade on its own will try to upgrade all the packages that you have installed. For both command there is a --dry-run flag so you can see what would be installed without actually doing it. Hugs ---- Yes, it even works with hugs. That is, cabal-install built by ghc can manage the installation of packages for hugs. In principle cabal-install should be able to be run by hugs but currently the zlib binding is using a function that hugs does not support. Note that for hugs, Cabal does not know what packages are already installed because there is no equivalent of the package database that ghc has. So that means cabal-install cannot do very sensible installation planning. It should work ok so long as all the dependencies are already installed. Windows ------- Yes, it even works on Windows. The one caveat is that cabal-install cannot currently upgrade itself because Windows makes it hard for a process to overwrite its own executable file. It needs more complex trickery with the Win32 API. In the meantime the workaround is to rename the cabal.exe file first eg to cabal-foo.exe, then run cabal-foo install cabal-install. Build reporting --------------- One feature that made it into this release is build reporting. cabal-install keeps logs of all packages that you install (at least packages from hackage, not local ones). It records a bit of information about each package, in particular whether the outcome was successful or not. You can see these build reports in ~/.cabal/packages/$server/build-reports.log. For example, there is one from my machine for xmonad: package: xmonad-0.7 os: linux arch: x86_64 compiler: ghc-6.8.2 client: cabal-install-0.5.1 flags: -testing small_base dependencies: X11-1.4.2 base-3.0.1.0 containers-0.1.0.1 directory-1.0.0.0 mtl-1.1.0.0 process-1.0.0.0 unix-2.3.0.0 install-outcome: InstallOk docs-outcome: NotTried tests-outcome: NotTried The plan in the longer term is to let people upload these build reports to hackage so we can get a wider range of testing data about the packages on hackage. Duncan

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The real Monad Transformer
by Henning Thielemann 13 Nov '08

13 Nov '08

It was argued that people avoid Haskell because of terms from Category theory like 'Monad'. This problem can now be solved by a wrapper which presents all the WWW without monads! Start e.g. at http://saxophone.jpberlin.de/MonadTransformer?source=http%3A%2F%2Fwww%2Ehas… Of course the tool is written in Haskell, that is, Haskell helps solving problems which only exist because of Haskell. Bug reports and feature requests can be tracked at https://sourceforge.net/projects/parallelweb

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ANNOUNCE: Graphalyze-0.1
by Ivan Miljenovic 29 Sep '08

29 Sep '08

I'd like to announce the initial release of my graph-theoretic analysis library, Graphalyze [1], the darcs repo for which is also available [2]. This is a pre-release of the library that I'm writing for my mathematics honours thesis, "Graph-Theoretic Analysis of the Relationships in Discrete Data". I'll also be releasing a tool that uses this library to analyse the structure of Haskell code, that I'm tentatively calling SourceGraph. As it stands, the library has a number of algorithms included, some of which I've developed from scratch (e.g. clique finder), and others are implementations of published algorithms (mainly the two clustering algorithms). The code is meant to be more readable than efficient, and I wanted to explore ways of developing algorithms that match more closely the way graphs work (which makes FGL a much nicer fit than matrix-based or list-based graph data structures). This library is only a pre-release, as whilst everything in there works (at least it does for me), I'd like to get some feedback from the community, especially since this is my first ever released solo piece of code (I've coded assignments, and worked on projects with others, but have never released anything that I've been solely responsible for before). In particular, have I written the .cabal file correctly? Also, I'd like advice on something else: the part of the library that I'd like to develop still is the reporting framework. The end goal of the library is for the user to specify which algorithms they want applied to their data, and then the library produces a document with the results. This document is _not_ meant to be machine readable. As such, I can think of three options: 1) Plain text, with graphs either in seperate image files (using graphviz) or else as plaintext (FGL's show function). 2) Generate LaTeX code. 3) Generate Pandoc [3] compatible Markdown, and let the user convert it into whatever format they prefer. I'm not a big fan of option 1), as it is probably the most unreadable in general. I'd like to use Pandoc, as it is theoretically possible to convert it to numerous other filetypes, however with inline linking there's still no way (at least I can find) to have images scaled to the correct size automatically. So unless I pre-scale the images, using option 3) and then converting to PDF via LaTex generation of the Markdown sources is probably out. As such, what would you all prefer to read as a documentation-style report of your software? 1) A PDF via LaTeX, which has the advantage of being printable and all in one file 2) HTML via Pandoc, which lets you have the images linked separately from the document, and thus no need to shrink them down (they can stay at the natively generated size, and thus easier to zoom in, etc.). Finally, I'll be giving my honours talk on this next Monday. So if you're in Brisbane on 6 October and interested, it'll be on at 2PM at the University of Queensland (where as part of it I'll be explaining to mathematicians why Haskell is a great language to use for mathematics... or at least trying to!). [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Graphalyze [2] http://code.haskell.org/Graphalyze/ [3] http://johnmacfarlane.net/pandoc -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Symposium videos
by Malcolm Wallace 27 Sep '08

27 Sep '08

Guerilla videos of the Haskell Symposium 2008 presentations. Enjoy. Regards, Malcolm

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ICFP programming contest results
by Malcolm Wallace 24 Sep '08

24 Sep '08

The ICFP programming contest results presentation: http://video.google.com/videoplay?docid=-4697764813432201693 Feel free to pass on this link to any other appropriate forum. Regards, Malcolm

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ANNOUNCE: graphviz-2008.9.20
by Ivan Miljenovic 21 Sep '08

21 Sep '08

The latest version of Matthew Sackman's Haskell bindings to Graphviz [1] are now available on Hackage [2]. The reason there's a new release only two weeks after the previous one is that I've made some extensions to it (hence why I'm writing the announcement) that Matthew has kindly included. Since Matthew doesn't recall writing an announcement for graphviz before, here is a brief synopsis of what it does. The Graphviz program is probably _the_ way of drawing graphs (note: this is graph-theory graphs, not function plotting). As it stands, there are currently at least four different Haskell bindings available for Graphviz that I've managed: * The inbuilt Graphviz module in FGL [3] * graphviz (which this announcement is for) * dotgen [4] * A really simple generator by Duncan Coutts [5] In addition to this, the following utilities on Hackage output graphs in Graphviz's .dot format (either using one of the above libraries or their own parser): * prof2dot : converts profiling information to .dot [custom, I think] [6] * flow2Dot : convert textual descriptions to .dot [also custom, I think] [7] * graphmod : draw the dependencies between Haskell modules [uses dotgen] [8] As it can be seen, there's a plethora of possible ways of creating .dot graphs in Haskell. What seperates the graphviz package from the others is: * It uses FGL graphs, rather than passing through lists of nodes and edges manually (of course, if you're not doing any other graph-related activity you might not want to use an FGL graph), whilst providing more control than the default FGL module. * A large list of attributes that can be used are available: http://hackage.haskell.org/packages/archive/graphviz/2008.9.20/doc/html/Dat… * A "sane" interface that provides a large degree of customizability (don't specify the attributes manually for each node/edge/etc., just pass through a function that will create the attribute you want). * Limited parsing of .dot format (note that as yet it can't convert a parsed DotGraph into an FGL graph). * The graphToGraph function allows you to pass a graph through Graphviz and then extract out positional information and combine it with the original graph. There are some things things that graphviz can't do, such as drawing undirected graphs and clusters (which dotgen can)... at least until now. The changes that I have made provide the additional functionality to graphviz: * Differentiate between undirected and directed graphs. Whilst FGL represents undirected graphs with a directed graph by duplicating all edges (an undirected edge {1,2} is represented by the two edges (1,2) and (2,1)), you don't really want to draw a graph this way. Furthermore, many reports say that graphviz's "neato" command is better at drawing undirected graphs than the normal "dot" command is. Thus, graphviz will now draw only one edge out of every directed pair. To do so, however, requires that the edge labels are an instance of Ord: if this is a problem for you, please contact either Matthew or myself and we'll see what else we can do (this is required because it's assumed that if two edges (1,2) and (2,1) are meant to represent the undirected edge {1,2}, then their labels must be the same). * Add clustering support. Graphs can be drawn (but as yet not parsed) to provide nested clustering support to arbitrary depth. To do so, you need to provide a function (LNode a -> NodeCluster c a), where NodeCluster is the following recursive data type that indicates in which subcluster a node in the graph belongs: data NodeCluster c a = N (LNode a) | C c (NodeCluster c a) The c type represents the cluster label, and is the parameter by which cluster attributes are assigned. Note that c has to be an instance of Ord. Clusters are not parseable, because there's no clear way of how to convert a cluster to an FGL graph. The interface for graphviz remains unchanged, so you can safely upgrade to this version. Here is an example function of how the library can be used to draw an FGL graph to a (very plain) Graphviz graph (well, it will convert it to the DotGraph datatype, which when shown produces the .dot graph code): graphviz :: (Graph g, Show a, Ord b, Show b) => String -> g a b -> DotGraph graphviz title g = graphToDot g attrs nattrs eattrs where attrs = [Label title] nattrs (_,a) = [Label (show a)] eattrs (_,_,b) = [Label (show b)] Enjoy! [1] http://graphviz.org/ [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphviz [3] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fgl [4] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dotgen [5] http://haskell.org/~duncan/WriteDotGraph.hs [6] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/prof2dot [7] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/flow2dot [8] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/graphmod -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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OpenSPARC project applicant chosen
by Duncan Coutts 20 Sep '08

20 Sep '08

I am very pleased to announce that we have chosen Ben Lippmeier for the OpenSPARC project. Congratulations Ben! Ben will spend three months hacking on GHC to make it perform well on the latest multi-core OpenSPARC chips. I would also like to thank the other people who applied. The reviewers were very impressed by the number of strong applications. About the project ----------------- http://haskell.org/opensparc/ It is a joint project between Sun Microsystems and the Haskell.org community. Sun has provided the funding for Ben to work on this full time for three months and has donated a powerful SPARC server for him and the rest of us to use. Ben will be working with Roman Leshchinskiy as a mentor and Darryl Gove as an adviser. Roman works on Data Parallel Haskell at UNSW and Darryl is a senior staff engineer in the SPARC compiler team at Sun. If you want to follow the progress we will be using the existing ghc development mailing list: http://www.haskell.org/mailman/listinfo/cvs-ghc and a corner of the ghc development wiki: http://hackage.haskell.org/trac/ghc/wiki/OpenSPARC Duncan (project coordinator)

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Haskell Weekly News: Issue 86 - September 20, 2008
by Brent Yorgey 20 Sep '08

20 Sep '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080920 Issue 86 - September 20, 2008 --------------------------------------------------------------------------- Welcome to issue 86 of HWN, a newsletter covering developments in the [1]Haskell community. Lots of NEW stuff this week! A new generics library, new versions of Pandoc and darcs, a new website for xmonad, a new GADT/type family inference engine for GHC, a Haskell binding for Qt, and some new, astonishingly elegant ideas from Oleg. Also, here's hoping that everyone has a lot of fun at ICFP! Announcements GHC version control. Simon Peyton-Jones [2]sent out a revised proposal for GHC version control. darcs 2.0.3pre1. Eric Kow [3]announced the first pre-release of [4]darcs 2.0.3, featuring a few major bug fixes and a handful of interesting features. EMGM. Sean Leather [5]announced a release of [6]Extensible and Modular Generics for the Masses (EMGM), a library for generic programming in Haskell using type classes. Pandoc 1.0.0.1. John MacFarlane [7]announced the release of [8]pandoc 1.0.0.1, the swiss army knife of text markup formats. Iteratee-based IO. oleg [9]described a [10]safe, declarative approach to input processing which will be the subject of a talk at DEFUN08 on September 27. MetaHDBC paper. Mads Lindstroem [11]announced a [12]draft version of a paper about the [13]MetaHDBC library, which uses Template Haskell to do type-safe database access. Comments are welcomed, especially about the overall quality of the paper, whether it can be called scientific, and anything Mads could do to improve the paper. qtHaskell 1.1.2. David Harley [14]announced a second preview release of [15]qtHaskell, a set of Haskell bindings for Trolltech's Qt. Discussion Library design question. Andre Nathan [16]asked for advice on designing a simple graph library. The resulting discussion included an analysis of using the State monad versus a more functional approach. A round of golf. Creighton Hogg [17]learns about laziness by [18]making grown men cry. XML (HXML) parsing :: GHC 6.8.3 space leak from 2000. Lev Walkin [19]discovers a nice example of an obscure class of space leaks while writing some XML-processing code, prompting an in-depth analysis by Simon Marlow. Proofs and commercial code. Daryoush Mehrtash [20]asked about automated proof tools and techniques, and their uses in the real world. Blog noise [21]Haskell news from the [22]blogosphere. * Creighton Hogg: [23]Haskell Cafe or: How I learned to stop worrying & love laziness. * Douglas M. Auclair (geophf): [24]Animal as RDR, part II. Doug continues his posts on RDR expert systems. * Ivan Lazar Miljenovic: [25]Getting Real World Haskell Down Under. * Douglas M. Auclair (geophf): [26]Animal: an RDR implementation study. Doug describes "ripple-down rules" expert systems, and illustrates the types needed to encode one in Haskell. * Mark Jason Dominus: [27]data Mu f = In (f (Mu f)). Mark writes about fixpoints of type constructors. * John Goerzen (CosmicRay): [28]Switched from KDE to xmonad. John has taken the plunge to xmonad and seems to like it so far! * Eric Kow (kowey): [29]darcs weekly news #4. Pre-release of darcs 2.0.3; darcs hacking sprint next month; code.haskell.org upgrades to darcs 2; and other news. * Mads Lindstroem: [30]MetaHDBC paper (draft). Mads's first paper ever, on using Template Haskell for type-safe database access. Comments welcome! * Braden Shepherdson: [31]xmonad-light 0.8 Released. * Manuel M T Chakravarty: [32]GHC HEAD just got a new inference engine for GADTs and type families.. * Magnus Therning: [33]Haskell and Time. Magnus describes the solution to a problem with Data.Time. * Dan Piponi (sigfpe): [34]Two Papers and a Presentation. * Xmonad: [35]New xmonad website launched. xmonad has a shiny new website! Quotes of the Week * Botje: GHC 11 will have shootout entries as primitives. * wjt: oh, i see what you're doing. ...no, i don't. *splode* * Benjamin Pierce: [on existential types] I have a term, and it has a type. So there. * bos: come on, real programmers use "(((,) <$>) .) . (<*>)" * quicksilver: #haskell : Sometimes we answer your question, sometimes we lay hideous traps which will devour your soul. It's a risk you take. * harrison: [on computing 1000000!] it is the same as factorial 999999 * 1000000, big deal About the Haskell Weekly News New editions are posted to [36]the Haskell mailing list as well as to [37]the Haskell Sequence and [38]Planet Haskell. [39]RSS is also available, and headlines appear on [40]haskell.org. To help create new editions of this newsletter, please see the information on [41]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [42]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/libraries/2008-September/010661.html 3. http://www.haskell.org//pipermail/haskell-cafe/2008-September/047664.html 4. http://www.darcs.net/darcs-2.0.3pre1.tar.gz 5. http://www.haskell.org//pipermail/haskell-cafe/2008-September/047751.html 6. http://www.cs.uu.nl/wiki/GenericProgramming/EMGM 7. http://www.haskell.org//pipermail/haskell-cafe/2008-September/047437.html 8. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/pandoc 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44828 10. http://okmij.org/ftp/Haskell/Iteratee/ 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/44713 12. http://lindstroem.files.wordpress.com/2008/09/metahdbc.pdf 13. http://www.haskell.org/haskellwiki/MetaHDBC 14. http://article.gmane.org/gmane.comp.lang.haskell.general/16425 15. http://qthaskell.berlios.de/ 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/44733 17. http://abstractabsurd.blogspot.com/2008/09/haskell-cafe-or-how-i-learned-to… 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/44724 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/44708 20. http://www.haskell.org//pipermail/haskell-cafe/2008-September/047440.html 21. http://planet.haskell.org/ 22. http://haskell.org/haskellwiki/Blog_articles 23. http://abstractabsurd.blogspot.com/2008/09/haskell-cafe-or-how-i-learned-to… 24. http://logicaltypes.blogspot.com/2008/09/animal-as-rdr-part-ii.html 25. http://ivanmiljenovic.wordpress.com/2008/09/19/getting-real-world-haskell-d… 26. http://logicaltypes.blogspot.com/2008/09/animal-rdr-implementation-study.ht… 27. http://blog.plover.com/prog/springschool95-2.html 28. http://changelog.complete.org/posts/756-Switched-from-KDE-to-xmonad.html 29. http://koweycode.blogspot.com/2008/09/darcs-weekly-news-4.html 30. http://lindstroem.wordpress.com/2008/09/18/metahdbc-paper-draft/ 31. http://braincrater.wordpress.com/2008/09/17/xmonad-light-08-released/ 32. http://justtesting.org/post/50500880 33. http://therning.org/magnus/archives/389 34. http://sigfpe.blogspot.com/2008/09/two-papers-and-presentation.html 35. http://xmonad.wordpress.com/2008/09/14/new-xmonad-website-launched/ 36. http://www.haskell.org/mailman/listinfo/haskell 37. http://sequence.complete.org/ 38. http://planet.haskell.org/ 39. http://sequence.complete.org/node/feed 40. http://haskell.org/ 41. http://haskell.org/haskellwiki/HWN 42. http://code.haskell.org/~byorgey/code/hwn/

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