July 2009 - Haskell-Cafe

Monoid wants a (++) equivalent
by Bryan O'Sullivan 06 Jul '09

06 Jul '09

I've thought for a while that it would be very nice indeed if the Monoid class had a more concise operator for infix appending than "a `mappend` b". I wonder if other people are of a similar opinion, and if so, whether this is worth submitting a libraries@ proposal over.

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Documentation design
by Isaac Dupree 06 Jul '09

06 Jul '09

(for reference, here's the blog-post I wrote that inspired me to ask this list for advice. I'll explain everything in this email anyway though. http://haddock2009.wordpress.com/2009/06/23/how-to-navigate-your-code/ ) My challenge: getting to know an existing code-base quickly and easily, so that I can hack on it. Haddock and HsColour are already pretty helpful at this, but they could be more helpful. (haddock with --ignore-all-exports, i.e. cabal haddock --internal, especially) My dream situation: both haddock-pages and hscolour-pages would be super-hyperlinked and super-readable. For example, haddock would list all a module's definitions, not just its exports. In HsColoured source, every identifier would link to its definition or the haddockumentation of its definition. and so forth. It would be so much easier to generate and browse this in HTML, than to get an IDE working, and it would be so much more readable than a mere text-editor (even with syntax hilighting) and quicker clicking on hyperlinks than grepping for everything. Actually I don't have the resources to worry about designing any HsColour stuff right now (its current design is mainly just a lexeme highlighter). But, with your advices, I can design an improvement on Haddock's ignore-exports mode, which currently has a few shortcomings: 1. you can't tell which identifiers in a module are exported 2. it doesn't document a module's re-exports at all 3. it still obeys {-# OPTIONS_HADDOCK hide #-} et al, even when they're not appropriate for reading documentation of internals 4. 2+3 means that some things may be found nowhere in the documentation at all! Not quite satisfying for something invoked by `cabal haddock --internal`. (Here's a haddock-generated page you can look at so you can figure out the formatting-details I'll be describing: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html and its source code http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/Data-List.ht… ) The ideal haddockumentation-formatting for this purpose isn't quite obvious though. For example, sometimes you want to think about a module in terms of its abstract interface, but sometimes you want to figure out how it's implemented (without reverting completely to text based code browsing). Maybe a compromise of some sort would be good. so... Here's a proposal, for a new mode (`haddock --all-internal`?, to be invoked by `cabal haddock --internal` rather than --internal's current effect of ignore-all-exports) : Files with no explicit export list can be treated as-is anyway. For all files that have an explicit export list, generate the synopsis-of-exports near the top, as usual. But have the index link, generally, to where functions are originally defined (modulo being from a non-internally-documented separate package, where it should link to the appropriate place), and have the fuller documentation below be a compilation of the identifiers *defined* in this module. Actually that would need some revision because the sections and subsections -- *, -- **, etc. defined in the export-list in the .hs, actually are displayed 1. above the table of contents, linking to places in 2. the full list of definitions. Which might be defined in the module in a different order than they're listed in the export list. Why not add the sections into the synopsis? In this case, instead of adding them to the main doc section. But hmm... in ordinary non-internal documentation, would it be nice to *additionally* have the sections marked in the synopsis (in addition to in the Contents and in the main docs section)? Maybe this mode should also abstain from "hiding" any module, because that would cause missing docs. Etc. Questions? Comments? Opinions? Does anyone want this feature, and/or not think it's particularly useful? -Isaac

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How to pretty print code efficiently
by John Ky 05 Jul '09

05 Jul '09

Hi, Currently I'm pretty printing code by building arrays of strings and calling indent. For example: instance JavaPrintableNamed AST.EnumeratedType where javaLinesNamed parentName (AST.EnumeratedType memberDefinitions) = [ "public enum " ++ asJavaId(parentName) , "{" ] ++ memberCodeLines ++ [ "}" , "" ] where memberCodeLines = indent $ javaLines memberDefinitions The indent function takes a list of strings and adds an indent to the beginning of every line. I can imagine this to be very inefficient as it builds many strings and concatenates them. In Ruby, I might do the same thing like this: class EnumeratedType < JavaPrintableNamed def writeTo(writer) writer.print "public enum " writer.puts self.asJavaId writer.puts "{" writer.indent do self.memberDefinitions.writeTo(writer) writer.puts end where above, the writer.indent takes care of the indent, and everything is appended to a stream, which doesn't seem so bad in terms of efficiency. I'm looking for a way to do something similar in Haskell. Anyone can give me a hand? Thanks -John

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Read & Show instance generation for GADTs?
by Conal Elliott 05 Jul '09

05 Jul '09

Are there any tools for generating Show & Read instances for GADTs? - Conal

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ANN: AC-Vector, AC-Colour and AC-EasyRaster-GTK
by Andrew Coppin 04 Jul '09

04 Jul '09

OK, so having released AC-HalfInteger, I got slightly carried away and released three other small packages. These are packages that many programs I write all end up using. I'm forever copying these files, so I made them into actual bonafide packages. http://hackage.haskell.org/package/AC-Vector-1.1.1 This provides two types, Vector2 and Vector3, which are unboxed vectors of Doubles, with arithmetic, dot product and cross product, and a few other useful items. http://hackage.haskell.org/package/AC-Colour-1.1.1 This provides two types, Colour and Colour8. Both implement simple RGB colour types with arithmetic. Colour has unboxed Double fields, and Colour8 has unboxed Word8 fields. My usual workflow is to do all the image generation with Colour, and to convert to Colour8 just before the data hits the I/O channels. You can, however, do arithmetic directly on Colour8. (I haven't extensively tested that it works properly though...) http://hackage.haskell.org/package/AC-EasyRaster-GTK-1.1.1 This is a layer over Gtk2hs. As you all probably know, Gtk2hs provides a Cairo binding that makes vector graphics wonderfully easy. However, *bitmapped* graphics is darned tricky. I basically had to sit in the #haskell channel with Duncan for a few hours trying to figure out how the hell to do it. This knowledge is now codified in the above package. Load it up and you don't need to know a thing about GTK; you can just create an ImageBuffer, write some pixels to it (efficiently!), save it to disk or display it on screen. (But you *can* access the underlying GTK+ resources if you wish...) In other news, it appears that the batch job to generate the documentation just ran, so you can view it all online. :-D Comments, suggestions, random flames, etc... [I'm particularly curios to know what Duncan will make of the GTK thing...]

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Re: [Haskell-cafe] ANN: AC-Vector, AC-Colour and AC-EasyRaster-GTK
by Andrew Coppin 04 Jul '09

04 Jul '09

Paul Johnson wrote: > Andrew Coppin wrote: >> Well, no, because now I'm going to have to spend a few hours trying >> to find out what CIE is before I can even use that library. >> >> I think really it's just aimed at a different problem. It looks like >> it's trying to specify actual real-world colours. [It's news to me >> that this isn't fundamentally impossible...] I'm only trying to >> specify colours on a computer screen. And as we all know, computer >> screens aren't calibrated in any way, and the same RGB value looks >> different on each display. But then, I'm only trying to write a >> fractal generator, so CIE specifications are somewhat overkill here. ;-) > Your display may not be calibrated, but those used for graphic design > certainly are. Indeed. And if you're in any kind of position where you *care* about such things, you should be using color, not AC-Colour. If, however, you just want to throw together pretty pictures, AC-Colour is simpler and easier. Different libraries for slightly different tasks. ;-) > On the package naming front: I appreciate your wish to avoid just > having another "colour" library. But "AC_Colour" doesn't help much. > "Simple_colour" might be better. Mmm, yeah. Naming everything with "AC" precludes name clashes and doesn't require too much thinking. Coming up with a better name requires thinking about what actually makes your package unique. And, of course, if another package comes along, that analysis may change. (E.g., I seem to recall there's a "newbinary" package which has actually been long since superceeded - so not so "new" any more!) If I name my package simple-colour, and then somebody else makes an even simpler one... the name becomes kind of meaningless. (Admitedly there's not too much danger of this happening...) I just like the idea of having definitely unique, distinctive package names. Otherwise I'd have to come up with stuff like geovector and trivicolour and so on... Arguably EasyRaster-GTK should have been a sufficiently unique name by itself though.

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Re: [Haskell-cafe] ANN: HalfInteger-1.1.1
by Andrew Coppin 04 Jul '09

04 Jul '09

Alexander Dunlap wrote: > Couple of suggestions: > > - You should put an (Integer i) => constraint on the halve function so > that it becomes impossible to create invalid HalfIntegers. > Right. Currently you can *make* such a HalfInteger. You just won't be able to *do* anything with it afterwards. It would probably be more sensible to just add a constraint there. > - The documentation for toHalfInteger is truncated. Also, why can't > you make the rounding more predictable? > ...wow. OK, I'm looking at the source, and it seems I must have got distracted at that moment or something, because I just 100% didn't actually finish writing the documentation! o_O That's pretty special. ;-) As I *should* have written, the rounding for something like toHalfInteger 0.25 is kind of unpredictable; but if you do toHalfInteger 0.5, the result is *guaranteed* to be exact. All the functions are carefully tuned to work correctly on things which really are half integers, and to give plausible results otherwise. Just don't let your life depend on 0.25 being mapped to exactly a half or to exactly zero... > Nice work! > Heh, thanks.

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Flow Graphs for Language-independent Code Representation
by Cetin Sert 04 Jul '09

04 Jul '09

Hi *^o^*, I'm working on a source code transformation project for numerical automatic differentiation for Fortran and C. I would love to know the best Haskell way/package available today to represent procedural (non-OO) code in a language-independent manner. Any tips or resource, paper references are most welcome! Regards, Cetin Sert

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Small Haddock question
by Andrew Coppin 04 Jul '09

04 Jul '09

This is irritating me now... Suppose I have something like the following: zero = 0 :: Int one = 1 :: Int two = 2 :: Int three = 3 :: Int How do I add Haddock comments to the end of each line? For some reason, Haddock doesn't like either of zero = 0 :: Int -- | Zero zero = 0 :: Int -- ^ Zero Either way it whinges about parse errors. How do I make it shut up and stop being so dense at me? :-} It's damned obvious what I want it to do...

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Haskell Weekly News: Issue 124 - July 4, 2009
by Brent Yorgey 04 Jul '09

04 Jul '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090704 Issue 124 - July 04, 2009 --------------------------------------------------------------------------- Welcome to issue 124 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements HLint 1.6. Neil Mitchell [2]announced the release of [3]HLint 1.6, a tool for automatically suggesting improvements to Haskell code. Haskell Implementers Workshop: accepted talks. Simon Marlow [4]announced that the list of talks at the [5]Haskell Implementers Workshop 2009 has now been posted. bloxorz clone. Patai Gergely [6]announced a [7]Haskell clone of the game "bloxorz", written by Viktor Devecseri. Fun with type functions. Simon Peyton-Jones [8]announced that he, Ken Shan, and Oleg have finished Version 2 of their [9]paper "Fun with Type Functions", which gives a programmer's tour of what type functions are and how they are useful. If you have a moment to look at, and wanted to help them improve it, leave comments on the linked wiki page. package Boolean: Generalized booleans. Conal Elliott [10]announced [11]Boolean, a new package for generalized booleans, which provides type classes with generalizations of Boolean values and operations, if-then-else, Eq and Ord. TernaryTrees-0.1.1.1 - An efficient ternary tree implementation of Sets and Maps. Alex Mason [12]announced the release of [13]TernaryTrees, a package that extends Data.Set ad Data.Map with some ternary tree structures, one of the more efficient ways of storing strings in a set. 6.12.1 planning. Simon Marlow [14]announced plans for a release of GHC 6.12.1, sometime around September. If you have the time and inclination to help with any of the listed features, please get involved! regular-0.1. José Pedro Magalhães [15]announced the release of the [16]regular library. Many generic programs require information about the recursive positions of a data type, such as generic fold, generic rewriting, and the Zipper data structure. Regular provides a fixed point view on data which allows these definitions for regular data types. It also serves as the basis for a [17]generic rewriting library. Google Summer of Code Progress updates from participants in the 2008 [18]Google Summer of Code. Haddock improvements. Isaac Dupree has made it easier to generate Haddock documentation [19]for non-exported functions, posted an [20]overview of the issues involved in getting proper cross-package documentation working, and his current [21]plan. EclipseFP. Thomas Ten Cate has done a lot of work on EclipseFP, including some [22]cosmetic updates and getting [23]error reporting to work better. space profiling. Gergely Patai is [24]working on a network protocol for his profiling grapher tool, so that other tools can monitor the profiling information. haskell-src-exts. Niklas Broberg has [25]released [26]haskell-src-exts version 1.0.0! fast darcs. Petr Rockai has completed [27]quite a bit of work on darcs, including a [28]beta release of darcs 2.3. Discussion Monoid wants a (++) equivalent. Bryan O'Sullivan [29]suggested adding a more concise operator to the Monoid class for 'mappend', leading to a long, bike-shed-ish (but hopefully still useful) discussion. Reflections on the ICFP 2009 programming contest. Justin Bailey began a [30]discussion on results and experiences from the ICFP 2009 programming contest. Blog noise [31]Haskell news from the [32]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Gergely Patai: [33]Playing and learning. * Ketil Malde: [34]A set of tools for working with 454 sequences. * Sebastian Fischer: [35]FP Overview. * Magnus Therning: [36]Making a choice from a list in Haskell, Vty (part 1). * David Amos: [37]Conjugacy classes, part 1. * Well-Typed.Com: [38]GHC and Windows DLLs. * Manuel M T Chakravarty: [39]Converting typed term representations: from HOAS to de Bruijn.. * >>> Ivan Uemlianin: [40]Haskell: sort and sortBy. * Gregory Collins: [41]Building a website with Haskell, part 3. * Michael Snoyman: [42]Hack sample- chat server. * Luke Palmer: [43]On the By functions. * Magnus Therning: [44]Dataenc finally making it into Debian. * Thomas ten Cate: [45]New build instructions. * Erik de Castro Lopo: [46]Three More for the Debian New Queue. * >>> Yuval Kogman: [47]What Haskell did to my brain. * Greg Bacon: [48]FFI: calling into kernel32.dll. * Greg Bacon: [49]Setting up a simple test with Cabal. * Ketil Malde: [50]Dephd updates. * Bryan O'Sullivan: [51]What's in a text API?. * Brent Yorgey: [52]2009 ICFP programming contest reflections. * Galois, Inc: [53]Galois, Inc. Wins Two Small Business Research Awards from Federal Agencies. * Greg Bacon: [54]Cleaning up your Haskell imports. * Douglas M. Auclair (geophf): [55]Realized Constants are Comonadic. Quotes of the Week * KF8NH: all monads are functors, but for Hysterical Raisins not all Monads are Functors. * lilac: lambda actually is just the greek letter l. it stands for lilac. * lilac: before mauke we all implemented map with a fold every time we needed it. * luqui: I'll just stick to my religion: I have a personal relationship with our lord and savior, the untyped lambda calculus. * copumpkin: I think I was implemented in haskell. I mean, my parents never used seq, ever. * Benjamin Russell: Haskell. "Avoid success at all costs." Made with dinosaur technology. About the Haskell Weekly News New editions are posted to [56]the Haskell mailing list as well as to [57]the Haskell Sequence and [58]Planet Haskell. [59]RSS is also available, and headlines appear on [60]haskell.org. To help create new editions of this newsletter, please see the information on [61]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [62]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17332 3. http://community.haskell.org/~ndm/hlint/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17331 5. http://haskell.org/haskellwiki/HaskellImplementorsWorkshop 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60907 7. http://just-bottom.blogspot.com/2009/07/playing-and-learning.html 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60846 9. http://haskell.org/haskellwiki/Simonpj/Talk:FunWithTypeFuns 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/60716 11. http://hackage.haskell.org/package/Boolean 12. http://www.haskell.org//pipermail/haskell-cafe/2009-June/063625.html 13. http://hackage.haskell.org/package/TernaryTrees 14. http://www.haskell.org//pipermail/haskell-cafe/2009-June/063681.html 15. http://www.haskell.org//pipermail/haskell/2009-July/021468.html 16. http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/Regular 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/rewriting 18. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 19. http://haddock2009.wordpress.com/2009/06/23/how-to-navigate-your-code/ 20. http://haddock2009.wordpress.com/2009/06/24/cross-package-documentation-par… 21. http://haddock2009.wordpress.com/2009/06/25/cross-package-plan-a/ 22. http://eclipsefp.wordpress.com/2009/06/20/cosmetics/ 23. http://eclipsefp.wordpress.com/2009/06/30/compiling-and-error-reporting/ 24. http://just-bottom.blogspot.com/2009/06/short-term-hp2any-plans.html 25. http://nibrofun.blogspot.com/2009/06/gsoc-status-report-week-4.html 26. http://hackage.haskell.org/package/haskell%2Dsrc%2Dexts 27. http://web.mornfall.net/blog/soc_progress_5.html 28. http://web.mornfall.net/blog/darcs_2.3_beta_1.html 29. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60754 30. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/60690 31. http://planet.haskell.org/ 32. http://haskell.org/haskellwiki/Blog_articles 33. http://just-bottom.blogspot.com/2009/07/playing-and-learning.html 34. http://blog.malde.org/index.php/2009/07/03/a-set-of-tools-for-working-with-… 35. http://www-ps.informatik.uni-kiel.de/~sebf/haskell/fp-overview.html 36. http://therning.org/magnus/archives/685 37. http://haskellformaths.blogspot.com/2009/06/conjugacy-classes-part-1.html 38. http://blog.well-typed.com/2009/07/ghcdlls/ 39. http://justtesting.org/post/134566537 40. http://llaisdy.wordpress.com/2009/07/03/haskell-sort-and-sortby/ 41. http://gregorycollins.net/posts/2009/07/02/building-a-website-part-3 42. http://blog.snoyman.com/2009/07/01/hack-sample-chat-server/ 43. http://lukepalmer.wordpress.com/2009/07/01/on-the-by-functions/ 44. http://therning.org/magnus/archives/672 45. http://eclipsefp.wordpress.com/2009/07/01/new-build-instructions/ 46. http://www.mega-nerd.com/erikd/Blog/CodeHacking/Debian/polyparse_dataenc_js… 47. http://nothingmuch.woobling.org/talks/takahashi.xul?data=yapc_na_2009/haske… 48. http://feedproxy.google.com/~r/gbacon/~3/o-lAJeIoUbk/ffi-calling-into-kerne… 49. http://feedproxy.google.com/~r/gbacon/~3/7rlf4Dd1JKU/setting-up-simple-test… 50. http://blog.malde.org/index.php/2009/06/16/dephd-updates/ 51. http://www.serpentine.com/blog/2009/06/30/python-and-haskell-text-apis-comp… 52. http://byorgey.wordpress.com/2009/06/29/2009-icfp-programming-contest-refle… 53. http://www.galois.com/blog/2009/06/29/galois-awarded-two-federal-sbirs/ 54. http://feedproxy.google.com/~r/gbacon/~3/AGNKaCB2-GI/cleaning-up-your-haske… 55. http://logicaltypes.blogspot.com/2009/06/realized-constants-are-comonadic.h… 56. http://www.haskell.org/mailman/listinfo/haskell 57. http://sequence.complete.org/ 58. http://planet.haskell.org/ 59. http://sequence.complete.org/node/feed 60. http://haskell.org/ 61. http://haskell.org/haskellwiki/HWN 62. http://code.haskell.org/~byorgey/code/hwn/

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