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CFP: Submit a talk proposal to CUFP
by Kathleen Fisher 02 Mar '09

02 Mar '09

Hi all, This year CUFP will be held in Edinburgh, Scotland on 4 September. Bryan O'Sullivan, co-author of Real World Haskell, will deliver the keynote presentation, but we're now seeking proposals for regular presentations to complete the program. As you know, CUFP is the place to go to discuss real-world applications of functional programming and to meet the people involved. If you've got something interesting to say, please consider proposing a presentation. The complete call for presentations is below. Kind regards Kathleen Fisher (CUFP 2009 program committee member) Commercial Users of Functional Programming Workshop (CUFP) 2009 Functional Programming As a Means, Not an End Call for Presentations Sponsored by SIGPLAN Co-located with ICFP 2009 Edinburgh, Scotland, 4 September 2009 __________________________________________________________ Presentation proposals due 15 May 2009 http://cufp.galois.com/2009/call.html __________________________________________________________ Functional languages have been under academic development for over 25 years, and remain fertile ground for programming language research. Recently, however, developers in industrial, governmental, and open-source projects have begun to use functional programming successfully in practical applications. In these settings, functional programming has often provided dramatic leverage, including whole new ways of thinking about the original problem. The goal of the CUFP workshop is to act as a voice for these users of functional programming. The workshop supports the increasing viability of functional programming in the commercial, governmental, and open-source space by providing a forum for professionals to share their experiences and ideas, whether those ideas are related to business, management, or engineering. The workshop is also designed to enable the formation and reinforcement of relationships that further the commercial use of functional programming. Providing user feedback to language designers and implementors is not a primary goal of the workshop, though it will be welcome if it occurs. Speaking at CUFP If you use functional programming as a means, rather than as an end, we invite you to offer to give a talk at the workshop. Alternatively, if you know someone who would give a good talk, please nominate them! Talks are typically 25 minutes long, but can be shorter. They aim to inform participants about how functional programming played out in real-world applications, focusing especially on the re-usable lessons learned, or insights gained. Your talk does not need to be highly technical; for this audience, reflections on the commercial, management, or software engineering aspects are, if anything, more important. You do not need to submit a paper! If you are interested in offering a talk, or nominating someone to do so, send an e-mail to francesco(at)erlang-consulting(dot)com or jim(dot)d(dot)grundy(at)intel(dot)com by 15 May 2009 with a short description of what you'd like to talk about or what you think your nominee should give a talk about. Such descriptions should be about one page long. Program Plans CUFP 2009 will last a full day and feature a keynote presentation from Bryan O'Sullivan, co-author of Real World Haskell. The program will also include a mix of presentations and discussion sessions. Topics will range over a wide area, including: * Case studies of successful and unsuccessful uses of functional programming; * Business opportunities and risks from using functional languages; * Enablers for functional language use in a commercial setting; * Barriers to the adoption of functional languages, and * Mitigation strategies for overcoming limitations of functional programming. There will be no published proceedings, as the meeting is intended to be more a discussion forum than a technical interchange. This will be the sixth CUFP, for more information - including reports from attendees of previous events and video of recent talks - see the workshop web site: http://cufp.galois.com/ __________________________________________________

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ANNOUNCE: The Industrial Haskell Group
by Duncan Coutts 02 Mar '09

02 Mar '09

We are pleased to announce the creation of the Industrial Haskell Group (IHG). The IHG is an organisation to support the needs of commercial users of the Haskell programming language. For more information, please see http://industry.haskell.org/ Currently, the main activity of the IHG is a collaborative development scheme, in which multiple companies fund work on the Haskell development platform to their mutual benefit. The scheme has started with three partners of the IHG, including Galois and Amgen. More details are available at http://industry.haskell.org/collab If your company is interested in joining then please e-mail info(a)industry.haskell.org -- Duncan Coutts, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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Take a break: write an essay for Onward! Essays
by Simon Peyton-Jones 02 Mar '09

02 Mar '09

Friends Writing papers is fun, we mostly only get to write one *kind* of paper. Here is an opportunity to write something in a totally different style: Submit an essay to Onward! Essays Deadline: 20 April 2009 http://onward-conference.org/calls/foressays An Onward! essay is a thoughtful reflection upon software-related technology. Its goal is to help the reader to share a new insight, engage with an argument, or wrestle with a dilemma. A successful essay is a clear and compelling piece of writing that explores a topic important to the software community. The subject area should be interpreted broadly, including the relationship of software to human endeavours, or its philosophical, sociological, psychological, historical, or anthropological underpinnings. An essay can be an exploration of its topic, its impact, or the circumstances of its creation; it can present a personal view of what is, explore a terrain, or lead the reader in an act of discovery; it can be a philosophical digression or a deep analysis. It can describe a personal journey, perhaps that by which the author reached an understanding of such a topic. I'm the program chair, and I'd love to get submissions from the POPL/ICFP/types community. Reflections on programming languages, types, testing, verification, software engineering, compilers, society, ... you name it. Anything to do with software. NB: Onward! is co-located with OOPSLA, but they are otherwise unrelated. OO is fine, but not required. Don't forget: 20th April. Simon PS: To get your imagination going, here are a couple of (strongly-contrasting) past essays: * Dan Grossman "The transactional memory / garbage collection analogy" http://www.cs.washington.edu/homes/djg/papers/analogy_oopsla07.pdf * Dick Gabriel "Designed as designer" http://dreamsongs.org/DesignedAsDesigner.html

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major speed improvement: regex-tdfa reaches 1.0.0
by ChrisK 01 Mar '09

01 Mar '09

Announcing the version 1.0.0 release of regex-tdfa. I am proud of this release. This is not just a bug fix release. It is a serious improvement in the asymptotic running time. The previous versions allowed bad combinations of pattern and searched text length to scale badly in the length of the text. Previously the worst case for text of length N was O(N^3). The new worst case asymptotic runtime scaled as O(N). There is never any backtracking. And the worst case storage space is independent of N. The package is on hackage at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-tdfa The darcs repository is at http://darcs.haskell.org/packages/regex-unstable/regex-tdfa/ All non-overlapping matches are found and returned, along with all captured (parenthesized) subexpressions. The result is precisely what Posix extended regular expressions are supposed to return. To be concrete, consider example text with length of N of (2^n)+2: > longInput = replicate (2^n) 'a' ++ "bc" And define 4 worst-case-scenario patterns. I wrote the code and I know how to kill it: > wcs0 = "a*b" > wcs1 = "a*c" > wcs2 = "(a|aa)*b" > wcs3 = "(a|aa)*c" wcs0 is easy. wcs1 causes the old code to backtrack. wcs2 causes the old code's storage to scale as O(N). wcs3 causes both backtracking and O(N) storage with the old code. The old code's time scales as O(N) for wcs0, O(N^2) for wcs1 and wcs2, and O(N^3) for wcs3. The new code is always O(N). The actual timings for the old code on my G4 laptop for wcs on 2^8 and 2^9 and 2^10 are: Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 8 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 8 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(257,1)),(1,(-1,0))]] 263,776,756 bytes allocated in the heap user 0m1.017s sys 0m0.058s Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 9 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 9 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(513,1)),(1,(-1,0))]] 1,998,647,452 bytes allocated in the heap user 0m7.083s sys 0m0.289s Reason:compare-tdfa chrisk$ time ./Test-TDFA-np wcs3 10 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA-np wcs3 10 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1025,1)),(1,(-1,0))]] 15,653,277,200 bytes allocated in the heap user 0m53.350s sys 0m2.056s The doubling of length is causing a nearly eight-fold time increase. The heap allocation is also increasing nearly eight-fold. The new code with the same input pattern and texts gives: Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 8 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 8 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(257,1)),(1,(-1,0))]] 2,135,324 bytes allocated in the heap user 0m0.017s sys 0m0.017s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 9 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 9 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(513,1)),(1,(-1,0))]] 3,588,656 bytes allocated in the heap user 0m0.024s sys 0m0.017s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 10 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 10 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1025,1)),(1,(-1,0))]] 6,345,436 bytes allocated in the heap user 0m0.038s sys 0m0.018s Note that the heap allocation for the 1026 character example above is 2466 times less than the old code. That was too fast to prove the scaling, so take more input: Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 20 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 20 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(1048577,1)),(1,(-1,0))]] 5,708,574,848 bytes allocated in the heap user 0m26.023s sys 0m0.985s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 wcs3 21 +RTS -sstderr 2>&1 | head -4 ./Test-TDFA2-0.99.19-np2 wcs3 21 +RTS -sstderr Test for [Char] Right [array (0,1) [(0,(2097153,1)),(1,(-1,0))]] 11,416,354,056 bytes allocated in the heap user 0m52.656s sys 0m1.985s The length and time both doubled, as did the heap allocation. And the new code has searched two million characters in the time the old code searched one thousand. How about away from the worst case scenario? On the testing suite the new code is running slightly slower: Reason:compare-tdfa chrisk$ time ./Test-TDFA-np -r 1 100 > /dev/null user 0m4.841s sys 0m3.019s Reason:compare-tdfa chrisk$ time ./Test-TDFA2-0.99.19-np2 -r 1 100 > /dev/null user 0m5.970s sys 0m3.012s So that is an increase of execution time of 14%. This small dip in performance might be reclaimable with more optimization. I think the gain in worst case performance already offsets the slight cost. The code for String is complete. The strict and lazy bytestrings and the (Seq Char) are currently using the String code for matching. This will be improved in a future release. Cheers, Chris The small print: regex-tdfa will still behave badly in space and time if given a pathological pattern, e.g. "(((a|aa){0,100}){0,100}){0,100}". But, I am hopeful than I can improve regex-tdfa to behave well with the patterns like this one. That is my vague goal for a future version 2.0.0 release. The very small print: I have been using ghc-6.10.1, and I think I have carried over cabal switches to make ghc-6.8.3 also work. The library probably can work with ghc-6.6, but the cabal file will need editing first as well as fixes to "Text.Regex.TDFA.NewDFA.copySTU".

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haskell documentation
by ppk＠cse.iitk.ac.in 01 Mar '09

01 Mar '09

Hi, I am a Arch linux + GHC user. I found it difficult to download documentations for GHC and all the modules. The GHC site does not seem to have a single tar.gz file by which one could down load the entire documentation tree. Same problem for modules build via yaourt. Of course one could build it directly from the appropriate cabal package but is there an automatic way via pacman/yaourt for example ? Regards ppk

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Announcement: A Haskell binding for the Augeas API
by Jude 01 Mar '09

01 Mar '09

All, I've published a Haskell FFI binding for the Augeas configuration editing API on Hackage. Please let me know if you find any problems with anything. Cheers, Jude Links ===== Hackage http://hackage.haskell.org/cgi-bin/hackage-scripts/package/augeas Source: http://code.haskell.org/augeas/ Bugs: http://trac.haskell.org/augeas/ <http://hackage.haskell.org/trac/c2hs/>

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Haskell Weekly News: Issue 107 - February 28, 2009
by Brent Yorgey 28 Feb '09

28 Feb '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090228 Issue 107 - February 28, 2009 --------------------------------------------------------------------------- Welcome to issue 107 of HWN, a newsletter covering developments in the [1]Haskell community. Announcements Google Summer of Code 2009 - mentors wanted!. Eric Kow [2]reminded everyone that darcs will be applying to be a mentoring organisation for the Google Summer of Code project 2009, and is seeking people to serve as mentors. You need not be a darcs expert to serve as a mentor! c2hs 0.16.0. Duncan Coutts [3]announced the release of [4]c2hs version 0.16.0, a tool which assists in the development of Haskell bindings to C libraries by extracts interface information from C header files and generating Haskell code with foreign imports and marshaling. The major change in this release is that it now uses the [5]Language.C library. X Haskell Bindings 0.2. Antoine Latter [6]announced the 0.2.* series release of the [7]X Haskell Bindings, mostly aimed at making the API prettier. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the [8]X protocol C-language Binding (XCB). text and text-icu, fast and comprehensive Unicode support using stream fusion. Bryan O'Sullivan , on behalf of the Data.Text team, [9]announced the release of preview versions of two new packages: [10]text 0.1, providing fast, packed Unicode text support with modern stream fusion, and [11]text-icu 0.1, which augments text with comprehensive character set conversion support and normalization (and soon more), via bindings to the ICU library. Boston Area Haskell User's Group, first meeting on Saturday February 28th. Shae Matijs Erisson [12]announced the first meeting of the [13]Boston Area Haskell User's Group this Saturday, February 28, at 2pm. Directions are on the web page; you can also check out the [14]mailing list. New version of Hieroglyph released: Hieroglyph 1.1 is on hackage. Jeff Heard [15]announced the release of a new version of [16]Hieroglyph; the biggest change is that it now uses Russell O'Connor's excellent [17]Data.Colour library. bug fix for regex-tdfa, version 0.97.4 (and "regex-ast"). ChrisK [18]announced another bug fix release for the [19]regex-tdfa package, which fixes another tricksy bug. This is now the only known regex library that passes the entire test suite. Hac5: April 17-19, Utrecht -- Book Now!. Sean Leather [20]announced some updated information regarding the [21]5th Haskell Hackathon. The executive summary: hotel or hostel accommodation may be hard to come by, so book your room now, and check out the website for lots of useful information. pkgenv - disposable, isolated pkg environments. Paolo Losi [22]announced a tool, [23]pkgenv, which facilitates setting up isolated, disposable package environments. Blog noise [24]Haskell news from the [25]blogosphere. * JP Moresmau: [26]A high-level GUI library for Haskell. * Magnus Therning: [27]More fun with Cabal, visualising dependencies. Giant graphs are fun! * Magnus Therning: [28]A no-no in my book (found in Cabal). * Bryan O'Sullivan: [29]Finally! Fast Unicode support for Haskell. Data.Text is here! * happstack.com: [30]Happstack now outputs Apache Combined Logs. * GHC / OpenSPARC Project: [31]Benchmarking. * Christophe Poucet (vincenz): [32]Fibonacci in the Type System. * Eric Kow (kowey): [33]inkscape layers. * Magnus Therning: [34]Another reason to create distro-specific packages for Haskell modules. * boegel: [35]Using Haskell to win the Netflix Prize. * Magnus Therning: [36]Simple Cabal parsing. * GHC / OpenSPARC Project: [37]Bugfixes and pretty graphs. * Jeff Heard: [38]New version of Hieroglyph released.. * Chris Done: [39]Vgrabbj hacking. * Conal Elliott: [40]Paper: Beautiful differentiation. Another draft paper from Conal. * happstack.com: [41]Momentum builds as we approach Happstack 0.2. * Luke Palmer: [42]RTS Research. * GHC / OpenSPARC Project: [43]Sanity. * Darcs: [44]darcs weekly news #18. * Don Stewart (dons): [45]Can Haskell give me a pony?. The answer is: Yes! Haskell can do that. * Neil Mitchell: [46]Hoogle package search. * Alex Mason: [47]AVar changes. * Xmonad: [48]Using gimp under xmonad. It can actually be quite nice, despite what you might think. * FP-Syd: [49]Sydney FP Group: FP-Syd #12.. * Eric Kow (kowey): [50]implementing join in terms of (>>=). * GHC / OpenSPARC Project: [51]Triage. * Benjamin L. Russell: [52]Learning Haskell through Category Theory, and Adventuring in Category Land: Like Flatterland, Only About Categories. Quotes of the Week * lilac: haskell's learning curve is like this: | * cowardlydragon: [from a reddit comment thread] Don't get me started on monad. What is that, a man with a single testicle? About the Haskell Weekly News New editions are posted to [53]the Haskell mailing list as well as to [54]the Haskell Sequence and [55]Planet Haskell. [56]RSS is also available, and headlines appear on [57]haskell.org. To help create new editions of this newsletter, please see the information on [58]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [59]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org//pipermail/haskell-cafe/2009-February/056798.html 3. http://www.haskell.org//pipermail/haskell/2009-February/021052.html 4. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/c2hs 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/language%2Dc 6. http://article.gmane.org/gmane.comp.lang.haskell.general/16888 7. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 8. http://xcb.freedesktop.org/ 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53780 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/text-icu 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53761 13. http://www.haskell.org/haskellwiki/Boston_Area_Haskell_Users%27_Group 14. http://groups.google.com/group/bostonhaskell 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53549 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hieroglyph 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/colour 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53525 19. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex%2Dtdfa 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53510 21. http://haskell.org/haskellwiki/Hac5 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/53448 23. http://bitbucket.org/pao/pkgenv/raw/488bfe8e58dd/pkgenv 24. http://planet.haskell.org/ 25. http://haskell.org/haskellwiki/Blog_articles 26. http://jpmoresmau.blogspot.com/2009/02/high-level-gui-library-for-haskell.h… 27. http://therning.org/magnus/archives/534 28. http://therning.org/magnus/archives/523 29. http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-… 30. http://blog.happstack.com/2009/02/26/happstack-now-outputs-apache-combined-… 31. http://ghcsparc.blogspot.com/2009/02/benchmarking.html 32. http://cpoucet.wordpress.com/2009/02/26/fibonacci-in-the-type-system/ 33. http://koweycode.blogspot.com/2009/02/inkscape-layers.html 34. http://therning.org/magnus/archives/522 35. http://boegel.kejo.be/?q=node%2F8 36. http://therning.org/magnus/archives/514 37. http://ghcsparc.blogspot.com/2009/02/bugfixes-and-pretty-graphs.html 38. http://vis.renci.org/jeff/2009/02/24/new-version-of-hieroglyph-released/ 39. http://chrisdone.com/blog/html/2009-02-25-vgrabbj.html 40. http://conal.net/blog/posts/paper-beautiful-differentiation/ 41. http://blog.happstack.com/2009/02/23/momentum-builds-as-we-approach-happsta… 42. http://lukepalmer.wordpress.com/2009/02/24/rts-research/ 43. http://ghcsparc.blogspot.com/2009/02/sanity.html 44. http://blog.darcs.net/2009/02/darcs-weekly-news-18.html 45. http://donsbot.wordpress.com/2009/02/22/can-haskell-give-me-a-pony/ 46. http://neilmitchell.blogspot.com/2009/02/hoogle-package-search.html 47. http://axman6.homeip.net/blog/2009/02/avar-changes.html 48. http://xmonad.wordpress.com/2009/02/21/using-gimp-under-xmonad/ 49. http://www.mega-nerd.com/erikd/Blog/FP-Syd/fp-syd-12.html 50. http://koweycode.blogspot.com/2009/02/implementing-join-in-terms-of.html 51. http://ghcsparc.blogspot.com/2009/02/triage.html 52. http://dekudekuplex.wordpress.com/2009/01/16/learning-haskell-through-categ… 53. http://www.haskell.org/mailman/listinfo/haskell 54. http://sequence.complete.org/ 55. http://planet.haskell.org/ 56. http://sequence.complete.org/node/feed 57. http://haskell.org/ 58. http://haskell.org/haskellwiki/HWN 59. http://code.haskell.org/~byorgey/code/hwn/

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ANNOUNCE: c2hs 0.16.0
by Duncan Coutts 28 Feb '09

28 Feb '09

All, c2hs version 0.16.0 is out and is available from hackage http://hackage.haskell.org/cgi-bin/hackage-scripts/package/c2hs What is c2hs ============ The c2hs tool assists in the development of Haskell bindings to C libraries. It extracts interface information from C header files and generates Haskell code with foreign imports and marshaling. The major advantages of using c2hs compared to writing foreign imports by hand (or using hsc2hs) are: * Cross-language type safety: C functions are imported with the correct Haskell types. * Saves time: boilerplate marshaling code is generated. Changes in this release ======================= The major change in this release is that it now uses the Language.C library. This brings the code full circle. Benedikt Huber split out and developed the Language.C library from the C parser I originally wrote for c2hs some years ago. Other changes since 0.15.x: * Works better on OSX, it now uses gcc -E to do the pre-processing of C header files. Previously it used cpp, however on OSX the cpp program appears to operate in an antiquated compatibility mode. * "enum hooks" are now implemented but not yet documented * A couple fixes in the default mapping of C names to Haskell names. * A number of other bugs fixes. Credits ======= Benedikt Huber gets the credit for majority of the work in this release. Thanks also to John Lato for numerous cleanup patches. Links ===== Home page: http://www.cse.unsw.edu.au/~chak/haskell/c2hs/ Bug tracker: http://hackage.haskell.org/trac/c2hs/ Duncan

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ANN: gitit 0.5.1
by John MacFarlane 26 Feb '09

26 Feb '09

I've just uploaded gitit 0.5.1 to HackageDb. Gitit is a wiki program that uses git or darcs as a filestore and HAppS as a server. Changes: * Major code reorganization, making gitit more modular. * Gitit can now optionally be built using Happstack instead of HAppS (just use -fhappstack when cabal installing). * Fixed bug with directories that had the same names as pages. * Added code from HAppS-Extra to fix cookie parsing problems. * New command-line options for --port, --debug. * New debug feature prints the date, the raw request, and the processed request data to standard output on each request. * Files with ".page" extension can no longer be uploaded. * Apostrophes and quotation marks now allowed in page names.

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ANN: bug fix for regex-tdfa, version 0.97.4 (and "regex-ast")
by ChrisK 24 Feb '09

24 Feb '09

Hello, The regex-tdfa package has had a series of bug fix releases (0.97.1 and 2 and 3 and now 4). This 0.97.4 releases finishes fixing the bug that was only mostly fixed in the 0.97.1 release. An example of the fixed bug: Apply the regex pattern (BB(B?))+(B?) to the text BBBB. The "BB" in the pattern should be used twice and both "B?" should match nothing. My code grouped the "+" wrong and matched the "BB" once and then both the "B?" matched a "B". The case fixed here was not initially caught because of how I search for unknown bugs. I use "Arbitrary" from QuickCheck to generate random patterns and strings to search, and compare regex-tdfa to another POSIX engine. Because I am on OS X, I am limited by the the native POSIX libraries bugs: this bug in regex-tdfa was triggered only when the native POSIX was also buggy. But the source of most of my unit tests is AT&T research [1], and they have a "libast" with a POSIX implementation. I have adapted my regex-* wrapper packages to make a "regex-ast" Haskell interface, but the difficulties with the AT&T headers prevent me from releasing this on hackage. This "regex-ast" has given me access to a less buggy POSIX back-end, and randomized testing has led to catching the bug fixed here (as well as a few bug reports back to AT&T). So while regex-tdfa will not win many speed contests, it is the only POSIX regular expression library I have running that passes all the unit tests. [1] http://www.research.att.com/sw/download/ http://www.research.att.com/~gsf/testregex/ http://www.research.att.com/~gsf/testregex/re-interpretation.html

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