- Haskell-Cafe - Haskell.org

Building documentation only?
by Andrew Cowie 09 Mar '15

09 Mar '15

I've got a sandbox set up to build a local copy of Haddock documentation for various packages I'm using. Is there a way to get Cabal to just run Haddock and not actually build the packages in question? If the haddock program needs the compiled definitions then no, but I'm getting the impression it just runs over the raw sources. The config file I'm using at the moment is a very simple: $ cat cabal.config Documentation: True $ which is doing the trick to get Haddock run, I'm just wondering if there's ActualBuild: False equivalent? AfC

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ANNOUNCE: fgl 5.5.1.0
by Ivan Lazar Miljenovic 09 Mar '15

09 Mar '15

I'm pleased to announce that - after being pestered about it for the past few months ;-) - I've released a new version of the Functional Graph Library that should* now be compatible with GHC 7.10. fgl is now developed on GitHub: https://github.com/haskell/fgl * In that I can't test it on my own machines -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Haskell.org Committee Financial Statement 2014
by Gershom B 09 Mar '15

09 Mar '15

Dear Haskellers, The Haskell.org Committee [1] manages funds for haskell.org and oversees haskell.org infrastructure. The funds available to Haskell.org generally come from two sources: 1) Mentor payments from the Google Summer of Code program. 2) Since the end of 2013, occasional donations [2] from the Haskell community at large. Our funds are held by Software in the Public Interest, a 501(c)3 US non-profit, through which we also accept donations. In return for its services, SPI receives 5% of donations to Haskell.org. According to our charter, "Each year, the committee will post a statement of the haskell.org assets, and the transactions for that year.” We apologize for having been delinquent in this regard. Included in this message is a brief statement of Haskell.org assets over the period 31 December 2013 - 31 December 2014, as well as an approximate breakdown of expenses. The statements we receive from the SPI are not in the most usable format [3], and we hope to provide more accurate accounting in the future. Note that this statement does not reflect 2014 GSoC income, as that had not posted as of 31 December 2014. Thus the fact that we are in the black this year is entirely due to your generous donations. Thank you all so much! 1. Income and Expenses Total income over 2014: 5,187.00 Total expenses over 2014: 2,523.22 ---- Net income over 2014: 2,663.78 2. Expense breakdown Approximate monthly hosting fees (Hetzner): 160.00 Total approximate hosting fees: 1920.00 Other approximate expenses: 603.22 (Other expenses consist of A] payment processing fees for received funds and B] the 5% of donated funds transferred to the SPI). 3. Total Balance Balance as of 31 December 2013: 23,759.13 Balance as of 31 December 2014: 26,422.91 [1] https://wiki.haskell.org/Haskell.org_committee [2] https://wiki.haskell.org/Donate_to_Haskell.org [3] Those wishing to examine further for themselves can find the reports posted to the spi-general list: http://lists.spi-inc.org/pipermail/spi-general/ Best, Gershom Bazerman for the Haskell.org Committee

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CFP: TFPIE 2015
by Johan Jeuring 09 Mar '15

09 Mar '15

Trends in Functional Programming in Education (TFPIE 2015) Call for papers https://wiki.science.ru.nl/tfpie/TFPIE2015 The 4th International Workshop on Trends in Functional Programming in Education, TFPIE 2015, will be held on June 2, 2015 in Sophia-Antipolis in France. It is co-located with the Symposium on Trends in Functional Programming (TFP 2015) which takes place from June 3 - 5. *** Goal *** The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2015 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2015 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), and Soesterberg, The Netherlands (2014). *** Program Committee *** Peter Achten, Radboud University Nijmegen, The Netherlands Edwin Brady, University of St Andrews, UK Johan Jeuring, Utrecht University and Open University, The Netherlands (Chair) Shriram Krishnamurthi, Brown University, US Rita Loogen, Philipps-Universität Marburg, Germany Marco Morazan, Seton Hall University, US Norman Ramsey, Tufts University, US *** Submission Guidelines *** TFPIE 2015 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: - FP and beginning CS students - FP and Computational Thinking - FP and Artificial Intelligence - FP in Robotics - FP and Music - Advanced FP for undergraduates - Tools supporting learning FP - FP in graduate education - Engaging students in research using FP - FP in Programming Languages - FP in the high school curriculum - FP as a stepping stone to other CS topics - FP and Philosophy *** Best Lectures *** In addition to papers, we request “best lecture” presentations. What is your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. *** Submission *** Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2015 It is expected at at least one author for each submitted paper will attend the workshop. *** Important Dates *** April 7, 2015: Early Registration for TFP closes April 27, 2015: Submission deadline for draft TFPIE papers and abstracts May 3 2015: Notification of acceptance for presentation ?? (Probably May 22 2015): Registration for TFPIE closes - as does late registration for TFP June 2, 2015: Presentations in Sophia-Antipolis, France July 7, 2015: Full papers for EPTCS proceedings due. September 1, 2015: Notification of acceptance for proceedings September 22, 2015: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full version; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn.

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Difficulty making a TH template for a monadic expression
by Michael Jones 08 Mar '15

08 Mar '15

I’m at wits end as to how to express a monadic expression in TH. I’ll give here two ways to express a non TH version, and then a TH expression that does not quite work. It generates code that compiles, but it does not evaluate properly like the non TH version. Fundamentally, the problem is use of a recursive function using quasi quoting similar to what is in the standard Show example. Perhaps someone will have an idea on how to fix it. I have made several attempts and failed. Non TH Example A: Do notation ————————————— let r = BG.runBitGet flags (do let bits = [] v <- BG.getBit bits <- return $ if v then I1_7:bits else bits v <- BG.getBit bits <- return $ if v then I1_6:bits else bits v <- BG.getBit bits <- return $ if v then I1_5:bits else bits v <- BG.getBit bits <- return $ if v then I1_4:bits else bits v <- BG.getBit bits <- return $ if v then I1_3:bits else bits v <- BG.getBit bits <- return $ if v then I1_2:bits else bits v <- BG.getBit bits <- return $ if v then I1_1:bits else bits v <- BG.getBit bits <- return $ if v then I1_0:bits else bits return $! bits) Non TH Example B: Bind notation —————————————— let r = BG.runBitGet flags ( return [] >>= (\bits -> ifM BG.getBit (return $ I0_7:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_6:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_5:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_4:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_3:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_2:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_1:bits) (return $ bits)) >>= (\bits -> ifM BG.getBit (return $ I0_0:bits) (return $ bits))) A TH for Example B: ———————— let bitsP = varP $ mkName "bits" let bitsE = varE $ mkName "bits" let makeBits [] = [| "" |] makeBits (name:names) = [| (\bits -> ifM BG.getBit (return $ $(conE name) : $bitsE) (return $ $bitsE)) >>= $(makeBits names) |] parse <- [d| $(varP (mkName $ "parse" ++ nameBase name)) = do flags <- G.getByteString 1 let r = BG.runBitGet flags (return [] >>= $(makeBits bitNames)) case r of Left error -> fail error Right x -> return x |] This generates: parseTCA9535_INPUT_PORT_0_BITS = do {flags_0 <- Data.Binary.Strict.Get.getByteString 1; let r_1 = Data.Binary.Strict.BitGet.runBitGet flags_0 (GHC.Base.return [] GHC.Base.>>= ((\bits_2 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_7 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_3 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_6 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_4 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_5 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_5 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_4 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_6 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_3 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_7 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_2 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_8 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_1 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ((\bits_9 -> Control.Conditional.ifM Data.Binary.Strict.BitGet.getBit (GHC.Base.return GHC.Base.$ (I0_0 GHC.Types.: bits)) (GHC.Base.return GHC.Base.$ bits)) GHC.Base.>>= ""))))))))); Problems with TH ———————— The problem is the () that interferes with the order of evaluation, and the termination at the end ( “” ). I’m no so worried about the termination. I can put something harmless there. The parens are the main problem. Calling a quasi quoter recursively is the cause, as it nests the evaluation. I tried things like building the bits in a list, but that does not work because the BG.getBit has to run in the BitGit monad. I know I can write a simple evaluation that just returns a list of Bools and only TH for bit names, but in the final version the size of bit fields needs to be dynamic, so I need to dynamically generate code piece by piece. I would prefer to use quasi quoting rather than build the whole thing with data types so that it is more readable. If anyone knows of a module on hackage that does something similar, perhaps you can point me to that so I can study it. Thanks…Mike

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ghc -O2 out of memory
by Kees Bleijenberg 08 Mar '15

08 Mar '15

I've written a program that reads a Excel file, parses the contents and generates a haskell module. Every cell in the xls has it's own function in the module. This worked fine. Now I have a bigger xls. The resulting module Xls.hs contains 30000 lines haskell code (without comment). I created a testprogram test.hs that calculates and prints one cell. I did ghc --make test.hs and everything works fine. The generated execuatable is very slow. I did ghc --make -O2 test.hs. The compilations takes 15 minutes and aborts with 'ghc: out of memory'. I'am working on Win 7 64 bits , ghc version = 7.8.3. What can I do to fix this? I do need -O2. I found with smaller xls's that optimization speeds up the executable dramatically. Before I start experimenting, does it help to split up the xls .hs in seperate files? I.e. the cells that refer to other cells and cells that don't refer to other cells. Or will I still get 'out of memory' because the optimization is global? Kees

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[Announce] New release of SBV is out
by Levent Erkok 08 Mar '15

08 Mar '15

A new release of SBV is out (v4.1): http://hackage.haskell.org/package/sbv-4.1 The main change in this release is the connection to Berkeley's ABC <http://www.eecs.berkeley.edu/~alanmi/abc/> system, which is an industrial strength synthesis and verification system. SBV can now generate proof goals that are discharged by ABC, using state-of-the-art SAT based techniques. ABC is especially extremely well-tuned for dealing with problems in the bit-vector theory, and is heavily used in the hardware industry as a backend verification tool. Also included in this release is better support for IEEE-floats, and a reworked implementation of the connection to the Boolector <http://fmv.jku.at/boolector/> solver. Thanks to Adam Foltzer of Galois for contributing the connection to ABC, and Alan Mischenko from Berkeley to add the necessary infrastructure to ABC to allow for this bridge to be built. Full release notes: https://github.com/LeventErkok/sbv/blob/master/CHANGES.md SBV web page: http://leventerkok.github.io/sbv/ -Levent.

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C2HS parse error on Windows ...
by aditya siram 07 Mar '15

07 Mar '15

Hi all, c2hs runs into the following error on all of my .chs files, but only on Windows: c:\\program files\\haskell platform\\2014.2.0.0\\mingw\\bin\\../lib/gcc/x86_64-w64-mingw32/4.6.3/../../../../x86_64-w64-mingw32/include/stddef.h:20: (column 11) [ERROR] >>> Syntax error ! The symbol `__attribute__' does not fit here. My c2hs version is: C->Haskell Compiler, version 0.23.1 Snowbounder, 31 Oct 2014 build platform is "x86_64-mingw32" <1, True, True, 1> This is the command being run: "c:\Users\deech\AppData\Roaming\cabal\bin\c2hs.exe" "--cpp=c:\Program Files\Haskell Platform\2014.2.0.0\mingw\bin\gcc.exe" "--cppopts=-E" "--cppopts=-D__GLASGOW_HASKELL__=708" "--cppopts=-Dmingw32_BUILD_OS=1" "--cppopts=-Dx86_64_BUILD_ARCH=1" "--cppopts=-Dmingw32_HOST_OS=1" "--cppopts=-Dx86_64_HOST_ARCH=1" "--cppopts=-I./c-src" "--cppopts=-I./" "--cppopts=-IC:/MinGW/include" "--cppopts=-IC:\Users\deech\Downloads\fltkhs-0.1.0.1/c-src" "--cppopts=-IC:\Users\deech\Downloads\fltkhs-0.1.0.1" "--include=dist\build" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\process-1.2.0.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\directory-1.2.1.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\time-1.4.2\include" "--cppopts=-IC:\ProgramFiles\Haskell Platform\2014.2.0.0\lib\Win32-2.3.0.2\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\bytestring-0.10.4.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\base-4.7.0.1\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib\integer-gmp-0.5.1.0\include" "--cppopts=-IC:\Program Files\Haskell Platform\2014.2.0.0\lib/include" "--output-dir=dist\build" "--output=Graphics\UI\FLTK\LowLevel\HorValueSlider.hs" "src\Graphics\UI\FLTK\LowLevel\HorValueSlider.chs" A little Googling turned up this thread: http://haskell.1045720.n5.nabble.com/BUG-string-h-FC4-x86-64-td3196369.html which suggested I pass -D__attribute__(A)= to c2hs's opts. I tried it and it led to other errors. I didn't pursue any further because it's an old thread. I'm not sure what stddef.h is and I'm unfamiliar with Windows. Any help is appreciated. Thanks! -deech

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Imperative graph algorithm, (tail?) recursion, and speed
by Jeffrey Brown 07 Mar '15

07 Mar '15

Suppose I have a general (not a tree) directed graph, and I would like to find all the "pure descendents" of a node N -- that is, all nodes M for which (1) N is an ancestor of M, and (2) every partial or maximal sequence of predecessors starting from M either consists entirely of descendents of N, or else includes N itself. I have an imperative algorithm (below) for doing that. I want to know how hard it would be to implement in Haskell. It's complex, but basically it sets up a few lists like "members of this list have had all their descendents processed", "members of this list have been processed but their descendents have not been", "members of this list have not been processed at all", etc. Then I iterate through the graph, moving nodes from one collection to the other until the "to be processed" list is empty. I would like a function Graph -> Graph that does that and does not need to rely on a monad. The only way I can think of involves a few mutually recursive functions, each of which passes not only the original graph of interest, but all the lists described in the previous paragraph, around to the others. I don't understand Haskell's evaluation strategy well enough to anticipate the result, but my vague sense is that a lot of copies of the same data would be floating around, ruining the speed of it. Python code for the algorithm: def descendedOnlyFrom(gset): "All Gnodes n for which every ancestry of n includes a Gnode in gset (which can be a set or a list)." # For efficiency improvement ideas and verbose comments, # see treeSearch/all.py/node.descendedOnlyFrom if 1: # variables # "pure" = "descended only from the calling Glist" pe = set(gset) # determined Pure, yet to Explore children of pf = set() # determined Pure, Finished exploring children of pb = set(gset) # determined Pure, Both kinds: pe | pf ud = set() # purity UnDetermined # descended from root, but might have parents outside of pb udp = {} # "Parents of the UnDetermined" # This is a dictionary, from gnodes to sets of gnodes. # The other four variables are sets. while pe: while pe: k = 1 i = pe.pop(); pf.add(i) for c in set(i._children()): if c in pb | ud: continue # If already handled, do not repeat. if set(c._parents()) <= pb: pe.add(c); pb.add(c) else: ud.add(c); udp[c] = set(c._parents()) - pb for i in ud: ipf = udp[i] & pb # (i)'s (p)arents newly (f)ound in pb if ipf: udp[i] -= ipf if udp[i]==set(): ud.remove(i); del( udp[i] ) pe.add(i); pb.add(i) break return pb

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SPDX and hackage
by Mike Meyer 07 Mar '15

07 Mar '15

I stumbled across the SPDX (https://spdx.org/) Possibly the hackage license list should be expanded to incorporate this in some way? Or at least the OSI-approved entries?

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