- Haskell-Cafe - Haskell.org

The rmonad package is mysterious
by Simon Marechal 03 Dec '13

03 Dec '13

I tried to do something simple using the rmonad package (attached). I followed the example that's in haddocks (it is wrong, constraints has no arguments), grabbed the list of extensions from rmonad's source, but this program doesn't typecheck: Could not deduce (Hashable a) arising from a use of `HM.singleton' This seems to be an obvious use of this package ... am I missing something ?

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how to factorize propagation of a function over a data type
by TP 03 Dec '13

03 Dec '13

Hi, Let us consider the following example: ----------------------- class FooClass a where foo1 :: a -> a foo2 :: a -> a instance FooClass Integer where foo1 v = 1 foo2 v = 2 data Bar = Bar1 Integer | Exp1 Bar Bar | Exp2 Bar Bar deriving Show instance FooClass Bar where foo1 b = case b of Bar1 i -> Bar1 (foo1 i) Exp1 b1 b2 -> Exp1 (foo1 b1) (foo1 b2) Exp2 b1 b2 -> Exp2 (foo1 b1) (foo1 b2) foo2 b = case b of Bar1 i -> Bar1 (foo2 i) Exp1 b1 b2 -> Exp1 (foo2 b1) (foo2 b2) Exp2 b1 b2 -> Exp2 (foo2 b1) (foo2 b2) main = do let a = Bar1 3 let b = Bar1 4 let c = Exp1 (Exp2 a b) b print c print $ foo1 c print $ foo2 c ----------------------- We obtain as expected: $ runghc propagate_with_duplicated_code.hs Exp1 (Exp2 (Bar1 3) (Bar1 4)) (Bar1 4) Exp1 (Exp2 (Bar1 1) (Bar1 1)) (Bar1 1) Exp1 (Exp2 (Bar1 2) (Bar1 2)) (Bar1 2) My question is related to the code inside the Fooclass instance definition for Bar: we have repeated code where only "foo1" or "foo2" changes. So the first idea is to write a higher-order function, but it does not work: ----------------------- class FooClass a where foo1 :: a -> a foo2 :: a -> a instance FooClass Integer where foo1 v = 1 foo2 v = 2 data Bar = Bar1 Integer | Exp1 Bar Bar | Exp2 Bar Bar deriving Show propagate :: FooClass a => a -> (a->a) -> a propagate v f = case v of Bar1 i -> Bar1 (f i) Exp1 b1 b2 -> Exp1 (f b1) (f b2) Exp2 b1 b2 -> Exp2 (f b1) (f b2) instance FooClass Bar where foo1 b = propagate b foo1 foo2 b = propagate b foo2 main = do let a = Bar1 3 let b = Bar1 4 let c = Exp1 (Exp2 a b) b print c print $ foo1 c print $ foo2 c ----------------------- The problem is that the type variable `a` in the definition of `propagate` cannot match both the type of i, i.e. an integer, and the type of b1 and b2, i.e. Bar. Putting the function propagate in the typeclass does not help. How to factorize my code? Thanks in advance, TP

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Type-level case
by Mike Ledger 03 Dec '13

03 Dec '13

Hi. This is more of a brain dump than anything well thought out, but it's been in the back of my mind for a while. It's occurred to me that with the upcoming release of GHC 7.8, which features closed type families, we've effectively been given type-level pattern matching that behaves the same as expression-level pattern matching. What I think could follow is type-level case syntax. For example: type family Example a where Example 100 = 60 Example 120 = 15 Example x = x * 30 contrived :: Sing a -> Sing b -> Sing (Example (a+b)) might instead be expressed as: contrived :: Sing a -> Sing b -> Sing (case a+b of 100 -> 60 120 -> 15 x -> x*30) -- but with something other than -> in the patterns, -- since that conflicts with the type (->), and there -- are probably too many arrows already Similarly I think if-then-else could be lifted to the type level, also. Some problems with this are that it could pollute "complex" type signatures even further (although currently the situation isn't very good due to haddock/ghc not listing type family instances), and it would get quite cumbersome quickly to have to type out contrived2 :: Proxy (a, b) -> Sing (case a+b of { 100 -> 60; 120 -> 15; x -> x*30 }) -> ... -- Mike

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PhD position at Ghent University
by Tom Schrijvers 03 Dec '13

03 Dec '13

The Programming Languages Group of Ghent University (UGent) invites applicants for a PhD position on the project Reasoning about Coroutines under the direction of Tom Schrijvers. The project concerns reasoning techniques (like type systems and program analysis) for coroutines in its many forms (like delimited continuations and effect handlers). It is conducted in collaboration with the declarative languages group of KU Leuven university and our international partners. We seek applicants at an international level of excellence. As a successful applicant, you have a master degree in Computer Science or equivalent. Ideally, you also have a strong, documented interest in doing research. Strong problem-solving and programming skills are essential. Prior knowledge of functional programming, logic programming, type systems or program analysis are an advantage. The PhD position is for 4 years and starts between January and October 2014. The position is fully funded by the Fund for Scientific Research Flanders (FWO). The salary is compatible with other Belgian PhD rates and among the better ones in Europe and abroad. You will become part of UGent's dynamic and growing Programming Languages Group. UGent is one of the major universities in the Dutch-speaking region of Europe. It distinguishes itself as a socially committed and pluralistic university in a broad international perspective. Our university is located in the beautiful city of Ghent, which is one of Europe’s greatest discoveries, according to Lonely Planet. Please direct your inquiries and applications by e-mail to Tom Schrijvers < tom.schrijvers(a)ugent.be>, principal investigator on this project. To apply, send as soon as possible: 1) a letter of interest (including motivation relevant to the research topic), 2) your detailed curriculum vitae (including study curriculum rankings, relevant research experience and publications), 3) your diploma and transcripts (including translation if possible). We will determine the start date together with the selected candidate. See here for more information: * http://users.ugent.be/~tschrijv/phdposition3.html * http://users.ugent.be/~tschrijv/research.html * http://www.ugent.be/en/research/doctoralresearch -- prof. dr. ir. Tom Schrijvers Programming Languages Group Department of Applied Mathematics and Computer Science University of Ghent Krijgslaan 281 S9 9000 Gent Belgium Phone: +32 9 264 4805 http://users.ugent.be/~tschrijv/

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Call for Papers: 15th Symposium on Trends in Functional Programming, May 2014, Utrecht
by Simon Thompson 02 Dec '13

02 Dec '13

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2014 =========== 15th Symposium on Trends in Functional Programming May 26-28, 2014 Utrecht University Soesterberg, The Netherlands http://www.cs.uu.nl/wiki/TFP2014/WebHome The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below), described in draft papers submitted prior to the symposium. A formal post-symposium refereeing process then selects a subset of the articles presented at the symposium and submitted for formal publication. Selected papers will be published as a Springer Lecture Notes in Computer Science (LNCS) volume. TFP 2014 will be the main event of a pair of functional programming events. The other is the International Workshop on Trends in Functional Programming in Education (TFPIE). TFPIE will take place on May 25th. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh (Scotland) in 2003, in Munich (Germany) in 2004, in Tallinn (Estonia) in 2005, in Nottingham (UK) in 2006, in New York (USA) in 2007, in Nijmegen (The Netherlands) in 2008, in Komarno (Slovakia) in 2009, in Oklahoma (USA) in 2010, in Madrid (Spain) in 2011, St. Andrews (UK) in 2012 and Provo (Utah, USA) in 2013. For further general information about TFP please see the TFP homepage. INVITED SPEAKERS TFP is pleased to announce talks by the following two invited speakers: John Hughes of Chalmers, Goteborg, Sweden, is well-known as author of Why Functional Programming Matters, and as one of the designers of QuickCheck (together with Koen Claessen); the paper on QuickCheck won the ICFP Most Influential Paper Award in 2010. Currently he divides his time between his professorship and Quviq, a company that performs property-based testing of software with a tool implemented in Erlang. Dr. Geoffrey Mainland received his PhD from Harvard University where he was advised by Greg Morrisett and Matt Welsh. After a two year postdoc with the Programming Principles and Tools group at Microsoft Research Cambridge, he is now an assistant professor at Drexel University. His research focuses on high-level programming language and runtime support for non-general purpose computation. SCOPE The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Using functional techniques to reason about imperative/object-oriented programs Debugging for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2014 program chair, Jurriaan Hage at J.Hage(a)uu.nl. BEST PAPER AWARDS To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. SPONSORS TFP is financially supported by NWO (Netherlands Organisation for Scientific Research), Well-Typed and Erlang Solutions. PAPER SUBMISSIONS Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (16 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate whether the main author or authors are research students. In the case of a full student paper, the paper will receive additional feedback by one of the PC members shortly after the symposium has taken place. We shall use EasyChair for the refereeing process. IMPORTANT DATES Submission of draft papers: March 17, 2014 Notification: March 24, 2014 Registration: April 7, 2014 TFP Symposium: May 26-28, 2014 Student papers feedback: June 9th, 2014 Submission for formal review: July 1st, 2014 Notification of acceptance: September 8th, 2014 Camera ready paper: October 8th, 2014 PROGRAM COMMITTEE Peter Achten Radboud University Nijmegen Emil Axelsson Chalmers Lucilia Camarao de Figueiredo Universidade Federal de Ouro Preto Laura Castro University of A Coruna Frank Huch Christian-Albrechts-University of Kiel Matthew Fluet Rochester Institute of Technology Jurriaan Hage (chair) University of Utrecht Yukiyoshi Kameyama University of Tsukuba Andrew Kennedy Microsoft Research Tamas Kozsik Eotvos Lorand University Ben Lippmeier University of New South Wales Luc Maranget INRIA Jay McCarthy Brigham Young University Marco T. Morazan Seton Hall University Ricardo Pena Universidad Complutense de Madrid Alexey Rodriguez madvertise Sven-Bodo Scholz Heriot-Watt University Manuel Serrano INRIA Sophia Antipolis Simon Thompson University of Kent Tarmo Uustalu Inst of Cybernetics David Van Horn Maryland University Janis Voigtlaender University of Bonn Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Looking for reliable heterogeneous vectors
by Sergey Bushnyak 02 Dec '13

02 Dec '13

Hello, everyone. I'm looking for reliable library or idea how to implement heterogenous vector properly. It may seem odd, but I want elements not only be different types but also functions, something like that, pseudocode: hvec [a b (c->d) [a] ...] -- can be any type let hvec = hvec [ "stuff" 5 getUrl [1, 4, 5]] So far I found *vector-heterogenous* package, but can't decide is it good to build on or create something on my own. Any thoughts and ideas are appreciated. Thanks.

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possible CS major seeking advice
by Dennis Raddle 02 Dec '13

02 Dec '13

Sort of off-topic for Haskell, just seeking general advice. (I do love Haskell.) I'm 45, have a B.S. from Caltech and 20+ years of programming experience with NASA (JPL), and now I'm thinking of going back to school to get a Ph.D. in computer science, with a goal of teaching at the university level. I'd like some advice about a possible path. Currently I have an illness which prevents me from handling full-time school, and I am receiving a small disability income. That's the bad news; the good news is that it looks like recovery is on the horizon, perhaps a few years out. Getting admitted to graduate school poses a problem. The only people who know my recent work are my supervisors at NASA. My work at NASA was very uncreative, just grinding through boring code. I was getting gradually sicker and my productivity was going down. Then I got laid off. I'm sure they weren't happy with my productivity. So I'm not too optimistic about getting a glowing letter from my direct boss. However, I did work with two scientists there--they were project leaders, not my boss--and I made a good impression. It's been something like five years since I worked with them and I don't know how well they will remember, but I think they would give me good letters if I can locate them and they remember me. Another possible good letter would come from a fellow I know with a Ph.D. in mathematics. We have worked closely over the years on something very hard to describe called the Feldenkrais Method. It's not math or computer science, but it does require a lot of creativity and learning about learning. I have demonstrated dedication, focus, and intelligence in my work with him. He could give me a good letter, but it's questionable how well it would be received as it's not about CS directly. Another path would be to attend a local state college first and have some professors get to know me, then get letters from them. I'm near California State University Northridge and California State University LA. I hope I could easily get admitted to the M.S. program there. I have some prerequisites to get out of the way; my CS classes at Caltech include only half the normal B.S. requirements, and I am rusty at many things (discrete mathematics, calculus, formal logic, etc.--never used any of these in my job and it's been 20+ years). Although clearly full-time school is out of the question for a few years, I could attend part-time and take some of these prerequisites. For both my M.S. and Ph.D. I want to get admitted to the very best school I can. I'm sure the school determines much of the career that follows. So I would not want to finish the M.S. at the California State schools, but rather transfer to somewhere more prestigious eventually. My next problem is determining an area of specialization. As a professor, I think it's the teaching and mentoring that will satisfy me the most. To feel good about my job I need to work with people and not stick my nose in a computer screen all the time. If I can find a job with good teaching and mentoring opportunities, I know I will LOVE it. I will talk all the time about the pleasure of having a job I love. I'll want to get up in the morning (and that was a big problem with my job at JPL; I was getting depressed). But what will be my area of specialization? As an undergrad I was most drawn to discrete mathematics and algorithms. I also love learning Haskell and would probably be interested in languages. I never really connected with any other classes. But should I specialize in algorithms or languages? I don't know. A priority for me is interacting with people collaboratively, so it might be good to specialize in an area that gets me out in the practical world sometimes. Maybe artificial intelligence? I'm even thinking about the intersection of C.S. and teaching, like devising programs that help teach mathematics and CS through artificial intelligence. But I don't know about artificial intelligence in particular. I would be interested in hearing what people think about areas of CS that would get me involved in real-world applications. Although teaching is my passion, it would be good to stay open to a job in industry should that become desirable for financial reasons. I'm poor right now, have little retirement savings, and I'm blowing through them quickly due to the high medical costs I have. Although people say, "Do what you love, the money will follow." I wonder if those people have ever been poor, especially sick and poor. At some point money becomes more important. But my first preference is teaching. I just don't want to close any doors. Any advice welcome, Dennis

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Re: [Haskell-cafe] possible CS major seeking advice
by Dennis Raddle 02 Dec '13

02 Dec '13

Michal, But I'm not "better than them." My job didn't involve any CS, and my prior coursework represents only through about the junior year. I want the whole experience of a Ph.D., especially getting mentored. An earned Ph.D. also seems to give me the best job options. That's my thought, anyway. Dennis On Sun, Dec 1, 2013 at 2:00 PM, MJG <mjgajda(a)gmail.com> wrote: > Dear Dennis, > > What about old-fashioned attempt to pass PhD exams that some schools ? > Or take online courses for the last year in the domain that you plan to > complete your PhD in, just to prove that you're as good, or better than > their students? > > I believe you're not the only one that tries to complete PhD later than > most students. (I think late mr. Jobs had a similar idea to stress out > after being kicked out of his own company.) > -- > Best regards > Michal > >

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Constraint-folding
by Andras Slemmer 01 Dec '13

01 Dec '13

Hi, I stumbled upon something pretty neat, and although I'm 95% sure Oleg did this already 10 years ago in Haskell98 I thought I'd share it because I find it gorgeous! The basic issue I was having is that whenever I wrote class instances for a lifted type (we'll use Nat): class Class (n :: Nat) instance Class Zero instance (Class m) => Class (Succ m) I always had to litter my code with "(Class n) =>" restrictions even in places where they just shouldn't belong. However my gut feeling was that the generic instance "should" be implied, as we covered all cases. A while ago I proposed a new syntax to do just this ( https://ghc.haskell.org/trac/ghc/ticket/6150) which failed miserably, and for good reason! However there is a way to do it anyway:) What we need is basically a way to "construct" an instance for the fully polymorpic case: "instance Class n". We cannot do this directly as it would overlap with our original instances (and we couldn't implement it anyway), we need another way of representing class instances: type W p = forall a. (p => a) -> a W p simply "wraps" the constraint p into a function that eliminates the constraint on a passed in value. Now we can treat a constraint as a function. We will also need a way to "pattern match" on our lifted types, we will do this with an indexed GADT: data WNat n where -- W for Witness WZero :: WNat Zero WSucc :: WNat n -> WNat (Succ n) And finally the neat part; one can write a general typeclass-polymorphic induction principle on these wrapped constraints (or a "constraint-fold"): natFold :: WNat n -> W (p Zero) -> (forall m. W (p m) -> W (p (Succ m))) -> W (p n) W (p Zero) in the p ~ Class case corresponds to "instance Class Zero", and (forall m. W (p m) -> W (p (Succ m))) corresponds to "instance (Class m) => Class (Succ m)" This function is precisely what we need in order to construct the generic instance! (Note: the implementation of natFold is NOT trivial as we need to wrestle with the type checker in the inductive case, but it is a nice excercise. The solution is here: http://lpaste.net/96429) Now we can construct the generic instance: genericClass :: WNat n -> (Class n => a) -> a genericClass n = natFold n (\x -> x) (\f x -> f x) -- Cannot use id as that would try to unify away our constraints Or equivalently: class WNatClass n where witness :: WNat n instance WNatClass Zero where witness = WZero instance (WNatClass m) => WNatClass (Succ m) where witness = WSucc witness genericClass' :: (WNatClass n) => (Class n => a) -> a genericClass' = genericClass witness Now we can decouple all our "(Class n) =>" and similar constraints, all we need is a WNatClass restriction, which I think is a good enough trade-off (and it's not really a restriction anyway). What do you think? ex

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free vs. operational vs. free-operational
by Alejandro Serrano Mena 01 Dec '13

01 Dec '13

Dear Café, I've been reading lately about the relation between the 'free' package and the 'operational' package for rolling your own monads [1] [2]. Furthermore, I've discovered that the 'free-operational' package, which is some sort of bridge between the two worlds, and provides not only Monad but also Applicative and Alternative instances for ProgramT. The problem is that right now everything is a little confused in my head. In particular, I have the following questions: - I've read that free allows you to 'bake algebraic laws' in the resulting monad. How does this work? Why doesn't operational offer that feature? - One of the things I really like from the free package is that it provides support for many monad transformer stacks, whereas operational does not? Is there any special restriction why operational cannot do this? Would it be possible to provide similar instances for free-operational? - It seems that free gives more features (Alternative, Applicative) with the same work. In which situations should I prefer operational to free? I really like the separation between providing a data type and then a interpretation that operational embodies... - Should I replace my usage of operational with free-operational altogether? Thanks for the help :) [1] http://www.reddit.com/r/haskell/comments/17a33g/free_functors_the_reason_fr… [2] http://stackoverflow.com/questions/14263363/is-operational-really-isomorphi…

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Re: [Haskell-cafe] options for the RTS in a dll
by Nicolas Wu 01 Dec '13

01 Dec '13

On Sun, Dec 1, 2013 at 10:10 AM, Kees Bleijenberg <k.bleijenberg(a)lijbrandt.nl> wrote: > But when I call hs_init_ghc with rtsoptions –h I get 3 lines with on each > line: Can’t open profiling report file <unknown>.hp. > > With –p I get missing profiling report <unknown>.prof > > Any idea what I’am doing wrong? Sounds odd. Have you ensured you have write permissions where the profiling files will be created?

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options for the RTS in a dll
by Kees Bleijenberg 01 Dec '13

01 Dec '13

I've written a windows dll in Haskell. The calling program is written in Delphi (pascal). I want to profile this dll. Because you don't have a command line in a dll for +RTS. -RTS, I call the dll with hs_init_ghc (a exported function in the dll). I had to translate some parts of rtsopts.h to Delphi. Everyting seems okay. The program does not hang, no catastrophic failures. When I start with the parameter for rtsoptions in hs_init_ghc I get: with -t --machine-readable ->machine readable overview on the screen. with -B sounds the bell with each garbage collection, and also --info works as expected. But when I call hs_init_ghc with rtsoptions -h I get 3 lines with on each line: Can't open profiling report file <unknown>.hp. With -p I get missing profiling report <unknown>.prof Any idea what I'am doing wrong? Kees

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[ANN] XSLT2 for C/C++: alpha realease of Saxon-HE 9.5 (and soon Xpath2, Xquery)
by Olivier JEULIN 29 Nov '13

29 Nov '13

Hello, for those working with XML and XSLT/XQuery/XPath, you may be interested to know that Saxonica is releasing an alpha version of its free (and open source) XSLT2/Xquery engine Saxon-HE 9.5. (I'm not affiliated with Saxon, I'm just spreading the news :-) ) The good news is: this finally brings XSLT 2 to C/C++, instead of XSLT 1 (which is already supported by libxml2). XSLT 2 is a MUCH more mature version of XSLT, with cleaner definition of function and a nice functional approach. XSLT 3 will be even better (higher order functions) but may not be supported by the free version of Saxon. http://www.saxonica.com/saxon-c/index.xml I hope that someone will make a binding for haskell ^^,

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10 PhD studentships in Nottingham
by Graham Hutton 29 Nov '13

29 Nov '13

Dear all, The School of Computer Science in Nottingham is advertising 10 fully-funded PhD studentships. Applicants in the area of the Functional Programming lab (fp.cs.nott.ac.uk) are encouraged! If you are interested in applying, please contact a potential academic supervisor in the FP lab prior to submitting your application. Best wishes, Graham +-----------------------------------------------------------+ 10 Fully-Funded PhD Studentships School of Computer Science University of Nottingham, UK Applications are invited for up to ten fully-funded PhD studentships in the School of Computer Science at the University of Nottingham, starting on 1st October 2014. The topics for the studentships are open, but should relate to the interests of one of the School¹s research groups: Agents Lab; Automated Scheduling, Optimisation and Planning; Computer Vision Lab; Functional Programming Lab; Intelligent Modelling and Analysis; Mixed Reality Lab; Networked Systems. The studentships are for three years and include a stipend of £13,726 per year and tuition fees, and are available to students of any nationality. Applicants are normally expected to have a first-class Undergraduate or Masters degree in Computer Science or a related discipline, and should discuss their interest and obtain the support of a potential supervisor in the School before applying. To apply, please submit the following items by email to <Christine.Fletcher(a)nottingham.ac.uk>: (1) a brief covering letter that describes your reasons for wishing to pursue a PhD, any ideas you have regarding possible areas or topics, and the name of a potential supervisor; (2) a copy of your CV, including your actual or expected degree class(es), and results of all University examinations; (3) an example of your technical writing, such as a project report or dissertation; (4) contact details for two academic referees. Closing date for applications: 10th January 2014 +-----------------------------------------------------------+ -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Fwd: vector fails to build with ghc on arm-linux-androideabi
by Herwig Hochleitner 29 Nov '13

29 Nov '13

Hello, I'm trying to build the openpgp libs for android. I can build and run HaskellActivity from the HelloWorld sample, but as when I try to install vector, I get the following build failure: ==================== $ arm-linux-androideabi-cabal install --reinstall --force-reinstall vector ... [ 5 of 19] Compiling Data.Vector.Fusion.Stream.Monadic ( Data/Vector/Fusion/Stream/Monadic.hs, dist/build/Data/Vector/Fusion/Stream/Monadic.o ) Loading package ghc-prim ... linking ... ghc: /home/androidbuilder/.ghc/android-14/arm-linux-androideabi-4.8/lib/arm-unknown-linux-androideabi-ghc-7.7.20130921/ghc-prim-0.3.1.0/HSghc-prim-0.3.1.0.o: unhandled ELF relocation(Rel) type 28 ghc: unable to load package `ghc-prim' Failed to install vector-0.10.9.1 ... ==================== It seems somewhat related to this closed bug: https://ghc.haskell.org/trac/ghc/ticket/7824 Am I doing something stupid? Can I fix this? cheers

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Query information about a haskell source file from the command-line
by Thiago Padilha 29 Nov '13

29 Nov '13

Is there any command-line tool that outputs information about a source haskell module? I'm looking for something like 'ghc-mod browse'(which displays all symbols exported by an installed module) but that works for plain haskell source files. Any ideas?

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Master thesis project - Haskell STM
by Johan Astborg 28 Nov '13

28 Nov '13

Dear Haskellers, I found Haskell and became enlightened for the first time in many years. I choose to continue on this path, and choose Haskell for my master thesis. I got some nice ideas from people on the #haskell channel . Altogether, I have elaborated a topic: "Evaluating Intel TSX in a MVCC based STM implementation for Haskell" The idea is to investigate whether the "new" Intel TSX can bring any value in terms of performance and saftey when implemented in a MVCC based STM to be used in the Haskell runtime system (GHC). The MVCC based STM using TSX will be evaluated and compared to the existing implementation, compiled with the two settings STM_CG_LOCK and STM_FG_LOCKS respectively. The biggest challange still, is to convince Lund University, LTH, to accept my own master thesis project. I have to present a detailed synopsis about the project, for them to choose an examinator and supervisor. As they put it, the examinator "must have time" and it's up to that person to decide whether or not this project can be reality. Feedback on any of these is highly appreciated: 1) Ideas and thoughts about this topic 2) Anyone interested in supervising (mainly formal) the project outside of LTH Thanks, Johan Astborg

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Return of the revenge of the revisit of the extensible records, reiterated
by oleg＠okmij.org 28 Nov '13

28 Nov '13

First of all, I should point out that faster extensible records have already been developed, within the HList framework: Just Do It While Compiling! Fast Extensible Records In Haskell http://www.fing.edu.uy/~mviera/papers/pepm13.pdf The authors did it without needing the total order on labels. However, one of the encoding of labels described in the HList paper had total order. I guess we weren't motivated enough to exploit it. > The real benefit of keeping the row sorted is that { x = 0 , y = 0 } and { > y = 0, x = 0 } have the same type. When a row is not sorted, as in HList, > then if we for example have an instance Eq for a row (because all elements > support Eq) then for using (==) both arguments would have to the same order > in the row or we need a manual call to a permutation function. When keeping > the row ordered, this is not necessary. The same kind of problem > occurs > > The same kind of problem occurs when we fix the type of a function to > a specific row: ( using whishful syntax ) > > f :: Rec [ x = Int , y = Int] -> Int > > If the row is not ordered, then f { y = 0 , x = 0 } will not typecheck and > will require a manual call to permute the row. This is all very true. However, if we wish to pass the function f above the record {y=0, x=0} (with permuted fields), we most likely wish to pass that function a record {x=0, y=0, z='a'} with more fields. Most of the time when we deal with extensible records, we really wish to explore their extensibility. Keeping fields sorted does not help at all in the latter problem -- we must manually insert the call to the subtyping coercion function. Once we do that, the problem with the order of the fields disappears. I also would like to point out that there are two sorts of record types. One sort is Rec [x: Int, y:Bool] in the imagine syntax. Current HList types are uglier versions of the above. But there is another sort: (HasField r x Int, HasField r y Bool) => r It represents an extensible record type. Extensibility is build in, and the order of the fields is immaterial. Quite a few functions on records can be given the above type. Furthermore, the second sort can be used not only with structural subtyping but also with nominal subtyping.

1 0

Compiling to STG problem
by Maarten Dungen 27 Nov '13

27 Nov '13

Dear all, While trying to retrieve the STG using ghc I bumped into the following problem: I try to compile the source file in a more or less standard way, found in many examples on the web: ... setTargets targets _ <- load LoadAllTargets mgraph <- depanal [] False mapM_ (compileModSummary) mgraph Then I compile the individual files through the following pipeline (also more or less standard, I thought): compileModSummary = do ... stg <- parseModule theMod >>= typecheckModule >>= desugarModule >>= liftIO . hscSimplify env . coreModule >>= liftIO . tidyProgram env >>= prepPgm env . fst >>= liftIO . coreToStg dynflags … Then I do a dump to (just to check the results): writeFile “filename” (show . showOutputable $ stg) The problem is, if I do a stg dump from the command line (like <compiler> -ddump-stg --make Main.hs (where <compiler> is the intended compiler program) the dump is different from the stg dump I do at writefile, to the extent that functions are missing, which gives problems when linking the results. They are numbered functions, like ‘value1’, etc. I’m not very much into the ghcmake stuff, and I’m probably missing a lot, however I have been struggling with this for a couple of days now, and it is not getting any clearer. I guess my question would be, why is there a difference, and how could I avoid this? Any help or pointers appreciated. kind regards, Maarten p.s. This is just pseudo code. I necessary, I could probably strip my sources into a working example that displays the problem, if that would help.

2 1

Monad classes and FreeT
by Alejandro Serrano Mena 27 Nov '13

27 Nov '13

Dear Café, I'm continuing my travel through operational and free, and was wondering: which is the reason why there's no instance such as (Functor f, MonadReader e m) => MonadReader e (FreeT f m) included in the 'free' package? It seems reasonable to me to have those instances. At least, there's the corresponding one for MonadIO. Should Free be considered as some monad to have 'at the bottom of the stack' as IO is? Thanks in advance.

2 2

btc-e interfacing + bot
by Miro Karpis 27 Nov '13

27 Nov '13

Am thinking to inteface btc-e + make a bot. Anybody willing to join forces? m.

4 3

Re: [Haskell-cafe] using external instance declarations
by Kata 26 Nov '13

26 Nov '13

The problem is that your definition of arbitrary for the Building instance isn’t indented under the ‘instance Arbitrary Building’, so it’s getting interpreted as two top-level statements: one that Building is an Arbitrary of Instance, and one that defines a value named ‘arbitrary’. Hence the error message. To fix this, just indent the definition of arbitrary like you did in the Glass definition. On Tuesday, November 26, 2013 at 11:06 AM, Kees Bleijenberg wrote: > I have a Building with a field glass: Glass. > I want to use quickcheck. Therefor I wrote a TestGlass.hs with the Arbitrary instance declaration for Glass. I also want to make Building an instance of Arbitrary. For the field glass in the Building I need the arbitrary :: Gen Glass function out of TestGlass.hs. > How do I export and use the instance declarations from TestGlass.hs? > > Glass.hs > module Glass( > Glass(..)) > where > data Glass = Glass Int > > TestGlass.hs > module TestGlass() > where > import Test.QuickCheck > import Test.QuickCheck.Gen > import Glass > > instance Arbitrary Glass where > arbitrary = do > n <- choose (1,8) :: Gen Int > return $ Glass n > > > Building.hs > module Building () > where > import Glass > import TestGlass > import Test.QuickCheck > import Test.QuickCheck.Gen > > data Building = Building { > glass :: Glass > } > instance Arbitrary Building where > arbitrary = do > g <- arbitrary :: (Gen Glass) > return Building { glass = g} > > > When I compile Building I get: > Building.hs:13:23: > Ambiguous occurrence `arbitrary' > It could refer to either `Building.arbitrary', > defined at Building.hs:12:1 > or `Test.QuickCheck.arbitrary', > imported from `Test.QuickCheck' at Building.hs:5:1-22 > (and originally defined in `Test.QuickCheck.Arbitrary') > > It looks like the compiler doesn’t look at the instance declarations in the TestGlass module. > What is wrong in my code? > I want to split the testcode as much as possible from the non-test code and I don’t want to merge the modules Building and Glass (they are both already big). > > Kees > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org (mailto:Haskell-Cafe@haskell.org) > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

1 0

using external instance declarations
by Kees Bleijenberg 26 Nov '13

26 Nov '13

I have a Building with a field glass: Glass. I want to use quickcheck. Therefor I wrote a TestGlass.hs with the Arbitrary instance declaration for Glass. I also want to make Building an instance of Arbitrary. For the field glass in the Building I need the arbitrary :: Gen Glass function out of TestGlass.hs. How do I export and use the instance declarations from TestGlass.hs? Glass.hs module Glass( Glass(..)) where data Glass = Glass Int TestGlass.hs module TestGlass() where import Test.QuickCheck import Test.QuickCheck.Gen import Glass instance Arbitrary Glass where arbitrary = do n <- choose (1,8) :: Gen Int return $ Glass n Building.hs module Building () where import Glass import TestGlass import Test.QuickCheck import Test.QuickCheck.Gen data Building = Building { glass :: Glass } instance Arbitrary Building where arbitrary = do g <- arbitrary :: (Gen Glass) return Building { glass = g} When I compile Building I get: Building.hs:13:23: Ambiguous occurrence `arbitrary' It could refer to either `Building.arbitrary', defined at Building.hs:12:1 or `Test.QuickCheck.arbitrary', imported from `Test.QuickCheck' at Building.hs:5:1-22 (and originally defined in `Test.QuickCheck.Arbitrary') It looks like the compiler doesn't look at the instance declarations in the TestGlass module. What is wrong in my code? I want to split the testcode as much as possible from the non-test code and I don't want to merge the modules Building and Glass (they are both already big). Kees

1 0

Witnessing lifted types?
by Andras Slemmer 25 Nov '13

25 Nov '13

Hi, not sure whether this has been addressed before. Basically the goal is to have a standardised way of witnessing lifted types (=simulating pattern matching on type indices). A particular problem this would be useful for: Given a standard natural-indexed vector (Vec n) provide an Applicative instance for it with n left polymorphic. The issue is that we don't have a way of pattern matching on n, therefore we cannot implement pure/<*>. The way I addressed situations like this before was to have two Applicative instances, one for Vec Zero and one for Vec (Succ n), however I think there is a way to decouple this way of "pattern matching on types" by introducing a GADT: data WNat n where WZero :: WNat Zero WSucc :: WNat n -> WNat (Succ n) and a class class WNatClass n where witness :: WNat n instance WNatClass Zero where witness = WZero instance (WNatClass n) => WNatClass (Succ n) where witness = WSucc witness Now whenever we need to pattern match on a natural index we can just put a WNatClass restriction on it and pattern match on the automatically constructed witness. For the Vec example: instance (WNatClass n) => Applicative (Vec n) where pure = pure' witness where pure' :: WNat n -> a -> Vec n a pure' WZero _ = VecNil pure' (WSucc w) a = a ::: pure' w a (<*>) = app' witness where app' :: WNat n -> Vec n (a -> b) -> Vec n a -> Vec n b app' WZero _ _ = VecNil app' (WSucc w) (f ::: fs) (a ::: as) = f a ::: app' w fs as We can also generalise this concept to any index type with PolyKinds, although I'm not 100% sure why it works in general: class Construct (a :: k) where data Wit a :: * class (Construct a) => Witness a where witness :: Wit a The idea is that each instance of Construct will leave the type 'a' polymorphic and will only bind the kind 'k' and provide an indexed witness: instance Construct (n :: Nat) where data Wit n where WZero :: Wit Zero WSucc :: Wit n -> Wit (Succ n) and the Witness instances will be the same as with WNatClass. We need two classes because one will define the witness type, the other will do the "pattern matching". The part I don't understand is that together with the (n :: Nat) instance we can also have instance Construct (a :: SomeOtherType) where ... without triggering any 'overlapping' diagnostic, even though both instances are "fully polymorphic". I am assuming this is because internally the compiler adds a kind parameter to the class that disambiguates the instances? If so then I think this is a nice uniform way of handling lifted type witnesses. (The instances can be generated automatically too). What do you think? Is there a better way of doing this? Is the decoupling even worth the trouble? Is the performance hit big compared to the explicit instance splitting?

2 1

IDE
by Corentin Dupont 25 Nov '13

25 Nov '13

Hi cafe, I would like to know which IDE are you using? I use Leksah, I like the GUI design and constant compilation process. However, the development seems to be slowing down: last version date from early 2012. The installation process is very painful. There is FPComplete IDE coming up, but it's commercial. I'm experimenting with it, anyway: how to compile using cabal files? It doesn't seem to recognize them. Will there be an off-line version? I'm interested to know if you are using vim to develop: which extension are you using? I'm interested in continuous compilation, project files browsing, code completion, search-in-files. Best, Corentin

24 28

New Functional Programming Job Opportunities
by Functional Jobs 25 Nov '13

25 Nov '13

Here are some functional programming job opportunities that were posted recently: Software Developer - Functional Programming at Genetec http://functionaljobs.com/jobs/8660-software-developer-functional-programmi… Cheers, Sean Murphy FunctionalJobs.com

1 0

[ANNOUNCE]hPDB - Is it the fastest parallel PDB parser? Part of structural bioinformatics library collection...
by Michal J Gajda 25 Nov '13

25 Nov '13

Dear Haskellers, I would like to present a benchmark of Protein Databank parsers that indicates that one written in Haskell seems to outpace all others when using 4 or more of parallel cores: hPDB - Haskell library for processing atomic biomolecular structures in Protein Data Bank format -- Michal Jan Gajda BMC Research Notes.2013, 6:483. DOI: 10.1186/1756-0500-6-483 URL: http://www.biomedcentral.com/1756-0500/6/483 Please let me know if you know of any other parsers that could be added to this benchmark. Along with hTalos, and parseSTAR parser libraries for nuclear magnetic resonance data it adds to growing collection of bioinformatic libraries written in Haskell. Together with CloudHaskell and modern 48-core machines, they allow to process multigigabyte bioinformatic databases in a matter of few minutes (slightly over 8 minutes in case of over 10GB of PDB.) If interested, please see: http://biohaskell.org/. -- Best regards Michał J. Gajda

1 0

Munich Haskell Meeting
by Heinrich Hördegen 24 Nov '13

24 Nov '13

Dear all, on Wed, 27th of November, once again, our monthly Haskell meeting will take place in Munich at 19h30 at Cafe Puck. If you plan to join, please go to: http://www.haskell-munich.de/dates and hit the button. Have a nice week! Heinrich

1 0

Stacked return
by Dmitry Bogatov 24 Nov '13

24 Nov '13

Hi, list! I want to write function, that will stack `return` as much times, as necessery. In code, I want <$> magicLift 2 :: IO Int <$> magicLift 2 :: Maybe [Int] both be valid. My best approach is following (not work) {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} class Monad m => MonadS m where liftS :: a -> m a instance (Monad m) => MonadS m where liftS = return but <$> :t liftS 2 liftS 2 :: (Monad m, Num a) => m a What would you suggest? -- Best regards, Dmitry Bogatov <KAction(a)gnu.org>, Free Software supporter and netiquette guardian. git clone git://kaction.name/rc-files.git --depth 1 GPG: 54B7F00D Html mail and proprietary format attachments are forwarded to /dev/null.

3 5

Lista de emails cadastro email lista emails gratis
by Ed Soares 24 Nov '13

24 Nov '13

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1 0

Hackage home page content should feature cabal install instructions
by John D. Ramsdell 23 Nov '13

23 Nov '13

As I read the content at hackage.haskell.org, I thought about what a new user interesting in using the site would like to know. The most important question is how to use the programs and libraries provided by the site. Thus, the content that should be featured is how to install packages using cabal install assuming Haskell platform has been installed. Exploring the site might be the next topic, followed by the support section and the other topics. In short, most users want to know how to use the packages provided by the site, and not so much about the server that powers the site. John

2 1

Is there any "purely algebraic" Linear Algebra library?
by Hiromi ISHII 23 Nov '13

23 Nov '13

Hi, I'm recently implementing computational algebra library (available on http://hackage.haskell.org/package/computational-algebra ), build on top of ekmett's `algebra` library. My `computational-algebra` library currently provides very basic functionalities which is rather slow. There are many techniques to speeding up calculation utilizing linear algebra. So I want to implement those efficient algorithms. But, I couldn't find any *purely algebraic* linear-algebra library. As for the most famous library `hmatrix`, this library requires "Field" to be convertible between Double or Real numbers, and due to such constraints, it cannot treat genral coefficient fields, such as Rational (which is not closed under sin or exponentials) or finite fields. So I have to give up using this library. I noticed there are some additional candidates such as: * `linear` by Edward Kmett * `vector-space` by Conal Elliot But neither of them provides necessary functionalities which is available in `hmatrix`, such as determinant for arbitrary dimensional matrices and rank function , etc. Is there any other library providing the functionalities like above which can be used with general coefficient fields? Or is there any good document on the efficient implementation for linear algebra on Haskell? -- Hiromi ISHII konn.jinro(a)gmail.com

1 0

Dynamic package information with Setup.hs
by Thiago Padilha 22 Nov '13

22 Nov '13

I'm writing a cabal package that provides bindings to a C library. I've written a shell script that will download and build this C library to a subdirectory of the user's HOME(~/.cabal-tmp/{lib,include}). Currently I have the following Setup.hs that automatically runs the script before installing: import Distribution.Simple import Distribution.Simple.Setup import Distribution.PackageDescription import System.Process main :: IO () main = defaultMainWithHooks simpleUserHooks { preConf = buildDeps } buildDeps :: Args -> ConfigFlags -> IO HookedBuildInfo buildDeps _ _ = do rawSystem "sh" ["./scripts/build-deps.sh"] return emptyHookedBuildInfo I've tried adding the following lines: extra-lib-dirs: ${HOME}/.cabal-tmp/lib include-dirs: ${HOME}/.cabal-tmp/include But it complains about syntax errors and I found no other way to expand the user's HOME directory in the .cabal file. If I use relative paths in the 'extra-lib-dirs' an error is reported(cabal 1.16). Full paths are also needed for linking against this package as ghc needs to know the linker flags for the native library. Obviously I cant know the full path the library will be installed in advance, as I dont know the HOME directory of the user installing the package until the Setup.hs script is running. My question: How can I use the Setup.hs hooks to update those two fields dynamically?

4 4

ANN: New Haskell.org committee members
by Jason Dagit 22 Nov '13

22 Nov '13

The Haskell.org committee has selected new members following the October self-nomination period. The new members are: * Adam Foltzer * Nicolas Wu * Andres Loeh Thank you to everyone who submitted a self-nomation. We had many very strong candidates and it was not easy for us to narrow the selection down to just three people. I would like to add, that if you've self-nominated in the past but not be picked, please self-nominate again in the future. Cheers, Jason

1 0

Product Profunctor and Contravariant
by Tom Ellis 20 Nov '13

20 Nov '13

Does anyone recognise these typeclasses: import Data.Profunctor (Profunctor) import Data.Functor.Contravariant (Contravariant) class Profunctor p => ProductProfunctor p where empty :: p () () (***!) :: p a b -> p a' b' -> p (a, a') (b, b') class Contravariant f => ProductContravariant f where point :: f () (***<) :: f a -> f b -> f (a, b) They are both a bit like Applicative, and ProductProfunctor is basically Arrow without the Category part. I'm finding ProductProfunctor useful for marshalling data from a database into Haskell, and both of them come up a lot inside my database library. Has anyone ever seen these before? Has Edward Kmett written a library for these already? Thanks, Tom

1 1

QuickCheck-like tests with GHC.Generic deriving
by Alexander Solla 20 Nov '13

20 Nov '13

I am looking for a QuickCheck-like test framework which exposes data generators (like QuickCheck's Arbitrary class) with Generic defaults. I have seen that SmallCheck's Serial class has Generic defaults, but it isn't particularly good for my purpose (I'd like to use the generator to populate deeply nested data types, and SmallCheck's generator requires computing a few million values before I get any interesting ones) Something "random" would be more useful for my purpose. I know that the plan depends on my vaguely abusing the test-case generator, but I plan on doing some testing anyway, so I figured I should reuse the instance. That said, I'd be willing to use any random value type class with Generic-default instances. Does anybody have any suggestions?

4 3

Re: [Haskell-cafe] QuickCheck-like tests with GHC.Generic, deriving
by Janis Voigtlaender 20 Nov '13

20 Nov '13

Alexander Solla writes: > I am looking for a QuickCheck-like test framework which exposes data > generators (like QuickCheck's Arbitrary class) with Generic defaults. > > I have seen that SmallCheck's Serial class has Generic defaults, but it > isn't particularly good for my purpose (I'd like to use the generator to > populate deeply nested data types, and SmallCheck's generator requires > computing a few million values before I get any interesting ones) > Something "random" would be more useful for my purpose. > > I know that the plan depends on my vaguely abusing the test-case generator, > but I plan on doing some testing anyway, so I figured I should reuse the > instance. > > That said, I'd be willing to use any random value type class with > Generic-default instances. > > Does anybody have any suggestions? I think what you want is: http://hackage.haskell.org/package/testing-feat See also the paper: http://dx.doi.org/10.1145/2430532.2364515 Specifically, the technique solves the "populate deeply nested data types" issue. You can efficiently jump to the so-and-so-many-millionth value in the enumeration without having to create all smaller values. Best, Janis.

1 0

Need help with very simple C++ FFI call
by Thiago Padilha 20 Nov '13

20 Nov '13

Hi I'm trying write a ffi binding to the v8 javascript engine (C++ library). Theres one already at https://github.com/sol/v8 but I want to do it again as an exercise to improve by haskell skills. I chose this library be because it will force me to deal with impure functions using monads. Since its not a trivial library, it will also improve my knowledge of writing FFI bindings and cabal packages in case I want to wrap more C++ libraries in the future. My first step is to port the 'hello world' example in v8 embedders guide(https://developers.google.com/v8/get_started) as a haskell binding. So I have downloaded/compiled v8 and created the following directory structure: src/V8.hs cbits/haskell-v8.cpp # v8 libraries deps/lib/libv8_base.a deps/lib/libv8_snapshot.a # v8 headers deps/include/ Here's the contents of the haskell-v8.cpp file: http://pastebin.com/RfYCCxFQ (basically a copy of the v8 embedders example function, except that it returns a char pointer). and here's the haskell module: http://pastebin.com/fnXVbEeU I compiled a shared library exposing the c "hello" function with the following command: $ g++ \ -shared -o libhaskellv8.so \ -I./deps/include \ -L./deps/lib \ ./cbits/haskell-v8.cpp \ -lv8_base \ -lv8_snapshot \ -lpthread \ -lrt And loaded into ghci with the following: $ ghci -L. -lhaskellv8 src/V8.hs The problem is that I get a segmentation fault when I call the 'hello' function from ghci. To ensure the library was compiled correctly, I successfully called it from python: $ python -c \ 'from ctypes import CDLL, c_char_p; lv8=CDLL("libhaskellv8.so"); lv8.hello.restype = c_char_p; print lv8.hello()' Hello, World! I have selectively uncommented lines from the c++ file, and the segmentation faults starts happening when I uncomment line 14 (HandleScope handle_scope(isolate)). What am I missing here?

5 13

FLOPS 2014 2nd CFP
by Eijiro Sumii 19 Nov '13

19 Nov '13

NEWS: - Journal publications in JFP (Jounral of Functional Programming) and TPLP (Theory and Practice of Logic Programming) are planned (see below). - Hyakumangoku Matsuri ( https://www.google.com/search?q=hyakumangoku%20matsuri&tbm=isch ) is scheduled *just* after FLOPS 2014. Call For Papers =============== Twelfth International Symposium on Functional and Logic Programming (FLOPS 2014) June 4-6, 2014 Kanazawa, Japan http://www.jaist.ac.jp/flops2014/ FLOPS is a forum for research on all issues concerning declarative programming, including functional programming and logic programming, and aims to promote cross-fertilization and integration between the two paradigms. Previous FLOPS meetings were held at Fuji Susono (1995), Shonan Village (1996), Kyoto (1998), Tsukuba (1999), Tokyo (2001), Aizu (2002), Nara (2004), Fuji Susono (2006), Ise (2008), Sendai (2010), and Kobe (2012). Topics ====== FLOPS solicits original papers in all areas of functional and logic programming, including (but not limited to): - Language issues: language design and constructs, programming methodology, integration of paradigms, interfacing with other languages, type systems, constraints, concurrency and distributed computing. - Foundations: logic and semantics, rewrite systems and narrowing, type theory, proof systems. - Implementation issues: compilation techniques, memory management, program analysis and transformation, partial evaluation, parallelism. - Applications: case studies, real-world applications, graphical user interfaces, Internet applications, XML, databases, formal methods and model checking. The proceedings will be published as an LNCS volume. The proceedings of the previous meetings (FLOPS 1999, 2001, 2002, 2004, 2006, 2008, 2010, and 2012) were published as LNCS 1722, 2024, 2441, 2998, 3945, 4989, 6009, and 7294. PC Co-Chairs ============ Michael Codish (Ben-Gurion University of the Negev) Eijiro Sumii (Tohoku University) PC Members ========== Lars Birkedal (Aarhus University) Michael Codish (Ben-Gurion University of the Negev) [co-chair] Marina De Vos (University of Bath) Moreno Falaschi (Universita degli studi di Udine) Carsten Fuhs (University College London) John Gallagher (Roskilde Universitet / IMDEA Software Institute) Samir Genaim (Universidad Complutense de Madrid) Laura Giordano (Universita del Piemonte Orientale) Ichiro Hasuo (University of Tokyo) Fritz Henglein (University of Copenhagen) Andy King (University of Kent) Oleg Kiselyov Vitaly Lagoon (MathWorks) Shin-Cheng Mu (Academia Sinica) Keiko Nakata (Institute of Cybernetics at Tallinn University of Technology) Luke Ong (University of Oxford) Peter Schachte (University of Melbourne) Takehide Soh (Kobe University) Eijiro Sumii (Tohoku University) [co-chair] Tachio Terauchi (Nagoya University) Joost Vennekens (KU Leuven) Janis Voigtlaender (Universitaet Bonn) Stephanie Weirich (University of Pennsylvania) Local Chair =========== Yuki Chiba (JAIST) Submission ========== Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. See also ACM SIGPLAN Republication Policy: http://www.sigplan.org/Resources/Policies/Republication Submissions should fall into one of the following categories: - Regular research papers: they should describe new results and will be judged on originality, correctness, and significance. - System descriptions: they should contain a link to a working system and will be judged on originality, usefulness, and design. - Declarative pearls: new and excellent declarative programs or theories with illustrative applications. System descriptions and declarative pearls must be explicitly marked as such in the title. Submissions must be written in English and can be up to 15 pages long including references, though pearls are typically shorter. Authors are required to use LaTeX2e and the Springer llncs class file, available at: http://www.springer.de/comp/lncs/authors.html Regular research papers should be supported by proofs and/or experimental results. In case of lack of space, this supporting information should be made accessible otherwise (e.g., a link to a Web page, or an appendix). Papers should be submitted electronically at: https://www.easychair.org/conferences/?conf=flops2014 Important Dates =============== Submission deadline: December 13, 2013 Author notification: February 10, 2014 Camera-ready copy: March 7, 2014 Journal Publication =================== - Journal of Functional Programming and - Theory and Practice of Logic Programming 2-4 of the best papers in each of the two areas: Functional Programming and Logic Programming, will be invited for inclusion in a designated FLOPS section within each of the two journals. The Theory and Practice of Logic Programming papers will appear as "Rapid Publications". All of the these submissions are expected to represent high-quality revisions and extensions of the selected FLOPS papers and will be reviewed under the standard criteria of each journal. Venue ===== Main Hall, Ishikawa Prefectural Museum of Art, 2-1 Dewa-machi, Kanazawa, Ishikawa 920-0963 JAPAN. Some Previous FLOPS =================== FLOPS 2012, Kobe: http://www.org.kobe-u.ac.jp/flops2012/ FLOPS 2010, Sendai: http://www.kb.ecei.tohoku.ac.jp/flops2010/ FLOPS 2008, Ise: http://www.math.nagoya-u.ac.jp/~garrigue/FLOPS2008/ Sponsor ======= Japan Society for Software Science and Technology (JSSST), Special Interest Group on Programming and Programming Languages (SIG-PPL) In Cooperation With =================== ACM SIGPLAN Asian Association for Foundation of Software (AAFS) Association for Logic Programming (ALP)

1 0

New Functional Programming Job Opportunities
by Functional Jobs 19 Nov '13

19 Nov '13

Here are some functional programming job opportunities that were posted recently: Compiler Engineer at BAE Systems http://functionaljobs.com/jobs/8656-compiler-engineer-at-bae-systems Cheers, Sean Murphy FunctionalJobs.com

3 2

Incorrect behavior in Data.Complex ?
by jared simpson 19 Nov '13

19 Nov '13

Prelude Data.Complex> 0**2 0.0 Prelude Data.Complex> 0**2 :: Complex Double NaN :+ NaN Prelude Data.Complex> exp $ 2 * log 0 :: Complex Double NaN :+ NaN Prelude Data.Complex> log 0 :: Complex Double (-Infinity) :+ 0.0 Prelude Data.Complex> 2 * it :: Complex Double (-Infinity) :+ NaN Prelude Data.Complex> exp it :: Complex Double NaN :+ NaN So Complex uses the default implementation of **. Then when 2*(-inf :+ 0) is evaluated. We do (2 * -inf - 0*0) :+ (2*0 + -inf*0). Which because of -inf*0 sets the imaginary part to NaN. Then exp (-inf :+ NaN) = exp x cos y :+ exp x sin y which becomes 0 * cos NaN :+ 0 * sin NaN. So we end up with NaN :+ NaN. So is there a library I should be using, or is this a bug?

2 2

FP Complete Launches Free Community edition of FP Haskell Center
by Natalia Muska 18 Nov '13

18 Nov '13

https://www.fpcomplete.com/business/blog/fp-complete-launches-free-communit… -- Natalia Muska Marketing Manager FP Complete, Inc. Natalia(a)fpcomplete.com 865-506-6513 skype: natalia.s.muska

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Error cabal update: "Unsucessful HTTP code: 404"
by Vaniax 18 Nov '13

18 Nov '13

Hi, I have a big problem with a fresh installation of the Haskell-Platform 2013.2 on Windows 7. When I try to run `cabal update` I get the following error message: "|Downloading the latest package list from hackage.haskell.org cabal: Failed to download http://hackage.haskell.org/packages/archive/00-index.tar.gz : ErrorMisc "Unsucessful HTTP code: 404" When I try ||`wget http://hackage.haskell.org/packages/archive/00-index.tar.gz`everything works alright. I'm using no proxies or something like that. Maybe someone know whats going wrong? A parallel Windows-XP installation of the platform works fine. Vaniax |

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Canberra interest?
by Tony Morris 18 Nov '13

18 Nov '13

Hello, I am from Brisbane, Australia and it is my mission to teach functional programming to all and especially Australia. I am tasked with this mission by my employer, NICTA, which is funded by the Australia government. With support from NICTA, I usually run (free) courses to assist in this mission and have done so in Sydney, Melbourne and Brisbane. However, I often wonder about any interest in Canberra. I do not find any user interest groups related to Functional Programming or language-specific such as Haskell when I search, so I was hoping to seek out any expressions of interest here. Are any of you from Canberra? If so, are you interested in learning more about functional programming? Would you be interested in attending a 2 or 3 day workshop? Do you have peers who would also be interested? If these people exist, how might I contact them? Thanks for any tips! -- Tony Morris http://tmorris.net/

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Word rigid in "`a' is a rigid type variable..."
by Vlatko Basic 16 Nov '13

16 Nov '13

Hi Cafe, in an example function f :: a -> Bool f a = let b = "x" in a == b compiler complains with `a' is a rigid type variable bound by the type signature for f :: a -> Bool I'm puzzled with the choice of word 'rigid' here. I see these types as - 'b' has "rigid/unchangeable" type (only String), and - 'a' has "soft/variable" type (any type, no constraints). Why is it called rigid? Where does the meaning (in this context) come from? Best regards, vlatko

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Re: [Haskell-cafe] how to call a callback in a haskell dll
by Donn Cave 15 Nov '13

15 Nov '13

Quoth "Kees Bleijenberg" <k.bleijenberg(a)lijbrandt.nl>, > My program creates a Windows dll. The calling program calls a function with > strings as parameters. Works fine. > > I want to add a extra parameter. This extra parameter is a callback: a > function Int -> Int: stdcall. In Haskell I want to call this function. So I > have to convert the pointer to a (formal) Haskell function. > > In the examples for the FFI, Haskell provides the callback. I need an > example or documentation. It's unclear to me whether the Haskell program initially chooses the function and creates a pointer to it, or that happens in C/C++. In the former case, I think Foreign.StablePtr serves that purpose. In the latter case, Haskell will receive the function as something like FunPtr (CInt -> CInt), and you need a "dynamic" foreign function to convert the pointer, like foreign import ccall "dynamic" iiPtrStub :: FunPtr (CInt -> CInt) -> (CInt -> CInt) That's lightly documented in the library docs under Foreign.Ptr. Donn

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Tool for visualisation of graph reduction step by step
by Miguel Ramos 15 Nov '13

15 Nov '13

Hello, It has already been asked for on this list, and I think one does not exist, however: (a) Does anyone know of a tool for the stepwise visualisation of graph reduction? I am aware that it could only be used for minimal examples and that the output would be a bit implementation-specific. My interest is not debugging, but simply producing presentation slides. (b) What tools do people use for plotting static program graphs, such as those in books, papers and slides? I am currently using graphviz (dot) but I am not being able to tame it to make the graphs look good and proper for papers and slides. I also have a minimal interpreter, which can currently output each step to graphviz, but it still does not handle enough of the language to be usable and I don't want to divert the focus of my work. Thank you very much, Miguel Lopes Santos Ramos

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Re: [Haskell-cafe] Tool for visualisation of graph reduction step by step
by Stephen Tetley 15 Nov '13

15 Nov '13

On 14 November 2013 12:03, Miguel Ramos <org.haskell(a)miguel.ramos.name> wrote: > > (b) What tools do people use for plotting static program graphs, such as > those in books, papers and slides? Graphviz can be tamed somewhat with ranking - see the examples in the manual. If you want pretty, hand coded graphs then TikZ is a handsome option. It has the obvious edges with or without arrowheads, but also the "anchor" abstraction which is a very neat way of placing edges.

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how to call a callback in a haskell dll
by Kees Bleijenberg 15 Nov '13

15 Nov '13

My program creates a Windows dll. The calling program calls a function with strings as parameters. Works fine. I want to add a extra parameter. This extra parameter is a callback: a function Int -> Int: stdcall. In Haskell I want to call this function. So I have to convert the pointer to a (formal) Haskell function. In the examples for the FFI, Haskell provides the callback. I need an example or documentation. Kees

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ANNOUNCE: Haskell Pdf Presenter (hpdfp) 0.2.2
by Michael D. Adams 15 Nov '13

15 Nov '13

ANNOUNCE: Haskell Pdf Presenter (hpdfp) 0.2.2 I'm pleased to announce the first public release of the Haskell Pdf Presenter (hpdfp). Project home page: http://michaeldadams.org/projects/haskell-pdf-presenter/ Project on Hackage: http://hackage.haskell.org/package/haskell-pdf-presenter/ Project repository: http://michaeldadams.org/repos-pub/hg/haskell-pdf-presenter/ What it is ========== The Haskell Pdf Presenter (hpdfp) is a tool for presenting PDF-based slide shows. For example, as a presenter, I like to see the next slide before it is shown to the audience as well as how much allotted time remains. I was never quite satisfied with the existing tools for this, so I wrote my own and hpdfp is the result. Though I originally wrote it for my own use, the tool has matured over time, and I now wish to share it with others. Aside from being a useful tool, I think hpdfp is a good example of elegance and economy in program design. Despite being only a thousand lines long, this program is full of features that may not be obvious at first glance so please be sure to look at the available help. Status ====== I've been using this tool in my own talks for over a year now, and it is fairly stable and feature complete. I've only tested it on Ubuntu so I don't know if it ports to other platforms. I'd love to hear any field reports about how it runs on other platforms. Future Directions ================= I have a long TODO list of ideas I may implement in the future, but most development has been driven by the practical considerations that I discover as I use the tool. If you have a use case for a particular feature, please let me know. ================ Feature requests, bug reports, suggestions or feedback as well as contributions to the documentation or implementation are most welcome. Michael D. Adams

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