February 2016 - Haskell-Cafe

[TFP 2016] 1st call for papers
by Peter Achten 02 Feb '16

02 Feb '16

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2016 =========== 17th Symposium on Trends in Functional Programming June 8-10, 2016 University of Maryland, College Park Near Washington, DC http://tfp2016.org/ 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). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. TFP 2016 will be the main event of a pair of functional programming events. TFP 2016 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 7nd. 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; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * Soesterberg (The Netherlands) in 2014; * and Inria Sophia-Antipolis (France) in 2015. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == 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 High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation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 simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: 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 Debugging and profiling 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 2016 program chair, David Van Horn. == 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 CyberPoint, Galois, Trail of Bits, and the University of Maryland Computer Science Department. == 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 (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2016 Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site: http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0 == IMPORTANT DATES == Submission of draft papers: April 8, 2016 Notification: April 15, 2016 Registration: May 13, 2016 TFP Symposium: June 8-10, 2016 Student papers feedback: June 14, 2016 Submission for formal review: July 14, 2016 Notification of acceptance: September 14, 2016 Camera ready paper: October 14, 2016 == PROGRAM COMMITTEE == Amal Ahmed Northeastern University (US) Nada Amin École Polytechnique Fédérale de Lausanne (CH) Kenichi Asai Ochanomizu University (JP) Małgorzata Biernacka University of Wroclaw (PL) Laura Castro University of A Coruña (ES) Ravi Chugh University of Chicago (US) Silvia Ghilezan University of Novi Sad (SR) Clemens Grelck University of Amsterdam (NL) John Hughes Chalmers University of Technology (SE) Suresh Jagannathan Purdue University (US) Pieter Koopman Radboud University Nijmegen (NL) Geoffrey Mainland Drexel University (US) Chris Martens University of California, Santa Cruz (US) Jay McCarthy University of Massachusetts, Lowell (US) Heather Miller École Polytechnique Fédérale de Lausanne (CH) Manuel Serrano INRIA, Sophia-Antipolis (FR) Scott Smith Johns Hopkins University (US) Éric Tanter University of Chile (CL) David Van Horn (Chair) University of Maryland (US) Niki Vazou University of California, San Diego (US)

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Instance match surprise
by Wojtek Narczyński 02 Feb '16

02 Feb '16

Dear List, Why does the first instance match? ANY is neither Eq nor Typeable. I thought I had some basic understanding of type classes, and now this... wojtek@biuro:~/src/he$ cat minimatch.hs {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE MultiParamTypeClasses #-} module MiniMatch where import Data.Typeable data A130 = A130 deriving (Eq) data ANY = ANY class AtmAcct a class Against q class (AtmAcct a, Against q) => Match a q where match :: a -> q -> Bool instance AtmAcct A130 instance Against ANY instance (Eq a, Eq q, Typeable a, Typeable q, AtmAcct a, Against q) => Match a q where match _ _ = False instance (AtmAcct a) => Match a ANY where match _ _ = True m1 = match A130 ANY -- offending line wojtek@biuro:~/src/he$ ghc minimatch.hs [1 of 1] Compiling MiniMatch ( minimatch.hs, minimatch.o ) minimatch.hs:21:6: error: • Overlapping instances for Match A130 ANY arising from a use of ‘match’ Matching instances: instance (Eq a, Eq q, Typeable a, Typeable q, AtmAcct a, Against q) => Match a q -- Defined at minimatch.hs:18:10 instance AtmAcct a => Match a ANY -- Defined at minimatch.hs:19:10 • In the expression: match A130 ANY In an equation for ‘m1’: m1 = match A130 ANY -- Thanks, Wojtek Narczyński

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why is rpar/rpar always faster (book Simon Marlow)?
by Kees Bleijenberg 01 Feb '16

01 Feb '16

I'am reading the book Parallel and Concurrent Programming in Haskell. The book has an explanation of the Eval monad. It compares rpar/rpar (example 2-1), rpar/rseq (example 2-2), rpar/rseq/rpar (example 2-3) and rpar/rpar/rseq/rseq in rpar.hs The examples run all in the total time 0.82 s. When I run rpar/rpar (example2-1) on my computer total time is 1.34 s. All other examples have total time 2.22 s. I'am running the examples exactly as written in the book. I tried the examples in opposite order, but the rpar/rpar example remains a lot faster. I wonder why the other examples are so much slower and why is it so different from the book? I run the examples on a computer with 4 cores. I'am using ghc version 7.10.1 on Win64. The Haskell version is 32 bits. If I run the examples with +RTS -N1 all examples use the same time (2.20 sec). Kees

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Question, re: failed attempt at constraining a Traversable instance.
by David Banas 01 Feb '16

01 Feb '16

Hi all, I’m trying to do this: data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a) instance Functor Tree where fmap g Empty = Empty fmap g (Leaf x) = Leaf (g x) fmap g (Node t1 x t2) = Node (fmap g t1) (g x) (fmap g t2) instance Foldable Tree where foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r instance (Monoid (f (Tree a))) => Traversable (Tree (f a)) where sequenceA Empty = pure Empty sequenceA (Leaf f) = Leaf <$> f sequenceA (Node t1 f t2) = (sequenceA t1) `mappend` (Leaf <$> f) `mappend` (sequenceA t2) And I’m being told this: The first argument of ‘Traversable’ should have kind ‘* -> *’, but ‘Tree (f a)’ has kind ‘*’ In the instance declaration for ‘Traversable (Tree (f a))’ And I don’t quite understand what I’m asking for that’s forbidden. Is it that I’m trying to declare that only a certain subset of Trees are Traversable, and that’s not okay? It’s got to be all Trees or no Trees are Traversable? Thanks, -db

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Share a variable across GHCI sessions: Possible?
by Jeffrey Brown 01 Feb '16

01 Feb '16

Suppose v is a view onto some data in a graph[1]. You ask GHCI to (show $ nodes v). You would like to ask GHCI in another window to (show $ disambiguations v), referring to the same v. Is it possible? My motivation is to show disambiguations that are about the nodes. Examples of disambiguations would be "a ! character adjacent to the left of a word means it requires money", or "CAP stands for Coastal Alliance of Pharoahs", or "a(/n)b means a needs b". [1] Using the Functional Graph Library, I am writing a graph database editor, Digraphs With Text: https://github.com/JeffreyBenjaminBrown/digraphs-with-text DWT is exceptionally flexible. Relationships can be of any arity, and can involve other relationships. For instance, in DWT the relationship "_ needs _ in order to _" has a natural representation; I am unaware of any other system in which it does. I would *love* help! And I take job offers seriously! -- Jeffrey Benjamin Brown

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