June 2014 - Haskell-Cafe

Splitting HList
by Gautier DI FOLCO 15 Jun '14

15 Jun '14

Hello, I want to know if it is possible to split a HList? I want to have a function like this: splitV :: HList (s ++ s') -> (HList s, HList s') splitV = _ So I have begun by something which I thought simple: type family HSplit (ts :: [k]) (xs :: [k]) :: ([k], [k]) type instance HSplit ts xs = ([xs], SndHSplit ts xs) type family SndHSplit (ts :: [k]) (xs :: [k]) :: [k] type instance SndHSplit ts '[] = ts type instance SndHSplit (t ': ts) (x ': xs) = SndHSplit ts xs But I get the following error: H.hs:133:50: The second argument of ‘SndHSplit’ should have kind ‘[k0]’, but ‘xs’ has kind ‘*’ In the type ‘([xs], SndHSplit ts xs)’ In the type instance declaration for ‘HSplit’ I don't understand why because xs and the first element of the tuple have the same kind ([k]). Thanks by advance for your help/explanations.

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RFC: Unicode primes and super/subscript characters in GHC
by Mikhail Vorozhtsov 15 Jun '14

15 Jun '14

Hello lists, As some of you may know, GHC's support for Unicode characters in lexemes is rather crude and hence prone to inconsistencies in their handling versus the ASCII counterparts. For example, APOSTROPHE is treated differently from PRIME: λ> data a +' b = Plus a b <interactive>:3:9: Unexpected type ‘b’ In the data declaration for ‘+’ A data declaration should have form data + a b c = ... λ> data a +′ b = Plus a b λ> let a' = 1 λ> let a′ = 1 <interactive>:10:8: parse error on input ‘=’ Also some rather bizarre looking things are accepted: λ> let ᵤxᵤy = 1 In the spirit of improving things little by little I would like to propose: 1. Handle single/double/triple/quadruple Unicode PRIMEs the same way as APOSTROPHE, meaning the following alterations to the lexer: primes -> U+2032 | U+2033 | U+2034 | U+2057 symbol -> ascSymbol | uniSymbol (EXCEPT special | _ | " | ' | primes) graphic -> small | large | symbol | digit | special | " | ' | primes varid -> (small { small | large | digit | ' | primes }) (EXCEPT reservedid) conid -> large { small | large | digit | ' | primes } 2. Introduce a new lexer nonterminal "subsup" that would include the Unicode sub/superscript[1] versions of numbers, "-", "+", "=", "(", ")", Latin and Greek letters. And allow these characters to be used in names and operators: symbol -> ascSymbol | uniSymbol (EXCEPT special | _ | " | ' | primes | subsup ) digit -> ascDigit | uniDigit (EXCEPT subsup) small -> ascSmall | uniSmall (EXCEPT subsup) | _ large -> ascLarge | uniLarge (EXCEPT subsup) graphic -> small | large | symbol | digit | special | " | ' | primes | subsup varid -> (small { small | large | digit | ' | primes | subsup }) (EXCEPT reservedid) conid -> large { small | large | digit | ' | primes | subsup } varsym -> (symbol (EXCEPT :) {symbol | subsup}) (EXCEPT reservedop | dashes) consym -> (: {symbol | subsup}) (EXCEPT reservedop) If this proposal is received favorably, I'll write a patch for GHC based on my previous stab at the problem[2]. P.S. I'm CC-ing Cafe for extra attention, but please keep the discussion to the GHC users list. [1] https://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts [2] https://ghc.haskell.org/trac/ghc/ticket/5108

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Second Call for Papers: OCL 2014
by Achim D. Brucker 13 Jun '14

13 Jun '14

(Apologies for duplicates) CALL FOR PAPERS 14th International Workshop on OCL and Textual Modeling Applications and Case Studies (OCL 2014) Co-located with ACM/IEEE 17th International Conference on Model Driven Engineering Languages and Systems (MODELS 2014) September 28-30 (tbc), 2014, VALENCIA, SPAIN http://www.software.imdea.org/OCL2014/ Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but some of their features are difficult to formalize and lack the level of precision required to create complete and unambiguous specifications. Limitations of the graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. Topics of interest include (but are not limited to) =================================================== - Mappings between textual modeling languages and other languages/formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for -- validation, verification, and testing, -- model transformation and code generation, -- metamodeling and DSLs, and -- query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports -- usage of textual modeling languages and tools in complex domains, -- usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing applications and case studies of textual modeling as well as test suites and benchmark collections for evaluating textual modeling tools. Venue ===== The workshop will be organized as a part of MODELS 2014 Conference in Valencia, Spain. It continues the series of OCL workshops held at UML/MODELS conferences: York (2000), Toronto (2001), San Francisco (2003), Lisbon (2004), Montego Bay (2005), Genova (2006), Nashville (2007), Toulouse (2008), Denver (2009), Oslo (2010), Zurich (2011, at the TOOLs conference), 2012 in Innsbruck, and 2013 in Miami. Similar to its predecessors, the workshop addresses both people from academia and industry. The aim is to provide a forum for addressing integration of OCL and other textual modeling languages, as well as tools for textual modeling, and for disseminating good practice and discussing the new requirements for textual modeling. Workshop Format =============== The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. Submissions =========== Two types of papers will be considered: * short papers (6 pages) and * full papers (10 pages) in LNCS format. Submissions should be uploaded to EasyChair (https://www.easychair.org/conferences/?conf=ocl2014) The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a pre-conference edition of CEUR (http://www.ceur-ws.org) Authors of selected papers will be invited to submit an extended version of their workshop paper to a special issue of the Electronic Communications of the EASST (http://journal.ub.tu-berlin.de/eceasst) Important Dates =============== Submission of papers: July 11, 2014 Notification: August 8, 2014 Workshop date: one day during September 28-30, 2014 Organizers ========== Achim D. Brucker, SAP AG, Germany Carolina Dania, IMDEA Software Institute, Madrid, Spain Geri Georg, Colorado State University, Fort Collins, Colorado, USA Martin Gogolla, University of Bremen, Germany Programme Committee (partly confirmation pending) =================== Michael Altenhofen, SAP AG, Germany Thomas Baar, University of Applied Sciences Berlin, Germany Mira Balaban, Ben-Gurion University of the Negev, Israel Tricia Balfe, Nomos Software, Ireland Fabian Buettner, Ecole des Mines de Nantes, France Achim D. Brucker, SAP AG, Germany Jordi Cabot, INRIA-Ecole des Mines de Nantes, France Yoonsik Cheon, University of Texas, USA Dan Chiorean, Babes-Bolyai University, Romania Robert Clariso, Universitat Oberta de Catalunya, Spain Tony Clark, Middlesex University, UK Manuel Clavel, IMDEA Software Institute, Madrid, Spain Carolina Dania, IMDEA Software Institute, Madrid, Spain Birgit Demuth, Technische Universitat Dresden, Germany Marina Egea, Atos Research, Madrid, Spain Geri Georg, Colorado State University, Fort Collins, Colorado, USA Martin Gogolla, University of Bremen, Germany Pieter Van Gorp, Eindhoven University of Technology, The Netherlands Heinrich Hussmann, LMU Munchen, Germany Tihamer Levendovszky, Vanderbilt University, USA Shahar Maoz, Tel Aviv University, Israel Istvan Rath, Budapest University of Technology and Economics, Hungary Bernhard Rumpe, RWTH Aachen, Germany Shane Sendall, Snowie Research SA, Switzerland Michael Wahler, ABB Switzerland Ltd Corporate Research, Switzerland Claas Wilke, Technische Universitat Dresden, Germany Edward Willink, Willink Transformations Ltd., UK Burkhart Wolff, Univ Paris-Sud, France Steffen Zschaler, King’s College, London, UK -- Dr. Achim D. Brucker, SAP AG, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, http://www.brucker.ch/

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Re: [Haskell-cafe] ANN: io-memoize 1.1
by Peter Simons 13 Jun '14

13 Jun '14

Hi Dan, > 1. Create an empty cache with newCache > 2. fetch repeatedly from the cache, each time providing a fallback in > case it is empty. > > Fetching from a Cache is thread safe: only one "fallback" will execute > at a time, and after the first successful fallback, the cached value > will be set and no other fallbacks will be called. I'm not sure whether I get this correctly. If multiple threads fetch values from one cache, will only one of those threads run at a time? Or will those that fetch pairwise different values still run concurrently? In other words, does the cache have a global lock or is there a lock per value? Best regards, Peter

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Not in scope
by Julian K. Arni 13 Jun '14

13 Jun '14

I have a lot of boilerplate code that th-desugar has made significantly more manageable (thanks Richard!). Somewhere in the midst of it, I have: >> type_equal (DContT n1) (DContT n2) = {...} Which, when I compile with cabal, gives me: src/Language/Haskell/TH/Alpha.hs:180:13: Not in scope: data constructor ‘DContT’ Perhaps you meant one of these: ‘DConT’ (imported from Language.Haskell.TH.Desugar), ‘DConE’ (imported from Language.Haskell.TH.Desugar), ‘DConPa’ (imported from Language.Haskell.TH.Desugar) src/Language/Haskell/TH/Alpha.hs:180:25: Not in scope: data constructor ‘DContT’ Perhaps you meant one of these: ‘DConT’ (imported from Language.Haskell.TH.Desugar), ‘DConE’ (imported from Language.Haskell.TH.Desugar), ‘DConPa’ (imported from Language.Haskell.TH.Desugar) Huh? Of course 'DConT' is what I meant - that's exactly what I wrote! What in the world is going on? GHC is happy with all the other constructors! I tried rewriting, just to be sure I didn't *somehow* get a tricky unicode character in there...

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Cross compiling Haskell from Linux to Windows with GHCs LLVM backend?
by Rob Stewart 13 Jun '14

13 Jun '14

Hi, I compile my code with GHC on Linux, and don't have ready access to a Windows or a Mac operating system. Is it possible to use the GHC LLVM backend as a means to cross compile Haskell code to target multiple operating systems? I had envisaged it possible to generate the LLVM IR using GHCs -keep-llvm-files flag, and using LLVMs target triple flag to specify the CPU architecture and operating system of the users machine. I'd like to compile on Linux, to target WIndows and Mac machines. Strangely I cannot find blog posts or tutorials online for cross-compiling Haskell with GHC via LLVM. Is it possible? Thanks, -- Rob

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Re: [Haskell-cafe] [Haskell] ANN: io-memoize 1.1
by Kim-Ee Yeoh 13 Jun '14

13 Jun '14

On Thu, Jun 12, 2014 at 4:47 PM, Dan Burton <danburton.email(a)gmail.com> wrote: > Have you ever wanted to restrict an IO action such that it could only be > invoked once? Now you can with System.IO.Memoize.once (formerly known as > ioMemo). > (Moving to cafe for dicussion ...) I may want a one-time only IO action, although so far the need hasn't arisen yet. ;) In the spirit of pilfering while the buns are still hot out of the oven, is there a backstory for this package you could possibly sketch out? Some canonical use case maybe? -- Kim-Ee

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Opening for OpenGL, C++ Development.
by Manoj Chaudhari 12 Jun '14

12 Jun '14

Hello, We are looking for Software Developers with OpenGL experience. - Should have experience in C++/Xcode, OpenGL/DirectX/IOS. - Experience with Shafer programming, Multi-threaded applications, Graphics in CAD domain. - The role is of Software Development on primary CAD application like CATIA. - Good skills in Geometry, algorithms, Mathematics, API's, Graphics-will be a added advantage. Experience : 2 to 6 years. If anyone is interested on learning more about this opportunity and potential salary ranges, please email me at : manoj_chaudhari2(a)3dplmsoftware.com Regards, Manoj Chaudhari

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Troubles installing EclipseFP
by Vagif Verdi 12 Jun '14

12 Jun '14

Hi, i'm trying to install eclipsefp. Ubuntu 14.04, ghc 7.6.3, cabal-install 1.20. I did it with a fresh .cabal and .ghc folders. Nothing else was installed. After restarting eclipse it started doenloading and building haskell libs, and stopped with this error: Cabal==1.16.0/installed-c6e..., SourceGraph => Cabal<1.7) rejecting: SourceGraph-0.2, 0.1 (conflict: buildwrapper => Cabal==1.16.0/installed-c6e..., SourceGraph => Cabal<1.5) Backjump limit reached (change with --max-backjumps). Note: when using a sandbox, all packages are required to have consistent dependencies. Try reinstalling/unregistering the offending packages or recreating the sandbox.

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ghc-options: -dynamic in package refused by Hackage
by JP Moresmau 12 Jun '14

12 Jun '14

Hello, what's the recommended way to make a package dynamic? 1. I need to make the executable in my package dynamic otherwise I run into https://ghc.haskell.org/trac/ghc/ticket/8376 2. I've set ghc-options: -dynamic in my Cabal file and that solves my issues. 3. I can't upload my package to Hackage, I get a "'ghc-options: -d*' debug flags are not appropriate for a distributed package" error. I hadn't realized -dynamic is for debugging purposes... So is there another way to make my package dynamic and uploadable to Hackage? Or should I just not put the flag in the cabal flag and let my users pass the flag when they install? Thanks! JP -- JP Moresmau http://jpmoresmau.blogspot.com/

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