- Haskell-Cafe - Haskell.org

Fwd: Problem with loading unix-compat in GHCi on Windows: is suggested solution acceptable?
by German Zhivotnikov 16 Jun '14

16 Jun '14

Hi all, There is a minor problem with unix-compat module on Windows: when one tries to load it (or the module that depends on it) into GHCi, i.e. in REPL mode, - GHCi refuses to load unix-compat with a message like that: ghc.exe: (skipped).cabal-sandbox\x86_64-windows-ghc-7.8.2\unix-compat-0.4.1.1\HSunix-compat-0.4.1.1.o: unknown symbol 'snprintf' ghc.exe: unable to load package 'unix-compat-0.4.1.1' Note that it only concerns REPL mode: when GHC is building a binary that uses unix-compat, - it produces correct executable that works fine. My hypothese is that this is because in typical Win32 build environment snprintf resides in libmingwex.a, which is static library, which GHCi is incapable of loading. Please correct me if I'm wrong. There is a solution - to make unix-compat depend on MSVCRT.DLL (instead of static mingwex.a) and replace 'snprintf' with Microsoft's '_snprintf' (and there's also stat/_stat to be replaced). However this introduces at least new dependency on MSVCRT.DLL, and maybe something else, which might be unexpected. Therefore, before accepting the solution into official codebase, it would be great to have an input - if anyone can foresee possible unintended side effects from suggested solution for code that depends on unix-compat module. Corresponding pull request resides at https://github.com/jystic/unix-compat/pull/12/files - could you possibly take a look if you've got something to say on that issue. Thank you in advance.

1 0

Uploading to hackage fails: bad file names in tarball
by Arie Peterson 16 Jun '14

16 Jun '14

Since some time, I have been unable to upload packages to Hackage, via either the 'cabal upload' command, or using the web form. The error message it gives is this: ==== ✂ ==== Hackage username: AriePeterson Hackage password: Uploading dist/np-linear-0.1.1.1.tar.gz... Error: dist/np-linear-0.1.1.1.tar.gz: 400 Bad Request Error: Invalid package Invalid windows file name in tar archive: "np-linear-0.1.1.1\\src\\Aux.hs". For portability, hackage requires that file names be valid on both Unix and Windows systems, and not refer outside of the tarball. ==== ✂ ==== The tarball is created by 'cabal sdist': cabal-install version 1.18.0.2 using version 1.18.1.1 of the Cabal library. I also installed the newest cabal-install, on another machine, but this did not help (same error). I also tried to create a tarball by hand, using 'tar --format=ustar', but this again resulted in the same error message. By the way, I'm on linux, not Windows, so it is not clear how the backslashes get in the file names. What could be going on?

3 3

improved jhc manual
by John Meacham 16 Jun '14

16 Jun '14

Hi all, I just wanted to show off the new jhc manual http://repetae.net/computer/jhc/manual.html If anyone has any feedback, that would be great, even better would be patches of course :) Manual writing is not my strong point. The entire manual is in the darcs repo as markdown formatted files or as literate code embedded in the source files. Something I need to figure out is how to get haddock to not barf on jhc's input files. A problem with haddock is that it tries to replicate ghc's module chasing algorithm and falls down when anything is slightly off, jhc's ability to handle recursive modules throws it for a loop. Now I can easily get jhc to spit out fully resolved module names, it does so with the --annotate-source option, but need some sort of hook into haddock saying "don't try to resolve module names, here they all are." Even haddock just having a 'keep going' option would be great to get something out there. Or even improving haddock to handle recursive module imports. John -- John Meacham - http://notanumber.net/

4 7

type families and type classes
by Gautier DI FOLCO 15 Jun '14

15 Jun '14

Hi all, I have a bunch of data types which are "divided" in other data types as following: type FileName = String data FileWish = File FileName deriving (Show, Eq) data FileFact = FileExist | FileDontExist deriving (Show, Eq) data FileAction = FileCreate deriving (Show, Eq) observe :: FileWish -> [FileFact] observe :: undefined plan :: FileWish -> FileFact -> [FileAction] plan (File _) FileDontExist = [FileCreate] plan (File _) FileExist = [] perform :: FileWish -> [FileAction] -> IO () perform :: undefined I want to have a model as extensible as possible, even if I'm new to Haskell, I think that it's preferable to base parts of system on behavior (type classes) rather than data types. So I have File that give a Wish, a Fact (via observe) and a Action (via plan). I want to put observe, plan and perform in different type classes (let's say Observable, Plannable and Performable). When I create a new thing (like File) I want, for example, that : observe :: Wish e -> [Fact e] where e is File. But I want (Fact e) be an instance of Plannable. And so on. At first glance, I think I have to use this: https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/t… But it is coupled to data type and one type class. If you have any hints for me. Maybe I don't take the right way to solve my problem. Thanks in advance.

1 0

Taking a number to a power and taking its mod
by Rafael Almeida 15 Jun '14

15 Jun '14

Hello, I've been trying to do a problem from SPOJ which requires me to find prime numbers in a range. I've been battling with several possibility, so far I have had no luck. I remember primality tests from college. So I looked up the one I knew: fermat's little theorem. It requires me to do this check: a^(p-1) `mod` p == 1 However, taking a number to a large power is very slow. So it was even worse than the solution I was already trying. I'm not here for your guys to give me the solution. But I'm here to understand how can I do that operation quickly. This wiki entry implements powMod http://www.haskell.org/haskellwiki/Testing_primality Calling that funcion with powMod 999999527 2 (999999527-1) is very fast. What's going on? Can someone shed me some light? []'s Rafael

2 2

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.

2 4

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

3 2

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/

1 0

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

2 1

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...

3 2