October 2008 - Haskell-Cafe

having fun with GADT's
by Anatoly Yakovenko 03 Oct '08

03 Oct '08

I dont remember where i saw it, but i think someone had an example of a list whose type is the maximum element in the list. I've been trying to reproduce that with GADT's. data One = One data Two = Two data Three = Three data MaxList t where Elem1 :: MaxList One Elem2 :: MaxList Two ML1Cons1 :: MaxList One -> MaxList One -> MaxList One ML1Cons2 :: MaxList One -> MaxList Two -> MaxList Two ML2Cons1 :: MaxList Two -> MaxList One -> MaxList Two ML2Cons2 :: MaxList Two -> MaxList Two -> MaxList Two a = ML2Cons2 Elem2 $ ML2Cons1 Elem2 $ ML1Cons1 Elem1 $ Elem1 so one problem is the tedium of defining a cons for each possible combination. The other problem is that i cant define a usefull tail that makes any sense. mlTail :: MaxList Two -> MaxList t mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b this one doesn't work, and probably because there is nothing that i could do with the return value. mlTail :: MaxList Two -> MaxList Two mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b --wont compile because b is a MaxList One will only work for lists that only contain Two's, which is not what i want either. So is this somehow possible? Thanks

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Building gtkhs, OpenSolaris x86
by Lally Singh 03 Oct '08

03 Oct '08

Hey folks, I know it seems an obtuse OS to build on, but trust me, it's pretty nice despite the hassles. I'm getting these three errors (repeated a few times) while building gtkhs-0.9.13 on ghc 6.8.3, and was hoping for any suggestions on where to go from here: tools/c2hs/base/general/Map.hs:16:7: Could not find module `Data.Map': it is a member of package containers-0.1.0.2, which is hidden tools/c2hs/base/errors/Errors.hs:44:0: Failed to load interface for `Position': Use -v to see a list of the files searched for. glib/System/Glib.hs:13:0: Failed to load interface for `System.Glib.UTFString': Use -v to see a list of the files searched for. What did I screw up? Is there something else I should load? Maybe an older version of gtkhs? ghc? Thanks for any help! -- H. Lally Singh Ph.D. Candidate, Computer Science Virginia Tech

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Alex and Flex
by Manlio Perillo 03 Oct '08

03 Oct '08

Hi. I'm starting to write a CSS parser with Alex and Happy. The grammar is defined here: http://www.w3.org/TR/CSS21/grammar.html However I have noted that there are some difference in the syntax between Alex and Flex? What is the rationale? One more thing. Here: http://www.haskell.org/alex/doc/html/alex-files.html it seems that there is an error with macrodef := @smac '=' set | @rmac '=' regexp it should be macrodef := $smac '=' set | @rmac '=' regexp Thanks Manlio Perillo

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Monoids [Stacking monads]
by Andrew Coppin 03 Oct '08

03 Oct '08

Ryan Ingram wrote: > Newtypes is the general (& sadly unsatisfactory) answer: > Oh dear. Well that _is_ pretty unsatisfactory... Given the constraints of the Haskell type system, could we do better in principle?

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Source of 16x16 Sudokus?
by Murray Gross 03 Oct '08

03 Oct '08

Folks: For research on the behavior of parallel Haskell, does anyone know of a source for graded (easy through evil) 16x16 Sudoku puzzles? Our hardware runs too fast for us to get meaningful timings on 9x9's. I suppose we could insert time wasters, but I think that would also distort the results . . . . Thanks in advance, Murray Gross Brooklyn College

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Kind-agnostic type classes
by Florian Weimer 03 Oct '08

03 Oct '08

I'm trying to encode a well-known, informally-specified type system in Haskell. What causes problems for me is that type classes force types to be of a specific kind. The system I'm targeting however assumes that its equivalent of type classes are kind-agnositic. For instance, I've got class Assignable a where assign :: a -> a -> IO () class Swappable a where swap :: a -> a -> IO () class CopyConstructible a where copy :: a -> IO a class (Assignable a, CopyConstructible a) => ContainerType a class (Swappable c, Assignable c, CopyConstructible c) => Container c where size :: (Num i, ContainerType t) => c t -> IO i I suppose I could address this with creating aliases for the relevant classes, but I wonder if there is a better workaround. I see that the ML module system has a similar restriction on type sharing. Is there a fundamental reasons behind this?

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Re: [Haskell-cafe] Haskell participating in big science like CERN Hadrian...
by Rafael Gustavo da Cunha Pereira Pinto 03 Oct '08

03 Oct '08

> > > > On Fri, Oct 3, 2008 at 07:47, Dougal Stanton <dougal(a)dougalstanton.net>wrote: > >> 2008/10/3 Galchin, Vasili <vigalchin(a)gmail.com>: >> > Hello, >> > >> > One of my interests based on my education is "grand challenge >> science". >> > Ok .. let's take the CERN Hadrian Accelerator. >> > >> > Where do you think Haskell can fit into the CERN Hadrian effort >> > currently? >> > >> > Where do you think think Haskell currently is lacking and will have >> to >> > be improved in order to participate in CERN Hadrian? >> >> Is that the experiment where Picts are accelerated to just short of >> the speed of light in order to smash through to the Roman Empire? ;-) >> > Man, that was almost as good as the Large Hardon Collider<http://largehardoncollider.com/> !!! > >> I don't know what the main computational challenges are to the LHC >> researchers. The stuff in the press has mostly been about >> infrastructure --- how to store the gigabytes of data per second that >> they end up keeping, out of the petabytes that are produced in the >> first place (or something). >> >> > There is a lot of data filtering, looking for the right trigger event... -- Rafael Gustavo da Cunha Pereira Pinto Electronic Engineer, MSc.

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Is Haskell-Cafe down?
by Benjamin L.Russell 03 Oct '08

03 Oct '08

About two hours ago, I sent two follow-ups to the "Announcing OneTuple-0.1.0" thread on the Haskell-Cafe mailing list, neither of which has appeared in either my newsreader or my Inbox, even though they have both appeared on the Web archive; viz.: [Haskell-cafe] Re: Announcing OneTuple-0.1.0 http://www.haskell.org/pipermail/haskell-cafe/2008-October/048633.html [Haskell-cafe] Re: Announcing OneTuple-0.1.0 http://www.haskell.org/pipermail/haskell-cafe/2008-October/048636.html Is Haskell-Cafe down? -- Benjamin L. Russell

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mysql (hsql-mysql-1.7) on Linux with GHC 8.3 - cabal issues
by Anton Tayanovskyy 03 Oct '08

03 Oct '08

Hello, I had some difficulty building hsql and hsql-mysql (native driver) packages under GHC 8.3 on Fedora 9. Namely, they do not install with cabal install, because of a few API changes. Is this considered all right as GHC 8.3 is still experimental, or should the packages be updated? If so, can somebody please do it. I love when things just work with cabal install! The problem looks very basic -- just some Cabal file incompatibilities. However I am not experienced with the Cabal build process, so I'll just write what I did to get it to work on my platform, maybe it will help someone. == hsql.cabal == name: hsql version: 1.7 license: BSD3 author: Krasimir Angelov <ka2_mail(a)yahoo.com> category: Database description: Simple library for database access from Haskell. exposed-modules: Database.HSQL, Database.HSQL.Types build-depends: base, old-time build-type: Simple ghc-options: -O2 extensions: ForeignFunctionInterface, TypeSynonymInstances, CPP, RankNTypes, DeriveDataTypeable == hsql-mysql.cabal == name: hsql-mysql version: 1.7 license: BSD3 author: Krasimir Angelov <kr.angelov(a)gmail.com> category: Database description: MySQL driver for HSQL. ghc-options: -O2 build-depends: base, hsql, Cabal, old-time extensions: ForeignFunctionInterface, CPP include-dirs: Database/HSQL, /usr/include/mysql build-type: Simple extra-source-files: Database/HSQL/HsMySQL.h extra-libraries: mysqlclient extra-lib-dirs: /usr/lib/mysql exposed-modules: Database.HSQL.MySQL == hsql-mysql*/Setup.lhs == #!/usr/bin/runghc \begin{code} import Distribution.Simple main = defaultMain \end{code} Of course this hsql-mysql.cabal should not mention Fedora-specific locations as /usr/lib/mysql and /usr/include/mysql but I don't know how to make that generic. The original version had a big custom Setup.lhs file which wouldn't compile with the new Cabal and which I couldn't tweak myself. Thanks, --A

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ANN: Haskell-Embedded System Design: ForSyDe 3.0 and Tutorial
by Alfonso Acosta 03 Oct '08

03 Oct '08

Hi everyone, I am glad to announce the 3.0 release of ForSyDe's implementation, now available from HackageDB. The ForSyDe (Formal System Design) methodology has been developed with the objective to move system design (e.g. System on Chip, Hardware and Software systems) to a higher level of abstraction. ForSyDe is implemented as a Haskell-embedded behavioral DSL (Domain Specific Language). >From this release, ForSyDe includes a new deep-embedded DSL and embedded compiler. We have also published tutorial which should be much more user-friendly than the Haddock documentation and the ForSyDe research papers. ForSyDe includes two DSL flavours which offer different features: 1) Deep-embedded DSL (ForSyDe.Signal) Deep-embedded signals, based on the same concepts as Lava, are aware of the system structure. Based on that structural information ForSyDe's embedded compiler, can perform different analysis and transformations. o Thanks to Template Haskell, computations are expressed in Haskell, not needing to specifically design a DSL for that purpose. o Embedded compiler backends: + Simulation + VHDL (with support for Modelsim and Quartus II) + GraphML (with yFiles graphical markup support.) o Synchronous model of computation. o Support for components. o Support for fixed-sized vectors à la VHDL. 2) Shallow-embedded DSL (ForSyDe.Shallow.Signal) Shallow-embedded signals are modeled as streams of data isomorphic to lists. Systems built with them are unfortunately restricted to simulation, however, shallow-embedded signals provide a rapid-prototyping framework with which to experiment with Models of Computation (MoCs). o Synchronous MoC. o Untimed MoC. o Continuous Time MoC. o Domain Interfaces allow connecting various subsystems with different timing (domains) regardless of their MoC. o Deep-embedded models can be integrated through simulation. Links ==== ForSyDe website: http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/ ForSyDe tutorial: http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/files/tutorial/t… HackageDB package page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/ForSyDe Darcs repository: darcs get http://www.ict.kth.se/org/ict/ecs/sam/projects/forsyde/www/darcs/ForSyDe/

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