[Haskell-cafe] ANNOUNCE: rethinkdb 0.1.0
Greetings, I am pleased to announce a Haskell client library for RethinkDB[1]. RethinkDB[2] is a newly released, open source, distributed database. Its simple yet powerful API seemed well suited to be accessed from a language like Haskell. This haskell library is modelled upon the existing Javascript and Python API and adds static type checking. Here is an example from the RethinkDB javascript tutorial[3] ported to Haskell: run h $ orderBy [reduction] . groupedMapReduce (! Stname) mapF (0 :: NumberExpr) (R.+) . filter' filterF . pluck [Stname, POPESTIMATE2011, Dem, GOP] . zip' $ eqJoin (table county_stats) Stname (table polls) where mapF doc = ((doc ! POPESTIMATE2011) R.* ((doc ! GOP) R.- (doc ! Dem))) R./ (100 :: Int) filterF doc = let dem = doc ! Dem :: NumberExpr; gop = doc ! GOP in (dem R. gop) `and'` ((gop R.- dem) R. (15::Int)) What is the advantage of RethinkDB? [4] What's really special about all RethinkDB queries is that the program you wrote gets sent to the server, broken up into chunks, sent to relevant shards, executed completely in parallel (to the degree that the query makes possible -- complex queries often have multiple parallelization and recombination stages), but as a user you don't have to care about that at all. You just get the results. [...] Of course the visceral experience you get from using RethinkDB isn't just about the query language, or parallelization, or pleasant client libraries. It's about hundreds upon hundreds of examples like it, some large, some small, that add up to a completely different product. The team is fastidious about every command, every pixel, every algorithm, sometimes even every assembly instruction, so that people can use the product and at every step say `Wow, I can't believe how easy this was, how do they do that?!!' I hope this library can help other Haskell programmers use this new database. Etienne Laurin [1] http://hackage.haskell.org/package/rethinkdb [2] http://www.rethinkdb.com [3] http://www.rethinkdb.com/docs/tutorials/elections/ [4] http://www.quora.com/RethinkDB/What-is-the-advantage-of-RethinkDB-over-MongoDB ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: rethinkdb 0.1.0
http://www.quora.com/RethinkDB/What-is-the-advantage-of-RethinkDB-over-MongoDB How about a URL for those who prefer not to be sold by Facebook? Sorry I did not realise there was an intrusive login dialog on that page. You can click on the close link in the login dialog to view the content of the page. Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundeps and overlapping instances
| Abandoning fundeps would be a sad day for type-level programming. | There are many things other than overlaps that you can do with fundeps | and constraint kinds that you cannot currently do with type families, | such as: | | - Partial application or higher-order programming. | - Short-circuit evaluation, lazy evaluation or type-level case. Etienne, I think it would be a good service to make Haskell wiki page describing the difference between fundeps and type families, and in particular describing things that can be done with the former but not the latter. Simon Thanks for the idea. Here it is. http://hackage.haskell.org/trac/ghc/wiki/TFvsFD I posted my comments on the matter along with many additional comments and examples that I found. +1 That would be great. I'll link to Etienne's wiki from the Discussion page I've started for NewAxioms http://hackage.haskell.org/trac/ghc/wiki/NewAxioms In particular, it would be good to tease out where we're getting interference or inter-dependence between different type-level extensions: Overlaps Fundeps UndecidableInstances (that is, breaking the coverage conditions) ScopedTypeVariables I did not check what extensions were turned on in my examples. Given that that the Fundeps idea is taken from relational theory, and relations is just another way of representing functions, there ought to be close correspondence to type-level functions. I put a few examples of the unexpected behaviour of Fundeps on the Wiki page. To me, NewAxioms is aiming at type-level case, to provide a different style of defining type functions, as well as dis-overlapping overlaps. I am eager to see that in action. Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundeps and overlapping instances
Hello, 2012/6/1 Iavor Diatchki iavor.diatc...@gmail.com: There is no problem if an instances uses a type family in it's assumption---the instances should be accepted only if GHC can see enough of the definition of the type family to ensure that the functional dependency holds. This is exactly the same as what it would do to check that a super class constraint holds. GHC cannot see enough of the definition because type families are open. The type instances are not guaranteed to all be in scope when the class instance is defined. 2012/6/1 AntC anthony_clay...@clear.net.nz: Some of Oleg's instances are awesome (and almost impenetrable -- the TTypeable code is a tour de force). It's all so *dys-functional* (IMO). It's like a typed Prolog with a different order of evaluation. My take is that we should abandon Fundeps, and concentrate on introducing overlaps into type functions in a controlled way (what I've called 'dis- overlapped overlaps'.) Abandoning fundeps would be a sad day for type-level programming. There are many things other than overlaps that you can do with fundeps and constraint kinds that you cannot currently do with type families, such as: - Partial application or higher-order programming. - Short-circuit evaluation, lazy evaluation or type-level case. To study the differences, I have been porting parts of the Prelude to both type classes and type families. http://code.atnnn.com/projects/type-prelude/repository/entry/Prelude/Type.hs http://code.atnnn.com/projects/type-prelude/repository/entry/Prelude/Type/Families.hs Etienne Laurin On Wed, May 30, 2012 at 11:14 PM, Etienne Laurin etie...@atnnn.com wrote: 1. Check that an instance is consistent with itself. For example, this should be rejected: instance C a b because it allows C Int Bool and C Int Char which violate the functional dependency. This check may not always be as straightforward. When would this be a valid instance? instance K a b ⇒ C a b With a few extra extensions, K could be a type family. C currently has the kind (a - b - Constraint), with no mention of functional dependencies. Perhaps the kind of C should include the functional dependencies of C? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundeps and overlapping instances
2012/5/31 Iavor Diatchki iavor.diatc...@gmail.com: Hello, the notion of a functional dependency is well established, and it was used well before it was introduced to Haskell (for example, take a look at http://en.wikipedia.org/wiki/Functional_dependency). So I'd be weary to redefine it lightly. Indeed, GHC's functional dependencies are not the same. I see you have already talked about this on the GHC bug tracker. http://hackage.haskell.org/trac/ghc/ticket/1241 1. Check that an instance is consistent with itself. For example, this should be rejected: instance C a b because it allows C Int Bool and C Int Char which violate the functional dependency. This check may not always be as straightforward. When would this be a valid instance? instance K a b ⇒ C a b With a few extra extensions, K could be a type family. C currently has the kind (a - b - Constraint), with no mention of functional dependencies. Perhaps the kind of C should include the functional dependencies of C? Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fundeps and overlapping instances
Hello, I disagree with your example. 1. Check that an instance is consistent with itself. For example, this should be rejected: instance C a b because it allows C Int Bool and C Int Char which violate the functional dependency. Functional dependencies are not used to pick types, they are used to pick instances. class C a b | a → b where k ∷ a f ∷ a → Maybe b The functional dependency allows you to have a method such as k that doesn't use all the arguments of the class. I expect to be able to make a instance that works for any b. instance C Int b where k = 2 f _ = Nothing Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: cabal-ghci 0.1
Hello fellow hackers. Here is a helpful package I wrote to ease the development of projects using cabal. It includes a :cabalset ghci command to set ghci options for your project, and a cabal-ghci executable to launch ghci with those options. Do you get errors when loading your project into ghci? Prelude a ← return 1 interactive:1:3: Not in scope: `←' Prelude :load Main Could not find module `Main': it is not a module in the current program, or in any known package. cabalset fixes these problems for you. Prelude :cabalset :set -i/home/atnnn/up1/src/dist/build/autogen :set -i/home/atnnn/up1/src/web :set -XUnicodeSyntax :set -Wall Prelude a ← return 1 interactive:1:12: Warning: Defaulting the following constraint(s) to type `Integer' (Num t0) arising from the literal `1' Prelude :load Main Ok, modules loaded: Main, Application, Handlers. This works from any sub-directory of your project and accepts the following arguments: -fflagenable flag -f-flag disable flag exec load options for the exec executable To install: $ cabal update $ cabal install cabal-ghci $ cat ~/.ghci :m + Distribution.Dev.Interactive :def cabalset cabalSet :cabalset :m - Distribution.Dev.Interactive ^D Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: cabal-ghci 0.1
Here is a helpful package I wrote to ease the development of projects using cabal. Is :cabalset custom per project or could I put the same things in my ~/.ghci? Everytime I run :cabalset or cabal-ghci, it looks for a .cabal file in my current directory or any of its parents, it loads the cabal file and it generates a list of ghci options for that project. Did you know that cabal-dev supports loading your project into ghci? Yes :) Sadly, some of my test and build scripts don't yet work with cabal-dev. (I'm trying to understand how cabal-ghci is different than existing tools.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: cabal-ghci 0.1
thank you very much for this helpful tool! :) I notice that Haddock has trouble parsing the documentation: http://hackage.haskell.org/packages/archive/cabal-ghci/0.1/logs/failure/ghc-7.2 Is that error hard to fix? I have uploaded a new version of the source with haddock documentation. Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Input and output of mathematical expressions
Henning Thielemann lemming at henning-thielemann.de writes: On Thu, 9 Jun 2011, Jacek Generowicz wrote: On 2011 Jun 9, at 16:59, Chris Smith wrote: Ae you looking to do this in a web application, or client-side? Since one of your requirements is to display a typeset equation, that makes a bit of difference. In a web-based setting, the best way to do that is probably MathML, whereas a GUI will be a bit harder. Yes, this pretty much summarizes my (ignorant) thoughts on it so far (GUI: hard; MathML: relatively easy), which is why I suspect that running it as a local web application might be the simplest way to go. Concerning a local GUI: How about running LaTeX for Tex-PDF, generate a PNG from PDF by ghostscript and show the PNG? I am working on an alternative solution for a local GUI. I am developing an equation editor and manipulator in Haskell, using gtk2hs. A prototype is available on Hackage as casui. Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [GSoC] Parallel Benchmarking and Profiling
Hello, I am putting together a student proposal to participate in Google's Summer of Code with one of the following project ideas. Parallel programming benchmarking and benchmark suite - http://hackage.haskell.org/trac/summer-of-code/ticket/1544 Are there open source projects and real world applications that rely on GHC's parrallel programming primitives and libraries? I have found many references to LOLITA, but it seems to be old and not available online. The idea page suggests porting existing benchmark suites such as PARSEC, but PARSEC is 5G of C code. Most of it seems to come from existing applications already written in C. It might also be interesting to automate the discovery of optimal strategies through empirical data, and to modify the thresholds dynamically. Parallel profiling tools for GHC - http://hackage.haskell.org/trac/summer-of-code/ticket/1559 Simon Marlow wrote on the idea page that Gransim was ported to a more up-to-date GHC. The documentation available on the web seems to be for GHC 0.29 but it describes many options for logging and visualising the activity of threads and processors over time. Getting GHC to display that information on the frontpanel would make a nice project. Do you have any comments or suggestions? Thank you, Etienne Laurin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
