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ANNOUNCE: Groundhog 0.1.0.1 - high-level database library
by Boris Lykah 14 Sep '12

14 Sep '12

I am happy to announce a new version of Groundhog, a library for fast high-level database access: http://hackage.haskell.org/package/groundhog http://hackage.haskell.org/package/groundhog-th http://hackage.haskell.org/package/groundhog-postgresql http://hackage.haskell.org/package/groundhog-sqlite Groundhog has been completely overhauled since the last release. Notably, it got support for PostgreSQL and natural foreign keys. I believe that it is a big step forward as this brings more flexibility to the design of the relational schemas while keeping the applications independent of the storage layer. Some of the solutions, particularly schema migration were based on Persistent code. Please see examples at http://github.com/lykahb/groundhog/tree/master/examples. Features: * Support for Sqlite and PostgreSQL. * Natural and composite foreign keys. Earlier it was possible to reference an entity only by the mandatory integer primary key. Now an entity can have several keys including autoincrement primary key (optional) and unique keys which have one or more columns. * Full support of embedded datatypes. You can access a field that contains an embedded datatype as a whole, or access some of the inner subfields individually. This powerful mechanism has allowed implementation of the composite keys, and can be used in future to work with PostgreSQL composite types or MongoDB embedded documents. Instead of serializing value to string, the Groundhog backends flatten tree of embedded datatypes to db columns. * Projections. You can choose what columns to query from a table in a type-safe manner. * Initialization and migration of database schema. * Sum types and polymorphic types. * Expression DSL for use in queries. * Basic list support. * YAML-based settings mechanism. It separates datatype definition and description which facilitates modularity. The settings are inferred from the analysis of the difinition, and overridden with values set by user. The Criterion benchmarks are available at http://lykahb.github.com/groundhog/SqliteBench.html and http://lykahb.github.com/groundhog/PostgreSQLBench.html. Future plans: * Support for joins * Database indexes * Investigate options for implementing MongoDB and MySQL backends Your feedback, suggestions for improvement and criticism are welcome. -- Regards, Boris

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ANN: Cumino 0.3 - Now supports sandboxed environments (e.g, Hsenv ones)
by Alfredo Di Napoli 14 Sep '12

14 Sep '12

Hi Cafè, I'm glat to annouce the third major improvement of my VIm plugin Cumino: https://github.com/adinapoli/cumino This one is a juicy one. If you have a sandboxed environment enabled (e.g. one created with Hsenv) and you start vim from the same shell, Cumino will automatically uses at startup the right ghci instance. This means that if you have installed only some packages in your sandbox env, you will have them available inside ghci :) Feedback are welcome, as always. A.

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What is the good way to work with list comprehension and UTCTime?
by Magicloud Magiclouds 14 Sep '12

14 Sep '12

Hi, Simple usage, I could make an instance of Enum to UTCTime, so [utcTime..] could work. But that is so stiff. How if sometimes I want to step by 1 min, sometimes I want to step by 1 sec? So I think some way like [ t | addUTCTime last 60 ] could be nice. But I cannot figure it out.... Any idea? -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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[ANN] Cumino 0.2 - Now supports pretty indentation through stylish-haskell
by Alfredo Di Napoli 14 Sep '12

14 Sep '12

Hi everyone, in case you have missed it, I've released a Vim plugin called Cumino: http://adinapoli.github.com/cumino/ It does one simple thing: It allows communication between Vim and tmux, in particular to a ghci session. With Cumino you can fire-up Vim, load a ghci session and interact with it with only few keystrokes. The plugin also supports visual selection: you can select for example a function (even with all its signature!) and you can send it to ghci. The visual selection supports imports, custom types and typeclasses. It's a simple idea but so damn useful, imho. This release also adds the possibility to prettify the code using the excellent stylish-haskell: select a snippet, simply indent in the usual way ( = ) and voilà, now your code is indented! Feedback are highly appreciated, as well as contributions. There are still some issues with some terminals (for example urxvt does not work right now) but the plugin has been tested against gnome-terminal, xterm and mlterm. I'll post in reddit too for completeness! Bye! Alfredo

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Is Hackage down?
by C K Kashyap 14 Sep '12

14 Sep '12

Is it just me or is Hackage indeed been going down more frequently of late? Regards, Kashyap

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How do I generate random numbers using random-fu, with platform-agnostic code?
by Andrew Pennebaker 14 Sep '12

14 Sep '12

I can't figure out how to use Data.Random.Source.IO to generate random numbers in a multiplatform way. I can generate random numbers in Unix using Data.Random.Source.DevRandom, and there is an example in the GitHub documentation for Windows using Data.Random.Source.MWC, but there is no example code for using Data.Random.Source.IO. Cheers, Andrew Pennebaker www.yellosoft.us

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Fwd: How Type inference work in presence of Functional Dependencies
by Dan Doel 13 Sep '12

13 Sep '12

Copying the mailing list, because I forgot. On Thu, Sep 13, 2012 at 5:18 AM, satvik chauhan <mystic.satvik(a)gmail.com> wrote: > Consider the code below : > > {-# LANGUAGE > MultiParamTypeClasses,FlexibleInstances,FunctionalDependencies,UndecidableInstances,FlexibleContexts > #-} > class Foo a c | a -> c > instance Foo Int Float > f :: (Foo Int a) => Int -> a > f = undefined > > Now when I see the inferred type of f in ghci > >> :t f > >> f :: Int -> Float > > Now If I add the following code > > g :: Int -> Float > g = undefined > > h :: (Foo Int a) => Int -> a > h = g > > > I get the error > > Could not deduce (a ~ Float) > > > I am not able to understand what has happened here ? The restriction "Foo > Int a" should have restricted the type of h to "Int -> Float" as shown in > the inferred type of f. The answer, I believe, is that the difference between the fundep implementation and type families is local constraint information. Fundeps do no local propagation. So in your first definition, you've locally provided 'Int -> a', which is acceptable to GHC. Then it figures out externally to the function that '(Foo Int a) => Int -> a' is actually Int -> Float. In the second definition, you're trying to give 'Int -> Float', but GHC only knows locally that you need to provide 'Int -> a' with a constraint 'Foo Int a' which it _won't_ use to determine that a ~ Float. This is not inherent to fundeps. One could make a version of fundeps that has the local constraint rules (easily so by translating to the new type families stuff). But, the difference is also the reason that overlapping instances are supported for fundeps and not type families. But I won't get into that right now. -- Dan

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How Type inference work in presence of Functional Dependencies
by satvik chauhan 13 Sep '12

13 Sep '12

Consider the code below : {-# LANGUAGE MultiParamTypeClasses,FlexibleInstances,FunctionalDependencies,UndecidableInstances,FlexibleContexts #-} class Foo a c | a -> c instance Foo Int Float f :: (Foo Int a) => Int -> a f = undefined Now when I see the inferred type of f in ghci > :t f > f :: Int -> Float Now If I add the following code g :: Int -> Float g = undefined h :: (Foo Int a) => Int -> a h = g I get the error Could not deduce (a ~ Float) I am not able to understand what has happened here ? The restriction "Foo Int a" should have restricted the type of h to "Int -> Float" as shown in the inferred type of f. - Satvik

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Re: [Haskell-cafe] [ANN] Cumino 0.2 - Now supports pretty indentation through stylish-haskell
by Roman Cheplyaka 13 Sep '12

13 Sep '12

Ah, okay. I was just confused by the fact that it uses tmux, and thought that I was misusing it. Yes, I also usually keep ghci in a separate window (and I am an xmonad user, too). I just thought that this offers a different experience and wanted to try it out. Anyway, thanks for clarifying. On Wed, Sep 12, 2012 at 5:24 PM, Alfredo Di Napoli < alfredo.dinapoli(a)gmail.com> wrote: > Hi Roman, > > Cumino was thought to operate in another terminal. Personally, but this is > only a personal taste, having to switch between terminal tabs or tmux panes > is not the fastest workflow. Being an Xmonad user, i can easily swap > between terminals (read ghci and vim) simply with mod + j or mod + k. > So the answer to your answer is: You can't, Cumino will always start in > another terminal window. Is the same behaviour of Slime, though. > > Sent from my iPad > > On 12/set/2012, at 17:06, Roman Cheplyaka <roma(a)ro-che.info> wrote: > > So, suppose that I'm in a terminal vim session, and I want to start ghci > (in the current terminal). What do I do? > > <localleader>cc starts a new terminal, which is not what I want. > > On Wed, Sep 12, 2012 at 3:03 PM, Alfredo Di Napoli < > alfredo.dinapoli(a)gmail.com> wrote: > >> Hi everyone, >> >> in case you have missed it, I've released a Vim plugin called Cumino: >> >> http://adinapoli.github.com/cumino/ >> >> It does one simple thing: It allows communication between Vim and tmux, >> in particular to a ghci session. With Cumino you can fire-up Vim, >> load a ghci session and interact with it with only few keystrokes. The >> plugin also supports visual selection: you can select for example a >> function (even with all its signature!) >> and you can send it to ghci. The visual selection supports imports, >> custom types and typeclasses. >> >> It's a simple idea but so damn useful, imho. >> >> This release also adds the possibility to prettify the code using the >> excellent stylish-haskell: select a snippet, simply indent in the usual way >> ( = ) and voilà, now >> your code is indented! >> >> Feedback are highly appreciated, as well as contributions. >> There are still some issues with some terminals (for example urxvt does >> not work right now) but the plugin has been tested against gnome-terminal, >> xterm and mlterm. >> >> I'll post in reddit too for completeness! >> >> Bye! >> Alfredo >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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[Hackage] Bug report and proposal
by Stayvoid 12 Sep '12

12 Sep '12

Hello, I found a bug: "source" points to the wrong page. [1] I know that bugs should be reported via Github. But I don't have an account and don't want to create one. There might be others who don't want to use Github. Why rely on external bug tracker? I assume that it has been chosen because of its features, but it doesn't have the most important one (i.e. anonymous posting). What's better: to have more features or to have less bugs? Is it possible to move away from Github? What about a separate mailing list for bugs? I'm sorry if this sounds to harsh; I'm not good at writing. I don't want to attack or blame anyone. I'm also sorry if this message is not appropriate, but I haven't found a better place. [1] http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.ht… Cheers

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