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Small language with parser in Haskell and Faker
by Alex Gaziev 05 Jan '15

05 Jan '15

Hi all! As for beginner – it was pretty hard to me to parse YAML or JSON. Too much information, too much functions for such a simple task (in Ruby it is really simple, because of duck typing). So I wrote mine super simple language for data files – Giml – and two parsers for it – in Ruby and in Haskell. Aim of this language - to be fast and so simple that you need only couple pages of code of any language without heavy dependencies to implement parser. Here is the manifest: https://github.com/gazay/giml. Parser in Haskell: https://github.com/gazay/gimlh It was written mostly for my library Faker, which was nicely discussed on reddit ( http://www.reddit.com/r/haskell/comments/2rb8ym/haskell_library_for_generat…) so I have a lot of plans what to do in future with Faker. But I didn't present Giml anywhere and it will be really great if someone can take a look (there only couple pages of code) and tell me what can be improved, what can be rewritten in better way and so on. I didn't use Parsec for a reason in this library as I wanted to write my parser as clean of dependencies as possible, but maybe it will improve performance or something else?

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ANN: git-vogue - a pre-commit check framework for haskell code quality
by Christian Marie 05 Jan '15

05 Jan '15

There are no standards in the Haskell community when it comes to IDEs and editors. As such we've found ourselves without a common benchmark for linting, formatting and code quality checks. Within our development team at Anchor, we wanted a tool that would: * Install in one command * Require nothing to be learned for a new developer * Tell that developer what they need to fix in the code that they modify. We wanted to to satisfy these needs, whilst saving developers from the drudgery of installing, configuring and running a suite of tools independently. Let's face it, if it's difficult to run the formatters and linters and not a part of your established work flow, some developers just aren't going to bother. We built such a tool: http://anchor.github.io/git-vogue/ To install and configure, just: cabal install git-vogue # Wait 15 minutes cd your-project git vogue init All staged files will now be checked on pre-commit. If you wish to check the whole repo: git vogue check --all You can automatically apply stylish-haskell fixes to staged files: git vouge fix Or the whole repo: git vogue fix --all Thank you to thsutton, groberts, oswynb, glasnt, tranma, barneydesmond and sio for your development efforts, and everyone who has taken the time to test and provide feedback.

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hxt: How to Unpickle Multiple Adjacent Elements
by Jimmy Lu 04 Jan '15

04 Jan '15

Hi, With xml element having DTD like following: <!ELEMENT entry ((art*, formula?, table?), hw, hsl?, (pr | altpr)?, (ahw, hsl?, (pr | altpr)?)*, vr?, fl?, lb*, in*, ((dx) | (cx?, def?))?, dro*, dxnl*, uro*, syns*)> I want to unpickle the sequence hw, hsl?, (pr | altpr)?, (ahw, hsl?, (pr | altpr)?)* into Haskell data type [Headword] where data Headword = Hw { hwText :: String , hwSl :: Maybe String , hwPr :: Maybe Pronunciation } However in the hxt pickle API I cannot found a way to extract a sequence of adjacent elements. Is there any one knowing how to do it? Thanks, Jimmy Lu

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ANN: Cabal 1.22 and cabal-install 1.22
by Johan Tibell 04 Jan '15

04 Jan '15

On behalf of the cabal developers, I'm happy to announce the Cabal 1.22 release! To install: cabal update && cabal install Cabal-1.22.0.0 cabal-install-1.22.0.0 Please report bugs at https://github.com/haskell/cabal/issues. Pre-built binaries should be available with a week or so. Non-exhaustive list of changes: * Support GHC 7.10. * Experimental DWARF debug info output on GHC 7.10 (--enable-debug-info). * Preliminary support for relocatable packages. * Cabal can now be used inside a cabal exec environment. * Fix solver bug where the user's manual flag choice was ignored. * Add GHCJS support. * Improved command line documentation. * Build C sources with -fPIC when GHC is using dynamic libraries. * Preliminary support for package keys (a step on the way to NixOS-like packages). * Add a 'user-config' command to help users manage ~/.cabal/config. * HPC support improved. Here are all the contributors to this release, ordered by number of commits: 181 Mikhail Glushenkov 48 Johan Tibell 35 Edward Z. Yang 34 Christiaan Baaij 32 Thomas Tuegel 24 Ben Armston 19 Ian D. Bollinger 17 Lennart Spitzner 12 Luite Stegeman 11 Herbert Valerio Riedel 10 Duncan Coutts 9 Erik de Castro Lopo 8 Andres Loeh 5 Chris Wong 5 Iain Nicol 5 Heather 5 Jake Wheat 4 Daniel Trstenjak 4 Tuncer Ayaz 4 Neil Vice 4 Rudy Matela 2 David Feuer 2 Bertram Felgenhauer 2 Fujimura Daisuke 2 Iustin Pop 2 John Chee 2 Keshav Kini 2 Maxwell Swadling 2 Michael Snoyman 2 Owen Stephens 2 Sergey Vinokurov 2 Thomas Miedema 2 Vincent Hanquez 2 jake 1 Brent Yorgey 1 Maximilian Tagher 1 Anton Dessiatov 1 phischu 1 Bob Ippolito 1 Miëtek Bak 1 Bardur Arantsson 1 Nikita Karetnikov 1 tchakkazulu 1 Peter Trško 1 Austin Seipp 1 Ryan Mulligan 1 RyanGlScott 1 Samuel Gélineau 1 Sergei Trofimovich 1 jpmoresmau 1 Simon Hengel 1 Thomas M. DuBuisson 1 Harry Garrood 1 Isamu Mogi 1 kosmikus 1 David Fox 1 Curtis Gagliardi 1 Antonio Nikishaev 1 Karel Gardas 1 Travis Cardwell 1 Chris Allen 1 Matthew William Cox

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[ANN] Haskell client for Event Store
by Yorick Laupa 04 Jan '15

04 Jan '15

Hi, I'd like to announce my Event Store TCP client. It licensed under BSD3. You can find the source on Github <http://github.com/YoEight/eventstore>. Package is available on Hackage <http://hackage.haskell.org/package/eventstore-0.5.0.0>. Here's a list of supported features: * Single event writes. * Batch writes. * Transactional writes. * Stream deletion. * Single event reads. * Range reads from regular streams and from $all stream (backward and forward). * Volatile subscriptions (regular stream and $all). * Catch-up subscriptions (regular stream and $all). * Authenticated connection. Will be implemented: * Persistent subscriptions. * SSL connection. I originally wrote that library because I need it for a real project. I only implemented features I need first, so feel free to open a ticket (or better a pull request) on Github for something you need or a bug you've experienced. I'll be as fast as I can. Few notes on the code itself. This implementation uses a Functional Reactive Programming (FRP) library named Sodium <https://hackage.haskell.org/package/sodium>. Connection bookkeeping (operation and subscription management for instance) was amazingly easy to implement with it. I only tested that library with EventStore 3.0.1. Hope you enjoy it. Regards, Yorick

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ECMA262 (Javascript) interpreter
by Fabian Bergmark 04 Jan '15

04 Jan '15

I have been implementing an ECMA-262 (Javascript) interpreter over the last few weeks. I have been following http://www.ecma-international.org/ecma-262/5.1 and tried to keep my implementation as close to the specification as possible. The code can be found here https://github.com/fabianbergmark/ECMA-262 So far I have implemented the core language, but has yet to write all the specification functions (Array.splice, String.substring etc.). Before I do this and release it on hackage, I would appreciate feedback on my implementation. The issues I see at the time are: * The parser is slow for deeply nested code * Strict mode is not implemented * Interpret.hs is ~ 6k lines * SubType.hs uses IncoherentInstances, and a better implementation would be nice. At the moment it works but for one case. To test the code, install the cabal package and run ecma262 on a .js file. One host object, console.log is provided and prints to stdout. Fabian Bergmark

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servant-pandoc
by Matthew Pickering 04 Jan '15

04 Jan '15

Dear list, As a quick and easy way to render API documentation to many more formats I thought it wise to create a new pandoc renderer. For those who don't know, pandoc is a multi-format document conversion tool which currently supports 24 different output formats.[1] The rendering is quite faithful to the current `markdown` renderer, if people find this package useful then I can look to fine tune the representation. Note: The package will not build until servant-docs 0.3 is released which will hopefully be tomorrow or the day after. Below are some examples of the rendering and links to the package. examples: https://github.com/mpickering/servant-pandoc/tree/master/examples github: https://github.com/mpickering/servant-pandoc hackage: http://hackage.haskell.org/package/servant-pandoc [1]: http://pandoc.org/ Matt

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Updating tar for ghc 7.10 FAM compatibility
by Darren Grant 03 Jan '15

03 Jan '15

Hi all, Does anyone know who I can reach out to in order to get the tar hackage updated for ghc 7.10? Unfortunately, Duncan's email bounced. Cheers, Darren Grant

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Proof that scanl can be written as foldr?
by Cristian Ontivero 03 Jan '15

03 Jan '15

Hello, I'm trying to solve the exercise 4.6.5 of Bird's "Introduction to functional programming using Haskell". Let me quote: "Prove that scanl f e can be written as a foldr, if f is associative with unit e. Can scanl f e be written as a foldl without any assumptions on f and e?" So far reasoning by myself and googling a bit I reached to the following scanl definition using foldl (without any assumptions afaik): scanl f e = foldl (\xs next -> xs ++ [f (last xs) next]) [e] Furthermore, previously on the same chapter, it says that: scanl f e = foldr g [e] where g x xs = e : map (f x) xs Using this definition, I tried proving it by induction, but since I got stuck, I tried seeing if I could find some way to use the first duality theorem (with the foldl definition), or fusion, but to no avail. The induction proof I wrote is the following: scanl f e = foldr g [e] where g y ys = e : map (f y) ys By the principle of extensionality, this is equivalent to: scanl f e xs = foldr g [e] xs where g y ys = e : map (f y) ys We prove this equality by induction on xs. Case([]). For the left-hand side we reason scanl f e [] = {scanl.1} [e] For the right-hand side foldr g [e] [] = {foldr.1} [e] Case(x:xs). For the left-hand side we reason scanl f e (x:xs) = {scanl.2} e : scanl f (f e x) xs = {f has unit e} e : scanl f x xs = {induction hypothesis} e : foldr g [x] xs For the right-hand side foldr g [e] (x:xs) = {foldr.2} g x (foldr g [e] xs) = {definition of g} e : map (f x) (foldr g [e] xs) = {definition of map} e : foldr ((:) . (f x)) [] (foldr g [e] xs) I'm not even sure the last step is useful, but I thought maybe I could combine both foldrs into a single one (that's why I thought about the fusion law). Anyway, any help or pointer that can lead me in the right direction is very much appreciated. Thanks in advance.

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Handling Postgresql array types
by Riaan 03 Jan '15

03 Jan '15

This is a question about database query libraries. I am trying to do some analytics on a Postgresql database and up to now have been using Database.HDBC for most of my querying. One of the columns on the database is a two dimensional float8 array. I tried using Database.PostgreSQL.Simple but got stuck on this array as I could not figure out how to extend the built in conversion functions to cater for something like this. So went back to HDBC. But now my queries are starting to get fairly long and I have been looking at libraries like Persistent with Esqualeto, HaskellDB and Groundhog to make my queries a little more composable and type safe. However I have not been able to find any examples of any of these libraries using postgres arrays and given my postgresql-simple experience I worried that I might similarly be unable, because of my low level of haskell ability, to extend the conversion functions. So to my question. Does anyone have experience with one of these libraries in dealing with postgresql arrays and could someone perhaps send me a simple example that I could use as a basis. Failing that, can anyone advise me on which of these libraries have the most haskell newbie (LYAH trained, but still struggling with RWH) friendly approach to writing new conversion functions? Thanks Riaan

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