July 2013 - Haskell-Cafe

Roshask
by Tijn van der Zant 02 Oct '13

02 Oct '13

Hi, I want to use Haskell to program my robot using ros. I've found roshask https://github.com/acowley/roshask and I was wondering if someone on this list has experience with it and can tell me how good it is. Thanx! --Tijn

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HTML framework for web-ui
by Vlatko Basic 01 Oct '13

01 Oct '13

Hi, I'd like to start using web pages as the UI for apps. I found out for yesod, snapp and happstack as the candidates. Would you recommend any of them as better for app ui (not "classical" web pages)? Or maybe another one? thanks, vlatko

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An APL library for Haskell
by Simon Peyton-Jones 16 Sep '13

16 Sep '13

Friends Many of you will know the array language APL<http://en.wikipedia.org/wiki/APL_%28programming_language%29>. It focuses on arrays and in particular has a rich, carefully-thought-out array algebra. An obvious idea is: what would a Haskell library that embodies APL's array algebra look like? In conversation with John Scholes and some of his colleagues in the APL community a group of us developed some ideas for a possible API, which you can find on the Haskell wiki here: http://www.haskell.org/haskellwiki/APL However, we have all gone our separate ways, and I think it's entirely possible that that the idea will go no further. So this message is to ask: * Is anyone interested in an APL-style array library in Haskell? * If so, would you like to lead the process of developing the API? I think there are quite a few people who would be willing to contribute, including some core gurus from the APL community: John Scholes, Arthur Whitney, and Roger Hui. Simon

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Haskell / Functional Programmers Group in Madrid (Spain)?
by Alejandro Serrano Mena 04 Sep '13

04 Sep '13

Hi, Is there any Haskell or functional programmers user group in the region of Madrid? If not, I think it could be a great idea to get to know each other, and share experiences. Furthermore, we could try to organize some meetings with presentations, hackatons and so on (my personal ambition is to be able to organize another "ekmett Workshop" as the Japanese one - http://comonad.com/reader/2013/japanese-workshop-1/) I know there is some locations along Madrid dedicated to open source promotion, like http://madridonrails.com/, and which we could use for these meetings. I'm really looking forward to hearing from you! PS: Maybe a bare "Haskell" group is not big enough (at least according to Haskellers.com) but a "functional programmers" one may well be.

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Ideas on a fast and tidy CSV library
by Justin Paston-Cooper 21 Aug '13

21 Aug '13

Dear All, Recently I have been doing a lot of CSV processing. I initially tried to use the Data.Csv (cassava) library provided on Hackage, but I found this to still be too slow for my needs. In the meantime I have reverted to hacking something together in C, but I have been left wondering whether a tidy solution might be possible to implement in Haskell. I would like to build a library that satisfies the following: 1) Run a function <<f :: a_1 -> ... -> a_n -> m (Maybe (b_1, ..., b_n))>>, with <<m>> some monad and the <<a>>s and <<b>>s being input and output. 2) Be able to specify a maximum record string length and output record string length, so that the string buffers used for reading and outputting lines can be reused, preventing the need for allocating new strings for each record. 3) Allocate only once, the memory where the parsed input values, and output values are put. 4) The library's main function should take some kind of data structure describing the types of the function, the function itself and the filenames of input and output (could also be stdin/stdout). I am not sure yet what would be that best value of <<m>>. I would like to most importantly efficiently, and if possible, purely allow changes in state to a number of variables, such as an aggregation over a certain field in the input. I do not currently have knowledge of the FFI, and how it might be used in this case. I would appreciate any suggestions as to where I should look further. Regards, Justin Paston-Cooper

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Rank N Kinds
by Wvv 10 Aug '13

10 Aug '13

It was discussed a bit here: http://ghc.haskell.org/trac/ghc/ticket/8090 Rank N Kinds: Main Idea is: If we assume an infinite hierarchy of classifications, we have True :: Bool :: * :: ** :: *** :: **** :: ... Bool = False, True, ... * = Bool, Sting, Maybe Int, ... ** = *, *->Bool, *->(*->*), ... *** = **, **->*, (**->**)->*, ... ... RankNKinds is also a part of lambda-cube. PlyKinds is just type of ** (Rank2Kinds) class Foo (a :: k) where <<==>> class Foo (a :: **) where *** is significant to work with ** data and classes; more general: Rank(N)Kinds is significant to work with Rank(N-1)Kinds First useful use is in Typeable. In GHC 7.8 class Typeable (a::k) where ... <<==>> class Typeable (a ::**) where ... But we can't write data Foo (a::k)->(a::k)->* ... deriving Typeable If we redeclare class Typeable (a ::***) where ... or even class Typeable (a ::******) where ... it becomes far enough for many years I'm asking to find other useful examples -- View this message in context: http://haskell.1045720.n5.nabble.com/Rank-N-Kinds-tp5733482.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Installling Leksah on ghc7.6.3 with haskell-platform 2013?
by Carlo Hamalainen 10 Aug '13

10 Aug '13

Hi, I'm trying to install Leksah from hackage on my Debian testing laptop, which has ghc 7.6.3 and the Haskell Platform 2013. I fixed a bunch of errors about "catch" not being exported from the Prelude, but now I'm stuck on these two errors in leksah-server-0.8.0.5: [10 of 13] Compiling IDE.Utils.GHCUtils ( src/IDE/Utils/GHCUtils.hs, dist/build/IDE/Utils/GHCUtils.o ) src/IDE/Utils/GHCUtils.hs:94:40-62: Not in scope: data constructor `Opt_ReadUserPackageConf' src/IDE/Utils/GHCUtils.hs:161:44-50: Not in scope: data constructor `Opt_Cpp' Perhaps you meant one of these: `Opt_CSE' (imported from GHC), `Opt_Pp' (imported from GHC) Where have Opt_ReadUserPackageConf and Opt_Cpp gone in ghc 7.6.3? Cheers, -- Carlo

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Why are field selectors functions? [was: ghc-users A possible alternative to dot notation for record access]
by AntC 08 Aug '13

08 Aug '13

No! This isn't more bikeshedding about notation. It's a bit of Haskell archaeology. > On Sun, Jun 30, 2013 at 2:59 AM, Judah Jacobson wrote: [This isn't exactly what Judah wrote.] > ... > > Instead of `x f` (to access field x of record f), > maybe we could write `f{x}` as the record selection. > The more I thought about that ... We use { ... } to declare records, build them, update them. We use { ... } in pattern matching to access named fields. Why don't we use { ... } to access named fields in terms? The syntax `e{ foo }` is unused in H98. (Or at least it was in 1998.) Can someone who was there at the time (1994?, TRex?) remember if that was ever considered? In the declaration, the build/update, and pattern match: data R = MkR { foo :: Int } r = MkR { foo = 7 } \ (MkFoo { foo }) -> ... -- using NamedFieldPuns `foo` is clearly bound to an Int. So why is there this `foo` thing that isn't an Int? AntC

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Haddock GSOC project progress
by Mateusz Kowalczyk 05 Aug '13

05 Aug '13

Greetings cafe, As some of you might know, I'm hacking on Haddock as part of Google Summer of Code. I was recently advised to create a blog and document some of what I have been doing recently. You can find the blog at [1] if you're interested. The first post goes over the work from the last month or so. Future posts should be shorter and on more specific topics. There's an overview of what has happened/changed/will change at the bottom of the post if you're short on time. Thanks. [1] - http://fuuzetsu.co.uk/blog -- Mateusz K.

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Re: [Haskell-cafe] [Haskell] Spam on the Haskell wiki
by Henk-Jan van Tuyl 03 Aug '13

03 Aug '13

On Mon, 16 Jul 2012 00:03:49 +0200, Henk-Jan van Tuyl <hjgtuyl(a)chello.nl> wrote: > > I am willing to do administrator tasks. > >> 4. ReCAPTCHA enabled for 'edits adding new, unrecognized external >> links' - which is all of the spam. > > This is already enabled. The HaskellWiki is still flooded with spam; we should take some measure to reduce the stream severely. Most spam seems to be created (semi-)automated; the pages do not contain links, the usernames end with two digits, most of the time. Some cures I have thought up: - Verify new wiki accounts, before granting them rights, based on e-mails in the Haskell mailing lists (or subscription of a Haskell mailing list) - Let new users only change pages, not create new pages - Block creation of usernames o ending with two or more digits o with more than one x or q o starting with "buy" o longer than 20 characters o with more than 4 consonants in a row - Block creation of pages with words in a certain list (Coach, Vuitton, Chanel, handbags, purses, outlet, luggage, "Nike Air Jordan") Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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