- Haskell-Cafe - Haskell.org

ANN: fixed-vector
by Aleksey Khudyakov 13 Nov '12

13 Nov '12

Hello cafe! I want to announce library for the small vectors of fixed length fixed-vector[1]. Fixed means that vector's length is determined by its type. Generic API can work with both ATD-based vector like complex or Vec written below and array-based ones. > data Vec a = Vec a a a It's based on post by Roman Leschinsiy[2]. Library also provide array-based vectors with memory representation similar to onves from vector package. It's more compact though because there is no need to store lengh and and offset to first element. [1] http://hackage.haskell.org/package/fixed-vector [2] http://unlines.wordpress.com/2010/11/15/generics-for-small-fixed-size-vecto…

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Reminder and Forward: Wednesday 14 November 2012 NYHUG Inaugural Meetup: Ozgun Ataman on Practical Data Processing and Gershom Bazerman on Putting Cloud Haskell to Work
by Jay Sulzberger 12 Nov '12

12 Nov '12

Below is a version of the announcement sent to the haskell-cafe and the haskell mailing lists by Gershom Bazerman on 9 October 2012. oo--JS. <blockquote what="official New York Haskell Users Group announcement" rsvp="Yes, see below." more="http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 [page was last modified on 11 November 2012 at 00:56] http://www.haskell.org/haskellwiki/Haskell http://www.reddit.com/r/haskell http://www.aosabook.org/en/ghc.html http://en.wikipedia.org/wiki/Type_inference [page was last modified on 15 September 2012 at 15:37] http://en.wikipedia.org/wiki/Hindley%E2%80%93Milner [page was last modified on 9 October 2012 at 17:40] http://www.users.waitrose.com/~hindley/ http://www.cs.ru.nl/~henk/ http://www.usingz.com/ http://en.wikipedia.org/wiki/Curry-Howard [page was last modified on 14 September 2012 at 22:01] http://www.paultaylor.eu/stable/prot.pdf ftp://ftp.cs.cmu.edu/usr/rwh/www/home/courses/logic/www/handouts/curry-howa… http://www.students.science.uu.nl/~3448584/TypeSystems.pdf http://www.math.ias.edu/~vladimir/Site3/Univalent_Foundations_files/2011_Go… http://math.andrej.com/2012/11/08/how-to-implement-dependent-type-theory-i/ http://math.andrej.com/2012/11/11/how-to-implement-dependent-type-theory-ii/ http://math.andrej.com/2012/10/03/am-i-a-constructive-mathematician/" exclamation-of-old-lisper-upon-first-seeing-curry-howard-theorem: "But this is clearly wrong! Look I have a function string-length which has type String->Int, but 'String->Int' is not a theorem of any usual intuitionistic propositional logic." insight-of-newbie-coming-to-haskell-from-lisp: "Lisp's now buried background would require, if a student of Lisp were to ask for an outline of this background, a book of perhaps a hundred pages. Haskell, and more generally, all the New Crazy Types programming systems, would require three hundred pages." edits="some adventitious markup and some blank space removed"> Subject: Wednesday 14 November, NY Haskell Inaugural Meetup: Practical Data Processing _and_ Putting Cloud Haskell to Work Date: Fri, 12 Oct 2012 18:05:02 -0400 From: Gershom B <gershomb(a)gmail.com> To: lisp(a)lispnyc.org ====================================================== What: New York Haskell Users Group Meeting When: Wednesday, November 14, 2012 7 PM - 9 PM Where: Pivotal Labs, 841 Broadway, 8th floor (Just south of Union Square) http://maps.google.com/maps?q=841+Broadway,+New+York RSVP: http://www.meetup.com/NY-Haskell/ ====================================================== * 7 PM - Practical Data Processing With Haskell * 8 PM - Putting Cloud Haskell to Work for Distributed Computing -------------------------------------------------------------------------------------- 7 PM - Practical Data Processing With Haskell: Ozgun Ataman will give an introductory talk on Haskell, diving right in with how you can start using Haskell for practical data manipulation tasks today. You'll be introduced to a typical setup for Haskell development and given a demonstration of how a common data format (CSV, JSON, etc.) can be parsed, processed and finally output using Haskell. The talk will include a small actual Haskell program to be modified live and some commentary around using Haskell in practical applications. 8 PM - Putting Cloud Haskell to Work for Distributed Computing: Gershom Bazerman will give an overview of the new distributed-process library that implements Cloud Haskell, providing computation across heterogeneous nodes through a message passing interface. He will discuss what this new tool provides out of the box, and what you'll have to bring to the table. The talk will include some code samples using the new library, as well as some experience about what it's like to use Haskell for distributed computing in the real world. Speaker Biographies: Ozgun Ataman is the founder of Soostone, a management consulting and analytics company built on Haskell. He is the author of many open-source Haskell libraries, and is a contributor to the Snap web framework. Gershom Bazerman is a developer at S&P Capital IQ. He is most well known in the Haskell community as the author of the JMacro library for programmatic generation of JavaScript, and for one well-received April fools joke. -------------------------------------------------------------------------------------- We're kicking off the New York Haskell Users Group with two great talks, one for people just getting started and one for those with some experience already. Both should be accessible and enjoyable no matter how much (or little) you already know. Food and refreshments will be provided, courtesy of the generosity of Pivotal Labs, and after the talks, we're planning to keep the discussion going over food and drink at a nearby establishment. </blockquote> Distributed poC TINC: Jay Sulzberger <secretary(a)lxny.org> Corresponding Secretary LXNY LXNY is New York's Free Computing Organization. http://www.lxny.org

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Hard drive thrashing with modern controllers
by timothyhobbs＠seznam.cz 12 Nov '12

12 Nov '12

Hello, I have a very general question that doesn't exactly relate to Haskell. Do I need to worry about hard drive thrashing with a modern controller? I understand, that such "thrashing" can significantly reduce the lifespan of modern SSD drives. For example, if I do: import Control.Monad foo = do forever $ writeFile "filename.foo" "Hello world!" will that destroy those sectors of my SSD after the rated 3000 write cycles? The reason I ask, is that I have a program here where I would like to save a set of files after every change/operation and I'm wondering if I should check if the files I'm saving have actually changed or if this will be handled by the OS... Thank you Timothy

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Strange behavior with listArray
by Alex Stangl 12 Nov '12

12 Nov '12

I'm stymied trying to figure out why the program below blows up with <<<loop>>> when I use "f 0" for building the array, but if I substitute g or h in place of f, they work fine. Is this a bug or am I overlooking something? I am using GHC 7.4.2. Thanks, Alex P.S. Forgive the seemingly pointless program; I distilled this test from a longer actual program that was exhibiting this behavior. -------- import Data.Array((!),Array,elems,listArray) import Data.List(intercalate) solve = let a :: Array Int Int a = listArray (0, 3) (0 : f 0) f k = if k > 0 then f (a!0) else 0 : f 1 g k = k : a!(k+1) : a!(k+1) : a!(k+2) : a!(k+3) : [] h k = a!k : h (k+1) in (intercalate " " . map show . elems) a main = putStrLn solve

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how to inject another source into conduit
by Alexander V Vershilov 12 Nov '12

12 Nov '12

Hello. I have problems with writing next code (using network-conduit) slightly simplified version: > app ad = appSource ad $$ sink > where > cMap = M.fromList [ ("upload", cmdUpload), ("download", cmdDownload) ] > sink = takeLine >>= \c -> case c of Just run -> run ; Nothing -> return () > cmdUpload = {- ... -} CB.sinkFile path > cmdDownload = do > {- code here -} > CB.sourceFile path $$ appSink ad -- this will not work because of > -- type error And I'm catching "cannot construct the infinite type". I've found an example in [1], but it's not exactly solves my problem, as all the logic is inside conduit, and it will break upload function. [1] http://www.yesodweb.com/blog/2012/06/conduit-0-5 -- Alexander Vershilov

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GHC for mobile devices?
by Andrew Pennebaker 12 Nov '12

12 Nov '12

I'd love to use Haskell directly for making mobiles apps. How can we make this happen, porting GHC to Android, iOS, and Windows Phone? -- Cheers, Andrew Pennebaker www.yellosoft.us

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Re: [Haskell-cafe] Motion to unify all the string data types
by John Lato 12 Nov '12

12 Nov '12

> > From: Francesco Mazzoli <f(a)mazzo.li> > > At Sat, 10 Nov 2012 15:16:30 +0100, > Alberto G. Corona wrote: > > There is a ListLike package, which does this nice abstraction. but I > don't > > know if it is ready for and/or enough complete for serious usage. I?m > > thinking into using it for the same reasons. > > > > Anyone has some experiences to share about it? > > I've used it in the past and it's solid, it's been around for a while and > the > original author knows his Haskell. > > Things I don't like: > > * The classes are huge: > < > http://hackage.haskell.org/packages/archive/ListLike/3.1.6/doc/html/Data-Li… > >. > I'd much rater prefer to have all those utilities functions outside the > type > class, for no particular reason other then the ugliness of the type > class. > Speaking as the ListLike maintainer, I'd like this too. But it's difficult to do so without sacrificing performance. In some cases, sacrificing *a lot* of performance. So they have to be class members. However, there's no reason ListLike has to remain a single monolithic class. I'd prefer an API that's split up into several classes, as was done in Edison. Then 'ListLike' itself would just be a type synonym, or possibly a small type class with the appropriate superclasses. However this seems like a lot of work for relatively little payoff, which makes it a low priority for me. * It defines its own wrappers for `ByteString': > < > http://hackage.haskell.org/packages/archive/ListLike/3.1.6/doc/html/Data-Li… > >. > The community's view on newtypes is funny. On the one hand, I see all the time the claim "Just use a newtype wrapper to write instances for ..." (e.g. the recent suggestion of 'instance Num a => Num (a,a)'. On the other, nobody actually seems to want to use these newtype wrappers. Maybe it clutters the code? I don't know. I couldn't think of a better way to implement this functionality, patches would be gratefully accepted. Anyway, you really shouldn't use these wrappers unless you're using a ByteString to represent ASCII text. Which you shouldn't be doing anyway. If you're using a ByteString to represent a sequence of bytes, you needn't ever encounter CharString. > * It doesn't have instances for `Text', you have to resort to the > `listlike-instances' package. > Given that text and vector are both in the Haskell Platform, I wouldn't object to these instances being rolled into the main ListLike package. Any comments on this? John L.

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Motion to unify all the string data types
by Andrew Pennebaker 12 Nov '12

12 Nov '12

Frequently when I'm coding in Haskell, the crux of my problem is converting between all the stupid string formats. You've got String, ByteString, Lazy ByteString, Text, [Word], and on and on... I have to constantly lookup how to convert between them, and the overloaded strings GHC directive doesn't work, and sometimes ByteString.unpack doesn't work, because it expects [Word8], not [Char]. AAAAAAAAAAAAAAAAAAAH!!! Haskell is a wonderful playground for experimentation. I've started to notice that many Hackage libraries are simply instances of typeclasses designed a while ago, and their underlying implementations are free to play around with various optimizations... But they ideally all expose the same interface through typeclasses. Can we do the same with String? Can we pick a good compromise of lazy vs strict, flexible vs fast, and all use the same data structure? My vote is for type String = [Char], but I'm willing to switch to another data structure, just as long as it's consistently used. -- Cheers, Andrew Pennebaker www.yellosoft.us

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Re: [Haskell-cafe] GHC for mobile devices?
by Casey Basichis 11 Nov '12

11 Nov '12

I've been looking for the last two days through every nook and cranny of google to find information about building for iOS. It seems to be the case that it was once possible to get ios running and now its a bit questionable. I've tried ghc-ios, ghc-iphone and a few others which are all somewhat out of date. If anyone has any experience on that platform I would greatly appreciate some guidance in getting it up and running. As for you notion of "hard truth," and "dumb apps acting as web front ends" its pretty blase to assume that anyone interested in this thread will share that perspective in terms of their own goals on these platforms. I compose professionally on my phone, its certainly not a toy for my purposes. I also have no interest whatsoever in getting Cocoa commands into Haskell. I just want a functional way of working with data. I would greatly prefer to go the Haskell route, but have been considering OCaml as well as they seem to have an active and enthused interest in iOS. I would love a bit of perspective on whether OCaml would be worth pursing in the long run for the short term benefit of having a more mature mobile implementation.' Thanks, Casey >Yes, I've seen some of the work done on this and I think he's also >looked into OCaml on Android. > >To be completely honest it's not really the language that's such the >barrier: the hard truth is that any Android app doing anything of >interest is necessarily going to be using the Android framework. >Android programming (at least, presubaly iOS too) is not a lot of >advanced construction, it's mostly dumb apps acting as web frontends, >I'd posit that this is probably why people have been mostly content >with the Android API for so long anyway. > >So the main barrier is being able to interface with the Java side of >things (obviously) in a way that doesn't completely kill perf either >(this sounds nontrivial...). Then you need to give a sane >reimplementation of the Android API within Haskell. > >kris -- Casey James Basichis Composer - Cartoon Network http://www.caseyjamesbasichis.com caseybasichis(a)gmail.com 310.387.7540

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size of Haskell Platform
by Doug McIlroy 11 Nov '12

11 Nov '12

This note is an offshoot of "curl package broken in Windows", where this item appeared: > Did you know that Strawberry Perl includes a cygwin gcc? > ... > Maybe Haskell Platform could do the same. The suggestion brought to mind a true-life parable: the pump station at Tok. (Tok is the third corner--after Anchorage and Fairbanks--of Alaska's triangular core of long-distance highways.) When I visited Tok long ago, it was a village of several hundred souls, almost all of whom were employed by one government agency or another, principal among which were the highway department, the Alaska Communication Service and the pump station, which kept fuel flowing to Eielson Air Force Base. The mission of the station was to keep one pump running 24 hours a day. Most of the time, of course, the pump hummed along by itself. To assure that, there had to be a standby machine, an operator to watch over both, and a mechanic who could fix them if need be. For such a lonely job it was deemed well to have two operators. And there had to be two operators for each of several shifts. A little redundancy on the mechanical side seemed wise, too. The crew and their families, say nothing of the pumps themselves, needed to be housed, and the installation needed to be supplied with the necessities of life. (The nearest supermarket was in Fairbanks, 300 miles away.) These needs demanded a motor pool and property maintenance cadre, whose very presence reinforced the need. Thus the support team to keep one pump going ballooned to about 100 people--a chain reaction that barely avoided criticality. So it seems to be with Haskell Platform, which aims to include "all you need to get up and running"--"an extensive set of standard libraries and utilities with full documentation." I get the impression that the Platform is bedeviled by the same prospect of almost unfettered growth. [One ominous sign: the description of the Haskell Platform at lambda.haskell.org/platform/doc/current/start.html suggests that one must join some mysterious Cabal, whose nature is hidden by a link to nowhere, simply to get started.] What principles guide the selection of components for "all you need to get up and running"? Doug McIlroy

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