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ANNOUNCE: keera-network-sms-diamondcard
by Ivan Perez 14 Dec '11

14 Dec '11

My fellow haskellers, I wrote a very simple library to send SMSs using the DiamondCard VoIP provider. At the present time, it uses the HTTP interface to contact the provider (there's a SOAP interface, but I haven't been able to make it play along with shoap). The current API is quite straightforward: sendSMS :: String -> String -> String -> String -> [ String ] -> IO SMSDeliveryResult sendSMS accountID pinCode message fromNumber toNumbers I don't like submitting alpha-stage software to hackage, so it's only in github for now: https://github.com/ivanperez-keera/keera-network-sms-diamondcard In a few days I plan to release a small GTK frontend that I've been using for a few months. If you give either of them a try, I'd be glad to know where it got you. Cheers, Ivan Perez

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A Mascot
by heathmatlock 14 Dec '11

14 Dec '11

I liked Go's mascot, and I figure it couldn't hurt to have our own. I spent the past hour making this: http://i.imgur.com/Mib6Q.png What do you think? -- Heath Matlock +1 256 274 4225

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Off The Beaten Track: Call for Participation
by David Walker 14 Dec '11

14 Dec '11

Off The Beaten Track: Underrepresented Problems for Programming Language Researchers http://www.cs.princeton.edu/~dpw/obt/ A Workshop Co-located with POPL 2012 Philadelphia, USA January 28, 2012 Come and join us for OBT -- we have a great program filled with a diverse set of problems and ideas for programming language researchers. And at the end of the day, we will have an open mic session to discuss directions for the PL community. Our program is now up here: http://www.cs.princeton.edu/~dpw/obt/obt_program.html And you can register here: https://regmaster3.com/2012conf/POPL12/register.php A broader explanation of the workshop goals: Programming language researchers have the principles, tools, algorithms and abstractions to solve all kinds of problems, in all areas of computer science. However, identifying and evaluating new problems, particularly those that lie outside the typical core PL problems we all know and love, can be a significant challenge. Hence, the goal of this workshop is to identify and discuss problems that do not often show up in our top conferences, but where programming language researchers can make a substantial impact. The hope is that by holding such a forum and associating it directly with a top conference like POPL, we can slowly start to increase the diversity of problems that are studied by PL researchers and that by doing so we will increase the impact that our community has on the world. While many workshops associated with POPL have become more like mini-conferences themselves, this is not the goal for Off the Beaten Track. The workshop will be informal and structured to encourage discussion. It will also be centered around problems and problem areas as opposed to fully-formed solutions.

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acid state
by Anatoly Yakovenko 13 Dec '11

13 Dec '11

So I am trying to understand how acid state works. The HelloWorld example has a type Message = String data Database = Database [Message] $(deriveSafeCopy 0 'base ''Database) -- Transactions are defined to run in either the 'Update' monad -- or the 'Query' monad. addMessage :: Message -> Update Database () addMessage msg = do Database messages <- get put $ Database (msg:messages) It seems to me that since the Dababase is a list of messages every update would require acid-state to rewrite the list into the file, so each update would get slower as the list gets bigger, but what I am seeing is that updates are constant time regardless of the size of the list. So how does it work?

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AFRP is not (necessarily) imperative
by Ertugrul Söylemez 13 Dec '11

13 Dec '11

Hello fellows, after a few discussions on IRC and via private mail I feel obligated to point out that arrows and in particular AFRP do not force you to use an imperative style in any way. You can use a style very similar to SHE's idiom brackets. I will demonstrate this using the Netwire library. The following code has a very imperative feel to it and also looks quite ugly: myWire = proc _ -> do fps <- avgFpsInt 1000 100 -< () t <- time -< () let x = 3 + t y <- integral 0 -< t returnA -< printf "%8.2f %8.2f %8.2f" fps x y Let's improve this code. The magic lies in identifying behaviors from classic FRP. The arrow variables from the above code can be seen as the behaviors, but that's not very useful for getting rid of the imperative style. A better way to look at it is that every wire that ignores its input (i.e. has a fully polymorphic input type) is a behavior, so let's find them. First of all it is impossible to write a proper Num instance for wires. The underlying problem is the same as for writing a Num instance for functions. However, the Wire type forms a vector space, and the next release of Netwire will include the corresponding instances (see the vector-space package by Conal Elliot). With them we can write: x = constant 3 ^+^ time The x wire is our first behavior. Passing x to a generic wire is simply regular arrow composition, giving you behaviors as functions of other behaviors, hence: y = integral 0 <<< x Also fps is just a simple behavior: fps = avgFpsInt 1000 100 To get to the final output there are multiple ways. Perhaps the nicest way is to exploit the Applicative instance, giving you: myWire = liftA3 (printf "%8.2f %8.2f %8.2f") fps x y where fps = avgFpsInt 1000 100 x = constant 3 ^+^ time y = integral 0 <<< x Looks much more declarative, no? For more complicated compositions or generic wires use banana brackets or the combinator syntax in arrow notation. Examples: myWire = proc x -> (someWire -< x) ^+^ (otherWire -< 15) myWire = proc x -> (| f (someWire -< x) (otherWire -< 15) |) This closely resembles idiom bracket notation, but allows you to be explicit about inputs, takes care of creating side channels and gives you the full power of arrows, including ArrowChoice and ArrowLoop. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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Chuan-Kai Lin's Unimo framework
by Jean-Luc Delatre 13 Dec '11

13 Dec '11

Does anybody has an hands on experience of using Chuan-Kai Lin's Unimo framework? https://sites.google.com/site/chklin/research It looks interesting but it seems it amounts to add an extra layer of interpretation (the monads encoding as a data type) and the paper lacks examples of actual uses of the framework. jld

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Linear types using kinds?
by Gregory Crosswhite 13 Dec '11

13 Dec '11

Hey everyone! So, I was on LtU reading about F* http://lambda-the-ultimate.org/node/4318 and an idea just occurred to me which *must* have occurred to someone smarter than me, so I would love your feedback on the following question: Could Haskell be extended to support linear/affine types (in order to have, for example, more efficient resource management) by extending the kind system to include such types? Or, even if the answer were yes, does the use of monads and higher-order types (like those used in "runST" function for the ST monad) make linear/affine types completely redundant in Haskell. Thanks a lot! Greg

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indentation blues
by Ben Kolera 13 Dec '11

13 Dec '11

I am fairly new to haskell, but I really like the emacs haskell mode. It is a bit strict but it generally does what I want it to. Unfortunately I can't really compare to the haskell vim mode since I only did Scala and Perl back when I was a heavy vim user. The one useful thing that I can add is that there are some really good packages out there for modal vi keybindings in emacs. If you truly like the vim keybindings better then you can still use them in emacs. I hope that helps a little bit. On Tue, Dec 13, 2011 at 10:50 AM, Martin DeMello <martindemello(a)gmail.com> wrote: > The vim autoindent for haskell is really bad :( Is there a better > indent.hs file floating around somewhere? Alternatively, is the emacs > haskell mode better enough that it's worth my time learning my way > around emacs and evil? > > martin > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Module name space question
by Christoph Breitkopf 12 Dec '11

12 Dec '11

Hi, I recently asked about what interfaces to implement for a new data type. Following the rule that the last 10% of work take the second 90% of time, some other questions have come up. If anyone wants to look at the code in question: http://www.chr-breitkopf.de/comp/IntervalMap Some time ago, I was looking for a data structure to search in sets of possibly overlapping intervals, and found only Data.SegmentTree, which did not fit my needs (nice term for "I did not understand the type signatures"). So I started to roll my own IntervalMap implementation. But yesterday I used Hayoo instead of Hoogle for the first time, and found Data.IntervalMap.FingerTree. This has an Interface that I _do_ understand, and, while slightly different from my aims (depite the name, it seems more like a multi-map and does not offer lookup of specific keys), it raises some tasks/questions: Tasks: Benchmark against my implementation, and maybe scrap own if it performs worse. And questions: 1. Why doesn't Hoogle find this? 2. Module name space pollution I would have been so bold to name my module Data.IntervalMap. Now, since even Ross Patterson uses a submodule name instead, what is the accepted practice? If I decide to release my class after all, what should be the name? Data.IntervalMap.RedBlackTree ? Or even Data.IntervalMap.MyDomaindNameOrSomething. An I even have a module Data.IntervalMap.Interval, so if Ross had decided to put his Interval type into a separate module, even FingerTree vs RedBlackTree would not have prevented a name clash. 3. Are there more wothwile operations on this data structure? Data.IntervalMap.FingerTree has 'dominators', which I missed. A function to extract the interval with the largest endpoint might be useful, too. Any more ideas? TIA, Chris

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Cabal: Disjunctive Build-Depends
by Matthew Farkas-Dyck 12 Dec '11

12 Dec '11

Hello all. I have written some code that can be compiled with either of two libraries, with no modification. How can I tell Cabal? I tried "||" but it failed to parse. I could find which package is available in the build script, and then call defaultMainNoRead with the appropriate GenericPackageDescription, but I'm not sure how to find this system-agnostically. Thanks for any help. Cheers, Matthew Farkas-Dyck

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