January 2010 - Haskell-Cafe

Atom's `__global_clock' and `__scheduling_clock'.
by Jason Dusek 03 Jan '10

03 Jan '10

I am mystified by the relationship between Atom's `__global_clock' and the `scheduling_clock'. For example, here is some generated code: /* Includes omitted. */ static uint64_t __global_clock = 0; /* Subroutine declarations omitted. */ void main(void) { { static uint8_t __scheduling_clock = 0; if (__scheduling_clock == 0) { __r0(); /* main.set_up_pins */ __r1(); /* main.set_up_timer */ __scheduling_clock = 0; } else { __scheduling_clock = __scheduling_clock - 1; } } __global_clock = __global_clock + 1; } Looking at code generated by an older version of Atom, it seems like there used not be separate "global" and "scheduling" clocks: /* From http://code.sw17ch.com/blog/atom/blink_atom.c */ void blink_atom(void) { if (__clock % 1 == 0) { r0(); /* blink_atom.decrement */ } if (__clock % 2 == 0) { r1(); /* blink_atom.reset */ } if (__clock % 2 == 1) { r2(); /* blink_atom.flip */ } __clock = __clock + 1; } I would like to know how the `__global_clock' influences execution in the present system. -- Jason Dusek

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lazily-loaded structures
by Jeff Davis 01 Jan '10

01 Jan '10

I'm relatively new to haskell. Let's say I have a simple program like this: import Data.Map type Tree = String type StringMap = Map String String f :: StringMap -> Tree -> Tree f _ y = y ++ "!" getStringMap :: IO StringMap getStringMap = return (Data.Map.fromList [("k1","v1")]) main :: IO () main = do m <- getStringMap s <- getLine putStr $ show (f m s) ++ "\n" Ignore the implementation of f and getStringMap for now. Assume f is a fairly complex function that uses the Map during the process of transforming the Tree argument into the result Tree (here I defined Tree as a string just so that it would compile). getStringMap reads the whole Map into memory at once. However, now let's say that the whole Map is too large, so I decide to store it over a network in a remote database system instead. And then I define another function like: type Connection = String getStringMapValue :: Connection -> String -> IO String that takes a connection string and a key and returns the value. My question is this: how do I change my program to make StringMap a lazily-loaded structure based on getStringMapValue without changing f? Regards, Jeff Davis

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ANN: HPath-0.0.2
by Jason Dusek 01 Jan '10

01 Jan '10

This version of `HPath' depends on new release of `haskell-src-exts' with improved pretty printing. http://hackage.haskell.org/package/HPath-0.0.2 No other changes have been made. -- Jason Dusek

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Linking in Large ByteStrings
by Tom Hawkins 01 Jan '10

01 Jan '10

I have a large tarball I want to link into an executable as a ByteString. What is the best way to do this? I can convert the tarball into a haskell file, but I'm afraid ghc would take a long time to compile it. Is there any way to link constant data directly with ghc? If not, what's the most efficient way to code large ByteStrings for fast compilation?

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ANNOUNCE: restyle-0.1.0
by Daniel Fischer 01 Jan '10

01 Jan '10

I have the pleasure to announce restyle-0.1.0, a tool for the conversion of Haskell source between camelCase and separated_words style. If you want to read your local haddockumentation in your favourite separated-words style, it can do that too, with a liberal choice of separation characters. If you prefer to do your coding in separated_words, it may be as easy as one restyle to then deliver your cool library to the world in the prevalent camelCase (well, it'll probably take a few minor version bumps before that, but we can hope). If you love underscores or hyphens, give it a try. If it sucks, at least it wasn't *your* wasted effort :)

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Timing in atom -- how consistent?
by Jason Dusek 01 Jan '10

01 Jan '10

I'm working with Atom to program an ATtiny25. I am curious about how consistent the timings actually are. Consider John Van Enk' example of blinking a LED on an Arduino: http://code.sw17ch.com/blog/atom/blink_atom.c We see that sometimes `setLED' is executed and sometimes not. When `__clock' is incremented, it will be incremented sometimes sooner, sometimes later. Also, I am a little puzzled by the `__coverage` variable. What does it do? As for my project/motivation -- I'm just trying to blink a little LED on much less robust/rich kit -- the Trippy RGB Waves kit from Lady Ada. I am (gratuitously) exploring ways to program it with Haskell. -- Jason Dusek

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ANN: WFLP 2010 Call for participation
by Pablo Nogueira 01 Jan '10

01 Jan '10

******************************************************************** Call For Participation WFLP2010 19th International Workshop on Functional and (Constraint) Logic Programming Madrid, Spain, January 17, 2010 http://babel.ls.fi.upm.es/events/wflp2010/ ********* colocated with Principles of Programming Languages POPL 2010 http://www.cse.psu.edu/popl/10/ ******************************************************************** IMPORTANT DATES Hotel reservation deadline: December 28, 2009 VENUE WFLP2010 and all POPL'10 affiliated events will take place at the Melia Castilla Hotel, Madrid. REGISTRATION To register for WFLP2010, follow the link from the POPL 2010 page, at http://www.cse.psu.edu/popl/10/ SCOPE The aim of the Workshop on Functional and (Constraint) Logic Programming is to bring together researchers interested in functional programming and (constraint) logic programming with special emphasis on the integration of both paradigms and of other declarative programming extensions. It promotes the cross-fertilizing exchange of ideas and experiences among researchers and students from the different communities interested in the foundations, applications, and combinations of high-level declarative programming languages and related areas. INVITED SPEAKER Mariangiola Dezani (University of Torino, Italy) ACCEPTED PAPERS Transforming Functional Logic Programs into Monadic Functional Programs Bernd Brassel, Sebastian Fischer, Michael Hanus and Fabian Reck Mixed-level Embedding and JIT Compilation for an Iteratively Staged DSL George Giorgidze and Henrik Nilsson An Access Control Language based on Term Rewriting and Description Logic Michele Baggi, Demis Ballis and Moreno Falaschi Lazy and Faithful Assertions for Functional Logic Programs Michael Hanus Parameterized Models for On-line and Off-line Use Pieter Wuille and Tom Schrijvers A Denotational Semantics for Curry Jan Christiansen, Daniel Seidel and Janis Voigtlander A Declarative Debugger of Missing Answers for Functional and Logic Programming Rafael del Vado Virseda and Fernando Perez Morente Efficient and Compositional Higher-Order Streams Gergely Patai Bridging the gap between two Concurrent Constraint Languages Alexei Lescaylle Daudinot and Alicia Villanueva Garcia Large scale random testing with QuickCheck on MapReduce framework Shigeru Kusakabe and Yuuki Ikuta Automated verification of security protocols in tccp Alexei Lescaylle Daudinot and Alicia Villanueva Garcia Implementation and Evaluation of a Declarative Debugger for Java Herbert Kuchen and Christian Hermanns PROGRAM CHAIR Julio Marino (Universidad Politecnica de Madrid, Spain) PROGRAM COMMITTEE Maria Alpuente (Universidad Politecnica de Valencia, Spain) Sergio Antoy (Portland State University, USA) Bernd Brassel (CAU Kiel, Germany) Olaf Chitil (Univ. of Kent, UK) Rachid Echahed (CNRS-IMAG, France) Santiago Escobar (Universidad Politecnica de Valencia, Spain) Moreno Falaschi (Universita di Siena, Italy) Murdoch Gabbay (Heriot-Watt University, UK) Maria Garcia de la Banda (Monash University, Australia) Victor Gulias (Lambdastream SL, Spain) Michael Hanus (CAU Kiel, Germany) Herbert Kuchen (Univ. of Muenster, Germany) Francisco Lopez-Fraguas (Universidad Complutense de Madrid, Spain) James Lipton (Wesleyan University, USA) Mircea Marin (Univ. of Tsukuba, Japan) Juan Jose Moreno-Navarro (Ministry of Science & Innovation, Spain) Brigitte Pientka (McGill University, Canada)

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Use of the Try typeclass
by Edward Z. Yang 01 Jan '10

01 Jan '10

Hello all, I am currently playing with the new cadre of failure libraries, and I'm trying to figure out how to use the monadic version of Failure while also getting the Try typeclass, which appears to be the standardized mechanism for marshalling values from specific monads into the failure monad. Unfortunately, it only seems to be defined when I import Control.Failure, and this module is fairly incompatible with Control.Monad.Failure, as demonstrated by this GHCI transcript: ezyang@javelin:~/Documents/tmr$ ghci Prelude> :m +Control.Failure Prelude Control.Failure> :m +Control.Monad.Failure Prelude Control.Failure Control.Monad.Failure> :t failure <interactive>:1:0: Ambiguous occurrence `failure' It could refer to either `Control.Failure.failure', imported from Control.Failure or `Control.Monad.Failure.failure', imported from Control.Monad.Failure I'm using MTL, which might be the reason why there's all sorts of unhappiness. :-) Cheers, Edward

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Haskell Hackathon in Boston January 29th-31st?
by Ravi Nanavati 01 Jan '10

01 Jan '10

After all of the fun I had at Hac Phi, I've been thinking for a while that it would be fun to organize a Boston hackathon (to have all of the hackathon fun without the long drive). After some recent chats with my MIT friends, it seems like the weekend just after IAP (January 29th-January 31st) might be a good one. I've created a page to start organizing this hackathon (which I'm calling HacBOS unless someone comes up with a catchier name) here: http://www.haskell.org/haskellwiki/HacBOS If you'd be interested in attending a Boston hackathon, please add yourself to the possible attendees list on that page. If the proposed weekend does NOT work for you, but you're still interested in attending a Boston hackathon please indicate what other weekends during MIT's IAP (January 4th-January 29th) might work for you. I'm looking forward to making HacBOS happen! Thanks, - Ravi Nanavati

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