August 2013 - Haskell-Cafe

Contracts
by Julian Arni 08 Aug '13

08 Aug '13

I've come across interesting papers - and old, sometimes inaccessible, repositories - related contracts in Haskell (Dana Xu and SPJ's papers; haskellcontracts and the Programatica Project). And then some newer, apparently not quite mature projects (Dan Rosen's repositories, for instance). Is there anything in between - mature, but not abandoned? Thanks, Julian

3 4

ANN: FunGEn 0.4.2, an easy cross-platform OpenGL/GLUT game engine
by Simon Michael 08 Aug '13

08 Aug '13

I'm pleased to announce the hackage release of FunGEn 0.4! (Actually 0.4.2 as my 0.4 announcement did not reach the mail lists.) FunGEn (Functional Game Engine) is a BSD-licensed, cross-platform, OpenGL/GLUT-based, imperative game engine/framework. With very few dependencies and two example games, it's one of the easiest ways to get started with game development in Haskell. FunGEn was probably the first Haskell game framework, created by Andre Furtado in 2002 (!). Here's his original feature list: * Initialization, updating, removing, rendering and grouping routines for game objects; * Definition of a game background (or map), including texture-based maps and tile maps; * Reading and intepretation of the player's keyboard input; * Collision detection; * Time-based functions and pre-defined game actions; * Loading and displaying of 24-bit bitmap files; * Some debugging and game performance evaluation facilities; * Sound support (actually for windows platforms only... :-[ ) What's new in 0.4.x: * a new hakyll-based website, incorporating the old site content * new haddock documentation * tested with GHC 7.6 * fixed buggy input when holding down keys on windows * input handlers now receive mouse position and modifier state (inspired by Pradeep Kumar; see fungentest.hs for examples) * added q as quit key in examples Home: http://joyful.com/fungen Hackage: http://hackage.haskell.org/package/FunGEn Code: http://hub.darcs.net/simon/fungen Install from hackage: $ cabal update $ cabal install FunGEn Install source and run examples: $ darcs get http://hub.darcs.net/simon/fungen $ cd fungen $ cabal install $ (cd examples/pong; ghc pong; ./pong) $ (cd examples/worms; ghc worms; ./worms) Contribute patches: - log in to hub.darcs.net and fork http://hub.darcs.net/simon/fungen - push changes to your branch - give me a "pull request" on #haskell-game I have maintained FunGEn very sporadically. If you'd like to take it and run with it, or co-maintain, let's chat! I'm sm on the #haskell-game IRC channel. -Simon

1 0

Installing wxHaskel on Snow Leopard
by Eduardo Sato 08 Aug '13

08 Aug '13

Hello, guys. Has anybody tried to install wxhaskell on Snow Leopard? I followed these instructions: http://www.haskell.org/haskellwiki/WxHaskell/Mac , but got an error: src/haskell/Graphics/UI/WXCore/WxcClassesAL.hs:13085:1: Unacceptable argument type in foreign declaration: CInt When checking declaration: foreign import ccall safe "static wxLogWindow_Create" wxLogWindow_Create :: Ptr (TWindow a) -> CWString -> CBool -> CBool -> IO (Ptr (TLogWindow ())) src/haskell/Graphics/UI/WXCore/WxcClassesAL.hs:13085:1: Unacceptable argument type in foreign declaration: CInt When checking declaration: foreign import ccall safe "static wxLogWindow_Create" wxLogWindow_Create :: Ptr (TWindow a) -> CWString -> CBool -> CBool -> IO (Ptr (TLogWindow ())) Failed to install wxcore-0.90.0.3 cabal: Error: some packages failed to install: wx-0.90.0.1 depends on wxcore-0.90.0.3 which failed to install. wxcore-0.90.0.3 failed during the building phase. The exception was: ExitFailure 1 http://lpaste.net/91634 I'm using ghc 7.6.3. I've heard the above problems are related to GHC 7.6.3 being more pedantic about FFI declarations. Is there any way around it? Thanks -- Eduardo Sato

4 7

Call for Participation: Workshop on Functional Art, Music, Modeling and Design
by Brent Yorgey 08 Aug '13

08 Aug '13

====================================================================== FARM 2013: Call for Participation ACM SIGPLAN Workshop on Functional Art, Music, Modeling and Design Boston, Massachusetts, USA 28th September, 2013 (directly after ICFP) http://www.cis.upenn.edu/~byorgey/farm13/ ====================================================================== The functional programming community is largely interested in writing beautiful programs. This workshop is intended to gather researchers and practitioners interested in writing beautiful programs that generate beautiful artifacts. Such artifacts may include visual art, music, 3D sculptures, animations, GUIs, video games, physical models, architectural models, choreographies for dance, poetry, and even physical objects such as VLSI layouts, GPU configurations, or mechanical engineering designs. The goal of FARM is to gather together researchers, practitioners, and educators in this interdisciplinary field, as well as anyone else with even a casual interest in the area. We wish to share ideas, look for common ground, and encourage more activity. We also hope to legitimize work in the field and facilitate potential collaboration among the participants. Registration ------------ Deadline for early registration: 22 August 2013 https://regmaster3.com/2013conf/ICFP13/register.php This is the registration site for ICFP 2013 and all the affiliated workshops including FARM 2013. Accepted papers and demonstrations ---------------------------------- - Samuel Aaron and Alan F. Blackwell. From Sonic Pi to Overtone: Creative Musical Experiences with Domain-Speciﬁc and Functional Languages - Henrik Bäärnhielm, Mikael Vejdemo-Johansson and Daniel Sundström. Using Haskell as DSL for controlling immersive media experiences (Demo) - Guillaume Baudart, Louis Mandel and Marc Pouzet. Programming Mixed Music in ReactiveML - Jean Bresson, Raphael Foulon and Marco Stroppa. Reduction as a Transition Controller for Sound Synthesis Events - Kelsey D'Souza. PySTEMM - A STEM Learning Tool for Exploring and Building Executable Concept Models (Demo) - Andy Gill and Brent A. Yorgey. Functional active animation (Demo) - Jason Hemann and Eric Holk. Visualizing the Turing Tarpit - Paul Hudak. Euterpea: From Signals to Symphonies (Demo) - David Janin, Florent Berthaut, Myriam Desainte-Catherine, Yann Orlarey and Sylvain Salvati. The T-Calculus : towards a structured programing of (musical) time and space - David Janin and Florent Berthaut. LiveTuiles for tiled composition of audio patterns (Demo) - Thomas Jordan. Spontaneous Musical Explorations of Visible Symmetric Structures (Demo) - Hendrik Vincent Koops, José Pedro Magalhães and W. Bas de Haas. A Functional Approach To Automatic Melody Harmonisation - José Pedro Magalhães, Bas De Haas, Gijs Bekenkamp, Dion ten Heggeler and Tijmen Ruizendaal. Chordify: Chord Transcription for the Masses (Demo) - Donya Quick and Paul Hudak. Grammar-Based Automated Music Composition in Haskell - Chung‐chieh Shan and Dylan Thurston. Braiding in circles (Demo) Workshop Organization --------------------- Workshop Chair: Paul Hudak Program Chair: Conal Elliott Publicity Chair: Brent Yorgey Program Committee ----------------- - Daniel Cukier (AgileAndArt) - Conal Elliott (Tabula) (chair) - Kathleen Fisher (Tufts University) - Richard Gabriel (IBM Research) - George Giorgidze (University of Tübingen) - Paul Hudak (Yale University) - José Pedro Magalhães (University of Oxford) - Alex McLean (University of Leeds) - John Peterson (Western State Colorado University) - Michael Sperber (Active Group) - Henning Thielemann (Martin-Luther-Universität Halle-Wittenberg) - Brent Yorgey (University of Pennsylvania)

1 0

Proposal for adding finallyError to MonadError
by David Sorokin 08 Aug '13

08 Aug '13

Hi, Café! I have a proposal. I offer to add a new function to the MonadError type class: finallyError :: MonadError e m => m a -> m b -> m a This is a generalization of the standard finally function that has the following signature: finally: IO a -> IO b -> IO a Like function finally, the finallyError function runs the first computation and then runs the second computation regardless of whether an error might arise in the first computation. The first computation defines the result. Introducing semantics of a possible cancellation of the m computation, the finallyError function accepts an additional meaning. The second computation must be performed even in case of cancelling the computation, while function catchError must be ignored. It literally means that the finallyError function cannot be expressed in terms of the catchError function. This idea is essentially inspired by the F# async workflow that does allow cancelling the Async computation. I implemented a similar monad Simulation.Aivika.Cont.Cont for my simulation library Aivika [1]. My monad Cont is an extension of the standard monad with the same name. It uses continuations (namely, three different continuations within one computation). It supports the exception handling and it allows cancelling the computation (the liftIO function should also call finallyError to catch the possible cancellation event if my Cont was a generic monad transformer). In the simulation the cancellation of the computation (actually, of the discontinuous process) is a typical use case. Therefore it should be executed as fast as possible. If I raised a specialized IOException for the cancellation event, then it would be a more costly operation. This is a practical point why the finallyError function cannot be expressed in terms of catchError. Another reason is that the catchError function can eat the cancellation exception, which would be absolutely unacceptable. This is a theoretical reason for introducing finallyError. The finallyError function is very useful for guaranteed releasing the external resources (such as the modeled entities in Aivika) in case of raising an exception and even in case of cancelling the active computation, which is important for simulation, for example. Regarding the standard instances of MonadError, the finallyError function seems to be simple for implementing. It is difficult mainly for the Cont-based monads. So, in Aivika it is more difficult than catchError for my Cont monad. The actual name of the function is not important but here it looks consistent with other functions of the MonadError type class. Finally, the finallyError function can be actually defined in an additional type class, which would extend MonadError like that how the ArrowChoice type class extends Arrow. Kind regards, David Sorokin [1] https://github.com/dsorokin/aivika

1 0

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

2 1

ANN: Monad.Reader Issue 22
by Edward Z. Yang 08 Aug '13

08 Aug '13

I am pleased to announce that Issue 22 of the Monad Reader is now available. http://themonadreader.files.wordpress.com/2013/08/issue22.pdf Issue 22 consists of the following two articles: * "Generalized Algebraic Data Types in Haskell" by Anton Dergunov * "Error Reporting Parsers: a Monad Transformer Approach" by Matt Fenwick and Jay Vyas * "Two Monoids for Approximating NP-Complete Problems" by Mike Izbicki Feel free to browse the source files. You can check out the entire repository using Git: git clone https://github.com/ezyang/tmr-issue22.git If you’d like to write something for Issue 23, please get in touch! Cheers, Edward

3 2

Is there a Galois correspondence between a Haskell class hierarchy and a given instance hierarchy?
by Patrick Browne 08 Aug '13

08 Aug '13

1 0

ANNOUNCE: tasty, a new testing framework
by Roman Cheplyaka 08 Aug '13

08 Aug '13

I am pleased to announce the first release of tasty, a new testing framework for Haskell. It is meant to be a successor to test-framework (which is unmaintained). Tasty supports HUnit, SmallCheck, QuickCheck, and golden tests out of the box (through the standard packages), but it is very extensible, so you can write your own test providers. Please see the home page for more information: http://documentup.com/feuerbach/tasty Roman

8 18

Module names from a function name
by Jong-won Choi 08 Aug '13

08 Aug '13

Hi, I asked this question to beginner mailing list and no luck so far, so I'm trying here. How can I get all the module names which (re-)export a given function name? I'd like to fix Emacs Haskell mode - interactive documentation browser and I need the list of such module names. Thanks! - Jong-won

2 1