- Haskell-Cafe - Haskell.org

Constructor discipline and dependent types.
by Patrick Browne 17 Jul '11

17 Jul '11

Hi, My understanding of the constructor discipline (CD) is that it is a restriction on the form of an equation that guarantees that the equation represents an executable function. The CD restricts the LHS of an equation to consist of a function name, constructors, and variables. Also there should be no new variables on the RHS. So CD permits function to be defined and prohibits general assertions which are more in the domain of a specification language. Question 1: Is the above a reasonable understanding of CD? Question 2: I have read that the lack of dependent types (DT) prevents writing general assertions in Haskell. Is CD related to DT? If so how are they related? Regards, Pat This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

2 1

Animas/Yampa: ArrowChoice?
by Ertugrul Soeylemez 16 Jul '11

16 Jul '11

Hello all, I really like the way Animas (fork of Yampa) represents reactive systems, and I would love to write some of my simulations using it. Unfortunately most of what I want to do requires dynamic systems, which can be boiled down to me believing to need an ArrowChoice instance for the SF arrow, because I have to choose between different signal paths depending on the input signal or events. Animas appears to be only suitable for robot-like systems with specific, predefined actors. Is there anything I can do about it? Is it difficult to write the ArrowChoice instance? Or is there a different solution, which I overlooked? Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

4 3

urWeb, Haskell and dependent types ....
by Vasili I. Galchin 16 Jul '11

16 Jul '11

Hello, Here is probably a good paper to get people up to speed on dependent types (ironically written by two contributors to this mailing list??): okmij.org/ftp/papers/lightweight-static-capabilities.pdf Vasili

1 0

How to determine minimal dependency of package
by yi huang 15 Jul '11

15 Jul '11

I'm writing my first haskell package, how do i determine the minimal dependency of it, for example, it use Data.Data, how do i know which version of base package first introduce Data.Data module, i can't find the answer with google. -- http://www.yi-programmer.com/blog/

4 3

Domain-Specific Languages: Call for Participation
by Chung-chieh Shan 15 Jul '11

15 Jul '11

DSL 2011: IFIP Working Conference on Domain-Specific Languages 6-8 September 2011, Bordeaux, France **** Call for Participation: Online registration deadline July 30, 2011 **** Details of the program and accommodation are available at http://dsl2011.bordeaux.inria.fr. == Invited Speakers == - Jeremy Gibbons - University of Oxford, UK. - Claude Kirchner - INRIA, France. == Distilled Tutorials on Domain-Specific Languages == The purpose of these tutorials are not to give a general overview, but to make the attendees aware of one point and to make them master it. - Jerzy Karczmarczuk. Specific "scientific" data structures, and their processing. - Oleg Kiselyov. Implementing explicit and finding implicit sharing in embedded DSL. - Keiko Nakata. A total interpreter for While with interactive I/O. - Josef Svenningsson. Combining deep and shallow embeddings for EDSLs. - Walid Taha. Accurate programming: thinking about programs in terms of properties. - William Cook. Build your own partial evaluator in 90 minutes. == DSL Technical Papers == - Basile Starynkevitch. MELT a Translated Domain Specific Language Embedded in the GCC Compiler. - Azer Bestavros and Assaf Kfoury. A Domain-Specific Language for the Incremental and Modular Design of Large-Scale Verifiably-Safe Flow Networks. - Tiark Rompf, Kevin J. Brown, Hassan Chafi, Hyoukjoong Lee, Arvind K. Sujeeth, Martin Odersky and Kunle Olukotun. Building-Blocks for Performance Oriented DSLs. - Dominic Orchard and Alan Mycroft. Efficient and Correct Stencil Computation via Pattern Matching and Static Typing. - Tim Bauer, Martin Erwig, Alan Fern and Jervis Pinto. Adaptation-Based Programming in Haskell. - Eric Walkingshaw and Martin Erwig. A DSEL for Studying and Explaining Causation. - Lucas Beyak and Jacques Carette. SAGA: A DSL for story management.

1 0

GHC API output files options problem
by Marianna Rapoport 15 Jul '11

15 Jul '11

Hi all, we are working on a Haskell support plugin for IntelliJ IDEA, and need to provide correct compilation of Haskell programs. We compile the latter using GHC API, with options specifying .hi and .o paths. For some reason, unlike a standalone GHC compilation, GHC API ignores the values of the outputFile and outputHi flags. Please find attached a minimal example where "err_test.hs" uses GHC API to compile "src/A.hs". Thus, "test_ghc.sh" and "test_my.sh" should do the same, but the first works correctly while the latter puts "use.o" and "use.hi" to the "src" folder. To launch "test_my.sh", please change the value of lib in "err_test.hs" according to your GHC installation path. Thank you very much in advance! Marianna Rapoport, amaurremi(a)gmail.com Oleg Sobolev, sobolev_ov(a)mail.ru

1 0

HaskellDB DB Layout Description
by Tom Murphy 15 Jul '11

15 Jul '11

Hi, I've found good explanations of the HaskellDB combinators, but I can't find good information about how to correctly define the database layout. Can anyone point me to a resource, or give a quick example? Thanks! Tom

2 2

Request for comments: dbus-core 0.9
by John Millikin 15 Jul '11

15 Jul '11

I think I'm pretty close to releasing the next version of my D-Bus library, dbus-core. This is a big release that changes a lot of the API, so I'd like to see if anybody 1) has any problems with the new APIs or 2) has any suggested improvements. haddock: https://john-millikin.com/temp/dbus-core_0.9/ tarball: https://john-millikin.com/temp/dbus-core_0.9.tar.gz pdf: https://john-millikin.com/temp/dbus-core_0.9.pdf examples: https://john-millikin.com/temp/dbus-core_0.9/examples/ Notable improvements in this release are: • Merges dbus-core and dbus-client. The modules "DBus.Client" and "DBus.Client.Simple" provide a very nice, high-level API to common D-Bus operations. Note: I've reverted to the dbus-client_0.3 API for this, since not many users liked the monad-based API introduced in 0.4. • The class Variable was split into IsAtom, IsValue, and IsVariant. Together these let the rest of the type conversion API go away -- you no longer have to worry about Array, Structure, or Dictionary (except in a few, rare cases). • Support for custom transports (eg, a pipe or in-memory buffer). • Improved support for custom authentication mechanisms. Also, while the docs are obviously not finished, I'm interested to know if anyone finds any parts of the library confusing -- those'll get extra doc love.

1 0

Call for GUI examples - Functional Reactive Programming
by Heinrich Apfelmus 14 Jul '11

14 Jul '11

Dear Haskellers, Can GUI programming be liberated from the IO monad? Functional Reactive Programming (FRP) promises as much, and I'm trying to make this dream a reality with my [reactive-banana][] library. Having released version 0.4.0.0, I am now looking for example programs to direct the future evolution of the library. Do you know any *small GUI programs* that you would *like* to see *implemented with Functional Reactive Programming?* I'm sure that some of you * are interested in FRP and would like to learn from a few simple but beautiful examples * or have written small GUI programs that they are unhappy with because they were not purely functional * or have thought about FRP before and concocted a few examples that are very tricky to implement with FRP * or have written a nice little GUI application that simply makes a great example. I would love to hear your examples, so that I can try to convert them to FRP style and test my library against them! Strictly speaking, it doesn't have to be an example with a graphical interface, I'm also interested in audio and animation examples, though I'm currently focusing on GUIs. Here a few examples of what I am looking for: * I think that Tim Docker's minimal step sequencer [hbeat][] simply makes a great example. I hope that wxHaskell offers a platform-independent way to play sound. * While editing the [Haskell Weekly News][hwn], Brent Yorgey wrote a little command-line [program to gather newsworthy items][zipedit]. But wouldn't a GUI be great? Since I'm only interested in the GUI, someone would have to supply the feed parser for this example to be viable. Maybe the current editor, Daniel Santa Cruz, might be interested? * Notes of a musical performance can be modeled as event streams (MIDI), as Henning Thielemann has [done with great effect][midi streams]. Surely, reactive-banana should be up to the task, but writing an arpeggiator seems impossible at the moment. [reactive-banana]: http://hackage.haskell.org/package/reactive-banana [zipedit]: http://byorgey.wordpress.com/2008/06/21/zipedit/ [hbeat]: http://dockerz.net/twd/hBeat [midi streams]: http://hackage.haskell.org/package/streamed [hwn]: http://www.haskell.org/haskellwiki/Haskell_Weekly_News Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com

19 39

Re: [Haskell-cafe] FFI for a beginner
by Donn Cave 14 Jul '11

14 Jul '11

>> The docs <http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#glasgo…> >> say that -#include pragmas no longer work, but fail to explain how to >> load code without them. Suffice to say I have no recourse but trial >> and error." > > Ah, now that is a GHC documentation question. Can you tell us what > should the docs should say instead? Then we can fix the docs. - I believe I would say (agreeing with M Parès) that hsc2hs serves this purpose - put "#include <termios.h>" in the .hsc file and use hsc2hs features like #const and (#peek x, y). The termios example could cover a lot more ground by operating on the termios struct and calling tcsetattr directly from Haskell, using hsc2hs # macros (I append an example implementation), but you'd also want to explain that hsc2hs is only needed for these # macros, not for FFI in general. But hsc2hs as of GHC 7.0.3 generates a "{-# INCLUDE" pragma, which of course is cause for complaint from ghc. So there might be more to be fixed, beyond just the documentation. That line probably has no actual purpose other than to annoy ghc, and as a workaround it can simply be removed from the .hs file. - My impression is that Greencard isn't the best way to get started with FFI and hasn't been for a decade or so, so it should probably be purged from docs. - The "root" page needs some attention from someone who understands what "safe" and "unsafe" mean. Currently (under "Improving efficiency") it cites the conventional interpretation that a function must be "safe" if it calls back into the runtime, but neglects to mention that it must also be "safe" if it is not to block execution of other threads, including bound OS threads - so related to efficiency issues you might want to make any slow I/O operation "safe" to avoid this. There may be other points about "unsafe" that need to be documented. Donn -------- {-# LANGUAGE ForeignFunctionInterface #-} module TTY (clearICANON) where import Data.Word (Word32) import Foreign import Foreign.C #include <termios.h> type TCFlag = (#type tcflag_t) type Speed = (#type speed_t) data Termios = Termios { termios_c_iflag :: TCFlag , termios_c_oflag :: TCFlag , termios_c_cflag :: TCFlag , termios_c_lflag :: TCFlag , termios_c_cc :: [CChar] , termios_c_ispeed :: Speed , termios_c_ospeed :: Speed } deriving Show instance Storable Termios where sizeOf _ = #size struct termios alignment _ = alignment (undefined::CDouble) peek a = do iflag <- (#peek struct termios, c_iflag) a oflag <- (#peek struct termios, c_oflag) a cflag <- (#peek struct termios, c_cflag) a lflag <- (#peek struct termios, c_lflag) a cc <- peekArray 20 ((#ptr struct termios, c_cc) a) ispeed <- (#peek struct termios, c_ispeed) a ospeed <- (#peek struct termios, c_ospeed) a return (Termios iflag oflag cflag lflag cc ispeed ospeed) poke a (Termios iflag oflag cflag lflag cc ispeed ospeed) = do (#poke struct termios, c_iflag) a iflag (#poke struct termios, c_oflag) a oflag (#poke struct termios, c_cflag) a cflag (#poke struct termios, c_lflag) a lflag pokeArray ((#ptr struct termios, c_cc) a) (take 20 (cc ++ repeat 0)) (#poke struct termios, c_ispeed) a ispeed (#poke struct termios, c_ospeed) a ospeed foreign import ccall "tcgetattr" tcgetattr :: CInt -> Ptr Termios -> IO CInt foreign import ccall "tcsetattr" tcsetattr :: CInt -> CInt -> Ptr Termios -> IO CInt setLFlag :: TCFlag -> Termios -> Termios setLFlag c a = a { termios_c_lflag = ((termios_c_lflag a) .|. c) } clearLFlag :: TCFlag -> Termios -> Termios clearLFlag c a = a { termios_c_lflag = ((termios_c_lflag a) .&. (complement c)) } setTTYAttr :: CInt -> (Termios -> Termios) -> IO () setTTYAttr fd fn = alloca $ \ termiosp -> do status <- tcgetattr fd termiosp if status == 0 then do termios <- peek termiosp poke termiosp (fn termios) status <- tcsetattr fd (#const TCSAFLUSH) termiosp if status == 0 then return () else throwErrno "tcgetattr" else throwErrno "tcgetattr" clearICANON = setTTYAttr 0 (clearLFlag (#const ICANON))

1 0