November 2009 - Haskell-Cafe

Re: [Haskell-cafe] hackage is down.
by scooter.phd＠gmail.com 02 Nov '09

02 Nov '09

Untenable for many "corporate" users administratively prohibited from running any P2P software. First really creative use of a DHT I've seen in 6 years, kudos. ------Original Message------ From: Shelby Moore Sender: haskell-cafe-bounces(a)haskell.org To: haskell-cafe(a)haskell.org ReplyTo: shelby(a)coolpage.com Subject: Re: [Haskell-cafe] hackage is down. Sent: Nov 1, 2009 19:57 Opportunity cost minimization problem: >> No no no! Why not download the normal (signed) cabal list from the >> DHT (and optionally directly from hackage.haskell.org)? These are all >> the packages that would appear on the website. Why serve any other >> content? All nodes in the DHT may check and make sure the file (or >> fragment) being served is properly signed. >> >> Any desire for popularity or tagging capability should be separate. >> > Because single single hackage private key can be bruteforsed or stolen > far easier than lots and lots keys of random people. > > > >>> + User maintains list of trusted people's open keys, in order to >>> validate authenticity and see trusted ratings. >> >> This would need further explanation, but in general I'm against >> requiring user interaction on this level. > You choose who's moderating packages for you. Some well-known community > moderators and your trusted friends. If no one rated package yet, then > you download and rate, so people who trust you can make decision based > on your rate. > Kind of social network. In short, P2P introduces non-determinism. Non-determinism is natural law and otherwise order is not permanent (e.g. ends in non-composability, errors, vulnerabilities, etc): http://www.haskell.org/pipermail/haskell-cafe/2009-November/068432.html What is needed is some way to set up upper bound to the level of non-determinism in some useful domain: http://www.haskell.org/pipermail/haskell-cafe/2009-October/068382.html (space determinism in Haskell) Which are really opportunity cost minimizations: http://forum.bittorrent.org/viewtopic.php?id=28 (my architectural comments about BitTorrent free loading) http://goldwetrust.up-with.com/technology-f8/computers-t112-15.htm#2189 (long winded, not so coherent brainstorming) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Sent from my Verizon Wireless BlackBerry

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ghci REPL output under Haskell Platform on Mac OS X
by Mark Lentczner 01 Nov '09

01 Nov '09

My ghci installation has a very annoying behavior: When it takes input, the result is displayed on the same line as the input, overwriting the prompt and input. Viz.: [1015] : ghci GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. 7relude> 3 + 4 Prelude> Note the 7 that overwrites the P in Prelude. I have had several prior versions of ghci installed, most recently 6.10.1, and they never had this problem. (In other words, I saw: Prelude> 3 + 4 7 Prelude> Those prior gchi's were installed from the GHC binaries. Most recently I decided to give Haskell Platform a try, and I installed that. That is the point at which this behavior started. My environment: Haskell Platform 2009.2.0.2 GHC 6.10.4 (installed w/Haskell Platform) Mac OS X 10.6.1 Oddly, I have GHC 6.10.4 installed from GHC binaries on a Mac OS X 10.5 machine at work, and the newline behavior is correct. So the issue could be Haskell Platform vs. GHC installs... or it could be 10.5 vs. 10.6 Anyone seen anything like this? - Mark

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hSeek in Windows
by Philippos Apolinarius 01 Nov '09

01 Nov '09

As many people guess, I am trying to port programs from Clean 1.3 to Haskell (and also to Clean 2.2, which is easier, but not much easier). Late Professor Wellesley wrote an interesting data base manager in Clean 1.3 that I would like to see in Haskell and Clean 2.2. However, when I tried to implement the BTree algorithm, GHC compiler did not accept hSeek and other IO operations. D:\Programs\GHC-PROGS\docs\textut>ghc btree.hs --make [1 of 1] Compiling Main ( btree.hs, btree.o ) Linking btree.exe ... D:\Programs\GHC-PROGS\docs\textut>btree.exe btree.exe: teste.txt: hSeek: illegal operation (seek operations on text-mod dles are not allowed on this platform) To make a long story short, the program compiles, but does not run. This is interesting, because when Clean compiles an input/output operation it certainly executes it. In any case, what I should do in order to make file operations work on Windows? I need random access to text files. __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now http://ca.toolbar.yahoo.com.

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Calling Haskell from C, Linking with gcc?
by John Velman 01 Nov '09

01 Nov '09

I think if I knew which libraries to add to the gcc link, I could make this work, but can't seem to find out from the documentation. Here are more specifics: I'd like to build a Cocoa program on OS X with the Aqua user interface using Xcode, but using a Haskell module with functions accessed through the foreign export interface. In fact this seems to fit in well with the Apple Model-View-Control programming pattern, with Haskell implementation of the Model, maybe some of the Control, and Cocoa implementation of the View and some of the Control. I've put together a short program (from the Wiki calling Haskell from C example) and compiling and linking with ghc it runs as advertised. As an experiment, I put the c main program into an Xcode project, added the haskell module .o and stub.o, stub.h files. Also added the HsFFI.h. Then did a build and run. As expected I got a bunch of missing entry points (26, if I recall correctly). Adding libffi.a and libHSrts.a brings me up to 56 missing entry points. Searching the other lib files for these seems pretty hopeless. Any pointers to documentation, or other help will be greatly appreciated! Thanks, John Velman

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Newcomers question
by b1g3ar5 01 Nov '09

01 Nov '09

I'm trying: instance Num b => Num (a -> b) where fromInteger = pure . Prelude.fromInteger negate = fmap Prelude.negate (+) = liftA2 (Prelude.+) (*) = liftA2 (Prelude.*) abs = fmap Prelude.abs signum = fmap Prelude.signum but the compiler rejects it with: src\Main.hs:24:9: Could not deduce (Show (a -> b), Eq (a -> b)) from the context (Num b) arising from the superclasses of an instance declaration at src\Main.hs:24:9-29 Possible fix: add (Show (a -> b), Eq (a -> b)) to the context of the instance declaration or add an instance declaration for (Show (a -> b), Eq (a -> b)) In the instance declaration for `Num (a -> b)' Could someone please explain this to me? I thought that it might be that it couldn't work out the functions necessary for (a->b) to be in the classes Show and Eq - so I tried adding definitions for == ans show, but it made no difference. Thanks

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Re: [Haskell-cafe] ANN: mecha-0.0.2
by Tom Hawkins 01 Nov '09

01 Nov '09

> Neat! What a cool idea. > >> data Solid = Solid (Vector -> Bool) > > With a type like this, how is it possible to make solids without hard edges? Now the only way is to create a new primitive. In the future I want to have blended versions of the set operations to apply fillets or bevels at the joints. But I'm not sure how to do this yet. > Why did you choose a monadic interface? Is there a technical or > semantic problem with a statement like: I was originally thinking a monad would be needed to prevent re-meshing difference instances of the same solid, as well has to generate a bill-of-materials, 2D prints, etc. But you're right, I don't think it's needed. Thanks. See mecha-0.0.2: example :: IO () example = view design design :: Asm design = assemble [ color (0, 0, 0.8) $ place 1 0.06 8 $ difference sphereCube cyl3 , move (-4, 0, 0) $ color (0.8, 0, 0) $ place 1 0.08 8 $ sphereCube , move ( 0, 4, 0) $ color (0, 0.8, 0) $ place 1.5 0.08 8 $ cyl3 ] sphereCube = intersection sphere $ scaleXYZ 0.75 cube cyl = scale (0.5, 0.5, 1.2) $ cylinder cyl3 = unions [cyl, rotateX (pi / 2) cyl, rotateY (pi / 2) cyl]

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Monad Comprehensions
by Günther Schmidt 01 Nov '09

01 Nov '09

Hi all, once again I find myself merely scratching the surface of the power of Haskell, which is exciting and frustrating at the same time. While real world demands require me to find / develop solutions quickly (abstractions for querying data sets) I keep catching glimpses of all this power. But for someone like me it's difficult to assess from these glimpses alone which to study first. In the last few weeks I kept bugging people here on this list about DSLs, so I could create my own to express queries / relational algebra. I'd later choose then to compile this to SQL or to in-memory code. Next thing I notice that I've overlooked list comprehension all this time, which already express quite a lot of what I'd need. And then, on top of it all, monad comprehension, or rather monads period. The thing that particularly set me off was a video from Dan Piponi: http://vimeo.com/6590617 It certainly made me realize how little I have understood how much power merely monads give you. In short, I'm truly lost. If anyone else, with roughly the same starting point as me, has found their way through this jungle I'd certainly appreciate some tips. In particular I wonder if someone has been able to follow what Dan demonstrates in this video, or was it a jaw-dropping experience for everyone else just as me? Günther

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ANNOUNCE: dbus-core 0.5 and dbus-client 0.1
by John Millikin 01 Nov '09

01 Nov '09

These are pure-Haskell client libraries for using the D-Bus protocol. D-Bus is heavily used for inter-application IPC on Free and open-source desktop platforms, such as Linux, OpenSolaris, and FreeBSD. These libraries allow applications written in Haskell to inter-operate with other components of recent GNOME, KDE, and XFCE desktops. This is the first "real" release of these libraries; dbus-core has been published on Hackage for some time, but mostly just to make sure I got the Cabal bits right. I feel they are now stable / featureful enough for public use. Both are available on Hackage: http://hackage.haskell.org/package/dbus-core http://hackage.haskell.org/package/dbus-client --------- "dbus-core" is an implementation of the D-Bus protocol, specifically the parts relevant to clients. Eventually, it will probably grow some functions useful for implementing a message bus as well. It includes type mapping / conversion, an implementation of the wire format (marshaling / unmarshaling), data types for the currently defined message types (METHOD_CALL, METHOD_RETURN, ERROR, and SIGNAL) and a basic parser / generator for introspection documents. It is roughly equivalent in purpose to libdbus. By itself, a protocol implementation is somewhat cumbersome to use, so "dbus-client" is a high-level wrapper. It provides some abstractions like remote object proxies, exported object trees, synchronous method calls, signal reception, and name reservation. Messages are received and processed in separate IO threads, allowing asynchronous method call and signal handling. The purpose between splitting the library into two packages is stability; "dbus-core", ideally, will change only rarely -- performance improvements, new message / data types, etc. It provides a base level of functionality which more specialised libraries may use. "dbus-client" is an example of what such a library could look like, though for now it's not very Haskell-y (IO everywhere, exceptions, explicit locking). By separating the protocol from the client libs, alternative client libs can safely depend on the protocol implementation. --------- To see a sample of the library working, there's a clone of the "dbus-monitor" utility in <dbus-core/Examples>. Documentation is currently a bit lacking, so for now, the best documentation is the PDF of the source code itself, and the (rather barren) Haddock output: https://dl.getdropbox.com/u/1947532/dbus-core_0.5.pdf https://dl.getdropbox.com/u/1947532/dbus-core_0.5/index.html https://dl.getdropbox.com/u/1947532/dbus-client_0.1.pdf https://dl.getdropbox.com/u/1947532/dbus-client_0.1/index.html Once more people have used it without any major API issues, I'll write up a manual and populate the Haddock entries. Please respond with any feedback, difficulties, or suggestions. I'm particularly interested in ways to improve the public API, since I would rather make any breaking changes *before* anything big depends on these libraries.

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ATTN: Singapore based Haskellers - Singapore FP Users Group First Meeting
by Max Cantor 01 Nov '09

01 Nov '09

We are organizing a Functional Programming Users Group in Singapore and our first meeting is Monday, November 2nd at 6 pm. We will meet initially in the Lobby of 8 Shenton Way. Map: http://bit.ly/1PzqlB -or- http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=8+Shenton+Way,+… If you have any trouble, please feel free to call me at +65-9329-6139 Max

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The (>|) function in Control.Parallel.Strategies
by Wei Hu 31 Oct '09

31 Oct '09

The documentation of (>|) says that it "evaluates the first argument before the second". The function is defined as (http://www.haskell.org/ghc/docs/6.10-latest/html/libraries/parallel/src/Con…) (>|) :: Done -> Done -> Done {-# INLINE (>|) #-} (>|) = Prelude.seq I'm curious why it's defined as Prelude.seq, instead of pseq? The semantics seems to require pseq here. I also found the following comment that doesn't make sense to me: The operators >| and >|| are alternative names for `seq` and `par`. With the introduction of a Prelude function `seq` separating the Prelude function from the Strategy function becomes a pain. The notation also matches the notation for strategic function application.

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