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a problem about Regex in Real World Haskell
by wolf python london 13 Nov '10

13 Nov '10

hi ,folks , I'm a newbie of haskell and learn haskell using the textbook "Real World Haskell". in the page 201, ghci> "good food" =~ ".ood" :: [String] my output is here https://gist.github.com/675024 it doesn't match what the textbook gives . And I found the ebook of Real World Haskell doesn't match it ,either(just like my output ) . I was wondering How I can fix this problem about Regex. much thanks ~ -- ________________________ wolf python london(WPL) Do as you soul should do ! ________________________

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HUnit Control.Exception assertFailure?
by Mark Spezzano 13 Nov '10

13 Nov '10

Hi, I'm trying to follow some examples of HUnit from a webpage. Basically I want my _application_ code to call the "error" function when a certain condition is met (namely when a supplied String to a function is longer than 80 characters). I want my _test_ code to "catch" this error. Unfortunately the example code that I'm following uses the older style of Exception handling. Does anyone know how to catch this exception using the newer Control.Exception module? Basically I want to 1. Call error msg when String length > 80 for some function 2. Catch thrown error from step 1 and do absolutely nothing. (i.e. the "expected failure" was caught) 3. If the error is uncaught (in step 2; for whatever reason) then call "assertFailure somemsg" and my _test_ code should fail since the error it was expecting to occur didn't happen. Thanks, Mark Spezzano

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Type Directed Name Resolution
by John Smith 13 Nov '10

13 Nov '10

Type-directed name resolution, as originally proposed for Haskell', has now been proposed for GHC. Obvious benefits of this are that conflicting function names from imported modules can be used without qualification (verbose) or pseudo-Hungarian renaming (verbose, and requires that you control the source, and perform the same renaming in all dependencies). This is important for both readability and programming in the large, particularly where records are concerned, as the duplicate name problem cannot be alleviated with typeclasses, and it is often desirable to have the same field names for many records in the same module. http://hackage.haskell.org/trac/ghc/ticket/4479 http://hackage.haskell.org/trac/haskell-prime/wiki/TypeDirectedNameResoluti…

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Serialization of (a -> b) and IO a
by C. McCann 13 Nov '10

13 Nov '10

Oops, forgot to send this to the list... sorry, Sjoerd. On Thu, Nov 11, 2010 at 11:54 AM, Sjoerd Visscher <sjoerd(a)w3future.com> wrote: >> You would lose many uses of equational reasoning in your programs. Have you >> every substituted 'x * 2' for the expression 'x + x' in one of your programs, >> or vice versa? You can no longer do that, because someone may be serializing >> the function you're writing, checking how it's implemented, and relying it. > > Yes, but it would not break any existing code. It would only break code that knowingly did the wrong thing. Or code that unknowingly depends transitively on code that does the wrong thing. In that regard it would be much like unsafePerformIO, and about as trustworthy. Better off just having any such "serialize" be safely in IO, and let people who want to live dangerously just use unsafePerformIO to get around it. >> We already have a weak case of this, since (\x -> undefined x) can be >> distinguished from undefined using seq, but that can be hand-waved away by not >> worrying about bottoms so much. That isn't going to work for serialize. > > Why not? I'd venture that perhaps because seq only behaves differently when one possible outcome is _|_. An unsafe serialize could distinguish between two non-bottom values, which means the sketchy behavior could be free to wreak havoc in code that's not crashing. For instance, assuming serialize can be applied to functions of any type, it would probably be trivial to write a function (isExpr :: a -> Bool) that reports whether an arbitrary term is a primitive value or the result of some expression, which then lets you write a function with type (forall a. a -> a) that is NOT equivalent to id, which could then be passed freely into any other piece of code you like. That sounds like buckets of fun, doesn't it? - C.

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cabal update error
by Daniel Díaz 13 Nov '10

13 Nov '10

Hi all, I just installed the Haskell Platform, and when I try "cabal update", I have the following output: > Downloading the latest package list from hackage.haskell.org > cabal: failed This error does not give me information about what is wrong. Has anyone had this error before? I would appreciate an explanation (or possible explanation), rather than an "update it manually". Thanks in advance. -- Daniel Díaz

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Serialization of (a -> b) and IO a
by Jesse Schalken 13 Nov '10

13 Nov '10

Is it possible to serialize and deserialize a function to/from binary form, perhaps using Data.Binary, for example? What about an IO action? If so, is there a way the serialized representation could be architecture-independent? I have been shown how useful it can be to store functions inside data structures, and while looking at data serialization for the purpose of persistence I wondered "since functions are just values in Haskell, why can't we persist them, too?". To me the idea has interesting implications. For example, an arbitrary program could simply be represented by a serialization of `IO ()`. In fact, you could load any program into memory from a file and use Control.Concurrent.forkIO to run it, and later kill it, giving you the beginnings of an operating environment. If such a serialization is architecture independent then to my understanding you have the beginnings of a virtual machine. You could break your program into pieces and store them in a database and load them when needed, or even pull updates to each piece individually from down the web etc, enabling interesting methods of software distribution. It would make very cool stuff possible. I have had a look at hs-plugins, but it is unclear how to derive a simple pair of functions `(a -> b) -> ByteString` and `ByteString -> Either ParseError (a -> b)`, for example, from the functionality it provides, if it is possible at all. I guess such a thing requires thorough digging into the depths of GHC, (or maybe even LLVM if an architecture independent representation is sought, but I don't know enough to say.). Perhaps this is more a question for those interested and knowledgable in Haskell compilation (and, to some extent, decompilation). If not Haskell, are there any languages which provide a simple serialization and deserialization of functions?

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an evil type hangs GHC
by Petr Pudlak 12 Nov '10

12 Nov '10

Hi, I was playing with the following example I found in D.A.Turner's paper Total Functional Programming: > data Bad a = C (Bad a -> a) > > bad1 :: Bad a -> a > bad1 b@(C f) = f b > > bad2 :: a > bad2 = bad1 (C bad1) To my surprise, instead of creating a bottom valued function (an infinite loop), I managed to send the GHC compiler (ver. 6.12.1) to an infinite loop. Could anybody suggest an explanation? Is this a GHC bug? Or is this "Bad" data type so evil that type checking fails? Thanks, Petr

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"Haskell is a scripting language inspired by Python."
by Jonathan Geddes 12 Nov '10

12 Nov '10

This is off topic (almost regardless of the topic), but It gave me a laugh. Hope you all enjoy it, too. I was telling a friend about the power and elegance of Haskell. When I mentioned that it has influenced many other programming languages, including his favorite language (Python) he retorted by saying that I was mistaken and it was, in fact, the other way around: Python inspired Haskell. The following link was his source of information (or FUD, as the case may be). http://www.datarecoverylabs.com/ultimate-computer-language-guide.html It's called "The *Ultimate* Computer Language Guide," and it's on the internets, so it must be correct, right? --Jonathan

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ANNOUNCE: The Fibon benchmark suite (v0.2.0)
by David Peixotto 12 Nov '10

12 Nov '10

I'm pleased to announce the release of the Fibon benchmark tools and suite. Fibon is a set of tools for running and analyzing benchmark programs in Haskell. Most importantly, it includes an optional set of benchmark programs including many programs taken from the Hackage open source repository. The source code for the tools and benchmarks are available on github https://github.com/dmpots/fibon http://github.com/dmpots/fibon-benchmarks The Fibon tools (without the benchmarks) are available on hackage. http://hackage.haskell.org/package/fibon The package needs to be unpacked and built in place to be able to run any benchmarks. It can be used with the official Fibon benchmarks or you can create your own suite and just use Fibon to run and analyze your benchmark programs. Some more documentation is available on the fibon wiki https://github.com/dmpots/fibon/wiki Fibon Tools =================================================================== Fibon is a pure Haskell framework for running and analyzing benchmark programs. Cabal is used for building the benchmarks. The benchmark harness, configuration files, and benchmark descriptions are all written in Haskell. The benchmark descriptions and run configurations are all statically compiled into the benchmark runner to ensure that configuration errors are found at compile time. The Fibon tools are not tied to any compiler infrastructure and can build benchmarks using any compiler supported by cabal. However, there are some extra features available when using GHC to build the benchmarks: * Support in config files for using an inplace GHC HEAD build * Support in `fibon-run` for collecting GC stats from GHC compiled programs * Support in `fibon-analyse` for reading GC stats from Fibon result files The Fibon Benchmark Suite =================================================================== The Fibon benchmark suite currently contains 34 benchmarks from a variety of sources. The individual benchmarks and lines of code are given below. Dph _DphLib 316 Dotp 308 Qsort 236 QuickHull 680 Sumsq 72 ------------------------------ TOTAL 1612 Hackage Agum 786 Bzlib 432 Cpsa 11582 Crypto 4486 Fgl 3834 Fst 4532 Funsat 16085 Gf 23970 HaLeX 4035 Happy 5833 Hgalib 819 Palindromes 496 Pappy 7313 QuickCheck 4495 Regex 6873 Simgi 5134 TernaryTrees 722 Xsact 2783 ------------------------------ TOTAL 104210 Repa _RepaLib 8775 Blur 77 FFT2d 89 FFT3d 103 Laplace 274 MMult 133 ------------------------------ TOTAL 9451 Shootout BinaryTrees 63 ChameneosRedux 96 Fannkuch 27 Mandelbrot 68 Nbody 192 Pidigits 26 SpectralNorm 97 ------------------------------ TOTAL 569

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Manatee - The Haskell/Gtk+ Integrated Live Environment first version release!
by Andy Stewart 12 Nov '10

12 Nov '10

Hi all, I am proud to announce the release my gtk2hs project : Manatee - The Haskell/Gtk+ Integrated Live Environment http://hackage.haskell.org/package/manatee Screenshots at : http:goo.gl/MkVw Code at https://patch-tag.com/r/AndyStewart/ beginning with manatee-* Manatee is Haskell integrated environment written in Haskell. The goal of the Manatee project is to provide a fast, safe and flexible integrated environment for haskell hacking. You can consider it is new environment mix Gnome and Emacs. Like Gnome to provide friendly graphics interface and work efficient like Emacs. Manatee use multi-processes framework, any sub-module running in separate process to protected core won't crash. So it minimize your losses when some unexpected exception throw in extension. Now i have implement below sub-modules in Manatee: Editor Webkit Browser File Manager Image Viewer IRC Client Multimedia Player PDF Viewer Process Manager RSS/Atom reader >From some friends feedback, manatee can't work in XMonad, i will fix it soon. You can play it in Gnome. Enjoy! :) Below are steps to build Manatee: 1) Install C library: In Debian use below command: sudo aptitude install libgtksourceview2.0-dev libgconf2-dev libwebkit-dev libcurl4-openssl-dev libgtkimageview-dev libpoppler-glib-dev poppler-data libtagc0-dev -y 2) Install Gtk2hs: cabal install gtk2hs-buildtools gtk And make sure HOME.cabalbin/ in your PATH. 3) Install Manatee: cabal install manatee-core manatee-anything manatee-browser manatee-editor manatee-filemanager manatee-imageviewer manatee-ircclient manatee-mplayer manatee-pdfviewer manatee-processmanager manatee-reader manatee That's all, then type command manatee to play it! :) "manatee-core" "manatee-anything" "manatee" are core packages, must be install, other extension package you can choose you want. Example, if you not install manatee-imageviewer, when you open Image file, manatee will call default image-viewer in your system instead. Manatee will show you "search interface" when you startup it. You can type some filepath or url to open it, example, you can type Haskell file to open in editor, and type url to open in browser. Below are quick play keys: "F2" ==> startProcessManager "F3" ==> startFeedReader "F4" ==> startFileManager "F5" ==> startBrowser "F6" ==> loginIrcDefaultChannel "F7" ==> startIrc Manatee project still in early develop stage, just core framework finish, many details still not perfect. But i think it's good start to build Real-World application in Haskell. Below are high task in my TODO list: Perfect current sub-module: IDE features, code completion browser JavaScript framework graphics custom system etc. Terminal emulator: support MVC design, not like VTE widget Mail-client BT-Client Proxy bridge: to build uniform proxy interface to fighting GFW!!! Jabbar client: video support etc. Spell checker CHM viewer DVI viewer LaTex editor PS viewer Multi-thread download manager Org-Mode : http://orgmode.org/ Twitter client Network toolkit: sniffer etc. Multi-Language translater offline support Too many ideas lying in my TODO list.... Any suggestion and contribution are welcome! :) -- Andy

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