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type Parser a = GenParser Char () a newtype GenParser tok st a = Parser (State tok st -> Consumed (Reply tok st a)) As i know, the Parser type is just an alias of GenParser. Then can the second line be replaced as below? newtype GenParser tok st a = GenParser Char () (State tok st -> Consumed (Reply tok st a)) If it can , then what is the new type ? Sincerely! ----- fac n = foldr (*) 1 [1..n]

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Hello, -Cafe, I'm looking for an interesting topic to hack on in my thesis. The thesis should be rather "theoretical"/abstract (writing a mail client in Haskell is not, for example), dealing with FP or related fields. I've had a few (blurry) ideas, ranging from investigating (possibilities for) Haskell extensions, to zygohistomorphic prepromorphisms, but nothing concrete, possibly because I'm not familiar with these areas enough to see what could be done -- which brings up a question whether it is a good idea to even try hacking on a topic like this. However, I'm eager to learn so if you have a topic you'd need somebody to work on, or just an interesting (or maybe even an uninteresting) idea, i'd be grateful for suggestions. :) Thanks, Matus

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Hi! My students have the task to program an interactive chatbot. We have run into a problem that I can't solve either: When we read the user's input through > t <- getLine it is not possible to delete typos before hitting enter and thereby sending the input off to the system (at least in OS X, bash). I didn't find that terribly problematic, but of course it is a bit of a show stopper from their point of view. The input is then used to generate a reply in purely functional code, and the reply sent to the command line via putStr. Is there a more clever way to interact with the user that would allow editing ones text before sending it to the bot? I guess we could try with a website, but don't know off hand how to do that, either, although I've seen beautiful webservers made in Haskell... Regards, Torsten Otto

submitted by dons
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Hi, I am writing a little IPC system to make Haskell values and functions remotely invokable. To do so, I need (or so I believe) to make my objects accessible via a generic interface as in: class AFun f where afun :: Data a => f -> ([Dynamic] -> a) So my generic object is something that takes an array of parameters, that being Dynamic can be anything, and returns a Data, that I can easily serialise and send back on the wire. I start by defining an instance for functions: instance (Typeable a,AFun b) => AFun (a->b) where afun f (p:ps) = let Just v = fromDynamic p in afun (f v) ps afun _ _ = error "Too few arguments" So far so good, but when I try to define an instance for values: instance Data v => AFun v where afun f [] = f afun _ _ = error "Too many arguments" I get: Couldn't match expected type `a' against inferred type `v' `a' is a rigid type variable bound by the type signature for `afun' at /home/titto/.quid2/state/ubuntu.local.8080/wikidata/haskell

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submitted by chak
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Haskellers, I present to you fdo-notify, a client library for FreeDesktop.org's Desktop Notifications protocol. This is the DBUS protocol served by NotifyOSD and other notifications systems, which allows a wide variety of applications to present notifications to the user in a uniform way. The library should not require knowledge of DBus or the Desktop Notifications protocol itself, at least once fully documented (there should be enough haddocumentation for basic use already). Hackage: http://hackage.haskell.org/package/fdo-notify Mercurial: http://bitbucket.org/taejo/fdo-notify/ Basic notifications and updated/replacement notifications are supported. Images are not yet supported (adding support should be easy, but which Image type? Is there a de facto standard imaging library like the Python Imaging Library?) and nor are signals. Signals allow an application to be informed when some action is taken on the notification (NotifyOSD doesn't support actions, but other implementations might). The library is r

Hi List, this is rather trivial, but maybe someone else finds these useful: darcs get http://code.haskell.org/~daniels/haskell-snippets/ Especially the LANGUAGE ones have saved me quite some typing :) Additions welcome. Usage: If not already installed, get YASnippet: http://code.google.com/p/yasnippet/ and put this into your .emacs: (load-file "some-path/haskell-snippets.el") to expand a snippet, just enter the macro string (these are listed in the haskell-snippets.el file) and press <tab>. If the snippet has holes, press <tab> again to jump to the next hole. Greetings, Daniel

When GHC 6.12.1 is released, I'm going to have a go at porting it to DragonFly BSD (32-bit incarnation). Is the porting page on the wikiup-to-date?

submitted by dons
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Already a few months ago I completed my Bachelor computer science by writing a small paper and attending and presenting at a student conference. Well anyway, the topic I wrote about is parser construction techniques. The paper talks about parser generators (ANTLR in specific), parser combinators (Parsec 2) and a nice novel combination of the two (Tinadic Parsing, still to published somewhere in the future).

Anyway I hope this paper might be interesting to some people reading my blog. The paper comes with quite some code examples and it's probably not a very hard read. So you might consider it a small tutorial on parser construction techniques (or even learn some Parsec while you're at it :) ).

My paper can be found here at the website of the University of Twente.

The accompanying code examples can be found here. If someone would really appreciate it, I might consider writing some more documentation.



As you might have noticed blog posts were a bit scarce the last weeks, because of my silly ambition of taking 3 instead of 2 courses :P. Anyway, I'm liking the pace but my side activities suffer a bit, so I'll probably switch back after next period.
(People waiting for the extended state monad implementation: I haven't given up yet!)

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.3.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Darcs repo: http://code.haskell.org/haskell-src-exts Version 1.3.0 is a new major release, following the PVP, as it contains a few backwards-incompatible changes, making the 1.2.x branch a very short parenthesis in history. There are two main new things in 1.3.0: fixity application is now handled uniformly regardless of which AST you use, simple or annotated, and the parser now supports multiple modules in the same source file. haskell-src-exts-1.3.0: ==================== * The *.Fixity modules now export the same Fixity type (incidentally the one previously used by the simple un-annotated parsing) and the same helper functions. If you've done all your Fixity handling using the helper functions (infix_, infixl_, infixr_), or if you've only used fixities for the un-annotated AST, you're safe. Only if you've manua

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