Re: [Haskell-cafe] Re: Functional progr., infinity, and the Universe
Stepan Golosunov wrote: 1:_|_ is certainly finite. And what is length _|_ ? _|_, of course!! :-) The point being, length is well-defined only for total lists; it is undefined for partial lists. But this doesn't mean that a partial list isn't finite. What is "finite list" then? Is ones = 1:ones also finite? Hmmm... never tried to write all this down in one place before, but I think this covers all cases: A partial list is one that ends in _|_. A total list is one that ends in []. A finite list is either partial or total. Any other list is infinite. So "ones" is infinite. -Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ReadP and MonadFix
Thanks for your response! I searched for something more found: An Abstract Monadic Semantics for Value Recursion, Eugenio Moggi, Amr Sabry http://citeseer.ist.psu.edu/moggi03abstract.html Section 4 of this paper says something about References and Continuations. But it will be quite hard to translate this into actual code. Could you please point me to the running examples you were talking about? I'm going to create MonadFix instance for the P monad and then I'll see what can I achieve with that. 2006/6/23, Levent Erkok <[EMAIL PROTECTED]>: Gracjan: To declare "ReadP" an instance of MonadFix; you'll first have to make the P monad into a MonadFix instance. That can be done using existing techniques in the literature. ReadP is essentially the continuation monad transformer wrapped around P. It's well known in the value-recursion literature that continuation monad is too "strong" to have a value-recursion operator. I am not aware of any "simple" solutions in that space. Hence, ReadP is beyond the realm of current theories of value recursion. Having said that, I'd also like to point out that Amr Sabry and Eugenio Moggi, and independently Magnus Carlsson has done some interesting work to extend value recursion to the world of continuations; which might help with your particular problem. Essentially, you end up adding some extra infrastructure to your monad, and then forgo some of the basic axioms of value recursion. But you can get running examples! Maybe all you'll need is a MonadFix instance of P; which is definitely doable with the current techniques. Anything further would actually make a nice research paper... -Levent. (I could provide references to above work if needed; all is available on the net freely, anyhow.) On 6/23/06, Gracjan Polak <[EMAIL PROTECTED]> wrote: > Hi all, A question for hot summer day: Text.ParserCombinators.ReadP.ReadP is an instance of Monad. Could it be an instance of MonadFix too? I'm not that sharp in Haskell to write it myself, but it seems I could make use of such a beast. :) Anybody willing to share? This will also present the advantage of Lazy over Eager Parser Combinators, mentioned in some other thread. -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Binary IO
Hello jeff, Saturday, June 24, 2006, 10:19:17 AM, you wrote: > I would greatly appreciate it if someone could post a small example or two > illustrating how to do > binary IO in Haskell using the most widely used binary IO lib (if > there is such a thing). Failing that, I would > appreciate a link to some Haskell code that does binary IO that I could study. the most widely used is NewBinary lib. but nevertheless i suggest you to use my own Streams library. it's close enough to NewBinary in overall ideology, but simpler, easy to install and may become new standard in this area because it has innumerous number of features Download: http://www.haskell.org/library/Streams.tar.gz Installation: run "make install" with my lib, binary I/O can be performed using Handles. there are just a number of new I/O operations what reads and writes words of specified size: main = do h <- openBinaryFile "test" ReadMode i <- getWord32le h j <- getWord8 h hout <- openBinaryFile "test" WriteMode putWord32le hout (1::Int) putWord8hout (2::Int) ... you can use all the Handle operations (hSeek, hFilesize and so on) and even mix binary and text I/O. there are also features to define operations that read and write whole data structures library docs are still unfinished. i will send existing bits of documentation to you via email. i plan to publish final docs at http://haskell.org/haskellwiki/Library/AltBinary but at this moment this page contains only feature list -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
