Sven Panne wrote:
Am Mittwoch, 7. Februar 2007 20:51 schrieb Benjamin Franksen:
[...] XCB implements the full protocol (which already makes for a daunting amount of data types and routines). On top of that it implements a very lean connection management and request handling API that allows (this is one of the highlights) single-threaded as well as multi-threaded access.
Hmmm, the presentation in the paper is the other way round: The lower layer is the XCB_Connection layer, handling connections, requests and replies. On top of that, the XCB_Protocol layer implements, well, the protocol, including (un-)marshaling to/from C.
You're right, sorry for the confusion.
See the very readable paper http://www.linuxshowcase.org/2001/full_papers/massey/massey.pdf
After reading that paper and browsing around a bit, I think a slightly bolder approach might make sense for Haskell, in effect creating XHB ("X Protocol Haskell Binding"): I guess that the bulk of the code is in the XCB_Protocol layer, and that layer is already generated via an XML description for the C binding. If we can use the same technique to generate Haskell code, "only" a Haskell version of the connection layer would be needed to get a full XHB. This would have a few advantages:
* There is no dependency on the XCB library, so XHB should work on *any* platform, including e.g. MinGW without any X11 libs. An X11 server is of course still needed... :-)
* Data is only (un-)marshaled once. Using XCB, there would be 2 steps: Haskell <=> C <=> X protocol
* The availability of protocol extensions is determined by XHB alone, not by any underlying XCB implementation.
I agree that this would be nice. (Disclaimer: I haven't the slightest clue about XSLT and how it is used to generate code from XML protocol descriptions. However, I assume this won't be that much harder than to find some method to 'auto-ffi' the huge XCB_Protocol API into Haskell.) Have you seen this: lists.freedesktop.org/archives/xcb/2006-January/001278.html ? The sources are here http://webcvs.freedesktop.org/xcb/xhsb/ It could be starting point, at least...
I am not sure if this is a realistic way to go, especially I am unsure about the amount of work needed to implement the functionality of the XCB_Connection layer directly in Haskell.
Yes, this is going to be the most difficult part. I have taken a look at another XCB paper, which is about the XCB_Connection layer and explains how the problem has been modeled using the Z specification language (freedesktop.org/software/xcb/usenix-zxcb.pdf). Very interesting, this. I wonder if one could derive a Haskell solution (more or less) directly from the Z spec. Or, maybe, even simplify the spec, leveraging Haskell's more high-level interface to multithreading (STM?).
Let's see if I can find a more or less stand-alone version of XCB (with no need to build all of X.Org) and understand how it is actually implemented.
Sources can be downloaded from the XCB site (a handful of tar.gz files). Build and install was rather uncomplicated here (debian/etch, amd64). Unfortunately, freedesktop.org seems to be down at the moment, so none of the above links will work until they are online again. Ben