Most of the same code used by mod_virgule to manage and render article replies could be used to allow replies to diary entries. Diary replies could be rendered only when viewing a specific diary entry (and not in the recentlog or when viewing someone's page). Rendering a link saying "this diary entry has 5 comments" would require a virgule_db_dir_max call, but that wouldn't be too horrible.
Reply threading, with proper indentation, would be nice to have as well. One way to do that would be to add a parent key field to replies, and a tree would be built in memory before rendering. The existing database wouldn't need to be changed. All replies to an article or diary entry would need to be read to memory before rendering, but it wouldn't be that much more expensive than what's being done by the current code. Maybe the depth of the reply tree would need to be limited somehow.
In this brave new era of Web 2.0, rounded corners, and self-important "engineers" riding the latest faddish web framework bandwagon, the idea of a web site written as a C module for Apache is intriguing. I seem to have arrived a bit late to the party, but I hope I can still somehow contribute to (what's left of) this community.
I wrote a patch for mod_virgule that allows the editing of article comments. Here it is.
New HTML Parser: The long-awaited libxml2 based HTML parser code is live. It needs further work but already handles most markup better than the original parser.
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If you're a C programmer with some spare time, take a look at the mod_virgule project page and help us with one of the tasks on the ToDo list!