On Mon, Feb 05, 2007 at 06:44:10PM -0500, Robert Grimm wrote: > Rats! does support incremental parsing, in the sense that it does not > require the entire input to be available at parsing time. I.e., you > can parse some production, process the result, and then parse the > next production. Whether that helps in implementing text editors, I'm > not sure. It does help with reducing the resource requirements for > very large inputs and with processing interactive input one > expression at a time.
Does Rats! tell the caller that the parse is incomplete? Can the caller undo all or part of a parse in progress? That would allow an interactive program to read multiline expressions and allow already-read lines to be cancelled... not a true text editor but still a useful feature. On true text editors: as much as I've thought this out (which isn't a lot), I'm looking for a way to relate the text buffer to the parser tree and back, and a way for the parser to adapt to random changes in the text. The first item means that the text should be "enriched" with pointers into the parse tree, perhaps one pointer per line instead of one per character. And the parse tree should store information about the beginning and ending text positions for each node. With both of those data structures, it should be possible to do the kinds of movement and editing commands I'm looking for. I wouldn't expect the standard Rats! code to have data structures like that, but if there's a way to add them as some kind of action code, that would probably be fine. The second item means that if the user changes the text, the parser updates the parts of the parse tree that need updating and then generates new attributes for the text. Does Rats! keep the parser state in a form that can be saved (so the text can be "enriched" with that also)? Can you pass the new state and new text back to the parser? I'll probably have to deal with erroneous text. I suspect that's a matter for the grammar writer, but I could be wrong. -- Derek _______________________________________________ PEG mailing list PEG@lists.csail.mit.edu https://lists.csail.mit.edu/mailman/listinfo/peg
