Derek,
Rats! just has enough support for consuming a stream in pieces, but
no support for incomplete parses. From what you state, you probably
have to closely integrate the parser with the editor, while Rats!-
generated parsers are designed for programs that consume text but not
modify it on the fly.
Robert
On Feb 5, 2007, at 8:42 PM, Derek Peschel wrote:
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
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