Hello Francisco, On Mon, May 6, 2013 at 9:00 AM, Francisco Mota <fmot...@gmail.com> wrote:
> Is there an off-the-shelf available incremental parser for PEGs? > > Incremental parsing is where a small change in the input string > necessitates only a small amount of additional processing. The idea is that > you parse the string once, and then adding or removing characters from the > string in the middle causes only a small amount of reprocessing. > This is advice I remember from the ANTLR lists, which you can search online: http://antlr.1301665.n2.nabble.com/ - Add additional, catch-all/catch-some rules at the points in which you'd like recovery to happen. PEG parsers are outstanding at skipping over input. For example, in parsing embedded SQL in COBOL, I have a rule similar to this one for skipping over uninteresting parts: skip_uninteresting_sql = {!'END-EXEC ANY} ; With "*!*END-EXE" being a negative lookahead for the end-of-statement word, and "ANY" matching any input character. The above is inefficient, but it gives the idea. The actual rule for the compiler generator I'm using (Grako), uses a perl-style regular expression that's handled by the Python re library (DFAs), so it's cool: skip_uninteresting_sql = ?/(?:.|\n)*?(?=END-EXEC)/? ; That regular expression means "match anything until END-EXEC is in sight". As we've been discussing on another thread, these kind of techniques are possible because PEG does not require a tokenizer, so parsers are in complete control of the interpretation of input stream, even on character-by-character base. Cheers, -- Juancarlo *Añez*
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