Jeffrey Kegler's blog about Marpa, his new parsing algorithm, and other topics of interest
Marpa resources
The Ocean of Awareness blog: home page, chronological index, and annotated index.
Jeffrey Kegler's blog about Marpa, his new parsing algorithm, and other topics of interest
The Ocean of Awareness blog: home page, chronological index, and annotated index.
To those who have noted that Marpa::XS does not come with a lexer, I'd respond that, in a very real sense it does -- Perl. Perl5 is a powerful lexical analyzer.
If you're trying to figure out how to write your first Marpa parser, I'd recommend a close look at Wolfgang Kinkeldei's recent posting about his Marpa-powered CSS parser. Wolfgang lays his parser out in a very elegant fashion, and I find his code makes an excellent template.
Especially nice-looking is Wolfgang's lexer.
Wolfgang follows one of the two
main strategies for lexical analysis in
Perl:
he consumes the input using substitution
(s/ ... / ... /) commands.
The other strategy is to use the Perl regex search position
to track the progress of the lexical analysis.
In the search-position strategy,
your cases consist of a lot of
match commands using the \G anchor
and the gc modifier:
m/\G ... /gc.
An excellent tutorial on this
kind of lexing,
albeit in a non-Marpa context,
can be found in
Mark Jason Dominus's book,
Higher Order Perl.
Mark's coverage of lexing is in
Chapter 8, "Parsing", on pages 359-375.
Mark's book can be read
on-line.
I highly recommend Mark's book
and own a paper copy.
Actually, regular expressions are well within Marpa's capabilites, and lexical analysis could be done in Marpa. But a look at Mark and Wolfgang's code should convince you that lexical analysis is easy to do in Perl.
posted at: 21:31 | direct link to this entry