On Thursday, May 20, 2004 Alexander Farber said: > Hi, > > why doesn't the question mark in the optarg(?) > below work as I expect? In the trace I see that > optarg consumes the ">" character and then the > option rule fails, since the final ">" is missing. > > Isn't P:RD supposed to backtrack and say > "ok, the optarg(?) didn't match anything here"?
Um, why would it do this? In fact, "optarg" *does* match zero or one times, it is "option" that does not match. This is a simple problem with your grammar where you got (exactly...) what you asked for. As an example, if you change optarg it will be "better": optarg: /[^\s>]+/ Also, there is more than one way to do it but I don't "like" your first rule for option "/<option/" but would prefer '<' 'option' as it is easier to maintain. If the problem is that there should not be a space between '<' and 'option' than change skip. But this is not related to your question, this is just me butting into your style... ;-) > > Of course the script below works when I change > the optarg from /\S+/ to /\w+/, but I'm curious, > why doesn't optarg(?) mean "ZERO or one" here? > > Thank you > Alex > > #!/usr/bin/perl -w > > use strict; > use vars qw($parser $text %option); > use Data::Dumper; > use Parse::RecDescent; > $RD_WARN = 1; > $RD_HINT = 1; > $RD_TRACE = 120; > $parser = Parse::RecDescent->new(q( > > genfile: chunk(s) /^\Z/ > chunk: option | <error> > option: /<option/i /\w+/ optarg(?) ">" { > push @{$::option{lc $item[2]}}, $item[-2]; > } > optarg: /\S+/ > > )) or die 'Bad grammar'; > $text .= $_ while (<DATA>); > defined $parser->genfile($text) or die 'Bad text'; > print STDERR Data::Dumper->Dump([\%option], [qw(option)]); > __DATA__ > <option one> > <option two> > -- Intel, Corp. 5000 W. Chandler Blvd. Chandler, AZ 85226 -- Intel, Corp. 5000 W. Chandler Blvd. Chandler, AZ 85226
