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Re: question when learning P::RD?

by duelafn (Vicar)
on Aug 28, 2016 at 17:26 UTC ( #1170623=note: print w/replies, xml ) Need Help??


in reply to question when learning P::RD?

If you add $::RD_TRACE = 1; to your script, P::RD will print out a trace of the parse which can help with the debugging. In this case, it shows that the /.+/ms pattern gobbles up "Z 034309201607258" (P::RD can't backtrack into the pattern, it will only backtrack whole rules). Your middle rule should leave the "Z" line at the end. For instance:

#!/usr/bin/perl use strict; use warnings; use 5.014; use Parse::RecDescent; # $::RD_TRACE = 1; my $text = <<'CONTENT'; Y 034309201607258 1 Q 02751VACANT / CLOSE G .... ... ... T RCRC 0810010 T RDRD 0810010 A 22OP A 13O A 12O P 3472CHSK00010014 Z 034309201607258 CONTENT my $parser1 = Parse::RecDescent->new(<<'GRAMMAR'); startrule : HeadRule OtherRule(s) TrailerRule HeadRule : /^Y.+$/m TrailerRule: /^Z.+$/m OtherRule: /^(?![YZ]).*$/m GRAMMAR print "Valid data\n" if defined($parser1->startrule($text));

Also, your parser2 shows why you should almost always end your top-level rule with a /\Z/ pattern so that parsing fails if P::RD doesn't consume the whole string.

Good Day,
    Dean

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