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#! /usr/local/bin/perl -sw
use vars qw($animal);
use Parse::RecDescent;
$grammar = q {
object: thing[article=>'a'](s)
| thing[article=>'the'](s)
thing: <matchrule:$arg{article}>
<matchrule:${\scalar reverse $::animal}>
a: 'a'
the: 'the'
cat: 'cat' { print "meow\n"; $::animal = 'god' }
dog: 'dog' { print "woof\n" }
};
unless( $parser = new Parse::RecDescent( $grammar ))
{
die "bad grammar; bailing\n";
}
$/ = "";
while (defined ($input = <DATA>))
{
$::animal = reverse 'cat';
print STDERR "parsing...\n";
unless( defined $parser->object( $input ))
{
die "error in input; bailing\n";
}
print STDERR "...parsed\n";
}
__DATA__
a cat
a cat
a cat
a dog
the cat
the dog
the dog
the dog
the dog
a dog
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