Re: Odd behaviour with Regular Expressions

[David Manura]

Paul,

Consider the following example:

===============================
use Parse::RecDescent;
my $grammar = <<'TEXT';
ident :  /^(?!(return|exit|if))[A-Za-z0-9_]*/
{
    print "pattern matched OK\n";
    print $item[1];
}
TEXT
my $p = new Parse::RecDescent($grammar);
$p->ident('test if');
================================
This outputs

================================
pattern matched OK
test
================================
as you expect, so you're on the right track.  Perhaps the '*' is causing ident 
to match the empty string ('').  For example, this

  $p->ident('.test if');

outputs

=================================
pattern matched OK
=================================

-davidm

PerlDiscuss - Perl Newsgroups and mailing lists wrote:
I am attempting to create a rule that will match any string apart from
those that are keywords in my language.
I have developed the following regular expression, which acheives this,
but, when trying to access a word that is accepted by the regular
expression, via $item[1], nothing is returned ( I have also tried
$item[0], $item[2] etc). I have placed a print statement in as a debugging
aid, to prove that the rule works properly debugging aid:
When entering a keyword, such as "return", as expected, nothing is
printed. However, when entering a non-keyword, such as "foo" 
only the string "pattern matched OK" is printed, and the value of the
matched word ($item[1]) is not printed.

Can anyone tell me where I am going wrong here? 

Followin is the  offending piece of code

Paul Kennerley

ident :  /^(?!(return|exit|if))[A-Za-z0-9_]*/
{
    print "pattern matched OK\n";
    print $item[1];
}