use Parse::RecDescent;  
my $teststr="blah1,blah2(blah3,blah4(blah5,blah6(blah7))),blah8";  
my $grammar = q {
 list: <leftop: item ',' item> 
 item: word '(' list ')' <commit>
     | word 
 word: /\w+/  
};  
my $parser = new Parse::RecDescent ($grammar) or die "Bad grammar!\n";

defined $parser->list($teststr) or print "Bad text!\n";
