#Either
local $_ = $$s;

#Or
s//$$s/; #tricky.. ;-)

##</code><code>##

sub lexer {
   my ($parser) = shift;
   my $s = $parser->YYData->{INPUT};
   
   # I don't get your line: 'm/\G\s+/gc;  skip any spaces'
   my %dispatch = (
                    INT  => qr/\G(\d+)/gc, 
                    ID   => qr/\G([A-Z]\w*)/gc,
                    #.. and so on ..
                  );
   
   while (my ($key, $regex) = each %dispatch) {
      return ($key, $1) if $$s =~ $regex;
   }
}