use Regexp::Common 'list';
my $re = qr{
        \w+  # word characters (word or function name)
        (?:\($RE{list}{-pat=>'\w+'}\))? # (optional parameters)
        }x;
my $x = 'joe,sam,x(monkey,lemur)';
my @x = ($x =~ m{$re}g);
print join("\n", @x);


##</code><code>##

joe
sam
x(monkey,lemur)