http://groups.google.com.tw/groups?hl=zh-TW&lr=&ie=UTF-8&oe=UTF-8&frame=right&th=b77b7abd0dff3c01&seekm=379D97BE.41BAB077%40bbc.co.uk#link1 FMTEYEWTK on Prototypes in Perl Tom Christiansen
http://search.cpan.org/src/DCONWAY/Class-Multimethods-1.70/tutorial.html Multiple Dispatch and Subroutine Overloading in Perl Damian Conway