in reply to intro to references

When I tried busunsl's link above, I got a "404 Not Found." The next logical step was to try the "Wayback Machine", where I found this copy of Joseph N. Hall's PErl Graphical Structures (PEGS) (tar archive).

Further Googling led to Effective Perl: Intermediate and Advanced Topics, which contains a number of pages on PEGS.

(Thanks to busunsl for this tutorial.)