[plt-scheme] Draw and save coordinates on every mouse event on canvas?

Hi,
I am newbie in scheme, just started yesterday. So, please don't mind
if I am overlooking anything simple.

I want to draw circular points on every click on the drawing window
(or canvas). Also I want to save the coordinates in an array. After
every click a connecting line should be drawn (from last point) and so
on.

Now, I don't understand how I should put a canvas. As I can see in
Dr.Scheme manual , it is recommended to use world.ss.  But I don't
understand how will I get the coordinates and save in an array? Also
how that line can be drawn?

Any suggestion is appreciated.

Thanks in advance.