Create a new Mainstack and save it, just to be safe!

Add a couple of fields and a button.

Set the button's script to this:

on mouseUp
  put url "http://www.runrev.com/" into field 1
  put getLinks(field 1) into field 2
end mouseUp

Edit the stack script and create a function for getLinks. Start with returning what it has sent:

function getLinks pPageSource
  return pPageSource
end getLinks

If you try clicking on the button at this point, you will see that the whole page source appears in field 2.

We're going to use the filter function, and it needs the text to be in separate lines. So, we want every link to be in a line of its own. The replace function can do this nicely. Add these two lines to the script (before the "return" line, of course!):

 ...