By the way, here's a quick way to avoid a (slow) loop through the sentence,
alias stresslink {
var %a
!.echo -q $regsub($1-,/(\S*?(?:www\.|tps?://)\S*)/gi,\1,%a)
return %a
}
For example, $stresslink($1-) will accomplish underlining of the relevant urls.
The underline (ctrl+u) code that appears before the \1 can be joined/replaced with any control code you wish to use.