SM::ToHtml does not convert urls to hyperlinks

I am trying to use my own output formatter with SimpleMarkup. Things seems to work, except for hyperlinks not working as expected. I tried to use SM::ToHtml to simplify things, and even if does not deal with hyperlinks. Here is the code snippet I am using.

require 'rdoc/markup/simple_markup'
require 'rdoc/markup/simple_markup/to_html'
s = "This is *bold*. These are urls - www.foo.com , http://www.foo.com , foo[http://www.foo.com]"
p = SM::SimpleMarkup.new
puts p.convert(s, SM::ToHtml.new)

The output of this is as shown below. The word "bold" was surrounded by the <b> tag, but the urls were not surrounded with <a href> tags.

<p>
This is <b>bold</b>. These are urls - www.foo.com , http://www.foo.com , foo[http://www.foo.com]
</p>

Is there a way to make this happen?

Regards,
Shri