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Yesterday I’ve reviewed the cl-difflib and today I want to show you a library which uses cl-difflib to compare HTML files. It parses both HTML’s into nodes and compares these node lists:

POFTHEDAY> (html-diff:html-diff
            "
<p>This is the HTML <b>Hello World</b>:</p>
<ul>
  <li>First item</li>
  <li>Second iem</li>
  <li>Third item</li>
</ul>
"
            "
<p>This is the HTML <i>Hello World</i>:</p>
<ul>
  <li>First item</li>
  <li>Second item</li>
  <li>Third item</li>
</ul>
")

;; Result
"
<p>This is the HTML <del class=\"diff\"><b></del><ins class=\"diff\"><i></ins>Hello World<del class=\"diff\"></b></del><ins class=\"diff\"></i></ins>:</p>
<ul>
  <li>First item</li>
  <li>Second <del class=\"diff\">iem</del><ins class=\"diff\">item</ins></li>
  <li>Third item</li>
</ul>
"
4 ;; don't touched nodes
3 ;; replaced nodes
0 ;; inserted nodes
0 ;; deleted nodes

Here is the result rendered by the browser:

<p>This is the HTML <del class=\"diff\"><b></del><ins class=\"diff\"><i></ins>Hello World<del class=\"diff\"></b></del><ins class=\"diff\"></i></ins>:</p>
<ul>
  <li>First item</li>
  <li>Second <del class=\"diff\">iem</del><ins class=\"diff\">item</ins></li>
  <li>Third item</li>
</ul>

You can see how it highlighted the fixed typo in the item word, but wasn’t able to figure out how to process changed tag around “Hello World” :(

Such a library can be used to compare HTML documents rendered by some markup engined. For example, cl-markdown uses it in its test suite, to compare results produced by CL engine and original Perl version of Markdown.