Derivatives and Integrals An Annotated Discourse

<section xml:id="literate-programming" label="literate-programming">
  <title>Literate Programming</title>
  <p>
    There is support for literate programming using the <tag>fragment</tag> tag.
    It should always contain an <attr>@xml:id</attr> or a <attr>@filename</attr> attribute,
    and may contain <tag>code</tag> segments as well as <tag>fragref</tag> segments referencing other fragments.
    The final code is to be assembled starting from a fragment with a filename attribute and traversing the tree of fragment references.
  </p>
  <p>
    For example here is the gcd algorithm in Python.
    Note that indentation is hard to get right at the moment.
  </p>
  <fragment filename="gcd.py">
  <title>The GCD algorithm</title>
  <code>
  def gcd(a, b):
  while(b):
  </code>
  <fragref ref="gcd-loop"/>
  <code>                        return a</code>
  </fragment>
  <p>
    The key part is the inner part of the loop:
  </p>
  <fragment xml:id="gcd-loop">
  <title>The key loop part</title>
  <code>
  a, b = b, a % b
  </code>
  </fragment>
  <p>
    This double assignment changes both a and b.
  </p>
</section>