Hi,
I have a problem where I need to construct a tree from an xml file:
The xml file looks like this:
<feeAgreement>
     <feeClauses clauseid="1" rootclause="false">
          <computationUnit name="xxxx">
                  <complexComputationUnit clauseid="2"/>
          </computationUnit>
     </feeClauses>
    <feeClauses clauseid="2" rootclause="false">
          <computationUnit name="yyyy">
                 <complexComputationUnit clauseid="3"/>
          </computationUnit>
     </feeClauses>
    <feeClauses clauseid="3" rootclause="false">
          <computationUnit name="zzzz">
               <complexComputationUnit clauseid="1"/>
          </computationUnit>
     </feeClauses>
</feeAgreement>

Now, I would like to typically use recursion to construct the tree, starting
at the first feeClauses element. When I get to the complexComputationUnit
element's clauseid attribute, I would like to go over and find the clause
with the clauseid specified here.
The problem is, I need to know if the clause is already present, as in the
case of clause 3, which refers to clause 1. Here, I need not get the first
clause.
I cannot seem to think of a way of checking while transforming whether I
have the clause already in the transformed part.
Any help would be greatly appreciated.

You have a cycle in your dependencies. You can check for this by
keeping the elements you already visited in a parameter

  <xsl:template name="do-tree">
    <xsl:param name="node"/>
    <!-- set of visited nodes -->
    <xsl:param name="visited"/>
    <!-- process the currenttly visited node -->
    <xsl:copy-of select="$node"/>
    <!-- get referenced node -->
    <xsl:variable name="referenced" select="//feeClauses[
       @clauseid=$node/cumputationUnit/complexComputatioUnit/@clauseid]"/>
    <!-- check whether the referenced node has been visited -->
    <xsl:if test="count($referenced|$visited)!=count($visited)">
       <xsl:call-template name="do-tree">
          <xsl:with-param name="node" select="$referenced"/>
          <!-- don't forget to add the referenced node to the visited list -->
          <xsl:with-param name="visited" select="$referenced|$visited"/>
       </xsl:call-template>
   </xsl:if>
  <xsl:template>