/*

Example of c++ code: 

    xmlDocPtr doc;
    xmlNodePtr cur;
    doc = xmlParseFile(docname.c_str());
    if (doc == NULL ) {
        fprintf(stderr,"Document not parsed successfully. \n");
        return;
    }
    cur = xmlDocGetRootElement(doc);
    if (cur == NULL) {
        fprintf(stderr,"empty document\n");
        xmlFreeDoc(doc);
        return;
    }

    cur = cur->xmlChildrenNode;
    while (cur != NULL) {
        printf("child: %s\n", cur->name);

        cur = cur->next;
    }
    
*/

/*
 
    Default strategies:
      - what to do with unspecified nodes
      
    Node content strategy:
      - send as-is
      - apply transforms (all / named)
      -  ?? skip
      
    Processing order: 
      - dependencies
 
 */

query = function(tree: XmlTree): [XmlTree]
{
    children :  context(children) = 
      case default
        []
      
      case (tree[0]: NeedChildren(childrenFilters), ApplyTransform(transFilters))
      {
        loop fold (tree[1]->child: Tree(Leaf) | childrenFilters; []->accum).
            {accum  + traverse(child): cases(transFilters) };
      }

    node = 
      case (node.tag == "style:style"; class = node[attrs, "style:name"]; exists(class, ParaKnownClasses))
      {
        [class, node[attrs, "style:display-name"]];
      }
      
      case default
        [] ;
      
      Tree[node children] | node + children
}

  /*
traverse = function(trees: [XmlTree]) : [XmlTree]
  loop fold(trees->tree: Tree; []->acc) 
    acc + traverse(tree)
   */