pre-post-order:: <tree> x <bindings> -> <new-tree>
where
<bindings> ::= (<binding> ...)
<binding> ::= (<trigger-symbol> *preorder* . <handler>) |
(<trigger-symbol> *macro* . <handler>) |
(<trigger-symbol> <new-bindings> . <handler>) |
(<trigger-symbol> . <handler>)
<trigger-symbol> ::= XMLname | *text* | *default*
<handler> :: <trigger-symbol> x [<tree>] -> <new-tree>
The pre-post-order function, in the (sxml transform)
module, visits the nodes and nodelists pre-post-order (depth-first).
For each <Node> of the form (name <Node> ...), it
looks up an association with the given name among its
<bindings>. If failed, pre-post-order tries to locate a
*default* binding. It’s an error if the latter attempt fails as
well. Having found a binding, the pre-post-order function first
checks to see if the binding is of the form
(<trigger-symbol> *preorder* . <handler>)
If it is, the handler is ’applied’ to the current node. Otherwise, the
pre-post-order function first calls itself recursively for each child of
the current node, with <new-bindings> prepended to the
<bindings> in effect. The result of these calls is passed to the
<handler> (along with the head of the current <Node>). To be
more precise, the handler is _applied_ to the head of the current node
and its processed children. The result of the handler, which should also
be a <tree>, replaces the current <Node>. If the current
<Node> is a text string or other atom, a special binding with a
symbol *text* is looked up.
A binding can also be of a form
(<trigger-symbol> *macro* . <handler>)
This is equivalent to *preorder* described above. However, the
result is re-processed again, with the current stylesheet.
Output the fragments to the current output port.
The fragments are a list of strings, characters, numbers, thunks,
#f, #t – and other fragments. The function traverses the
tree depth-first, writes out strings and characters, executes thunks,
and ignores #f and '(). The function returns #t if
anything was written at all; otherwise the result is #f If
#t occurs among the fragments, it is not written out but causes
the result of SRV:send-reply to be #t.