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 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 ofSRV:send-reply
to be#t
.