Warning: This is the manual of the legacy Guile 2.2 series. You may want to read the manual of the current stable series instead.

7.20.4 Transforming SXML

7.20.4.1 Overview

SXML expression tree transformers

Pre-Post-order traversal of a tree and creation of a new tree

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.

7.20.4.2 Usage

Scheme Procedure: SRV:send-reply . fragments

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.

Scheme Procedure: foldts fdown fup fhere seed tree

Scheme Procedure: post-order tree bindings

Scheme Procedure: pre-post-order tree bindings

Scheme Procedure: replace-range beg-pred end-pred forest