3 XML Transformation

3.1 stylesheet

syntax

A stylesheet is a set of rules for transformation of XML. The stylesheet syntax allows one to intermix a sequence of xml-micro's, xml-macro's, and top-level Scheme expressions.

The grammar for stylesheet is given below:

stylesheet-form ::= (stylesheet body-item*)

body-item ::= xml-micro-form
            | xml-macro-form
            | top-level-sceheme-expression

A stylesheet form evaluates to a stylesheet object.

The semantics of top-level definitions within a stylesheet is identical to that of PLT Scheme's units.

3.2 xml-micro

syntax

An xml-micro performs a single transformation of its argument. The result of this transformation is not further "expanded".

The grammar for xml-micro is:

micro-form ::= (xml-micro trigger-tag
                 expression)

trigger-tag ::= element-tag
              | *text*
              | *data*

The expression in an xml-micro must evaluate to a function of which takes an XML node as its argument, and (generally) returns a node or nodeset.

3.3 xml-macro

syntax

An xml-macro performs a transformation of its argument; the result of this transformation further "expanded" until no further transformations are possible.

The grammar for xml-macro is:

macro-form ::= (xml-macro trigger-tag
                 expression)

trigger-tag ::= element-tag
              | *text*
              | *data*

The expression in an xml-macro must evaluate to a function of which takes an XML node as its argument, and returns a node or nodeset.

No further transformations of a node are possible when no more xml-micros or xml-macros are triggered by that node under the stylesheet being applied.

3.4 stylesheet->expander

function

stylesheet->expander :: stylesheet -> (function node -> node))

This function converts a stylesheet to an expander function. The return-result may be applied to an XML node to apply the stylesheet's transformations.

3.5 compound-stylesheet

syntax

This form is used to combine multiple stylesheets. The result of evaluating a compound-stylesheet is a new stylesheet object.

The grammar for a compound-stylesheet is given below:

compound-ss-form ::= (compound-stylesheet expression+)

Each expression must evaluate to a stylesheet object.

3.6 Example

The example below is a complete working stylesheet which translates a collection of poetry into HTML. The 'micro' for the poem element formats a poem into HTML. The 'macro' for the book element creates a skeletal HTML document, with a new contents element which contains both a table of contents element and the poems to be formatted. The 'micro' for the contents element formats the table of contents and uses xml-expand to invoke the expander on each of the poems.

poetry->html is bound to the result of applying stylesheet->expander to the stylesheet, producing a function which takes a single argument: the poetry book element.

(define poetry->html
  (stylesheet->expander
   (stylesheet
     
     (define-element toc)
     (define-element contents)
     
     (xml-micro poem
       (lambda (x)
         (xml-match x
           [(poem title: ,t poet: ,a tag: ,m
                  (stanza (line ,l1) (line ,l) ...) ...)
            (h4:div (h4:p) (h4:a h4:name: m) (h4:strong t) (h4:br) (h4:em a)
                    (list (h4:p) l1 (list (h4:br) l) ...) ...)])))
     
     (xml-micro contents
       (lambda (x)
         (xml-match x
           [(contents (toc (poem title: ,t poet: ,a tag: ,m . ,rest) ...) ,p* ...)
            (h4:div (h4:p) "Table of Contents:"
                    (h4:ul
                     (h4:li (h4:a h4:href: (string-append "#" m) t)) ...)
                    (xml-expand p*) ...)])))
     
     (xml-macro book
       (lambda (x)
         (xml-match x
           [(book title: ,bt ,p* ...)
            (h4:html
             (h4:head (h4:title bt))
             (h4:body
              (h4:h1 bt)
              (contents (toc p* ...)
                        p* ...)))])))
     
     )))