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Finding Elements and Text Within an XML Document

Problem

You want to get to a specific part of a XML document. For example, you want to get the text of an a tag which the class "foo"

Solution

The simplest solution is to use the SXPath library. This is a Scheme implementation of XPath. The query above would be written as

> (define query (sxpath '(// (a (@ (equal? (class "hometoc")))) *text*)))

> (define document
  '(*TOP*
    (html (head (title "Foo"))
          (body (h1 "Foo")
                (p
                 (a (@ (class "bar")) "don't want this")
                 (a (@ (class "foo")) "this is the answer"))))))
     
> (query document)
("this is the answer")

The meaning of the query is as follows:

• // search in all the elements of the tree
• a for elements called a
• (@ (equal? (class "hometoc"))) with an attribute named class with value "hometoc"
• *text* and return the text of this result

Discussion

SXPath works on SXML in the example above. To convert XML to SXML, use the SSAX parser. To convert badly-formed HTML to SXML use HtmlPrag. If you use WebIt there are versions of SXPath and SSAX that work with it.

Comments about this recipe

Contributors

-- HectorEGomezMorales - 05 May 2004

-- NoelWelsh - 08 Jul 2004