Functional Clojure wrapper for Michael Kay's Saxon XSLT and XQuery Processor (from Saxonica Limited).
A jar is available on Clojars. Use the following formula
in your project.clj :dependencies:
[clojure-saxon "0.9.4"]
The library has been tested against Clojure 1.3, 1.4, & 1.6.
###Query
The top-level function is query; it takes an XQuery or XPath expression, an
optional namespace map, and a node. Here's returning a sequence of the names of
all elements in a document:
user=> (require '[saxon :as xml])
nil
user=> (xml/query "distinct-values(//element()/local-name())" xmldoc)
("html" "head" "title" "style" "body" "p" "a")
Here's the same, limiting elements to those in the XHTML namespace:
user=> (xml/query "distinct-values(//xhtml:*/local-name())" {:xhtml "http://www.w3.org/1999/xhtml"} xmldoc)
("html" "head" "title" "style" "body" "p" "a")
Compiled XQuery expressions are cached:
user=> (def complex-exp "//element()[@type='text/css']//local-name(parent::element()) = 'head'")
#'user/complex-exp
user=> (time (xml/query complex-exp xmldoc))
"Elapsed time: 1.747 msecs"
true
user=> (time (xml/query complex-exp xmldoc))
"Elapsed time: 0.226 msecs"
true
but query accepts a compiled function (the result of compile-xquery or compile-xpath,
below) as its first argument as well. (The results of the query are not cached.)
###Compile-xquery, Compile-xpath
compile-xquery and compile-xpath are the lower-level functions behind query.
They take expressions and an optional namespace map, and return a function that applies
the compiled expression to a node.
user=> (xml/compile-xquery "distinct-values(//element()/local-name())")
#<saxon$compile_xquery__302$fn__314 saxon$compile_xquery__302$fn__314@48c5186e>
user=> ((xml/compile-xquery "distinct-values(//element()/local-name())") xmldoc)
("html" "head" "title" "style" "body" "p" "a")
compile-xquery and compile-xpath cache their query arguments as well.
###Compiling XML
Use compile-xml to produce the Saxon in-memory representation, an "XdmNode."
user=> (def xmldoc (xml/compile-xml (java.net.URL. "http://hdwdev.artsci.wustl.edu")))
#'user/xmldoc
compile-xml takes a File, URL, InputStream, Reader, raw String, or an XdmNode.
user=> (xml/compile-xml "<root/>")
#<XdmNode <root/>>
###XSLT
compile-xslt takes the same arguments as compile-xml and returns a function
that applies the compiled stylesheet to a node, with an optional map of parameters.
###Singletons
When the result of a query is a single item, the query functions return a singleton instead of a sequence of one item, e.g.
user=> (xml/query "count(//element())" xmldoc)
7
I find this inconsistency convenient, but it might be a bad design choice. User feedback appreciated.
###Laziness
Traversal of nodes is somewhat lazy, though not strictly so. The Clojure code
realizes the first two items of the return sequence, and the Saxon Java processor
seems to keep a few items ahead as well. E.g. in xmldoc, with 7 element nodes:
user=> (def returned (xml/query "for $e in //element() return trace(($e/local-name()), \"hit\")" xmldoc))
hit [1]: xs:string: html
hit [1]: xs:string: head
hit [1]: xs:string: title
#'user/returned
user=> (nth returned 0)
"html"
user=> (nth returned 1)
"head"
user=> (nth returned 2)
hit [1]: xs:string: style
"title"
user=> (nth returned 3)
hit [1]: xs:string: body
"style"
user=> (nth returned 4)
hit [1]: xs:string: p
"body"
user=> (nth returned 5)
hit [1]: xs:string: a
"p"
user=> (nth returned 6)
"a"
As you can see, three items are realized when the function is first executed, and from when the third item is touched onward, realizing an item also realizes the next item in the background.
###Helper Functions
node-path returns an absolute XPath to a node:
user=> (map xml/node-path (xml/query "//element()" xmldoc))
("/html" "/html/head[1]" "/html/head[1]/title[1]" "/html/head[1]/style[1]" "/html/body[1]" "/html/body[1]/p[1]" "/html/body[1]/a[1]")
with-default-ns adds a default namespace to an XQuery expression:
user=> (xml/query (xml/with-default-ns "http://www.w3.org/1999/xhtml" "//*/local-name()") xmldoc)
("html" "head" "title" "style" "body" "p" "a")