Transforming an XML Tree with Scala Partial Functions

In my last blog, I outlined how I found the Scala XML library a pleasant solution for unpleasant XML format conversion jobs. In those jobs, I had to completely transform the document from one grammar to another. When you need to make small tweaks to a document, the library a bit more of a hassle. This page by Burak Emir, the author of the Scala XML library, states: “The Scala XML API takes a functional approach to representing data, eschewing imperative updates where possible. Since nodes as used by the library are immutable, updating an XML tree can a bit verbose, as the XML tree has to be copied.” A verbose example follows. Here is what I needed to do. Whenever I had a Filename.java, I had to replace it with the actual file name, with each line preceded by a line number. That part is simple: def getExample(node: Node) = {io.Source.fromFile(new File((node \ "p").toString)).getLines().map( w => {w} )} But how can you say “Do this for all , and leave the rest alone?” In a functional program, you need to copy the tree, so I figured I should write a universal transformer method. /** * Transforms all descendants matching a predicate. * n a node * pred the predicate to match * trans the transformation to apply to matching descendants */ def transformIf(n: Node, pred: (Node)=>Boolean, trans: (Node)=>Node): Node = if (pred(n)) trans(n) else n match { case e: Elem => if (e.de...

Date: May, 16 2010
Url: http://www.java.net/blog/cayhorstmann/archive/2010/05/16/transforming-xml-tree-scala-partial-functions

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