Tutorial

This tutorial teaches you all you need to know about TreeRegex source code modification. The tutorial is broken into three parts:

• Part 1 discuses what TreeRegex expressions and replacement strings are and how to use them for simple instrumentation
• Future parts coming soon!

Throughout this tutorial we will be using the TreeRegex implementation available here.

What is a TreeRegex?

Simply put, a TreeRegex, or a TreeRegex pattern, is a pattern describing a tree of text. A tree, for the purposes of TreeRegex, is a tree of strings.

Similarly, a TreeRegex pattern can be thought of as a tree of regular expressions. If you are not familiar with regular expressions, I recommend reading the tutorial here before continuing.

Any regular expression (once escaped) is a valid TreeRegex pattern. For instance .* matches any tree that is just a string. TreeRegex augments regular expressions by letting you specify the height (or depth) of the string in the tree. For instance, if you wanted to find a tree that has one child and that child is any string, you would write the TreeRegex (%.*%). In TreeRegex patterns and trees, we use (% and %) to deliminate subtrees.

A TreeRegex tree is only made up of plain text and (% and %), but a TreeRegex pattern has further metacharacters. A TreeRegex pattern can also contain a @ which matches any immediate subtree or (* and *) which matches a subtree, even if it is not an immediate subtree. These are explained in Instrumenting JavaScript Conditions in part 1.

What is a Replacement String

While TreeRegex patterns provide a means of matching trees, it is of little use without the ability to modify those trees. Similar to regular expressions, TreeRegex replacment strings specify what to replace a matched tree with. These will also be trees.

TreeRegex replacement strings are trees that can have special metacharaters to represent captured values from the TreeRegex pattern. These are a dollar sign ($) followed by a single digit (similar to some regular expression replacement string formats).

A simple replacement string could just be Tree, while a more complicated one may be (%Tree: $1%). These are further explained in the next section.

Now you are ready to continue to the first part of the tutorial here.