Hi,

The RB AST is in 3.8a unstable. In a second step, I added the 
ParseTreeSearcher and the RBParser/RBScanner.

The AST implementation is much nicer then the one we had in Squeak 
before: It encodes the parent of the treenode
and provides a Visitor implementation (RBProgramNodeVisitor).

Here is a short Tutorial.

We want to parse an expression:

tree := RBParser parseExpression: '3 + 4'

Now we have the AST (Abstrakt syntax tree). Have a look at it with the 
ObjectExplorerer:

tree explore

We can easily walk across the tree using the RBProgramNodeVisitor:

RBProgramNodeVisitor new visitNode: tree.

Of course, nothing happens, as all the visitor-methods are only stubs 
in this class.
So you need to subclass that to do anything usefull.
As an example, we would like to walk the tree and get all Literals back.

So we make a subclass:

RBProgramNodeVisitor subclass: #TestVisitor
	instanceVariableNames: 'literals'
	classVariableNames: ''
	poolDictionaries: ''
	category: 'Compiler-AST-Visitors'

initialize
	literals := Set new.

literals
	^literals

acceptLiteralNode: aLiteralNode
	literals add: aLiteralNode value.
	

(TestVisitor new visitNode: tree) literals

and we get back:   a Set(3 4). Nice, simple and most important: No need 
to
clutter the AST classes, the designs get much more modular.

The plan is to move over to this AST step by step. So if you are doing 
anything using
the current AST, consider to move over to the RB AST. It will make your 
live much simpler.

       Marcus