AST Manipulation and Common Subexpression Elimination

["Martin v. Löwis"]

Robert Kern wrote:
> 1. Can I do better than brute-force traversing the AST and trying to match each
> subtree to the other subtrees (using something like the match() function given
> in the parser module example)?

Certainly: you could do hashing or sorting. For hashing, define some 
hash function for expressions, preferably recursively

> 2. Are there good tools out there for doing AST transformations like this? Are
> there any GUI tools for messing with the AST? I know that I will want to
> interactively select which subexpressions are eliminated in this fashion.

GUI yes, interactive no: You might want to take a look at the 
dotty/graphviz tool suite.

Regards,
Martin