matz / ruby-lang.org (Yukihiro Matsumoto) wrote in message news:<1091501355.227383.29355.nullmailer / picachu.netlab.jp>...
 
>   * I admit disclosing abstract syntax tree to Ruby programs can open
>     new possibilities.  it's good for users at the moment, I guess.
>     but it is very bad in a long run unless I design it perfectly.
>     I'm sure I will change my mind in AST design and alas, here comes
>     another big field of incompatibility.


is this really a problem? 
IMO a developer accessing the AST (or just the parser) 
should be aware of what he's doing and expect some breakage. 
IIRC python has modules to access, the AST, the parser and the VM
internals, and this has proved quite ufeful even if python changed
much over time..