Versioning AST's has been on my mind for some time as well, I got interested it as a way to store source-code in a coding-style-neutral way (check it in & out w

Versioning AST's has been on my mind for some time as well, I got interested it as a way to store source-code in a coding-style-neutral way (check it in & out with whatever coding style you're used to), and to be able to categorize check-ins based on the type of changes to the code (only comments, moved code, variable renames, etc). Probably you already know about it, but have a look at papers aboht the tree edit/tree distance problem: http://scholar.google.nl/scholar?q=tree+edit+problem&hl=nl&as_sdt=0&as_vis=1&oi=scholart&sa=X&ei=3YT-UMXSOITBtAbKmYDABQ&ved=0CCoQgQMwAA http://scholar.google.nl/scholar?q=tree+edit+problem&hl=... It's exactly what you would need to store versioned trees such as AST's.