Well, on 1.9 it's not quite as nice as 1.8. The ruby-core team decided to change ruby so that after parsing the source the AST would be thrown away as part of some kind of optimization. That means things like ParseTree don't work anymore, and you can't inspect the AST of a Proc at runtime.

However, with sourcify you can sort of emulate the 1.8 behaviour, but it's not perfect. It uses ripper to parse the file where the Proc is defined, and then provides the same callbacks that ParseTree does. It mostly seems to work, but it does run into problems if two Procs are defined on the same line, eg: users.select { ... }.select { ... }.

I'm actually a little disappointed that ruby-core decided to go in this direction. I think that decision will end up costing the community because it makes it harder for runtime introspection of code. It means less tools will be written on top of the runtime, and things like Ambition become harder if not impossible to do reliably. I'm glad to see Rubinius is going in the opposite direction though.