Is the REPL the same environment as your running code?

If your environment has stuff added dynamically (for example every Rails app) you need to attach to the live environment - an OO version of gdb. And once you’re doing that, you’ve basically got Smalltalk without the nice presentation layer.

Update: by presentation layer I mean I can ask to inspect a live object and open a window that shows not just it’s instance variables and the messages it responds to, but read the documentation (the equivalent of Rubydoc) and source code (including editing that source code if I wanted to).