Two alternatives to also know about, if you're new to Emacs Lisp.<p>* Lisp Interaction mode (like in your `<i>scratch</i>` buffer). Press `C-j` to eval the expression to left of the point, and insert the result in your buffer. Then you can leave the result there, edit it into a new code, undo to hide it, etc.<p>* Emacs Lisp mode (like when you're editing any `.el` file) can also do a lot of things that people normally do in a REPL. Say, you're working on some code in the file, and it's running, and you want to change one of the functions. Just edit the function in the file, and hit `M-C-x` to evaluate the `defun` that the point is in, and see the value in the echo area. Or evaluate a region, or the entire file. (At one point, I also had a pretty-printer hooked up, so that it could do better transient display of values.) You can also selectively instrument functions for Edebug from here.<p>This seems simple today, but it used to blow away the development languages and tools most people were using.