I'm not sure if this is exactly what you are talking about, but with racket-mode in Emacs you can write some program, run it (C-c C-k), then add some s-expr and

I'm not sure if this is exactly what you are talking about, but with racket-mode in Emacs you can write some program, run it (C-c C-k), then add some s-expr and evaluate only that (C-x C-e) in the current context.