Slime or Slimv with a file/buffer as the REPL input it's one of the best things ever. Refactor your code doing crazy data mangling on functons? On Lisp you just

Slime or Slimv with a file/buffer as the REPL input it's one of the best things ever. Refactor your code doing crazy data mangling on functons? On Lisp you just redefine functions/macros with ease. With the rest of languages the complexity raises exponentially.