I was fairly happy doing REPL development with Scheme, and then I decided to give Common Lisp a try and I discovered what REAL REPL-driven development is. The

I was fairly happy doing REPL development with Scheme, and then I decided to give Common Lisp a try and I discovered what REAL REPL-driven development is. The first time I changed some data representation from a defclass to a defstruct and SBCL asked me what I wanted to do with existing instances of the type was mindblowing.