The vision we have of conversational programming takes in much more than rapid turn around time and convenient debugging aids: our most interesting programs are never wrong and never final. [...] What is new is the requirement to make variable in our languages what we had previously taken as fixed. I do not refer to new data classes now, but to variables whose values are programs or parts of programs, syntax or parts of syntax, and regimes of control.

The Synthesis of Algorthmic Systems, 1966