At the simplest level, this reminds me of input in C64 BASIC. You could hit RETURN anywhere on on any line and that line would get parsed as if you'd just types

At the simplest level, this reminds me of input in C64 BASIC. You could hit RETURN anywhere on on any line and that line would get parsed as if you'd just types it in. You could cursor around, edit previously-entered lines, and so on. It was pretty neat.