ed reimplementation contest

Let's reimplement ed with modern languages!

10 INPUT
20 PRINT "?"
30 GOTO 10

Guess what would be cool. A thread about actual, fully functional ed reimplementations in readers' languages of choice, not reimplementations of the most tired joke in the history of programming. This is about as entertaining or useful as learning that the `hello world' program in a language I've never heard about is approximately ``print "hello world"'' (Thanks, Wikipedia. I really appreciate you).