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@robpike @dabeaz MTS had something like readline built into the terminal handler (you could grab a line from anywhere on the screen, modify it, and enter), so the line editor was almost a full screen editor... for quite a while, nobody saw the need to develop a full screen editor, but eventually it was done.

(One wonders why unix didn't do something similar, but instead required every interactive program to use readline and provide its own recall system)