TTY line collector

The original intention in the design of the system was to permit the user to construct his own I-O interface routines, if he so desired. Owing to the time pressures we were never able to implement some of the features necessary for this, and even so we would still have had to supply standard interfaces for the user who desired them. For these reasons we supplied a standard subprocess in all user processes which collected characters from the TTY and transmitted characters to the TTY. The program in this subprocess normally collected a complete line up to a carriage return before returning to the caller. This program had a fairly sophisticated built in editing routine that permitted copying portions of a previous line, skipping portions of a previous line and replacing portions of a previous line. These functions could be controlled on the basis of the characters in that line, for example, skip up to a given letter. These functions were controlled by the control keys on the TTY, and were arranged in a simple regular pattern on the keyboard. For the purpose of editing lines already existing in files, a subprocess could call the line collector with a line to be edited as if it had been a previous line.