On-line user languages

The principal differences between on-line and off-line user languages are discussed in some detail. The characteristic features of the OPL programming language are mentioned together with experiences of Project MAC, pointing at increased efficiency in the use of computers.Work reported herein was supported by Project MAC, and M. I. T. research program sponsored by the Advanced Research Projects Agency, Department of Defense, under Office of Naval Research contract NONR-4102(01). Reproduction in whole or in part is permitted for any purpose of the United States Government.