The design of an execute primitive for the APL*PLUS system

In the original design of APL/360 the user was provided with only three direct methods of having a character string interpreted as an APL statement to be evaluated: direct entry for immediate evaluation; entry as the result of a request for evaluated input (quad input); and entry of a statement to be made part of a user-defined function (with evaluation deferred until such later time as the function was invoked by the user). Note that in all three cases the only source of the characters was direct manual entry by the user.