On the locus of program flow within and among secondary functions

Abstract

Several authors have considered the problem of control of program flow in secondary (user-written) functions in APL and forms which would give APL equivalents of the control structures of more traditional languages have been proposed. Rather than expanding or altering the means of controlling program flow in APL, this paper suggests restricting the forms, but not the power, of branching. The motivation and implications are presented and the advantages and disadvantages are weighed. Problems of migration of functions and questions regarding the resumption of suspended functions are considered. Consideration of function call and the system variable, @@@@ LC , suggests a generalization of secondary-function execution with regard to program flow among user-written functions. This provides an alternate view of suspended functions and permits branching to be generalized to include co-routines.