An implementation of structured programming in APL
Martin Osborne · The Computer Journal · 1978
Inclusion of user defined ‘keyword’ functions in programs gives APL the appearance of a structured programming language. The keyword functions have names such as IF, REPEAT, etc. and are preceded by the operator →. When these functions are incorporated in a program, the program reads and executes like a structured program. A program containing keyword functions must be preprocessed by a user defined analyser. The analyser checks the syntax of the constructs being implemented by the keyword functions and generates vectors which are stored in the program. As the programs is executed, the keyword functions examine these vectors to determine the flow of control in the program.