Previously, this book discussed how to invoke another exec as an external routine (Writing Subroutines and Functions). You can also invoke an exec from another exec explicitly with the EXEC command or implicitly by member name. Like an external routine, an exec invoked explicitly or implicitly can return a value to the caller with the RETURN or EXIT instruction. Unlike an external routine, which passes a value to the special variable RESULT, the invoked exec passes a value to the REXX special variable RC.