Structured programming with limited private types in Ada

Abstract

Many traditional styles of programming cannot cope with the limitations of Ada limited private types. We present a style of programming that enables structured programming in Ada with limited private types. The problem of "finalization" is safely and cleanly handled through the use of a generic package which guarantees that a variable of the limited private type will be finalized even in the presence of exceptions.Finalization is often desired in order to perform automatic garbage collection , whether by reference counting or by marking. We have proved our structured technique by developing a garbage-collected Lisp system in Ada in which the Lisp values are instances of a limited private type. The Ada code was so highly structured, that it was generated automatically using a simple compiler. The garbage collector in this system was easily and safely implemented, and different garbage collection techniques were tested without affecting user code.