Visual editing of data structures

A data structure editor that depicts the internal data structures of a program graphically is presented. The editor offers new capabilities for the graphical construction and editing of data structures. Once data structures have been built graphically, they can be used for testing programs or fragments of programs. The data editor is integrated into a programming environment where it may be used as a debugging aid for the programmer, and it is closely tied to the run-time system of the environment, allowing it to control the duration of execution in a way similar to setting breakpoints. The history of all variables is kept, so the user can retrace the steps by which a variable reached its current state