When we write a program that manipulates data structures, we often draw and manipulate a visual image of the structures in our mind. In order to immediately connect those mental images with the data objects created by the program, we propose a live programming environment, called Kanon, specialized for data structure programming. It automatically executes a program being edited, and draws objects and their mutual references as a node-link diagram. In order to visualize information relevant to the programmer’s concern, it offers two visualization modes based on the cursor position in the editor. It also offers two interactive mechanisms that relate elements in the program to elements on the diagram, and vice versa. The implementation includes a novel technique for mental map preservation of visual diagrams.