JPie is a visual programming environment supporting live construction of Java applications. Class modifications, such as declaring instance variables and overriding methods, take effect immediately on existing instances of the class to encourage experimentation in an educational setting. Because programs are edited live, editing gestures must transform the program from one well-formed state to another, without intermediate ambiguous states. To accomplish this, JPie’s visual representation provides capsules, which represent logical code units, and semantic regions, which represent different aspects of a program. A capsule’s meaning depends upon its containing semantic region. Similarly, a gesture, which involves manipulation of a capsule, is interpreted on the basis of the semantic region in which it occurs. This paper describes how capsules and semantic regions visually expose the structure of JPie programs and support live program editing through natural atomic gestures
