The authors describe work on development of a software system for writing and testing programs for a computer controlled manipulation. The authors examine in particular how the development of working programs is facilitated by the use of an interactive system based on an interpreter. The paper presents the main features of Pointy the system developed at Stanford Artificial Intelligence Laboratory as a tool for writing assembly programs. The user, interacting with the manipulator, constructs an incremental model of the objects involved in the assembly and develops the corresponding symbolic program. 13 references.