Teaching Programmers to Think of Program Dynamics.

Many students in their first year in the University have some idea of programming based on courses in high school and grade school. Such knowledge, however, is highly unsystematic. Their behavior in practice is to choose variables, loops and other constructs by some form of trial and error, and use a debugger to beat the code into shape. Teaching systematic programming has followed an arc starting from formal approaches in the early days to current ideas like recipes for systematic programming and tool based approaches that show language statements and their dynamic behavior together to build intuition relating statics and dynamics. In this position paper, we present a different approach that asks students to program by first planning a trace, and then choosing statements that generate that trace. This approach allows us to explain the choices of variables, ordering of program statements, and loop invariants in a natural way. Our experience is that students think more systematically, and have a better understanding of causal aspects of program statements.