A theory of the planning and debugging of computer programs is formalized as a context free grammar, which is used to reveal the constituent structure of problem solving episodes by parsing protocols in which programs are written, tested, and debugged. This is illustrated by the detailed analysis of an actual session with a beginning student working on a typical introductory LOGO project. The virtues and limitations of the context-free form of the grammar as a technique for summarizing certain insights into the structure of planning and debugging are discussed, and 17 references are listed. (Author/LLS)