Structural Abstraction A Mechanism for Modular Program Construction Approved by:

To Mom, for teaching me to live life with courage and joy. iii Acknowledgements I wish I could say that careful planning and a tenacious drive toward a grand vision lead me to where I am today. But the truth is, this dissertation is the result of a series of serendipitous events in my life. I seem to have the good fortune of meeting the right people at the right time. For them, I am extremely grateful. I had never written a single line of program when I entered MIT as a freshman. My choice of Computer Science as a major of study was the result of me being goaded by my peers, who claimed that the introductory computer science course (originally code-named 6.001) was extremely demanding, and my stubborn disbelief that there could be anything that is too demanding for me. Signing up for 6.001 was the beginning of the end. I thank my fellow freshmen for luring me into this course. I also thank the faculty of MIT for having cultivated the proper reputation for the course, and for having made computer science enchanting