Notes: Monday 4 March 2002

Schedule

• Before doing PS5, you should read SICP, through 3.3.2 (p. 217-261). Sorry I forgot to put the Notes Wednesday or on PS5.
• Lab hours for PS5: Monday, 8-9:30pm
• Friday, 8 March: Problem Set 5
• 9-17 March: Spring Break
• Before 18 March: GEB all of Part I

Notes

Places, Frames and Envrionments

• Names identify places. (define x expr) and (lambda (x) expr) both create places named x.
• Frames hold names. All names must be inside a frame.
• An environment is a pointer to a frame.
• All frames except the outermost frame have pointers to a parent frame.
• The global environment is a pointer to the outermost frame. The outermost frame contains all the Scheme primitives.

Compound Application Rule

1. Construct a new frame, enclosed in the environment of this procedure (that is, the parent of this frame is the frame this procedure's environment points to)
2. Make places in that frame with the names of each parameter
3. Put the values of the parameters in those places
4. Evaluate the body in the new environment

Why must expressions be evaluated in an environment?

How do we find the value associated with a name in an environment?

Links

CS101 Exam
CS201 Exam
CS415 Assignment
CS655 Problem Set [Answers]
PhD Qualifying Exam

University of Virginia Department of Computer Science CS 200: Computer Science

David Evans evans@virginia.edu Using these Materials