CSE-321 Programming Languages Abstract Machine E POSTECH May 1, 2006 박성우

2 Operational Semantics of -Calculus explicit analysis of an expression

3 Key Ideas in Environment Semantics No substitutions –Delay the substitution [v / x] e as much as possible. store [v / x] in the environment. proceed to evaluate e. replace x by v only if necessary. A closure stores the values of all free variables in a given -abstraction.

4 Environment Semantics

5 Abstract Machine E explicit analysis of an expression and no substitution

6 Outline Overview V Abstract machine E Fixed point construct

7 Abstract Machine C + Environment Semantics

8 States of the Abstract Machine E

9 Definition

10 State Transition

11 State Transition

12 State Transition

13 Example

14 Outline Overview V Abstract machine E V Fixed point construct

15 Reduction Rule

16 fix for creating recursive functions

17 Abstract Syntax and Typing

18 Reduction

19 Outline Overview V Abstract machine E V Fixed point construct V Midterm

20 Score Distribution

21 55 Points Given for Free Problem 1: SML programming (20 points) –Question 1 from Assignment 2 –Question 2 from SML Style Guide –Question 3 from Assignment 2 Problem 2: reductions (10 points) –Question 1 and 2 from Course Notes Problem 5: substitution (15 points) –From Assignment 4 Problem 7: abstract machine C (10 points) –From Assignment 5

22 Average The midterm was designed with an anticipated average of 70. –55 points given for free –15 points from the rest Average = No question was particularly difficult, except the encoding of 'halve'. –2 students solved the 'halve' problem.

23 Conclusion Average –Positive (falls a bit short of expectation.) –Except inductive proofs using rule induction. Assignment 6 written part Don't get frustrated by your midterm score. –Midterm counts for only 10% of your final grade. –Final exam will be assigned 30% (tentatively). –Assignments 7 and 8 will be more important than the midterm.

24 A Question for Students 36 students got 20+ points on the functional set problem of Assignment 2. –26 students got 30 points. Only 14 students got empty, singleton, member, insert correct on Question 1-3. How did this happen?