Download CS 784 Spring 2009 Final Exam: Static Fields, Attribute Grammars, Axiomatic Semantics and more Exams Programming Languages in PDF only on Docsity!
Wright State University Department of Computer Science and Engineering
CS 784 Spring 2009 Prasad
Final Exam (40 pts)
1 Interpreter for Object-Oriented Language (8 + 8 pts)
Consider the interpreter for OOPL given in the files 5-3.scm and 5-4-4.scm. We explore introducing static fields into class definitions. Static fields associate some state with a class; all the instances of a class share this state. Static fields can appear in a method body. For example, one might write the following program and obtain as the result, the list (01):
class c static next_serial_number field my_serial_number method get_serial_number () my_serial_number method initialize () begin set my_serial_number = next_serial_number; set next_serial_number = add1(next_serial_number); end let o1 = new c1() o2 = new c1() in list (send o1 get_serial_number(), send o2 get_serial_number())
Explain all the modifications to the interpreter code to incorporate the static fields shown in the grammar rule for class definition below, informally and clearly first, and formally in code later. Initialize each static field to 0, by default.
(class-decl ("class" identifier "extends" identifier (arbno "static" identifier) (arbno "field" identifier) (arbno method-decl) ) a-class-decl)
Specifically, locate all the changes to the original interpreter code on the accompanying interpreter code handout and/or locate changes/insertions using file name, page number, and line numbers.
2 Attribute Grammars (8 pts)
Consider the following grammar for the base-3 numerals T.
T ::= 0 | 1 | 2 | T T
Write an attribute grammar to determine the numeric value of these numerals. For instance, V alue(201) = 19, V alue(1010) = 30, etc.
3 Axiomatic Semantics (5 + 3 pts)
Determine the following weakest preconditions. (Assume all variables are of integer type.)
wp( {if odd(j) then k := ki; j := j-1 else i := ii; j := j div 2}, [ k*(i^j) = n ] ) =?
wp( {while i > 0 do i := i - 5;}, i = 0) =?
4 Algebraic Specification (8 pts)
Give an algebraic specification of the ADT Int Bag that supports the following operations: empty, insert, isEmpty, count, union and intersection. (Recall that a bag is a homogeneous collection of values where duplication is significant, but the order of values is not.) Informally,
- empty: Yields the empty bag.
- insert: Takes an integer and a bag as input, and yields the bag resulting from introducing one occur- rence of the integer into the bag.
- isEmpty: Checks if the bag is empty.
- count: Takes an integer and a bag as input, and yields the number of occurrences of the integer in the bag.
- union: Takes two bags as input, and yields the bag containing integers that belong to either bags. (That is, union([1,1,2], [2,3]) = [1,1,2,2,3], etc.)
- intersection: Takes two bags as input, and yields a bag containing integers that belong to both the bags. (That is, intersection([1,1,2], [1,1,1,2,3]) = [1,1,2], intersection([1,2,2,2,3],[1,1,2,4]) = [1,2], intersection([1],[2]) = [], etc)
