Assignment #6 (Concepts of Programming Languages Chapter 6 Problem Set)

Problem Set:

15.What are the arguments for and against Java’s implicit heap storage recovery, when compared with the explicit heap storage recovery required in C++? Consider real-time systems. 

Answer:
Implicit eliminates the creation of dangling pointers. Disadv: cpu-time to do recovery, sometimes when there’s plenty of heap storage so recovery isn’t necessary.

16.What are the arguments for the inclusion of strong type checking in Java, although they were not included in C or C++?

Answer:

Java are strongly typed in the same sense as Ada. Types can be explicitly cast, which could result in a type error. However, there are rules of a language have an important effect on the value of an arithmetic operator with one floating-point operand and one integer operand is legal. The value of the integer operand is coerced to floating-point, and a floating point operation takes place. This is what is usually intended by the programmer.

17.  What kind of conversion is called a nonconverting cast? Explain with example in Ada language

Answer:

Ada is nearly strongly typed. It is only nearly strongly typed because it allows programmers to breach the type-checking rules by specifically requesting that type checking be suspended for a particular type conversion. This temporary suspension of type checking can be done only when an instantiation of the generic function Unchecked_Conversion is called. Such functions can be instantiated for any pair of subtypes. One takes a value of its parameter type and returns the bit string that is the parameter’s current value. No actual conversion takes place; it is merely a means of extracting the value of a variable of one type and using it as if it were of a different type. This kind of conversion is sometimes called a nonconverting cast.

Assignment #6 (Concepts of Programming Languages Chapter 6 Review Questions)

Review Questions :

16.What array operations are provided specifically for single-dimensioned arrays in Ada?   

Answer:

Catenation specified by the ampersand (&)

17. Define row major order and column major order.

Answer:

Row major order: the elements of the array that have as their first subscript the lower bound value of that subscript are stored first, followed by the elements of the second value of the first subscript, and so forth. If the array is a matrix, it is stored  by rows.

Column major order: the elements of an array that have as their last subscript the lower bound value of that subscript are stored first, followed by the elements of the second value of the last subscript, and so forth. If the array is a matrix, it is stored by columns.

18. What is an access function for an array? 
Answer:

Access function maps subscript expressions to an address in the array

20. What is the structure of an associative array? 
Answer:

Unordered collection of elements indexed by an equal number of KEYS.

21.  What is the purpose of level numbers in COBOL records?

Answer:

The level numbers in COBOL records are used to establish a hierarchical structure of related records.

22. Define fully qualified and elliptical references to fields in records.

Answer:

Fully qualified reference to fields in records is one in which all intermediate record names, from the larges enclosing record to  the specific field, are named in the reference.

Elliptical references to fields in records is when the field is named, but any or all of the enclosing record names can be omitted, as long as the resulting reference is unambiguous in the referencing environment.

23. What is the primary difference between a record and a tuple?

Answer:

A tuple is similar to a record, but do not have names for their constituent parts.            

24. Are the tuples of Python mutable?

Answer:

No, they aren’t.

Assignment #5 (Concepts of Programming Languages Chapter 5 Problem Set)

Problem Set

7. Assume the following JavaScript program was interpreted using static-scoping rules. What value of x is displayed in function sub1? Under dynamic-scoping rules, what value of x is displayed in function sub1 ?
Answer :
var x;
function sub1() {
document.write(“x = ” + x + “<br />”);
}
function sub2() {
var x;
x = 10;
sub1();
}
x = 5;
sub2();

Answer:
Static scope: x=5, Dynamic scoping: x=10.

8. Consider the following JavaScript program:
Answer :
var x, y, z;
function sub1() {
var a, y, z;
function sub2() {
var a, b, z;
. . .
}
. . .
}
function sub3() {
var a, x, w;
. . .
}
List all the variables, along with the program units where they are declared, that are visible in the bodies of sub1, sub2, and sub3, assuming static scoping is used.
Answer:
Sub1: a(sub1), y(sub1), z(sub1), x(main)
Sub2: a(sub2), b(sub2), z(sub2), y(sub1), x(main)
Sub3: a(sub3), x(sub3), w(sub3), y(main), z(main)

9. Consider the following Python program:
Answer :
x = 1;
y = 3;
z = 5;
def sub1():
a = 7;
y = 9;
z = 11;
. . .
def sub2():
global x;
a = 13;
x = 15;
w = 17;
. . .
def sub3():
nonlocal a;
a = 19;
b = 21;
z = 23;
. . .
. . .
List all the variables, along with the program units where they are
declared, that are visible in the bodies of sub1, sub2, and sub3, assumingstatic scoping is used.

Answer:
point 1 :  x = 1(main), y = 9 (sub1), z = 11(sub1) ,a = 7(sub1);
point 2 :  x =15(sub2), w = 17(sub2), a = 13(sub2), y = 9(sub1);
point 3 :  x = 15(sub2), b = 21(sub3), a = 19(sub1), z = 23(sub3), w = 17(sub 2);
point 4 :  x = 15(sub2), b = 21(sub3), a = 19(sub1), z = 23(sub3), w = 17(sub 2);

10. Consider the following C program:
Answer :

void fun(void) {
int a, b, c; /* definition 1 */
. . .
while (. . .) {
int b, c, d; /*definition 2 */
. . . 1
while (. . .) {
int c, d, e; /* definition 3 */
. . . 2
}
. . . 3
}
. . . 4
}
For each of the four marked points in this function, list each visible variable,
along with the number of the definition statement that defines it.

Answer:
Point 1: a:1, b:2, c:2, d:2
Point 2: a:1, b:2, c:3, d:3, e:3
Point 3: a:1, b:2, c:2, d:2
Point 4: a:1, b:1, c:1

11. Consider the following skeletal C program:
Answer :
void fun1(void); /* prototype */
void fun2(void); /* prototype */
void fun3(void); /* prototype */
void main() {
int a, b, c;
. . .
}
void fun1(void) {
int b, c, d;
. . .
}
void fun2(void) {
int c, d, e;
. . .
}
void fun3(void) {
int d, e, f;
. . .
}
Given the following calling sequences and assuming that dynamic scoping
is used, what variables are visible during execution of the last function
called? Include with each visible variable the name of the function in
which it was defined.
a. main calls fun1; fun1 calls fun2; fun2 calls fun3.Answer:
var a = main ; var b = fun1 ; var c = fun2 ;var d,e,f = fun3

b. main calls fun1; fun1 calls fun3.Answer:
var a = main; var b,c = fun1; var d,e,f = fun3

c. main calls fun2; fun2 calls fun3; fun3 calls fun1.
Answer:
var a= main; var b,c,d = fun1 ;var e,f = fun3

d. main calls fun3; fun3 calls fun1.
Answer:
var a = main; var b,c,d = fun1; var e,f = fun3

e. main calls fun1; fun1 calls fun3; fun3 calls fun2.
Answer:
var a=main;var c,d,e=fun2; var b =fun1; var f= fun3

f. main calls fun3; fun3 calls fun2; fun2 calls fun1.
Answer:
var a=main; var b,c,d = fun1; var f= fun3;var e=fun2

12. Consider the following program, written in JavaScript-like syntax:
// main program
var x, y, z;
Answer :
function sub1() {
var a, y, z;
. . .
}
function sub2() {
var a, b, z;
. . .
}
function sub3() {
var a, x, w;
. . .
}
Given the following calling sequences and assuming that dynamic scoping
is used, what variables are visible during execution of the last subprogram
activated? Include with each visible variable the name of the unit
where it is declared.
a. main calls sub1; sub1 calls sub2; sub2 calls sub3.Answer:
a x w in sub3. b, z in sub2, y in sub1.

b. main calls sub1; sub1 calls sub3.Answer:
a x w in sub3, y z in sub1.

c. main calls sub2; sub2 calls sub3; sub3 calls sub1.Answer:
a y z in sub1, x w in sub3, b in sub2.

d. main calls sub3; sub3 calls sub1.Answer:
a y z in sub1; x w in sub3;

e. main calls sub1; sub1 calls sub3; sub3 calls sub2.Answer:
a b z in sub2, x w in sub3; y in sub1.

f. main calls sub3; sub3 calls sub2; sub2 calls sub1.Answer:

a y z in sub1; b in sub2; x w in sub3.

Assignment #4 (Concepts of Programming Languages Chapter 4 Problem Set)

Problem Set 

A=Answer

6. Given the following grammar and the right sentential form, draw a parse tree and show the phrases and simple phrases, as well as the handle.
A=
S → AbB bAc A → Ab aBB B → Ac cBb c a.

a. aAcccbbc
S -> AbB -> aBBbB -> aAcBbB -> aAccBbbB -> aAcccbbc

b. AbcaBccb
S -> AbB -> AbcBb -> AbcAcb -> AbcaBBcb -> AbcaBccb

c. baBcBbbc
S -> bAc -> baBBc -> baBcBbc -> baBcBbbc

7. Show a complete parse, including the parse stack contents, input string, and action for the string id * (id + id), using the grammar and parse table in Section 4.5.3.
A=

8. Show a complete parse, including the parse stack contents, input string, and action for the string (id + id) * id, using the grammar and parse table in Section 4.5.3.
A=

9. Write an EBNF rule that describes the while statement of Java or C++. Write the recursive-descent subprogram in Java or C++ for this rule.
A=

<while_stmt> -> WHILE ‘(‘ (<arith_expr> | <logic_expr>) ‘)’ <block> <block> -> <stmt> | ‘{‘ <stmt> {<stmt>} ‘}’

10. Write an EBNF rule that describes the for statement of Java or C++. Write the recursive-descent subprogram in Java or C++ for this rule.
A=

Assume the following non-terminals are given: <type>, <id>, <literal>, <assign>, <expr>, and <stmt_list>.

<for> -> for ‘(‘ [[<type>] <id> = <expr> {, [<type>] <id> = <expr>}] ; [<expr>] ; [<expr> {, <expr>}] ‘)’ ‘{‘ <stmt_list> ‘}’

Assignment #5 (Concepts of Programming Languages Chapter 5 Review Questions)

Review Question

A=Answer

16. What is the referencing environment of a statement?
A=The referencing environment of a statement is the collection of all variables that are visible in the statement. The referencing environment of a statement in a static-scoped language is the variables declared in its local scope plus the collection of all variables of its ancestor scopes that are visible.

17. What is a static ancestor of a subprogram? What is a dynamic ancestor of a subprogram?
A=The static ancestors of a subprogram sub() are all the procedures in the program within which the procedure sub() is defined, i.e., the definition of the procedure sub() is nested. The definition of a procedure may be directly nested within only one procedure, called its static parent procedure. However, this static parent procedure may itself be nested within another procedure, and so on up to the main() program. All these procedures are considered to be static ancestors of the procedure sub(). Simply put, the static ancestors are those that strictly contain the subprogram in question.
The dynamic ancestors of a subprogram sub() are all the procedures called before sub() during the execution of a program, that have not yet finished executing. These are the procedures that are waiting for procedure sub() to finish executing before they can terminate. Simply put, dynamic ancestors are those that are called to reach the subprogram in question.

18. What is a block?
A=Such vari-ables are typically stack dynamic, so their storage is allocated when the section is entered and deallocated when the section is exited

19. What is the purpose of the let constructs in functional languages?
A=“let” introduces a new variable scope, and allows you to bind variables to values for that scope. It is often read as “let x be [value] in …”

20. What is the difference between the names defined in an ML let construct from the variables declared in a C block?

Assignment #4 (Concepts of Programming Languages Chapter 4 Review Questions)

REVIEW QUESTION :

A=Answer

16.  What is the FIRST set for a given grammar and sentential form ?

A=

FIRST( ) = {a => * a } (If => *  ,   is in FIRST( ))   

in which =>* means 0 or more derivation steps.

17.Describe the pairwise disjointness test.

A=It is a test of non-left recursive grammar that indicates whether left recursion can be done. It requires the ability to compute a set based on the RHSs of a given nonterminal symbol in a grammar.

18.What is left factoring ?

A=Left factoring is the action taken when a grammar leads backtracking while marking parsing/syntax tree.

19.What is a phrase of a sentential form ?

A=A phrase is a subsequence of a sentential form that is eventually reduced to a single non-terminal

20.What is a simple phrases of a sentential form?

A=simple phrases is just a phrase that takes a single derivation step from its root nonterminal node.

Assignment #3 (Concepts of Programming Languages Chapter 3 Problem Set)

Problem Set :

a=Answer

14. Draw parse trees for the sentences aabb and aaaabbbb, as derived from the grammar of Problem 13

a. 

15. Convert the BNF of Example 3.1 to EBNF. 

a.

EBNF:

<program> → begin <stmt_list> end

<stmt_list> → <stmt> { ;  <stmt_list>}

<stmt> → <var> = <expression>

<var> → A | B | C

<expression> → <var> { (+|-) <var>}

16. Convert the BNF of Example 3.3 to EBNF. 

a.
<assign> → <id> = <expr>
<id> → A | B | C
<expr> → <expr> {(+ | *) <expr>}
| <id>

17. Convert the following EBNF to BNF: S → A{bA} A → a[b]A 

a. 

S -> A | AX
X -> bA | bAX
A -> aA | abA

18. What is the difference between an intrinsic attribute and a nonintrinsic synthesized attribute?

a. An intrinsic attribute is an inherent characteristic of a terminal symbol in the grammar. So the value of the attribute is determined solely from the terminal symbol. A nonintrinsic synthesized attribute is an attribute of a non-terminal symbol in the grammar.