Assignment #5

Source:

Concepts of Programming Languages, Robert W. Sebesta.

Chapter 5: Names, Bindings, and Scopes, page 235-240

By:
Name : Helena Natanael
NIM  : 1801380333

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Review Question:

6. What is the l-value of a variable? What is the r-value?
The l-value of variable is the address of a variable because the address is required when the name of a variable appears in the left side of an assignment. 
The r-value of variable is a variable’s value because it is required when the name of the variable appears in the right side of an assignment statement.

7. Define binding and binding time.
A binding is an association between an attribute and an entity, such as between a variable and its type or value, or between an operation and a symbol. While the time at which a binding takes place is called binding time.

8. After language design and implementation [what are the four times bindings can take place in a program?]
The compile time binding, the load time binding, the link time binding, the run time binding.

9. Define static binding and dynamic binding.
A static binding is when the binding occurs before run time begins and remains unchanged throughout program execution. If the binding first occurs during run time or can change in the course of program execution, it is called dynamic binding.

10. What are the advantages and disadvantages of implicit declarations?
The advantage of implicit declarations is that simple in naming conventions. In this case, the compiler or interpreter binds a variable to a type based on the syntactic form of the variable’s name. While the disadvantage of implicit declarations is it can be detrimental to reliability because they prevent the compilation process from detecting some typographical and programmer errors.


Problem Set:

6. Consider the following JavaScript skeletal program:
// The main program
var x;
function sub1() {
var x;
function sub2() {
. . .
}
}
function sub3() {
. . .
}
Assume that the execution of this program is in the following unit order:
main calls sub1
sub1 calls sub2
sub2 calls sub3

a. Assuming static scoping, in the following, which declaration
of x is the correct one for a reference to x?
i. sub1
sub1: sub1

ii. sub2
sub2: sub1

iii. sub3
sub3: main

b. Repeat part a, but assume dynamic scoping.
i. sub1
sub1: sub1
ii. sub2
sub2: sub1
iii. sub3
sub3: sub1

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?
var x;
function sub1() {
document.write("x = " + x + "<br />");
}
function sub2() {
var x;
x = 10;
sub1();
}
x = 5;
sub2();

static scoping rule = 5
dynamic scoping rule = 10


8. Consider the following JavaScript program:
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.

Variable                       Where Declared
In Sub1:
a                                             Sub1
y                                             Sub1
z                                             Sub1
x                                             Main
In Sub2:
a                                             Sub2
b                                             Sub2
z                                             Sub2
y                                             Sub1
x                                             Main
In Sub3:
a                                             Sub3
x                                             Sub3
w                                            Sub3
y                                             Main
z                                             Main


9. Consider the following Python program:
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, assuming
static scoping is used.

Variable                       Where Declared
In Sub1:
a                                              Sub1
y                                              Sub1
z                                              Sub1
x                                              Main
In Sub2:
a                                              Sub2
x                                              Sub2
w                                             Sub2
y                                              Main
z                                              Main
In Sub3:
a                                              Sub3
b                                              Sub3
z                                              Sub3
w                                             Sub2
x                                              Sub2
y                                              Main


10. Consider the following C program:
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.

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