Assignment #9

Source:
Concepts of Programming Languages, Robert W. Sebesta.

Chapter 9: Subprograms, page 436-439

By:
Name : Helena Natanael
NIM  : 1801380333

---

Review Question:

6. What is a Ruby array formal parameter?
Ruby supports a complicated but highly flexible actual parameter configuration. The initial parameters are expressions, whose value objects are passed to the corresponding formal parameters. The initial parameters can be following by a list of key => value pairs, which are placed in an anonymous hash and a reference to that hash is passed to the next formal parameter. These are used as a substitute for keyword parameters, which Ruby does not support. The hash item can be followed by a single parameter preceded by an asterisk. This parameter is called the array formal parameter.

7. What is a parameter profile? What is a subprogram protocol?

Parameter profile is the number, order, and types of its formal parameters. Subprogram protocol is its parameter profile plus, if it is a function, its return type. In languages in which subprograms have types, those types are defined by the subprogram’s protocol.

8. What are formal parameters? What are actual parameters?
- Formal parameters are the parameters in the subprogram header.

- Actual parameters are a list of parameters to be bound to the formal parameters of the subprogram which must be included with the name of the subprogram by the subprogram call statements.

 9. What are the advantages and disadvantages of keyword parameters?
- The advantage : they can appear in any order in the actual parameter list. 

- The disadvantage : the user of the subprogram must know the names of formal parameters.

10. What are the differences between a function and a procedure?
A function returns value but procedures do not. Function are structurally resemble procedures but are semantically modeled on mathematical parameter.



Problem Sets:

6. Present one argument against providing both static and dynamic local variables in subprograms.
In subprograms local variables can be static or dynamic;  
If local variable treated statically:
This allows for compile-time allocation/ deallocation and ensures proper type checking but does not allow for recursion.
If local variables treated dynamically:
This allows for recursion at the cost of run-time allocation/ deallocation and initialization because these are stored on a stack, referencing is indirect based on stack position and possibly time-consuming.


7. Consider the following program written in C syntax:
void fun (int first, int second) {
first += first; second += second;
}
void main() {
int list[2] = {1, 3};
fun(list[0], list[1]);
}
For each of the following parameter-passing methods, what are the values
of the list array after execution?
a. Passed by value : 1,3
b. Passed by reference : 2,6
c. Passed by value-result : 2,6


8. Argue against the C design of providing only function subprograms.
If a language provides only functions, then either programmers must live with the restriction of returning only a single result from any subprogram, or functions must allow side effects, which is generally considered bad. Since having subprograms that can only modify a single value is too restrictive, C’s choice is not good.


9. From a textbook on Fortran, learn the syntax and semantics of statement functions. Justify their existence in Fortran.

The Fortran 1966 standard provided a reference syntax and semantics, but vendors continued to provide incompatible extensions. These standards have improved portability.

10. Study the methods of user-defined operator overloading in C++ and Ada, and write a report comparing the two using our criteria for evaluating languages.
One of the nice features of C++ is that you can give special meanings to operators, when they are used with user-defined classes. This is called operator overloading. You can implement C++ operator overloads by providing special member-functions on your classes that follow a particular naming convention. For example, to overload the + operator for your class, you would provide a member-function named operator+ on your class. Meanwhile for Ada, since much of the power of the language comes from its extensibility, and since proper use of that extensibility requires that we make as little distinction as possible between predefined and user-defined types, it is natural that Ada also permits new operations to be defined, by declaring new overloading of the operator symbols.

Assignment #8

Source:

Concepts of Programming Languages, Robert W. Sebesta.

Chapter 8: Statement-Level Control Structures, page 381-382

By:
Name : Helena Natanael
NIM  : 1801380333
P.S.: Happy New Year 2015! :)

---

Review Question:

6. What is unusual about Python’s design of compound statements?
Python uses indentation to specify compound statements. 
For example,
if x < y :
x = y
print "value of x is modified".
All statements equally indented are included in the compound statement.

7. Under what circumstances must an F# selector have an else clause?

An F# selector have an “else” clause if the “if” expression does return a value.

8.What are the common solutions to the nesting problem for two-way selectors?
A programmer should avoid syntactic entity because in some cases, syntactic entity leads to ambiguous meaning when it is compiled. Another way to avoid the issue of nested selection statements is to use an alternative means of forming compound statements.


 9. What are the design issues for multiple-selection statements?
1. What is the form and type of the expression that controls the selection?• How are the selectable segments specified?
2. Is execution flow through the structure restricted to include just a single selectable segment?
3. How are the case values specified?
4. How should unrepresented selector expression values be handled, if at all?

10. Between what two language characteristics is a trade-off made when deciding whether more than one selectable segment is executed in one execution of a multiple selection statement?
The C# switch statement differs from that of its C-based predecessors in two ways. First, C# has a static semantics rule that disallows the implicit execution of more than one segment. The rule is that every selectable segment must end with an explicit unconditional branch statement: either a break,
which transfers control out of the switch statement, or a goto, which can transfer control to one of the selectable segments (or virtually anywhere else).

As with C, if there is no break at the end of the selected segment, execution continues into the next segment.



Problem Sets:

6. Analyze the potential readability problems with using closure reserved words for control statements that are the reverse of the corresponding initial reserved words, such as the case-esac reserved words of ALGOL 68. For example, consider common typing errors such as transposing characters.
The potential readability problem is the typing errors. It’s very possible to occur if we don’t type the code carefully.


7. Use the Science Citation Index to find an article that refers to Knuth (1974). Read the article and Knuth’s paper and write a paper that summarizes both sides of the goto issue.
An alternative viewpoint is presented in Donald Knuth's Structured Programming with go to Statements, which analyzes many common programming tasks and finds that in some of them GOTO is the optimal language construct to use.[7] In their quasi-standard book on the C programming language, Dennis Ritchie and Brian Kernighan warn that goto is "infinitely abusable", but also suggest that it could be used for end-of-function error handlers and for multi-level breaks from loops.


8. In his paper on the goto issue, Knuth (1974) suggests a loop control statement that allows multiple exits. Read the paper and write an operational semantics description of the statement.
Operational semantics are a category of formal programming language semantics in which certain desired properties of a program, such as correctness, safety or security, are verified by constructing proofs from logical statements about its execution and procedures, rather than by attaching mathematical meanings to its terms (denotational semantics).


9. What are the arguments both for and against the exclusive use of Boolean expressions in the control statements in Java (as opposed to also allowing arithmetic expressions, as in C++)?

The primary argument for using Boolean expressions exclusively as control expressions is the reliability that results from disallowing a wide range of types for this use. In C, for example, an expression of any type can appear as a control expression, so typing errors that result in references to variables of incorrect types are not detected by the compiler as errors. No , it would not be a good idea. Although this custom precedence sounds like increasing flexibility, requiring parentheses to show a custom precedence would impact in readability and writability of a program.

10. In Ada, the choice lists of the case statement must be exhaustive, so that there can be no unrepresented values in the control expression. In C++, unrepresented values can be caught at run time with the default selector. If there is no default, an unrepresented value causes the whole statement to be skipped. What are the pros and cons of these two designs (Ada and C++)? 

---- C++ :
1. Control expression can be only an integer type 

2. Selectable segments can be statement sequences, blocks, or compound statements 

3. Construct is encapsulated 

4. Any number of segments can be executed in one execution of the construct (there is no implicit branch at the end of selectable segments) (a trade-off between reliability and flexibility–convenience) - To avoid it, the programmer must supply a break statement for each segment.
5. default clause is for unrepresented values (if there is no default, the whole statement does nothing) 

 ----- Ada:

 1. Constant lists can include: - Subranges e.g., 10..15
- Boolean OR operators
e.g., 1..5 | 7 | 15..20
2. Lists of constants must be exhaustive - Often accomplished with others clause
- This makes it more reliable.

Assignment #7

Source:

Concepts of Programming Languages, Robert W. Sebesta.

Chapter 7: Expressions and Assignment Statements, page 342-344

By:
Name : Helena Natanael
NIM  : 1801380333

---

Review Question:

6. What associativity rules are used by APL?
In APL, all operators have the same level of precedence. Thus, the order of evaluation of operators in APL expressions is determined entirely by the associativity rule, which is right to left for all operators.

7. What is the difference between the way operators are implemented in C++ and Ruby?

What sets Ruby apart from the C-based languages in the area of expressions is that all of the arithmetic, relational, and assignment operators, as well as array indexing, shifts, and bitwise logic operators, are implemented as methods. For example, the expression a + b is a call to the + method of the object referenced by a, passing the object referenced by b as a parameter.

8. Define functional side effect.
A side effect of a function, naturally called a functional side effect, occurs when the function changes either one of its parameters or a global variable. (A global variable is declared outside the function but is accessible in the function.)

 9. What is a coercion?
Coercion is an implicit type of conversion only if they are widening (from a “smaller” type to a “larger” type). So int to float coercions are done across the assignment operator, but float to int coercions are not.

10. What is a conditional expression?
Conditional Expression is a logical feature of programming language which perform different actions based on true or false. 
In trinary, the format is statement ? action_1 (if true) : action_2 (if false).



Problem Sets:

6. Should C’s single-operand assignment forms (for example, ++count) be included in other languages (that do not already have them)? Why or why not?
Yes C should, because it will ease the increment or even decrement while we use in looping rather than manually by the assigning, and also by using that we can easily know that it is not operation, instead it is an increment or decrement which is usually used in repetition.

7. Describe a situation in which the add operator in a programming language would not be commutative.
It wouldn’t be commutative when it deals with the negative integers.

8. Describe a situation in which the add operator in a programming language would not be associative.
It is not associative when it includes the other operator with higher precedence like the multiplication and division.

9.Assume the following rules of associativity and precedence for expressions:

Precedence                    

Highest                          *, /, not

                                      +,–,&,mod

                                      (unary)

                                      =, /=, < , <=, >=, >

                                      and
Lowest                           or, xor
Associativity                  Left to right


Show the order of evaluation of the following expressions by parenthesizing all sub expressions and placing a superscript on the right parenthesis to indicate order. For example, for the expression
a+b*c+ d
the order of evaluation would be represented as
((a + (b * c)¹)² + d)³

1. a * b – 1 + c

( ( (a * b)¹– 1)² + c)³
2. a* ( b – 1) / c mod d
( ( (a* ( b – 1)¹ )²/ c )³ mod d)⁴
3. (a – b) / c & (d * e / a – 3)
( ( (a – b)¹/ c)² & ( ( (d * e)³ / a)⁴ – 3)⁵ )⁶
4. –a or c = d and e
( (–a)¹ or ( (c = d)² and e)³ )⁴
5. a > b xor c or d <= 17
( ( (a > b)¹ xor c)³ or (d <= 17)² )⁴
6. –a + b
( – (a + b)¹ )²

10. Show the order of evaluation of the expressions of Problem 9, assuming that there are no precedence rules and all operators associate right to left.

a. ( a * ( b – ( 1 + c )¹ )² )³
b. ( a * ( ( b – 1 )² / ( c mod d )¹ )³ )⁴
c. ( ( a – b )⁵ / ( c & ( d * ( e / ( a – 3 )¹ )² )³ )⁴ )⁶
d. ( – ( a or ( c = ( d and e )¹ )² )³ )⁴
e. ( a > ( xor ( c or ( d <= 17 )¹ )² )³ )⁴
f. ( – ( a + b )¹ )²

Assignment #6

Source:

Concepts of Programming Languages, Robert W. Sebesta.

Chapter 6: Data Types, page 312-314

By:
Name : Helena Natanael
NIM  : 1801380333

---

Review Question:

6. What are the advantages of user-defined enumeration types?
Enumeration types can provide advantages in both readability and reliability. First is no arithmetic operations are legal on enumeration types; this prevents adding days of the week, for example. And second, no enumeration variable can be assigned a value outside its defined range.

7. In what ways are the user-defined enumeration types of C# more reliable than those of C++?

C# enumeration types are like those of C++, except that they are never coerced to integer. So, operations on enumeration types are restricted to those that make sense. Also, the range of values is restricted to that of the particular enumeration type. 

8.What are the design issues for arrays?

• What types are legal for subscripts?
• Are subscripting expressions in element references range checked?
• When are subscript ranges bound?
• When does array allocation take place?
• Are ragged or rectangular multidimensioned arrays allowed, or both?
• Can arrays be initialized when they have their storage allocated?
• What kinds of slices are allowed, if any?

9.Define static, fixed stack-dynamic, stack-dynamic, fixed heap-dynamic, and 
heap-dynamic arrays. What are the advantages of each?
A static array is one in which the subscript ranges are statically bound and storage allocation is static. The advantage of static arrays is efficiency: No dynamic allocation or deallocation is required.

A fixed stack-dynamic array is one in which the subscript ranges are statically bound, but the allocation is done at declaration elaboration time during execution. The advantage of fixed stack-dynamic arrays over static arrays is space efficiency.

A stack-dynamic array is one in which both the subscript ranges and the storage allocation are dynamically bound at elaboration time. The advantage of stack-dynamic arrays over static and fixed stack-dynamic arrays is flexibility.

A fixed heap-dynamic array is similar to a fixed stack-dynamic array, in that the subscript ranges and the storage binding are both fixed after storage is allocated. The advantage of fixed heap-dynamic arrays is flexibility the array’s size always fits the problem.

A heap-dynamic array is one in which the binding of subscript ranges and storage allocation is dynamic and can change any number of times during the array’s lifetime. The advantage of heap-dynamic arrays over the others is flexibility: Arrays can grow and shrink during program execution as the need for space changes.

10.What happens when a nonexistent element of an array is referenced 
in Perl?
A reference to a nonexistent element in Perl yields undef, but no error is reported.


Problem Sets:

6.Explain all of the differences between Ada’s subtypes and derived types.
A derived type is a new type that is based on some previously defined type with which it is not equivalent, although it may have identical structure. Derived types inherit all the properties of their parent types. Consider the following example:
type Celsius is new Float;
type Fahrenheit is new Float;

The types of variables of these two derived types are not equivalent, although their structures are identical. Furthermore, variables of both types are not type equivalent with any other floating-point type. Derived types can also include range constraints on the parent type, while still inheriting all of the parent’s operations.

On the other hand Ada subtype is a possibly range-constrained version of an existing type. A subtype is type equivalent with its parent type. Ada’s derived types are very different from Ada’s subrange types.
For example, consider the following type declarations:
type Derived_Small_Int is new Integer range 1..100; subtype Subrange_Small_Int is Integer range 1..100;
Variables of both types, Derived_Small_Int and Subrange_Small_Int, have the same range of legal values and both inherit the operations of Integer.

However, variables of type Derived_Small_Int are not compatible with any Integer type. On the other hand, variables of type Subrange_Small_Int are compatible with variables and constants of Integer type and any subtype of Integer.

7. What significant justification is there for the -> operator in C and C++?
The justification of –> operator in c and c++ is writability. In c ++ there are 2 ways a pointer record can be used to reference a field in that record. It is slightly easier to write p –> q than(*p).q.

8. What are all of the differences between the enumeration types of C++ and those of Java?
In Java they can include fields, constructors, and methods. The possible values of an enumeration are the only possible instances of the class. All enumeration types inherit toString, as well as a few other methods. An array of the instances of an enumeration type can be fetched with the static method values. The internal numeric value of an enumeration variable can be fetched with the ordinal method. No expression of any other type can be assigned to an enumeration variable. Also, an enumeration variable is never coerced to any other type.

9.The unions in C and C++ are separate from the records of those languages, rather than combined as they are in Ada. What are the advantages and disadvantages to these two choices?
The advantage: Unconstrained variant records in Ada allow the values of their variants to change types during execution. 

The disadvantage: the type of the variant can be changed only by assigning the entire record, including the discriminant. This disallows inconsistent records because if the newly assigned record is a constant data aggregate, the value of the tag and the type of the variant can be statically checked for consistency.

10. Multidimensional arrays can be stored in row major order, as in C++, or in column major order, as in Fortran. Develop the access functions for both of these arrangements for three-dimensional arrays.
Let the subscript ranges of the three dimensions be named min(1), min(2), min(3), max(1), max(2), and max(3). Let the sizes of the subscript ranges be size(1), size(2), and size(3). Assume the element size is 1.

Row Major Order:
location(a[i,j,k]) = (address of a[min(1),min(2),min(3)])
+((i-min(1))*size(3) + (j-min(2)))*size(2) + (k-min(3))
Column Major Order:
location(a[i,j,k]) = (address of a[min(1),min(2),min(3)])
+((k-min(3))*size(1) + (j-min(2)))*size(2) + (i-min(1))

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

---

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