Final Questions

Question 1

Describe the concept of ‘Referential Transparency’

Answer 1

An expression is said to be referentially transparent, if it can be substituted for the value it evaluates to, without changing the behavior of the program. Expressions with side-effects are not referentially transparent.

Question 2

Describe the concept of ‘Short-circuit Evaluation’

Answer 2

Short-circuit evaluation is a form of lazy-evaluation in which given a binary boolean expression, the second (right-hand side) argument is evaluated only if the evaluation of the first (right-hand side) argument does not suffice to determine the overall value of the expression. For example, in the expression ‘b1 and b2’, b2 is evaluated only if b1 is true, as otherwise the expression would be known to be false regardless of the value of b2.

Question 3

What is a Mixed-mode Expression?

Answer 3

An expression that contains operands of different types. For example: 1 + 41.0 is a mixed-mode expression.

Question 4

Describe the concept of Closure of a function

Answer 4

A function closure is programming device that includes a function definition along with an environment that includes bindings for some (or all) of the free variables in said function. In other words, it is a partially evaluated function. For example:

fun add x y = x + y;
plusOne = add 1;
plusOne 3;
val it = 4 : int;

in the code above plusOne is a partially evaluated version of add that includes an environment in which x is bound to 1.

Question 5

What is a compound assignment operator?

Answer 5

A compound assignment operator is one that serves as an abbreviation of performing an operation on a variable and assigning the result to the same variable. For example, if one were to add a value to a variable and the assign the result to the same variable: x = x + 42, then this could be be abbreviated using an addition compound assignment as: x += 42.

Question 6

What is operator precedence, and why is it important?

Answer 6

Operator precedence refers to binding priority established between the different operators in a language and their arguments. For example, if * has precedence over +, then the expression 3 * 7 + 21 is interpreted as (3 * 7) + 21 instead of 3 * (7 + 21), because the 7 binds with the * before it binds with the +. Operator precedence is used to solved semantic ambiguities while parsing expressions in programs.

Question 7

What is the difference between Procedures, Functions and Methods?

Answer 7

A procedure (or sub-routine), in the strictest of senses, is a sub-task, a sequence of instructions, that may be invoked throughout the program. A function, on the other hand, takes an (optional) input and produces an output. A method, on the other hand, is a concept from OO programming where the execution of a function is associated with a target object: side-effects, if any, are contained to that object as the method is seen as an agent of mediation between the rest of the program and the object. In modern parlance, the distinction between procedure and function has been blurred, but the distinction between function/procedure and method is very punctuated.

Question 8

What is a parallel assignment operator?

Answer 8

A feature by which multiple variables are assigned values in a single statement. For example: int a, b, c := 1, 2, 3; – in this case a is assigned 1, b is assigned 2, and c is assigned 3.

Question 9

What is the difference between formal parameters, actual parameters, and arguments.

Answer 9

Formal parameters are the names given to the inputs to a function, used in the body of the function to access those inputs. Arguments are the values bound to the formal parameters after a function call. For example, if a function is declared as int f(int x); and called with f(42); then the formal parameter is x and the argument is 42. If the function is passed a variable name such as f(y); then y is sometimes known as the actual parameter, though this is sometimes also used to refer to arguments in general.

Question 10

What is a pure function?

Answer 10

A pure function is a function with no side effects.

Question 11

Describe the concepts of overflow or underflow.

Answer 11

The result of an arithmetic operation that results in a value that exceeds the storage capacity (greatest possible value for overflow, least possible value for underflow). For example, for a signed 32 bit integer 2^31 + 1, or -2^31 - 1.

Question 12

Describe overloading.

Answer 12

When a function or operator is given multiple behaviors depending on the arguments/operands. For example, in Java + performs addition if the operands are integers, or concatenation if the operands are strings.

Question 13

Describe conditional assignment statements.

Answer 13

An assignment operator in which the value assigned depends on a given condition. For example, in Java, this is achieved using the ternary operator int x = cond ? 42 : 0;

Question 14

Select all that apply to the SML programming language.

Answer 14

a. Everything is a function.
b. Interpreted.
c. Supports concurrent
programming.
d. Dynamically Typed.
e. Functions are allowed to
have side-effects.
f. Garbage Collected.
g. Polymorphic.
h. All recursive functions are
optimized into loops.
i. SML supports
polymorphism,encapsulation,
and information hiding.
Therefore, SML is Object-
Oriented.

Answers: e, f, g.

Question 15

Name a few of the different issues that play a role in the design of programming languages

Answer 15

Problem Domain, Programming philosophy/paradigm, Computer Architecture, Implementation.

Question 16

Name 3 of the most important programming paradigms

Answer 16

Imperative/procedural, Functional/declarative/applicative, Logical/constraint-based (Object-oriented).

Question 17

Name the main evaluation criteria for programming language design

Answer 17

Simplicity
Orthogonality
Level of abstraction
Portability
Cost
Expressivity

Question 18

How is criteria of Simplicity applied to programming language design?

Answer 18

The language feature set should be minimal, with rules on how to apply them and combine them as simple and clear as possible.

Question 19

How is criteria of Orthoganility applied to programming language design?

Answer 19

Primitives can be combined in relatively small number of ways, and every combination is legal and meaningful.

Question 20

How is criteria of Abstraction applied to programming language design?

Answer 20

The language provides mechanisms to define powerful data abstractions that approximate constructs in the problem domain.

Question 21

How is criteria of Portability applied to programming language design?

Answer 21

Programs written in the language can be moved from the system they were created to other systems with relative ease.

Question 22

How is criteria of Cost applied to programming language design?

Answer 22

The cost of using the language (development, compilation, maintenance, execution, etc.) is manageable.

Question 23

How is criteria of Expressivity applied to programming language design?

Answer 23

The language provides concise, different ways of defining algorithms and computations.

Question 24

Give an example of a pair of evaluation criteria that are in tension with each other, and explain why

Answer 24

Simplicity vs. Expressivity: If a language is simple it means it provides a limited set of primitive constructs, and limited, clear rules for how to combine them, which means that there are relatively few ways to define the same computation in concise ways, hurting the expressive power of the language.

Question 25

What are the main technologies used to implement programming languages?

Answer 25

Compilers
Interpreters
Virtual Machines

Question 26

What are Reserved Words in Programming Languages?

Answer 26

These are especial words that cannot be used as names (variables, functions, etc.) in the program, since they are used for other purposes in the language (names of primitive constructs, keywords, etc.).

Question 27

Describe the terms L-value and R-value of a variable

Answer 27

The L-value is the memory address of a variable, and the R-value is the value stores in that memory address.

Question 28

Describe the term Aliasing in reference to variables

Answer 28

Aliasing refers to the situation when a single memory address has more than one name, in other words, two or more variables share the same L-value.

Question 29

What is the difference between static and dynamic typing?

Answer 29

In static typing the type of a variable is determined statically, that is, before the program is executed, either by syntactic features like a type declaration, or special variable names, or during compilation like type inference. On the other hand, with dynamic typing, the type of a variable cannot be determined until the program is executed and a value is assigned to the variable.

Question 30

What are the differences between unary, binary and ternary operators.

Answer 30

Unary operators only need one operand to function (such as i++), binary needs two operands to function (such as 8/2), and ternary operators (also called conditional operators) need three operands to function (condition?expression1:expression2;)

Question 31

Difference between infix and prefix operators?

Answer 31

Infix operators go between the operands (A+B), prefix operators go before the operands (+AB).

Question 32

What are operation side effects?

Answer 32

In programming a side effect is when a procedure changes a variable from outside its scope.

Question 33

What is short circuiting?

Answer 33

It’s the semantics of some Boolean operators in some programming languages in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND function evaluates to false, the overall value must be false; and when the first argument of the OR function evaluates to true, the overall value must be true.

Question 34

What is a subprogram call?

Answer 34

A subprogram call is either a procedure_call_statement or a function_call; it invokes the execution of the subprogram_body.

Question 35

Difference between methods and functions?

Answer 35

Functions are defined in structural language and methods are defined in object oriented languages.

Question 36

What is a parameter profile?

Answer 36

A subprogram header contains a list of formal parameters. The parameter profile of a subprogram contains information about its formal parameters. The information contains number, type, and order of formal parameters.

Ex. header “void fun(int a, float b, char c);

Here the information inside the parenthesis is parameter profile. The parameter profile of the subprogram fun() tells that there are 3 parameters which are of type int, float, and char in the specified order.

Question 37

Parameter passing vs non local variables

Answer 37

If the variable has a local declaration (that is, it is a local variable or parameter), the compiler will use the local variable or parameter, even if a non-local variable (static variable or instance variable) with the same name exists. Local variables, therefore, take precedence over non-local variables.

Question 38

Difference between formal parameters vs actual parameters.

Answer 38

The term parameter (sometimes called formal parameter) is often used to refer to the variable as found in the function definition, while argument (sometimes called actual parameter) refers to the actual input supplied at function call