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Concepts of programming language – Chapter 16

1.   What are the three primary uses of symbolic logic in formal logic?

• to express propositions

• to express the relationships between propositions, and

• to describe how new propositions can be inferred from other propositions that are assumed to be true.

2.   Two parts of a compound term are:  a functor, which is the function symbol that names the relation, and an ordered list of parameters, which together represent an element of the relation.

3.   Propositions can be stated in two modes: one in which the proposition is defined to be true, and one in which the truth of the proposition is something that is to be determined. In other words, propositions can be stated to be facts or queries.

5.   Antecedents are the right side of clausal form propositions, whereas Consequents are the left side of clausal form propositions, because it is the consequence of the truth of the antecedent.

7. What are the forms of Horn clauses ?
• Have a single atomic proposition on the left side
• empty left side.

9. What does it mean for a language to be nonprocedural ?
– Language in which the programs do not exactly state how a result is to be computed but rather describe the form of the result.

11. An uninstantiated variable is a variable that has not been assigned a value.

13.  Conjunctions contain multiple terms that are separated by logical AND operations.

PROBLEM SET

1.”All predicate calculus propositions can be algorithmically converted to clausal form”. Is this statement true or false?

This statement is true. Nilsson (1971) gives proof that this can be done, as well as a simple conversion algorithm for doing it.

2. Describe how a logic programming language is different from a general programming language.

Programming that uses a form of symbolic logic as a programming language, unlike other general programming language, is often called logic programming; languages based on symbolic logic are called logic programming languages, or declarative languages.

7.   Horn clauses can be in only two forms: They have either a single atomic proposition on the left side or an empty left side. The left side of a clausal form proposition is sometimes called the head, and Horn clauses with left sides are called headed Horn clauses. Headed Horn clauses are used to state relationships, such as

likes( bob, trout ) likes( bob, fish ) x fish( trout )

8. Critically comment on the following statement : “ Logic programs are nonprocedural”
– It is true, because logical programs use lots of different processes based on its conditions. If a certain logical requirement is true, then a program will execute the corresponding process, instead of procedurally executing the statements.

10.  Using the internet for reference, find some of the applications of expert systems.

• Expert system in healthcare: The Electronic health record (EHR) is designed to replace the traditional medical and bring together a more versatile, expansive and robust expert system to provide greater quality care.

• Expert systems in the financial field: Loan departments are interested in expert systems for morgages because of the growing cost of labour, which makes the handling and acceptance of relatively small loans less profitable.

• A new application for expert systems is automated computer program generation. Funded by a US Air Force grant, an expert system-based application (hprcARCHITECT) that generates computer programs for mixed processor technology (FPGA/GPU/Multicore) systems without a need for technical specialists has recently been commercially introduced

Concepts of programming language – Chapter 15

2. A lambda expression specifies the parameters and the mapping of a function.

3. Atoms and lists were parts of the original LISP.

6. Simple list is a list which membership of a given atom in a given list that does not include sublists.

7. REPL stand for read-evaluate-print loop.

8. Three parameters to IF are: a predicate expression, a then expression, and an else expression.

18. A function is tail recursive if its recursive call is the last operation in the function. This means that the return value of the recursive call is the return value of the nonrecursive call to the function. It is important to specify repetition to be tail recursive because it is more efficient(increase the efficiency).

22. During reader phase of a common LISP language processor, There is a special kind of macro, named reader macros or read macros, that are expanded. A reader macro expands a specific character into a string of LISP code. For example, the apostrophe in LISP is a read macro that expands to a call to QUOTE.

24. What is stored in an ML evaluation environment?

A table called the evaluation environment stores the names of all implicitly and explicitly declared identifiers in a program, along with their types. This is like a run-time symbol table.

29. Curried function let new functions can be constructed from them by partial evaluation.

30. Partial evaluation means that the function is evaluated with actual parameters for one or more of the leftmost formal parameters.

33. Explain the process of currying.
The process of currying replaces a function with more than one parameter with a function with one parameter that returns a function that takes the other parameters of the initial function.

35. A language is nonstrict if it does not have the strict requirement.

43. What is the syntax of a lambda expression in F#?

The following lambda expression illustrates their syntax:
(fun a b −> a / b)

PROBLEM SET

2. Give the general form of function declaration in ML.

Function declarations in ML appear in the general form
fun function_name( formal parameters ) = expression;

8. How is the functional operator pipeline ( | > )used in F#?

The pipeline operator is a binary operator that sends the value of its left operand, which is an expression, to the last parameter of the function call, which is the right operand. It is used to chain together function calls while flowing the data being processed to each call.

Consider the following example code, which uses the high-order functions filter and map:

let myNums = [1; 2; 3; 4; 5]
let evensTimesFive = myNums

|> List.filter (fun n −> n % 2 = 0)

10. What does the following Scheme function do?

(define ( x lis)

(cond

(( null? lis) 0 )

(( not(list? (car lis)))

(cond

((eq? (car lis) #f) (x (cdr lis)))

(else (+1 (x (cdr lis))))))

(else (+ (x (car lis)) (x (cdr lis))))

x returns the number of non-#f atoms in the given list

|> List.map (fun n −> 5 * n)

Concepts of programming language – Chapter 14

6 . What is exception propagation in Ada?

Exception propagation allows an exception raised in one program unit to be handled in some other unit in its dynamic or static ancestry. This allows a single exception handler to be used for any number of different program units. This reuse can result in significant savings in development cost, program size, and program complexity.

9. What is the scope of exception handlers in Ada?

Exception handlers can be included in blocks or in the bodies of subprograms, packages, or tasks.

10. What are the four exceptions defined in the Standard package of Ada?

There are four exceptions that are defined in the default package, Standard:

Constraint_aError

Program_Error

Storage_Error

Tasking_Error

11. are they any predefined exceptions in Ada?

Yes, they are.

12. What is the use of Suppress pragma in Ada?

The suppress pragma is used to disable certain run-time checks that

are parts of the built-in exceptions in Ada.

14. What is the name of all C++ exception handlers?

Try clause.

30. In which version were assertions added to Java?

Assertions were added to Java in version 1.4.

31. What is the use of the assert statement?

The assert statement is used for defensive programming. A program may be written with many assert statements, which ensure that the program’s computation is on track to produce correct results.

32. What is event-driven programming?

Event-driven programming is a programming where parts of the program are executed at completely unpredictable times, often triggered by user interactions with the executing program.

33. What is the purpose of a Java JFrame?

The JFrame class defines the data and methods that are needed for frames. So, a class that uses a frame can be a subclass of JFrame. A JFrame has several layers, called panes.

34. What are the different forms of assert statement?

There are two possible forms of the assert statement:

assert condition;

assert condition : expression;

PROBLEM SET:

1.What mechanism did early programming languages provide to detect or attempt to deal with errors?

Early programming languages were designed and implemented in such a way that the user program could neither detect nor attempt to deal with such errors. In these languages, the occurrence of such an error simply causes the program to be terminated and control to be transferred to the operating system.

2.Describe the approach for the detection of subscript range errors used in C and Java.

In C subscript ranges are not checked. Java compilers usually generate code to check the correctness of every subscript expression. If any exception generates, then an unchecked exception is thrown.

6.In languages without exception-handling facilities, it is common to have most subprograms include an “error” parameter, which can be set to some values representing “OK” or some other value representing “error in procedure”. What advantage does a linguistic exception-handling facility like that of Ada have over this method?

There are several advantages of a linguistic mechanism for handling exceptions, such as that found in Ada, over simply using a flag error parameter in all subprograms. One advantage is that the code to test the flag after every call is eliminated. Such testing makes programs longer and harder to read. Another advantage is that exceptions can be propagated farther than one level of control in a uniform and implicit way. Finally, there is the advantage that all programs use a uniform method for dealing with unusual circumstances, leading to enhanced readability.

7.In languages without exception-handling facilities, we could send an error-handling procedure as parameter to each procedure that can detect errors than must be handled. What disadvantage are there to this method?

There are several disadvantages of sending error handling subprograms to other subprograms. One is that it may be necessary to send several error handlers to some subprograms, greatly complicating both the writing and execution of calls. Another is that there is no method of propagating exceptions, meaning that they must all be handled locally. This complicates exception handling, because it requires more attention to handling in more places.

14. Summarize the arguments in favor of the termination and resumption models of continuation.

The resumption model is useful when the exception is only an unusual condition, rather than an error. The termination model is useful when the exception is an error and it is highly unlikely that the error can be corrected so that execution could continue in some useful way.

Concepts of programming language – Chapter 13

1. Three possible levels of concurrency in programs:
• instruction level (executing two or more machine instructions simultaneously),
• statement level (executing two or more high-level language statements simultaneously)
• unit level (executing two or more subprogram units simultaneously)

2. In an SIMD computer, each processor has its own local memory. One processor controls the operation of the other processors. Because all of the processors, except the controller, execute the same instruction at the same time, no synchronization is required in the software.

5. Unit-level concurrency is best supported by MIMD computers.

6. Vector processor have groups of registers that store the operands of a vector operation in which
the same instruction is executed on the whole group of operands simultaneously.

7. Physical concurrency is several program units from the same program that literally execute simultaneously.

Logical concurrency is multiple processors providing actual concurrency, when in fact the actual execution of programs is taking place in interleaved fashion on a single processor.

8. A scheduler manages the sharing of processors among the tasks. If there were never any interruptions and tasks all had the same priority, the scheduler could simply give each task a time slice, such as 0.1 second, and when a task’s turn came, the scheduler could let it execute on a processor for that amount of time.

16. A task descriptor is a data structure that stores all of the relevant information about the execution state of a task.

18. The purpose of a task-ready queue is to be storage of tasks that are ready to run.

21. A binary semaphore is a semaphore that requires only a binary-valued counter.

A counting semaphore is a synchronization object that can have an arbitrarily large number of states.

30. Ada terminate clause, when selected, means that the task is finished with its job but is not yet terminated. Task termination is discussed later in this section.

34. Sleep method in Java blocks the the thread.

35. Yield method in Java surrenders the processor voluntarily as a request from the running thread.

36. The join method in Java is used to force a method to delay its execution until the run method of another thread has completed its execution.

55. Concurrent ML is an extension to ML that includes a fform of threads and a form of synchronous message passing to support concurrency.

56. The use of spawn primitive of CML is to take the function as its parameter and to create a thread.

57. The use of subprograms BeginInvoke and Endinvoke in F# is to call threads asynchronously.

60. What is the type of an F# heap-allocated mutatable variable?

A mutable heap-allocated variable is of type ref

63. The FORALL statement of High-Performance Fortran is to specifies a sequence of assignment statements that may be executed concurrently.

Problem Set

1. Explain clearly why a race condition can create problems for a system.

Race condition can create problems for a system, because two or more tasks are racing to use the shared resource and the behavior of the program depends on which task arrives first (and wins the race).

2. The different ways to handle deadlock:

– Ignoring deadlock

– Detection

– Prevention

– Avoidance

3. Busy waiting is a method whereby a task waits for a given event by continuously checking for that event to occur. What is the main problem with this approach?

Busy-waiting or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a method of waiting a specific length of time. Processor speeds vary greatly from computer to computer, especially as some processors are designed to dynamically adjust speed based on external factors, such as the load on the operating system. Busy waiting may loop forever and it may cause a computer freezing

Concepts of programming language – Chapter 12

2.   The problems associated with programming using abstract data types are:

• In nearly all cases, the features and capabilities of the existing type are not quite right for the new use.

• The type definitions are all independent and are at the same level.

3.   The advantage of inheritance is inheritance offers a solution to both the modification problem posed by abstract data type reuse and the program organization problem. If a new abstract data type can inherit the data and functionality of some existing type, and is also allowed to modify some of those entities and add new entities, reuse is greatly facilitated without requiring changes to the reused abstract data type.

4.   Message protocol is the entire collection of methods of an object.

6. Describe a situation where dynamic binding is a great advantage over its absence.
– There is a base class, A, that defines a method draw that draws some figure associated with the base class. A second class, B, is defined as a subclass of A. Objects of this new class also need a draw method that is like that provided by A but a bit different. With overriding, we can directly modify B’s draw function. But without it, we either make a specific function in A for B and inherit it.

7.   Dynamic dispatch is the third characteristic (after abstract data types and inheritance) of object-oriented programming language which is a kind of polymorhphism provided by the dynamic binding of messages to method definitions.

8.   An abstract method is an implemented method which all of descendant class should have and it is included in Building.

An abstract class is  a class that includes at least one abstract method.

10.  An inner class is  a nonstatic class that is nested directly in another class.

12.  All Smalltalk objects are allocated from the heap and are referenced through reference variables, which are implicitly dereferenced.

15.  Smalltalk supports single inheritance; it does not allow multiple inheritance.

19.  C++ heap-allocated objects are deallocated using destructor.

29.  No Objective-C doesn’t support it. Objective-C only supports single inheritance.

31.  The root class in Objective-C is called NSObject

38.  Boxing is primitive values in Java 5.0+ which is implicitly coerced when they are put in object context. This coercion converts the primitive value to an object of the wrapper class of the primitive value’s type.

49.  Access control in Ruby is different for data than it is for methods. All instance data has private access by default, and that cannot be changed. If external access to an instance variable is required, accessor methods must be defined.

PROBLEM SET

2.    In what ways can “compatible “ be defined for the relationship between an overridden method and the overriding method?

Every overriding method must have the same number of parameters as the overridden method and the types of the parameters and the return type must be compatible with those of the parent class.

3.   Compare the inheritance of C++ and Java.

• In Java, all objects are Inherited, either directly or indirectly. While in C++ a class can be defined to stand on its own without an ancestor.

•  The meaning of protected member access specifier is somewhat different in Java. In Java, protected members of a class “A” are accessible in other class “B” of same package, even if B doesn’t inherit from A (they both have to be in the same package).

•  Java uses extends keyword for inheritence. Unlike C++, Java doesn’t provide an inheritance specifier like public, protected or private. Therefore, we cannot change the protection level of members of base class in Java, if some data member is public or protected in base class then it remains public or protected in derived class. Like C++, private members of base class are not accessible in derived class. Unlike C++, in Java, we don’t have to remember those rules of inheritance which are combination of base class access specifier and inheritance specifier.

5.    Compare abstract class and interface in Java.

• First and major difference between abstract class and interface is that, abstract class is a class while interface is a interface, means by extending abstract class you can not extend another class because Java does not support multiple inheritance but you can implement multiple inheritance in Java.
• Second difference between interface and abstract class in Java is that you can not create non abstract method in interface, every method in interface is by default abstract, but you can create non abstract method in abstract class. Even a class which doesn’t contain any abstract method can be abstract by using abstract keyword.
• Third difference between abstract class and interface in Java is that abstract class are slightly faster than interface because interface involves a search before calling any overridden method in Java. This is not a significant difference in most of cases but if you are writing a time critical application than you may not want to leave any stone unturned.
• Fourth difference between abstract class vs interface in Java is that, interface are better suited for Type declaration and abstract class is more suited for code reuse and evolution perspective.
• Another notable difference between interface and abstract class is that when you add a new method in existing interface it breaks all its implementation and you need to provide an implementation in all clients which is not good. By using abstract class you can provide default implementation in super class.

7.   What is one programming situation where multiple inheritance has a significant disadvantage over interfaces?

A situation when there are two classes derived from a common parent and those two derived class has one child.

9.   Give an example of inheritance in C++, where a subclass overrides the superclass methods.

class Enemy{

protected:

int Hp;

public:

void attack(){

cout<<”Enemy Attacks using GUN!!”<<endl;
}
};

class BossEnemy: public Enemy{

public:

void attack(){

cout<<”Boss Enemy attacks using MAGIC!!”<<endl;
}
};

10.  Explain one advantage of inheritance.

One of the key benefits of inheritance is to minimize the amount of duplicate code in an application by sharing common  code amongst several subclasses. Where equivalent code exists in two related classes, the hierarchy can usually be  refactored to move the common code up to a mutual superclass. This also tends to result in a better organization of  code and smaller, simpler compilation units.

17.  What are the different options for object destruction in Java?

There is no explicit deallocation operator. A finalize method is implicitly called when the garbage collector is about to reclaim the storage occupied by the object.

Concepts of programming language – Chapter 11

1.  Two kinds of abstractions in programming languages are process abstraction and data abstraction.

5.   The first design issue for abstract data types is the form of the container for the interface to the type. The second design issue is whether abstract data types can be parameterized. The third design issue is what access controls are provided and how such controls are specified.

6.   Explain how information hiding is provided in an Ada package.
There are two approaches to hiding the representation from clients in the package specification. One is to include two sections in the package specification—one in which entities are visible to clients and one that hides its contents.

9.   Package specification, is an Ada package which provides the interface of the encapsulation (and perhaps more)
Body package, is an Ada package which provides the implementation of most, if not all, of the entities named in the associated package specification.

10.   The ‘with’ clause in Ada makes the names defined in external packages visible.

15.   The purpose of a C++ destructor is to deallocate heap space (memory) that the object or class used.

16.   A destructor has no return types.

20.   Limited private types are useful when the usual predefined operations of assignment and comparison are not meaningful or useful.

21.   Intializers in Objective-C are constructors.

26.   The purpose of a Destructor is usually to clear off unused variables and clean up the memory. Java has in built memory handling mechanisms (Garbage collection) that clear off unused memory automatically. Hence there is no requirement for destructor methods. So that Java doesn’t need any destructor

27.   Methods in Java must be defined completely in a class.

28.   Java classes are allocated  from the heap and accessed through reference variables.

PROBLEM SET

2. Suppose someone designed a stack abstract data type in which the function top returned an access path (or pointer ) rather than returning a copy of the top element. This is not a true data abstraction. Why ? Give an example that illustrates the problem.

– The problem with this is that the user is given access to the stack through the returned value of the “top” function. For example, if p is a pointer to objects of the type stored in the stack, we could have:

p = top(stack1);

*p = 42;

These statements access the stack directly, which violates the principle of a data abstraction.

4.   The advantages of the nonpointer concept in Java?

• There is no memory leak such as dangling pointers or unnamed variables.

• Memory access via pointer arithmetic – this is fundamentally unsafe. Java has a robust security model and disallows pointer arithmetic for this reason.

• Array access via pointer offsets – Java does this via indexed array access so you don’t need pointers. A big advantage of Java’s indexed array access is that it detects and disallows out of bounds array access, which can be a major source of bugs.

• References to objects – Java has this, it just doesn’t call them pointers. Any normal object reference works as one of these.

8.   Some drawbacks of user-defined generic classes in Java 5.0 are: for one thing, they cannot store primitives. Second, the elements cannot be indexed. Elements must be added to user-defined generic collections with the add method.

9.   If the constructor is absent in Java and C++, it will be automatically made by the compiler.

11.  Destructors in C# are rarely used because it uses garbage collection for most of its heap objects.

12.  Classes in Ruby are dynamic in the sense that members can be added at any time. This is done by simply including additional class definitions that specify the new members.