Run For Leprosy 2015

Kesan saya sebagai pelari di run for leprosy ini sangatlah senang bisa berpatisipasi untuk bisa lari sehat mengelilingi alam sutera sekaligus ikut mendonasikan uang untuk diberikan kepada orang yang lebih membutuhkan dibanding saya sendiri, contohnya orang-orang yang mempunyai penyakit kusta. Acara ini seru sekali bisa berkumpul bersama teman-teman bukan hanya teman-teman BINUS tetapi juga teman-teman dari luar BINUS, dan juga bisa lari bareng dan sehat bareng teman-teman lainnya. Pesan saya untuk acara kedepannya adalah agar bisa lebih menarik lagi dan kalau bisa disesering mungkin adakan acara ini agar kita bisa berpatisipasi lagi mengikuti acara yang seru ini.

Kusta merupakan penyakit yang pada zaman dahulu merupakan penyakit yang mengerikan yang tidak dapat disembuhkan oleh dokter manapun dan jika kita berada di dekat orang tersebut, maka kita bisa tertular penyakit tersebut dan banyak orang menjauhi orang yang terkena penyakit tersebut. Zaman sekarang penyakir kusta ini sudah dapat diobati melalui terapi. Komitmen saya terhadap penyakit kusta ini adalah untuk tidak mendiskriminasi orang-orang yang memiliki penyakit tersebut dan membantu orang tersebut berobat agar bisa cepat sembuh, karena mereka juga manusia yang butuh bersosial dengan orang-orang disekitarnya dan kita juga sebagai manusia pasti juga bisa merasakan jika kita berada di posisi tersebut. Saran saya agar bagaimana bisa bersosialisasi yang baik terhadap penyakit kusta adalah dengan cara buatlah dia tertawa atau senang karena dengan tertawa bisa membantu orang tersebut cepat sembuh dari penyakit manapun dan dia dapat melupakan penyakitnya tersebut seperti orang-orang yang lainnya yang dapat bersosialisasi dengan orang manapun

By pamaan

Concept of Programming Languages chapter 16

2.What are the two parts of a compound term?

  • A compound term is composed of two parts, a functor and an ordered list of parameter

5. What are the antecedents? Consequent?

  • The right side of a clausal form proposition is called the antecendent. The left side is called the consequent because it is the consequence of the truth antecendent

7. What are the forms of Horn clauses?

  • Horn clauses can be in only two forms: they have either a single atomic proposition on the left side or an empty left side.

8. What is the basis concept of declarative semantics?

  • The basic concept of this semantics is that there is a simple way to determine the meaning of each statement, and it does not depend on how the statement might be used to solve a problem

10. What are the three forms of a Prolog term?

  • constant, a variable, or a structure

11. What is an uninstantiated variable?

  • variable that has not been assigned a value

Problem Set :

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

  • The statement is true. this was proven by Nilsson (1971) by using a simple conversion algorithm

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

  • Logical programming language uses a form of symbolic logic, the syntax of logic programming logic is remarkably different from that of the imperative and functional languages
By pamaan

Concept of Programming Languages 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)

By pamaan

Concept of Programming Languages Chapter 14

Review question

1. Define exception, exception handler, raising an exception, disabling an exception, continuation, finalization, and built-in exception.
Answer: An exception is an unusual event that is detectable by either hardware or software and that may require special processing. The special processing that may be required when an exception is detected is called exception handling. The processing is done by a code unit or segment called an exception handler. An exception is raised when its associated event occurs. In some situations, it may be desirable to ignore certain hardware-detectable exceptions—for example, division by zero—for a time. This action would be done by disabling the exception. After an exception handler executes, either control can transfer to somewhere in the program outside of the handler code or program execution can simply terminate. We term this the question of control continuation after handler execution, or simply continuation. In some situations, it is necessary to complete some computation regardless of how subprogram execution terminates. The ability to specify such a computation is called finalization. Built-in exceptions have a built-in meaning, it is generally inadvisable to use these to signal program-specific error conditions.  Instead we introduce a new exception using an exception declaration, and signal it using a raise expression when a run-time violation occurs.  That way we can associate specific exceptions with specific pieces of code, easing the process of tracking down the source of the error.

2. When is an exception thrown or raised?
Answer: The exception thrown or raised when there is throw clause of a method lists that have checked exception which could throw and does not handle.

10. What are the four exceptions defined in the Standard package of Ada?
Answer: The four exception defined in the standard package of Ada are Constraint_Error, Program_Error, Storage_Error, Tasking_Error

11. What is the use of suppress pragma in Ada?
Answer: An Ada pragma is a directive to the compiler. Certain run-time checks that are parts of the built-in exceptions can be disabled in Ada programs by use of the Suppress pragma, the simple form of which is pragma Suppress(check_name) where check_name is the name of a particular exception check. The Suppress pragma can appear only in declaration sections. When it appears, the specified check may be suspended in the associated block or program unit of which the declaration section is a part. Explicit raises are not affected by Suppress. Although it is not required, most Ada compilers implement the Suppress pragma.

13. Describe three problems with Ada’s exception handling.
Answer: There are several problems with Ada’s exception handling. One problem is the propagation model, which allows exceptions to be propagated to an outer scope in which the exception is not visible. Also, it is not always possible to determine the origin of propagated exceptions. Another problem is the inadequacy of exception handling for tasks. For example, a task that raises an exception but does not handle it simply dies. Finally, when support for object-oriented programming was added in Ada 95, its exception handling was not extended to deal with the new constructs. For example, when several objects of a class are created and used in a block and one of them propagates an exception, it is impossible to determine which one raised the exception.

14. What is the name of all C++ exception handlers?
Answer: Each catch function is an exception handler. A catch function can have only a single formal parameter, which is similar to a formal parameter in a function definition in C++, including the possibility of it being an ellipsis (. . .). A handler with an ellipsis formal parameter is the catch-all handler; it is enacted for any raised exception if no appropriate handler was found. The formal parameter also can be a naked type specifier, such as float, as in a function prototype. In such a case, the only purpose of the formal parameter is to make the handler uniquely identifiable. When information about the exception is to be passed to the handler, the formal parameter includes a variable name that is used for that purpose. Because the class of the parameter can be any user-defined class, the parameter can include as many data members as are necessary.

15. Which standard libraries define and throw the exception out_of_range in C++?
Answer: The exception out_of_range in C++ thrown by library container classes

16. Which standard libraries define and throw the exception overflow_error in C++?
Answer: the exception overflow_error in C++ thrown by math library functions

19. State the similarity between the exception handling mechanism in C++ and Ada
Answer: In some ways, the C++ exception-handling mechanism is similar to that of Ada. For example, unhandled exceptions in functions are propagated to the function’s caller.

20. State the differences between the exception handling mechanism in C++ and Ada
Answer: There are no predefined hardware-detectable exceptions that can be handled by the user, and exceptions are not named. Exceptions are connected to handlers through a parameter type in which the formal parameter may be omitted. The type of the formal parameter of a handler determines the condition under which it is called but may have nothing whatsoever to do with the nature of the raised exception.

24. What is the difference between checked and unchecked exceptions in Java?
Answer: Exceptions of class Error and RuntimeException and their descendants are called unchecked exceptions. All other exceptions are called checked exceptions. Unchecked exceptions are never a concern of the compiler. However, the compiler ensures that all checked exceptions a method can throw are either listed in its throws clause or handled in the method. Note that checking this at compile time differs from C++, in which it is done at run time. The reason why exceptions of the classes Error and RuntimeException and their descendants are unchecked is that any method could throw them. A program can catch unchecked exceptions, but it is not required.

26. How can an exception handler be written in Java so that it handles any exception?
Answer: The exception handlers of Java have the same form as those of C++, except that every catch must have a parameter and the class of the parameter must be a descendant of the predefined class Throw-able. The syntax of the try construct in Java is exactly as that of C++, except for the finally clause.

28. What is the purpose of Java finally clause?
Answer: A finally clause is placed at the end of the list of handlers just after a complete try construct. The semantics of this construct is as follows: If the try clause throws no exceptions, the finally clause is executed before execution continues after the try construct. If the try clause throws an exception and it is caught by a following handler, the finally clause is executed after the handler completes its execution. If the try clause throws an exception but it is not caught by a handler following the try construct, the finally clause is executed before the exception is propagated

Problem Set

1 . What mechanism did early programming languages provide to detect or attempt to deal with errors?
Answer:
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. The typical operating system reaction to a run-time error is to display a diagnostic message, which may be meaningful and therefore useful, or highly cryptic. After displaying the message, the program is terminated.

2. Describe the approach for the detection of subscript range errors used in C and Java.
Answer:
Java compilers usually generate code to check the correctness of every subscript expression (they do not generate such code when it can be determined at compile time that a subscript expression cannot have an out-of-range value, for example, if the subscript is a literal). In C, subscript ranges are not checked because the cost of such checking was (and still is) not believed to be worth the benefit of detecting such errors. In some compilers for some languages, subscript range checking can be selected (if not turned on by default) or turned off (if it is on by default) as desired in the program or in the command that executes the compiler.

5. From a textbook on FORTRAN, determine how exception handling is done in FORTRAN programs.
Answer:
For example, a Fortran “Read” statement can intercept input errors and end-of-file conditions, both of which are detected by the input device hardware. In both cases, the Read statement can specify the label of some statement in the user program that deals with the condition. In the case of the end-of-file, it is clear that the condition is not always considered an error. In most cases, it is nothing more than a signal that one kind of processing is completed and another kind must begin. In spite of the obvious difference between end-of-file and events that are always errors, such as a failed input process, Fortran handles both situations with the same mechanism.

6. In languages without exception-handling facilities, it is common to have most subprograms include an “error” parameter, which can be set to some value 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?
Answer:
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 a language without exception handling facilities, we could send an error-handling procedure as a parameter to each procedure that can detect errors that must be handled. What disadvantages are there to this method?
Answer:
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.

By pamaan

Concept of Programming Languages chapter 13

Review Questions

1. What are the three possible levels of concurrency in programs?
Concurrency in software execution can occur at four different levels: 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), and program level (executing two or more programs simultaneously).

2. Describe the logical architecture of an SIMD computer.
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. Perhaps the most widely used
SIMD machines are a category of machines called vector processors. They 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. Originally, the kinds of programs that could most benefit from this architecture were in scientific computation, an area of computing that is often the target of multiprocessor machines. However, SIMD processors are now used for a variety of application areas, among them graphics and video processing. Until recently, most supercomputers were vector processors.

3. Describe the logical architecture of an MIMD computer.
Computers that have multiple processors that operate independently but whose operations can be synchronized are called Multiple-Instruction Multiple- Data (MIMD) computers. Each processor in an MIMD computer executes its own instruction stream. MIMD computers can appear in two distinct configurations: distributed and shared memory systems. The distributed MIMD machines, in which each processor has its own memory, can be either built in a single chassis or distributed, perhaps over a large area. The shared-memory MIMD machines obviously must provide some means of synchronization to prevent memory access clashes. Even distributed MIMD machines require synchronization to operate together on single programs. MIMD computers, which are more general than SIMD computers, support unit-level concurrency. The primary focus of this chapter is on language design for shared memory MIMD computers, which are often called multiprocessors.

4. What level of program concurrency is best supported by SIMD computers?
Statement-level concurrency

5. What level of program concurrency is best supported by SIMD computers?
Unit-level concurrency

6. Describe the logical architecture of a vector processor.
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. Originally, the kinds of programs that could most benefit from this architecture were in scientific computation, an area of computing that is often the target of multiprocessor machines.

7. What is the difference between physical and logical concurrency?
There are two distinct categories of concurrent unit control. The most natural category of concurrency is that in which, assuming that more than one processor is available, several program units from the same program literally execute simultaneously. This is physical concurrency. A slight relaxation of this concept of concurrency allows the programmer and the application software to assume that there are multiple processors providing actual concurrency, when in fact the actual execution of programs is taking place in interleaved fashion on a single processor. This is logical concurrency.

8. what is the work of a scheduler?
A run-time system program called a scheduler manages the sharing of processors among the tasks.

34. What does the Java sleep method do?
The sleep method has a single parameter, which is the integer number of milliseconds that the caller of sleep wants the thread to be blocked. After the specified number of milliseconds has passed, the thread will be put in the task-ready queue. Because there is no way to know how long a thread will be in the task-ready queue before it runs, the parameter to sleep is the minimum amount of time the thread will not be in execution. The sleep method can throw an InterruptedException, which must be handled in the method that calls sleep.

35. what does the Java yield method do?
The yield method, which takes no parameters, is a request from the running thread to surrender the processor voluntarily. The thread is put immediately in the task-ready queue, making it ready to run. The scheduler then chooses the highest-priority thread from the task-ready queue. If there are no other ready threads with priority higher than the one that just yielded the processor, it may also be the next thread to get the processor.

36. what does the Java join method do?
The join method is used to force a method to delay its execution until the run method of another thread has completed its execution. join is used when the processing of a method cannot continue until the work of the other thread is complete.

37. What does the Java interrupt method do?
The interrupt method is one way to communicate to a thread that it should stop. This method does not stop the thread; rather, it sends the thread a message that actually just sets a bit in the thread object, which can be checked by the thread. The bit is checked with the predicate method, isInterrupted. This is not a complete solution, because the thread one is attempting to interrupt may be sleeping or waiting at the time the interrupt method is called, which means that it will not be checking to see if it has been interrupted. For these situations, the interrupt method also throws an exception, InterruptedException, which also causes the thread to awaken (from sleeping or waiting). So, a thread can periodically check to see whether it has been interrupted and if so, whether it can terminate. The thread cannot miss the interrupt, because if it was asleep or waiting when the interrupt occurred, it
will be awakened by the interrupt.

42. What kind of Java object is a monitor?
In Java, a monitor can be implemented in a class designed as an abstract data type, with the shared data being the type. Accesses to objects of the class are controlled by adding the synchronizedmodifier to the access methods.

47. How are explicit locks supported in Java?
Java 5.0 introduced explicit locks as an alternative to synchronized method and blocks, which provide implicit locks. The Lock interface declares the lock, unlock, and tryLock methods. The predefined ReentrantLock class implements the Lock interface. To lock a block of code, the following idiom can be used:
Lock lock = new ReentrantLock();
. . .
Lock.lock();
try {
// The code that accesses the shared data
} finally {
Lock.unlock();
}

48. What kinds of methods can run in a C# thread?
Rather than just methods named run, as in Java, any C# method can run in its own thread.

55. What is Concurrent ML?
Concurrent ML (CML) is an extension to ML that includes a form of threads and a form of synchronous message passing to support concurrency. The language is completely described in Reppy (1999).

59. Who developed the monitor concept?
The monitor concept is developed and its implementation in Concurrent Pascal is described by Brinch Hansen (1977)

Problem Set

1 . Explain why a race condition can create problems for  a system.
a race condition creates problem because when a race condition happens 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. What are the different ways to handle deadlock?
When deadlock occurs, assuming that only two program units are causing the deadlock, one of the involved program units should be gracefully terminated, thereby allowed the other to continue.

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?
The main problem with busy waiting is that machine cycles are wasted in the process.

4. In the producer-consumer example of Section 13.3, suppose that we incorrectly replaced the release(access) in the consumer process with wait(access). What woud be the result of this error on execution of the system?
Deadlock would occur if the release(access) were replaced by a wait(access) in the consumer process, because instead of relinquishing access control, the consumer would wait for control that it already had.

By pamaan

Concept of Programming Languages chapter 12

2. What are the problems associated with programming using abstract data types?

-The features and capabilities of the existing type are not really understanding by the beginner
-The type definitions are all independent and at the same level

4. What is message protocol?
Message protocol: The entire collection of methods of an object.

5. What is an overriding method?
Overriding method: A method that overrides the inherited method.

7. What is dynamic dispatch?
Dynamic dispatch: The third characteristic of object-oriented programming language which is a kind of polymorhphism provided by the dynamic binding of messages.

12. From where are Smalltalk objects allocated?
Smalltalk objects are allocated from the heap and are referenced through reference variables, which are implicitly dereferenced.
15. What kind of inheritance, single or multiple, does Smalltalk support?
Smalltalk supports single inheritance; it does not allow multiple inheritance.

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

29. Does Objective-C support multiple inheritance?
No, it doesn’t. Objective-C is not support it. It supports the single inheritance only.

33. What is the purpose of an Objective-C category?
The purpose of an Objective-C category: to add certain functionalities to different classes and also to provide some of the benefits of multiple inheritance, without the naming collisions that could occur if modules did not require module names on their functions.

38. What is boxing?
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.

39. How are Java objects deallocated?
By implicitly calling a finalizemethod when the garbage collector is about to reclaim the storage occupied by the object.

PROBLEM SET

3. Compare the inheritance of C++ and Java!
Java:
– All classes inherit from the Object class directly or indirectly
– If we create a class that doesn’t inherit from any class, then it automatically inherits from Object Class
– Members of the grandparent class are not directly accessible
– Protected members of a class “A” are accessible in other class “B” of same package, even if B doesn’t inherit from A
– Java uses extends keyword for inheritance
– We don’t have to remember those rules of inheritance which are combination of base class access specifier and inheritance specifier
– Methods are virtual by default
– Uses a separate keyword interface for interfaces and abstract keyword for abstract classes and abstract functions

C++:
– Private members of base class are not accessible in derived class
– Have the forest of classes. When we create a class that doesn’t inherit from anything, we create a new tree in forest
– Support the multiple inheritance
– Default constructor of parent class is automatically called, but if we want to call parametrized the constructor of a parent class, we
must use Initalizer list
– Use virtual keyword
5. Compare abstract class and interface in Java!
– 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.

– 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.

– The abstract class are slightly faster than interface because interface involves a search before calling any overridden method in Java

– The interface are better suited for Type declaration and abstract class is more suited for code reuse and evolution perspective

– 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 ship{

 public:
void sink(){
cout << “sink” << endl;
 }
 };
class titanic:public class ship{
 public:
void sink()
 {
 cout << “Sink! Titanic has been fallen!” << endl;
 }
 }

10. Explain one advantage of inheritance!
Provides a framework for the definition of hierarchies of related classes that can reflect the descendant relationship in the problem space.
12. Compare inheritance and nested classes in C++! Which of these supports an is-a relationship?
Inheritance is where one class (child class) inherits the members of another class (parent class).

Nested class is a class declared entirely within the body of another class or interface.

17. What are the different options for object destruction in Java?
There is no explicit deallocation operator.

By pamaan

Concept of Programming Languages chapter 11

2. Define abstract data type.
data type that satisfies the following conditions:
-The representation of objects of the type is hidden from the program units that use the type, so the only direct operations possible on those objects are those provided in the type’s definition.
-The declarations of the type and the protocols of the operations on objects of the type, which provide the type’s interface, are contained in a single syntactic unit. The type’s interface does not depend on the representation of the objects or the implementation of the operations. Also, other program units are allowed to create variables of the defined type.

8. What is the difference between private and limited private types in Ada?
Limited private is more restricted form and objects of a type that is declared limited private have no built-in operations.

10. What is the use of the Ada with clause?
With clause makes the names defined in external packages visible; in this case Ada. Text_IO, which provides functions for input of text.

11. What is the use of the Ada use clause?
The with clause makes the names defined in external packages Visible.

12. What is the fundamental difference between a C++ class and an Ada package?
Ada packages are more generalize encapsulations that can define any number of types.

15. What is the purpose of a C++ destructor?
The purpose of a C++ desctructor is as a debugging aid, in which case they simply display or print the values of some or all of the object’s data members before those members are deallocated.

16. What are the legal return types of a desctructor?
Destructor has no return types and doesn’t use return statements.

20. What is the use of limited private types?
An alternative to private types is a more restricted form: limited private types. Nonpointer limited private types are described in the private section of a package specification, as are nonpointer private types. The only syntactic difference is that limited private types are declared to be limited private in the visible part of the package specification. The semantic difference is that objects of a type that is declared limited private have no built-in operations. Such a type is useful when the usual predefined operations of assignment and comparison are not meaningful or useful. For example, assignment and comparison are rarely used for stacks.

21. What are initializers in Objective-C?
The initializers in Objective-C are constructors.

22. What is the use of @private and @public directives?
The use is to specify the access levels of the instance variables in a class definition.

27. Where are all Java methods defined?
All Java methods are defined in a class.

30. What is a friend function? What is a friend class?
a “friend” of a given class is allowed access to public, private, or protected data in that class. Normally, function that is defined outside of a class cannot access such information.
Class that can access the private and protected members of the class in which it is declared as a friend. On declaration of friend class all member function of the friend class become friends of the class in which the friend class was declared.

Problem set

4. What are the advantages of the nonpointer concept in Java?
Any task that would require arrays, structures, and pointers in C can be more easily and reliably performed by declaring objects and arrays of objects. Instead of complex pointer manipulation on array pointers, you access arrays by their arithmetic indices. The Java run-time system checks all array indexing to ensure indices are within the bounds of the array. You no longer have dangling pointers and trashing of memory because of incorrect pointers, because there are no pointers in Java.

10. Which two conditions make data type “abstract”?
The representation of objects of the type is hidden from the program units that use the type, so the only direct operations possible on those objects are those provided in the type’s definition.
The declarations of the type and the protocols of the operations on objects of the type, which provide the type’s interface, are contained in a single syntactic unit. The type’s interface does not depend on the representation of the objects or the implementation of the operations. Also, other program units are allowed to create variables of the defined type.

12. How are classes in Ruby made dynamic?
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. Moreover, even predefined classes of the language, such as String, can be extended.

13. Compare and contrast the data abstraction of Java and C++.
Java support for abstract data types is similar to that of C++. There are, however, a few important differences. All objects are allocated from the heap and accessed through reference variables. Methods in Java must be defined completely in a class. A method body must appear with its corresponding method
header. Therefore, a Java abstract data type is both declared and defined in a single syntactic unit. A Java compiler can inline any method that is not overridden. Definitions are hidden from clients by declaring them to be private. Rather than having private and public clauses in its class definitions, in Java access modifiers can be attached to method and variable definitions. If an instance variable or method does not have an access modifier, it has package access.

19. Compare Java’s packages with Ruby’s modules.
In Ruby, the require statement is used to import a package or a module. For example, the extensions package/module is imported as follows.
require ‘extensions’
External files may be included in a Ruby application by using load or require. For example, to include the external file catalog.rb, add the following require statement.
require “catalog.rb”
The difference between load and require is that load includes the specified Ruby file every time the method is executed and require includes the Ruby file only once.
In Java, the import statement is used to load a package. For example, a Java package java.sql is loaded as follows.

By pamaan

Concept of Proggramming Languages chapter 10

1. By “simple” it means that subprograms cannot be nested and all local variables are static

2. Which of the caller of callee saves execution status information ?

-Either can save the execution status

3. Execution status information be stored for the linkage to a subprogram

4. What is the task of a linker?
Its first task is to find the files that contain the translated subprograms referenced in that program and load them into memory. Then, the linker must set the target addresses of all calls to those subprograms in the main program to the entry addresses of those subprograms.

6. What is the difference between an activation record and an activation record instance?
An activation record is the format, or layout, of the moncode part of a subprogram, whereas an activation record instance is a concrete example of an activation record, a collection of data in the form of an activation record.

8. What kind of machines often use registers to pass parameters?
RISC machines, parameters are passed in registers

11. What is an EP, and what is its purpose?
EP is a point or first address of the activation record instance of the main program. It is required to control the execution of a subprogram.

14. What are two potentialproblems with the static-chain method?
•  It is difficult for a programmer working on a time-critical program to estimate the costs of nonlocal references, because the cost of each reference depends on the depth of nesting between the reference and the scope of declaration.
•  Subsequent code modifications may change nesting depths, thereby changing the timing of some references, both in the changed code and possibly in code far from the changes.

PROBLEM SET

6. Although local variables in Java methods are dynamically allocated at the beginning of each activation, under what circumstances could the value of a local variable in a particular activation retain the value of previous activation?
If the variable is declared as static. Static modifier is a modifier that makes a variable history – sensitive.

7. It is stated in this chapter that when nonlocal variables are accessed in a dynamic-scoped language using the dynamic chain, variable names must be stored in the activation records with the values. If this were actually done, every nonlocal access would require a sequence of costly string comparisons on names. Design an alternative to these string comparisons that would be faster.

Using approach that uses an auxiliary data structure called a display. Or, to write variable names as integers. These integers act like an array. So when the activation happens, the comparisons will be faster.

8.   Pascal allows gotos with nonlocal targets. How could such statements be handled if static chains were used for nonlocal variable access? Hint:Consider the way the correct activation record instance of the static parent of a newly enacted procedure is found(see Section 10.4.2).

Based on the hint statement, the target of every goto in a program could be represented as an address and a nesting_depth, where the nesting_depth is the difference between the nesting level of the procedure that contains the goto and that of the procedure containing the target. Then, when a goto is executed, the static chain is followed by the number of links indicated in the nesting_depth of the goto target. The stack top pointer is reset to the top of the activation record at the end of the chain.

9.   The static-chain method could be expanded slightly by using two static links in each activation  record instance where the  second points to the static grandparent activation record instance. How would this approach affect the time required for subprogram linkage and nonlocal references?

Including two static links would reduce the access time to nonlocals that are defined in scopes two steps away to be equal to that for nonlocals that are one step away. Overall, because most nonlocal references are relatively close, this could significantly increase the execution efficiency of many programs.

11.    If a compiler uses the static chain approach to implementing blocks, which of the entries in the activation records for subprograms are needed in the activation records for blocks?

There are two options for implementing blocks as parameterless subprograms: One way is to use the same activation record as a subprogram that has no parameters. This is the most simple way, because accesses to block variables will be exactly like accesses to local variables. Of course, the space for the static and dynamic links and the return address will be wasted. The alternative is to leave out the static and dynamic links and the return address, which saves space but makes accesses to block variables different from subprogram locals.

By pamaan

Concept of Programming Languages chapter 9

1. What are the three general characteristics of subprograms?
• Each subprogram has a single entry point.
• The calling program unit is suspended during the execution of the called
subprogram, which implies that there is only one subprogram in execution
at any given time.
• Control always returns to the caller when the subprogram execution
terminates.

2. What does it mean for a subprogram to be active?
A subprogram is said to be active if, after having been called, it has begun execution but has not yet completed that execution.

3. What is given in a header of a subprogram?
A subprogram header, which is the first part of the definition, serves several purposes. First, it specifies that the following syntactic unit is a subprogram definition of some particular kind.1 In languages that have more than one kind of subprogram, the kind of the subprogram is usually specified with a special word. Second, if the subprogram is not anonymous, the header provides a name for the subprogram. Third, it may optionally specify a list of parameters.

4. What characteristic of Python subprograms sets them apart from those of other languages?
One characteristic of Python functions that sets them apart from the functions of other common programming languages is that function def statements are executable. When a def statement is executed, it assigns the given name to the given function body. Until a function’s def has been executed, the function cannot be called. Consider the following skeletal example:
if . . .
def fun(. . .):
. . .
else
def fun(. . .):
. . .

5. What languages allow a variable number of parameters?
C# allows methods to accept a variable number of parameters, as long as they are of the same type.

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.

23. What is Automatic Generalization?
The type inferencing system of F# is not always able to determine the type of parameters or the return type of a function. When this is the case, for some functions, F# infers a generic type for the parameters and the return value. This is called automatic generalization.

24. What is an overloaded subprogram?
An overloaded subprogram is a subprogram that has the same name as another subprogram in the same referencing environment.

25. What is ad hoc binding?
Ad hoc binding is when the environment of the call statement that passed the subprogram as an actual parameter.

26. What is multicast delegate?
All of the methods stored in a delegate instance are called in the order in which they were placed in the instance. This is called a multicast delegate.

30. What are the design issues for functions?
The following design issues are specific to functions:
• Are side effects allowed?
• What types of values can be returned?
• How many values can be returned?

31. What two languages allow multiple values to be returned from a function?
Ruby allows the return of more than one value from a method. Lua also allows functions to return multiple values.

Problem Set
3. Argue in support of the template functions of C++. How is it different from the template functions in other languages?
C++ templated classes are instantiated to become typed classes at compile time. For example, an instance of the templated Stack class, as well as an instance of the typed class, can be created with the following declaration:
Stack<int> myIntStack;
However, if an instance of the templated Stack class has already been created for the int type, the typed class need not be created.

6 . Compare and contrast PHP’s parameter passing with that of C#.
PHP’s parameter passing is similar to that of C#, except that either the actual parameter or the formal parameter can specify pass-by-reference. Passby- reference is specified by preceding one or both of the parameters with an ampersand.

8 . Argue against the Java design of not providing operator overloading
Arithmetic operators are often used for more than one purpose. For example, + usually is used to specify integer addition and floating-point addition. Some languages—Java, for example—also use it for string catenation. This multiple use of an operator is called operator overloading and is generally thought to be acceptable, as long as neither readability nor reliability suffers.

12 . Research Jensen’s Device, which was a widely known use of pass-by-name parameters, and write a short description of what it is and how it can be used.
Implementing a pass-by-name parameter requires a subprogram to be passed to the called subprogram to evaluate the address or value of the formal parameter. The referencing environment of the passed subprogram must also be passed. This subprogram/referencing environment is a closure. Pass-by-name parameters are both complex to implement and inefficient. They also add significant complexity to the program, thereby lowering its readability and reliability. Because pass-by-name is not part of any widely used language, it is not discussed further here. However, it is used at compile time by the macros in assembly languages and for the generic parameters of the generic subprograms in C++, Java 5.0, and C# 2005.

15. How is the problem of passing multidimensional arrays handles by Ada?
Ada compilers are able to determine the defined size of the dimensions of all arrays that are used as parameters at the time subprograms are compiled. In Ada, unconstrained array types can be formal parameters. An unconstrained array type is one in which the index ranges are not given in the array type definition. Definitions of variables of unconstrained array types must include index ranges. The code in a subprogram that is passed an unconstrained array can obtain the index range information of the actual parameter associated with such parameters

By pamaan

Concept of Programming Languages chapter 8

Review Question

1. What is definition of control structure?
Control Structure : Control statement and the collection of statements whose execution it controls.

2. What did Bohm and Jocopini prove about flowchart?The algorithms that can be expressed by flowcharts can be coded in a programming language with only two control statements: one for choosing between two control flow paths and one for logically controlled iterations.

3. What is the definition of block?
Block : An anonymous method that is sent to the method (whose call precedes it) as a parameter

4. What is/are the design issue(s) for all selection and iteration control statements?
There is only one design issue that is relevant to all of the selection and iteration control statements: Should the control structure have multiple entries?

9. What are the design issues for multiple-selection statement?
The following is a summary of these design issues:
-What is the form and type of the expression that controls the selection?
– How are the selectable segments specified?
– Is execution flow through the structure restricted to include just a single selectable segment?
– How are the case values specified?
– How should unrepresented selector expression values be handled, if at all?

12. On what previous language was C’s switch statement based?
C’s switch statement is based from the ALGOL 68.

14.  What are the design issues for all iterative control statement
– How is the iteration controlled?
– Where should the control mechanism appear in the loop statement?

21.  What are the design issues for logically controlled loop statements?
The design issues are whether the control should be pretest/posttest and whether the logically controlled loop should be a special form of a counting loop or a separate statement.
23. What are the design issues for user-located loop control mechanisms?
The design issues for such a mechanism are the following:
– Should the conditional mechanism be an integral part of the exit?
– Should only one loop body be exited, or can enclosing loops also be exited?

29. How are iterator implemented in Ruby?
Ruby predefines several iterator methods, such as times and upto for counter-controlled loops and each for simple iterations of arrays and also the hashes too.

PROBLEM SET

1. What design issues should be considered for two-way selection statements?
The design issues for two-way selectors can be summarized as follows:
• What is the form and type of the expression that controls the selection?
• How are the then and else clauses specified?
• How should the meaning of nested selectors be specified?

2. Python uses indentation to specify compound statements. Give an example in support of this statement!
Python uses indentation to specify compound statements. For example,
if a > b :
a = b
print “case 7″

3. How can a straightforward grammar for a two-way selector statement lead to the problem of syntactic ambiguity? Give an example!
That ambiguous grammar was as follows:
<if_stmt> →if <logic_expr> then <stmt>
| if <logic_expr> then <stmt> else <stmt>
The issue was when a selection statement is nested in the then clause of a selection statement, it is not clear to which, if an else clause should be associated.

14. State one of the main legitimate needs for gotos!
Premature exits from loops.

By pamaan