Chapter 15-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

1. Define functional form, simple list, bound variable, and referential transparency.

A higher-order function, or functional form, is one that either takes one or more functions as parameters or yields a function as its result, or both. A simple list is the problem of membership of a given atom in a given list that does not include sublists. A bound variable is a variable that never changes in the expression after being bound to an actual parameter value at the time evaluation of the lambda expression begins. A referential transparency is the execution of a function always produces the same result when given the same parameters

 

2. What does a lambda expression specify?

In Scheme, a nameless function actually includes the word LAMBDA, and is called a lambda expression. For example, (LAMBDA (x) (* x x)) is a nameless function that returns the square of its given numeric parameter. This function can be applied in the same way that named functions are: by placing it in the beginning of a list that contains the actual parameters.

 

7. What does the abbreviation REPL stand for?

REPL stand for read-evaluate-print loop

 

8. What are the three parameters to IF?

The Scheme two-way selector function, named IF, has three parameters: a predicate expression, a then expression, and an else expression. A call to IF has the form (IF predicate then_expression else_expression)

 

11. What are the two forms of DEFINE?

DEFINE takes two lists as parameters. The first parameter is the prototype of a function call, with the function name followed by the formal parameters, together in a list. The second list contains an expression to which the name is to be bound.

 

12. Describe the syntax and semantics of COND.

The syntax of COND is

(COND

(predicate1 expression1)

(predicate2 expression2)

. . .

(predicaten expressionn)

[(ELSE expressionn+1)]

)

The semantics of COND is as follows: The predicates of the parameters are evaluated one at a time, in order from the first, until one evaluates to #T. The expression that follows the first predicate that is found to be #T is then evaluated and its value is returned as the value of COND. If none of the predicates is true and there is an ELSE, its expression is evaluated and the value is returned. If none of the predicates is true and there is no ELSE, the value of COND is unspecified. Therefore, all CONDs should include an ELSE.

 

27. What is the use of the fn reserved word in ML?

The predicate function is often given as a lambda expression, which in ML is defined exactly like a function, except with the fn reserved word, instead of fun, and of course the lambda expression is nameless.

 

29. What is a curried function?

Curried functions are interesting and useful because new functions can be constructed from them by partial evaluation.

 

30. What does partial evaluation mean?

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

 

31. Define reader macros.

Reader macros or read macros, that are expanded during the reader phase of a LISP language processor. 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. Users can define their own reader macros to create other shorthand constructs.

 

32.What is the use of evaluation environment table?

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. When an identifier is declared, either implicitly or explicitly, it is placed in the evaluation environment.

 

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.

 

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

The syntax in F# is (fun a b −> a / b)

 

 

Problem set

6. Refer to a book on Haskell programming and discuss the features of Haskell

Haskell features lazy evaluation, pattern matching, list comprehension, type classes, and type polymorphism.

Lazy evaluation or call-by-need is an evaluation strategy which delays the evaluation of an expression until its value is needed (non-strict evaluation) and which also avoids repeated evaluations (sharing). The sharing can reduce the running time of certain functions by an exponential factor over other non-strict evaluation strategies, such as call-by-name.

Pattern matching is the act of checking a perceived sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually has to be exact. The patterns generally have the form of either sequences or tree structures. Uses of pattern matching include outputting the locations (if any) of a pattern within a token sequence, to output some component of the matched pattern, and to substitute the matching pattern with some other token sequence.

List comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions.

Type class is a type system construct that supports ad-hoc polymorphism. This is achieved by adding constraints to type variables in parametrically polymorphic types. Such a constraint typically involves a type class T and a type variable a, and means that a can only be instantiated to a type whose members support the overloaded operations associated with T.

Polymorphism is a programming language feature that allows values of different data types to be handled using a uniform interface.

 

7. What features make F# unique when compared to other languages?

F# has a full-featured IDE, an extensive library of utilities that supports imperative, object-oriented, and functional programming, and has interoperability with a collection of nonfunctional languages. F# includes a variety of data types. Among these are tuples, like those of Python and the functional languages ML and Haskell, lists, discriminated unions, an expansion of ML’s unions, and records, like those of ML, which are like tuples except the components are named. F# has both mutable and immutable arrays.

 

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)

|> List.map (fun n −> 5 * n)

 

Chapter 14-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

1. Define exception, exception handler, raising an exception, disabling an exception, continuation, finalization, and built-in exception.

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.

 

7. Where are unhandled exceptions propagated in Ada if raised in a subprogram?

A block? A package body? A task?

When an exception is raised in a block, in either its declarations or executable statements, and the block has no handler for it, the exception is propagated to the next larger enclosing static scope, which is the code that “called” it. The point to which the exception is propagated is just after the end of the block in which it occurred, which is its “return” point. When an exception is raised in a package body and the package body has no handler for the exception, the exception is propagated to the declaration section of the unit containing the package declaration. If the package happens to be a library unit (which is separately compiled), the program is terminated.

If an exception occurs at the outermost level in a task body (not in a nested block) and the task contains a handler for the exception, that handler is executed and the task is marked as being completed. If the task does not have a handler for the exception, the task is simply marked as being completed; the exception is not propagated. The control mechanism of a task is too complex to lend itself to a reasonable and simple answer to the question of where its unhandled exceptions should be propagated.

 

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

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?

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.

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?

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++?

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++?

the exception overflow_error in C++ thrown by math library functions

 

19. State the similarity between the exception handling mechanism in C++ and Ada

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

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?

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?

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 Throwable. 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?

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?

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.

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.

For example, a Fortran “Read” statement can intercept inputerrors 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?

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?

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.

Chapter 13-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

1. What are the 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. 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

 

7. What is the difference between physical and logical concurrency?

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.

 

16. What is a task descriptor?

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

21. What is a binary semaphore? What is a counting semaphore?

Binary semaphore is a semaphore that requires only a binary-valued counter, like the one used to provide competition synchronization. A counting semaphore is a synchronization object that can have an arbitrarily large number of states.

 

30. What is purpose of an Ada terminate clause?

The purpose of an Ada terminate clause is to mark that the task is finished with its job but is not yet terminated.

 

34. What does the Java sleep method do?

Sleep method blocks the the thread.

 

35. What does the Java yield method do?

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

 

36. What does the Java join method do?

Java forces a method to delay its execution until the run method of another thread has completed its execution.

 

37. What does the Java interrupt method do?

Interrupt becomes one way to communicate to a thread that it should stop.

 

55. What is Concurrent ML?

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

 

56. What is the use of the spawn primitive of CML?

The use of Spawn primitive of CML is to create a thread.

 

57. What is the use of subprograms BeginInvoke and EndInvoke in F#?

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

 

58. What is the use of the DISTRIBUTE and ALIGN specification of HPC?

The use of DISTRIBUTE and ALIGN specification of HPC is to provide information to the compiler on machines that do not share memory, that is, each processor has its own memory.

 

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 clearly why a 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). The importance of competition synchronization should now be clear.

 

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?

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.

Chapter 12-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

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

-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.

 

5. What is an overriding method?

Overriding method is method that overrides the inherited method.

 

6. Describe a situation where dynamic binding is a great advantage over its absence.

Consider the following situation: 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 because the subclass objects are slightly different. So, the subclass overrides the inherited draw method. If a client of A and B has a variable that is a reference to class A’s objects, that reference also could point at class B’s objects, making it a polymorphic reference. If the method draw, which is defined in both classes, is called through the polymorphic reference, the run-time system must determine, during execution, which method should be called, A’s or B’s.

 

7. What is dynamic dispatch?

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.

 

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.

 

25. What is mixins in objective-C?

Mixins are sometimes used to add certain functionalities to different classes. And, of course, the class still has a normal superclass from which it inherits members. So, mixins 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.

 

33. What is the purpose of an Objective-C category?

The purpose of an Objective-C category is 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.

– In Java, all classes inherit from the Object class directly or indirectly. Therefore, there is always a single inheritance tree of classes in Java, and Object class is root of the tree. In Java, if we create a class that doesn’t inherit from any class then it automatically inherits from Object Class. In C++, there is forest of classes; when we create a class that doesn’t inherit from anything, we create a new tree in forest.

– In Java, members of the grandparent class are not directly accessible.

– 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.

– In Java, methods are virtual by default. In C++, we explicitly use virtual keyword.

– Java uses a separate keyword interface for interfaces, and abstract keyword for abstract classes and abstract functions.

– Unlike C++, Java doesn’t support multiple inheritance. A class cannot inherit from more than one class. A class can implement multiple interfaces though.

– In C++, default constructor of parent class is automatically called, but if we want to call parametrized constructor of a parent class, we must use Initalizer list. Like C++, default constructor of the parent class is automatically called in Java, but if we want to call parametrized constructor then we must use super to call the parent constructor

 

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 becauseJava 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.

 

10. Explain one advantage of inheritance.

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 and is also allowed to modify some of those entities and add new entities, reuse is greatly facilitated without requiring change to the reused abstract data type. Programmers can begin with an existing abstract data type and design a modified descendant of it to fit a new problem requirement. Furthermore, inheritance provides a framework for the definition of hierarchies of related classes that can reflect the descendant relationship in the problem space.

 

13. Descripbe the mechanism of dynamic dispatch with an example in Java. Is it possible to dynamically dispatch the data members?

In C++, a method must be defined as virtual to allow dynamic binding. In Java, all method calls are dynamically bound unless the called method has been defined as final, in which case it cannot be overridden and all bindings are static. Static binding is also used if the method is static or private, both of which disallow overriding.

 

16. State why java is said to be more pure object-oriented than C++.

Java’s design for supporting object-oriented programming is similar to that of C++, but it employs more consistent adherence to object-oriented principles. Java does not allow parentless classes and uses dynamic binding as the “normal” way to bind method calls to method definitions. This, of course, increases execution time slightly over languages in which many method bindings are static. At the time this design decision was made, however, most Java programs were interpreted, so interpretation time made the extra binding time insignificant. Access control for the contents of a class definition are rather simple when compared with the jungle of access controls of C++, ranging from derivation controls to friend functions. Finally, Java uses interfaces to provide a form of support for multiple inheritance, which does not have all of the drawbacks of actual multiple inheritance.

 

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.

Chapter 11-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

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.

import java.sql.*;

Chapter 10-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

Review question

4. What is the task of a linker?

Task of a linker 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.

 

5. What are the two reasons why implementing subprograms with stack-dynamic local variables is more difficult than implementing simple subprograms?

-The compiler must generate code to cause the implicit allocation and deallocation of local variables.

Recursion adds the possibility of multiple simultaneous activations of a subprogram, which means that there can be more than one instance (incomplete execution) of a subprogram at a given time, with at least one call from outside the subprogram and one or more recursive calls. The number of activations is limited only by the memory size of the machine. Each activation requires its activation record instance.

 

15. Explain the two methods of implementing blocks.

– Blocks can be implemented by using the static-chain process for implementing nested subprograms. Blocks are treated as parameterless subprograms that are always called from the same place in the program. Therefore, every block has an activation record. An instance of its activation record is created every time the block is executed.

– Blocks can also be implemented in a different and somewhat simpler and more efficient way. The maximum amount of storage required for block variables at any time during the execution of a program can be statically determined, because blocks are entered and exited in strictly textual order. This amount of space can be allocated after the local variables in the activation record. Offsets for all block variables can be statically computed, so block variables can addressed exactly as if they were local variables.

 

16. Describe the deep-access method of implementing dynamic scoping.

The dynamic chain links together all subprogram activation recor5s instances in the reverse of the order in which they were activated. Therefore, the dynamic chain is exactly what is needed to reference nonlocal variables in a dynamic-scoped language.

 

17. Describe the shallow-access method of implementing dynamic scoping.

Shallow access is an alternative implementation method, not an alternative semantics. The semantics of deep access and shallow access are identical. In the shallow-access method, variables declared in subprograms are not stored in the activation records of those subprograms.

 


Problem set

 8. Pascal allows gotos with nonlocal targets. How could such statements be handled if static chains were used for nonlocal variable access?

Finding the correct activation record instance of a nonlocal variable using static links is relatively straightforward. When a reference is made to nonlocal variable, the activation record instance containing the variable can be found by searching the static chain until a static ancestor activation record instance is found that contains the variable.

 

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?

The nesting of scopes is known at compile time, the compiler can determine not only that a reference is nonlocal but also the length of the static chain that must be followed to reach the activation records instance that contains the nonlocal object.

 

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?

A static chain is a chain of static links that connect certain activation record instances in the stack. During the execution of a subprogram P, the static link of its activation record instance points to an activation record instance of P’s static parent program unit. That instance’s static link points in turn to P’s static grandparent program unit’s activation record instance, if there is one. So, the static chain connects all the static ancestors of an executing subprogram, in order of static parent first. This chain can obviously be used to implement the accesses to nonlocal variables in static-scoped languages.

Chapter 9-Concepts of Programming Languages(Robert W. Sebesta)-Mr. Tri Djoko Wahjono, Ir, M.Sc.

 

Review Question

1. What are the three general characteristic of subprograms?

The three general characteristic of subprograms are:

– 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.

 

8. What are formal parameters? What are actual parameters?

The parameters in the subprogram header are called formal parameters. Subprogram call statements must include the name of the subprogram and a list of parameters to be bound to the formal parameters of the subprogram. These parameters are called actual parameters.

 

9. What are the advantages and disadvantages of the keyword parameter?

The advantage of keyword parameters is that they can appear in any order in the actual parameter list. The disadvantage to keyword parameters is that the user of the subprogram must know the names of formal parameters.

 

11. What are the design issues for subprograms?

The design issues for subprograms are:

– Are local variables statically or dynamically allocated?

– Can subprogram definitions appear in other subprogram definitions?

– What parameter-passing method or methods are used?

– Are the types of the actual parameters checked against the types of the

formal parameters?

– If subprograms can be passed as parameters and subprograms can be nested,

what is the referencing environment of a passed subprogram?

– Can subprograms be overloaded?

– Can subprograms be generic?

– If the language allows nested subprograms, are closures supported?

 

12. What are the advantages and disadvantages of dynamic local variable?

There are several advantages of stack-dynamic local variables, the primary one being the flexibility they provide to the subprogram. It is essential that recursive subprograms have stack-dynamic local variables. Another advantage of stack-dynamic locals is that the storage for local variables in an active subprogram can be shared with the local variables in all inactive subprograms.

The main disadvantages of stack-dynamic local variables are the following:

First, there is the cost of the time required to allocate, initialize (when necessary), and deallocate such variables for each call to the subprogram. Second, accesses to stack-dynamic local variables must be indirect, whereas accesses to static variables can be direct. This indirectness is required because the place in the stack where a particular local variable will reside can be determined only during execution. Finally, when all local variables are stack dynamic, subprograms cannot be history sensitive; that is, they cannot retain data values of local variables between calls.

 

13. What are the advantages and disadvantages of static local variable?

The primary advantage of static local variables over stack-dynamic local variables is that they are slightly more efficient—they require no run-time overhead for allocation and deallocation. Also, if accessed directly, these accesses are obviously more efficient. And, of course, they allow subprograms to be history sensitive. The greatest disadvantage of static local variables is their inability to support recursion. Also, their storage cannot be shared with the local variables of other inactive subprograms.

 

14. What languages allow subprogram definitions to be nested?

For a long time, the only languages that allowed nested subprograms were those directly descending from Algol 60, which were Algol 68, Pascal, and Ada. JavaScript, Python, Ruby, and Lua are also, most functional programming languages allow subprograms to be nested.

 

15. What are three semantic models of parameter passing?

Formal parameters are characterized by one of three distinct semantics models:

(1) They can receive data from the corresponding actual parameter; (2) they can transmit data to the actual parameter; or (3) they can do both. These models are called in mode, out mode, and inout mode, respectively.

 

20. What is the parameter-passing method of Python and Ruby called?

The parameter-passing method of Python and Ruby is called pass-by assignment.

Because all data values are objects, every variable is a reference to an object. In pass-by-assignment, the actual parameter value is assigned to the 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 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. Every version of an overloaded subprogram must have a unique protocol; that is, it must be different from the others in the number, order, or types of its parameters, and possibly in its return type if it is a function. The meaning of a call to an overloaded subprogram is determined by the actual parameter list (and/or possibly the type of the returned value, in the case of a function).

 

25. What is ad hoc binding?

Ad hoc binding is the environment of the call statement that passed the subprogram as an actual parameter.

 

26. What is a multicast delegate?

All of the methods stored in a delegate instance are called in the order in which they were placed in the instance called a multicast delegate.

 

27. What is the use of ad hoc polymorphism?

Ad hoc polymorphism  is an overloaded subprograms provide a particular kind of polymorphism.

 

30. What are the design issues for functions?

The design issues for functions are:

– Are side effects allowed?

– What types of values can be returned?

– How many values can be returned?

 

34. What is a closure?

Closure is a subprogram and the referencing environment where it was defined.

 

36. What languages allow the user to overload operators?

Ada, C++, C#, Ruby, and Python allow operator overloading.

 


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