Concept of Programming Languages – Chapter 16 (Logic Programming Languages)

CHAPTER 16

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

 

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

A compound term is composed of two parts: a functor, which is the function symbol that names the relation, and an ordered list of parameters, which

together represent an element of the relation. A compound term with a single

parameter is a 1-tuple; one with two parameters is a 2-tuple, and so forth.

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.1

8. What is the basic 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 Prolog term?

Constant, variable or structure.

13. What is a conjunction?

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

PROBLEM SET:

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

True.

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

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

6. Explain in which the arithmetic processing capabilities of LISP and Prolog are similar.

Arithmetic processing is simple to implement in LISP and Prolog.

7. In what way are the arithmetic processing capabilities of LISP and Prolog different?

LISP uses prefix operator in arithmetic processing, unlike Prolog.

Advertisements

Concept of Programming Languages – Chapter 15 (Functional Programming Languages)

CHAPTER 15

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

2. What does a lambda expression specify?
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.

5. Explain why QUOTE is needed for a parameter that is a data list.
To avoid evaluating a parameter, it is first given as a parameter to the primitive function QUOTE, which simply returns it without change.

6. What is a simple list?
A list which membership of a given atom in a given list that does not include sublists.

7. What does the abbreviation REPL stand for?
REPL stand for read-evaluate-print loop.

11. What are the two forms of DEFINE?
The simplest form of DEFINE is one used to bind a name to the value of an expression. This form is
(DEFINE symbol expression)
The general form of such a DEFINE is
(DEFINE (function_name parameters)
(expression)
)

13. Why are CAR and CDR so named?
The names of the CAR and CDR functions are peculiar at best. The origin of these names lies in the first implementation of LISP, which was on an IBM 704 computer. The 704’s memory words had two fields, named decrement and address, that were used in various operand addressing strategies. Each of
these fields could store a machine memory address. The 704 also included two machine instructions, also named CAR (contents of the address part of a register) and CDR (contents of the decrement part of a register), that extracted the associated fields. It was natural to use the two fields to store the two pointers
of a list node so that a memory word could neatly store a node. Using these conventions, the CAR and CDR instructions of the 704 provided efficient list selectors. The names carried over into the primitives of all dialects of LISP.

18. What is tail recursion? Why is it important to define functions that use recursion to specify repetition to be tail recursive?
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).

19. Why were imperative features added to most dialects of LISP?
LISP began as a pure functional language but soon acquired some important imperative features to increased its execution efficiency.

26. What is type inferencing, as used in ML?
Type inference refers to the automatic deduction of the type of an expression in a programming language. If some, but not all, type annotations are already present it is referred to as type reconstruction.

29. What is a curried function?
Curried functions a function which a 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.

32. What is the use of the 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.

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.

PROBLEM SET:

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.

9. What does  the following Scheme function do?

(define ( y s lis)
(cond
(( null? lis) ' () )
((equal? s (car lis)) lis)
(else (y s (cdr lis)))
))

y returns the given list with leading elements removed up to but not including the first occurrence of the first given parameter.
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

Concept of Programming Languages – Chapter 14 (Exception Handling and Event Handling)

CHAPTER 14

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

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

9. What is the scope of exception handlers in Ada?
Exception handlers can be included in blocks or in the bodies of subprograms, packages, or tasks.

10. What are the four exceptions defined in the Standard package of Ada?
There are four exceptions that are defined in the default package, Standard:

Constraint_aError 
Program_Error
Storage_Error
Tasking_Error

11. are they any predefined exceptions in Ada?
Yes, they are.

12. What is the use of Suppress pragma in Ada?
The suppress pragma is used to disable certain run-time checks that
are parts of the built-in exceptions in Ada.

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

30. In which version were assertions added to Java?
Assertions were added to Java in version 1.4.

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

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

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

34. What are the different forms of assert statement?
There are two possible forms of the assert statement:
assert condition;
assert condition : expression;

PROBLEM SET:

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

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

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

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

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

There are several advantages of a linguistic mechanism for handling exceptions, such as that found in Ada, over simply using a flag error parameter in all subprograms. One advantage is that the code to test the flag after every call is eliminated. Such testing makes programs longer and harder to read. Another advantage is that exceptions can be propagated farther than one level of control in a uniform and implicit way. Finally, there is the advantage that all programs use a uniform method for dealing with unusual circumstances, leading to enhanced readability.
7.In languages without exception-handling facilities, we could send an error-handling procedure as parameter to each procedure that can detect errors than must be handled. What disadvantage are there to this method?

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

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

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

Concept of Programming Languages – Chapter 13 (Concurrency)

CHAPTER 13

Lecturer: 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)

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.

8. What is the work of a scheduler?

Scheduler manages the sharing of processors among the tasks.

12. What is a heavyweight task? What is a lightweight task?

Heavyweight task executes in its own address space. Lightweight task all run in the same address space.

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.

18. What is the purpose of a task-ready queue?

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

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.

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?

– Ignoring deadlock

– Detection

– Prevention

– Avoidance

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

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

Concept of Programming Languages – Chapter 12 (Support for Object-Oriented Programming)

CHAPTER 12

Lecturer: 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.

4. What is message protocol?

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

5. What is an overriding method?

Overriding method is method that overrides the inherited method.

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.

29. Does Objective-C support multiple inheritance?

No Objective-C doesn’t support it. (It supports only single inheritance).

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.

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

class plan{
 public:
void fly(){
cout << “fly” << endl;
 }
 };
class jet:public class plan{
 public:
void fly()
 {
 cout << “Fly! Rocket jet activated!” << endl;
 }
 }

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.

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.

Inheritance does.

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.

Concept of Programming Languages – Chapter 11 (Abstract Data Types and Encapsulation Constructs)

CHAPTER 11

Lecturer: 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?

Use clause eliminates the need for explicit qualification of the references to entities from the named package.

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.

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.

43. What is a C++ namespace, what is its purpose?

In general, a namespace is a container for a set of identifiers and allows the disambiguation of homonym identifiers residing in different namespaces. The purpose is to help programs manage the problem of global namespace.

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.

9. What happens if the constructor is absent in Java and C++?

It will be made automatically by the built-up in.

10. Which two conditions make data type “abstract” ?

– The representation, or definition, of the type and the operations are contained in a single syntactic unit

– The representation of objects of the type is hidden from the program units that use the type, so only direct operations possible on those objects are those provided in the type’s definition

17. The namespace of the C# standard library, System, is not implicitly available to C# programs. Do you think this is a good idea? Defend your answer.

I think it is not, because it reduces its efficiency.

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.*;

Concepts of Programming Languages – Chapter 10 (Implementing Subprograms)

CHAPTER 10

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

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

  • A stack-dynamic local variable is more complex activation records. The compiler must generate code to cause implicit allocation and de-allocation of local variables
  • Recursion must be supported (adds the possibility of multiple simultaneous activations of a subprogram).

2.     What is the difference between an activation record and activation record instance?

The Format, or layout, of the non-code part of a subprogram is called an activation record.

An activation record stores all the information about subprogram calls, activation records stores the following data (in the following order)

  • Return address
  • Static link – to the static parent (where the subprogram is declared).
  • Dynamic link – to the caller of this subprogram.
  • Parameters
  • Local variables.

4.     What are the two steps in locating a nonlocal variable in a static-scoped language with stack-dynamic local variables and nested subprograms?

  • Find the correct activation record instance
  • Determine the correct offset within that activation record instance

5.     Define static chain, static depth, nesting_depth, and chain offset.

A static chain is a chain of static links that connects certain activation record instances

Static_depth is an integer associated with a static scope representing the scope’s nesting depth

The chain_offset or nesting_depth of a non-local reference is the difference between the static_depth of the reference and that of the scope where it is declared

6.     What are the two potential problems with the static chain methods?

  • A nonlocal reference is slow if the number of scopes between the reference and the declaration of the referenced variable is large
  • Time-critical code is difficult, because the costs of nonlocal references are not equal, and can change with code upgrades and fixes

7.     What is display?

One alternative to static chain is to use a display, for this approach, the static links are collected in a single array called a display. Display uses a pointer array to store the activation records along the static chain.

10.  Explain the two methods of implementing block?

Blocks are treated as parameter less subprograms that are always called from the same place in the program.

Block 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 exaction of program can be statically determined, because block are entered and exited in strictly textual order.

11.  Describe the deep access method of implementing dynamic scoping?

Deep Access – nonlocal references are found by searching the activation record instances on the dynamic chain. Length of chain cannot be statically determined every activation record instance must have variable names

12.  Describe the shallow access method of implementing dynamic scoping?

In case of shallow access names and values are stored in a global table. Using this method, space is allocated for every variable name that is in the program (one space for variable temp though there might be several declarations of temp in the different methods). When a sub-routine is called it saves the current value of the variable and replaces it with the value in its current scope and restores the value of the variable while exiting.

14.  Compare the efficiency of the deep access method to that of the shallow access method, in term of both call and nonlocal access?

The deep access methods provides fast subprogram linkage, but references to nonlocal, especially references to distant nonlocals (in term of the call chain), are costly. The shallow access methods provide much faster references to nonlocals, especially distant nonlocals, but are more costly in term of subprogram linkage.

 

PROBLEM SET:

7. It 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.

One very simple alternative is to assign integer values to all variable names used in the program. Then the integer values could be used in the activation records, and the comparisons would be between integer values, which are much faster than string comparisons.

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

Following the hint stated with the question, 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.

Concepts of Programming Languages – Chapter 9 (Subprograms)

CHAPTER 9

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

1.    What are the three general characteristics of subprograms?

  • Each subprogram has a single entry point, excluding co-routine.
  • The calling program 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.

4.     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 alist of parameters to be bound to the formal parameters of the subprogram. These parameters are called actual parameters.

5.     What are the advantages and disadvantages of keyword parameters?

The advantage of keyword parameter 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.

6.     What are the design issues for subprograms?

  • What parameter-passing method or methods are used?
  • Are the types of the actual parameters checked against the types of the formal parameters?
  • Are local variable statically or dynamically allocated?
  • Can subprogram definitions appear in other subprogram definitions?
  • If subprograms can be passed as parameters and subprograms can be nested, what is the referencing environment of a passed subprogram?
  • Can a subprogram be overloaded?
  • Can subprograms be generic?

7.     What are the advantages and disadvantages of dynamic local variables?

Advantages:

  • They provide flexibility to the subprogram
  • The storage of local variables in an active subprogram can be shared with the local variables in all inactive subprograms.
  • They efficiently used when computer has small memory (Faster Access).

Disadvantages:

  • Cost of the time required to allocate
  • Access to dynamic local variable must be indirect
  • The stack dynamic local variables, subprograms cannot be history sensitive

9.     What are the modes, the conceptual modes of transfer, the advantages, and the disadvantages or pass-by-value, pass-by-result, pass-by-value-result, and pass-by-reference parameter-passing models?

There are two conceptual models of how data transfers take place in parameter transmission. Either an actual value is copied or an access path is transmitted.

The advantage of pass-by-value is its speed.

The Disadvantages of pass-by-value are, when copies are used, additional storage is required.

Storage and copy operations can be costly.

Pass-by-result has all of the advantages and disadvantages of pass-by-value, but more disadvantages. An additional disadvantage is that there can be an actual parameter collision, because order of expressions matter.

Pass-by-value-result has the same advantages and disadvantages as pass-by-value and pass-by-result with some more advantages. The largest extra advantage of pass-by-value-result is that it solves pass-by-reference’s aliasing problems.

An advantage of pass-by-reference is that it is efficient in both time and space.

A disadvantage to pass-by-reference is the increase in time to access formal parameters because of the additional level of indirect addressing. Secondly, if only one way communication to the called subprogram is required, inadvertent and erroneous changes may be made to the actual parameter. Finally, aliasing should be expected with pass-by-reference. Since pass-by-reference makes access paths available to the called subprograms, it broadens their access to nonlocal variables. These aliasing problems lead to decreased readability and reliability.

10.  In what ways can aliases occur with pass-by-reference parameters?

Aliases can be occurring because pass-by-reference makes access paths available to the called subprograms.

17.  What is parametric polymorphism?

Parametric polymorphism is provided by a subprogram that takes a generic parameter that is used in a type expression that describes the types of the parameters of the subprogram. Both Ada and C++ provides a kind of compile-time parametric polymorphism.

18.  What causes a C++ template function to be instantiated?

C++ template functions are instantiated implicitly either when the function is named in a call or when its address is taken with the & processor.

19.  In what fundamental way do the generic parameters to a Java 5.0 generic method differ from those of C++ methods?

Java does not use objects exclusively, java have no enumeration or record type. Whereas C++ Classes can be defined to have no parent, that is not possible in Java. All Java Classes must be subclass of the root class.

20.  If a Java 5.0 method returns a generic type, what type of object is actually returned?

In Java any type or class can be returned by methods. Because methods are not types, they cannot be returned.

22.  What are the design issues for functions?

Two design issues are functions.

  1. Are side effects allowed?
  2. What types of values can be returned?

23.  In what ways are coroutines different from conventional subprogram?

Conventional subprograms are subordinate to their callers. When a routine calls a subprogram, execution suspends at that point in the program and resumes after the subprogram has run to completion. As a result, conventional subprogram invocation is atomic, much like a built-in statement in the programming language.

PROBLEM SET:

4. Suppose you want to write a method that prints a heading on a new output page,  along with a page number that is 1 in the first activation and that increases by 1 with each subsequent activation. Can this be done without parameters and without reference to nonlocal variables in Java? Can it be done in C#?

This can be done in both Java and C#, using a static (or class) data member for the page number.

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. Pass-by reference is specified by preceding one or both of the parameters with an ampersand.

7. Consider the following program written in C syntax:

void fun (int first, int second){
first += first;
second += second;
}
void main() {
int list [2] = {3,5};
fun(list[0], list[1]);
}

For each of the following parameter-passing methods, what are the values of the list array after execution?

a. Passes by value

b. Passes by reference.

c. Passes by value-result

(a) 3, 5

(b) 6, 10

(c) 6, 10

11. Compare the use of closures by programming languages.

Nearly all functional programming languages, most scripting languages, and at least one primarily imperative language, C#, support closures. These languages are static-scoped, allow nested subprograms, and allow subprograms to be passed as parameters.

15. How is the problem of passing multidimensional arrays handled 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.

Concepts of Programming Languages – Chapter 8 (Statement-Level Control Structures)

CHAPTER 8

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

1. What is the definition of control structure?

A control structure is a control statement and the collection of statements whose execution it controls.

2. What did Bohm and Jocopini prove about flowcharts?

It was proven that all algorithms that can be expressed by flowcharts can be coded in a programming languages 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?

In Ruby, block is a sequence of code, delimited by either breves or the do and and reserved words.

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?

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

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

9. What are the design issues for multiple-selection statements?

  • What is the form and type of the expression that controls the selection?
  • How are the selectable segments specified?
  • How are the case values specified?
  • How should unrepresented selector expression values be handled, if at all?
  • Is execution flow through the structure restricted to include just a single selectable segment?

14.  What are the design issues for all iterative control statements?

  • How is the iteration controlled?
  • Where should the control mechanism appear in the loop statement?

15.  What are the design issues for counter-controlled loop statements?

  • What are the type and scope of the loop variable?
  • Should it be legal for the loop variable or loop parameters to be changed in the loop, and if so, does the change affect loop control?
  • Should the loop parameters be evaluated only once, or once for every iteration?

21.  What are the design issues for logically controlled loop statements?

  • Should the control be pretest or post-test?
  • Should the logically controlled loop be a special form of a counting loop or a separate statement?

23.  What are the design issues for user-located loop control mechanisms?

  • 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?

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?

4. What are the limitations of implementing a multiple selector from two-way selectors and gotos?

A multiple selector can be built from two-way selectors and gotos, but the resulting

structures are cumbersome, unreliable, and difficult to write and read.

5. What are the arguments pro and con, for Java’s approach to specify compound statements in control statements?

• Compound statements are required in control statements when the body of the if

or else clause requires multiple statements.

• Java uses braces to form compound statements, which serve as the bodies of if

and else clauses.

9. Boolean expressions are necessary in the control statements in Java, as opposed to also allowing arithmetic expressions, as in C++. Give a conditional statement that is correct in C++ but not in Java.

int i=10;
if( i )
{
// block of statements
}

This block of statement is valid in C++ but not in Java.

11. Explain the advantages and disadvantages of the Java switch statement, compared to C++’s switch statement.

The Java variable in the argument of a switch statement can be of type integral ( byte,

short etc.), char and String( JDK 1.7 onwards), whereas in C++ the argument can be int

or char.

14. State one of the main legitimate needs for gotos.

Premature exits from loops.

Concepts of Programming Languages – Chapter 7 (Expressions and Assignment Statements)

CHAPTER 7

Lecturer: Mr. Tri Djoko Wahjono, Ir, M.Sc.

REVIEW QUESTION:

2. What is a ternary operator?

ternary operator is  conditional expressions that can be used anywhere in a program (in a C-based language) where any other expression can be used. In addition to the C-based languages, conditional expressions are provided in Perl, JavaScript, and Ruby.

3. What is a prefix operator?

prefix operators is the operators that precede the operands.

5. What is a nonassociative operator?

Operator with illegal expression.

 9. What is a coercion?
 A coercion is the implicit type convertion.
10. What is a conditional expression?
Conditional expression is a statement that uses if-then-else statements.
11. What is an overloaded operator?
An overloaded operator is the multiple uses of an operator.

28. What is a cast?

Cast is explicit type conversions. To specify a cast, the desired type is placed in parentheses just before the expression to be converted.

PROBLEM SET:

1. Run the code given in Problem 13 (in the problem set) on some system that supports C to determine the values of sum1 and sum2. Explain the result.

Suppose Type1 is a subrange of Integer. It may be useful for the difference between Type1 and Integer to be ignored by the compiler in an expression.

7. Describe a situation in which the add operator in a programming language would not be commutative.

An expression such as a + fun(b).

8. Describe a situation in which the add operator in a programming language would not be associative.

Consider the integer expression A + B + C. Suppose the values of A, B, and C are 20,000, 25,000, and -20,000, respectively. Further suppose that the machine has a maximum integer value of 32,767. If the first addition is computed first, it will result in overflow. If the second addition is done first, the whole expression can be correctly computed.

11. Write an BNF description of precendence and associativy rules defined for the expressions in Problem 9. Assume the only operands are the names a, b, c, d, and e.

<expr> → <expr> or <e1> | <expr> xor <e1> | <e1>
<e1> → <e1> and <e2> | <e2>
<e2> → <e2> = <e3> | <e2> /= <e3> | <e2> < <e3>
| <e2> <= <e3> | <e2> > <e3> | <e2> >= <e3> | <e3>
<e3> → <e4>
<e4> → <e4> + <e5> | <e4> - <e5> | <e4> & <e5> | <e4> mod <e5> | <e5>
<e5> → <e5> * <e6> | <e5> / <e6> | not <e5> | <e6>
<e6> → a | b | c | d | e | const | ( <expr> )

13. Let the function fun be defined as:

int fun (int *k){
*k += 4;
return 3 * (*k) - 1;
}

suppose fun is used in a program as follows:

void main(){
int i = 10, j = 10, sum1, sum2;
sum1= (i / 2) + fun( &i );
sum2 = fun ( &j ) + (j / 2);
}

What are the values of sum1 and sum2

a. if the operands in the expressions are evaluated left to right?

b. if the operands in the expressions are evaluated right to left?

(a) (left -> right) sum1 is 46; sum2 is 48
(b) (right -> left) sum1 is 48; sum2 is 46

15. Explain why it is difficult to eliminate functional side effects in C.

One reason functional side effects would be difficult to remove from C is that all of C’s subprograms are functions, providing the ability of returning only a single data value (though it could be an array). The problem is that in many cases it is necessary (or at least convenient) to return more than one data value, which is done through the use of pointer actual parameters, which are a means of creating functional side effects.

20.   Consider the following C program

int fun (int *i){
*i += 5;
return 4;
}
void main(){
int x = 3;
x = x + fun( &x );
}

What is the values of x after the assignment statement in main, assuming

a. operands are evaluated left to right.

b. operands are evaluated right to left.

(a) 7

(b) 12