chapter 8

Name: Billy
NIM: 1801374785

Kali ini saya akan menjawab Assignment #8 dari Chapter 8 Programming Language Concepts R Sebesta

Review Questions

6. What is unusual about Python’s design of compound statements?

*Python uses indentation to specify compound statements. For example,

if x > y :

x = y

print “case 1″

equally indent statements are grouped as one compound statement.

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

*If the expression returns a value, it must have an else clause.

8. What are the common solutions to the nesting problem for two-way selectors?

*The common solution is to force an alternative semantics, by using compound statements.

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

*-What is the form and type of the control statement?

-How are the selectable segments specified?

-Is execution flow through the structure restricted to include just a single selectable segment?

-How are case values specified?

-What is done about unrepresented expression values?

10. Between what two language characteristics is a trade-off made when deciding whether more than one selectable segment is executed in one execution of a multiple selection statement?

*In Ada, the choice lists of the case statement must be exhaustive, so that there can be no unrepresented values in the control expression. In C++, unrepresented values can be caught at run time with the default selector. If there is no default, an unrepresented value causes the whole statement to be skipped.

Problem Set

6. Analyze the potential readability problems with using closure reserved words for control statements that are the reverse of the corresponding initial reserved words, such as the case-esac reserved words of ALGOL 68. For example, consider common typing errors such as transposing characters.

*The potential readability problem is the typing errors. It’s very possible to occur if we don’t type the code carefully.

7. Use the Science Citation Index to find an article that refers to Knuth (1974). Read the article and Knuth’s paper and write a paper that summarizes both sides of the goto issue.

*An alternative viewpoint is presented in Donald Knuth's Structured Programming with go to Statements, which analyzes many common programming tasks and finds that in some of them GOTO is the optimal language construct to use.[7] In their quasi-standard book on the C programming language, Dennis Ritchie and Brian Kernighan warn that goto is "infinitely abusable", but also suggest that it could be used for end-of-function error handlers and for multi-level breaks from loops.

8. In his paper on the goto issue, Knuth (1974) suggests a loop control statement that allows multiple exits. Read the paper and write an operational semantics description of the statement.

*Operational semantics are a category of formal programming language semantics in which certain desired properties of a program, such as correctness, safety or security, are verified by constructing proofs from logical statements about its execution and procedures, rather than by attaching mathematical meanings to its terms (denotational semantics).

9. What are the arguments both for and against the exclusive use of Boolean expressions in the control statements in Java (as opposed to also allowing arithmetic expressions, as in C++)?

*The primary argument for using Boolean expressions exclusively as control expressions is the reliability that results from disallowing a wide range of types for this use. In C, for example, an expression of any type can appear as a control expression, so typing errors that result in references to variables of incorrect types are not detected by the compiler as errors. No , it would not be a good idea. Although this custom precedence sounds like increasing flexibility, requiring parentheses to show a custom precedence would impact in readability and writability of a program.

10. In Ada, the choice lists of the case statement must be exhaustive, so that there can be no unrepresented values in the control expression. In C++, unrepresented values can be caught at run time with the default selector. If there is no default, an unrepresented value causes the whole statement to be skipped. What are the pros and cons of these two designs (Ada and C++)?

*Ada was designed for military grade software development. The idea is that whenever you modify code in such a way that a new case emerges (for example adding a new value for an enumeration type), you are forced to manually revisit (and therefore re-validate) all the case statements that analyze it. Having a "default" is risky: you may forget that there is a case somewhere where the new case should not have been handled by the default.

chapter 7

Name: Billy
NIM : 1801374785

Kali ini saya akan menjawab assigntment #7 dari chapter 6 Programming Language Concepts R Sebesta E-book :

Review Questions No .6-10 :

6. What associativity rules are used by APL?

In APL, all operators have the same level of precedence. Thus, the order of evaluation of operators in APL expressions is determined entirely by the associativity rule, which is right to left for all operators.

For example, in the expression : A × B + C

the addition operator is evaluated first, followed by the multiplication operator (* is the APL multiplication operator). If A were 3, B were 4, and C were 5, then the value of this APL expression would be 27.

7. What is the difference between the way operators are implemented in C++ and Ruby?

What sets Ruby apart from the C-based languages in the area of expressions is that all of the arithmetic, relational, and assignment operators, as well as array indexing, shifts, and bitwise logic operators, are implemented as methods. For example, the expression a + b is a call to the + method of the object referenced by a, passing the object referenced by b as a parameter.

8. Define functional side effect.

A side effect of a function, naturally called a functional side effect, occurs when the function changes either one of its parameters or a global variable. (A global variable is declared outside the function but is accessible in the function.)

9. What is a coercion?

Coercion was defined as an implicit type conversion that is initiated by the compiler. 

Type conversions explicitly requested by the programmer are referred to as explicit conversions, or casts, not coercions.

10. What is a conditional expression?

If-then-else statements can be used to perform a conditional expression assignment. For example, consider :

if (count == 0)

       average = 0;

else

       average = sum / count;

In the C-based languages, this code can be specified more conveniently in an assignment statement using a conditional expression, which has the form

expression_1 ? expression_2 : expression_3.

Problem Set  No .6-10 :

6. Should C’s single-operand assignment forms (for example, ++count) be included in other languages (that do not already have them)? Why or why not?

Yes C should, because it will ease the increment or even decrement while we use in looping rather than manually by the assigning, and also by using that we can easily know that it is not operation, instead it is an increment or decrement which is usually used in repetition.

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

commutative.

It wouldn’t be commutative when it deals with the negative integers. Recall that we can consider subtraction as addition in which one of two operator is a negative integer.

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

It is not associative when it includes the other operator with higher precedence like the multiplication and division.

9. Assume the following rules of associativity and precedence for expressions:

Precedence Highest *, /, not

+, –, &, mod

– (unary)

=, /=, < , <=, >=, >

Lowest or, xor

Associativity Left to right

Show the order of evaluation of the following expressions by parenthesizing all sub expressions and placing a superscript on the right parenthesis to indicate order. For example, for the expression

a + b * c + d

the order of evaluation would be represented as

((a + (b * c)1)2 + d)3

a. a * b - 1 + c                  ((( a * b )1 - 1)2 + c )3
b. a*(b-1)/c mod d           ((( a * ( b - 1 )1 )2 / c )3 mod d )4
c. (a-b)/c&(d*e/a-3)         (((a - b)1 / c)2 & ((d * e)3 / a)4 - 3)5)6
d. -a or c = d and e           (( -a )1 or ( ( c = d )2 and e )3 )4
e. a>b xor c or d<=17      (((a > b)1 xor c)3 or (d <= 17)2 )4
f. –a + b                            (–( a + b )1 )2

10. Show the order of evaluation of the expressions of Problem 9, assuming that there are no precedence rules and all operators associate right to left.

(a) ( a * ( b – ( 1 + c )1 )2 )3
(b) ( a * ( ( b – 1 )2 / ( c mod d )1 )3 )4
(c) ( ( a – b )5 / ( c & ( d * ( e / ( a – 3 )1 )2 )3 )4 )6
(d) ( – ( a or ( c = ( d and e )1 )2 )3 )4
(e) ( a > ( xor ( c or ( d <= 17 )1 )2 )3 )4
(f) ( – ( a + b )1 )2