Prog Lang Homeworks

What are the design issues for names?

Case sensitivity Whether special words are reserved words are keywords Special characters Length Limit

What are the advantages of named constants?

Readability Used to parameterize programs

The first high-level language, designed by Konrad Zuse a. Plankalkul b. C c. IBM704 d. Ada

a

Racket is a dialect of which older language? a. COBOL b. LISP c. Assembly d. Fortran

b

Compute the weakest precondition given the following assignment statement and its postcondition: Show each step of your work. x = (y + 2) * 3 {x > 6}

x = (y + 2) * 3 {x > 6} (y + 2) * 3 > 6 y + 2 > 2 y > 0

Write the output of evaluating each of these Racket expressions, using correct Racket syntax. Note: expt is the exponent function, e.g. (expt 5 2) evaluates to 25. Hint: Don't forget that Racket lists must have a leading tick symbol, i.e. (1 2 3) is not the same expression as '(1 2 3). (+ 3 6) (/ 2 5) (/ 2 5.0) (* 2 (+ 1 7)) (= 3 2) (pair? '(1 2 3)) (or (and (= 3 (+ 1 2)) #t) #f) (car '(6 4 2)) (cdr '(1)) (car (cdr '(3 5 7)) (cons 5 7) (cons '(1 2) '(3 4)) (cons 3 (cons 6 (cons 9 '()))) ((λ (p) (p 7)) (λ (x) (* 3 x))) ((λ (x) ((λ (y z) (z x y)) 2 /)) 1)

9 2/5 0.4 16 #f #t #t 6 '() 5 '(5 . 7 ) '((1 2) 3 4) '(3 6 9) 21 1/2

Using the algorithm described in Section 4.4.2, remove direct left recursion form the following grammar rules. A → Aa | Abc | bc | d

A -> bcA' | dA' A' -> aA' | bcA' | epsilon

Define static binding and dynamic binding.

A binding is static if it first occurs before run time and remains unchanged throughout program execution A binding is dynamic if it first occurs during execution or can change during execution of the program

What is a block?

A method of creating static scopes inside program units

Convert the following EBNF grammar rules to BNF. Avoid left recursion. Your answer will be graded on both correctness and simplicity. A → B {(x|y) B} B → w[z]

A → BxA | ByA | B B → w | wz

Convert the following BNF rule with three RHSs to an EBNF rule with a single RHS. Conversion should remove all recursion A ⟶ B + A | B - A | B

A ⟶ B { (+|-) B }

What are the advantages and disadvantages of dynamic scoping?

Advantage: convenience Disadvantages: 1. While a subprogram is executing, its variables are visible to all subprograms it calls 2. Impossible to statically type check 3.Poor readability - it is not possible to statically determine the type of a variable

What is a static ancestor of a subprogram? What is a dynamic ancestor of a subprogram?

Enclosing static scopes (to a specific scope) are called its static ancestors. dynamic ancestors are those that are called to reach the subprogram in question.

A language is a collection of syntax rules that describe how to generate valid sentences. T/F

False

In programming languages, the use of keywords is more restrictive than reserved words. T/F

False

Like the if/else statement in Java and C++, the Racket else statement is optional. T/F

False

Python data types are declared explicitly. T/F

False

What is an alias?

If two variable names can be used to access the same memory location, they are called aliases

On what branch of mathematics is operation semantics based?

Imperative Machine Instructions

What is the purpose of the let constructs in functional languages?

It binds names to values in order to be used in an expression.

Variables can be characterized as a sextuple (6-tuple) of which six attributes?

Name, address, value, type, lifetime, and scope.

What is the potential danger of case-​sensitive names?

Names that look alike are different

Write a BNF grammar which generates the language described as: "The set of strings with a single x followed by an odd number of y's"

S → xY Y → yyY | y

Modify one or more rules of the following grammar so that the + operator has precedence over the * operator. S ⟶ X X ⟶ Y + X | Y Y ⟶ Z * Y | Z Z ⟶ 1 | 2 | 3 | 4

S ⟶ X X ⟶ Y * X | Y Y ⟶ Z + Y | Z Z ⟶ 1 | 2 | 3 | 4

Provide a similar Denotational Semantics description of octal integers below. Show both the syntax (i.e. the rules for ⟨oct_num⟩) and the semantics (i.e. the definitions for the Moct function).

Syntax: ⟨oct_num⟩ → ⟨oct_digit⟩ | ⟨oct_num⟩⟨oct_digit⟩ ⟨oct_digit⟩ → 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 Semantics: Moct('⟨oct_digit⟩') = ⟨oct_digit⟩ Moct(⟨oct_num⟩ '⟨oct_digit⟩') = 8 * Moct(⟨oct_num⟩) + ⟨oct_digit⟩

Define lifetime, scope, static scope, and dynamic scope.

The lifetime of a variable is the time during which it is bound to a particular memory cell The scope of a variable is the range of statements over which it is visible Static scope of a variable can be statically determined(prior to execution.) Dynamic scoping is based on the calling sequence of subprograms, not on their spatial relationship to each other. Thus, the scope can be determined only at run time

There are three reasons why lexical analysis is separated from syntax analysis: Simplicity, Efficiency, Portability T/F

True

Using the algorithm described in Section 4.4.2, remove direct left recursion form the following grammar rules. X → Xyy | Xz | Yx | w Y → Yy | Yw | zy | x

X -> YxX' | wX' X' -> yyX' | zX' | epsilon Y -> zyY' | xY' Y' -> yY' | wY' | epsilon

An algorithm was described to eliminate direct left recursion in a BNF grammar by replacing a left recursive LHS rule with two new LHS rules. Given the following set of X-rules... X ⟶ Xx | Xy | XY | zY | WX ...provide two new sets of rules to replace it that will eliminate direct left recursion. Hint: The two new sets of rules will be X-rules and Xʹ-rules.

X ⟶ zYX' | WXX' X' ⟶ xX' | yX' | YX' | ε

Although the + addition operator may be chained with multiple operands, it is actually a binary operator. Therefore, to evalute 2+3+5 we must first either (a) add 2+3 and combine the result with 5, or (b) add 3+5 and combine the result with 2. The property that describe which of these two strategies a language uses is called. a. Associativity b. Recursion c. Commutativity d. Reflexivity

a

Which of the following is NOT a characteristic of language evaluation criteria associated with Writability? a. Exception handling b. Data types c. Simplicity d. Syntax design

a

Select all that are examples of dynamic type binding. a. Python x = int(4.0) b. Perl $x = 4; c. Java int x = (int)4.0; d. C++ int x = 4;

a, b

Which of the following are categories of Dynamic Semantics? a. Denotational b. Axiomatic c. Syntactical d. Compile time e. Proportional f. Operational

a, b, f

Which of the following A-rules fail the Pairwise Disjointness Test? a. A → aB | BAb B → aB | b b. A ⟶ aB | bAb | Bb B ⟶ cB | d c. X → xy | Yy Y → yz | xz d. X → xy | Yy Y → yx | zx

a, c

Consider the following grammar: S → xSzB | A | y A → zA | z B → w | A Which of the following strings are in the language generated by this grammar? a. xyzw b. xzzzyzz c. xzzzzw d. xzw e. xzzzyw f. xzzz

a, c, f

What are some of the features of Functional Programming Languages? (select all that apply) a. The presence of anonymous (unnamed) functions b. Data abstraction c. Elimination (or minimization) of side effects d. Support for dynamic variables e. Based on first-order logic (FOL) f. Ability to pass functions as arguments to other functions g. Ability to return a function as a valid return type of a function h. Close semantic parallels with assembly language

a, c, f, g

Perform the pairwise disjointness test for each of the following grammar rules. Your answer should show the FIRST() function for each RHS, and then state whether the LHS rule passes or fails pairwise disjointness by examining all pairs of RHS FIRST()'s. To get you started, the first RHS is: FIRST(aB) = {a} a. A → aB | b | cBB b. B → aB | bA | aBb c. C → aaA | b | caB

a. FIRST(aB) = {a} FIRST (b) = {b} FIRST (cBB) = {c} They do not intersect and pass the test b. FIRST(aB) = {a} FIRST (bA) = {b} FIRST (aBb) = {a} They intersect and fail the test c. FIRST (aaA) = {a} FIRST (b) = {b} FIRST(caB) = {c} They do not intersect and pass the test

Perform the pairwise disjointness test for each of the following grammar rules. Your answer should show the FIRST() function for each RHS, and then state whether the LHS rule passes or fails pairwise disjointness. a. S → aSb | bAA b. A → b{aB} | a c. B → aB | a

a. FIRST(aSb) = {a} FIRST(bAA) = {b} No intersection, they pass the test b. FIRST(b{aB}) = {b} FIRST(a) = {a} No intersection, they pass the test c. FIRST(aB) = {a} FIRST(a) = {a} Intersection, they do not pass the test

On what branch of mathematics is denotational semantics based? a. Recursive Function Theory b. Linear Algebra c. Formal logic d. Combinatorics

a. Recursive Function Theory

The Readability of a program is affected by which characteristics? (check all that apply) a. Restricted aliasing b. Syntax design c. Simplicity d. Type checking

b, c

What is the primary use of attribute grammars? a. Defining dynamic semantics b. Enforcing type compatibility c. Enforcing BNF semantics d. Limiting memory usage

b. Enforcing type compatibility

On what branch of mathematics is axiomatic semantics based? a. Recursive Function Theory b. Formal Logic c. Combinatorics d. Linear Algebra

b. Formal Logic

At which possible binding time is a C or C++ static variable bound to a memory location? a. Language design time b. Language implementation time c. Load time d. Compile time e. Runtime

c

The first language designed specifically for text and string processing a. COBOL b. Fortran c. LISP d. SNOBOL

d

At which possible binding time is the Java + operator symbol bound to a memory location? a. Load time b. Language implementation time c. Runtime d. Compile time e. Language design time

e