Quiz 1 for Organization of Programming Languages

Language Categories

- Imperative - Functional - Logic - Markup/programming Hybrid

Grammar Ambiguity

2 or more distinct parse trees

BNF equivalent to <ident_list> → <identifier> {, <identifier>} (Be able to convert either direction to/from BNF-EBNF)

<ident_list> → <identifier> | <identifier> , <ident_list>

BNF equivalent to <proc_call> → ident [(<expr_list>)]

<proc_call> → <ident> | <ident> <expr_lists>

BNF equivalent to <term> → <term> (+|-) const (Be able to convert either direction to/from BNF-EBNF)

<term> → <term> + const | <term> - const

optomization

A collection of techniques that compilers may use to decrease the size and/or increase the execution speed of code

Hybrid Implementation Systems

A compromise between compilers and pure interpreters Use: Small and medium systems when efficiency is not the first concern

Blocks

A method for creating static scopes inside program units

Explicit Declaration

A program statement used for declaring the types of values

Portability

A property of a program that can run on more than one kind of computer.

<if_stmt> → if <logic_expr> then <stmt> if <logic_expr> then <stmt> else <stmt>

An Unambiguous Grammar for if-then-else

Byte code instructions

Are read and interpreted by the JVM

Binding

Association between an attribute and an entity, such as between a variable and its type or value, or between an operation and a symbol.

Why is type checking the parameters of a subprogram important?

Because run-time type checking is expensive.

Why is it useful for a programmer to have some background in language design, even though he or she may never actually design a programming language?

Because understanding the basic makes it easier ti learn and adopt new languages. it also helps to design and develop more better software. programmer's need to understand how their code will work to ensure it is fault tolerant and high performing.

Load Time

Bind a C or ++ static variable to a memory cell

Global Scope

C and C++ have both declarations and definitions of global data

what are the three general methods of implementing a programming language?

Compilation,pure interpretation, hybrid implementation systems

What produces faster program execution, a compiler or a pure interpreter?

Compiler.

Backus-Naur Form (BNF) is equivalent to

Context-Free Grammars

What are the three fundamental features of an object oriented programming language

Data abstraction,inheritance and dynamic (run-time) metho

Plankalkul

Designed by Konrad Zuse

attribute grammar

Device used to describe more of the structure of a programming language than can be described with a context-free grammar.

regular language

Finite automaton can be designed to recognize members of a class of regular language. The tokens of a programming language are regular language and a lexical analyzer is a finite automaton

A device that generates sentences of a language (one can determine if the syntax of a particular sentence is syntactically correct by comparing it to the structure of the generator

Generators

Context Free Grammar syntax

Grammar = (Start symbol, set of Non-terminals, set of Terminals, set of Production Rules)

What is aliasing?

Having two or more distinct referencing methods, or names, for the same memory cell

Type Binding

How is the type specified? When does the binding take place? IF static, specified by either an explicit or an implicit declaration.

Dynamic Binding

IF it occurs during execution or can change during execution of the program

Static Binding

If it occurs before run time and remains unchanged throughout program execution

What does it mean for a program to be reliable?

If it performs to its specifications under all conditions.

What is the disadvantage of having too many features in a language?

If you have multiple ways to accomplish a task, it makes it harder to learn a language and makes it less readable

How can user-defined operator overloading harm the readability of a program?

It could end up confusing the author or someone reading the code later on.

How can knowledge of programming language characteristics benefit the whole computing community?

It will provide insight on what functionally that certain languages provide works well, and what doesn't work well. this also will allow programmers design languages that contain the great characteristics of languages.

which language has grammar based on predicate logic

LOGLAN (logical languages, also include Lojban and Ceqli)

On what branch of mathematics is axiomatic semantics based?

Logic (logical description)

Are internal nodes terminal or nonterminal

Nonterminal

Three approaches to Dynamic Semantics:

Operational, Denotational and Axiomatic Semantics

what is operational semantics based on ?

Platform specific description

___ device reads input strings over the alphabet of the language and decides whether the input strings belong to the language (i.e.syntax analysis part of a compiler)

Recognition device

On what branch of mathematics is denotational semantics based?

Recursive Function Theory (mathematical description)

what is an example of two language design criteria that are in direct conflict with each other?

Reliability and cost of execution

What role does the symbol table play in a compiler?

Serves as a database for the compilation process in a compiler.

State Diagram

Shows the ways that a program could progress from each state to other states.

Are leafs terminal or nonterminal

Terminal

What is exception handling?

The ability of a program to intercept run time errors

How is the cost of compilers for a given language related to the design of the language?

The design of the language coulf affect how a program is executed. A program that requires many run time type check might require a higher quality compiler

Why is readability important to writability?

The easier it is to read, the easier it is to write, and the more reliable it is.

Linking and loading

The process of collecting system programs and linking them to user programs

What primitive control statement is used to build more complicated control statements in languages that lack them?

The selection statement plus GOTO is used to build more complicated control statements such as FOR loop

Why is the von Neumann bottleneck important?

The separation between the CPU and memory leads to the von Neumann bottleneck, the limited throughput(data transfer rate) between the CPU and memory compared to the amount of memory. Since CPU speed and memory size have increased much faster than the throughput between them, the bottleneck is an important problem.

Syntax Analysis

The stage in compilation where language statements are checked against the rules of the language, errors being reported if a statement is not valid.

Binding Time

Time at which binding takes place.

Let Construct

Two Parts 1. binds names to values 2. uses the names defined in the first part

What is the primary use of attribute grammars?

Type compatibility

Poor readability Poor modifiability Expression coding tedious Machine deficiencies

What's wrong with machine code?

Operator Precidence

When certain operation have precidence over others

Exception Handling

When there's an error, the program makes an error object and passes it off to the runtime system, which looks for a method in the call stack to handle it.

parse tree

a data structure that shows how a statement in a language is derived from the context-free grammar of the language; it may be annotated with additional information, e.g. for compilation purposes.

Implicit Declaration

a default mechanism for specifying types of variables through default conventions, rather than declaration statements

preprocessor

a program that processes a program immediately before the program is compiled

valid sentence

a sentential form that as only terminal symbols

define language

a set of sentences (characterized by the set of all valid statements / strings in that language. The cardinality of this set is potentially infinite)

define sentence

a string of characters over some alphabet

What is an example of a lack of orthogonality in the design of C?

a+b. If the data types are different, it affects the result

define non-terminal symbols

abstractions are used to represent classes of syntactic structures; they act like syntactic variables (often enclosed in angle brackets <>)

Dynamic Scope

based on the calling sequence of subprograms, not on their spatial relationship to each other. Thus the scope can be determined at run time.

Be able to use recursive BNF rules to describe lists of arbitrary length means:

be able to describe the list of potential sentences in the language generated by a particular grammar

Runtime

bind a non-static local variable to a memory cell

Compile Time

bind a variable to a type in C or Java

Language Implementation Time

bind floating point type to a representation

Language Design Time

bind operator symbols to operations

extended BNF rules: repetitions (0 to many occurrences) are placed inside ____

braces { }

extended BNF rules: optional parts (0 or 1) are placed in ___

brackets [ ]

define token

category of lexemes (i.e. noun, verb; descriptions of lexeme etc.)

What have been the strongest influences on programming language design over the past 60 years?

computer architecture, von neumann

define leftmost derivation

derivation in which the leftmost nonterminal in each sentential form is the one that is expanded (expand leftmost nonterminal first)

define derivation (given a set of grammar rules know how to give derivation)

determines the order that nodes of a parse tree are built (repeated application of rules, starting with the start symbol and ending with a sentence with all terminal symbol)

define recursion (syntactic lists are described using recursion)

determines the shape of the parse tree

define sentential form

every string of symbols in a derivation

define rightmost derivation

expand rightmost nonterminal first

Top-down parser

expands nonterminals to match incoming tokens and directly construct a derivation

define attribute grammar (also called Static Semantics)

extension to a CFG (context-free grammar; includes for each grammar symbol x there is a set A(x) of attribute values; each rule has a set of functions that define certain attributes of the nonterminals in the rule; each rule has a set of predicates to check for attribute consistency)

Extended BNF

few simple extensions to BNF which make expressing grammars more convenient; adds "syntactic sugar"

define grammar

formal description of a Language (must a have a finite non-empty set of rules)

what is the formal language-generation mechanism commonly used to describe the syntax of programming languages?

grammars

define parse tree (Be able to draw a parse tree to visualize a derivation)

hierarchical representation of a derivation

how can we eliminate ambiguity? (Be able to define or modify operator precedence in a BNF grammar)

if we use the parse tree to indicate precedence levels of the operators (operator precedence)

What is the name of the category of programming languages whose structure is dictated by the von Neumann computer architecture?

imperative

What two programming language deficiencies were discovered as a result of the research in software development in the 1970s?

incompleteness of type checking inadequacy of control statements

semantic functions of the form I(Xj) = f(A(X0), ..., A(Xn)), for 1 ≤ j ≤ n, define ___ attributes of the ___ (top-down)

inherited; RHS

a grammar is ambiguous if and only if: (Be able to prove ambiguity in a grammar, with Proof By Contradiction)

it generates a sentential form that has two or more distinct parse tree

Metalanguage

language that is used to describe another language

define lexeme

lowest level syntactic unit of a language (for example a word; i.e. ?, variableName, dog)

is it true that an abstraction (or nonterminal symbol) can have only one RHS

no

What are the advantages in implementing a language with a pure interpreter?

one of the advantages of implementing a language with a pure interpreter is easy implementation of many source-level debugging operations, because all run-time errors can refer to the source-level units. An example of this is an array index is found to be out of range.

which semantics is to describe the meaning of a statement or program by specifying the effects of running it on a machine

operational semantics

extended BNF rules: alternative part of RHSs are placed inside ___ and separted via ___ ___

parentheses; vertical bars

grammars can be formally utilized in two distinct ways: for ____ and for ___. (two approaches to describing syntax)

recognizers; generators

left associativity

rule that orders from the left operations that include multiple operators from the same precedence level.

Right associativity

rule that orders from the right operations that include multiple operators from the same precedence level.

operator associativity

rules determining the order in which operations of the same precedence are performed.

Each Production Rule has: •a left-hand side (LHS), which is a ___ ___, and •a right-hand side (RHS), which is a ___ of ___ and/or ___

single non-terminal; string of terminals and/or non-terminals

What language was the first to support the three fundamental features of object oriented programming?

smalltalk

what are the primary values of attribute grammars

static semantics specification and compiler design (static semantics checking)

find weakest precondition by

substitute sequence with the variable in the postcondition: (single statement ex. a = b+1 {a >1} b+1 > 1 b > 0 is precondition) (multiple statement ex. y=3*x+1; x=y+3 {x < 10} y+3 < 10 y < 7 3*x+1 < 7 3x < 6 x < 2 is precondition)

semantic functions of the form S(X0) = f(A(X1), ..., A(Xn)) define ___ attributes of the ___ (bottom-up)

synthesized; LHS

what does a linker do?

takes one or more object files generated by a compiler and combines them into a single executable file

define syntax

the form or structure of the expressions, statements and program units (formal method to describe how to determine a statement's set membership in a Language)

define semantics

the meaning of the expressions, statements, and program units

Scope

the range of statements over which it is visible, the cope rules of a language determine how references to names are associated with variables

load module

the user and system code together

define terminal symbols

they are lexemes

Be able to define or modify operator associativity in a BNF grammar. Associativity is affected by ___ __ ___, i.e. left associative operators are implemented using ___ recursion, right associative operators are implemented using ___ recursion.

type of recursion; left; right

Be able to "decorate" attributes on a parse tree given: (a) a set of BNF syntax rules, (b) a set of Semantic Rules, and (c) a set of predicates. Use Figures 3.6, 3.7, and 3.8 as a guide.

use of actual_type vs expected_type (type as in int or real)

compiler implementation

when programs are translated into machine language

is it true that these are recent variation in EBNF include: in place of arrow, a colon; in place of a vertical bar, separate lines; instead of (a|b), one of a b

yes

Reasons for Studying Concepts of Programming Languages

•Increased ability to express ideas •Improved background for choosing appropriate languages •Increased ability to learn new languages •Better understanding of significance of implementation •Better use of languages that are already known •Overall advancement of computing

Pure Interpretation

•No translation •Easier implementation of programs (run-time errors can easily and immediately be displayed) •Slower execution (10 to 100 times slower than compiled programs) •Often requires more space •Significant comeback with some Web scripting languages (e.g., JavaScript, PHP)

Readability

•Overall simplicity •Minimal operator overloading •Orthogonality •Data types •Syntax considerations

Language Evaluation Criteria

•Readability: the ease with which programs can be read and understood •Writability: the ease with which a language can be used to create programs •Reliability: conformance to specifications (i.e., performs to its specifications) •Cost: the ultimate total cost

Language Design Trade-Offs

•Reliability vs. cost of execution •Readability vs. writability •Writability (flexibility) vs. reliability

Programming Domains

•Scientific applications •Business applications •Artificial intelligence •Systems programming •Web software

Writability

•Simplicity and orthogonality •Expressivity

finite automaton

•Start state •Accepting state •A state •A transition edge from state to another

bottom-up pa

•Starts by the input string and ends with the start symbol •Reduces the string to the start symbol by inverting productions •Bottom up parsing traces a right most derivation in reverse

Cost

•Training programmers to use the language •Writing programs (closeness to particular applications) •Compiling programs •Executing programs •Language implementation system: availability of free compilers •Reliability: poor reliability leads to high costs •Maintaining programs

Reliability

•Type checking •Exception handling •Aliasing •Readability and writability

•Syntax analysis

•large-scale constructs expressions, statements, program units

•Lexical analysis

•small scale language constructs names and numeric literals •A pattern matcher •serves as the front end of a syntax analyzer •performs syntax analysis at the lowest level of program structure